Direct bandgap substrates and methods of making and using
View Patent ↗An indirect bandgap thin film semiconductor circuit can be combined with a compound semiconductor LED such as to provide an active matrix LED array that can have high luminous capabilities such as for a light projector application. In another example, a highly efficient optical detector is achievable through the combination of indirect and direct bandgap semiconductors. Applications can include display technologies, light detection, MEMS, chemical sensors, or piezoelectric systems. An LED array can provide structured illumination, such as for a light and pattern source for projection displays, such as without requiring spatial light modulation (SLM). An example can combine light from separate monolithic light projector chips, such as providing different component colors. An example can provide full color from a single monolithic light projector chip, such as including selectively deposited phosphors, such as to contribute individual component colors to an overall color of a pixel.
1. A method comprising:
providing an inorganic substrate with a substantially direct bandgap for light emission or absorption;
forming an insulating layer on a first side of the substrate;
forming an indirect bandgap semiconductor layer on the insulating layer;
selectively melting and crystallizing an active region of the indirect bandgap semiconductor layer formed on the insulating layer;
forming an electrical contact to the crystallized active region in the indirect bandgap semiconductor layer;
forming an electrical contact to the substrate; and
forming a window to the substrate, wherein the window is substantially transparent to light at a wavelength emitted or absorbed by the substantially direct bandgap of the substrate.
2. The method of claim 1 , comprising:
forming a thin film semiconductor transistor in the active region;
wherein forming an electrical contact to the crystallized active region in the indirect bandgap semiconductor layer comprises forming electrodes contacting the thin film semiconductor transistor;
forming an insulating layer over the thin film semiconductor transistor;
forming vias in the insulating layer over the thin film semiconductor transistor; and
wherein forming a window to the substrate comprises forming a transparent conductor contact to a light emitting or light absorbing area of the substrate.
3. The method of claim 1 , wherein providing the substrate comprises providing a compound semiconductor substrate comprising at least one of GaAs, AlGaAs, A 1 GaP, AlGaInP, GaAsP, GaP, GaN, AlGaN,InGaN, SiC, ZnSe, AlN, AlGaN, AlGaInN, C, InAlP, InSb, InAlSb, or HgCdTe.
4. The method of claim 1 , wherein selectively melting and crystallizing an active region comprises performing at least one of excimer laser crystallization, sequential lateral solidification, two-shot sequential lateral solidification, line sequential lateral solidification, or dot sequential later solidification.
5. The method of claim 1 , comprising:
forming a gate insulator on the selectively melted and crystallized active region of the silicon layer;
forming a gate on the gate insulator; and
forming an insulating layer over active region, the insulating layer comprising at least one of parylene, polyimide, SiOx, SiNx, SiNOx, DLC, HfO, Al 2 O 3 , TaOx, RuOx, metal oxide, nitride, fluoride, chloride, polymer, or fluorocarbon.
6. The method of claim 1 , comprising:
providing a phosphor, in or aligned with the window, the phosphor configured to pass a specified color of light in response to light at a wavelength emitted by the substantially direct bandgap of the substrate.
7. The method of claim 2 , wherein forming a transparent conductor contact comprises using at least one of ITO, ZnO, AZO, GZO, SnO, Au, Pt, Pd, CuO, TiO, RuO, InCdO, Ag, CdO, TiN, or a noble metal.
8. An apparatus comprising:
an inorganic light emitting or absorbing device formed from an inorganic substrate providing a substantially direct bandgap for light emission or absorption;
an insulating layer on a first side of the substrate;
an indirect bandgap semiconductor layer on the insulating layer;
a thin film semiconductor circuit, in the indirect bandgap semiconductor layer, the semiconductor circuit comprising a selectively melted and crystallized polycrystalline grain semiconductor active region;
an electrical connection, through the insulating layer, electrically connecting the inorganic light emitting or absorbing device with the thin film semiconductor circuit; and
a window to the substrate, wherein the window is substantially transparent to light at a wavelength emitted or absorbed by the substantially direct bandgap of the substrate.
9. The apparatus of claim 8 , wherein the inorganic light emitting or absorbing device comprises an inorganic light emitting diode (LED) formed in the substrate, the LED comprising:
an n+ GaAs cathode region of the substrate; and
an InAlP anode region of the substrate; and
wherein the apparatus comprises a plurality of the LEDs arranged in an active matrix array.
10. The apparatus of claim 8 , comprising:
a phosphor, in or aligned with the window, the phosphor configured to pass a specified color of light in response to light at a wavelength emitted by the substantially direct bandgap of the substrate.
11. The apparatus of claim 8 , comprising pixels, an individual pixel including a plurality of sub-pixels, an individual sub-pixel including a phosphor that is configured to receive light from an inorganic LED in the substrate and to pass a specified color of light in response to the received light, and wherein the individual sub-pixels individually contribute respective colors to an overall color of light provided by the individual pixel.
12. The apparatus of claim 8 , comprising a light projector or a direct-view display comprising the pixels, and wherein the pixels are monolithically integrated with the substrate.
13. The apparatus of claim 8 , comprising a light projector comprising the pixels, and wherein the pixels are configured to provide a directly addressed monolithic LED array light projection source configured to provide both a light source and a light modulator in the same component.
14. An apparatus comprising:
a light projector or a direct-view display, comprising:
a direct drive monolithic LED array light source configured to provide both a light source and a light modulator in the same component.
15. The apparatus of claim 14 , comprising a light projector including the direct drive monolithic LED array light source and comprising:
a projection lens, arranged to receive light from the light source.
16. The apparatus of claim 14 , wherein the light source comprises:
a direct drive red monolithic LED array light source;
a direct drive green monolithic LED array light source; and
a direct drive blue monolithic LED array light source.
17. The apparatus of claim 14 , wherein the direct drive monolithic LED array light source is configured to be capable of passive matrix operation.
18. The apparatus of claim 14 , wherein the direct drive monolithic LED array light source is configured to be capable of direct addressing operation.
19. The apparatus of claim 14 , comprising pixels, an individual pixel including a plurality of subpixels, an individual sub-pixel including a phosphor that is configured to receive light from an inorganic LED from an inorganic substrate and to pass a specified color of light in response to the received light, and wherein the individual sub-pixels individually contribute respective colors to an overall color of light provided by the individual pixel.
20. The apparatus of claim 16 , comprising a light mixer, arranged to mix light from the red, green, and blue direct drive monolithic LED array light sources for providing to a projection lens.
21. The apparatus of claim 20 , wherein the light mixer comprises a crossed dichroic.
22. The apparatus of claim 20 , wherein the light mixer comprises a mirror, a red transmitting dichroic, and a red and green transmitting dichroic.