Acceptor and compensating donor doping of single crystalline SnO (001) films grown by molecular beam epitaxy and its perspectives for optoelectronics and gas-sensing

TL;DR

This study explores doping strategies in single crystalline SnO films grown by molecular beam epitaxy, demonstrating how Ga and La dopants influence electrical properties and potential applications in optoelectronics and gas sensors.

Contribution

It provides new insights into acceptor and compensating donor doping of SnO films, including experimental growth, characterization, and ab-initio predictions of dopant behavior.

Findings

Ga acts as an acceptor increasing hole concentration

La acts as a compensating donor leading to semi-insulating films

Dopant solubility limits and secondary phase formation were identified

Abstract

(La and Ga)-doped tin monoxide (stannous oxide, tin (II) oxide, SnO) thin films were grown by plasma-assisted and suboxide molecular beam epitaxy with dopant concentrations ranging from $\approx5\times10^{18}$cm$^{-3}$ to $2\times10^{21}$cm$^{-3}$. In this concentration range, the incorporation of Ga into SnO was limited by the formation of secondary phases observed at $1.2\times10^{21}$cm$^{-3}$ Ga, while the incorporation of La showed a lower solubility limit. Transport measurements on the doped samples reveal that Ga acts as an acceptor and La as a compensating donor. While Ga doping led to an increase of the hole concentration from $1\times10^{18}$cm$^{-3}-1\times10^{19}$cm$^{-3}$ for unintentionally (UID) SnO up to $5\times10^{19}$cm$^{-3}$, La-concentrations well in excess of the UID acceptor concentration resulted in semi-insulating films without detectable $n$-type conductivity. Ab-initio calculations qualitatively agree with our dopant assignment of Ga and La, and further predict In$_\text{Sn}$ to act as an acceptor as well as Al$_\text{Sn}$ and B$_\text{Sn}$ as donor. These results show the possibilities of controlling the hole concentration in $p$-type SnO, which can be useful for a range of optoelectronic and gas-sensing applications.