Photovoltaic effect on the n-GaAs surface irradiated with low-energy Ar⁺ ions

A photovoltaic effect was observed under exposure to 810-nm laser light on the atomically clean surface of an n-GaAs wafer etched with Ar⁺ ions: open-circuit voltage in current–voltage (J–V) light characteristics was as high as 47 mV. The effect is due to the formation of a p–n structure under Ar⁺ ion bombardment in the near-surface bulk layer (~ 7 nm thick) via the conversion of the conductivity type of the near-surface layer from n to p. The effect of the conductivity type conversion under pure mechanical ion action manifested itself in that the Fermi level approached the valence band top, which was detected by high-resolution photoelectron spectroscopy with the use of a synchrotron radiation. The formation of the p–n junction in the structure was confirmed by dark J–V characteristics, which show a diode effect at voltages in the range (0–0.6) eV with a direct-to-reverse current ratio as large as 10³. The results obtained show that the near-surface bulk properties of n-GaAs treated by the most widely employed surface cleaning procedure via etching with a beam of Ar⁺ ions differ dramatically from the pristine deep bulk.