Contents I. Introduction
Germanium (Ge) is regarded as one of the best next generation semiconductor materials for complementary metal oxide semiconductor beyond the era of Silicon (Si) technology and photodetectors (PDs) for optical communication circuit, because of its high-carrier mobility and excellent light absorption property. However, strong Fermi-level pinning phenomenon near the valence band edge, which therefore results in low-hole barrier height , is plaguing the successful integration of Ge metal oxide semiconductor field effect transistors with Schottky source/drain junctions [1] and Ge metal semiconductor metal PDs [2]. Therefore, depinning process is essential to obtain high value and subsequently low-reverse (leakage) current in Schottky junction diode fabricated on intrinsic (slightly p-type [3]) Ge. Till now, two reported causes of pinning phenomenon are: 1) surface states such as dangling bond or vacancy defect [4] and 2) metal induced gap states [5] affected by electron wave function tailing into Ge. Recently, in the aspect of resolving the pinning problem, surface passivation method using sulfur or fluorine treatment [6], [7] and a thin insulator insertion method using , , , , or SiN [8]–[12] have been proposed to reduce the interfacial and metal induced gap states. However, the insertion of a thin insulating layer between metal and semiconductor can lead to current reduction by increasing the tunneling resistance.
