GainandPhotoluminescence Dynamics inDilute Nitride Semiconductor LaserMaterials

Thegainandphotoluminescence dynamics iscalculated microscopically forseveral GaInNAsstructures. Carrier scattering rates arecomputed microscopically andimplemented into anonequilibrium gainmodel. © 2004Optical Society ofAmerica OCIScodes:(140.5960) Semiconductor lasers, (140.3380) Lasermaterials Theexact knowledge ofoptical material properties iscritically important fortheunderstanding anddevel- opmentofnewoptical devices. Predictive capability canonlybeexpected fromatheory thatdoesnotrely onphenomenological, i.e. empirically orexperimentally determined parameters. While this theory wasdevel- opedsometimeagoforthecaseofequilibrium gainandabsorption insemiconductor structures (1, 2,3,4), nonequilibrium gainisoften calculated inarateequation modelwithphenomenological scattering times. Anextension oftheexisting microscopic theory totreat dynamical nonequilibrium effects isinprinciple straightforward, butextremely demanding withregards toCPUtimeandmemoryrequirements. Therefore, thedesirable long-time calculations, e.g., fromtheswitch-on ofoptical pumping tosteady state conditions, anddetailed parameter studies arenumerically prohibitive. Toovercome these difficulties wedeveloped a novel nonequilibrium laser gainmodelwitheffective microscopic relaxation rates forthecalculation oflaser dynamics. Themodelbridges thegapbetween thenumerically extensive fully microscopic calculations anda simple rate equation modelwhich haslittle predictive capability duetotheneedforinput ofexperimentally determined relaxation rates (5, 6). Thetwo-step evaluation process ofourmodelisasfollows: We microscopically calculate thecarrier density evolution after pulsed optical excitation, introducing asmall numberofoptically excited carriers inaddition toabackground carrier density inthermal equilibrium. Thecarrier distribution thusshowsa deviation fromthermal equilibrium around thetimeofexcitation which relaxes onaspecific timescale. This carrier density evolution enables ustoextract scattering rates forelectrons andholes aswell ascarrier-phonon scattering times. Inthesecond step, these effective relaxation rates areintroduced into theMaxwell-semiconductor Bloch equations. Thetimeevolution ofthecarrier density hascontributions fromcarrier-carrier scattering relaxing thesystem towards thermal equilibrium attheplasma temperature Tpandfromcarrier-phonon scattering equilibrating plasma andlattice temperature. We reflect this byusing thescattering rates inarelaxation ratemodelforthescattering terms inthesemiconductor Bloch equations (5),