Surfactant behavior and limited incorporation of Indium during in-situ doping of GeSn grown by MBE

TL;DR

This study investigates in-situ indium doping of GeSn grown by MBE, revealing surfactant effects, low incorporation levels, and defect formation, which limit its effectiveness for optoelectronic applications.

Contribution

It provides the first detailed analysis of indium as a p-type dopant in GeSn, highlighting its surfactant behavior and associated doping limitations during MBE growth.

Findings

In acts as a surfactant, forming mobile Sn-In droplets.

Maximum In incorporation is 2.8×10^18 cm^-3, much lower than previous reports.

In induces defect nucleation at low growth temperatures.

Abstract

GeSn is a promising group-IV semiconductor material for on-chip Si photonics devices and high-mobility transistors. These devices require the use of doped GeSn regions, achieved preferably in-situ during epitaxy. From the electronic valence point of view, p-type dopants of group-IV materials include B, Al, Ga and In. The latter element has never been investigated as p-type dopant in GeSn. In this work, we explore in-situ In p-type doping of GeSn grown by MBE. We demonstrate that In acts as a surfactant during epitaxial growth of GeSn:In, accumulating on surface and inducing segregation in the form of mobile Sn-In liquid droplets, strongly affecting the local composition of the material. In non-defective GeSn, we measure a maximal In incorporation of 2.8E18cm-3, which is two orders of magnitude lower than the values reported in the literature for in-situ p-type doping of GeSn. We further show that In induces the nucleation of defects at low growth temperatures, hindering out-of-equilibrium growth processes for maximization of dopant incorporation. This work provides insights on the limitations associated with in-situ In doping of GeSn, and discourages its utilization in GeSn-based optoelectronic devices.