2ND QUANTIZED STATE LASING AND GAIN SPECTRA MEASUREMENTS IN N-TYPE MODULATION-DOPED GAAS-ALGAAS QUANTUM-WELL LASERS

The emission characteristics of n-type modulation doped GaAs-AlGaAs qu antum-well lasers are studied for constant doping density and stepped doping density laser cores, Constant doping density cores are found to have a shift to shorter wavelength with increasing doping density but suffer from a corresponding large increase in threshold current densi ty, Stepped doping density cores exhibit clear wavelength shifting fro m the first to second quantized state transitions with increased dopin g near the quantum well while maintaining low threshold current densit ies, Threshold current densities of 440 A/cm(2) are measured for secon d quantized state lasing in stepped core lasers, Gain spectra are meas ured for the stepped doping density core devices and modulation doping is shown to improve the gain bandwidth by 50% over undoped devices.