Thermal stability of Te-hyperdoped Si: Atomic-scale correlation of the structural, electrical and optical properties

TL;DR

This study investigates the thermal stability of Te-hyperdoped silicon, revealing stability up to 400°C and detailing dopant migration and property degradation at higher temperatures, informing device fabrication processes.

Contribution

It provides atomic-scale insights into the structural, electrical, and optical changes in Te-hyperdoped Si during thermal annealing, a novel analysis for this material system.

Findings

Te-hyperdoped Si stable up to 400°C with improved properties

Dopant migration occurs above 400°C, forming inactive clusters

Structural, electrical, optical properties degrade at high annealing temperatures

Abstract

Si hyperdoped with chalcogens (S, Se, Te) is well-known to possess unique properties such as an insulator-to-metal transition and a room-temperature sub-bandgap absorption. These properties are expected to be sensitive to a post-synthesis thermal annealing, since hyperdoped Si is a thermodynamically metastable material. Thermal stability of the as-fabricated hyperdoped Si is of great importance for the device fabrication process involving temperature-dependent steps like ohmic contact formation. Here, we report on the thermal stability of the as-fabricated Te-hyperdoped Si subjected to isochronal furnace anneals from 250 {\deg}C to 1200 {\deg}C. We demonstrate that Te-hyperdoped Si exhibits thermal stability up to 400 {\deg}C with a duration of 10 minutes that even helps to further improve the crystalline quality, the electrical activation of Te dopants and the room-temperature sub-band gap absorption. At higher temperatures, however, Te atoms are found to move out from the substitutional sites with a migration energy of EM = 2.1+/-0.1 eV forming inactive clusters and precipitates that impair the structural, electrical and optical properties. These results provide further insight into the underlying physical state transformation of Te dopants in a metastable compositional regime caused by post-synthesis thermal annealing as well as pave the way for the fabrication of advanced hyperdoped Si-based devices.