J. W. Farmer

Charge transient spectroscopy

A new variation of the deep level transient spectroscopy technique is presented. In the new approach, the current transient is integrated, yielding a charge transient. A simple circuit for integrating the current is given and is analyzed. The charge transient technique is compared to previous capacitance transient and current transient techniques, and the advantages of the new method are discussed. The effects of diode leakage currents are also analyzed. Data are presented for defects in neutron irradiated Si.

Defect cascades produced by neutron irradiation in YBa2Cu3O7−δ

Abstract Defect cascades produced by fast neutron irradiation of YBa 2 Cu 3 O 7−δ single crystals were studied by transmission electron microscopy. The visible defects were found to have sizes between 1 and 5 nm. Defect densities were obtained as a function of neutron fluence between 2x10 21 and 8x10 21 m −2 ( E >0.1 MeV) and compared to damage calculations. The measured defect density scales linearly with fluence and amounts to 1x10 22 m −3 at a neutron fluence of 2x10 21 m −2 . The defect stability was studied at room temperature and through annealing to 400°C.

Defects in neutron irradiated SiC

Deep level transient spectroscopy and resistivity measurements have been used to characterize defects in as‐grown and neutron irradiated epitaxially grown 3C‐SiC on Si(100) substrates. The thick epilayers were free of defects; neutron irradiation induced an electron trap with an activation energy of 0.49 eV. The SiC‐Si interface has a large density of defects and dislocations. Most of the irradiation defects are confined to the lower two‐thirds of the band gap. Ninety percent of these defects can be removed by annealing at 350 °C.

High purity isotopically enriched 70Ge and 74Ge single crystals: Isotope separation, growth, and properties

[sup 70]Ge and [sup 74]Ge isotopes were successfully separated from natural Ge and zone purified. Several highly enriched, high purity [sup 70]Ge and [sup 74]Ge single crystals were grown by the vertical Bridgman method. The growth system was designed for reliable growth of low dislocation density, high purity Ge single crystals of very small weight ([similar to]4g). A [sup 70]Ge and a [sup 74]Ge crystal were selected for complete characterization. In spite of the large surface to volume ratio of these ingots, both [sup 70]Ge and [sup 74]Ge crystals contain low electrically active chemical net-impurity concentrations of [similar to]2[times]10[sup 12] cm[sup [minus]3], which is two orders of magnitude better than that of [sup 74]Ge crystals previously grown by two different groups.[sup 1,2] Isotopic enrichment of the [sup 70]Ge and the [sup 74]Ge crystals is 96.3% and 96.8%, respectively. The residual donors and acceptors present in both crystals were identified as phosphorus and copper, respectively. In addition less than 10[sup 11] cm[sup [minus]3] gallium, aluminum, and indium were found in the [sup 70]Ge crystal.

Neutron transmutation doping of isotopically engineered Ge

We report a novel approach for obtaining precise control of both p‐ and n‐type dopant concentrations in bulk Ge single crystals. High‐purity Ge single crystals of controlled 74Ge/70Ge isotope composition ratios were grown and subsequently doped by the neutron transmutation doping (NTD) technique. The resulting net‐impurity concentrations and the compensation ratios were precisely determined by the thermal neutron fluence and the [74Ge]/[70Ge] ratios of the starting Ge materials, respectively. Application of NTD to seven crystals with 0≤[74Ge]/[70Ge]≤4.34 lead to p‐type Ge:Ga,As with compensation ratios in the range 0–0.76. The ability to grow crystals with accurately controlled Ge isotope mixtures allows us to obtain ratios anywhere between 0 and 1 for both p‐ and n‐type doping.

Frequency‐scanned deep‐level transient spectroscopy

The output signal in a deep‐level transient spectroscopy experiment is a function of both the rate‐window settings and sample temperature. Usually, the rate window is held fixed and the temperature scanned to produce the deep‐level spectrum. We will demonstrate that a deep‐level spectrum can also be obtained by fixing the temperature and scanning the rate window.

Single scan deep‐level transient spectroscopy

A new single scan method for obtaining deep level trap parameters is presented. This method represents an improvement over previous single scan approaches because it does not involve numerical analysis and it uses data over the entire temperature range of the deep‐level transient spectroscopy peak. Data are presented for an isolated deep level, the E center. The usefulness of this new method is also demonstrated by an example of successful analysis of overlapping deep level signals. The new single scan method maintains the simplicity of the traditional method of data collection. However, the single temperature scan saves time and more important, is often more accurate than the traditional multitemperature scan technique.

Determination of oxygen in silicon by ratio of A center to E center

Oxygen concentration of silicon has been determined by the ratio of the A center to E center in gamma‐irradiated n‐type silicon. The concentrations of these defects were measured by the deep‐level transient spectroscopy technique. It has been found that the ratio of the A center to E center is simply proportional to that of oxygen to phosphorus content by a factor of 0.072. In addition to extending the range of sensitivity to oxygen to levels below that obtainable using infrared absorption, this new method permits easy determination of the distribution of oxygen.

Study of irradiation-induced defects in germanium

Radiation‐induced defects in germanium were studied using deep‐level transient spectroscopy and stress transient spectroscopy. Four electron traps have been identified: the planar four vacancy at Ec −0.09 eV, the divacancy at Ec −0.17 eV, the vacancy‐oxygen pair at Ec −0.27 eV, and the donor‐vacancy pair level at Ec −0.35 eV.

Systematic study of the superconducting and normal-state properties of neutron-irradiated MgB2

We have performed a systematic study of the evolution of the superconducting and normal state properties of neutron-irradiated