Electrical properties and defect model of tin-doped indium oxide layers

Abstract

Tin-doped In₂O₃ layers were prepared by the spray technique with doping concentrationsc _Sn between 1 and 20 at. % and annealed at 500 °C in gas atmospheres of varying oxygen partial pressures. The room-temperature electrical properties were measured. Maximum carrier concentrationsN=1.5×10²¹cm⁻³ and minimum resistivities ϱ=1.3×10⁻⁴ Ω cm are obtained if the layers are doped withc _Sn≈9 at. % and annealed in an atmosphere of oxygen partial pressurep _O2 ⋦10⁻²⁰ bar. At fixed doping concentration, the carrier mobility increases with decreasing oxygen pressure. The maximum obtainable mobility can be described in terms of electron scattering by ionized impurities. From an analysis of the carrier concentration and additional precision measurements of the lattice constants and film thicknesses, a defect model for In₂O₃:Sn is developed. This comprises two kinds of interstitial oxygen, one of which is loosely bound to tin, the other forming a strongly bound Sn₂O₄ complex. At low doping concentrationc _Sn≲4 at. % the carrier concentration is governed by the loosely bound tin-oxygen defects which decompose if the oxygen partial pressure is low. The carrier concentration follows from a relationN=K ₁ ·p _O2 ^−1/8 ·(3 ×10¹⁰ × c_Sn −N)^1/4 with an equilibrium constantK ₁=1.4×10¹⁵ cm^−9/4bar^1/8, determined from our measurements.