Gallium—nitride-on-handle substrate materials and devices and method of manufacture

Abstract

A gallium and nitrogen containing substrate structure includes a handle substrate member having a first surface and a second surface and a transferred thickness of gallium and nitrogen material. The structure has a gallium and nitrogen containing active region grown overlying the transferred thickness and a recessed region formed within a portion of the handle substrate member. The substrate structure has a conductive material formed within the recessed region configured to transfer thermal energy from at least the transferred thickness of gallium and nitrogen material.

Description

BACKGROUND OF THE INVENTION

This invention generally relates to manufacture of materials and devices. More particularly, the present invention provides a method and device using wafer-bonded crystals or the like in combination with optical devices composed of a gallium-containing nitride crystal. More specifically, embodiments of the invention include techniques for fabricating a light emitting diode device using bulk gallium nitride containing materials, for example for application to optoelectronic devices. In other embodiments, the invention provides a method of manufacture using an epitaxial gallium containing crystal with a release layer. Such crystals and materials include GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others, for manufacture of bulk or patterned substrates.

Progress has been made during the past decade and a half in the performance of gallium nitride (GaN) based light emitting diodes (LEDs). Devices with a luminous efficiency higher than 100 lumens per watt have been demonstrated in the laboratory, and commercial devices have an efficiency that is already superior to that of incandescent lamps, and competitive with that of fluorescent lamps. Further improvements in efficiency are desired to reduce operating costs, reduce electricity consumption, and decrease emissions of carbon dioxide and other greenhouse gases produced in generating the energy used for lighting applications.

Silicon-on-insulator substrates are well known in the art, and convey certain advantages compared to standard silicon substrates. Several authors have demonstrated GaN-on-insulator substrates. Tauzin et al. [Electronics Letters 41, 668 (2005) transferred the topmost portion from a 4-μm-thick GaN-on-sapphire epilayer onto a second sapphire substrate by means of SmartCut™ layer-transfer technology. The crystalline quality of the transferred layer was not particularly high in this case. O. Moutanabbir and U. Gösele [J. Electronic Mater. 39, 482 (2010)] transferred a layer from a free-standing, pseudo-bulk GaN wafer of unspecified quality to sapphire. Sapphire, while readily available and convenient to work with, suffers from a relatively low thermal conductivity and has a significant mismatch in the coefficient of thermal expansion with respect to the GaN layer. In addition, in cases where the nitride crystal in a GaN-on-insulator wafer is spatially inhomogeneous, we are not aware of any teachings about the best way to arrange fabricated devices with respect to structures in the GaN layer.

What is needed is a more manufacturable solution for fabricating high-quality GaN-on-handle substrates or wafers that are optimized for down-stream device processing and device designs and processing methods that are optimized to take advantage of the properties of the wafer.

BRIEF SUMMARY OF THE INVENTION

In a specific embodiment, the present invention provides a gallium and nitrogen containing optical device. The device includes a handle substrate member portion having a surface region. The handle substrate portion is characterized by a first coefficient of thermal expansion parallel to the surface. The device has an adhesion material (e.g., dielectric, conductor) overlying the surface region. The device also has a gallium and nitrogen containing region formed overlying the adhesion material. The gallium and nitrogen containing region is characterized by a second coefficient of thermal expansion parallel to the surface. The second coefficient of thermal expansion is substantially similar to the first coefficient of thermal expansion. The gallium and nitrogen containing region is formed from a donor gallium and nitrogen containing material transferred to the handle substrate. The device also includes at least one active region formed overlying the gallium and nitrogen containing region and at least one p-type region formed epitaxially overlying the active region.

In an alternative specific embodiment, the present invention provides a gallium and nitrogen containing device. The device includes a handle substrate member having a first surface region and a second surface region and at least one n-contact region overlying the first surface region. The device has a gallium and nitrogen containing material overlying the second region. The gallium and nitrogen containing material is transferred overlying the second region. The gallium and nitrogen containing material includes a core region. As used herein, the core region refers to a commonly known entity of a dot core GaN substrate from Sumitomo Electric Industries, Ltd, of Japan, or others. The device has an interface region overlying the gallium and nitrogen containing material and at least one n-type epitaxial growth region overlying the interface region. The device also has a core structure extending from the core region within the overlying gallium and nitrogen containing material and configured to extend through the at least one n-type epitaxial growth region. The device has an active region overlying the at least one n-type epitaxial growth region, a p-type region overlying the first active region and the second active region, and at least one p-contact region overlying the p-type region. As an example, the dot core GaN is described in “Dislocation reduction in GaN crystal by advanced-DEEP,” in the names of Motoki, et al., and published in Journal of Crystal Growth 305 (2007) 377-383, which is incorporated by reference herein.

In other embodiments, the invention provides a gallium and nitrogen containing device. The device has a handle substrate member having a first surface region, with gallium and nitrogen containing material overlying the first region. The gallium and nitrogen containing material is transferred overlying the first region. The gallium and nitrogen containing material comprises a core region. The device has an interface region overlying the gallium and nitrogen containing material and at least one n-type epitaxial growth region overlying the interface region. The device has a core structure extending from the core region within the overlying gallium and nitrogen containing material and configured to extend through the at least one n-type epitaxial growth region. The device has an active region overlying the at least one n-type epitaxial growth region and a p-type region overlying the first active region and the second active region. The device has a mesa structure, wherein material lateral to at least one mesa has been removed so as to expose at least one n-type epitaxial growth region. The device has at least one n-contact region overlying the exposed n-type region and at least one p-contact region overlying the p-type region.

Still further, the invention provides a method of processing a gallium and nitrogen containing material. The method includes providing a handle substrate having a surface region. The method includes transferring a thickness of gallium and nitrogen containing substrate material comprising at least one core region therein overlying the surface region. The device has depositing a gallium and nitrogen containing material using at least epitaxial growth overlying the thickness of gallium and nitrogen containing substrate material to form a thickness of epitaxially grown material comprising a core structure formed overlying the core region. The method includes subjecting the core structure to at least an etching process.

Moreover, the invention provides a gallium and nitrogen containing device. The device has a handle substrate member having a first surface region and a second surface region. The handle substrate member is conductive in characteristic and an exposed region characterizing the first surface region. The device has a gallium and nitrogen containing material overlying the second surface region. The gallium and nitrogen containing material is transferred overlying the second region. The gallium and nitrogen containing material comprises a core region. The device has an interface region overlying the gallium and nitrogen containing material. The device has at least one n-type epitaxial growth region overlying the interface region and a conductive structure extending from the core region and configured through portion between the two n-type epitaxial growth regions. The device has an active region formed overlying the n-type epitaxial growth region and a p-type region formed overlying the active region. The device has an n-type contact region formed overlying the conductive structure.

Still further, the present invention provides a gallium and nitrogen containing substrate structure. The structure includes a handle substrate member having a first surface and a second surface and a transferred thickness of gallium and nitrogen material. The structure has a gallium and nitrogen containing active region grown overlying the transferred thickness of gallium and nitrogen containing material and a recessed region formed within a portion of the handle substrate member. The substrate structure has a conductive material formed within the recessed region and is configured to transfer thermal energy from at least the transferred thickness of gallium and nitrogen material.

Still further, the present invention provides a gallium and nitrogen containing substrate structure. The substrate structure includes a handle substrate member having a first surface and a second surface and comprising a plurality of energy conversion materials and a transferred thickness of gallium and nitrogen material. The substrate structure includes a gallium and nitrogen containing active region grown overlying the transferred thickness of gallium and nitrogen containing material.

The present device and method provides for an improved gallium and nitrogen containing material and resulting device structures for optical and electronic devices. In other embodiments, the present method and resulting structure are easier to implement using conventional technologies. The invention provides a high quality GaN substrate and resulting devices. These and other benefits are further described below in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a nitride crystal and a handle substrate according to an embodiment of the present invention;

FIG. 2 is a diagram of a wafer-bonded nitride crystal and handle substrate according to an embodiment of the present invention;

FIG. 3 is a diagram of a wafer-bonded nitride crystal and handle substrate after removal of portion of the nitride crystal according to an embodiment of the present invention;

FIG. 4 is a diagram of a device structure according to an embodiment of the present invention;

FIG. 5 is a diagram of a vertical device structure according to an embodiment of the present invention;

FIG. 6 is a diagram of a lateral device structure according to an embodiment of the present invention;

FIG. 7 is a diagram of a vertical device structure having a roughened or patterned interface according to an embodiment of the present invention;

FIG. 8 is a diagram of a lateral device structure having a roughened or patterned interface according to an embodiment of the present invention;

FIGS. 9A-9C are diagrams of a vertical device structure on a patterned substrate according to an embodiment of the present invention;

FIGS. 10A and 10B are diagrams of a lateral device structure on a patterned substrate according to an embodiment of the present invention;

FIG. 11 is a diagram of a device structure on a patterned substrate illustrating singulation methods according to an embodiment of the present invention;

FIGS. 12A and 12B are diagrams of an alternative device structure on a patterned substrate illustrating singulation methods according to an embodiment of the present invention;

FIGS. 13A-13D are diagrams of additional device structures on a patterned substrate illustrating singulation methods according to an embodiment of the present invention;

FIG. 14 is a diagram showing a side view of a flip-chip device structure according to an embodiment of the present invention;

FIG. 15 is a diagram showing a top view of a flip-chip device structure according to an embodiment of the present invention;

FIG. 16 is a diagram showing a sandwiched vertical device structure according to an embodiment of the present invention;

FIG. 17 is a cross-sectional view diagram of a vertical thin-film device structure having a removed handle substrate in one or more embodiments;

FIG. 18 is a cross-sectional view diagram of a vertical thin-film device structure having a removed handle substrate in one or more embodiments;

FIG. 19 is a diagram showing a processing sequence of a substrate according to an embodiment of the present invention;

FIGS. 20A-20C are diagrams showing configurations of vias within a substrate according to an embodiment of the present invention; and

FIGS. 21A and 21B are diagrams showing a substrate comprising light emitting entities according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, in one set of embodiments the starting point for the present invention is a donor substrate 101 consisting essentially of a high quality nitride crystal or wafer. The nitride crystal comprises nitrogen and has a threading dislocation density below about 10⁸ cm⁻². The nitride crystal or wafer may comprise Al_xIn_yGa_1-x-yN, where 0≦x, y, x+y≦1, for example, GaN. In a preferred embodiment, the nitride crystal is substantially free of low-angle grain boundaries, or tilt boundaries, over a length scale of at least 3 millimeters.

The nitride crystal or wafer may have a large-surface orientation within ten degrees, within five degrees, within two degrees, within one degree, within 0.5 degree, or within 0.2 degree of (0 0 0 1), (0 0 0 −1), {1 −1 0 0}, {1 1 −2 0}, {1 −1 0 ±1}, {1 −1 0 ±2}, {1 −1 0 ±3}, {2 0 −2 ±1}, or {1 1 −2 ±2}. In one specific embodiment, the nitride crystal has a semipolar large-surface orientation, which may be designated by (hkil) Bravais-Miller indices, where i=−(h+k), l is nonzero and at least one of h and k are nonzero. The nitride crystal may have a dislocation density below 10⁷ cm⁻², below 10⁶ cm⁻², below 10⁵ cm⁻², below 10⁴ cm⁻², below 10³ cm⁻², or below 10² cm⁻². The nitride crystal may have a stacking-fault concentration below 10³ cm⁻¹, below 10² cm⁻¹, below 10 cm⁻¹ or below 1 cm⁻¹. The nitride crystal or wafer may have an optical absorption coefficient below 100 cm⁻¹, below 50 cm⁻¹, below 5 cm⁻¹, below 2 cm⁻¹, below 1 cm⁻¹, or below 0.3 cm⁻¹ at wavelengths between about 390 nm and about 700 nm. The nitride crystal may have an optical absorption coefficient below 100 cm⁻¹, below 50 cm⁻¹, below 5 cm⁻¹, below 2 cm⁻¹, below 1 cm⁻¹, or below 0.3 cm⁻¹ at wavelengths between about 700 nm and about 3077 nm and at wavelengths between about 3333 nm and about 6667 nm. The top surface of the nitride crystal may have an x-ray diffraction w-scan rocking curve full-width-at-half-maximum (FWHM) less than about 300 arc sec, less than about 200 arc sec, less than about 100 arc sec, less than about 50 arcsec, less than about 40 arcsec, less than about 30 arcsec, less than about 20 arcsec, or less than about 10 arcsec for the lowest-order symmetric and non-symmetric reflections. In some embodiments, the threading dislocations in the top surface of the nitride crystal are approximately uniformly distributed. In other embodiments, the threading dislocations in the top surface of the nitride crystal are arranged inhomogeneously as a one-dimensional array of rows of relatively high- and relatively low-concentration regions or as a two-dimensional array of high-dislocation-density regions within a matrix of low-dislocation-density regions. The relatively high-dislocation-density regions in a two-dimensional array may be referred to as cores or core regions and the nitride crystal may be referred to as a dot-core crystal or substrate.

Nitride crystal 101 may have a crystallographic radius of curvature greater than 0.1 meter, greater than 1 meter, greater than 10 meters, greater than 100 meters, or greater than 1000 meters, in at least one, at least two, or in three independent or orthogonal directions. Nitride crystal 101 may comprise regions having a relatively high concentration of threading dislocations separated by regions having a relatively low concentration of threading dislocations. The concentration of threading dislocations in the relatively high concentration regions may be greater than about 10⁶ cm⁻², greater than about 10⁷ cm⁻², or greater than about 10⁸ cm⁻². The concentration of threading dislocations in the relatively low concentration regions may be less than about 10⁶ cm⁻², less than about 10⁵ cm⁻², or less than about 10⁴ cm⁻². Nitride crystal 101 may have a thickness between about 100 microns and about 100 millimeters, or between about 1 millimeter and about 10 millimeters. Nitride crystal 101 may have a diameter of at least about 0.5 millimeter, at least about 1 millimeter, at least about 2 millimeters, at least about 5 millimeters, at least about 10 millimeters, at least about 15 millimeters, at least about 20 millimeters, at least about 25 millimeters, at least about 35 millimeters, at least about 50 millimeters, at least about 75 millimeters, at least about 100 millimeters, at least about 150 millimeters, or at least about 200 millimeters. The crystallographic orientation may be constant to less than about 2 degrees, less than about 1 degree, less than about 0.5 degree, less than about 0.2 degree, less than about 0.1 degree, or less than about 0.05 degree across the top surface of the nitride crystal.

The nitride crystal may be fabricated by hydride vapor phase epitaxy (HVPE), as described in U.S. Pat. No. 6,468,347, in US Patent Application US 2006/0228870A1, or by Fujito et al., J. Cryst. Growth, 311, 3011 (2009), by ammonothermal growth, as described in U.S. Pat. Nos. 6,656,615, 7,078,731, and 7,642,122, US Patent Application 2010/0031875, or U.S. patent application Ser. Nos. 12/988,772, 61/360,819, or 61/386,879, or by flux growth, as described by M. Imade et al., Applied Physics Express 3, 075501 (2010), each of which is hereby incorporated by reference in its entirety. In some embodiments the nitride crystal is doped, for example, with Si or O to form n-type material, with a dopant concentration between about 10¹⁷ cm⁻³ and 10²⁰ cm⁻³.

Referring again to FIG. 1, in one set of embodiments surface 105 of nitride crystal 101 is implanted with ions, forming an implanted/damaged region 103 according to methods that are known in the art. The ion implantation may be performed with at least one of H⁺, H₂⁺, He⁺, Ne⁺, Ar⁺, Kr⁺, Xe⁺, N⁺, or N₂⁺. The implantation energy be between about 10 keV and about 10 MeV, or preferably between about 20 keV and about 2 MeV. The ion fluence or dose may be between about 10¹⁶ cm⁻² and about 10¹⁹ cm⁻², between about 10¹⁷ cm⁻² and about 10¹⁸ cm⁻², or between about 2×10¹⁷ cm⁻² and about 4×10¹⁷ cm⁻². In some embodiments, the back side of crystal 101 is also implanted with ions, forming a second implanted/damaged region (not shown), with a similar ion composition, energy, and fluence, so as to minimize bow in crystal 101, as described by O. Moutanabbir and U. Gösele, J. Electronic Mater. 39, 482 (2010), which is hereby incorporated by reference in its entirety

Referring again to FIG. 1, a handle substrate 117 having surface 115 is also provided. Handle substrate 117 may comprise a single crystal, polycrystalline or amorphous material. Handle substrate 117 may comprise sapphire, aluminum oxide, mullite, silicon, silicon nitride, germanium, gallium arsenide, silicon carbide, MgAl₂O₄ spinel, zinc oxide, indium tin oxide (ITO), indium oxide, tin oxide, indium phosphide, beryllium oxide, chemical-vapor-deposition (CVD) diamond, single crystal diamond, YAG:Ce, gallium nitride, indium nitride, gallium aluminum indium nitride, aluminum oxynitride, or aluminum nitride. Other materials comprising transparent phosphors are described in U.S. Provisional Application No. 61/167,447 filed Apr. 7, 2009, commonly assigned, and hereby incorporated by reference herein. Handle substrate 117 may comprise an electrical insulator, a conducting oxide, a conducting transparent oxide, a luminescent material, a distributed bragg reflector (DBR) stack, a band-pass or an edge-pass filter stack, a semiconductor, a semimetal, or a metal. Handle substrate 117 may comprise substantially the same composition as crystal 101. In one specific embodiment, handle substrate 117 comprises crystals that have been merged or tiled together using another method. For example, handle substrate 117 may be formed using at least one of the tiling methods disclosed by Dwilinski et al. [US Patent Application No. 2008/0156254] or the method disclosed in U.S. patent application Ser. No. 12/635,645, which is hereby incorporated by reference in its entirety.

In one specific embodiment, handle substrate 117 comprises substantially the same composition as crystal 101 and has a crystallographic orientation within about 10 degrees, within about 5 degrees, within about 2 degrees, or within about 1 degree of that of crystal 101. Handle substrate 117 may comprise a glass, a glass-ceramic, or a ceramic. Handle substrate 117 may comprise an oxide of at least one of Si, Ge, Sn, Pb, B, Al, Ga, In, Tl, P, As, Sb, Pb, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, Mn, Zn, or Cd. In one specific embodiment, handle substrate 117 comprises oxygen-doped aluminum nitride. Handle substrate 117 may have a thermal expansion coefficient parallel to surface 115 between room temperature and about 700 degrees Celsius that is between about 2.5×10⁻⁶ K⁻¹ and about 7×10⁻⁶ K⁻¹. Handle substrate 117 may have a thermal expansion coefficient parallel to surface 115 between room temperature and about 700 degrees Celsius that is between about 5.5×10⁻⁶ K⁻¹ and about 6.5×10⁻⁶ K⁻¹. Handle substrate 117 may have a thermal expansion coefficient parallel to surface 115 between room temperature and about 700 degrees Celsius that within about 20%, within about 10% within about 5%, within about 2%, or within about 1% of that of nitride crystal 101. Handle substrate 117 may have a softening point, that is, where its viscosity has a value of about 10⁸ Poise, at a temperature between about 500 degrees Celsius and about 1400 degrees Celsius. Handle substrate 117 may have a glass transition temperature between about 600 degrees Celsius and about 1200 degrees Celsius. Handle substrate 117 may have a softening point, that is, where its viscosity has a value of about 10⁸ Poise, at a temperature between about 600 degrees Celsius and about 900 degrees Celsius. Surface 115 may be optically flat, with a deviation from flatness less than 1 micron, less than 0.5 micron, less than 0.2 micron, less than 0.1 micron, or less than 0.05 micron. Surface 115 may be very smooth, with a root-mean-square roughness less than 5 nanometers, less than 2 nanometers, less than 1 nanometer, less than 0.5 nanometer, less than 0.2 nanometer, less than 0.1 nanometer, or less than 0.05 nanometer, measured over an area of at least 10 microns×10 microns. Handle substrate 117 may be substantially transparent at visible wavelengths of light, such that one of ordinary skill in the art may be able to read printed words through handle substrate 117.

Adhesion layers 113 and 107 may be deposited on at least one of surface 115 of handle substrate 117 and surface 105 of donor substrate 101. Adhesion layers 113 and 107 may comprise at least one of SiO_x, GeO_x, SiN_x, AlN_x, GaO_x, Al₂O₃, Sc₂O₃, Y₂O₃, B₂O₃, R₂O₃, where R is a rare earth element, MgO, CaO, SrO, HfO₂, ZrO₂, Ta₂O₅, or B, Al, Si, P, Zn, Ga, Si, Ge, Au, Ag, Ni, Ti, Cr, Zn, Cd, In, Sn, Sb, Tl, or Pb, or an oxide, nitride, or oxynitride thereof. Adhesion layers 113 and/or 107 may be electrically insulating. Adhesion layers 113 and 107 may further comprise hydrogen. The adhesion layers 113 and 107 may be deposited by thermal evaporation, electron-beam evaporation, sputtering, chemical vapor deposition, plasma-enhanced chemical vapor deposition, or the like, or by thermal oxidation of a deposited metallic film. The thickness of adhesion layers 113 and 107 may between about 1 nanometer and about 10 microns, or between about 10 nanometers and about 1 micron. The adhesion layer(s) may be annealed, for example, to a temperature between about 300 degrees Celsius and about 1000 degrees Celsius. In some embodiments, at least one adhesion layer is chemical-mechanically polished. In a preferred embodiment, the root-mean-square surface roughness of at least one adhesion layer is below about 0.5 nanometer, or below about 0.3 nanometer over a 20×20 μm² area.

Referring again to FIG. 1 and also to FIG. 2, surfaces 109/209 of nitride crystal 101/201 or adhesion layer placed thereupon and surface 111/211 of handle substrate 117/217 or adhesion layer placed thereupon are placed in contract with one another and wafer-bonded. In a preferred embodiment, the wafer bonding operation is performed in a clean room, with less than 10,000, less than 1,000, less than 100, or less than 10 particles per cubic centimeter in the air. Particles may be removed from at least one of the surfaces immediately prior to wafer bonding by spraying, brushing, or rinsing with ionized nitrogen, a CO₂ jet, CO₂ snow, high-resistivity water, an organic solvent, such as methanol, ethanol, isopropanol, acetone, or the like. In some embodiments, surface 109/209 and surface 111/211 are brought into contact while immersed in a liquid. Optionally, at least one of the surfaces is exposed to a plasma to enhance wafer bonding.

Nitride crystal 101 may be pressed against handle substrate 117 with a pressure between about 0.1 megapascals and about 100 megapascals. In some embodiments, van der Waals forces are sufficient to obtain a good wafer bond and no additional applied force is necessary. Nitride crystal 101 and handle substrate 117 may be heated to a temperature between about 30 degrees Celsius and about 950 degrees Celsius, between about 30 degrees Celsius and about 400 degrees Celsius, or between about 30 degrees Celsius and about 200 degrees Celsius for a period between about 5 minutes and about 10 hours to strengthen the wafer bond. In some embodiments, heating of nitride crystal 101 and handle substrate 113 is performed while they are mechanically loaded against one another.

Referring again to FIG. 2 and to FIG. 3, in some embodiments, at least the surface region of bonded nitride crystal 201 having implanted/damaged region 203 and handle substrate 217/317 are heated to a temperature between about 200 degrees Celsius and about 800 degrees Celsius or between about 500 degrees Celsius and about 700 degrees Celsius to cause micro-bubbles, micro-cracks, micro-blisters, or other mechanical flaws within region 203. In one specific embodiment, surface region 306 is heated by means of optical or infrared radiation through handle substrate 217/317, and the distal portion 302 of crystal 201 may remain less than about 300 degrees Celsius, less than about 200 degrees Celsius, or less than about 100 degrees Celsius. In some embodiments, mechanical energy may be provided instead of or in addition to thermal energy. In some embodiments, an energy source such as a pressurized fluid is directed to a selected region, such as an edge, of bonded nitride crystal 201 to initiate a controlled cleaving action within region 203. After the application of energy, the distal portion 302 of nitride crystal 201 is removed, leaving a proximate portion 306 of nitride crystal 101 bonded to handle substrate 217/317.

In one set of embodiments, a release layer and a high quality epitaxial layer are functionally substituted for the ion-damaged layer, as described in U.S. Patent Application Ser. No. 61/386,879. The high quality epitaxial layer may be wafer-bonded to the handle substrate and may be separated from the nitride crystal by means of laser lift-off, preferential etching, photochemical etching, photoelectrochemical etching, or the like.

Referring again to FIG. 3, the newly exposed surface 304 of transferred layer 306 on GaN-on-handle wafer 320 may be polished, dry-etched, or chemical-mechanically polished according to methods that are known in the art to prepare an epi-ready surface.

In some embodiments, GaN-on-handle wafer 320 is used as a substrate for epitaxy. One or more edges of the wafer may be ground. The wafer may be placed in a suitable reactor and at least one epitaxial layer grown by MOCVD, MBE, HVPE, or the like. In a preferred embodiment, the epitaxial layer comprises GaN or Al_xIn_yGa_(1-x-y)N, where 0≦x, y≦1.

The GaN-on-handle wafer may be used as a substrate for fabrication into optoelectronic and electronic devices such as at least one of a light emitting diode (LED), a laser diode, a photodetector, an avalanche photodiode, a transistor, a rectifier, and a thyristor; one of a transistor, a rectifier, a Schottky rectifier, a thyristor, a p-i-n diode, a metal-semiconductor-metal diode, high-electron mobility transistor, a metal semiconductor field effect transistor, a metal oxide field effect transistor, a power metal oxide semiconductor field effect transistor, a power metal insulator semiconductor field effect transistor, a bipolar junction transistor, a metal insulator field effect transistor, a heterojunction bipolar transistor, a power insulated gate bipolar transistor, a power vertical junction field effect transistor, a cascode switch, an inner sub-band emitter, a quantum well infrared photodetector, a quantum dot infrared photodetector, a solar cell, and a diode for photoelectrochemical water splitting and hydrogen generation. Optionally, one or more devices may be flip-chip bonded for improved heat extraction.

In one specific embodiment, shown schematically in FIG. 4, the wafer is used to fabricate a high-voltage LED. In a preferred embodiment, nitride layer 401 is n-type doped, to a level between about 10¹⁷ cm⁻³ and about 3×10¹⁸ cm⁻³, and handle substrate 417 has a coefficient of thermal expansion that is approximately matched to that of nitride layer 401. In a preferred embodiment, handle substrate 417 is an electrical insulator. Nitride layer 401 and handle substrate 417 are bonded by means of adhesion layers 407 and 413. Active layer 431 and p-type layer 433 are deposited epitaxially on n-type nitride layer 401 according to methods that are known in the art, such as metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). Mesa structures are formed to generate singulated devices or form arrayed layouts with the various pixels of the LEDs to be subsequently interconnected. Typically, this will be achieved by utilizing reactive ion etching (RIE) or inductively-coupled plasma (ICP) dry etching or photo-electrochemical (PEC) etching to etch through the active region to expose the n-GaN layer. A layer of n-type AlGaN may serve as an etch stop during the mesa-forming process. A second etch process is then performed to expose the electrically inactive adhesion layers 407/413 and/or handle substrate 417 and is desirable to prevent conduction between the n-electrodes of adjacent pixels. The adhesion layers 407/413 and/or handle substrate 417 may serve as a selective stop-etch layer. The p-electrodes 435 are then deposited upon the mesa tops and may be substantially transparent to allow for a top-emitting device configuration. Transparency should be coupled with sufficient current spreading and may be achieved by utilizing an indium tin oxide (ITO) or zinc oxide (ZnO) layer, a thin metal layer (Ni/Au, Pt/Au, Pd/Au, Ag, Pt/Ag), or a mesh grid (not shown) for the p-electrode. A second isolation (passivation) layer, which may consist of a dielectric material such as SiO₂ or Si_xN_y may then be deposited over the mesas. This layer isolates the interconnect metal from shorting an adjacent device and serves as a passivation mechanism for the active region sidewalls. Finally, a second metal layer 437 is deposited to provide the n-electrode of each device and to enable interconnection of adjacent pixels. Several common embodiments for the n-electrode are Al/Au, Ti/Au, Al/Ni/Au, or Ti/Al/Ni/Au. The contacts may be heat treated or annealed to form ohmic or near-ohmic contracts. At least two, three, four, five, six, eight, ten, twelve, 15, 20, 25, 30, 40, 50, 60, 75, or more LEDs may be interconnected in series by means of wire bonds 439 to form a multi-pixel high-voltage LED. The LED may be operated at a voltage greater than 10V, greater than 20V, greater than 40, or greater than 100V.

Optionally, the high-voltage LED may be flip-chip bonded to a carrier substrate for improved extraction of light and/or or heat. Handle substrate 401 may be shaped or removed for improved light extraction. Handle substrate 401 may be removed by methods that are known in the art, such as laser lift-off, grinding, or lapping. Adhesion layers 407 and 413 may be removed by chemical etching, electrochemical etching, anodization, lapping, or the like. The back side 441 of nitride layer 401 may be patterned or roughened by methods that are known in the art, such as chemical etching or photoelectrochemical etching to improve light extraction. Light extraction may be optimized by means of microcavity effects, surface roughening, or formation of a photonic lattice, as described in U.S. patent application Ser. Nos. 12/569,337; 12/569;841; and 12/569,844; each of which is incorporated by reference in their entirety. The high-voltage LED may be singulated and incorporated into a package according to methods that are known in the art. One or more high-voltage LEDs 400 may be mounted in a fixture and incorporated into a lighting system. High-voltage LED 400 may be further processed according to methods described in U.S. Patent Application Ser. No. 61/362,584, which is hereby incorporated by reference in its entirety.

In some embodiments, as noted above, the nitride crystal may have threading dislocations that are arranged inhomogeneously as a two-dimensional array of high-dislocation-density regions, which will be referred to as cores, within a matrix of low-dislocation-density regions. Devices may be arranged with specific spatial arrangements with respect to the cores in order to optimize the yield or performance of the devices. In other embodiments, the nitride crystal may have threading dislocations that are arranged inhomogeneously as a one-dimensional array of alternating high-dislocation-density stripes and low-dislocation-density stripes.

FIG. 5 shows an LED epi layer structure grown on a GaN-on-handle (GaNOH) wafer, where the handle substrate is electrically conductive. The layer structure consists of at least one n-type (Al,Ga,In)N layer grown on top of the GaNOH wafer, followed by an active region with at least one and more typically multiple (Al,Ga,In)N layers. The active region is followed by at least one p-type (Al,Ga,In)N layer. The layer structures can be grown by either metal-organic chemical vapor deposition (MOCVD) or atomic-layer chemical vapor deposition (ALCVD) or atomic layer epitaxy (ALE) or molecular beam epitaxy (MBE).

In one embodiment, the GaNOH wafer consists of a very low dislocation density GaN (<10⁶-10⁷ cm⁻²) layer. The low dislocation density GaN layer can be formed by either dislocation bundling into organized cores or by using nanomasking approaches resulting in randomized cores. The circular regions encircling the cores have a gradient in dislocation or defect density and are known as the shell region. The regions between the shells are referred to as interstitial regions. The dopants in the shell and interstitial regions could be the same or different. Typical dopants are Si, O, P, Mg, etc.

FIG. 6 shows an LED epi layer structure grown on a GaN-on-handle (GaNOH) wafer, where the handle substrate is electrically insulating. The layer structure consists of at least one n-type (Al,Ga,In)N layer grown on top of the GaNOH wafer, followed by an active region with at least one and more typically multiple (Al,Ga,In)N layers. The active region is followed by at least one p-type (Al,Ga,In)N layer. Mesas are formed by etching through portions of the p-type and active layers and n-type and p-type contacts placed in the troughs between mesas and on top of the mesas, respectively.

FIG. 7 shows an LED epi layer structure grown on a roughened or a patterned GaNOH wafer, where the handle substrate is electrically conductive. The roughened or the patterned GaNOH wafer allows light scattering at the back side and improves light extraction from the LED device. The epi layer structure is similar to the one described in FIG. 5.

FIG. 8 shows an LED epi layer structure grown on a roughened or a patterned GaNOH wafer, where the handle substrate is electrically insulating. The roughened or the patterned GaNOH wafer allows light scattering at the back side and improves light extraction from the LED device. The epi layer, mesa, and electrical contact structures are similar to the ones described in FIGS. 5 and 6.

In the case of a wafer with organized dislocation cores, in a preferred embodiment the devices are formed between the core regions. FIGS. 9A-9C show the device layout using a square pitch GaNOH substrate, where the handle substrate is electrically conductive. The position of the p-contact, mesa and streets are shown in the figure. The substrate can have different regions with different dopant species and with different doping concentrations. The shell region encircles the core region and the interstitial regions are the region between the shells. There may be a gradient in defect density from the core region to the interstitial region. The pitch is defined by the spacing between two adjacent (nearest) cores. In one configuration, the LED consists of a square p-contact and a square mesa. In another configuration, the LED consists of a dog-ear pattern next to the core regions for p-contact and mesa. The core region of the substrate have very high density of extended defects and they can easily form a vertical current path. The cores could therefore be utilized as a shunt path for reducing series resistance in lateral device geometries.

FIGS. 10A and 10B show a device layout using a square pitch GaNOH substrate, where the handle substrate is electrically insulating. The position of the p-contact, mesa and streets are shown in the figure. Mesas may be formed by etching around the regions that will form the p-contact through the active layer and into the n-type material (either above or below the regrowth interface), and n-type and p-type contacts deposited. In one specific embodiment, the p-type contacts may be located predominantly over the interstitial regions and the n-type contacts may overlap the cores. In some embodiments at least one of the p-type contacts and the n-type contacts are transparent or semi-transparent. After deposition of the contacts the die may be singulated by sawing or scribing and breaking along the dashed lines in FIG. 10B.

In another configuration, shown in FIG. 11, several square devices may be laid out between two adjacent core regions. Following the fabrication of the devices, the wafer may be diced in the direction shown in the figure for singulation. The preferred directions to dice or scribe are either parallel or perpendicular to the m-plane of the wurtzite-structure nitride layer.

FIGS. 12A and 12B show a device layout using a hexagonal or triangular pitch GaNOH substrate. The positions of the p-contact, mesa and streets are shown in the figure. The substrate can have different regions with different dopant species and with different doping concentrations. In one configuration, the LED consists of a triangular p-contact and a triangular mesa. In another configuration, the LED consists of a dog-ear pattern next to the core regions for p-contact and mesa. The streets and the dicing directions are also shown in the figure.

Several additional core and wafer configurations for hexagonal-pitch dot core wafers are shown in FIGS. 13A-13D. Singulation, by slicing, sawing, or cleaving, may be performed along m-planes or along a-planes.

FIG. 14 shows a device layout in a flip-chip configuration. In one specific embodiment with this configuration, vias are etched through the core region of the wafer. Etching may be performed by reaction-ion etching, inductively-coupled plasma etching, or the like. An insulating layer, for example, SiO₂ or SiN_x, may be deposited on the side walls of the vias and a metal deposited inside the vias to provide n-type contacts. In another specific embodiment, vias are etched around the core regions of the wafer but the cores themselves are not removed and serve as contacts to the n-type layer. The top side view is shown in FIG. 15. N-contacts are formed through the vias, and therefore both n- and p-contacts are formed on the same side of the wafer. Etching vias through the core region removes the defective region of the material and may make the devices more reliable and robust.

FIG. 16 shows a sandwiched vertical structure with a conducting carrier substrate on the p-side. This configuration can be used with transparent conducting substrates like Zinc Oxide, Indium Tin Oxide, Tin-oxide, or the like or reflecting conducting substrates like Ag-coated Silicon, or the like. The conducting carrier substrate could also comprise at least one of AlO_x or CuO_x. FIG. 17 is a cross-sectional view diagram of a vertical thin-film device structure having a removed handle substrate, which has been debonded, etched, polished/ground, or cleaved in one or more embodiments. In an alternative embodiment. FIG. 18 is a cross-sectional view diagram of a vertical thin-film device structure having a removed handle substrate, which has been debonded, etched, polished/ground, or cleaved in one or more embodiments.

Ion implantantion may lead to defect formation and an implantation annealing may be required post-implantation to recover the original material quality. An in situ annealing step is an attractive way to recover the material from implantation damage. FIG. 19 shows a flow-chart for performing in situ annealing in a MOCVD chamber. The annealing is carried out at high temperature in the presence of ammonia and hydrogen gas. Forming gas and ammonia mixture could also be used. Reactor pressures of approximately one atmosphere or above and temperatures in excess of about 1000 or 1100° C. are preferable for annealing. At least one epitaxial film may be grown following the in situ annealing process.

In some embodiments the handle substrate is approximately homogeneous in composition and thickness. In other embodiments, shown schematically in FIGS. 20A-20C, the handle substrate comprises two or more vias or recesses, which may be filled with a conductive material capable of electrical and/or thermal conduction. The vias and/or recesses may be formed either before or after wafer-bonding a nitride layer to the handle substrate. In one set of embodiments, recesses are created in the handle substrate that allow for enhanced thermal conductivity without allowing electrical contact between the material in the recess(es) and the semiconductor materials. The conductive material may comprise a metal, such as copper, silver, or gold, a metal matrix composite, a particle-filled epoxy, silicone, or thermoplastic resin, or another material having a higher thermal conductivity than that of the handle substrate itself. The particles in a composite filler material may comprise at least one of diamond, cubic boron nitride, hexagonal boron nitride, graphite, silver, copper, aluminum nitride, beryllium oxide, aluminum oxide, or silicon carbide. This former geometry may be advantageous by allowing for an integrated thermal path out of a device that would otherwise require special packaging and/or heat sinking.

In another set of embodiments, through-vias are formed that penetrate the handle substrate and allow electrical contact between the conductive material and the semiconductor. This latter geometry may be advantageous for heterogeneous integration of mixed semiconductor technology systems (GaN, GaAs, Si, SiC, etc.) in that it significantly reduces the chip-to-chip interconnection distance reducing power consumption, heating, and interconnect delay.

In another specific embodiment, shown schematically in FIGS. 21A and 21B, the handle substrate may further comprise a down-converting light-emitting material, such as a phosphor. This geometry may advantageous as it allows for an integrated light conversion material for generation of white light through photon mixing of different wavelength photons (blue+yellow, for example). In another embodiment, multiple wavelength down-conversion materials are embedded in the substrate. These materials may be able to generate complex spectra when excited by photon emission from the epitaxial light emitting structures grown on them. The handle substrate may further comprise particles or grains having a different index of refraction than the matrix material so as to provide enhanced light scattering.

In a specific embodiment, the one or more entities comprises a phosphor or phosphor blend selected from one or more of (Y, Gd, Tb, Sc, Lu, La)₃(Al, Ga, In)₅O₁₂:Ce³⁺, SrGa₂S₄:Eu²⁺, SrS:Eu²⁺, and colloidal quantum dot thin films comprising CdTe, ZnS, ZnSe, ZnTe, CdSe, or CdTe. In other embodiments, the device may include a phosphor capable of emitting substantially red light. Such phosphor is selected from one or more of (Gd,Y,Lu,La)₂O₃:Eu³⁺, Bi³⁺; (Gd,Y,Lu,La)₂O₂S:Eu³⁺, Bi³⁺; (Gd,Y,Lu,La)VO₄:Eu³⁺, Bi³⁺; Y₂(O,S)₃:Eu³⁺; Ca_1-xMo_1-ySi_yO₄:, where 0.05≦x≦0.5, 0≦y≦0.1; (Li,Na,K)₅Eu(W,Mo)O₄; (Ca,Sr)S:Eu²⁺; SrY₂S₄:Eu²⁻; CaLa₂S₄:Ce³⁺; (Ca,Sr)S:Eu²⁺; 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ (MFG); (Ba,Sr,Ca)MgxP₂O₇:Eu²⁺, Mn²⁺; (Y,Lu)₂WO₆:Eu³⁺, Mo⁶⁺; (Ba,Sr,Ca)₃MgxSi₂O₈:Eu²⁺, Mn²⁺, wherein 1<x≦2; (RE_1-yCe_y)Mg_2-xLi_xSi_3-xP_xO₁₂, where RE is at least one of Sc, Lu, Gd, Y, and Tb, 0.0001<x<0.1 and 0.001<y<0.1; (Y, Gd, Lu, La)_2-xEu_xW_1-yMo_yO₆, where 0.5≦x.≦1.0, 0.01≦y≦1.0; (SrCa)_1-xEu_xSi₅N₈, where 0.01≦x≦0.3; SrZnO₂:Sm¹³; M_mO_nX wherein M is selected from the group of Sc, Y, a lanthanide, an alkali earth metal and mixtures thereof; X is a halogen; 1≦m≦3; and 1≦n≦4, and wherein the lanthanide doping level can range from 0.1 to 40% spectral weight; and Eu³⁺ activated phosphate or borate phosphors; and mixtures thereof. Of course, there can be other variations, modifications, and alternatives.

In one or more embodiments, wavelength conversion materials can be ceramic, thin-film-deposited, or discrete particle phosphors, ceramic or single-crystal semiconductor plate down-conversion materials, organic or inorganic downconverters, nanoparticles, or any other materials which absorb one or more photons of a primary energy and thereby emit one or more photons of a secondary energy (“wavelength conversion”). As an example, the wavelength conversion materials can include, but are not limited to the following:

• (Sr,Ca)₁₀(PO₄)6*DB₂O₃:Eu²⁺ (wherein 0<n₁)
• (Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu²⁺,Mn²⁺
• (Ba,Sr,Ca)BPO₅:Eu²⁺,Mn²⁺
• Sr₂Si₃O₈*2SrC₁₂:Eu²⁺
• (Ca,Sr,Ba)₃MgSi₂O₈:Eu²⁺, Mn²⁺
• BaA₁₈O₁₃:Eu²⁺
• 2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺
• (Ba,Sr,Ca)MgAl₁0O₁₇:Eu²⁺,Mn²⁺
• (Ba,Sr,Ca)Al₂O₄:Eu²⁺
• (Y,Gd,Lu,Sc,La)BO₃:Ce³⁺,Tb³⁺
• (Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu²⁺
• (Mg,Ca,Sr, Ba,Zn)₂Si_1—xO_4—2x:Eu²⁺ (wherein 0<x=0.2)
• (Sr,Ca,Ba)(Al,Ga,m)₂S₄:Eu²⁺
• (Lu,Sc,Y,Tb)_2—u—vCevCa_1-uLiwMg_2—wPw(Si,Ge)_3—w01_2—u/2 where —O.SSu^1; 0<v£Q.1; and OSw^O.2
• (Ca,Sr)₈(Mg,Zn)(SiO₄)₄C₁₂:Eu²⁻,Mn²⁻
• Na₂Gd₂B₂O₇:Ce³⁺,Tb³⁺
• (Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu²⁺,Mn²⁺
• (Gd,Y,Lu,La)₂O₃:Eu³⁺,Bi³⁺
• (Gd,Y,Lu,La)₂O₂S:Eu³⁺,Bi³⁻
• (Gd,Y,Lu,La)_vO₄:Eu³⁺,Bi³⁺
• (Ca,Sr)S:Eu²⁺,Ce³⁺
• (Y,Gd,Tb,La,Sm,Pr,Lu)₃(Sc,Al,Ga)_5—uO_12—3/₂n:Ce³⁺ (wherein 0^0^0.5)
• ZnS:Cu+,Cl˜
• ZnS:Cu+,Al³⁺
• ZnS:Ag+,Al³⁺
• SrY₂S₄:Eu²⁺
• CaLa₂S₄:Ce³⁺
• (Ba,Sr,Ca)MgP₂O₇:Eu2+,Mn²⁺
• (Y,Lu)₂WO₆:Eu³⁺,Mo⁶⁺
• (Ba,Sr,Ca)nSinNn:Eu²⁻ (wherein 2_n+4=3n)
• Ca₃(SiO₄)Cl₂:Eu²⁺
• ZnS:Ag+,Cl˜
• (Y,Lu,Gd)_2—nCanSi₄N_6-nC_1—n:Ce³+, (wherein OSn^O.5)
• (Lu,Ca,Li,Mg,Y)alpha-SiAlON doped with Eu²⁺ and/or Ce³⁺
• (Ca,Sr,Ba)SiO₂N₂:Eu²⁺,Ce³⁺

For purposes of the application, it is understood that when a phosphor has two or more dopant ions (i.e., those ions following the colon in the above phosphors), this is to mean that the phosphor has at least one (but not necessarily all) of those dopant ions within the material. That is, as understood by those skilled in the art, this type of notation means that the phosphor can include any or all of those specified ions as dopants in the formulation. Of course, there can be other variations, modifications, and alternatives.

While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.

Claims

1. A gallium and nitrogen containing device comprising: a gallium and nitrogen containing material, wherein, the gallium and nitrogen containing material comprises a first surface region, a second surface region, and at least one core region;the first surface region is opposite the second surface region; andthe at least one core region extends between the first surface region and the second surface region and through the gallium and nitrogen containing material;an interface region overlying the second surface region;at least one n-type epitaxial growth region overlying the interface region;a core structure extending from the at least one core region through the at least one n-type epitaxial growth region;an active region overlying the at least one n-type epitaxial growth region;a p-type region overlying the active region;a first handle substrate overlying the p-type region, wherein the first handle substrate is transparent, substantially transparent, or reflective; andat least one p-contact region overlying the first handle substrate.

2. The device of claim 1, wherein the interface region is characterized by a defect density of less than about 106 cm−2 to 107 cm−2 within a matrix region between adjacent core regions.

3. The device of claim 1, wherein the gallium and nitrogen containing material is provided from a dot core substrate.

4. The device of claim 1, wherein the first surface region comprises a patterned, textured, or roughened surface structure.

5. The device of claim 1, wherein, the at least one core region comprises a plurality of core regions; andthe plurality of core regions form a square array and a die is approximately square.

6. The device of claim 1, wherein, the at least one core region comprises a plurality of core regions; andthe plurality of core regions form a hexagonal array and a die is approximately triangular.

7. The device of claim 1, further comprising: an adhesion layer overlying the first surface region;a second handle substrate comprising a first surface region and a second surface region, wherein, the first surface region of the second handle substrate is opposite the second surface region of the second handle substrate; andthe second surface region of the second handle substrate overlies the adhesion layer; andat least one n-contact region overlying the first surface region of the second handle substrate.

8. The device of claim 1, further comprising at least one n-contact region overlying the first surface region.

9. The device of claim 1, wherein the first handle substrate comprises at least one through via or partial via.

10. The device of claim 1, wherein the first handle substrate is transparent or substantially transparent and comprises a down-converting light-emitting material.

11. A gallium and nitrogen containing device comprising: a gallium and nitrogen containing material, wherein, the gallium and nitrogen containing material comprises a first surface region, a second surface region, and at least one core region;the first surface region is opposite the second surface region; andthe at least one core region extends between the first surface region and the second surface region and through the gallium and nitrogen containing material;an interface region overlying the second surface region;at least one n-type epitaxial growth region overlying the interface region;a core structure extending from the at least one core region through the at least one n-type epitaxial growth region;an active region overlying the at least one n-type epitaxial growth region;a p-type region overlying the active region;one or more via or street structures providing an electrical barrier between adjacent core regions and a matrix region between the adjacent core regions;at least one electrical contact region overlying a core region surrounded by a via or street structure; andat least one handle substrate.

12. The device of claim 11, wherein the interface region is characterized by a defect density of less than about 106 cm−2 to 107 cm−2 within the matrix region.

13. The device of claim 11, wherein the gallium and nitrogen containing material is provided from a dot core substrate.

14. The device of claim 11, wherein the first surface region comprises a patterned, textured, or roughened surface structure.

15. The device of claim 11, wherein, the at least one core region comprises a plurality of core regions; andthe plurality of core regions form a square array and a die is approximately square.

16. The device of claim 11, wherein, the at least one core region comprises a plurality of core regions; andthe plurality of core regions form a hexagonal array and a die is approximately triangular.

17. The device of claim 11, further comprising: an adhesion layer overlying the first surface region; andat least one p-contact region overlying the p-type region, wherein, the at least one handle substrate comprises a first surface region and a second surface region;the first surface region is opposite the second surface region;the second surface region overlies the adhesion layer; andthe at least one electrical contact region comprises an n-type contact region.

18. The device of claim 11, further comprising: at least one n-contact region overlying the first surface region; andat least one p-contact region overlying the at least one core region; andwherein the at least one handle substrate comprises a first transparent or reflective handle substrate overlying the at least one p-type region.

19. The device of claim 11, wherein the at least one handle substrate comprises at least one through via or partial via.

20. The device of claim 11, wherein, the at least one handle substrate is transparent or substantially transparent; andthe at least one handle substrate comprises a down-converting light-emitting material.