GaN Schottky barrier photodiode on Si (111) with low-temperature-grown cap layer

In this work, GaN films were grown on three-inch silicon substrates by plasma-assisted molecular beam epitaxy (PAMBE) with AlN (about 200 nm) as the buffer layer. Finally, a thin AlN cap layer (50 nm) was grown on the GaN surface. Current-voltage (I-V) measurements before and after heat treatment were carried out. Different annealing temperatures (500-700 degrees C) were investigated. Under dark condition, the Schottky barrier height (SBH) derived by the I-V method is 0.48 eV for as-deposited Ni/AlN/GaN/AlN Schottky diode. On the other hand, the effective barrier heights of 0.52, 0.55, and 0.57 eV were obtained for Schottky diodes annealed at 500, 600, and 700 degrees C, respectively. We found that the SBHs of annealed Schottky diodes under dark and illuminated conditions were observed to be higher relative to the as-deposited Schottky diode. When annealed at 700 degrees C, the resulting Schottky diodes show a dark current of as low as 5.05 x 10(-5) A at 10 V bias, which is about two orders of magnitude lower than that of as-deposited Ni/AlN/GaN/AlN Schottky diode (2.37 x 10(-3) A at 10 V bias). When the sample was under illumination condition, the change of current was significant for the annealed samples as compared to the as-deposited sample. (C) 2009 Elsevier B.V. All rights reserved.