Experimental Determination of Velocity-Field Characteristic of Holes in GaN

This study presents a photo-assistedmethod to measure the drift velocity of carriers in semiconductors, and successfully used to determine the drift velocity of holes in GaN. A p-i-n diode with a buried p-type layer was designed and fabricated on a free-standing GaN substrate. By reverse-biasing the p-i-n diode and illuminating the cathode layer using an ultraviolet light simultaneously, photo-generated holes were injected into the depletion region and acceleratedby the electric field to reach the saturation velocity. The drift velocity (v(d))-electric field (E) characteristic can be obtained from the photocurrent induced by photo-generated holes. The measured hole drift velocity can be written as v(d)= mu LFE /[1+( mu LFE / v sat)(beta)](1/beta), where mu(LF) = 17 cm(2)/Vs is the low-field hole mobility, v sat = 6.63x10(6)cm/s is the saturation velocity, beta = 1.75 is the fitting parameter. The method presented in this study is a unique way of determining the saturation drift velocity of holes in GaN.