Optical and structural characterization of InGaAs/AlAsSb quantum wells grown by molecular beam epitaxy

We report here a photoluminescence (PL), secondary ion mass spectrometry (SIMS), and Fourier transform infrared spectroscopy (FTIR) study of highly Si-doped InGaAs/AlAsSb quantum wells (QWs) that are lattice-matched to InP substrates grown by molecular beam epitaxy (MBE). It is found that PL line-shape degradation caused by high Si doping to the upper (surface side) AlAsSb barrier can be controlled by inserting an undoped AlAsSb spacer layer. However, when doped to the lower (substrate side) AlAsSb barrier, the broadening of the spectra indicating degradation of the interface, found to be unavoidable even with a 10-nm spacer layer. SIMS depth profiles confirm the out-diffusion of In and Ga from the InGaAs well to the AlAsSb barriers and Al incorporation into the InGaAs well. This group-III species interdiffusion combined with the exchange reaction between As and Sb are confirmed to be the origin of the extraordinarily broad PL spectra. We also report the short wavelength inter-subband transitions ranging between 1.35 /spl mu/m to 2.0 /spl mu/m from coupled double quantum well structures. However, as is expected from PL and SIMS results, high doping shifts intersubband transition peaks toward longer wavelengths.