F.D. Auret

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.

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.

Influence of the electron beam evaporation rate of Pt and the semiconductor carrier density on the characteristics of Pt/n‐GaAs Schottky contacts

Schottky barrier diodes (SBDs) were fabricated on epitaxially grown n‐GaAs materials, with different free carrier densities, by electron beam (e‐beam) evaporation of Pt at various rates. The quality of the SBDs was evaluated by standard current‐voltage (I‐V) measurements, while the defects introduced during e‐beam evaporation were characterized by deep level transient spectroscopy (DLTS). The results showed that if the GaAs was shielded during Pt deposition from stray electrons originating at the e‐beam filament, high quality SBDs were formed. However, if the GaAs was not shielded during deposition, the quality of the diodes was poor and the degree to which their characteristics deviated from the ideal case increased as the total electron dose reaching the substrate increased (for slow evaporation rates) and as the free carrier density of the GaAs increased. DLTS revealed that several surface and subsurface defects were introduced during metallization without the electron shield and it is shown that these defects are responsible for the poor device quality. The nature of some of these defects depended on the free carrier density of the GaAs.

Electrical characterization of defects introduced during electron beam deposition of Pd schottky contacts on n-type Ge

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.

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.

Summary of Schottky barrier height data on epitaxially grown n- and p-GaAs

The Schottky barrier height values, as determined by the current‐voltage and capacitance ‐voltage techniques, of 43 metals which were fabricated by following the same cleaning procedure and using the same high-quality organometallic vapour phase epitaxially (OMVPE) grown (100) n-type GaAs material and 13 metals on molecular beam epitaxially grown (MBE) p-GaAs, are presented. Of all the metals involved in this study, Ga had the lowest mean Schottky barrier height of about 0.60 eV on n-GaAs and the highest on p-GaAs of 0.83 eV. Cu, Ag, Pt and Sb had the highest barrier heights of about 1 eV on n-GaAs. It was found that there exists no linear relationship between Schottky barrier height and metal work function as is suggested by the Schottky‐Mott theory, if all 43 metals are taken into account. Similar results were obtained if the metal work function was replaced by the Pauling or Miedema electronegativities. In contrast with this, if only a selected group of metals is chosen and more specifically those with the higher melting points which were deposited by means of an electron gun, an approximately linear tendency does exist between Schottky barrier height and metal work function. From this linear dependency, the density of states was determined to be about 6 〈 10 13 /eV per cm 2 and the average pinning position of the Fermi level as 0.55 eV below the conduction band.

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.

Lithium and electrical properties of ZnO

Hydrothermal grown n-type ZnO samples have been investigated by deep level transient spectroscopy (DLTS), thermal admittance spectroscopy (TAS), temperature dependent Hall effect (TDH) measurements, and secondary ion mass spectrometry (SIMS) after thermal treatments up to 1500 °C, in order to study the electrical properties of samples with different lithium content. The SIMS results showed that the most pronounced impurities were Li, Al, Si, Mg, Ni, and Fe with concentrations up to ∼5×1017 cm−3. The Li concentration was reduced from ∼1017 cm−3 in as-grown samples to ∼1015 cm−3 for samples treated at 1500 °C, while the concentration of all the other major impurities appeared stable. The results from DLTS and TAS displayed at least five different levels having energy positions of Ec−20 meV, Ec−55 meV, Ec−0.22 eV, Ec−0.30 eV, and Ec−0.57 eV (Ec denotes the conduction band edge), where the Ec−55 meV level is the dominant freeze out level for conduction electrons in samples treated at temperatures <1300 °C, wh...