Electron-beam-pumped lasing in epitaxial ZnSe thin films

We have observed lasing in ZnSe thin films grown epitaxially on (100) GaAs substrates under pulsed electron beam excitation in the transverse geometry. Films were grown using both molecular beam epitaxy (MBE) and organometallic vapor phase epitaxy (OMVPE). These films have been characterized using low-temperature photoluminescence (PL) and electrical transport measurements, as well as optical and electron microscopy. Lasing thresholds as low as 1 A/cm² have been determined for MBE-grown films (films thickness 4 μm, accelerating voltage 40 kV, temperature 16 K, pulse length 100 ns). This threshold rose with increasing temperature, but lasing could be observed at temperatures as high as 295 K. In spite of many similarities between the PL and electrical properties of the MBE and OMVPE films, our measurements on the latter films indicate that the lasing thresholds are somewhat higher in these materials (≥2x), but that the differences diminish as the electron accelerating voltage increases. Correlations between the lasing thresholds and other measured properties of the two materials are discussed. We find that the higher thresholds in the OMVPE films are due to increased cavity losses resulting from scattering by the textured film surfaces.