The Si/GaAs(110) heterojunction discontinuity: Amorphous versus crystalline overlayers

Abstract

We have studied both the electrical and structural properties of the Si/GaAs(110) interface in an attempt to understand the factors affecting the valence-band discontinuity, ΔEv, and to gain insight into the fundamental properties of the amorphous silicon overlayers. In order to differentiate between effects due to intrinsic material properties and those due to extrinsic defects, we grew the interfaces at three different temperatures and performed postgrowth anneals in ultrahigh vacuum. Such growths resulted in overlayers with varied crystalline perfection. In situ ultraviolet and x-ray photoemission spectroscopies, low-energy electron diffraction, and surface extended x-ray absorption fine-structure measurements were obtained for both amorphous and crystalline overlayers. We found a valence-band offset of 0.23±0.1 eV for both amorphous and crystalline Si on GaAs provided that the amorphous Si had either been annealed to or grown at sufficiently high temperatures, i.e., 375 and 300 °C, respectively. For the 20 °C grown unannealed Si, the valence-band maximum was diffuse and shifted to higher kinetic energy with respect to the GaAs substrate core levels resulting in a larger apparent offset of 0.55 eV. These effects were most probably due to dangling bond states in the Si overlayer.