Ohmic contact formation on n-type Ge

Abstract

Severe Fermi level pinning at the interface between n-Ge and a metal, leads to the formation of a Schottky barrier, almost independent on the metal work function. Therefore it seems impossible to form metal Ohmic contacts on moderately, n-type doped Ge layers. For p-type Ge the Fermi level pinning works opposite: all metal contacts show Ohmic behavior. This fixed behavior can be altered by the introduction of a thin Ge 3 N 4 layer. Ge 3 N 4 seems effective in reducing Fermi level pinning and therefore allows the formation of Ohmic contacts on n-type Ge and a rectifying contact on p-type Ge.

The physics and chemistry of the Schottky barrier height

“…45, the insertion of a thin GeO x layer between Ge and common metals led to substantial increases in the n-type junction current and reductions in the p-type junction current (inset). 325 This decrease (increase) in the n-type (p-type) SBH for Ge has also been observed for different metals and for a variety of insulating materials inserted as the interlayer, including amorphous and crystalline Ge 3 N 4 , 326,327 Si 3 N 4 , 311 AlO x , 312,325 MgO, 328 TaN, 314 and organic molecules. 297 The nominal SBH obtained from MIS stack typically showed a much stronger dependence on the metal work function than without the insulating interlayer, as shown in Fig.…”

Ultrashallow Ohmic contacts for n-type Ge by Sb δ-doping

“…Several approaches have been explored to overcome this problem. [13][14][15] Very recently, Yamane et al demonstrated a reduction in the Fermi level pinning even for metal/Ge contacts by using an atomically controlled interface between metal and Ge. 16 In this study, we combine high-concentration ␦-doping techniques with the formation of atomically controlled metal/Ge contacts.…”

Current-Voltage Characteristics of Nanowires Formed at the Co-Ge99.99Ga0.01Interface

“…It is not enough to compare the work functions for Ge and metal in order to specify the type of the contact created between a Ge surface and a metal. The effect of the Fermi level pinning appearing in the interface between metal and n-type Ge causes the contact to be rectifying and rises the Schottky barrier the height of which is almost independent of the used metal work function [17,18]. On the other hand, due to the Fermi level pinning for p-type Ge, the contact of this semiconductor with metal show Ohmic behavior for all metals [17,18].…”