Arsenic-doped GaN films were grown via metalorganic chemical vapor deposition using trimethylgallium, ammonia, and arsine precursors. The arsenic concentration increases from 3×1016 to 5×1017 cm−3 in response to a change in arsine mole fraction from 3.3×102 to 3.2×104 ppm. The electron mobility increases with arsenic content reaching a maximum value of 374 cm2/V s at 300 K. In addition, the integrated photoluminescence intensity exhibits a 35-fold increase in magnitude at 300 K. To explain these findings, a simple physical model is proposed in which arsenic “impurities” occupy otherwise vacant sites on both the gallium and nitrogen sublattices.
Arsenic-doped GaN films and GaNAs films have been synthesized by MOCVD. Samples were grown on sapphire, GaN-coated sapphire, and GaAs substrates. Composition, structure, and phase distribution were characterized by EPMA, SIMS, XRD, and TEM. The arsenic content increases demonstrably as the growth temperature descreases from 1030 to 700 ˚C. In the high temperature limit, high quality arsenic-doped GaN forms on GaN-coated sapphire. In the low temperature regime, nitrogen-rich GaNAs forms under some growth conditions, with a maximum arsenic mole fraction of 3%, and phase segregation in the form of GaAs precipitates occurs with an increase in arsine pressure. Preferential formation of the nitrogen-rich phase on GaN-coated sapphire suggests the presence of substrate-induced "composition pulling".
Spatially resolved values of the Al-Ga interdiffusion coefficient for p-i-n and n-i-p AlGaAs-GaAs device structures are found to be nearly identical in magnitude, but to vary with position by a factor of 2 across a 1 μm thick multiple quantum well active region. These observations are in marked contrast with theoretical predictions given that the Fermi level to valence-band energy separation changes by 0.7 eV across the intrinsic region and suggest that impurity-free layer disordering does not provide the necessary uniformity in energy shift for photonic integrated circuit fabrication in its present state of development.
A simple experimental approach has been employed to obtain thermochemical parameters for cation vacancy formation and migration in the AlGaAs heterostructure system. Cation vacancies are injected into the free surface by annealing under an arsenic-rich ambient. Their presence is detected by monitoring the local rate of Al–Ga interdiffusion at imbedded quantum well markers. The sample is unusually thick allowing us to separately identify contributions from the vapor, epilayer, and substrate phases. The entropies and enthalpies of vacancy formation and migration are (5.2±5.7) kB and (1.8±0.5) eV and (11.3±4.4) kB and (3.3±0.4) eV, respectively.
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