We report a novel technique for quantum well intermixing which is simple, reliable and low cost, and appears universally applicable to a wide range of material systems. The technique involves the deposition of a thin layer of sputtered SiO2 and a subsequent high temperature anneal. The deposition process appears to generate point defects at the sample surface, leading to an enhanced intermixing rate and a commensurate reduction in the required anneal temperature. Using appropriate masking it is possible to completely suppress the intermixing process, enabling large differential band gap shifts (over 100 meV) to be obtained across a single wafer.
We demonstrate a novel (to the best of our knowledge) 40 GHz passively mode-locked AlGaInAs/InP 1.55 μm laser with a low divergence angle (12.7°×26.3°), timing jitter of 1.2 ps (10 kHz-100 MHz), and a radio frequency linewidth of 25 kHz.
Selective postgrowth control of the photoluminescence ͑PL͒ wavelength has been demonstrated for a single layer self-organized In 0.5 Ga 0.5 As/GaAs quantum dot ͑QD͒ structure. This was achieved by rapid thermal processing of dots using different dielectric caps. Selective band gap shifts of over 100 meV were obtained between samples capped with sputtered and plasma enhanced silica deposition, with the band gap shift under regions covered with plasma enhanced chemical vapor deposition SiO 2 less than 70 meV. The effects of different caps on the PL linewidth were also observed. The differential band gap shift will enable the integration of passive and active devices in QD systems.
Impurity-free vacancy disordering (IFVD) using SiO 2 and SrF 2 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-in 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 dB1cm 01 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 superluminenscent diodes.
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