The electrical properties, presence of deep electron and hole traps and photoluminescence spectra were measured for undoped a-GaN films grown by metal-organic chemical vapor deposition (MOCVD) in a two-stage process using a high V/III ratio at the first stage and low V/III ratio at the second stage. Growth was performed on r-sapphire substrates with a high temperature GaN nucleation layer. The films showed a full width at half maximum of 450-470 arcseconds for the (11-20) x-ray rocking curve with little anisotropy with respect to the sample rotation around the growth direction. The stacking fault (SF) density determined by selective etching was ∼5 104cm -1. The residual donor concentration was 1014-10 15cm-3, with a very low density (2.5 10 13cm-3) of electron traps located at Ec- 0.6 eV, which are believed to be one of the major non-radiative recombination centers in nonpolar GaN. Consequently, the films showed a high intensity of bandedge luminescence with negligible contribution from defect bands associated with SFs. In contrast to previously studied nonpolar GaN films, the a-GaN layers showed a high concentration of gallium-vacancy-related acceptors near E v 1 eV and a strong yellow luminescence band, both indicating that growth conditions were effectively N-rich. a-AlGaN/GaN heterojunctions with thin heavily Si doped AlGaN barriers made on a-GaN substrates showed two-dimensional electron gas (2DEG) concentrations of 1.2 1013cm-3, with 2DEG mobility of 80 cm2/Vs. Capacitance-voltage profiling of Schottky diodes on these HJs suggest that the 2DEG is fully depleted by the built-in voltage of the Schottky diode.
Bibliographical noteFunding Information:
The work at IRM was supported in part by the International Science and Technology Center ICTS Grant No. 3870 and Russian Foundation for Basic Research RFBR Grant Nos. 10-02-00566-a and 11-02-00718-a. The work at Chonbuk National University was supported by the National Research Foundation of Korea (NRF) funded by the Korea government (MEST) (2010-0024973). A.Y.P. gratefully acknowledges support from the Brain Pool Program of Korean Government during his stay at Chonbuk National University.
ASJC Scopus subject areas
- Physics and Astronomy(all)