Monte carlo simulation and rate equation based analysis of algan/gan spin lasers considering the role of dislocation defects

Abstract

This work investigated the spin relaxation profiles and lasing performance of GaN/AlGaN material system considering the role of defects. Spin polarized carriers injected into the material system through MnAs ferromagnetic contact have been modeled using Ensemble Monte Carlo (EMC) method to simulate their internal kinetics incorporating the major scattering mechanisms of III-N materials that has been used to determine its SOC terms and spin relaxation profiles under different material conditions. Furthermore, the relaxation out- comes are fed to the rate equation model of spin laser made of AlGaN active and cladding layers to study the effect of defect density and relaxation time on the lasing performance of the active medium. The work shows that the spin relaxation time and length approach higher for higher composition of Al in AlxGa1-xN, for GaN to AlN it increases from 77.8 to 889.9 ps and from 424 to 972 nm, similarly spin diffusivity decreases for higher content of Al in the alloy, where it falls from 11.6 cm2/s for GaN to 4.2 cm2/s for AlN. In fact for different doping density the relaxation profile of AlN stays strong compared to GaN. However, tuning defect density in the model shows interesting minima feature in spin relaxation time curve at dislocation defect density around 4 x 108 cm-2 for GaN and 3 x 107 for AlN, which has further showed major significance in lasing performance outcome. The simulation also shows that for fixed composition of AlGaN (x=0.3) the mobility and spin diffusivity non-linearly fall with increasing defects and rise with increasing temperature near room condition. The maximum spin relaxation time, length, spin diffusivity and carrier mobility have been found for Al0.3Ga0.7N are 202.12 ps, 504.25 nm, 6.29 cm2/s and 258.24 cm2/Vs, respectively. Solving the rate equation of GaN/AlGaN lasing system with the relaxation parameters extracted from the Monte Carlo model, the light-intensity curves of the laser have been produced to study the lasing performance where it shows the minimum threshold currents of 5 A/cm2 for conventional and 8 A/cm2 for spin lasing at room temperature near defect density of 107 cm-2. The maximum threshold reduction (TR) value for the lasing system with Al0.3Ga0.7N active layer has been found as 43.17% at around defect density of 5 x 108 cm-2 at low temperature of 50K. A high asymmetry between its hole and electron spin lifetime highly required for better spin lasing distinctively found as 1.52 ns and 202.12 ps, respectively.