Epitaxial synthesis of unintentionally doped p-type SnO (001) via suboxide molecular beam epitaxy

TL;DR

This paper reports the successful epitaxial growth of phase-pure, unintentionally p-type SnO(001) thin films using suboxide molecular beam epitaxy with a mixed SnO2+Sn source, operating across a wide temperature range without additional oxygen, and explores their properties for electronic applications.

Contribution

It introduces a novel MBE growth method for metastable SnO films using a mixed SnO2+Sn source, overcoming previous temperature and growth window limitations.

Findings

SnO films are transparent and unintentionally p-type.

Hole concentrations range from 0.9 to 6.0x10^{18}cm^{-3}.

Mobility ranges from 2.0 to 5.5 cm^2/V·s.

Abstract

By employing a mixed SnO$_2$+Sn source, we demonstrate suboxide molecular beam epitaxy growth of phase-pure single crystalline metastable SnO(001) thin films at a growth rate of ~1.0nm/min without the need for additional oxygen. These films grow epitaxially across a wide substrate temperature range from 150 to 450{\deg}C. Hence, we present an alternative pathway to overcome the limitations of high Sn or SnO$_2$ cell temperatures and narrow growth windows encountered in previous MBE growth of metastable SnO. In-situ laser reflectometry and line-of-sight quadrupole mass spectrometry were used to investigate the rate of SnO desorption as a function of substrate temperature. While SnO ad-molecules desorption at Ts = 450{\deg}C was growth-rate limiting,the SnO films did not desorb at this temperature after growth in vacuum. The SnO (001) thin films are transparent and unintentionally p-type doped, with hole concentrations and mobilities in the range of 0.9 to 6.0x10$^{18}$cm$^{-3}$ and 2.0 to 5.5 cm$^2$/V.s, respectively. These p-type SnO films obtained at low temperatures are promising for back-end-of-line (BEOL) compatible applications and for integration with n-type oxides in p-n heterojunction and field-effect transistors