Electron transport in N-polar AlGaN:Si films grown by MOVPE on annealed and sputtered AlN templates

Abstract

N-polar AlGaN films have the potential to improve the performance of optoelectronic and electronic devices, owing to their reversed polarization electric field orientation when compared with their metal-polar counterparts. However, the inferior surface morphology and electrical properties of these films have hindered the performance of N-polar devices, falling behind their metal-polar counterparts. This study develops an epitaxial strategy for fabricating AlGaN:Si films with a step-and-terrace surface morphology, achieved through the utilization of high growth temperature in conjunction with a substantial off-cut angle. The N-polar Al0.36Ga0.64N:Si film exhibits an electron mobility of 74.8 cm2/Vs at a free electron concentration of 3.7 × 1019 cm−3, surpassing previously reported values in the literature. Temperature-dependent mobility analysis confirms that ionized impurity scattering is the dominant factor influencing electron mobility in the degenerate N-polar AlGaN:Si films. Enhanced threading dislocation scattering is observed to cause an anomalous reduction in mobility at lower temperatures. A comparison of experimental and theoretical mobilities across the full range of Al content highlights that the decline in mobility for high Al-content AlGaN:Si is due to compensation defects. This study offers an epitaxial approach for N-polar AlGaN:Si films and delves into the underlying electron transport mechanisms, driving advances in N-polar light-emitting diodes and high electron mobility transistors.