Effect of cavity length on stimulated emission from Fabry-Pérot Gunn lasers

Emission characteristics from GaAlAs–GaAs–GaAlAs Gunn devices of different lengths placed in Fabry-Pérot cavities have been investigated. The emission from the device of length of $194μm$ is stimulated in nature, whereas for the other two devices of lengths of 100 and $50μm$⁠, the emission is spontaneous. Lasing action in such devices, when biased above the threshold of negative differential resistance, arises from the band to band recombination of impact-ionized nonequilibrium electron hole pairs created within the propagating high field Gunn domains. Quantitative results evaluated using nonequilibrium semiconductor-statistics show that reduction in the length of the device leads to (a) a shift of the gain peak towards higher energies and (b) an increase in the average nonequilibrium carrier temperature. As a result, lasing in very short devices is inhibited and only ultra-bright-spontaneous emission is observed.