Selective quantum-well intermixing in GaAs-AlGaAs structures using impurity-free vacancy diffusion

Impurity-free vacancy disordering (IFVD) using SiO₂ and SrF₂ dielectric caps to induce selective quantum-well (QW) intermixing in the GaAs-AlGaAs system is studied. The intermixing rate of IFVD was found to be higher in n-i-p and intrinsic than in p-i-n structures, which suggests that the diffusion of the Group III vacancy is not supported in p-type material. Single-mode waveguides have been fabricated from both as-grown and bandgap-tuned double-quantum-well (DQW) laser samples. Propagation losses as low as 8.5 dB cm^-1 were measured from the bandgap-tuned waveguides at the lasing wavelength of the undisordered material, i.e., 860 nm. Simulation was also carried out to study the contribution of free-carrier absorption from the cladding layers, and the leakage loss induced by the heavily p-doped GaAs contact layer. It was found that the leakage loss contributed by the GaAs cap layer is significant and increases with wavelength. Based on IFVD, we also demonstrate the fabrication of multiple-wavelength lasers and multichannel wavelength division multiplexers using the one-step “selective intermixing in selected area” technique. This technique enables one to control the degree of intermixing across a wafer. Lasers with bandgaps tuned to five different positions have been fabricated on a single chip. These lasers showed only small changes in transparency current, internal quantum efficiency, or internal propagation loss, which indicates that the quality of the material remains high after being intermixed. Four-channel wavelength demultiplexers based on a waveguide photodetector design have also been fabricated. Photocurrent and spontaneous emission spectra from individual diodes showed that the absorption edge was shifted by different degrees due to the selective degree of QW intermixing. The results obtained also imply that the technique can be used in the fabrication of broad-wavelength emission superluminescent diodes