Simulation of UV VCSEL with Grad AlGaN to improve output power and current spreading at high current

Abstract Traditional UV VCSELs with ITO current spreading layer are limited by the large absorption loss of ITO in UV spectral region, which makes electrically pumped UV VCSELs hardly to lase. This study proposes an optimized structure for UV VCSEL containing a graded AlGaN insertion layer and a much thinner ITO layer (10 nm) to improve the lateral current spreading and light output power. After the insertion of the graded AlGaN layer, the carrier concentration in the p-GaN region was significantly increased, which not only improved carrier injection efficiency but also reduced the voltage consumption in the p-GaN region, thereby decreasing the series resistance of the device. Simulation results show that UV VCSELs with the Grad AlGaN insertion layer exhibit significantly improved current spreading performance at high current. Compared with the traditional structure using 10 nm ITO current spreading layer, the light output power was increased from 0.85 to 1.34 mW at 20 mA, with an increasement by 57.7% and the series resistance was reduced from 101 to 51 Ω by 49.5%. On the other hand, the threshold current was slightly increased from 1.74 to 2.14 mA by 18.9% as a compromise.