Semipolar (11–22) AlN Grown on m-Plane Sapphire by Flow-Rate Modulation Epitaxy for Vacuum-Ultraviolet Photodetection

Semipolar (11–22) AlN films grown on m-plane sapphire are investigated by flow-rate modulation epitaxy (FME). The full width of half maximums (FWHMs) of thin AlN film for X-ray rocking curves (XRCs) are reduced from 1398 arcsec for traditional growth to 865 arcsec for III-FME. The reduced defect density is attributed to prolonged Al mobility, which results in the transition of growth mode from quasi three-dimensional to two-dimensional step flow. On-axis FWHM[11–23] and off-axis FWHM[0002] of XRCs for 6 μm-thick III-FME AlN film are reduced to 346 arcsec and 641 arcsec, respectively. Metal–semiconductor–metal AlN-based photodetectors prepared on the as-grown (11–22) AlN demonstrate the remarkable operating characteristics with a high photo-to-dark-current ratio of 740–2.27 × 104 and responsivity of 6–20 mA/W under 185 nm illumination, which implies promising application in vacuum-ultraviolet photodetection field.