Control of the band-gap shift in quantum-well intermixing using a germanium interlayer

A simple technique for controlling the shift in band gap in AlGaAs/GaAs and InGaAs/GaAs quantum-well (QW) structures is reported. It involves the evaporation of a thin Ge layer and then covering it with spin-on silica followed by rapid thermal annealing. The quantum-well intermixing was suppressed in the presence of this Ge layer between the sample surface and the spin-on silica. The interdiffusion rate was reduced by more than one order of magnitude compared to that without the Ge interlayer. The blueshift of the band gap can be controlled by varying the thickness of the Ge interlayer. A differential band-gap shift of more than 100 meV can be achieved with a 500 Å Ge interlayer for both the AlGaAs/GaAs and InGaAs/GaAs QW structures. The optical quality of the material was not deteriorated by the Ge cover compared to the $SiO2$ cover as seen from the photoluminescence intensity and spectral linewidth. Using an appropriate mask, this technique has the potential to tune the band gap in selected areas across a single wafer.