n-type conversion of SnS by isovalent ion substitution: Geometrical doping as a new doping route

TL;DR

This study demonstrates a novel geometrical doping method to convert SnS from p-type to n-type using isovalent Pb2+ substitution, supported by experimental and theoretical evidence, enabling new electronic applications for SnS.

Contribution

The paper introduces a new doping route called geometrical doping via isovalent ion substitution to achieve n-type SnS, overcoming limitations of conventional aliovalent doping.

Findings

Achieved n-type conduction in SnS with electron densities of 10^12 to 10^15 cm^-3.

Confirmed n-type behavior through photoemission spectroscopy and heterojunction measurements.

Density functional theory explains the role of geometrical size effects in facilitating n-type doping.

Abstract

Tin monosulfide (SnS) is a naturally p-type semiconductor with a layered crystal structure, but no reliable n-type SnS has been obtained by conventional aliovalent ion substitution. In this work, carrier polarity conversion to n-type was achieved by isovalent ion substitution for polycrystalline SnS thin films on glass substrates. Substituting Pb2+ for Sn2+ converted the majority carrier from hole to electron, and the free electron density ranged from 1012 to 1015 cm-3 with the largest electron mobility of 7.0 cm2/(Vs). The n-type conduction was confirmed further by the position of the Fermi level (EF) based on photoemission spectroscopy and electrical characteristics of pn heterojunctions. Density functional theory calculations reveal that the Pb substitution invokes a geometrical size effect that enlarges the interlayer distance and subsequently reduces the formation energies of Sn and Pb interstitials, which work as electron donors.