Electrical properties of undoped bulk ZnO substrates

Abstract

Undoped bulk ZnO crystals obtained from Tokyo Denpa show either resistive behavior [(5 3 10 4 )-(3 3 10 5 ) Ohm cm) or low n-type conductivity (n ' 10 14 cm ÿ3 ) with mobilities in the latter case of 130-150 cm 2 /V sec. The variation in resistivity may be related to the thermal instability of Li that is present in the samples. The Fermi level is pinned by 90-meV shallow donors that are deeper than the 70 meV and hydrogen-related 35-meV shallow donors in Eagle Pitcher and Cermet substrates. In all three cases, 0.3-eV electron traps are very prominent, and in the Tokyo Denpa material they dominate the hightemperature capacitance-frequency characteristics. The concentration of these traps, on the order of 2 3 10 15 cm ÿ3 , is about 20 times higher in the Tokyo Denpa ZnO compared to the two other materials. The other electron traps at E c ÿ0.2 eV commonly observed in undoped n-ZnO are not detected in conducting Tokyo Denpa ZnO samples, but they may be traps that pin the Fermi level in the more compensated high-resistivity samples.

Solvothermal growth of ZnO

“…A melt-grown sample was measured for comparison. The carrier concentration is very much lower in the hydrothermal sample than in the melt grown one and decreased with increasing 1/T from N ¼ 2 Â 10 16 cm À3 at 500 K (10 3 /T ¼ 20) to N ¼ 4 Â 10 13 at 100 K. Polyakov and co-worker [94] obtained very similar results of N ¼ 1.3e4.6 Â 10 13 and N ¼ 6.4 Â 10 11 at 300 K and 77 K, respectively, for measurements on four samples of TD ZnO as purchased. In both cases, the N value is clearly the effect of low-impurity, point defect, and dislocation concentrations, quite in good agreement with our results from XRD and impurity analysis.…”

Optical characterization of ZnO nanoparticles capped with various surfactants

“…A lot of work has been devoted in decreasing the defect emission by various techniques. Luminescence emission of ZnO particles depends on the method of fabrication [18,23], annealing conditions in various environments [24,25], presence of dopants [26] and on PVP coating [19,27,28].…”

Cathodoluminescence Studies of Electron Injection Effects in Wide-Band-Gap Semiconductors

“…Secondary Ion Mass Spectroscopy (SIMS) measurements revealed the Li concentration of about 3x10 16 cm -3 [25]. The Schottky contacts for EBIC measurements were deposited on the non-polar a-plane of ZnO crystal by electron beam evaporation of 80 nm-thick Au layer and subsequent lift-off.…”

“…Secondary Ion Mass Spectroscopy (SIMS) measurements revealed the Li concentration of about 3x10 16 cm -3 [25] (Li is often added to ZnO to increase the resistivity of initially n-type samples).…”