Electrical and optical properties of CVT-grown ZnO crystals
- PDF / 73,720 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 5 Downloads / 324 Views
1201-H05-16
Electrical and optical properties of CVT-grown ZnO crystals Koji Abe and Masanori Oiwa Department of Electrical and Electronic Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan ABSTRACT Effects of H2O partial pressure on ZnO crystal growth by chemical vapor transport (CVT) have been investigated. The use of H2O causes the increase in growth rate of ZnO, indicating that H2O acts as a dominant oxygen source in ZnO growth by CVT. The use of H2O also improves structural, electrical, and optical properties of the CVT-grown ZnO crystals. A sharp X-ray rocking curve for the ZnO (0002) reflection was obtained, and the full width at half maximum value was 38 arcsec. Strong near band edge emission was observed in photoluminescence spectra at room temperature. Both carrier concentration and Hall mobility increased with partial pressure of H2O. The dependence of the carrier concentration on temperature indicates that there exist two donors in the CVT-grown ZnO crystals. The estimated ionization energy for the shallow donor was 35±5 meV and that for the deep donor was 115±5 meV. INTRODUCTION Zinc oxide (ZnO) has attracted great attention because of its potential application for near-UV optoelectronic devices. Various crystal growth techniques such as hydrothermal growth, molecular beam epitaxy (MBE), and chemical vapor transport (CVT) have been used to produce ZnO crystals [1–4]. Hydrothermal growth is widely used to produce bulk ZnO crystals. However, hydrothermally grown ZnO crystals contain impurities from a mineralizer solution. Lithium, which is known as a common impurity in hydrothermally grown ZnO crystals, produces carrier compensation. The unintentional lithium doping can be a major obstacle to realize practical devices [1]. CVT has potential for high purity ZnO crystal growth because Zn and O atoms are transported from ZnO powder to seed crystals by the chemical reaction of ZnO with C (ZnO+C↔Zn+CO). Partial pressure in the reaction tube of CVT affects characteristics of ZnO crystals. We have reported that the residual carbon atoms in ZnO crystals decreases with increasing partial pressure of CO2 in the reaction tube [5]. When H2O is introduced into the reaction tube, the H2 partial pressure increases owing to the chemical reaction of H2O with Zn (H2O+Zn→ZnO+H2). In this study, effects of the partial pressure of H2O on CVT-grown ZnO crystals have been investigated. EXPERIMENTAL DETAILS ZnO crystals were grown by CVT. The details of the CVT system are described in a previous report [5]. A graphite crucible was filled with 1.8 g of 5N-purity ZnO powder and placed on the susceptor in a vertical quartz tube. Zn-polar ZnO substrates used as seed crystals were cut from a hydrothermally grown ZnO crystal. The ZnO substrate was fixed on the inside
of a crucible lid. Temperatures of the substrate (Ts) and ZnO powder (Tp) were defined as temperatures of the lid and susceptor. During 2-hour crystal growth, Ts and Tp were kept at 840°C and 1020°C, respectively. The quartz tube was fil
Data Loading...
