Interplay of native point defects with ZnO Schottky barriers and doping

Abstract

A combination of depth-resolved electronic and structural techniques reveals that native point defects can play a major role in ZnO Schottky barrier formation and charged carrier doping. Previous work ignored these lattice defects at metal-ZnO interfaces due to relatively low point defect densities in the bulk. At higher densities, however, they may account for the wide range of Schottky barrier results in the literature. Similarly, efforts to control doping type and density usually treat native defects as passive, compensating donors or acceptors. Recent advances provide a deeper understanding of the interplay between native point defects and electronic properties at ZnO surfaces, interfaces, and epitaxial films. Key to ZnO Schottky barrier formation is a massive redistribution of native point defects near its surfaces and interfaces. It is now possible to measure the energies, densities, and in many cases the type of point defects below the semiconductor-free surface and its metal interface with nanoscale precision. Depth-resolved cathodoluminescence spectroscopy of deep level emissions calibrated with electrical techniques show that native point defects can (1) increase by orders of magnitude in densities within tens of nanometers of the semiconductor surface, (2) alter free carrier concentrations and band profiles within the surface space charge region, (3) dominate Schottky barrier formation for metal contacts to ZnO, and (4) play an active role in semiconductor doping. The authors address these issues by clearly identifying transition energies of leading native point defects and defect complexes in ZnO and the effects of different annealing methods on their spatial distributions on a nanoscale. These results reveal the interplay between ZnO electronic defects, dopants, polarity, and surface nanostructure, highlighting new ways to control ZnO Schottky barriers and doping.

Energy-Band Alignment of BiVO4 from Photoelectron Spectroscopy of Solid-State Interfaces

“…31,75 However, even in the case of unreactive interfaces, such as those between two oxides used in the present study, bulk or surface defects may also result in a substantial variation of band alignment. 56,[76][77][78] As a consequence, one may expect a substantial dependence of band alignment on preparation conditions. For instance, different concentrations of oxygen vacancies in ZnO and metallic precipitates in Cu2O result in a variation of band alignment by more than 1 eV at the interface between these materials.…”

The physics and chemistry of the Schottky barrier height

“…347 As oxygen vacancies are common for oxide insulators and semiconductors, the management of oxygen concentration of oxide material is an important part of the control of its junction characteristics. [408][409][410] The use of a thin layer of epitaxial elemental semiconductor for the modification of compound semiconductor SBH 216,320,322,323,335,405,[411][412][413][414] was found to already exert its full effect with only $2ML in ICL thickness. This demonstrated adjustability in the SBH was originally discussed in terms of the properties of separate M-I and I-S interfaces and the band bending across the ICL layer 411,415 but was shown by ab initio calculations to be in quantitative agreement with the charge distribution resulted from interface bonds, 104,106,217 i.e., the ICL should be included inside the ISR.…”

Impact of Mg content on native point defects in MgxZn1−xO (0 ≤ x ≤ 0.56)

“…These native point defects can be electrically charged and can contribute to free carrier densities. [14][15][16][17] acceptors to partially compensate degenerate carrier densities in Ga-doped ZnO. 18 Similarly, defect complexes associated with V O can be associated with increased n-type doping in ZnO.…”