Optical and structural characteristics of Ga-doped ZnO films
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TRONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS
Optical and Structural Characteristics of Ga-doped ZnO Films O. A. Novodvorskya^, L. S. Gorbatenkoa, V. Ya. Panchenkoa, O. D. Khramovaa, Ye. A. Cherebiloa, C. Wenzelb, J. W. Barthab, V. T. Bublikc, and K. D. Shcherbachevc aInstitute
on Laser and Information Technologies, Russian Academy of Sciences, Shatura, Moscow oblast, 140700 Russia ^e-mail: [email protected] bInstitute of Semiconductor and Microsystem Technology, University of Technology, Dresden, D-01063 Germany cMoscow State Institute of Steel and Alloys (Technological University), Moscow, 119049 Russia Submitted July 2, 2008; accepted for publication September 2, 2008
Abstract—The n-ZnO films doped with Ga to the content 2.5 at % are produced by pulse laser deposition onto the (0001) oriented single crystal sapphire substrates. The transmittance spectra of the ZnO films in the range from 200 to 3200 nm are studied in relation to the Ga dopant content. It is established that an increase in the Ga content shifts the fundamental absorption edge to the blue region, but reduces the transparency of the ZnO films in the infrared spectral region. The dependence of the band gap on the level of doping with Ga is determined. The photoluminescence spectra of the ZnO films doped to different levels are recorded. It is established that the PL intensity and peak position vary unsteadily with the level of doping. X-ray diffraction studies of the structure of the films are carried out. It is found that the crystallographic parameters (the lattice constant c) of the ZnO film depend on the Ga dopant content and the conditions of deposition of the films. PACS numbers: 68.55.Ln, 78.55.Hx, 78.67.-n, 81.15.Fg DOI: 10.1134/S1063782609040034
1. INTRODUCTION In the last few years, the growing demand for solid sources and detectors of light in the blue and ultraviolet (UV) spectral regions stimulated extensive studies of several wide-gap semiconductors. The major activities in these fields were focused on GaN (the band gap Eg = 3.5 eV), ZnO (Eg = 3.4 eV), ZnSe (Eg = 2.9 eV), and 6H-SiC (Eg = 3.0 eV). Impressive progress was achieved in studies of the GaN-based materials. On the basis of GaN and related alloys, the light-emitting and laser diodes operating in the visible spectral region (460 nm) were developed [1, 2]. However, to make the emission efficient, a high In content in the InGaN alloy is required, which increases the UV absorption and poses severe problems in using the GaN-based materials to develop UV light-emitting and laser diodes [3]. Of considerable interest is ZnO as an alternative material to GaN for applications in devices. Zinc oxide exhibiting a high radiation resistance and high thermal and chemical stability is widely used in developing different devices, specifically, solar cells, in which zinc oxide serves as a material for low-resistivity transparent contacts. Due to its unique optical, acoustic, and electrical properties, zinc oxide found application in gas sensors, varistors, and generators of surface acoustic wav
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