On the Richardson constant of intimate metal-GaAs Schottky barriers

Careful measurements have been made of the temperature coefficient of the barrier height ( alpha ) and the Richardson constant (A**) for Schottky diodes consisting of Au and Cu contacts on GaAs. The metals were deposited at a pressure of approximately 10^-10 Torr so that there is no possibility of an oxide film between metal and semiconductor. The values obtained for alpha were (-2.3+or-0.3)*10^-4 eV K^-1 and (-3.2+or-0.3)*10^-4 eV K^-1 for Au and Cu, respectively, the corresponding values of A** being 1.5*10⁴ A m^-2 K^-2 and 16*10⁴ A m^-2 K^-2. The values for Al/GaAs diodes obtained previously were (-3.8+or-0.3)*10^-4 eV K^-1 and 0.41*10⁴ A m^-2 K^-2. The variation of alpha between metals implies that the interface states which determine the barrier height depend on the metal, and the substantial difference between the values of A** suggest that the band structure of the metal plays a role in determining the reflection coefficient for electron at the interface.