Structural and optical properties of ZnO films on SrTiO₃substrates by MOCVD

Abstract

ZnO films have been fabricated on (0 0 1), (0 1 1) and (1 1 1) SrTiO3 (STO) substrates by metal-organic chemical vapour deposition (MOCVD). It is interesting that the ZnO films on (0 0 1) and (0 1 1) STO substrates show polar and semipolar orientations, which are different from previous reports, while the same growing direction of polar ZnO with previous results is found on (1 1 1) STO. For the atomic arrangements, two orthogonal domains and a single domain are observed on (0 0 1) and (1 1 1) STO, respectively. Photoluminescence spectra show that every sample has a sharp near-band-edge emission peak at about 3.28 eV without any deep-level emission band between 1.5 and 2.8 eV, implying a high optical quality. A violet emission around 3.0 eV is observed only in ZnO films on (0 0 1) and (0 1 1) STO substrates grown at 600 °C, which is discussed briefly. Additionally, the semipolar ZnO does not weaken the emission efficiency along with the reduction in the polarization effect compared with polar ZnO. These results show that high-quality polar and semipolar ZnO films can be grown on STO substrates by MOCVD.

Valence Band Offsets of ZnO/SrTiO3, ZnO/BaTiO3, InN/SrTiO3, and InN/BaTiO3 Heterojunctions Measured by X-Ray Photoelectron Spectroscopy

“…The first In 3d 5/2 component located at 443.50±0.03 eV is attributed to the In-N bonding, and the second, at 444.52±0.03 eV, is identified to be due to surface contamination. This two-peak profile of the In 3d 5/2 spectra in InN is typical and have been demonstrated by other researchers (King et al, 2008;Piper et al, 2005;Yang et al, 2009). Comparison of their binding energy separation with previous results, we suggest that the second peak at 444.52±0.03 eV to the In-O bonding is due to contamination by oxygen during the growth process.…”

“…By linear extrapolation method, the strain induced shift in ZnO/BTO is less than 0.02 eV, which is much smaller than the aforementioned deviation of 0.09 eV. The error induced by band bending is checked to be much smaller than the average standard deviation of 0.09 eV given above (Yang et al, 2009). So the experimental obtained VBO value is reliable.…”

“…Thus, the ZnO overlayer in the heterojunction is almost completely strained and the strain-induced piezoelectric field effect can also be neglected. In addition, the error induced by band bending is checked to be much smaller than the average standard deviation of ±0.09 eV given above (Yang et al, 2009). Since the factors that can affect the ultimate result can be excluded from the measured result, the experimental obtained VBO value is reliable.…”

“…Since the factors that can affect the results can be excluded from the measured results, the experimental obtained VBO value is reliable. Making use of the band gap of InN (0.7 eV) (Yang et al, 2009) and SrTiO 3 (3.2 eV) (Baer et al, 1967), the CBO (∆E C ) is calculated to be 1.37 eV and the ratio of ∆E C /∆E V is close to 1:1. As shown in Fig.…”

Structural characterization of impurified zinc oxide thin films

“…There are studies that report the same dominant behavior of (110) preferred orientation of the ZnO-based thin films deposited on such substrates [41,42,43], but also some that presented (002) dominant orientation [44,45]. The preferential growth mode is influenced by both substrate cleaning process and deposition parameters.…”