Threshold carrier density in vertical cavity surface emitting lasers

A combination of spontaneous emission lifetime and spectral measurements is used to estimate the threshold carrier density in small diameter gain guided vertical cavity surface emitting lasers. Differential spontaneous emission lifetimes measured below threshold are extrapolated to a τth=0.4 ns at threshold. The corresponding threshold carrier density is Nth=7.9×1018 cm−3. The measured carrier densities are used to calculate spontaneous emission spectra. These are in agreement with the edge emission spectra obtained on cleaved laser chips. For the measured carrier density, we estimate the threshold gain at the emission wavelength of g=1640 cm−1.