We report our results of experimental study of photoelectrical properties of GaAs p-n and 1-h junctions illuminated with pulsed CO2 laser light. The current-voltage and voltage-power characteristics are investigated. It is demonstrated that photoemission of hot carriers across the potential barrier and the crystal lattice heating are the dominant mechanisms in the photovoltage formation. The obtained results show that hot-carrier effects in inhomogeneous GaAs can be used to detect very short infrared laser pulses.