Gold Schottky-barrier diodes ͑SBDs͒ were fabricated on vapor-phase-grown single-crystal ZnO. Deep-level transient spectroscopy, using these SBDs, revealed the presence of four electron traps, the major two having levels at 0.12 eV and 0.57 below the conduction band. Comparison with temperature-dependent Hall measurements suggests that the 0.12 eV level has a temperature activated capture cross section with a capture barrier of about 0.06 eV and that it may significantly contribute to the free-carrier density. Based on the concentrations of defects other than this shallow donor, we conclude that the quality of the vapor-phase-grown ZnO studied here supercedes that of other single-crystal ZnO reported up to now. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1452781͔During the past few decades, ZnO has been used in many, diverse products. Its applications, among others, include phosphors, piezoelectric transducers, varistors, alcohol synthesis catalysis, and gas sensing. In a recent review, however, where the properties of ZnO are summarized, 1 it was pointed out that ZnO can be used for several other, more advanced, electro-optical applications. Based on the fact that ZnO has a direct bandgap of 3.4 eV, it is expected to fulfill a similar role as GaN in optoelectronics, i.e., play an important role in realizing blue and ultraviolet light-emitting diodes and lasers, as well as daylight-blind UV detectors. Similar to that of GaN, its large band gap renders ZnO suitable for the fabrication of high-temperature, high-power devices with application, among others, in space where typical operating temperatures exceed 200°C. High-quality single-crystal ZnO can be successfully grown in bulk. 2 A very important consequence of this is that owing to the relatively close match in lattice constants, single-crystal ZnO may be used as a substrate to grow epitaxial GaN that is well oriented with respect to the substrate and that has a reduced defect density. 3 Further practical advantages of ZnO include amenability to conventional wet chemistry etching, which is compatible with Si technology 4 ͑unlike the case for GaN͒.An important issue in ZnO technology is establishing a technology for the fabrication of high-quality Schottkybarrier diodes ͑SBDs͒. SBDs are of key importance to probe defects in semiconductors by junction spectroscopic characterization techniques, such as deep-level transient spectroscopy ͑DLTS͒ ͑Ref. 5͒ and admittance spectroscopy ͑AS͒. 6 They are also important structures for metal-semiconductor field-effect transistors ͑MESFETs͒ and detectors. A limited amount of research regarding Schottky contacts to ZnO was carried out in the 1960s, where among other things the barrier height of some metal contacts to vacuum-cleaved ZnO was reported. 7 However, up to now, no systematic studies of surface characterization as a function of cleaning method have been performed; i.e., the influence of different cleaning methods on the surface quality of ZnO and the quality of Schottky contacts to ZnO have not been compared...

We have investigated the electrical properties of Cu Schottky contacts (SCs) on ( 201)-oriented b-Ga 2 O 3 thin films, which have been grown by pulsed laser deposition (PLD). The I-V characteristics of two different sample structures exhibit rectification ratios at AE2 V up to 7 orders of magnitude. The dominant current transport mechanism is thermionic emission. By fitting the I-V characteristics, we obtained the ideality factor n and the effective barrier height F eff B at temperatures between 50 and 320 K. Considering a Gaussian barrier height distribution, we determined a mean barrier height of 1.32 eV. The contacts are stable at high temperatures up to at least 550 K. At this temperature a homogeneous barrier height of 1.32 eV is found, consistent with the determined mean barrier height. The ideality factor for this temperature is 1.03 and barrier inhomogeneities do not influence current transport, making the contact close to ideal.Schematic band diagram of a Cu/b-Ga 2 O 3 Schottky contact at a temperature of 550 K. The inset shows a photographic image of the sample.

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We have investigated by deep level transient spectroscopy the hole and electron trap defects introduced in n-type Ge during electron beam deposition (EBD) of Pd Schottky contacts. We have also compared the properties of these defects with those introduced in the same material during high-energy electron irradiation. Our results show that EBD introduces several electron and hole traps at and near the surface of Ge. The main defect introduced during EBD has electronic properties similar to those of the V–Sb complex, or E center, introduced during high-energy particle irradiation of Ge. This defect has two levels E0.38 and H0.30 that correspond to its (−−,−) and (−,0) charge states.

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H-SiC samples of doping density 7.1 × 10 15 cm -3 has been investigated over the temperature range 40-300 K. Currentvoltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6 × 10 14 electrons-cm -2 . For both devices, the I-V characteristics were well described by thermionic emission (TE) in the temperature range 120 -300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8 × 10 15 to 6.8 × 10 15 cm -3 after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 Acm −2 K −2 for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.