S. Abdalla^1,, F. Marzouki¹, S. Al-ameer¹, S. Turkestani¹

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.

GaN diode, contact resistance, ideality factor, transport mechanism