Electron Mobility and Space‐Charge‐Limited Current Flow in Na‐Doped ZnO

With the aid of a technique which examines the transient drift in an applied field of electrons photoinjected into a single crystal specimen by a short pulse light, the electron mobility has been measured as a function of temperature in high‐resistivity, Na‐doped ZnO. The observed exponential temperature dependence of the mobility indicated that the drift mobility of electrons is controlled predominantly by thermal release from trapping states, of estimated density (5 to 22)×10 15 cm −2 , lying in a 0.24‐eV region below the conduction band edge. Ohmic contacts of In used to inject electrons into a single‐crystal specimen of the same material produced space‐charge‐limited currents at high fields. The observed current‐voltage and current‐temperature characteristics indicated that either a discrete level or a narrow band of electron traps existed in the 0.6‐eV region below the conduction band edge with a density of 2×10 13 cm −3 .