Reduction of Schottky barrier height for n-type Ge contact by using Sn electrode

Abstract

We have investigated the electrical properties of the Sn/n-Ge contact and estimated its Schottky barrier height (SBH). We prepared metal/n-Ge Schottky diodes by Sn, Al, and Au deposition on Ge substrates at room temperature. The current density–voltage characteristics of Sn, Al, Au/n-Ge contacts were measured, and the SBHs of these interfaces were estimated to be 0.35, 0.55, and 0.59 eV, respectively. The SBH of Sn/n-Ge contacts increases for samples annealed at 150–220 °C. We have also investigated the crystalline structure of the Sn layer on Ge(001) by X-ray diffraction analysis and examined the relationship between the crystalline structure and the SBH of Sn/Ge contacts. We found that a Sn layer deposited on Ge(001) at room temperature exhibits a preferentially oriented structure. We also performed hard X-ray photoelectron spectroscopy measurement of these metal/n-Ge samples and estimated the energy band bending of Ge near these metal/n-Ge interfaces. We found a small band bending of Ge in the Sn/n-Ge contact, which has a small SBH, in contrast to Au and Al/n-Ge contacts showing large band bending. The small SBH of the Sn/n-Ge contact can be attributed to the small work function of Sn and corresponds well to the SBH expected from the Schottky limit. The Sn/n-Ge contact has the potential to alleviate the Fermi level pinning.