Spectroscopic investigations of GaAsSb/GaAs based structures for 1.3 μm VCSEL applications

A spectroscopic investigation of GaAsSb/GaAs quantum well (QW) structures grown on GaAs substrates by molecular beam epitaxy is presented. Besides studying their temperature-dependent photoluminescence (PL), the low temperature PL of a series of GaAsSb/GaAs/AlGaAs structures, with varying GaAs spacer thickness is investigated. This latter study was undertaken to investigate the GaAsSb/GaAs band alignment. Blue shifts in the PL peak as a function of excitation laser intensity at a temperature of 10 K for the range of spacer thickness variation are studied. It is observed that significant blue shifting occurs only for spacers thicker than ∼2 nm. It is tentatively suggested that this is indicative of a transition from the electrons and holes being predominantly confined in the same layer (the QW) to being more strongly confined in adjacent layers, as the spacer thickness increases. The angle-dependent photomodulated reflectivity (PR) of similar samples is investigated. Here strong low energy interference oscillations (LEIO) are encountered, which tend to obscure any PR signals arising from the QW. The latter are exploited to estimate the refractive index of the layer responsible for the LEIO, and thus identify it. However, a way to avoid the LEIO is shown, by shortening the laser excitation wavelength, which results in measurable PR signals from the QW region, yielding several QW transition wavelengths.