The transient photocurrent flowing over a wide undoped AlGaAs barrier
has been investigated as a function of bias voltage, voltage polarity,
laser intensity and sample temperature. Excitation was by pulses of l
ength 100 ps from a Nd:YAG laser. The radiation, which uniformly illum
inated the top surface of the mesa, could produce excess carrier densi
ties of the order of 1 X 10(19) cm-3. The time constant of the decay f
or zero bias was 4 ns at 100 K. It was independent of laser intensity,
which suggests that the lifetime was determined by radiative recombin
ation in the contact regions. A trap-limited hole mobility of 2 cm2 V-
1 s-1 was deduced from the low-field data.