Light emitting diode
Disclosed is a light emitting diode using light of a short wavelength band. The light emitting diode includes a first conductivity type semiconductor layer having a front side and a back side, a second conductivity type semiconductor layer having a front side and a back side, an active layer formed between the back side of the first conductivity type semiconductor layer and the front side of the second conductivity type semiconductor layer, a first electrode electrically connected to the first conductivity type semiconductor layer, a second conductivity type reflective layer formed on the back side of the second conductivity type semiconductor layer, and a reflective part formed on the second conductivity type reflective layer to reflect light of a short wavelength band and light of a blue wavelength band and electrically connected to the second conductivity type semiconductor layer. The second conductivity type reflective layer includes DBR unit layers. Each of the DBR unit layers includes a low refractive index layer and a high refractive index layer adjacent to the low refractive index layer. The low refractive index layer and the high refractive index layer include Al x Ga 1-x N (0<x≦1) and Al y Ga 1-y N (0≦y<1, y<x), respectively.
1. A light emitting diode comprising:
a first conductivity type semiconductor layer having a front side and a back side;
a second conductivity type semiconductor layer having a front side and a back side;
an active layer formed between the back side of the first conductivity type semiconductor layer and the front side of the second conductivity type semiconductor layer;
a second conductivity type reflective layer formed on the back side of the second conductivity type semiconductor layer;
a reflective part formed on the back side of the second conductivity type reflective layer opposite the second conductivity type semiconductor layer to reflect light of a short wavelength (UVA wavelength) band and light of a blue wavelength band;
the reflective part electrically connected to the second conductivity type semiconductor layer wherein the second conductivity type reflective layer comprises distributed bragg reflector (DBR) unit layers for reflecting light of a short wavelength (UVA wavelength) band of 315 nm to 420 nm, each of the DBR unit layers comprises a low refractive index layer and a high refractive index layer adjacent to the low refractive index layer;
the low refractive index layer and the high refractive index layer comprise Al x Ga 1-x N (0<x≦1) and Al y Ga 1-y N (0≦y<1, y<x), respectively; and
the DBR unit layers are repeated in at least triplicate in the second conductivity type reflective layer, and when the total doping concentration of the second conductivity type dopant in the initial three DBR unit layers placed closest to the back side of the second conductivity type semiconductor layer and the total doping concentration of the second conductivity type dopant in the other DBR unit layers are defined as first and second doping concentrations, respectively, the first doping concentration is lower than the second doping concentration.
2. The light emitting diode according to claim 1 , wherein a phase-matching layer is formed between the second conductivity type semiconductor layer and the second conductivity DBR.
3. The light emitting diode according to claim 2 , wherein the phase-matching layer comprises Al x Ga 1-x N (0<x<1).
4. The light emitting diode according to claim 2 , wherein the phase-matching layer has a thickness of 5 nm to 50 nm.
5. The light emitting diode according to claim 1 , wherein the first doping concentration is from 1×10 16 cm −3 to 5×10 17 cm −3 and the second doping concentration is from 1×10 18 cm −3 to 1×10 21 cm −3 .
6. The light emitting diode according to claim 1 , wherein the doping concentration of the second conductivity type dopant in the DBR unit layer placed closest to the reflective part is higher than those in the other DBR unit layers to achieve improved ohmic contact.
7. The light emitting diode according to claim 1 , wherein the reflective part comprises a second conductivity type intermediate layer for improving ohmic contact and a reflective metal layer for reflecting light of a short wavelength band and light of a blue wavelength band.
8. The light emitting diode according to claim 7 , wherein the reflective metal layer comprises silver.
9. The light emitting diode according to claim 7 , wherein the second conductivity type intermediate layer has a thickness of 10 nm to 150 nm.
10. The light emitting diode according to claim 1 , wherein a sapphire substrate is located on the front side of the first conductivity type semiconductor layer.
11. The light emitting diode according to claim 1 , wherein the first conductivity type semiconductor layer is an n-type semiconductor layer and the second conductivity type semiconductor layer is a p-type semiconductor layer.
12. The light emitting diode according to claim 1 , wherein each of the DBR unit layers of the second conductivity type reflective layer comprises a first transition portion formed between the low refractive index layer and the high refractive index layer and whose Al content gradually decreases from the front to the back and a second transition portion formed between the high refractive index layer and the low refractive index layer of the next adjacent DBR unit layer and whose Al content gradually increases from the front to the back.
13. The light emitting diode according to claim 12 , wherein delta doping is applied to the starting and end points of each of the first transition portion and the second transition portion.
14. The light emitting diode according to claim 12 , wherein the Al content profile of each of the first transition portions and the second transition portions is linear or a quadratic curve.
15. The light emitting diode according to claim 1 , wherein the second conductivity type reflective layer has a thickness of 60 nm to 1500 nm.
16. The light emitting diode according to claim 1 , wherein each of the DBR unit layers has a thickness of 60 nm to 100 nm.
17. The light emitting diode according to claim 1 , wherein each of the low refractive index layers and the high refractive index layers of the DBR unit layers has a thickness of 30 nm to 50 nm.