Demonstrating the electron blocking effect of AlGaN/GaN superlattice cladding layers in GaN-based laser diodes

Abstract

Electron leakage currents seriously limit the power conversion efficiencies (PCEs) of gallium nitride (GaN)-based laser diodes (LDs). To minimize the leakage currents, electron blocking layers are generally applied in the p-type region. However, few works have discussed the electron blocking effect of a p-cladding layer, which is found to be critical in suppressing the leakage currents of an LD. In this work, we compare the blocking performance of uniform AlGaN p-cladding layers and AlGaN/GaN superlattice (SL) p-cladding layers with the same average Al component respectively. Both light-emitting diodes (LEDs) and LDs with the same epitaxy structures are characterized by light–current (L–I) and current–voltage (I–V) measurements. The latest analytical model of leakage currents is applied to fit the L–I curves of LEDs, where smaller leakage coefficients are observed in the SL structures compared with the uniform-layer structures. Eighty LDs with varying ridge widths are studied by comparing the threshold current densities, slope efficiencies, and PCEs. The SL-based p-cladding layer shows statistically significant advantages over a uniform AlGaN layer. The blocking effects of both scattering- and bound-state electrons in SLs are investigated theoretically. Repetitive reflection and thermal relaxation are responsible for the blocking effect of scattering-state electrons. Simulation results indicate that the tunneling effect of bound-state electrons through a miniband mechanism is insignificant at a large injection level due to a negative differential conductivity by the Esaki–Tsu effect. We demonstrate a better electron blocking performance of p-cladding layers based on SLs than uniform AlGaN layers in GaN-based LDs.