Radiation damage and substitutional chemical impurity effects in single-crystal germanium bombarded with 40-keV B+, Al+, Ga+, Ge+, P+, As+, and Sb+ ions

Abstract

Isochronal anneal studies have been made on n- and p-type germanium bombarded with germanium and several substitutional impurities, using the four-point and thermoelectric probes as means of indicating changes in sheet resistivity and majority carrier type. Electrical properties of diodes made from type converted samples were also determined. All bombardments were performed at 40 keV in a 24-in.-radius electromagnetic isotope separator at room temperature. These studies revealed the following. (1) Heavy-particle bombardment of germanium introduces acceptor states regardless of the identity of the bombarding species. (2) Annealing curves for n-type germanium indicate a two-stage process; details of the annealing process are dependent on the ion species used and the crystal orientation bombarded. (3) There is a crystallographic and mass dependence on the amount of change in sheet resistivity produced in n-type germanium. (4) Type conversion temperatures in p-type germanium were observed to occur at 450–475 °C for phosphorus, ~500 °C for arsenic, and slightly greater than 500 °C for antimony, suggesting that the ease of moving a particular species into an active lattice position is related to its atomic size. (5) Voltage–current and capacitance measurements indicate that large-area diodes of relatively good properties and reproducibility can be made by ion implantation in germanium.