Self-regulated charge transfer and band tilt in nm-scale polar GaN films

¹ Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
² Department of Chemical and Materials Engineering, and Electrical Engineering, Ira A. Fulton College of Engineering, Arizona State University, Tempe, AZ 85287-6006, USA

Corresponding author: tsai@mail.phys.nsysu.edu.tw

Received: 13 January 2006
Revised: 26 April 2006
Accepted: 25 August 2006
Published online: 28 October 2006

Abstract

Using first-principles calculation for the electronic structures of nm-scale [0001] GaN freestanding films, it is found that the Ga-terminated surface (S_Ga) has a positive electrostatic potential, while the N-terminated surface has a negative electrostatic potential (S_N), so that the energy bands tilt upwards from S_Ga to S_N. Additionally, it is determined that an intrinsic self-regulated charge transfer across the film limits the electrostatic potential difference across the film, which renders the local conduction band energy minimum at S_Ga approximately equal to the local valence band energy maximum at S_N. This effect is found to occur in films thicker than ~4 nm. If the dangling-bond/surface states at both S_Ga and S_N are passivated by pseudo-hydrogen atoms, the tilt of energy bands is similar, though the cross-film potential is reduced due to the extra H_5/4-Ga and N-H_3/4 dipole layers.