Light-emitting diode with strain-relaxed layer for reducing strain in active layer
View Patent ↗A light-emitting diode (LED) includes a first conductivity type semiconductor layer, a strain-relaxed layer over the first conductivity type semiconductor layer, an active layer over the strain-relaxed layer, and a second conductivity type semiconductor layer over the active layer. The strain-relaxed layer includes a strain-absorbed layer over the first conductivity type semiconductor layer and a surface-smoothing layer on the strain-absorbed layer filling the cavities. The strain-absorbed layer includes a plurality of cavities in a substantial hexagonal-pyramid form.
1. A light-emitting diode (LED) comprising:
a first conductivity type semiconductor layer;
a strain-relaxed layer over the first conductivity type semiconductor layer, the strain-relaxed layer comprising:
a strain-absorbed layer over the first conductivity type semiconductor layer, wherein the strain-absorbed layer containing a plurality of cavities each having a hexagonal top view and a triangular cross-section; and
a surface-smoothing layer on the strain-absorbed layer, the surface-smoothing layer filling the cavities;
an active layer over the strain-relaxed layer; and
a second conductivity type semiconductor layer over the active layer.
2. The LED as claimed in claim 1 , further comprising:
a transparent conductive layer over the second conductivity type semiconductor layer;
a second electrode on the transparent conductive layer;
a first electrode on the first conductivity type semiconductor layer; and
a substrate under the first conductivity type semiconductor layer.
3. The LED as claimed in claim 1 , further comprising a buffer layer formed between a substrate and the first conductivity type semiconductor layer.
4. The LED as claimed in claim 1 , further comprising discontinuous interface material between the strain-absorbed layer and the surface-smoothing layer formed by SiNx or SiOx.
5. The LED as claimed in claim 1 , wherein the strain-absorbed layer and the surface-smoothing layer are composed of different materials.
6. The LED as claimed in claim 1 , wherein the strain-absorbed layer is InGaN with a thickness from 0.1 μm to 1 μm.
7. The LED as claimed in claim 1 , wherein the surface-smoothing layer is GaN with a thickness from 100 Åto 1000Å.
8. The LED as claimed in claim 1 , wherein a ratio of area covered by the cavities to the area of the surface of the strain-absorbed layer is from 0.2 to 1.0.
9. The LED as claimed in claim 1 , wherein one of the cavities has a diagonal length from 100 nm to 1000 nm.
10. The LED as claimed in claim 1 , wherein each of the cavities contains six slopes to absorb a strain in horizontal direction and convert part of the strain in horizontal direction into vertical direction.