Patent Application
20110140071
1) Field
Embodiments of the present invention pertain to the field of hydride vapor phase epitaxy and, in particular, to nano-spherical group III-nitride materials and methods of forming nano-spherical group III-nitride materials.
2) Description of Related Art
Group III-V materials are playing an ever increasing role in the semiconductor and related, e.g. light-emitting diode (LED), industries. Often, group III-nitride materials are used because of their particularly useful optoelectronic characteristics.
Nano-spherical group III-nitride materials and methods of forming nano-spherical group III-nitride materials are described. In the following description, numerous specific details are set forth, such as fabrication conditions and material regimes, in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known features, such as facility layouts or specific tool configurations, are not described in detail in order to not unnecessarily obscure embodiments of the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale. Additionally, other arrangements and configurations may not be explicitly disclosed in embodiments herein, but are still considered to be within the spirit and scope of the invention.
Disclosed herein are nano-spherical group III-nitride materials. In one embodiment, such a nano-spherical group III-nitride material is included in a light-emitting diode (LED) structure or in a laser diode (LD) structure.
Also disclosed herein are methods of forming nano-spherical group III-nitride materials by hydride vapor phase epitaxy. In one embodiment, a method includes using a nano-spherical group III-nitride material to form a light-emitting diode (LED) structure or in a laser diode (LD) structure.
Key concepts pertaining to various embodiments of the present invention may lead to the formation of nano-spherical group III-nitride materials or to the incorporation of such materials into LED or LD related devices. Such concepts may include: (a) hydride or halide vapor phase epitaxy (HYPE), (b) the formation of gallium nitride or other group III nitrides, (c) dimensions on the micro- or nano-scale, (d) light-emitting diodes (LEDs), and (e) laser diodes (LDs). The materials and/or processes described herein may also pertain to electronic devices such as field emission transistors.
In accordance with an embodiment of the present invention, methods of producing nano-structural group III-nitrides on different substrates are disclosed. In an embodiment, the nano-structural group III-nitrides are or are essentially nano-spherical. The nano-spherical group III-nitrides structures are composed of nano-scale hexagonal-shaped rods. For example, in one embodiment, the rods have a diameter approximately in the range of 50 nanometers-100 nanometers and a length approximately in the range of 200 nanometers-500 nanometers are packed in a way to provide the nano-speherical structure. However, it is noted that the specific ranges provided for the hexagonal-shaped rods are merely an embodiment and that the nano-spherical group III-nitride materials described herein are not necessarily limited to those dimensions.
In accordance with an embodiment of the present invention, an LED or LD device is formed based on a nano-spherical group III-nitride material or the nano-spherical group III-nitride material is used as a high purity source of material for fabricating such devices. In the former case, in an exemplary embodiment, each of a plurality of nanorod group III-nitrides structures is composed of an n-type gallium nitride (n-GaN)/indium gallium nitride (InGaN)/multi-layer quantum well layers (MQWs)/aluminum gallium nitride (AlGaN)/p-type gallium nitride (p-GaN) core-shell structure. In an embodiment, each nano-sperical structure is a core-shell structure and, in particular embodiment, each nano-spherical structure is arranged to have a different composition. A group of such differing nano-spherical structures may be combined on a single substrate to cover a band-gap spectrum approximately in the range of 0.7 eV to 6.2 eV.
One-dimensional structures composed of GaN or other group III-nitride materials (e.g., binary and ternary alloys in an In—Al—Ga—N system) may provide unique material properties such as, but not limited to, a direct wide band gap approximately in the range of 0.7 eV to 6.2 eV, a high breakdown electric field, and high saturated velocities. In an embodiment, high saturated velocities may have great potential for novel device application, including for LEDs, LDs, and other related electronic devices. In accordance with an embodiment of the present invention, a controlled synthesis and reproducable assembling of nano-structured group III-nitride materials is the key to achieve and demonstrate efficient devices.
A nano-spherical group III-nitride material structure may be fabricated by HVPE for light-emmiting and laser device applications.
Referring to
With respect to substrate 104, in an embodiment, a sapphire substrate is used. However, a similar approach may be used even in the presence of a non-sapphire substrate. Such other substrates may include, but are not limited to a silicon substrate, a silicon carbide substrate, a lithium aluminum oxide substrate, a lithium gallium oxide substrate, a zinc oxide substrate, a magnesium oxide substrate, a scandium magnesium oxide substrate, or a glass substrate. In an embodiment, a film of the majority composition of nano-spherical gallium nitride structure 102, e.g. a gallium nitride film, is formed on the surface of substrate 104 during formation of nano-spherical gallium nitride structure 102. The film ultimately is sandwiched by nano-spherical gallium nitride (GaN) structure 102 and substrate 104, as is depicted in
In accordance with an embodiment of the present invention, nano-spherical group III-nitride material structures, such as the structures described in association with
Referring to
With respect to substrate 204, in an embodiment, a sapphire substrate is used. However, a similar approach may be used even in the presence of a non-sapphire substrate. Such other substrates may include, but are not limited to a silicon substrate, a silicon carbide substrate, a lithium aluminum oxide substrate, a lithium gallium oxide substrate, a zinc oxide substrate, a magnesium oxide substrate, a scandium magnesium oxide substrate, or a glass substrate. In an embodiment, a film of the majority composition of nano-spherical gallium nitride structure 202, e.g. a gallium nitride film, is formed on the surface of substrate 104 during formation of nano-spherical gallium nitride structure 202. The film ultimately is sandwiched by nano-spherical gallium nitride (GaN) structure 202 and substrate 204, as is depicted in
With respect to the chemical composition of nano-spherical gallium nitride structure 202, in an embodiment, nano-spherical gallium nitride structure 202 is composed entirely of or essentially entirely of gallium and nitrogen. The composition is the same composition as the gallium nitride film grown on the top surface of substrate 204 during growth of nano-spherical gallium nitride structure 202.
Referring to
In an embodiment, as determined by the morphology of nano-spherical gallium nitride structure 202 and its association with a gallium nitride film formed between substrate 204 and nano-spherical gallium nitride structure 202, nano-spherical gallium nitride structure 202 is not nucleated on the gallium nitride film surface surface, but rather is grown to its full size inside of an HVPE chamber (e.g., in the gas phase) and eventually “dropped off” onto the gallium nitride film sometime prior to completion of the growth.
Referring to
It is to be understood that varying structural or compostional nanosperical units may be fabricated. For example, in accordance with an embodiment of the present invention, with each concentric ring viwed as a core shell structure, a plurality of concentric rings assembled into a spherical shape, with at least two adjacent concentric rings composed of different material combinations to provide a different band-gap materials adjacent one another. In an embodiment, a device based on nano-spherical structures with differing concentric rings of material is used to provide a nGaN/InGaN MQWs/AlGaN/pGaN arrangement with each concentric ring forming one of the layers in the stack. In another embodiment, the incorporation of certain III-V elements, such as indium, is greater in a nano-sphere than in a one-dimensional material. This result may enable the opportunity to fabricate devices that cover the whole visible spectrum and crete a full color display from a single nanospherical particle. In a similar approach, laser diodes may be fabricated to have a tunable wavelength.
A nano-spherical group III-nitride material structure may be used as a base or backbone in the fabrication of a light-emitting diode (LED) device. Alternatively, nano-spherical group III-nitride material structure may serves as a source of high quality material that may be isolated and incorporated into a light-emitting diode (LED) device or other III-V material device. For example,
Referring to
Gallium nitride (GaN) film 506 may be a gallium nitride (GaN) film containing only gallium nitride (GaN) or may be a gallium nitride (GaN) alloy film, such as for an example aluminum gallium nitride (AlGaN). In an embodiment of the present invention, the aluminum gallium nitride film has a composition of AlxGa1-xN (0≦x≦1). The gallium nitride film or alloy film can have a thickness between 2-500 microns is typically formed between 2-15 microns. In an embodiment of the present invention, the gallium nitride film has a thickness of at least 3 microns to sufficiently suppress threading dislocations. In an embodiment, the source of gallium nitride in film 506 is a nano-spherical group III-nitride material.
Referring to
An example of a HVPE deposition chamber which may be utilized to deposit nano-spherical group III-nitride material structures or similar structures in accordance with embodiments of the present invention is illustrated and described with respect to
To react with the gas from the first source 610, precursor material may be delivered from one or more second sources 618. The one or more second sources 618 may comprise precursors suitable for forming nano-spherical group III-nitride material structures. The precursor may be delivered to the chamber 602 by flowing a reactive gas over and/or through the precursor in the precursor source 618. In one embodiment, the reactive gas may comprise a chlorine containing gas such as diatomic chlorine. The chlorine containing gas may react with the precursor source to form a chloride. In order to increase the effectiveness of the chlorine containing gas to react with the precursor, the chlorine containing gas may snake through the boat area in the chamber 632 and be heated with the resistive heater 620. By increasing the residence time that the chlorine containing gas is snaked through the chamber 632, the temperature of the chlorine containing gas may be controlled. By increasing the temperature of the chlorine containing gas, the chlorine may react with the precursor faster. In other words, the temperature is a catalyst to the reaction between the chlorine and the precursor mixture.
In order to increase the reactiveness of the precursor, the precursor may be heated by a resistive heater 620 within the second chamber 632 in a boat. The chloride reaction product may then be delivered to the chamber 602. The reactive chloride product first enters a tube 622 where it evenly distributes within the tube 622. The tube 622 is connected to another tube 624. The chloride reaction product enters the second tube 624 after it has been evenly distributed within the first tube 622. The chloride reaction product then enters into the chamber 602 where it mixes with the nitrogen containing gas to form a nitride layer or nano-structure on the substrate 616 that is disposed on a susceptor 614. In one embodiment, the susceptor 614 may comprise silicon carbide. The nitride layer or nano-structure may comprise gallium nitride or aluminum nitride for example. The other reaction products, such as nitrogen and chlorine, are exhausted through an exhaust 626.
In another aspect of the present invention, instead of being a source of material for a conventional LED or similar device, as described above in association with
Referring to
Embodiments of the present invention may also include formation of nano-spherical group III-nitride materials or related films by metal-organic chemical vapor deposition (MOCVD). An example of an MOCVD deposition chamber which may be utilized to deposit nano-spherical group III-nitride materials or related films, in accordance with embodiments of the present invention, is illustrated and described with respect to
The apparatus 800 shown in
The substrate carrier 814 may include one or more recesses 816 within which one or more substrates 840 may be disposed during processing. The substrate carrier 814 may carry six or more substrates 840. In one embodiment, the substrate carrier 814 carries eight substrates 840. It is to be understood that more or less substrates 840 may be carried on the substrate carrier 814. Typical substrates 840 may include sapphire, silicon carbide (SiC), silicon, or gallium nitride (GaN). It is to be understood that other types of substrates 840, such as glass substrates 840, may be processed. Substrate 840 size may range from 50 mm-100 mm in diameter or larger. The substrate carrier 814 size may range from 200 mm-750 mm. The substrate carrier 814 may be formed from a variety of materials, including SiC or SiC-coated graphite. It is to be understood that substrates 840 of other sizes may be processed within the chamber 802 and according to the processes described herein. The showerhead assembly 804 may allow for more uniform deposition across a greater number of substrates 840 and/or larger substrates 840 than in traditional MOCVD chambers, thereby increasing throughput and reducing processing cost per substrate 840.
The substrate carrier 814 may rotate about an axis during processing. In one embodiment, the substrate carrier 814 may be rotated at about 2 RPM to about 100 RPM. In another embodiment, the substrate carrier 814 may be rotated at about 30 RPM. Rotating the substrate carrier 814 aids in providing uniform heating of the substrates 840 and uniform exposure of the processing gases to each substrate 840.
The plurality of inner and outer lamps 821A, 821B may be arranged in concentric circles or zones (not shown), and each lamp zone may be separately powered. In one embodiment, one or more temperature sensors, such as pyrometers (not shown), may be disposed within the showerhead assembly 804 to measure substrate 840 and substrate carrier 814 temperatures, and the temperature data may be sent to a controller (not shown) which can adjust power to separate lamp zones to maintain a predetermined temperature profile across the substrate carrier 814. In another embodiment, the power to separate lamp zones may be adjusted to compensate for precursor flow or precursor concentration non-uniformity. For example, if the precursor concentration is lower in a substrate carrier 814 region near an outer lamp zone, the power to the outer lamp zone may be adjusted to help compensate for the precursor depletion in this region.
The inner and outer lamps 821A, 821B may heat the substrates 840 to a temperature of about 400 degrees Celsius to about 1200 degrees Celsius. It is to be understood that the invention is not restricted to the use of arrays of inner and outer lamps 821A, 821B. Any suitable heating source may be utilized to ensure that the proper temperature is adequately applied to the chamber 802 and substrates 840 therein. For example, in another embodiment, the heating source may comprise resistive heating elements (not shown) which are in thermal contact with the substrate carrier 814.
A gas delivery system 825 may include multiple gas sources, or, depending on the process being run, some of the sources may be liquid sources rather than gases, in which case the gas delivery system may include a liquid injection system or other means (e.g., a bubbler) to vaporize the liquid. The vapor may then be mixed with a carrier gas prior to delivery to the chamber 802. Different gases, such as precursor gases, carrier gases, purge gases, cleaning/etching gases or others may be supplied from the gas delivery system 825 to separate supply lines 831, 832, and 833 to the showerhead assembly 804. The supply lines 831, 832, and 833 may include shut-off valves and mass flow controllers or other types of controllers to monitor and regulate or shut off the flow of gas in each line.
A conduit 829 may receive cleaning/etching gases from a remote plasma source 826. The remote plasma source 826 may receive gases from the gas delivery system 825 via supply line 824, and a valve 830 may be disposed between the showerhead assembly 804 and remote plasma source 826. The valve 830 may be opened to allow a cleaning and/or etching gas or plasma to flow into the showerhead assembly 804 via supply line 833 which may be adapted to function as a conduit for a plasma. In another embodiment, apparatus 800 may not include remote plasma source 826 and cleaning/etching gases may be delivered from gas delivery system 825 for non-plasma cleaning and/or etching using alternate supply line configurations to shower head assembly 804.
The remote plasma source 826 may be a radio frequency or microwave plasma source adapted for chamber 802 cleaning and/or substrate 840 etching. Cleaning and/or etching gas may be supplied to the remote plasma source 826 via supply line 824 to produce plasma species which may be sent via conduit 829 and supply line 833 for dispersion through showerhead assembly 804 into chamber 802. Gases for a cleaning application may include fluorine, chlorine or other reactive elements.
In another embodiment, the gas delivery system 825 and remote plasma source 826 may be suitably adapted so that precursor gases may be supplied to the remote plasma source 826 to produce plasma species which may be sent through showerhead assembly 804 to deposit CVD layers, such as films, for example, on substrates 840.
A purge gas (e.g., nitrogen) may be delivered into the chamber 802 from the showerhead assembly 804 and/or from inlet ports or tubes (not shown) disposed below the substrate carrier 814 and near the bottom of the chamber body 803. The purge gas enters the lower volume 810 of the chamber 802 and flows upwards past the substrate carrier 814 and exhaust ring 820 and into multiple exhaust ports 809 which are disposed around an annular exhaust channel 805. An exhaust conduit 806 connects the annular exhaust channel 805 to a vacuum system 812 which includes a vacuum pump (not shown). The chamber 802 pressure may be controlled using a valve system 807 which controls the rate at which the exhaust gases are drawn from the annular exhaust channel 805.
It is to be understood that embodiments of the present invention may include the use of substrates, such as but not limited to a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, a silicon on diamond (SOD) substrate, a quartz (SiO2) substrate, a glass substrate, a zinc oxide (ZnO) substrate, a magnesium oxide (MgO) substrate, and a lithium aluminum oxide (LiAlO2) substrate. Any well know method, such as masking and etching may be utilized to form features, such as posts, from a planar substrate to create a patterned substrate. In a specific embodiment, however, the patterned substrate is a (0001) patterned sapphire substrate (PSS). Patterned sapphire substrates may be ideal for use in the manufacturing of LEDs because they increase the light extraction efficiency which is extremely useful in the fabrication of a new generation of solid state lighting devices. Other embodiments include the use of planar (non-patterned) substrates, such as a planar sapphire substrate.
In some embodiments, growth of a gallium nitride or related material on a substrate is performed along a (0001) Ga-polarity, N-polarity, or non-polar a-plane {112-0} or m-plane 1101-01, or semi-polar planes. In some embodiments, posts formed in a patterned growth substrate are round, triangular, hexagonal, rhombus shape, or other shapes effective for block-style growth. In an embodiment, the patterned substrate contains a plurality of features (e.g., posts) having a cone shape. In a particular embodiment, the feature has a conical portion and a base portion. In an embodiment of the present invention, the feature has a tip portion with a sharp point to prevent over growth. In an embodiment, the tip has an angle (θ) of less than 145° and ideally less than 110°. Additionally, in an embodiment, the feature has a base portion which forms a substantially 90° angle with respect to the xy plane of the substrate. In an embodiment of the present invention, the feature has a height greater than one micron and ideally greater than 1.5 microns. In an embodiment, the feature has a diameter of approximately 3.0 microns. In an embodiment, the feature has a diameter height ratio of approximately less than 3 and ideally less than 2. In an embodiment, the features (e.g., posts) within a discrete block of features (e.g., within a block of posts) are spaced apart by a spacing of less than 1 micron and typically between 0.7 to 0.8 microns.
It is also to be understood that embodiments may include a Group III-Nitride epitaxial film that can be suitably deposited by hydride vapor phase epitaxy or MOCVD, or the like, deposition. The Group III-Nitride film may be a binary, ternary, or quaternary compound semiconductor film formed from a group III element or elements selected from gallium, indium and aluminum and nitrogen. That is, the Group III-Nitride crystalline film can be any solid solution or alloy of one or more Group III element and nitrogen, such as but not limited to GaN, AlN, InN, AlGaN, InGaN, InAlN, and InGaAlN. However, in a specific embodiment, the Group III-Nitride film is an n-type gallium nitride (GaN) film. The Group III-Nitride film can have a thickness between 2-500 microns and is typically formed between 2-15 microns. Thicknesses greater than 500 microns are possible because of, e.g., the high growth rate of HYPE. In an embodiment of the present invention, the Group III-Nitride film has a thickness of at least 3.0 microns to sufficiently suppress threading dislocations. Additionally, as described above, the Group III-Nitride film can be doped. The Group III-Nitride film can be p-typed doped using any p-type dopant such as but not limited Mg, Be, Ca, Sr, or any Group I or Group II element have two valence electrons. The Group III-Nitride film can be p-type doped to a conductivity level of between 1×1016 to 1×1020 atoms/cm3.
It is also to be understood that embodiments of the present invention need not be limited to the fabrication of LEDs. For example, in another embodiment, devices other than LED devices may be fabricated, such as but not limited to field-effect transistor (FET) devices. In such embodiments, there may not be a need for a p-type material on top of a structure of layers. Instead, an n-type or un-doped material may be used in place of the p-type layer.
Thus, nano-spherical group III-nitride materials and methods of forming nano-spherical group III-nitride materials have been disclosed. In accordance with an embodiment of the present invention, a nano-spherical group III-nitride material is included in a light-emitting diode structure or in a laser diode structure.
This application claims the benefit of U.S. Provisional Application No. 61/286,310, filed Dec. 14, 2009, the entire contents of which are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61286310 | Dec 2009 | US |
