Bulk Gallium Arsenide Research Articles

Carbon, oxygen and silicon impurities in gallium arsenide

The concentrations of carbon, oxygen and silicon, together with boron, aluminium, sulphur and potassium, in various samples of bulk gallium arsenide have been determined by spark source mass spectrometry (SSMS) calibrated by independent chemical methods. Hall effect measurements and localised vibrational mode (LVM) infrared absorption measurements have been made on the same samples. It is inferred that the carbon atoms which show LVM absorption are located on arsenic lattice sites and act as acceptors. Calibrations for the LVM lines for CAS, SiGa, AlGa and BGa have been obtained. All samples examined contained a very low concentration of oxygen in the range (1-4)*1015 cm-3. Carbon concentrations of up to 1017 cm-3 were measured in deliberately doped material, while other crystals contained levels of 5*1015 cm-3 or lower.

Use of the ion microanalyzer for the characterization of bulk and epitaxial silicon and gallium arsenide

The ion microanalyzer permits a localized mass spectrometric analysis, i.e. the qualitative and quantitative analysis of the impurities contained in a small selected volume. This procedure makes possible the analysis of very thin epitaxial layers (for example silicon and gallium arsenide). As regards qualitative analysis, the apparatus is designed for the selection of ions. After the recording and analysis of the ion spectrum, a large number of the impurities present in the sample are determined qualitatively. Quantitative analysis can be performed with the equipment, but this requires the analysis of a homogeneous standard sample previously dosed by spark-source mass spectrometry. The quantitative analysis of bulk and epitaxial silicon and gallium arsenide is described and the limits of detection of the principal impurities are given. It is also shown how the possibility of localized analysis was exploited. A correlation was established between the existing impurities and the chemically revealed crystal imperfections. A comparative analysis of the distribution of the impurities in the epitaxial layers was also carried out. The periodic analysis of epitaxial layers makes it possible to follow the deterioration by contamination, if any, under the epitaxial conditions, and to improve the sample quality.

Properties of Gallium Arsenide Double-Injection Devices

The characteristics of identically fabricated double-injection devices made from oxygen-doped and chromium-doped bulk gallium arsenide are investigated. All these devices exhibit a current-controlled negative resistance once a threshold voltage is reached. The oxygen-doped devices and the thin chromium-doped devices (less than 3 mil) exhibit an abrupt current-controlled negative resistance followed by filamentary current conduction; this behavior is caused by double-injection transit-time effects. The thick chromium-doped devices (greater than 3 mil) exhibit a gradual, current-controlled negative resistance unaccompanied by filament formation; this behavior is due to excessive power dissipation resulting from high threshold voltages. The characteristics of the double-injection oxygen-doped devices show that a current saturation occurs in the prebreakdown region under certain conditions. The characteristics of the chromium-doped devices exhibit no such current saturation, only superlinear behavior. It is established that the oxygen devices have a threshold voltage for breakdown which is proportional to device length squared and that the chromium devices generally follow a similar law. Other evidence supporting the trapping barrier postulated by Lampert is also given. Filamentary conduction in the postbreakdown region is investigated by direct recording of the recombination radiation on infrared film. It is established that impedance variations and secondary breakdowns observed on the voltage-current characteristic are caused by movement of the filament position between the two injecting contacts. Filament position instabilities under cyclic excitation are observed and these effects are linked to a localized increase in the trapping barrier caused by heating along the filament site. Photographs of the recombination radiation emanating from both contacts establish the two-carrier nature of the postbreakdown filamentary state.