The surface of silicon-doped GaAs (100) grown by the vertical Bridgman method has been implanted with H+ ions at 30 keV for various doses from 10(14) to 10(17) cm(-2) and studied using photoacoustic and photoluminescence spectroscopy to understand the effects of hydrogen ion implantation on GaAs:Si. The results are compared with Raman measurements. All the measurements confirm the sign change of charge carriers at a dose of 10(15) cm(-2). (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.