Rapid thermal annealing of modulation-doped AlxGa1−xAs/GaAs heterostructures for device applications

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Abstract
High‐quality molecular beam epitaxial modulation‐doped heterostructures were flash annealed at several temperatures TA:750 °C≤TA≤900 °C using a rapid thermal annealing technique. Samples of bulk GaAs and bulk AlGaAs were also included in the study. Structural parameters were varied for the purpose of optimization and to determine mechanisms of electronic degradation. Layers were characterized by measurements of electron mobility (μ), sheet carrier density (ns), and by photoluminescence (PL) spectra. In all cases, the modulation‐doped heterostructures displayed decreases in μ, ns and PL intensity with increasing TA above 850 °C. These trends are attributed to vacancies and traps formed during the annealing process and to transfer of the amphoteric Si dopant from donor to acceptor lattice sites in the n‐AlxGa1−xAs layer. At TA=800 °C, the minimum temperature at which sufficient implant activation has been achieved, we have demonstrated that the most heat tolerant of the modulation‐doped structures studied retains over 95% of its original mobility and sheet carrier density, with no fundamental changes in the PL spectrum. This constitutes a primary technological advance towards high performance self‐aligned modulation‐doped GaAs/AlxGa1−xAs field effect transistors.