S. Abdalla, F. Marzouki, S. Al-ameer, S. Turkestani
International Journal of Physics. 2013, 1(2), 41-48DOI:
Abstract: The forward current–voltage (I–V) characteristics of n-GaN films on sapphire substrate are investigated over a temperature range of 80–300K, using two different types of metal/semiconductor contacts: Al/GaN and Au/GaN. Samples with Al metallic contacts show well defined ohmic behavior with linear forward and reverse I-V characteristics indicating no potential barrier. These measurements made at temperatures in the range 77K-300K show the influence of two donor levels: one is deep at 0.23ev, while the other is shallow at 0.013ev below the conduction band. These values have been confirmed by DSCL measurements and the density of electrons n0 is calculated as a function of temperature and found that n0 = 3.08x10^14cm-3 at 300K. Besides, the mobility of electrons µ has been calculated as a function of temperature and have been found that at 300K: µ = 175cm2/v.s. On the other hand, resistively deposited Au Schottky contacts on n-type GaN show net rectification behavior. In contrast to the published data, the I-V measurements revealed that these Au contacts exhibited bad rectification properties: relatively high reverse current and bad ideality factor (n = 11.5 at 80K). This discrepancy has been attributed to the presence of a series resistance with the Au/n-GaN Schottky diode. The potential drop across this resistance decreases n from 11.5 down to a logic value 1.2 at 80K. Index Terms—GaN diode; contact resistance; ideality factor; transport mechanism.