W.E. Meyer

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 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.

Electrical characteristics of Ar-ion sputter induced defects in epitaxially grown n-GaAs

Epitaxially grown n‐type GaAs was sputtered by bombarding it with Ar ions at energies of between 0.5 and 5 keV at a dose of 1013 ions/cm2. The fabrication of Au Schottky barrier contacts followed directly after the sputtering. The electrical characteristics of the the sputter induced defects were studied using deep‐level transient spectroscopy (DLTS). Several defects with discrete defect levels ranging from 0.05–0.70 eV below the conduction band, as well as defects with continuously distributed energies in the conduction band, were introduced during sputtering. Concentration depth profiling revealed that whereas some defects are located very close to the interface, others were detected several microns below the interface. The depth of some of these deep lying defects increased with sputter voltage. A possible explanation of the reduction in EL2 DLTS signal previously observed after sputtering is shown to be the sputter induced barrier height lowering.

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 ...

A deep level transient spectroscopy characterization of defects induced in epitaxially grown n-Si by low-energy He-ion bombardment

Epitaxially grown n-Si was bombarded with low-energy (1 keV) He ions. Deep level transient spectroscopy revealed that this introduced four prominent defects with energy levels at 0.14, 0.20, 0.30, and 0.55 eV, respectively, below the conduction band. The electronic properties and annealing behavior of these defects are different to those of the main defects, namely, divacancies (V2) and vacancy-phosphorous centers, observed after 5.4 MeV He-ion bombardment of the same material. We propose that, except for the defect with an energy level at Ec−0.14 eV, the defects introduced by 1 keV He-ion bombardment of n-Si may be related to: (1) vacancy clusters larger than divacancies, or (2) incorporation of He and H into V2 or higher-order vacancy clusters.

Electronic and annealing properties of a metastable He-ion implantation induced defect in GaAs

Abstract We have investigated, using DLTS, the properties of electrically active defects introduced in undoped and Si-doped epitaxially grown n-GaAs implanted with He-ions. Particular attention was paid to the introduction kinetics of the metastable Eα3 defect. We have found that Eα3 is not introduced during implantation, as previously believed, but thereafter upon annealing above 285 K. Its introduction is governed by first order kinetics and we suggest that it is formed as the result of larger irradiation induced clusters disintegrating. The concentration of Eα3 and the temperature range in which its metastable transformations occur, imply that it may play an important role in reversibly altering the free carrier concentration of ion-implanted GaAs.

Electrical characteristics of neutron irradiation induced defects in n-GaAs

Abstract Palladium Schottky barrier diodes (SBDs) on epitaxially grown n-GaAs were irradiated with neutrons from a reactor and a p(66)/Be (40) clinical source. From current-voltage (I–V) and capacitance-voltage (C–V) measurements it was found that neutron irradiation caused generation-recombination currents and resulted in a reduction in the free carrier concentrations of the epitaxial layers. A linear relation was found between the irradiation fluence, the free carrier removal and the reverse leakage current of neutron irradiated SBDs. Deep level transient spectroscopy (DLTS) indicated that five electron traps, Enl-En5, were introduced during neutron irradiation. These defects are shown to be responsible for the degradation of neutron irradiated SBDs.