Impact of Junction Depth and Abruptness on the Activation and the Leakage Current in Germanium n$^{+}$/p Junctions

TL;DR

This study investigates how junction depth and abruptness affect phosphorous activation and leakage currents in germanium n+/p junctions, revealing trade-offs between activation efficiency and leakage, and providing guidelines for high-performance device design.

Contribution

It presents experimental and simulation analysis of junction properties, highlighting the impact of abruptness on activation and leakage, and proposes a minimum Ge body thickness for leakage suppression.

Findings

Shallow, abrupt junctions have lower activation and higher leakage.

Deeper junctions improve activation but increase leakage.

A Ge body thickness below 5 nm reduces tunneling leakage to meet I_OFF standards.

Abstract

The phosphorous activation in Ge n$^{+}$/p junctions is compared in terms of junction depth, by using laser spike annealing at 860{\deg}C for 400$\mu$s. The reverse junction leakage is found to strongly depend on the abruptness of dopant profiles. A shallow and abrupt junction is shown to have lower phosphorous activation level, due to surface dose loss, and higher band-to-band tunneling (BTBT) leakage, when compared to the deep junction. Simulations were carried out to evaluate the lowest achievable OFF-state currents (I$_{OFF}$) for Ge double-gate FETs when using such an abrupt junction. Our results indicate that a Ge body thickness smaller than 5 nm is required to suppress the BTBT leakage and meet the requirement for the high performance devices defined by the International Technology Roadmap for Semiconductors (I$_{OFF}$ = 10$^{-7}$ A/$\mu$m).