Effect of p-dopant positioning in low-threshold, InGaAs/GaAs/AlGaAs, MQW GRINSCH lasers with GaAs etch-stop layer for multi-wavelength applications

Etch-stop layers have proven essential in fabricating devices such as distributed Bragg reflector (DBR) laser arrays which require a high degree of uniformity and precise depth positioning of the gratings. In this report, we investigate the dependence of the threshold current density and external quantum efficiency on the p-dopants' starting position in InGaAs/GaAs/AlGaAs quantum well graded-index separate-confinement heterostructure (GRINSCH) lasers with a GaAs etch-stop layer. The laser structures were grown by molecular-beam epitaxy with As₂. With the etch-stop layer approximately 200 nm above the active region's top AlGaAs graded layer, it is found that a significant fraction of injected carriers will recombine in the etch-stop layer if this layer is not sufficiently doped and if the p-dopants are not near enough to the graded layer in the active region. This results in a very high threshold current, a very low efficiency, and the presence of a high-energy peak, corresponding to the GaAs etch-stop layer acting as a quantum well, in the electroluminescence (EL) spectrum. On the other hand, with the dopants positioned correctly, we obtain very low threshold current densities and see no evidence of EL emission from the etch-stop layer. The experimental results are consistent with computer modelling performed with a commercial simulator. Results will also be presented on multiple-wavelength DBR lasers made from these structures.