Investigating the electrical properties of Si donors in AlxGa1–xN alloys

Abstract

In this paper a study of the electrical properties of Si-doped Al x Ga 1-x N is presented. The Al x Ga 1-x N layers, grown using the metalorganic chemical vapour deposition technique, were studied using variable temperature Hall effect and persistent photoconductivity measurements. High quality conducting Al x Ga 1-x N layers were obtained for 0≤x≤0.5, with the mobility decreasing from 215 cm 2 /V s (GaN) to 10 cm 2 /V s (Al 0.51 Ga 0.49 N), at 300 K. The carrier concentration of these layers was typically between 2.5 x 10 18 cm -3 and 7 × 10 17 cm -3 at 300 K. For Al x Ga 1-x N layers with 0 ≤x ≤ 0.41 the temperature dependence of the carrier concentration between 300 and 15 K could be studied, yielding the Si donor activation energy. The carrier concentrations of higher Al content samples (0.5 ≤ x ≤ 0.65) could not be accurately measured below 300 K, and thus the Si activation energy was obtained from the temperature dependence of the resistivity. It was found that the Si activation energy escalated with increasing Al content of the layers, and followed the trend predicted for a shallow hydrogen-like donor, up to x = 0.65. Illumination of the samples at low temperature with a blue LED showed that the layers exhibit little persistent photoconductivity, further confirmation that Si remains a shallow donor in Al x Ga 1-x N.