Molecular Self-Assembly at Bare Semiconductor Surfaces:  Investigation of the Chemical and Electronic Properties of the Alkanethiolate−GaAs(001) Interface

Abstract

High-resolution X-ray photoelectron spectroscopy (HRXPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and Raman scattering have been used to characterize the bonding and electronic properties of the interfaces formed by ambient-temperature, solution self-assembly of octadecanethiol and dodecanethiol under oxygen-free conditions on GaAs(001) surfaces. The combination of HRXPS and ToF-SIMS shows that both monolayers form direct S−[GaAs] attachment to the bare substrate with dominant As−S bonding and some fraction of Ga−S bonding, but the densely packed octadecanethiolate self-assembled monolayers (SAMs) are significantly more effective in protecting the interface from oxide regrowth compared to the less dense dodecanethiolate SAMs. Raman scattering measurements of the GaAs LO phonon modes indicate that the formation of these direct, oxide-free S−[GaAs] interfaces does not induce any significant changes in the GaAs surface electronic states, whereas control experiments with inorganic sulfide treatment does indicate a significant reduction in the surface traps, consistent with earlier reports. Overall these experiments show that the formation of direct alkane−S−[GaAs(001)] interfaces of high quality provides a method to passivate the GaAs surface against oxide regrowth but does not necessarily lead to changes in the surface electronic states.

Observation of surface enhanced IR absorption coefficient in alkanethiol based self-assembled monolayers on GaAs(001)

“…Long-chain alkanethiol selfassembled monolayers ͑SAMs͒ on GaAs͑001͒ have been studied in this context by a number of authors, both from the perspective of fundamental material science [1][2][3][4][5][6][7][8][9][10] and as a potential route to applications including surface passivation, 11 metal-molecule-semiconductor junctions, 12,13 the assembly of DNA hybridization probes, 14 and the immobilization of functional proteins such as avidin. 15 In these studies, Fourier transform infrared ͑FTIR͒ spectroscopy is frequently employed to investigate important SAM structural parameters such as molecular orientation 16 and the fraction of conformational defects.…”

Thiol passivation of MWIR type II superlattice photodetectors

“…Sulphur is chemically more reactive than oxygen so that replaces oxygen to form electrically stable surface sulfides. These reactions may be called interfacial self-cleaning reactions which are confirmed by XPS measurements [11,16]. The sulphur interaction with the InAs creates In x S y and As x S y (InAs + 2HS = In x' S y' +As x" S y" +H 2 ) and interaction with the GaSb creates Ga x S y and Sb x S y (GaSb + 2HS = Ga x' S y' + Sb x" S y" +H 2 ) on the surface.…”

“…It cleans the surface from conductive native oxides and satisfies dangling bonds [10][11][12]. Although thiol is mostly studied on GaAs [13][14][15][16] surfaces, some studies on InP [17], GaP [18], and InAs [11,12] and other III-V compounds have also been reported. McGuiness et al has shown that long chained octadecanethiol strongly reduces As and Ga oxides and prevents subsequent surface oxide re-growth [16] using X-ray photoelectron spectroscopy (XPS).…”

“…Although thiol is mostly studied on GaAs [13][14][15][16] surfaces, some studies on InP [17], GaP [18], and InAs [11,12] and other III-V compounds have also been reported. McGuiness et al has shown that long chained octadecanethiol strongly reduces As and Ga oxides and prevents subsequent surface oxide re-growth [16] using X-ray photoelectron spectroscopy (XPS). Knoben et al, showed that ODT can form a well ordered monolayer on InAs and reduce surface oxidation [11,12].…”

DNA Molecules on GaP (100) Surfaces: Spectroscopic Characterization and Biospecificity Assessment

“…[1,3,14] Recently, there has been an interest in extending such studies to III-V semiconductor substrates. [10,12] Gallium phosphide (GaP) is an attractive semiconductor material due to its usage in charge storage devices [23] and low-noise detection photodiodes. [19,24,25] This material offers promise for the fabrication of novel biosensors.…”