High Electron Mobility W-doped In 2 O 3 Thin Films
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0905-DD01-02.1
High Electron Mobility W-doped In2O3 Thin Films P. F. Newhouse, C.-H. Park, D. A. Keszler, J. Tate1, and P. S. Nyholm2 Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA 1 Department of Physics, Oregon State University, Corvallis, Oregon 97331-6507, USA 2 Hewlett-Packard Company, 1000 NE Circle Boulevard, Corvallis, Oregon 97330-4239, USA ABSTRACT High electron mobility thin films of In2-xWxO3+d (0 x 0.075) were prepared by pulsed laser deposition. The highest mobility polycrystalline and textured films show mobility >110 cm2/Vs on both amorphous SiO2 and single crystal yttria-stabilized zirconia substrates. The carrier density is in the range 1-3 x 1020 cm-3 at room temperature. The W dopant concentration for films with optimized electrical properties was x ~ 0.03. INTRODUCTION Reports of refractory metal doping of In2O3 with Ta, Mo, Zr, Ti, and co-doping with Mo and W [1,2,3,4,5] have shown that transparent In2O3 thin films exhibiting high carrier mobility μ >100 cm2/Vs can be prepared if W, Mo, or Ti is chosen as the dopant. Increasing the carrier mobility is the preferred route to optimizing the electrical conductivity, averting transparency losses from free carrier absorption [6]. Evaporated thin films of In2O3:Mo (IMO) on glass substrates [7] have exhibited μ ~ 130 cm2/Vs with electrical conductivity of ~ 5,900 S/cm [3]. Sputtered [8] and laser ablated [9] IMO films have demonstrated best-case mobilities of 83 cm2/Vs on glass and > 95 cm2/Vs on yttria-stabilized zirconia (YSZ), respectively. More recently, sputterdeposited In2O3:Ti [4] and PLD-deposited In2O3:W [5] films on amorphous SiO2 have yielded high mobility carriers of 83 cm2/Vs, and 104 cm2/Vs , respectively. These values are factors of two to three greater than those measured in commercial grade [9] In2O3:Sn (ITO; = 5,000 S/cm, n = 6.6 1020 cm-3, μ = 47 cm2/Vs) and research grade [10] In2O3:Sn ( ~ 13,000 S/cm, n = 1.9 1021 cm-3, μ = 42 cm2/Vs). Here we report improved mobilities in PLD-deposited In2xWxO3+y (IWO) films on amorphous substrates, and show transport and structure measurements. We also show that co-doping In2O3 with W and Sn produces films with conductivity between and carrier mobility between IWO and ITO. EXPERIMENTAL DETAILS Thin films were deposited onto heated GE 124 fused SiO2 and single crystal YSZ (001) substrates using pulsed laser ablation of ceramic targets. Films were prepared in two different chambers (a UHV chamber with a base pressure of 2 10-9 torr, and a HV chamber with base pressure 1 10-7 torr) using several targets prepared by different methods. IWO targets of about 60% of theoretical density were prepared by solid state synthesis from stoichiometric proportions of In2O3 and WO3 with xtarget = 0, 0.025, 0.0375, 0.05, 0.625, and 0.075. Commercially obtained IWO targets were 68-88% dense and had xtarget = 0, 0.02, and 0.05. We prepared IWO films from single targets, and also prepared multilayered films from targets of In2O3 and IWO in order to dilute the W c
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