Insulator-to-Metal Transition in Selenium-Hyperdoped Silicon: Observation and Origin

TL;DR

This study combines computational and experimental methods to elucidate the microscopic origin of insulator-to-metal transition and sub-band gap absorption in selenium-hyperdoped silicon, revealing defect-to-conduction band transitions and a Mott transition.

Contribution

It provides a detailed microscopic explanation for hyperdoped silicon's properties, highlighting defect-to-band transitions and the impurity-driven Mott transition as key mechanisms.

Findings

Sub-band gap absorption is due to defect-to-conduction band transitions.

The insulator-to-metal transition occurs at a specific defect concentration.

Quantum Monte Carlo confirms the transition is a Mott transition.

Abstract

Hyperdoping has emerged as a promising method for designing semiconductors with unique optical and electronic properties, although such properties currently lack a clear microscopic explanation. Combining computational and experimental evidence, we probe the origin of sub-band gap optical absorption and metallicity in Se-hyperdoped Si. We show that sub-band gap absorption arises from direct defect-to-conduction band transitions rather than free carrier absorption. Density functional theory predicts the Se-induced insulator-to-metal transition arises from merging of defect and conduction bands, at a concentration in excellent agreement with experiment. Quantum Monte Carlo calculations confirm the critical concentration, demonstrate that correlation is important to describing the transition accurately, and suggest that it is a classic impurity-driven Mott transition.