AFM image of the (a) ZnO Zn-face, (b) ZnO Zn-face (annealed), (c) ZnO O-face, (d) ZnO O-face (annealed), (e) ZnO/ZnO:Al on a-sapphire, and (f) GaInZnO-sample.
(a) XRD rocking-curve of the samples; the FWHM-values are summarized in Table I . (b) Transmission of the TRC contact layers on a fused quartz glass substrate. The inset depicts the contact geometry applied for the heteroepitaxial sample (a) and for all other samples (b).
(a) Cross-sectional TEM bright-field image of a TRC fabricated on a ≈25 nm thin ZnO-layer deposited on a-sapphire. (b) High resolution TEM lattice image (beam direction parallel to the [2-1-10] of ZnO) of the interfacial region between the ZnO and the nano-crystalline Ag x O.
Current-voltage characteristics of various TRC at room temperature.
Temperature dependence of the current-voltage characteristics.
Temperature dependence of the effective barrier height and the ideality factor.
Correlation between mean barrier height and barrier distribution width for Schottky contacts fabricated (a) on n-ZnO (data from this work and Refs. 28, 29, and 54–56 ) and (b) on various semiconductors using various contact metals (data from this work and Refs. 44 and 57–73 ). The dotted lines are linear fits through (0/0).
Temperature dependence of (a) the effective and mean barrier height of the contact on the heteroepitaxial sample extracted by IV- and CV-measurements, respectively, and (b) the width σ of the Gaussian barrier height distribution extracted from the difference of mean and effective barrier height. The red dash-dotted line indicates σ extracted from the temperature dependence of the effective barrier-height only; the grey box indicates the standard error of σ.
Calculated difference of pseudo barrier height and true barrier height (for ). The solid white contour line denotes a difference of 0.02 V. The dotted (dashed) contour line shows the variation of the latter contour line for of 1.2 (0.8) V.
Calculated difference between effective barrier heights of TED and TE theory using numerical approximation of Eq. (7) for and .
Maximal deviation of effective barrier height for and in dependence of mean barrier height and barrier distribution width. The shaded area of the 100 K-plot indicates the range, where, at least for part of the investigated mobility/net doping density—range, numerical calculation fails.
Calculated difference of effective barrier height extracted using full TED-model and using TE-model only for a mean barrier height of 1.2 V and a barrier distribution width of 120 mV. The white contour line indicates a difference of 0.02 V.
RMS-roughness determined by AFM, FWHM of the rocking curve obtained by XRD, net doping density for zero bias calculated from CV-measurements, and free electron density and mobility extracted from room temperature Hall-effect measurements.
Contact parameters extracted from the IV and CV-characteristics at RT and from their temperature dependence.
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