1. Field of the Invention
Embodiments relate generally to light emitting diode structures and related methods. More particularly, embodiments relate to enhanced performance light emitting diode structures and related methods.
2. Description of the Related Art
Although efficient light emitting sources predicated upon silicon based nanostructures may not yet have been demonstrated, such silicon nanostructure based light sources are clearly desirable. Such silicon nanostructure based light sources are desirable insofar as they may presumably be fabricated using otherwise conventional silicon nanostructure based processing fabrication tooling.
Since such silicon nanostructure based light sources are in particular very attractive in optical signal processing applications and related applications, desirable are silicon nanostructure based light sources, methods for fabrication thereof and methods for use thereof.
Embodiments include a silicon nanostructure based infrared light emitting diode structure and a method for fabricating the silicon nanostructure based infrared light emitting diode structure. The particular silicon nanostructure based light emitting diode structure in accordance with the embodiments utilizes a lateral p-i-n diode carrier injection (i.e., relative to a plane of a substrate over which is located and fabricated the silicon nanostructure), rather than a vertical p-i-n diode carrier injection. The particular silicon nanostructure based light emitting diode structure in accordance with the embodiments also includes, located over a Si substrate and a thick dielectric layer that is generally transparent to a light emitting diode emitted wavelength and also insulating electrically, a multilayer material layer comprising alternating, interposed and laminated sub-layers of: (1) a group IV nanocrystalline material; and (2) a dielectric material doped with at least one of erbium and neodymium. To define a waveguide mode, the multilayer material layer structure in accordance with the embodiments is further covered by a dielectric capping layer. However, other structural designs may also alternatively be proposed to localize a waveguide mode within a silicon nanostructure based infrared light emitting diode structure in accordance with the embodiments.
In a particular embodiment: (1) the group IV nanocrystal material may comprise a nanocrystalline silicon material (i.e., nc-Si); and (2) the dielectric material may comprise an erbium doped silicon oxide material (i.e., Er—SiOx).
Within the context of the embodiments as disclosed and the invention as claimed, a “sub-layer” with respect to a “multilayer material layer” is intended as comprising an individual one of: (1) a group IV nanocrystalline material; and (2) a dielectric material (as described above) which alternates with, is interposed between and laminated to an individual one of the other of: (1) the group IV nanocrystalline material; and (2) the dielectric material (as described above).
Within the context of the embodiments as disclosed and the invention as claimed, use of the terminology “over” for a particular layer or structure with respect to an additional layer or structure is intended to describe a relative vertical location of the particular layer or structure with respect to the additional layer or structure, absent necessary contact of the particular layer or structure with respect to the additional layer or structure. In contrast, use of the terminology “upon” for a particular layer or structure with respect to an additional layer or structure is intended to describe the same relative vertical location of the particular layer or structure with respect to the additional layer or structure, but with necessary contact of the particular layer or structure with respect to the additional layer or structure.
Within the context of the embodiments as disclosed and the invention as claimed, when materials of stoichiometric composition are described within an operational component, layer or structure also intended are related materials of non-stoichiometric composition.
Within the context of the embodiments as disclosed and the invention as claimed, a “structure” is generally intended as a physical assemblage of layers of described materials composition and location, while a “device” is generally intended as a “structure” that is electrically energized and optically active.
A particular light emitting diode structure in accordance with the embodiments includes a substrate (i.e., often but not exclusively a Si substrate, and including a thermal SiO2 layer to insulate a multilayer material layer structure in accordance with the embodiments from the Si substrate, and simultaneously also transparent to a wavelength emitted from the multilayer material layer structure). This particular light emitting diode structure also includes a multilayer material layer located over the substrate (and the optional additional insulating layer). The multilayer material layer includes: (1) a plurality of group IV nanocrystal material sub-layers; and (2) a plurality of dielectric material sub-layers doped with at least one of erbium and neodymium, and alternating with, interposed between and laminated to the plurality of group IV nanocrystal material sub-layers. The multilayer material layer structure is doped (i.e., typically but not necessarily exclusively by means of ion implantation) to provide a p-i-n diode. This particular light emitting diode structure also includes at least two electrodes, one edge coupled to each of a p region and an n region within the p-i-n diode. As well, this particular light emitting diode structure may also include a dielectric capping layer over the multilayer material layer to define a waveguide mode within the multilayer material layer.
A particular method for fabricating a light emitting diode structure in accordance with the embodiments includes forming over a substrate a multilayer material layer including: (1) a plurality of group IV nanocrystal material sub-layers; and (2) a plurality of dielectric material sub-layers doped with at least one of erbium and neodymium, and alternating with, interposed between and laminated to the plurality of group IV nanocrystal material sub-layers. This particular method also includes doping the multilayer material layer to form a p-i-n diode. This particular method also includes forming over the substrate at least two electrodes, one coupled to each of a p region and an n region within the p-i-n diode.
The objects, features and advantages of the embodiments are understood within the context of the Detailed Description of the Non-Limiting Embodiments, as set forth below. The Detailed Description of the Non-Limiting Embodiments is understood within the context of the accompanying drawings, that form a material part of this disclosure, wherein:
a shows a schematic perspective-view diagram of a silicon based light emitting diode nanostructure in accordance with the embodiments. The main elements are: Si substrate, a thermal SiO2 layer to insulate the multilayer material layer from the substrate and simultaneously provide a structure transparent to a wavelength emitted from the multilayer material layer structure, the multilayer material layer structure, and an insulating SiO2 capping layer to define a waveguide mode formed in the multilayer material layer structure.
a shows a schematic top-view diagram of a final device structure. p and n regions, and a waveguide coupler, are illustrated.
a shows I-V characteristics from Er doped SiO2/nc-Si multilayer material layers with 5 nm layers and a 50 μm of electrode spacing (black squares) and 15 nm layers and a 200 μm of electrode spacing (red (i.e., lighter gray shade) circles and a 50 μm of electrode spacing (red (i.e., lighter gray shade) open squares): on a linear scale in forward and reverse bias. The total thicknesses of the Si and SiO2 layers, as well as Er concentration, are the same in both cases.
a shows electroluminescence spectra from an Er doped SiO2/nc-Si multilayer with 15 nm layer thickness and electrode spacing of 40 μm under different applied forward voltages. A photoluminescence spectrum is shown for comparison.
a to
While the embodiments that follow describe most particularly results of studies of Er doped SiO2/nc-Si multilayer material layer that show within a light emitting diode device a strong electroluminescence (EL) under lateral carrier injection in forward bias, the embodiments are not intended to be so specifically limited. Rather, the embodiments are intended to include alternative doped dielectric/nc-group IV multilayer material layer compositions within the context of photoluminescence improvements and electroluminescence improvements. Thus, included within candidate multilayer material layer compositions for use within a light emitting diode structure or device in accordance with the embodiments are: (1) at least one lanthanide element dopant selected from the group consisting of erbium and neodymium, within any of several dielectric materials (i.e., silicon containing dielectric materials and alternative dielectric materials), including but not limited to silicon oxide, silicon nitride and silicon oxynitride or other dielectric materials like e.g., Al2O3 or stoichiometric erbium silicates (Er2SiO5 or Er2Si2O7), and (2) any of several group IV nanocrystal semiconductor materials, including but not limited to silicon, germanium, silicon-germanium alloy, silicon-carbon alloy, germanium-carbon alloy and silicon-germanium-carbon alloy group IV semiconductor materials.
Within a multilayer material layer in accordance with the embodiments, a thickness of a dielectric material sub-layer ranges from about 2 to about 50 nanometers, while a thickness of a group IV material sub-layer ranges from about 2 to about 50 nanometers, to provide a total thickness of a multilayer material layer from about 200 to about 1000 nanometers. As well, erbium and/or neodymium dopant concentrations within a doped silicon containing dielectric material sub-layer ranges from about 0.1 to about 2 atomic percent.
In addition, doping levels for forming a lateral p-i-n diode structure within a multilayer material layer in accordance with the embodiments range from about 1018 to about 1022 dopant atoms per cubic centimeter for a p dopant and from about 1018 to about 1022 dopant atoms per cubic centimeter for an n dopant. As will be discussed in further detail below, specific non-limiting ion implantation conditions may be used to secure the foregoing volume concentrations of a p dopant and an n dopant within a multilayer material layer in accordance with the embodiments.
A particular schematic perspective view diagram illustrating a lateral charge injection p-i-n light emitting diode structure in accordance with the embodiments is illustrated in
The embodiments more specifically provide results of studies of Er doped SiO2/nc-Si multilayer material layers that show: (1) strong photoluminescence (PL) under erbium in SiO2 matrix off-resonant optical pumping; and (2) strong electroluminescence (EL) under lateral carrier injection in forward bias. Carriers injected in the intrinsic region of the lateral p-i-n diode structure excite the Er ions located in the SiO2 layers. A major advantage of the embodied method and structure in accordance with the embodiments compared with vertical carrier injection is that transport is much easier and that the Er—Si distance is very well defined. Er doped SiO2/nc-Si multilayer material layers may also serve as waveguides to achieve amplification and eventually lasing, and minimize losses due to free carrier absorption because they act as horizontal multislot waveguides that confine an optical field into the SiO2 layers, away from the Si layers where the free carriers are injected. Since optical pumping of Er-doped silica waveguides sensitized by nc-Si has already produced net optical gain, the embodied ordered structures that are less susceptible to free carrier absorption losses should be able to achieve significant optical gain.
2.1 Fabrication of Electroluminescent Device
Multilayer material layer fabrication for electroluminescence studies was the same as generally described above except that deposition was on 5 μm thick thermally grown SiO2 on Si (100) wafers. Er doped SiO2/nc-Si multilayer structures were deposited using radio frequency magnetron sputtering. However, any other deposition technique with a nanometer resolution of thickness (e.g. molecular beam epitaxy (MBE)) may be used to produce similar multilayer structures. In this particular case, the following deposition rates were estimated: 0.0315 nm/s and 0.0383 nm/s for SiO2 and Si, respectively. Er doping SiO2 layer is achieved by co-sputtering Er with a pure Er metal target simultaneously with SiO2, while the Er concentration is controlled by the plasma power applied onto an Er target. A plasma power of 40 W was applied. Multilayers are fabricated by alternating deposition of multiple layers of nm-thin a-Si and Er-doped SiO2 thin films. Subsequently, deposited samples are thermal annealed in a furnace tube at 1050 C for 1 hour, to form the silicon nanostructure and to activate the Er atoms.
3.1 Current-Voltage Characteristics and Electroluminescence Results
Most studies on electrical pumping use vertical carrier injection where charge flow is limited by an oxide dielectric layer. The embodied approach instead makes use of a lateral p-i-n junction embedded into a multilayer material layer. To verify that lateral electrical injection had taken place, current-voltage measurements were performed. The I-V curves for multilayer material layer with different layer thicknesses, electrodes spacings, and widths are presented in
In order to confirm that electrons and holes are actually transferred to the Er ions, the infrared electroluminescence spectrum from multilayer material layers was measured. Typical EL spectra taken under forward bias for a structure with 15 nm thick Si and Er:SiO2 layers are shown in
In PL experiment, energy is transferred from Si nanostructures to Er via the Forster and/or Dexter processes. In EL studies, the detailed mechanisms for excitation of the Er ions under forward bias are not yet established. The injected carrier concentration in EL experiments is lower than the injected carrier concentration at high pump intensity. Therefore, concentration quenching and up conversion processes may be ruled out. Sequential transfer of negative and positive charges may occur.
Considered as an additional embodiment when fabricating a multilayer material layer in accordance with the embodiments is the addition of a substrate bias when fabricating over a substrate a multilayer material layer in accordance with the embodiments. Such a substrate bias may be in a range from about 0 W and 0 volts to about 30 W and 100 volts.
In comparison with
As is illustrated within
c shows the results of forming additional trenches through the multilayer material layer and also into the dielectric layer. As well,
Finally,
The embodiments illustrate that Er doped SiO2/Si multilayers may be used to achieve strong infrared photoluminescence and electroluminescence at the standard telecommunication wavelength of 1535 nm. Efficient photoluminescence was achieved because the Er ions located in thin SiO2 layers could be excited via energy transfer from nc-Si layers. Lateral carrier injection and electroluminescence in a lateral p-i-n configuration under forward bias are reported as a function of electrode spacing and layer thickness from precisely controlled multilayer material layer structures. These results are promising for the development of an on-chip silicon light source.
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference in their entireties to the same extent as if each reference was individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening.
The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it was individually recited herein.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed.
No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. There is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
This application is related to, and derives priority from, application Ser. No. 61/675,958, filed 26 Jul. 2012 and titled Light Emitting Diode Apparatus, Method, and Applications, the content of which is incorporated herein fully by reference.
The research that lead to the embodiments as described herein, and the invention as claimed herein, was funded by the United States AFOSR under MURI program with sub-award number 05710002027, award FA 9550-06-1-0470. The United States Government has rights in the invention as claimed herein.
Number | Date | Country | |
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61675958 | Jul 2012 | US |