Validation of the p-type Behavior of an Ag-doped ZnSe Film Grown Heteroepitaxially on GaAs(100) Substrate
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1012-Y03-16
Validation of the p-type Behavior of an Ag-doped ZnSe Film Grown Heteroepitaxially on GaAs(100) Substrate Takashi Narushima, Hiroaki Yanagita, and Masahiro Orita R&D Center, HOYA Corporation, 3-3-1 Musashino, Akishima-shi, Tokyo, 196-8510, Japan
ABSTRACT To validate p-type semiconducting behavior in Ag-doped ZnSe, single-crystal films were grown on GaAs(100) substrates using an evaporation method with ZnSe and Ag2Se powder sources. The heteroepitaxial relationship between ZnSe(100) and GaAs(100) was observed using X-ray diffraction and transmission electron microscopy; secondary phases containing silver or silver selenide were not detected. A film doped with Ag at 1 × 1020 atm⋅cm-3 had a conductivity of 1.5 × 10-5 S⋅cm-1. The hot-probe test indicated p-type polarity, with a clear and reproducible rectifying characteristic demonstrated by forming a ZnSe:Ag/p-GaAs:Zn junction. The work function of a ZnSe:Ag film measured by ultraviolet photoelectron spectroscopy was 6.3 eV. The ZnSe:Ag film is suitable as an injection layer in widegap semiconductor devices and organic light-emitting diodes. INTRODUCTION Widegap p-type semiconducting materials are key to the development of p-n junctionbased devices on glass and polymer substrates, including ultraviolet-blue light-emitting diodes (LED), laser diodes (LD), and solar cells. With polymer devices, heat-free deposition processes are essential. Given a wide band gap of ~2.7 eV, the ability of ZnSe to crystallize at low substrate temperatures has the potential to realize novel devices. Conventional single crystal ZnSe systems doped with N, Li, Cl, and Sb are reported in refs [1-6]. However, ZnSe films grown on glass and polymer substrates at low temperatures have a polycrystalline structure. Recent reports on the p-type semiconducting behavior of ZnSe poly-crystalline films heavily doped with Cu or Ag suggest that ZnSe has improved semiconducting performance over other doping constituents [7,8]. While a number of reports document Cu- and Ag-doped ZnSe systems [9,10], research interest has focused primarily on their luminescence properties. Initially, ZnSe poly-crystalline films were prepared using a vacuum deposition process with metal Zn and Se sources [7,8]. Then, the doping elements, Cu or Ag, were introduced by soaking the films in aqueous solutions of Cu(NO3)2 or Ag(NO3). However, to obtain the highestquality films and avoid contamination by impurities, vacuum processes that control all of the chemical elements present are considerably more reliable. In addition, single-crystal films that lack grain boundary effects are better for evaluating semiconducting properties, such as conductivity and carrier polarity. In this study, Ag-doped ZnSe single-crystal films were prepared using an evaporation process from ZnSe and Ag2Se. The chemical composition, crystallographic structure, and electronic properties of the films were evaluated. Although the Hall voltage was below detection,
a rectifying characteristic was clearly observed with a ZnSe:Ag / p-GaAs:Zn juncti
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