Cu-doped ZnSe Film with Stoichiometric Composition Deposited at Room Temperature using Compound Sources
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1012-Y03-28
Cu-Doped ZnSe Film with Stoichiometric Composition Deposited at Room Temperature using Compound Sources Masahiro Orita, Takashi Narushima, and Hiroaki Yanagita R&D Center, HOYA Corporation, Akishima-shi, 196-8510, Japan ABSTRACT Stoichiometric Cu-doped ZnSe crystalline films were prepared on glass substrates from ZnSe and Cu2Se powders using the evaporation method without intentional heating. Post-annealing treatment at 400∞C in a vacuum improved the crystallinity, and no secondary phase was observed using X-ray diffraction for a film with a Cu concentration of Cu/(Zn + Cu) = 0.10, which had a conductivity of 28 Scmñ1 and good transparency at green and red wavelengths. The thermal probe test indicated p-type carrier polarity, and the effects of annealing were confirmed by irradiating the as-deposited films with a YAG laser (λ = 355 nm). Possibility of producing transparent p-type conducting films on polymer substrates is demonstrated. INTRODUCTION ZnSe is a direct semiconductor with a band gap of 2.7 eV [1]. Its ability to crystallize at low temperatures offers the potential to realize p-n devices, such as light-emitting diodes, laser diodes, and solar cells, on polymer or glass substrates. Recent reports [2,3] that have studied the p-type semiconductor properties of polycrystalline ZnSe films heavily doped with Cu or Ag is of interest in these applications. A wet process was applied to penetrate the Cu or Ag in polycrystalline ZnSe films those were prepared using a conventional evaporation method. However, vacuum processes that control all of the chemical elements are more reliable in order to avoid penetration of unexpected impurities and to obtain high-quality films. Furthermore, study of low-temperature deposition processes is required for applications on polymer substrates. For depositing large areas on polymer substrates, the evaporation method is suitable and has been applied to the industrial production of indium tin oxide (ITO) films for touch panels. However, there are problems that a stoichiometric composition of ZnSe doped with Cu must be obtained and it must be crystallized without heating. To resolve these issues, we examined an evaporation process that uses ZnSe powder as the source material followed by laser annealing. According to several composition analyses of the vapor from heat-treated ZnSe, ZnSe (s) decomposes into Zn (g) and Se2 (g) [4], and the partial pressure of ZnSe (g) is lower than 0.1% of the total pressure [5]. Hence, the vapor has a Zn/Se = 1/1 composition. If all of the gas molecules stick to the substrate, a stoichiometric ZnSe film would be obtained. Cu2Se was tested as the source of the dopant Cu, to supplement Se at the same time. EXPERIMENTAL A vacuum chamber with a turbo molecular pump with an evacuation rate of 1500 Lsñ1 (Eiko) was used. The basal pressure was 1 × 10ñ7 Torr. Inside the chamber was a crucible container on which four 1-cc crucibles could be mounted. These crucibles can be heated to 1500∞C using a temperature-controlled Ta heater system. A rotating s
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