Semiconductor light emitting devices with non-epitaxial upper cladding
View Patent ↗The AlGaN upper cladding layer of a nitride laser diode is replaced by a non-epitaxial layer, such as metallic silver. If chosen to have a relatively low refractive index value, the mode loss from absorption in the non-epitaxial cladding layer is acceptably small. If also chosen to have a relatively high work-function, the non-epitaxial layer forms an electrical contact to the nitride semiconductors. An indium-tin-oxide layer may also be employed with the non-epitaxial cladding layer.
1. A semiconductor light emitting device, comprising:
a substrate;
a crystalline semiconductor cladding layer formed over said substrate;
a confinement heterostructure formed over said crystalline semiconductor cladding layer;
an active region formed within said confinement heterostructure;
a dielectric layer, formed as a stripe over said confinement heterostructure; and
a non-epitaxial cladding layer comprising a periodic grating of discontinuous lateral ridge waveguide elements formed over said dielectric layer, said non-epitaxial cladding layer having an electrical resistivity less than 1 ohm-cm;
whereby, at least said crystalline semiconductor cladding layer, said confinement heterostructure, and said non-epitaxial cladding layer together form a waveguide that guides light in the plane of said cladding layers.
2. The semiconductor light emitting device of claim 1 , wherein said confinement heterostructure comprises a material selected from the group consisting of: aluminum, indium, gallium.
3. The semiconductor light emitting device of claim 1 , wherein said non-epitaxial cladding layer is comprised of a metal.
4. The semiconductor light emitting device of claim 3 , wherein said non-epitaxial cladding layer is comprised of silver (Ag).
5. The semiconductor light emitting device of claim 1 , wherein said non-epitaxial cladding layer is both an upper cladding layer and a p-contact layer for the light emitting device.
6. The semiconductor light emitting device of claim 1 , wherein said non-epitaxial cladding layer is comprised of an optically transparent electrically conductive layer and a metal layer deposited above said optically transparent electrically conductive layer.
7. The semiconductor light emitting device of claim 6 , wherein said optically transparent conductive layer comprises a material selected from the group consisting of: indium tin oxide (ITO) and zinc oxide (ZnO).
8. The semiconductor light emitting device of claim 1 , wherein said non-epitaxial cladding layer forms an optical gain guide.
9. The semiconductor light emitting device of claim 1 , whereby said active region comprises indium gallium nitride (InGaN), and said semiconductor light emitting device emits light having a wavelength in the range of 350-550 nm.
10. The semiconductor light emitting device of claim 1 , wherein said semiconducting light emitting device is a semiconductor diode laser.
11. The semiconductor light emitting device of claim 1 , wherein said semiconducting light emitting device is a superluminescent diode.
12. The semiconductor light emitting device of claim 1 , wherein said non-epitaxial cladding layer is a composite comprising a conducting oxide and a metal.
13. The semiconductor light emitting device of claim 1 , whereby said active region comprises indium gallium aluminum nitride (InGaAIN), and said semiconductor light emitting device emits light having a wavelength in the range of 350-550 nm.
14. The semiconductor light emitting device of claim 13 , wherein said non-epitaxial cladding layer comprises a metal having a real component of its refractive index not exceeding 0.3 for wavelengths above 350 nm.
15. The semiconductor light emitting device of claim 1 , wherein said non-epitaxial cladding layer is disposed above a semiconductor layer forming an interface, the interface having an optical reflectivity exceeding 0.5 for light propagating from said confinement heterostructure.
16. A semiconductor laser diode, comprising:
a substrate;
an gallium nitride (GaN) template layer formed over said substrate;
a lower cladding layer comprising aluminum gallium nitride (AIGaN) formed over said template;
a gallium nitride (GaN) confinement heterostructure formed over said AIGaN cladding layer;
an indium gallium nitride (InGaN) multiple quantum well heterostructure active region formed within said confinement heterostructure, said active region for emitting light having a wavelength in the range of 365-550 nm;
an aluminum gallium nitride (AIGaN) electron blocking layer formed over said active region and within said confinement heterostructure;
an upper cladding layer comprising silver (Ag) formed over said confinement heterostructure; and
an optically transparent electrically conductive layer disposed between said confinement heterostructure and said upper cladding layer.
17. The semiconductor laser diode of claim 16 , wherein said upper cladding layer is also an electrical contact layer for the laser diode.
18. The semiconductor laser diode of claim 16 , wherein said optically transparent electrically conductive layer comprises indium tin oxide (ITO).
19. A semiconductor laser diode, comprising:
a substrate;
an gallium nitride (GaN) template layer formed over said substrate;
a lower cladding layer comprising aluminum gallium nitride (AIGaN) formed over said template;
a gallium nitride (GaN) confinement heterostructure formed over said AIGaN cladding layer;
an indium gallium nitride (InGaN) multiple quantum well heterostructure active region formed within said confinement heterostructure, said active region for emitting light having a wavelength in the range of 365-550 nm;
an aluminum gallium nitride (AIGaN) electron blocking layer formed over said active region and within said confinement heterostructure;
an upper cladding layer comprising silver (Ag) formed as a grating comprising discontinuous lateral ridge waveguide elements selectively formed over said confinement heterostructure; and
a dielectric layer, formed as a stripe over said confinement heterostructure and below said upper cladding layer.
20. The semiconductor laser diode of claim 19 , wherein said upper cladding layer form an optical gain guide.