Influences of thin active layer in (GaAl)As double-heterostructure lasers grown by liquid-phase epitaxy

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Abstract
Studies have been carried out on the influences of thinning the active layer in (GaAl)As double‐heterostructure (DH) lasers grown by liquid‐phase epitaxy (LPE). The measured peak gain varies sublinearly with current in the laser with a thin active layer of d∼0.05 μm while it varies linearly for d≲0.07 μm. This sublinear gain‐current relationship results from the rather wide graded‐band‐gap interface region formed by LPE and increases the lasing threshold. The photoluminescence (PL) peak of a DH sample with a thin active layer shifts to higher energies with the excitation due to the wide interface width, which agrees with the calculated results. High‐energy bumps observed in the PL spectra are more noticeable in the sample with the thinner active layer, which demonstrates that carriers recombine at the high‐energy portion of the interface region. The excitation dependence of PL intensity has shown that the nonradiative recombination rate is higher for the thinner active layer. Discussion is given concerning the causes for the rapid degradation of the lasers with the active layer thinner than a certain value.