Journal of Alloys and Compounds 509 (2011) 1980–1983 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Annealing effects on the p-type ZnO films fabricated on GaAs substrate by atmospheric pressure metal organic chemical vapor deposition Yen-Chin Huang a , Li-Wei Weng a , Wu-Yih Uen a,∗ , Shan-Ming Lan a , Zhen-Yu Li b , Sen-Mao Liao a , Tai-Yuan Lin c , Tsun-Neng Yang d a Department of Electronic Engineering, College of Electrical Engineering and Computer Science, Chung Yuan Christian University, Chung-Li 32023, Taiwan b Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 TA Hsueh Road, Hsinchu 30010, Taiwan c Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung 222, Taiwan d Institute of Nuclear Energy Research, P.O. Box 3-11, Lungtan 32500, Taiwan article info Article history: Received 31 July 2010 Received in revised form 18 October 2010 Accepted 24 October 2010 Available online 3 November 2010 Keywords: ZnO Post-annealing Atmospheric pressure metal-organic chemical vapor deposition Electrical properties P-type conductivity Optical properties Photoluminescence abstract The effects of post-annealing conducted at 500–650 ◦ C on structural, electrical and optical properties of ZnO film fabricated on GaAs (1 0 0) substrate by atmospheric pressure metal-organic chemical vapor deposition are investigated. X-ray diffraction analyses show that the Zn 3 As 2 and ZnGa 2 O 4 phases are produced for the specimens post-annealed at 500 ◦ C and above. Hall measurements indicate that stable p-type ZnO films with hole concentration ranging from 4.7 × 10 18 to 8.7 × 10 19 cm -3 can be obtained by modulating the annealing temperature from 500 to 600 ◦ C. In particular, room-temperature photo- luminescence (PL) measurements indicate that the superior-quality p-type film could be achieved by a post-annealing treatment at 600 ◦ C. Moreover, low temperature PL spectra at 10 K are dominated by the acceptor-related luminescence mechanisms for the films post-annealed at 550 ◦ C and above. The ionization energy of acceptor was calculated to be 133–146 meV, which is in good agreement with that theoretically predicted for the As Zn –2V Zn complex in ZnO. The interdiffused arsenic atoms in the film post-annealed at 600 ◦ C are suggested to form the As Zn –2V Zn complex quite effectively, resulting in the most enhanced p-type conductivity and improved material quality. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Zinc oxide (ZnO) is a wide band gap semiconductor with a direct band gap of 3.37 eV at room temperature and a large exciton bind energy of 60 meV, which makes it a good candidate for the applica- tions in highly efficient and stable room temperature ultra-violet (UV) lasers and light emitting diodes [1–3]. To achieve such goals, the growth of high-quality p-type ZnO is required. However, the fabrication of p-type ZnO films by doping is difficult due to the compensation effect of native n-type carriers released by the donor- type defects such as oxygen vacancies and zinc interstitials [4,5]. Recently, several groups have reported the growth of p-type ZnO by doping group V elements N [6],P [7], As [8], and Sb [9]; how- ever, their behavior in the lattice and the corresponding electronic levels are poorly understood. Among the group V elements exam- ined, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO due to its atomic radius is similar to that of oxygen. However, numerous experimental efforts made by differ- ∗ Corresponding author. Tel.: +886 3 265 4620; fax: +886 3 265 4699. E-mail addresses: chin099983@hotmail.com (Y.-C. Huang), uenwuyih@ms37.hinet.net (W.-Y. Uen). ent groups to implement this idea have not resulted in stable and reproducible p-type material yet. Moreover, J.L. Lyons et al. even reported that N is actually a deep acceptor in ZnO with an exceed- ingly high ionization energy of 1.3 eV based on their theoretical calculations [10]. Therefore, the suitability of N-doping for p-type conductivity in ZnO is required to be examined in more detail. On the other hand, it seems convincing that the behavior of other group V elements, such as As and Sb, as acceptors in ZnO does not stem from a simple substitution on the group VI-site, but rather from complexes of the type As(Sb) Zn –2V Zn with low enthalpies of formation [11]. A direct evidence for arsenic as a zinc-site impurity in ZnO has been presented by U. Wahl et al. using the emission chan- neling technique [12]. To achieve this purpose, several researchers have prepared ZnO films on GaAs substrates and annealed the spec- imens to have As atoms diffuse from the substrate into the ZnO films. In this way, p-type ZnO films have been obtained somehow under a strict annealing condition [6,13–15]. This work reports the p-type conductive behavior of ZnO films fabricated on semi-insulating GaAs substrate, regardlessly as- grown or post-annealed, using atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) technique. In particular, the effects of post-annealing on the p-type characteristics are sys- tematically investigated by analyzing the structural, electrical, and 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.10.108