Changes in silicon samples bombarded by 900–2300 eV hydrogen ions

Abstract

We have performed a series of statistically designed experiments to evaluate the changes which occur in silicon samples as a result of hydrogen ion bombardment. Single-crystal silicon and polycrystalline silicon, and also edge-defined film-fed growth (EFG) solar cell devices, were exposed to a hydrogen ion beam produced by a Kaufman ion source. The experimental parameters which were systematically varied include the maximum hydrogen ion energy (900, 1600 and 2300 eV), the energy spread of the ions in the beam, the ion current density (0.8, 1.4 and 2.0 mA cm −2), the total dose (1 × 10 18, 2 × 10 18 and 4 × 10 18 ions cm −2) and the bulk sample temperature during bombardment (200, 275 and 350 °C). We observed the changes in the short-circuit current, the open-circuit voltage, the photovoltaic conversion efficiency and the fill factor associated with the EFG devices, the change in the spectral reflectivity of the single-crystal silicon samples and the ratio of the numbers of SiH to SiH 2 groups present in the polycrystalline silicon samples. The results of our study indicate that the properties of hydrogen-ion-bombarded silicon change with both the maximum ion energy and the ion current density with a significant parametric interaction between the current density and the bulk sample temperature. The energy distribution of the ions present in the hydrogen ion beam affects the spectral reflectivity of single-crystal silicon. The changes associated with hydrogen ion bombardment are independent of dose for the conditions studied. The average absolute air mass 1 efficiency of EFG devices without intentionally applied antireflective coatings increased from 8.7% before exposure to 10.2% after exposure to the optimal conditions determined by this study.