Wet Chemical Functionalization of III−V Semiconductor Surfaces: Alkylation of Gallium Phosphide Using a Grignard Reaction Sequence

Abstract

Single-crystalline gallium phosphide (GaP) surfaces have been functionalized with alkyl groups via a sequential Cl-activation, Grignard reaction process. X-ray photoelectron (XP) spectra of freshly etched GaP(111)A surfaces demonstrated reproducible signals for surficial Cl after treatment with PCl(5) in chlorobenzene. The measured Cl content consistently corresponded to approximately a monolayer of coverage on GaP(111)A. In contrast, GaP(111)B surfaces treated with the same PCl(5) solution under the same conditions exhibited macroscale roughening and yielded XP spectra that showed irreproducible Cl surface content often below the limit of detection of the spectrometer. The Cl-activated GaP(111)A surfaces were reactive toward alkyl Grignard reagents. Sessile contact angle measurements between water and GaP(111)A after various levels of treatment showed that GaP(111)A surfaces became significantly more hydrophobic following reaction with either CH(3)MgCl or C(18)H(37)MgCl. GaP(111)A surfaces reacted with C(18)H(37)MgCl demonstrated wetting properties consistent with surfaces modified with a dense layer of long alkyl chains. High-resolution C 1s XP spectra indicated that the carbonaceous species at GaP(111)A surfaces treated with Grignard reagents could not be ascribed solely to adventitious carbon. A shoulder in the C 1s XP spectra occurred at slightly lower binding energies for these samples, commensurate with the formation of Ga-C bonds. High-resolution P 2p XP spectra taken at various times during prolonged direct exposure to ambient laboratory air indicated that the resistance of GaP(111)A to surface oxidation was greatly enhanced after surface modification with alkyl groups. GaP(111)A samples that had been functionalized with C(18)H(37)- groups exhibited less than 0.1 nm of surface oxide after 7 weeks of continuous exposure to ambient air. GaP(111)A surfaces terminated with C(18)H(37)- groups were also used as platforms in Schottky heterojunctions with Hg. In comparison to freshly etched GaP(111)A, the alkyl-terminated GaP(111)A samples yielded current-voltage responses that were in accord with metal-insulator-semiconductor devices and indicated that this reaction strategy could be used to alter rates of heterogeneous charge transfer controllably. The wet chemical surface functionalization strategy described herein does not involve thiol/sulfide chemistry or gas-phase pretreatments and represents a new synthetic methodology for controlling the interfacial properties of GaP and related Ga-based III-V semiconductors.

Quantitative Analysis of the Functionalization of Gallium Phosphide With Organic Azides

“…Before the GaP wafers were exposed to the azide reactants, the cleaned GaP wafers were subject to water contact angle in order to identify that the wafers were indeed clean and ready for functionalization. A clean GaP surface revealed a water contact angle of about 16°, which is consistent with previous reports (Flores‐Perez et al ., ; Mukherjee et al ., ). After functionalization with AAP and 4AB, the contact angle increased to about 33 ± 5° and 53 ± 5°, respectively (Table ).…”

Amorphous TiO 2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation

“…(32) n-GaP samples were prepared from n-GaP wafers that had a sulfur dopant density of ~ 5 × 10 17 cm -3 . Small (~ 0.3 cm 2 ) pieces were cut from the wafer using a scribe, and the pieces were then etched in 18.…”

Wet Chemical Functionalization of GaP(111)B through a Williamson Ether-Type Reaction

“…In this context, the lack of order mirrors that seen for GaP(111)A surfaces modified with straight alkyl chains through reaction with Grignard reagents. 21,33 However, at the same nominal surface coverages, the surface layers produced here appeared to be less effective at eliminating further oxidation of the underlying GaP substrate. 21 This discrepancy suggests a difference in the stability of the surface bond occurring at GaP(111)B surfaces modified by the Williamson ether approach or GaP(111)A surfaces modified by Grignard reagents (i.e., P−O−C vs Ga−C, respectively).…”