Vacancy-related Levels Research Articles

Effects of hydrogen radical treatment on piezoresistance coefficients of germanium

We investigate the effects of hydrogen radical treatment on piezoresistance coefficients of germanium under uniaxial stress up to ±500 μ strain over the temperature range −30 °C to 25 °C. Hydrogen radicals are produced by hydrogen gas (99.99%, 2.7 kPa) on a hot tungsten catalyst (1800 °C). The gauge factor and majority carrier on non-dope germanium dramatically changed from n- to p-type after the hydrogen radical treatment. The results suggest that the piezoresistance coefficients of germanium are seriously affected by vacancy-related levels around the midgap, which behave as donors or acceptors depending on the Fermi level and are passivated by the hydrogen radicals.

Detection of oxygen vacancy defect states in oxide nanobelts by using thermally stimulated current spectroscopy

Photoconducting properties of individual single crystalline Sn3O4 nanobelts were investigated by performing transport measurements. The nanobelts were found to exhibit large responsivity under ultraviolet (UV) illumination: the electric current in one single nanobelt greatly increases by about three orders of magnitude. Such photoconductive behavior was ascribed to the photogeneration of electron–hole pairs and to surface effects such as the oxidation and photoreduction of oxygen molecules (trapping). These mechanisms were found to be drastically modulated by the presence of oxygen vacancies which generates additional energy states that provide free electrons for conduction in our samples. In fact, we report the use of the thermally stimulated current spectroscopy as a powerful tool to study the presence of additional energy levels on Sn3O4 nanobelts as an approach to apply this technique in any high-resistivity nanomaterial. The experimental data provided two vacancy-related levels in 0.01 and 0.2 eV. On the basis of the transport measurements, a qualitative model to explain the response of these samples to UV light is proposed.

Low-temperature irradiation-induced defects in germanium:In situanalysis

The electronic properties of defects resulting from electron irradiation of germanium at low temperatures have been investigated. The recent success in preparing ${n}^{+}p$ junctions on germanium has opened a new opportunity to address fundamental questions regarding point defects and their related energy levels by allowing an access to the lower half of the band gap. In this work we apply various space-charge capacitance-transient spectroscopy techniques connected on line with the electron-beam facility. In $n$-type germanium we identify a level at about 0.14 eV below the conduction band whose properties resemble in many respects those of a defect assigned previously to the close vacancy-interstitial or Frenkel pair. This pair seems to annihilate over a small barrier at about 70 K, and its stability is particularly sensitive to the irradiation temperature and energy. We also observe two coupled levels at 0.08 and 0.24 eV below the conduction band stable up to 160 K. Recent independent theoretical work has predicted the existence of the single and double donor of the germanium interstitial with energy levels matching exactly these two values. Given these identifications hold, they mark a major difference with silicon where both the Frenkel pair and self-interstitial have never been caught. In $p$-type germanium, two levels were found. The shallower one, located at about 0.14 eV above the valence band, is tentatively assigned to the vacancy. It exhibits a field-driven instability at about 80 K making its analysis quite difficult. The application of a reverse bias, required by the space-charge spectroscopy, leads to a strong drift process sweeping this defect out of the observation area without necessarily provoking its annealing. Unlike silicon, in which the vacancy has four charge states, only one vacancy-related level seems to exist in germanium and this level is very likely a double acceptor. Finally, a very peculiar observation is made on a hole midgap trap, which, in many respects, behaves as the boron interstitial in silicon. This has led us to suggest that it may stem from the gallium interstitial, a natural dopant of our germanium materials, whose presence would be the fingerprint of the Watkins replacement mechanism in germanium.

Electronic states induced by a Ga vacancy in the GaAs1?xPx alloy

Self-consistent one-electron state calculations are carried out, for the first time, for a gallium vacancy in the GaAs1−xPx alloy. The cluster model, within the framework of the multiple-scattering Xα theory, is used to calculate several charge states of the vacancy. Suitable clusters have been considered in order to simulate the phosporous concentration x in the alloy and how the nearest-neghbors configurations affect the vacancy-related levels. It is found that the defect introduces a deep energy level into the band gap which follows the host-valence band edge as x varies. The same trend in donor and acceptor levels is observed, with a very small Mott–Hubbard potential energy. © 1993 John Wiley & Sons, Inc.