Double exponential I-V characteristics and double Gaussian distribution of barrier heights in (Au/Ti)/Al2O3/n-GaAs (MIS)type Schottky barrier diodes in wide temperature range

In this study, current conduction mechanisms of the sample (Au/Ti)/Al2O3/n-GaAs were investigated in detail using current-voltage (I-V) measurements in the temperature range of 80-380 K. The semilogarithmic I-V plots reveal two distinct linear regions with different slopes between 0.07-0.30 and 0.30-0.69 V which are called as Region I (RI) and Region II (RII), respectively. The ideality factor (n) and zero-bias barrier height (Phi(bo)) were found to be strong functions of temperature and voltage. In both regions, as the temperature increases, Phi(bo) increases, whereas the value of n decreases. The high value of n at low temperatures is an evidence of deviation from thermionic emission, and it cannot be explained solely by tunneling mechanism, the existence of surface states and interfacial layer. Therefore, the Phi(bo) versus q/kT plots were drawn for two linear regions of lnI-V plots, and these plots also revealed two distinct linear regions with different slopes between two temperature regions of 80-170 and 200-380 K which are called as low-and high-temperature range (LTR and HTR), respectively. Such behavior of these plots confirmed the existence of double Gaussian distribution (DGD) in the samples which in turn has mean barrier heights Phi(bo) and standard deviations (sigma(s)). These values were obtained from the intercept and slope of these plots as 0.38 eV and 0.061 V for LTR and as 0.88 eV and 0.142 V for HTR (in RI), whereas they were obtained as 0.37 eV and 0.061 V for LTR and as 0.92 eV and 0.148 V for HTR (in RII), respectively. Thus, the modified ln(I-s/T-2) -q(2)sigma(2)(s) /2k(2)T(2) versus q/kT plots were drawn, and the values of ((Phi) over bar (bo)) and effective Richardson constant (A*) were extracted from the intercept and slope of these plots as 0.39 eV and 7.07 A/cm(2) K-2 for LTR and as 0.92 eV and 8.158 A/cm(2) K-2 for HTR (in RI), whereas they were extracted as 0.38 eV and 7.92 A/cm(2) K-2 for LTR and as 0.94 eV and 4.66 A/cm(2) K-2 for HTR (in RII), respectively. These values of A* for two regions are close to the theoretical value (8.16 A/cm(2) K-2) of n-type GaAs.