Bias dependence of Schottky barrier height in GaAs from internal photoemission and current-voltage characteristics

Abstract

Bias dependence of Schottky barrier height φB was directly measured using an internal photoemission effect in Au-n-GaAs Schottky barrier diodes under both the forward and reverse applied voltages. φB increased by about 0.015–0.016 eV as the forward bias increased from 0 to 0.3 V. This is probably due to an applied-voltage-induced change in electron population in the interface states. The results were compared with the bias dependence derived from dark forward current-voltage (I-V) characteristics. Both bias dependences were in good agreement, indicating that nonideal forward I-V characteristics (a deviation from the ideal thermionic emission theory) could be fully explained by the bias dependence of φB for diodes of a relatively good quality (an ideality factor, n=1.02–1.07). The effective Richardson constant A** was calculated to be about 1.3–1.4×105 A K−2 m−2 for the diodes of the lower n values using the value of the measured Schottky barrier height at zero bias. These values of A** were higher than the calculated value of about 8×104 A K−2 m−2 and that of 0.41±0.15×104 A K−2 m−2 reported by Missous and Rhoderick [J. Appl. Phys. 69, 7142 (1991)]. This is probably due to an enhancement of an electron tunneling through the high density interface states in our case. φB decreased by about 0.05–0.06 eV when the reverse voltage increased from 0 to 3.0 V. An image force lowering effect could not account for this large reverse bias dependence of the barrier height. The nonideal reverse I-V characteristics could not be interpreted solely by the bias dependence of φB. This discrepancy was attributed to other leakage current mechanisms.