Characterization of high purity GaAs films grown by molecular-beam epitaxy from a solid As cracker

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Abstract
Two series of high-quality, unintentionally doped GaAs films were grown to evaluate a solid As cracker source with a graphite crucible. In the first series, material properties comparisons were made between a film grown with the As cracker in the dimer mode, a film from the same cracker source but in the tetramer mode, and lastly, a film from a conventional As cell. The film grown with the dimers had a n-type unintentional background doping level of 5×1014 cm−3 and a 104 000 cm2/V s mobility at 77 K. The films grown with As tetramers gave low p-type unintentional background doping levels of less than 1.1×1014 cm−3, respectively. Photoluminescence spectra taken of these films at 4 K showed various excitonic transitions and comparable C incorporation. In the second series, films grown at As2/Ga incorporation rate ratios of 1.1, 1.5, and 2.0 had layers that were p-type, resistive, and n type, respectively. Samples taken from the film grown at the 2.0 ratio had 77 K mobilities as high as 195 000 cm2/V s, with a corresponding net carrier concentration of 3.8×1014 cm−3. These mobility values are the highest reported for GaAs grown with a solid As dimer source. Results from a variable temperature van der Pauw measurements of another sample cut from this film gave a donor ionization energy of 2.6 meV.

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