Interface states of Ag/(110)GaAs Schottky diodes without and with interfacial layers

Abstract

GaAs(110) faces with different preparations—ultrahigh vacuum (UHV) cleaved, polished and etched, polished and sputtered—are prepared as Schottky diodes by the deposition of Ag. Diodes based on UHV-cleaved faces do show homogeneously distributed EL2 and EL5 states in deep level transient spectroscopy (DLTS). On polished and etched samples an additional interface state (IS) distribution with a density of 9×1011 eV−1 cm−2 at the DLTS maximum appears. These states can be caused by defects at the oxidic interfacial layer. Polishing and sputtering also evokes the IS distribution. The absence of a DLTS signal from metal-induced gap states (MIGS) which pin the Fermi level at 0.49 eV above the valence-band maximum is related to the absence of an interfacial layer in the UHV prepared Schottky diodes. The sputter process increases the electron density in a thin layer below the interface by an As excess. The corresponding smaller extent of the barrier causes an additional electron emission via tunneling processes from the IS distribution. Furthermore, a near-interface state, EL6 (VGa-VAs), shows up. Its concentration at the interface attains NEL6 =2.5×1016 cm−3 comparable to the shallow donor concentration.