Prospectives for AlN electronics and optoelectronics and the important role of alternative synthesis

Abstract

Future applications for emerging AlN semiconductor electronics and optoelectronics are facilitated by emerging doping technologies enabled by low temperature, non-equilibrium epitaxy. Defect and impurity compensation can be reduced by controlling the surface chemistry with reducing compensating vacancy concentrations being a key driver for lower temperature growth. Contrary to common understanding, low temperature, metal-rich vacuum processes are shown to have higher diffusion lengths than high temperature nitrogen-rich methods. This feature can be utilized to inhibit silicon-DX center formation without compromises in crystal quality. First principles calculations identify the valence split-off band as the dominant hole band contributing to impurity band formation (as opposed to the heavy and light hole bands in other nitrides). This anomalous band structure causes an impurity band to form at dopant concentrations similar to GaN even though AlN has a deeper isolated acceptor energy and results in hole mobilities that are substantially higher than possible in GaN. AlN hole concentrations of ∼4.4 × 1018 cm−3 and 0.045 Ω cm resistivity and electron concentrations of ∼6 × 1018 cm−3 and ∼0.02 Ω cm resistivity are shown and offer substantial promise for future generations of AlN bipolar electronic and optical devices.