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 ofGaN/AlGaN material system considering the role of defects.Spin polarizedcarriers injected into the material system through MnAs ferromagnetic contacthave been modeled using Ensemble Monte Carlo (EMC) method to simulatetheir internal kinetics incorporating the major scattering mechanisms of III-Nmaterials that has been used to determine its SOC terms and spin relaxationprofiles under different material conditions. Furthermore, the relaxation out-comes are fed to the rate equation model of spin laser made of AlGaN activeandcladdinglayerstostudytheeffectofdefectdensityandrelaxationtimeonthe lasing performance of the active medium.The work shows that the spinrelaxation time and length approach higher for higher composition of Al inAlxGa1-xN, for GaN to AlN it increases from 77.8 to 889.9 ps and from 424 to972nm,similarlyspindiffusivitydecreasesforhighercontentofAlinthealloy,where it falls from 11.6 cm2/s for GaN to 4.2 cm2/s for AlN. In fact for differentdopingdensitytherelaxationprofileofAlNstaysstrongcomparedtoGaN.However,tuningdefectdensityinthemodelshowsinterestingminimafeaturein spin relaxation time curve at dislocation defect density around 4 x108 cm-2for GaN and 3 x107for AlN, which has further showed major significance inlasingperformanceoutcome.Thesimulationalsoshowsthatforfixedcomposition of AlGaN (x=0.3) the mobility and spin diffusivity non-linearly fall withincreasing defects and rise with increasing temperature near room condition.The maximum spin relaxation time, length, spin diffusivity and carrier mobilityhavebeenfoundforAl0.3Ga0.7Nare202.12ps,504.25nm,6.29cm2/sand258.24 cm2/Vs, respectively.Solving the rate equation of GaN/AlGaN lasingsystemwiththerelaxationparametersextractedfromtheMonteCarlomodel,the light-intensity curves of the laser have been produced to study the lasingperformance where it shows the minimum threshold currents of 5 A/cm2 forconventional and 8 A/cm2for spin lasing at room temperature near defect density of 107 cm-2. The maximum threshold reduction (TR) value for the lasingsystemwithAl0.3Ga0.7Nactivelayerhasbeenfoundas43.17%atarounddefectdensity of 5x108 cm-2 at low temperature of 50K. A high asymmetry betweenitsholeandelectronspinlifetimehighlyrequiredforbetterspinlasingdistinctivelyfound as 1.52 ns and 202.12 ps, respectively.