Dopant activation in Sn-doped Ga2O3 investigated by X-ray absorption spectroscopy

S C Siah,C U Segre,R E Brandt,L T Schelhas,M D Heinemann,D Chua,K Lim,T Buonassisi,J Wright,R Jaramillo,R G Gordon,M F Toney,J D Perkins

doi:10.1063/1.4938123

Abstract

Doping activity in both beta-phase (β-) and amorphous (a-) Sn-doped gallium oxide (Ga2O3:Sn) is investigated by X-ray absorption spectroscopy (XAS). A single crystal of β-Ga2O3:Sn grown using edge-defined film-fed growth at 1725 °C is compared with amorphous Ga2O3:Sn films deposited at low temperature (&lt;300 °C). Our XAS analyses indicate that activated Sn dopant atoms in conductive single crystal β-Ga2O3:Sn are present as Sn4+, preferentially substituting for Ga at the octahedral site, as predicted by theoretical calculations. In contrast, inactive Sn atoms in resistive a-Ga2O3:Sn are present in either +2 or +4 charge states depending on growth conditions. These observations suggest the importance of growing Ga2O3:Sn at high temperature to obtain a crystalline phase and controlling the oxidation state of Sn during growth to achieve dopant activation.

Highlights

Doping activity in both beta-phase (β-) and amorphous (a-) Sn-doped gallium oxide (Ga2O3:Sn) is investigated by X-ray absorption spectroscopy (XAS)
Ga2O3 can be doped with tin, achieving donor concentrations above 1019 cm-3 when grown in bulk-crystal form[3] and above 1018 cm-3 when deposited by molecular-beam epitaxy (MBE) in the 540 to 600°C range.[4]
Identifying a means to achieve higher Sn dopant activation in lowtemperature atomic-layer deposition (ALD)- or pulsed-laser deposition (PLD)- deposited films could increase the industrial relevance of Ga2O3:Sn for cost-sensitive applications including field-effect transistors,[4] solar cells,[5,6,7] gas sensors,[8] and lasers.[9]