We have carried out a transmission electron microscopy based study of AlGaAs–Al(oxide) heterolayers created by lateral sidewall wet oxidation and identify the oxide phase formed as a consequence of the oxidation of AlAs to be γ-Al2O3, with the cubic Fd 3m structure. The oxide-semiconductor interface is weak and porous, possibly due to the high stress loads developed during oxidation, and we propose that the fast oxidation rates are a consequence of reactants transported to the oxidation front along the porous interface.

This paper presents a new type of electron bolometric ("hot electron") mixer. We have demonstrated a three order of magnitude improvement in the bandwidth compared with previously known types of electron bolometric mixers, by using the two-dimensional electron gas (2DEG) medium at the hetero-interface between AlGaAs and GaAs. We have tested both in-house MOCVD-grown material, and MBE material, with similar results. The conversion loss (L ,) at 94 GHz is presently 18 dB for a mixer operating at 20 K, and calculations indicate that L, can be decreased to about 10 dB in future devices. Calculated and measured curves of L, versus &o, and IDC, respectively, agree well. We argue that there are several different configurations of electron bolometric mixers, which will all show wide bandwidth, and that these devices are likely to become important as low-noise THz receivers in the future.

Interface recombination in GaAs at the GaAs/AlAs interface has been investigated before and after selective ‘‘wet oxidation’’ of the AlAs layer. Time-resolved photoluminescence of the band-edge GaAs emission has been used to characterize the interface recombination. Prior to oxidation, the interface recombination is low. After oxidation, the interface recombination has greatly increased, and is comparable to a free GaAs surface in air. However, isolating the GaAs layer from the oxide by a 30 nm layer of Al0.3Ga0.7As allows the interface recombination to remain low after the oxidation. These results help explain the low threshold currents which have been observed in vertical cavity lasers which use wet oxidation of AlAs for current confinement.

Ultrahigh mobility AlxGa1−xAs/GaAs two-dimensional electron gas (2DEG) structures were grown by conventional low-pressure organometallic vapor phase epitaxy (LP-OMVPE). We achieved maximum mobilities of 766 000 cm2/V s at 2.2 K and 171 000 cm2/V s at 77 K after exposure to light (to our knowledge, the highest ever by OMVPE growth), with a sheet carrier density of 4.9×1011/cm2. The high-mobility structures were obtained by either growing an AlGaAs-related buffer underneath the 2DEG structure or preconditioning of the reactor with an undoped AlGaAs run. The dark mobilities of samples grown with the preconditioning procedures and without the AlGaAs-related buffer are much higher than those with the buffer.

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