Light emitter with a conductive transparent p-type layer structure
A light emitting device includes an n-type layer, a p-type layer structure, a layer of p-type nano-dots imbedded in the p-type layer structure, and an active region sandwiched between the n-type layer and the p-type layer structure, where the p-type nano-dots possess a sheet density of 10 10 to 10 12 cm −2 , a lateral dimension of 2-20 nm, and a vertical dimension of 1-5 nm. The p-type layer structure with a layer of p-type nano-dots imbedded therein provides good vertical conductivity and UV transparency. Also provided is a method for making the light emitting device.
1. A light emitting device comprising:
an n-type layer;
a p-type layer structure;
a layer of p-type nano-dots imbedded in the p-type layer structure, and
an active region sandwiched between the n-type layer and the p-type layer structure.
2. The light emitting device according to claim 1 , wherein the p-type nano-dots possess a sheet density of 10 10 to 10 12 cm −2 , a lateral dimension of 2-20 nm, and a vertical dimension of 1-5 nm.
3. The light emitting device according to claim 2 , wherein the active region emits ultraviolet light with wavelengths from 235-365 nm.
4. The light emitting device according to claim 1 , wherein the p-type layer structure comprises a smooth p-type layer in direct contact with the active region, a rough p-type layer formed on the smooth p-type layer having protrusions with depressions formed between the protrusions, and a confining p-type layer,
wherein the layer of p-type nano-dots is formed on the rough p-type layer with the p-type nano-dots being formed in the depressions of the rough p-type layer, and the confining p-type layer is conformally formed on the layer of p-type nano-dots.
5. The light emitting device according to claim 4 , wherein the p-type layer structure comprises a plurality of layers of p-type nano-dots and a plurality of confining p-type layers alternately and conformally stacked with the layers of p-type nano-dots.
6. The light emitting device according to claim 5 , wherein the p-type nano-dots in the plurality of layers of p-type nano-dots are substantially vertically aligned.
7. The light emitting device according to claim 4 , wherein the smooth p-type layer, the rough p-type layer, and the confining p-type layer are made of AlGaN, with an Al-composition of the smooth p-type layer being equal to or higher than an Al-composition of the rough p-type layer, and an Al-composition of the confining p-type layer being substantially equal to the Al-composition of the rough p-type layer.
8. The light emitting device according to claim 7 , wherein the p-type nano-dots are made of GaN or InGaN with In-composition less than 10%, or AlGaN with Al-composition less than 5%.
9. The light emitting device according to claim 4 , wherein the smooth p-type layer has a thickness in a range of 5-30 nm, the confining p-type layer has a thickness in a range of 2-10 nm.
10. The light emitting device according to claim 4 , wherein the rough p-type layer has a base, the protrusions are formed on the base, the base has a thickness in a range of 0-10 nm, and the protrusions possess a sheet density of 10 10 to 10 12 cm −2 , a lateral dimension of 10-100 nm, and a vertical dimension of 5-30 nm.
11. The light emitting device according to claim 4 , wherein the layer of p-type nano-dots is a discontinuous layer.
12. The light emitting device according to claim 1 , wherein the p-type layer structure comprises a smooth p-type layer in direct contact with the active region, a first smooth confining p-type layer formed on the smooth p-type layer, and a second smooth confining p-type layer, wherein the layer of p-type nano-dots is formed on the first smooth confining p-type layer, and the second smooth confining p-type layer is formed on the layer of p-type nano-dots.
13. The light emitting device according to claim 12 , wherein the smooth p-type layer, the first smooth confining p-type layer, and the second smooth confining p-type layer are made of AlGaN, with an Al-composition of the smooth p-type layer being 5% higher than an Al-composition of the first smooth confining p-type layer, and an Al-composition of the second smooth confining p-type layer being substantially equal to the Al-composition of the first smooth confining p-type layer.
14. The light emitting device according to claim 13 , wherein the layer of p-type nano-dots are made of InGaN with an In-composition in a range of 0-10%, or AlGaN with an Al-composition in a range of 0-5%, inclusively.
15. The light emitting device according to claim 12 , wherein the p-type layer structure comprises a plurality of layers of p-type nano-dots and a plurality of second smooth confining p-type layers alternately stacked with the layers of p-type nano-dots.
16. The light emitting device according to claim 12 , wherein the layer of p-type nano-dots is a continuous layer including a wetting layer portion laterally surrounding the p-type nano-dots, and a thickness of the wetting layer portion is in a range of 0.6-1.0 nm.
17. The light emitting device according to claim 1 , wherein the p-type layer structure comprises a smooth p-type layer in direct contact with the active region and a smooth confining p-type layer, wherein the layer of p-type nano-dots is formed on the smooth p-type layer, and the smooth confining p-type layer is formed on the layer of p-type nano-dots.
18. The light emitting device according to claim 1 , further comprising an ohmic contact layer directly formed on the p-type layer structure.
19. The light emitting device according to claim 1 , further comprising a p-type GaN or InGaN ohmic contact layer formed on the p-type layer structure and with a thickness of 2-10 nm.