Monolithic Metal-Semiconductor-Metal Heterostructures Enabling Next-Generation Germanium Nanodevices.

Lukas Wind,Alois Lugstein,Xavier Maeder,Walter M Weber,Johann Michler,Masiar Sistani,Darius Pohl,Zehao Song,Bernd Rellinghaus

doi:10.1021/acsami.1c00502

Abstract

Low-dimensional Ge is perceived as a promising building block for emerging optoelectronic devices. Here, we present a wafer-scale platform technology enabling monolithic Al-Ge-Al nanostructures fabricated by a thermally induced Al-Ge exchange reaction. Transmission electron microscopy confirmed the purity and crystallinity of the formed Al segments with an abrupt interface to the remaining Ge segment. In good agreement with the theoretical value of bulk Al-Ge Schottky junctions, a barrier height of 200 ± 20 meV was determined. Photoluminescence and μ-Raman measurements proved the optical quality of the Ge channel embedded in the monolithic Al-Ge-Al heterostructure. Together with the wafer-scale accessibility, the proposed fabrication scheme may give rise to the development of key components of a broad spectrum of emerging Ge-based devices requiring monolithic metal-semiconductor–metal heterostructures with high-quality interfaces.

Highlights

The down-scaling of integrated circuits enabled a significant reduction of the power consumption and costs of modern microelectronic devices
We present a wafer-scale approach to achieve monolithic Al-Ge-Al heterostructures with abrupt metalsemiconductor junctions via a thermally induced Al-Ge exchange reaction
Based on extensive transmission electron microscopy (TEM) investigations on the AlGe exchange for vapor−liquid solid[29] grown Ge nanowires, we propose that Al propagation is governed by Ge diffusion via surface channels on the Al to the extended contact pads.[25]

Summary

Introduction

The down-scaling of integrated circuits enabled a significant reduction of the power consumption and costs of modern microelectronic devices. Arising repercussions of short-channel effects[1] promoted the integration of new materials, processes, and device architectures for emerging device concepts.[2,3] In this context, low-dimensional Ge structures such as nanomembranes[4,5] and nanowires[6,7] have received significant attention due to their superior electrical[8,9,2] and optical[10−12] properties. Due to the ability to host superconducting pairing correlations,[13−15] Ge gained increasing attention for encoding, processing, or transmitting quantum information.[14,16,17] In this respect, highly transparent superconducting Al contacts[18] are a crucial prerequisite for Josephson field-effect transistors integratable in gate-tunable superconducting qubits.[19] Further, the combination of the swave superconductor Al and Ge with a strong spin-orbit coupling of holes could be an attractive candidate to study Majorana zero modes.[14,15]

Methods

Results

Conclusion