OPTICAL GAIN IN ZNS EPILAYERS

The variable stripe length method is used to study optical gain in MOV PE-grown ZnS/GaAs epitaxial layers. Optical gain and spontaneous emiss ion spectra are extracted from experimental results. A net optical gai n of about 30 cm(-1) under excitation by a XeCl laser having a power d ensity of 100 kWcm(-2) is observed at very low temperatures (T < 20 K) and it is rapidly quenched for higher temperatures. Gain is interpret ed to be due to stimulated emission from the bound exciton state and f rom the biexciton ground state towards free exciton levels. The spectr al shape of the gain spectrum is well fitted by the sum of these two c ontributions. Smaller gain at lower photon energies is obtained due to exciton-exciton collisions.