M. J. Legodi

Electrical characterization of 1.8 MeV proton-bombarded ZnO

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation.

Electrical Characterization of Vapor-Phase-Grown Single-Crystal ZnO

Gold Schottky-barrier diodes (SBDs) 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.

The influence of high energy proton bombardment on the electrical and defect properties of single-crystal ZnO

We report on the electrical and defect characterization of Au Schottky diodes formed on single-crystal ZnO, before and after irradiating with high-energy (1.8 MeV) protons. Prior to bombardment we observed that several electron traps (E1-E4), with energies between 0.10 and 0.57 eV below the conduction band, are present in the ZnO. High-energy proton bombardment introduces two electron traps (Ep1 and Ep2), with extremely low introduction rates (η) of 2.4 and 1.9 cm-1, respectively. Schottky barrier properties such as the reverse leakage current deteriorated from 1×10-9 A for an unirradiated diode to 1×10-6 A after bombarding it with a dose of 4.2×1014 cm-2 protons. Compared to GaN we found that ZnO is remarkably resistant to high-energy proton bombardment.

Effects of hydrogen, oxygen, and argon annealing on the electrical properties of ZnO and ZnO devices studied by current-voltage, deep level transient spectroscopy, and Laplace DLTS

Effects of annealing ZnO in hydrogen, oxygen, and argon have been investigated using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS) measurements. Current-voltage (IV) measurements indicate a decrease in zero–bias barrier height for all the annealed samples. Conventional DLTS measurements reveal the presence of three prominent peaks in the un-annealed and annealed samples. A new peak with an activation enthalpy of 0.60 eV has been observed in the H2 annealed samples, while an estimated energy level of 0.67 eV has been observed in Ar annealed samples. O2 annealing does not introduce new peaks but causes a decrease in the concentration of the E3 peak and an increase in concentration of the E1 peak. The concentrations of all the intrinsic defects have decreased after H2 and Ar annealing; with Ar annealing giving peaks with the lowest concentrations. The E2 peak anneals out after annealing ZnO in Ar and H2 at 300 °C. From the annealing behaviour of E3, we have attributed to transition metal ...

Characterization of electron-irradiated n-GaN

Using deep level transient spectroscopy, we have investigated the electron trap defects introduced in n-GaN grown using the epitaxial lateral overgrowth technique during high energy electron irradiation from a 90Sr radionuclide source. The results indicate that the major electron-irradiation-induced defect labeled ER3 is not a single defect level but is made up of at least three defect levels (ER3b–ER3d). One of these defects, ER3d, has an activation energy and introduction rate of 0.22 eV and 0.43 cm−1, respectively. The total introduction rate of the three defects (ER3b–ER3d) is approximately 1.0 cm−1.

A comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

very low reverse currents of the order of 10 � 10 A at a reverse voltage of 1.0 V whereas the e-beam deposited contacts have reverse currents of the order of 10 � 6 A at 1.0 V. Average ideality factors have been determined as (1.43 60.01) and (1.66 60.02) for the resistively evaporated contacts and e-beam deposited contacts, respectively. The IV barrier heights have been calculated as (0.721 60.002) eV and (0.624 60.005) eV for the resistively evaporated and e-beam deposited contacts, respectively. Conventional DLTS measurements reveal the presence of three prominent defects in both the resistive and e-beam contacts. Two extra peaks with energy levels of 0.60 and 0.81 eV below the conduction band minimum have been observed in the e-beam deposited contacts. These have been explained as contributing to the generation recombination current that dominates at low voltages and high leakage currents. Based on the reverse current at 1.0 V, the degree of rectification, the dominant current transport mechanism and the observed defects, we conclude that the resistive evaporation technique yields better quality Schottky contacts for use in solar cells and ultraviolet detectors compared to the e-beam deposition technique. The 0.60 eV has been identified as possibly related to the unoccupied level for the doubly charged oxygen vacancy, Vo 2þ . V C 2011 American Institute of Physics. [doi:10.1063/1.3658027]

Deep levels introduced in n-GaN grown by the ELOG technique by high-energy electron irradiation

Abstract We have used deep level transient spectroscopy (DLTS) to investigate the electron trap defects introduced in n-GaN grown, using the epitaxial lateral overgrowth technique during high-energy electron irradiation from a 90Sr radionuclide source. The results indicate that, apart from the major defect with an energy level at 0.20 eV below the conduction band (supposed to be related to the VN), at least four other defects with energy levels centered about 0.90±0.15 eV, are introduced. From modeling, ignoring temperature dependent capture cross-section effects we have determined their activation energies, and temperature independent capture cross sections, commonly known as the DLTS signature.

Laplace current deep level transient spectroscopy measurements of defect states in methylammonium lead bromide single crystals

The Israel Ministry of Science’s Tashtiot program.and the NRF Nanotechnology Flagship Program (Project No. 88021).

The fine structure of electron irradiation induced EL2-like defects in n-GaAs

The authors gratefully acknowledge the financial support of the South African National Research Foundation (NRF) and the University of Pretoria.

Electrical characterisation of epitaxially grown n-GaN bombarded with high- and low-energy protons

Abstract Using deep-level transient spectroscopy (DLTS), we have found that 1 MeV proton bombardment introduces the ER3, nitrogen vacancy related defect, at a rate of 290±50 cm −1 . Further, using capacitance–voltage (C–V) measurements, we have found that 1 MeV protons remove free carriers at a rate of 3880±380 cm −1 . However, when bombarding GaN with 0.5 keV protons, we did not observe the ER3 defect. We propose that 0.5 keV protons indeed introduce the ER3 defect, but that it is passivated by hydrogen.