Defect characterization by DLTS of AlGaNUV Schottky photodetectors

Deep traps are studied in MBE grown n-AlxGa1-xN Schottky photodiodes using deep level transient spectroscopy (DLTS). These daylight blind UV photodetectors have cut-off wavelengths of 300 and 250 nm, for x = 0.12 and 0.41, respectively. Other investigations of deep centers are those by Gotz et al. who studied MOCVD Al0.12Ga0.88N (Appl. Phys. Lett. 69 (1996) 2379) and by Polyakov et al. who looked at p-AlGaN using an AlGaN/GaN heterojunction LED p-i-n structure (Solid State Electron. 43 (1999) 1929). Our photodiodes were MBE grown with carrier density (59) x 10(17) cm(-3). We detect two levels, EOA2 and EOA1 in each photodetector, below 320 K, independent of the A1 mole fraction, x. For AlxGa1-xN with x = 0.41, EOA2 has a DLTS signature (E-C-0.567 eV; 1.1 X 10(-14)cm(2)) While the signature for the second defect, EOA1, is (E-C-0.274eV; 3.1 x 10(-13) cm). From a comparison with as-grown defects in MBE grown n-GaN, it would appear, based on DLTS signatures that EOA1 is the same as E-1 (E-C-0.234eV) observed by Wang et al. (Appl. Phys. Lett. 72 (1998) 1211) and EOA2 is the 0.61 eV level reported by Gotz et al. (Appl. Phys. Lett. 69 (1996) 2379), Furthermore, proton irradiation introduces an additional electron trap, EpR1, at 0.187 eV. We also determine that He-ions remove carriers in AlGaN, at a rate of 23 770 cm(-1), eighty times higher than in GaN. (C) 2001 Elsevier Science B.V. All rights reserved.