Carrier Compensation Induced by Thermal Annealing in Al-Doped ZnO Films

• Main Authors: Takashi Koida, Tetsuya Kaneko, Hajime Shibata
• Format: Article
• Language: English
• Published: MDPI AG 2017-02-01
• Series: Materials
• Subjects: transparent conducting oxides; ZnO; doping; carrier compensation; mobility
• Online Access: http://www.mdpi.com/1996-1944/10/2/141

This study investigated carrier compensation induced by thermal annealing in sputtered ZnO:Al (Al2O3: 0.25, 0.5, 1.0, and 2.0 wt %) films. The films were post-annealed in a N2 atmosphere at low (1 × 10−23 atm) and high (1 × 10−4 atm) oxygen partial pressures (PO2). In ZnO:Al films with low Al contents (i.e., 0.25 wt %), the carrier density (n) began to decrease at annealing temperatures (Ta) of 600 °C at low PO2. At higher PO2 and/or Al contents, n values began to decrease significantly at lower Ta (ca. 400 °C). In addition, Zn became desorbed from the films during heating in a high vacuum (i.e., <1 × 10−7 Pa). These results suggest the following: (i) Zn interstitials and Zn vacancies are created in the ZnO lattice during post-annealing treatments, thereby leading to carrier compensation by acceptor-type Zn vacancies; (ii) The compensation behavior is significantly enhanced for ZnO:Al films with high Al contents.