Probing the Atomic Arrangement of Sub-Surface Dopants in a Silicon Quantum Device Platform

TL;DR

This study uses X-ray photoelectron diffraction to precisely determine the atomic arrangement of phosphorus dopants in silicon delta-layers, confirming their substitutional nature and resolving longstanding debates about their structure.

Contribution

It demonstrates the effectiveness of XPD in analyzing sub-surface dopant structures and provides definitive structural insights into Si:P delta-layers for quantum device applications.

Findings

Dopants primarily substitute Si atoms from the host material.

No evidence of P-P dimerization inhibiting free carriers.

XPD effectively characterizes sub-surface dopant arrangements.

Abstract

High-density structures of sub-surface phosphorus dopants in silicon continue to garner interest as a silicon-based quantum computer platform, however, a much-needed confirmation of their dopant arrangement has been lacking. In this work, we take advantage of the chemical specificity of X-ray photoelectron diffraction to obtain the precise structural configuration of P dopants in sub-surface Si:P $\delta$-layers. The growth of $\delta$-layer systems with different levels of doping is carefully studied and verified using X-ray photoelectron spectroscopy and low-energy electron diffraction. Subsequent XPD measurements reveal that in all cases, the dopants primarily substitute with Si atoms from the host material. Furthermore, no signs of free carrier-inhibiting P$-$P dimerization can be observed. Our observations not only settle a nearly decade-long debate about the dopant arrangement but also demonstrate that XPD is well suited to study sub-surface dopant structures. This work thus provides valuable input for an updated understanding of the behavior of Si:P $\delta$-layers and the modeling of their derived quantum devices.