S. A. Goodman

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.

Electrical characterization of two deep electron traps introduced in epitaxially grown n-GaN during He-ion irradiation

Epitaxial n-GaN was irradiated with 5.4-MeV He ions. Capacitance–voltage (C–V) measurements showed that 5.4-MeV He ions remove free carriers at a rate of 6200±300 cm−1 in the first micron below the surface. Deep level transient spectroscopy (DLTS) revealed that, in addition to the radiation-induced defects previously detected by DLTS at 0.18–0.20 eV below the conduction band, He-ion irradiation introduced two additional prominent defects, ER4 (EC-0.78 eV) and ER5 (EC-0.95 eV) at rates of 1510±300 and 3030±500 cm−1, respectively. Capture cross-section measurements revealed that electron capture kinetics of ER5 is similar to that of a line defect.

PROTON BOMBARDMENT-INDUCED ELECTRON TRAPS IN EPITAXIALLY GROWN N-GAN

Using deep-level transient spectroscopy, we have studied the electrical properties of defects introduced in epitaxially grown n-GaN during 2-MeV proton bombardment. The main defects detected, ER2 and ER3, are introduced at rates of 400±150 and 600±100 cm−1, respectively, and have energy levels at 0.16±0.03 and 0.20±0.01 eV, respectively, below the conduction band. A less prominent defect, ER1, with an energy level at 0.13±0.01 eV below the conduction band, is introduced at a rate of 30±10 cm−1. The small capture cross section of ER3 [(8±4)×10−18 cm2] implies that it is in a neutral or negative state when above the Fermi level.

Radiation induced defects in MOVPE grown n-GaN

Abstract It is well known that exposure of semiconductor surfaces to energetic particles introduce both optically and electrically active defects. Hydrogen and He-ion implantation has been used in GaN-based microelectronic processes. He-ion implantation produced high resistivity GaN at a fluence that is compatible with photoresist masking techniques. Heavier ion implantation has the added advantage that the depth resolution of the incident ions can be ‘tuned’ for specific applications (lifetime tailoring, etc.). Using deep level transient spectroscopy the defects in as-grown n-GaN as well as those introduced during high energy proton, He-ion and electron bombardment are characterised. Prior to irradiation, four electron defects (EO1–EO3 and EO5) were observed in the as-grown GaN. Two defects ER1 and ER2, not previously observed after electron irradiation, were observed after high energy electron irradiation. He-ion, proton and electron irradiation introduced a defect ER3. Defects ER1 and ER2 were also observed after proton bombardment, whereas two deeper lying defects (ER4 and ER5) were observed after the He-ion bombardment. The electronic properties, introduction rates and the annealing kinetics of the particle induced and as-grown major defects are presented. The influence of defect removal on the Schottky barrier diode properties are also discussed.

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.

Sputter deposition-induced electron traps in epitaxially grown n-GaN

We have used deep level transient spectroscopy to study the electrical properties of defects introduced in epitaxial n-GaN during sputter deposition of Au Schottky contacts. Four defects, located 0.22±0.02, 0.30±0.01, 0.40±0.01, and 0.45±0.10 eV below the conduction band, were characterized. The first of these defects has similar electronic properties as a radiation induced defect in GaN, while the second appears to be the same as a defect in the as-grown material. The latter two defects have not previously been observed in as-grown or processed epitaxial GaN.

Electrical characterization of defects introduced in n-GaAs by alpha and beta irradiation from radionuclides

We investigated defect production in n-type GaAs with two different free-carrier densities (4×1014 and 1×1016/cm3) by using particles liberated from radionuclides. 90Sr and 241Am were employed as beta and alpha sources, respectively. The results obtained for electron irradiation showed that the same set of primary defects can be produced by beta irradiation from the Sr source as by electrons produced in an accelerator. Similarly, the defects produced by alpha irradiation from the Am source closely resemble those introduced by alpha irradiation in a Van de Graaff accelerator. It was found that the relative concentrations of the primary defects in electron-irradiated GaAs are different to those in alpha-particle irradiated GaAs. Further, for the first time, an alpha irradiation induced defect which seems to be related to the doping concentration was observed in the 1016/cm3 Si doped GaAs. It is concluded that the use of radionuclides is an inexpensive and convenient method to introduce and to study radiation induced defects in semiconductors.

The effect of alpha-particle and proton irradiation on the electrical and defect properties of n-GaAs

Radiation damage effects were studied in n-GaAs grown by organo-metallic vapour phase epitaxy (OMVPE) for a wide range of alpha-particle (2.0 MeV and 5.4 MeV) and proton (2.0 MeV) particle fluences, using an americium-241 (Am-241) radio-nuclide and a linear Van de Graaff accelerator as the particle sources. The samples were irradiated at 300 K, after fabricating palladium Schottky barrier diodes (SBDs) on the 1.2 × 1016 cm3 Si-doped epitaxial layers. The irradiation-induced defects are characterized using conventional deep level transient spectroscopy (DLTS). A correlation is made between the change in SBD characteristics and the quantity and type of defects introduced during irradiation. It is shown that the two parameters most susceptible to this irradiation are the reverse leakage current of the SBDs and the free carrier density of the epilayer. The introduction rate and the “signatures” of the alpha-particle and proton irradiation-induced defects are calculated and compared to those of similar defects introduced during electron irradiation.

Suppression of rare-earth implantation-induced damage in GaN

We have studied the damage induced by 80 keV Er implantation in epitaxial GaN/sapphire layers at room temperature and at 450°C. The dopant distribution and lattice damage were investigated using Rutherford backscattering, channeling spectrometry and X-ray diffraction, whereas photoluminescence was used to probe the optical response. Random implantation results in substantial damage accumulation, which is difficult to recover during subsequent annealing. To reduce the ion-induced damage, we applied channeled implantation, i.e. directing the Er-beam along the nitride c-axis. Using this implantation geometry, a drastic decrease in the induced damage is observed. Channeled implantation generally results in green luminescence lines at room temperature, whereas no Er-related luminescence is observed after random implantation.