Structural and electrical characterisation of PtS from H2S-converted Pt

Abstract

A manufacturing-compatible 300 mm chamber reactor for atomic layer deposition or chemical vapour deposition, and pre-fitted with H2/H2S gases that can be uniformly delivered to the wafer surface, is employed to thermally convert Pt to PtS in a H2/H2S gaseous atmosphere for 7 hours at a chamber temperature of 550 °C. Prior to conversion, platinum layers 5 nm thick are uniformly deposited by electron beam evaporation onto ∼30 nm of amorphous aluminium sesquioxide deposited by atomic layer deposition on, (a) p-type silicon, and (b) c-plane sapphire. Structural characterisation is performed by high-resolution cross-sectional transmission-electron microscopy, scanning-electron microscopy and Raman spectroscopy, confirming the formation of continuous films of polycrystalline platinum monosulfide (PtS) with a ∼15 nm thickness. Electrical characterisation is performed by 4-point resistivity and Hall-effect transport measurements on van der Pauw structures of PtS on aluminium sesquioxide on c-plane sapphire, and by back-gate junctionless MOSFET device measurements for PtS on aluminium sesquioxide on p-type silicon, showing that PtS behaves as a semiconductor with a mobility of ∼16 cm2/V.s and with an n-type carrier concentration of ∼1.2 × 1015 cm−3. Advanced commercial-grade Sentaurus simulations, alongside density-functional theory calculations, agree well with the experimental observations and suggest a large bandgap of ∼1.58 eV may be possible that could lead to a low off-current and a high Ion/Ioff ratio, suggesting that PtS may be an advanced material candidate for future device integration with CMOS and for 3D integration applications in Beyond-CMOS and More-than-Moore technologies.