We experimentally investigate the characteristics of light emission of optically excited Ga(NAsP) multiple quantum-well structures grown pseudomorphically on a GaP substrate by metal-organic vapor-phase epitaxy. The emission power as a function of excitation power shows at temperatures from a clear threshold after excitation with short laser pulses. The emission spectra become narrow at threshold and shift to higher energies. A well defined mode structure is observed above threshold. Complementary, quasi-steady-state gain measurements using the stripe-length method yield positive modal gain values of up to at room temperature, thus validating that the structures show laser action.
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The Hakki-Paoli method is intrinsically valid only for continuous wave excitation. Transient gain dynamics and our limited spectral resolution reduce the peak-to-valley ratios in the mode spectra so that we obtain gain values lower than the real ones. We therefore expect that the actual values of the modal gain at are even larger.
