TRANSIENT PHOTOCURRENT INDUCED IN GALLIUM NITRIDE BY 2-PHOTON ABSORPTION

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