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Anomalous growth rate reduction and associated composition divergence with increasing aluminum flux in m-plane AlGaN grown by plasma-assisted molecular beam epitaxy at low temperature (565 °C) are observed and investigated. We find that the AlGaN growth rate under conventional gallium-rich conditions decreases rapidly with increasing aluminum flux, contrary to expectations. Moreover, the aluminum fraction of these layers increases super-linearly with aluminum flux, indicating substantial nitrogen and gallium loss from the crystal surface. Indium surfactant assisted epitaxy (ISAE) is found to mitigate this effect significantly. ISAE AlGaN layers do not exhibit a significant decrease in the growth rate with increasing aluminum flux, and their aluminum compositions increase linearly with aluminum flux. Transmission electron microscopy (TEM) images reveal the presence of high-aluminum composition defects within the conventionally grown AlGaN layers, which are significantly reduced in ISAE AlGaN layers. Spatial correlation of these defects with local areas of reduced growth rate observed in an (In)Al0.30Ga0.70N/In0.16Ga0.84N multiple quantum well (MQW) structure suggests that these phenomena have a causal relationship. We attribute the growth rate reduction to the loss of nitrogen and gallium due to site-blocking effects of aluminum adatoms. TEM imaging indicates that high-quality, virtually defect-free (In)Al0.24Ga0.76N/In0.16Ga0.84N MQWs can be grown at 565 °C with negligible indium incorporation into the barriers. [ABSTRACT FROM AUTHOR]

The use of an indium surfactant considerably alters the composition and morphology of low-temperature non-polar m-plane (10 1 ¯ 0) AlxGa1−xN (x ∼ 0.2) and of silicon-doped AlGaN/InGaN multiple quantum wells grown by plasma-assisted molecular beam epitaxy. This paper compares heterostructures grown with indium surfactant with those grown under conventional stoichiometric and gallium-rich conditions at the relatively low temperature necessary for growth of In0.16Ga0.84N quantum wells (565 °C). Stoichiometric growth results in rough, inhomogeneous AlGaN layers that are unsuitable for optical devices. Gallium-rich growth produces a smoother AlGaN layer, reduced inhomogeneities, and sharper interfaces as compared to stoichiometric growth. However, due to the low temperature, gallium-rich growth leads to the formation of an unintentional GaN layer on top of each AlGaN barrier, reducing the energies of confined electronic states in the quantum wells. An indium surfactant enables two-dimensional AlGaN growth at low temperature, producing atomically flat surface morphology and sharp heterostructure interfaces. Indium surfactant assisted epitaxy also eliminates the high aluminum alloy inhomogeneities observed with conventional stoichiometric and gallium-rich growth. Even though partial indium incorporation into the AlGaN layer is found at the studied temperatures, the high-quality, uniform non-polar In0.055Al0.19Ga0.755N/In0.16Ga0.84N quantum wells grown with indium surfactant display bright and narrow photoluminescence that is essential for device applications. [ABSTRACT FROM AUTHOR]

We establish the relationships between growth conditions, strain state, optical and structural properties of nonpolar m-plane (10 1 ¯ 0) InGaN with indium composition up to 39% grown by plasma-assisted molecular beam epitaxy. We find that indium mole fraction as a function of growth temperature can be explained by an Arrhenius dependence of InN decomposition only for high temperature and low indium composition InGaN films. For the samples following the Arrhenius behavior, we estimate the effective activation energy for InN thermal decomposition in m-plane InGaN to be about 1 eV. This value is approximately a factor of two smaller than that reported for c-plane InGaN films. At low growth temperatures, InGaN layers show less efficient indium incorporation than predicted by Arrhenius behavior. We attribute the lower than expected indium composition at low temperatures to the strain-induced compositional pulling effect. We demonstrate that at 540 °C, the increase in the InGaN layer thickness leads to a preferential strain relaxation along the a-direction and an increase in the indium composition. For the indium mole fraction up to x ∼ 0.16, 30-nm-thick m-plane InGaN layers can be coherently grown on GaN with smooth morphology and pronounced low-temperature photoluminescence indicating that the material quality is suitable for device applications. [ABSTRACT FROM AUTHOR]