Gain characteristics of ZnSe/(Zn,Mg)(S,Se)/(Zn,Mg)(S,Se) quantum well lasers

A systematic investigation of the gain dependence on temperature, well width (3, 5, 7 nm), and excitation intensity in MBE grown ZnSe/(Zn,Mg)(S,Se)/(Zn,Mg)(S,Se) quantum-well lasers has been performed. At low lattice temperature (100 K) we find a rather low threshold density of 30 kW/cm 2 . We observe an exponential increase of the threshold density with increasing temperature for the 5 and 7 nm samples and an even stronger increase for the 3 nm sample. The characteristic temperatures (T O ) are 105 and 118 K for the 5 and 7 nm samples, respectively. The low T O values are mainly attributed to thermionic emission of carriers out of the quantum well due to the small total band offset of 156 meV between the strained ZnSe layer and the (Zn,Mg)(S,Se) barriers. At high temperatures and carrier densities contributions from higher subbands can clearly be seen in the gain spectra. The experimental results are in good agreement with calculations in the framework of a microscopic theory which includes the detailed coupled band structure and many-particle effects.