Atomic-layer doping of SiGe heterostructures for atomic-precision donor devices

TL;DR

This paper demonstrates atomic-layer phosphorus doping of SiGe heterostructures compatible with atomic-precision fabrication, revealing electron localization primarily in the donor layer through transport measurements and modeling.

Contribution

It introduces a process for post-growth atomic-layer doping of SiGe heterostructures suitable for atomic-precision fabrication, with detailed characterization and modeling of electron localization.

Findings

Doped heterostructures exhibit high electron density and mobility similar to pure Si and Ge.

Electrons are mainly localized in the donor layer, not in a buried Si well.

The process preserves substrate structure and elastic state for atomic-precision applications.

Abstract

As a first step to porting scanning tunneling microscopy methods of atomic-precision fabrication to a strained-Si/SiGe platform, we demonstrate post-growth P atomic-layer doping of SiGe heterostructures. To preserve the substrate structure and elastic state, we use a T $\leq 800^\circ$C process to prepare clean Si$_{0.86}$Ge$_{0.14}$ surfaces suitable for atomic-precision fabrication. P-saturated atomic-layer doping is incorporated and capped with epitaxial Si under a thermal budget compatible with atomic-precision fabrication. Hall measurements at T$=0.3$ K show that the doped heterostructure has R$_{\square}=570\pm30$ $\Omega$, yielding an electron density $n_{e}=2.1\pm0.1\times10^{14}$cm$^{-2}$ and mobility $\mu_e=52\pm3$ cm$^{2}$ V$^{-1}$ s$^{-1}$, similar to saturated atomic-layer doping in pure Si and Ge. The magnitude of $\mu_e$ and the complete absence of Shubnikov-de Haas oscillations in magnetotransport measurements indicate that electrons are overwhelmingly localized in the donor layer, and not within a nearby buried Si well. This conclusion is supported by self-consistent Schr\"odinger-Poisson calculations that predict electron occupation primarily in the donor layer.