Transient photocurrent induced in gallium nitride by two-photon absorption

We have studied the subband gap induced, transient photocurrent in an epitaxial GaN film immersed in an electrolyte solution. For photon energies near the midgap position, one- and two-photon (TP) contributoins were observed in the photocurrent. The one-photon term exhibited a sublinear intensity dependence and was attributed to carrier generation from traps in the gap. The TP current was negligible for energies below E(gap/2). Above this energy, the dispersion was consistent with previous calculations of the TP absorption coefficient [beta(omega)] in direct gap semiconductors. A relationship between the TP photocurrent and beta(omega) determined a value for the latter of similar to 1.5 cm/GW at photon energies above E(gap/2). (C) 1996 American Institute of Physics.