Quantification of discrete oxide and sulfur layers on sulfur‐passivated InAs by XPS

Abstract

The initial quality and stability in air of InAs(001) surfaces passivated by a weakly-basic solution of thioacetamide (CH 3 CSNH 2 ) is examined by XPS. The S-passivated InAs(001) surface can be modeled as a sulfur-indium-arsenic 'layer-cake' structure, such that characterization requires quantification of both arsenic oxide and sulfur layers that are at most a few monolayers thick. This thickness range complicates the quantitative analysis because neither standard submonolayer nor thick-film models are applicable. Therefore, we develop a discrete-layer model and validate it with angle-resolved XPS data and electron attenuation length (EAL) calculations. We then apply this model to empirically quantify the arsenic oxide and sulfur coverage on the basis of the corresponding XPS intensity ratios.

Surface passivation of InAs(001) with thioacetamide

“…9 For XPS data, peak binding energy ͑BE͒ and full width at half maximum ͑FWHM͒ are reported with 0.1 eV precision. 9 A home-built LPS setup 10 We find that the TAM passivation of InAs is remarkably efficient ͑Fig. 1͒.…”

“…The attenuation lengths for XPS photoelectrons in InAs are 0.691 nm for As 2p 3/2 and 3.11 nm for As 3d, thus the As 2p photoelectrons originate almost exclusively in the top few atomic layers. 9 S-passivated InAs͑001͒ ͑InAs-S͒ can be modeled as a stack of alternating In and As crystal planes passivated by a layer of chemisorbed S atoms. 4,9 This S / In/ As "layer-cake" structure is almost exclusively terminated by an In layer with chemisorbed S, which ensures minimal exposure of the topmost As layer to the environment.…”

“…9 S-passivated InAs͑001͒ ͑InAs-S͒ can be modeled as a stack of alternating In and As crystal planes passivated by a layer of chemisorbed S atoms. 4,9 This S / In/ As "layer-cake" structure is almost exclusively terminated by an In layer with chemisorbed S, which ensures minimal exposure of the topmost As layer to the environment. 4,9 Some oxidation of the top In layer will be unavoidable in ambient because of imperfections in the S-passivation layer.…”

“…4,9 This S / In/ As "layer-cake" structure is almost exclusively terminated by an In layer with chemisorbed S, which ensures minimal exposure of the topmost As layer to the environment. 4,9 Some oxidation of the top In layer will be unavoidable in ambient because of imperfections in the S-passivation layer. The small difference between the chemical shifts for In-O x and In-S makes it difficult to distinguish these In 3d components by XPS.…”

“…Fitting and quantitative analysis of the In 3d data are described in detail elsewhere. 9 Oxidation of As requires breaching the top two layers of the S / In/ As layer cake. In combination with the surface sensitivity of As 2p photoelectrons, this requirement makes the As-O x / As-In intensity ratio a reliable quantitative measure of surface reoxidation after passivation ͓Fig.…”