Wet Chemical Functionalization of III–V Semiconductor Surfaces: Alkylation of Gallium Arsenide and Gallium Nitride by a Grignard Reaction Sequence

Abstract

Crystalline gallium arsenide (GaAs) (111)A and gallium nitride (GaN) (0001) surfaces have been functionalized with alkyl groups via a sequential wet chemical chlorine activation, Grignard reaction process. For GaAs(111)A, etching in HCl in diethyl ether effected both oxide removal and surface-bound Cl. X-ray photoelectron (XP) spectra demonstrated selective surface chlorination after exposure to 2 M HCl in diethyl ether for freshly etched GaAs(111)A but not GaAs(111)B surfaces. GaN(0001) surfaces exposed to PCl(5) in chlorobenzene showed reproducible XP spectroscopic evidence for Cl-termination. The Cl-activated GaAs(111)A and GaN(0001) surfaces were both reactive toward alkyl Grignard reagents, with pronounced decreases in detectable Cl signal as measured by XP spectroscopy. Sessile contact angle measurements between water and GaAs(111)A interfaces after various levels of treatment showed that GaAs(111)A surfaces became significantly more hydrophobic following reaction with C(n)H(2n-1)MgCl (n = 1, 2, 4, 8, 14, 18). High-resolution As 3d XP spectra taken at various times during prolonged direct exposure to ambient lab air indicated that the resistance of GaAs(111)A to surface oxidation was greatly enhanced after reaction with Grignard reagents. GaAs(111)A surfaces terminated with C(18)H(37) groups were also used in Schottky heterojunctions with Hg. These heterojunctions exhibited better stability over repeated cycling than heterojunctions based on GaAs(111)A modified with C(18)H(37)S groups. Raman spectra were separately collected that suggested electronic passivation by surficial Ga-C bonds at GaAs(111)A. Specifically, GaAs(111)A surfaces reacted with alkyl Grignard reagents exhibited Raman signatures comparable to those of samples treated with 10% Na(2)S in tert-butanol. For GaN(0001), high-resolution C 1s spectra exhibited the characteristic low binding energy shoulder demonstrative of surface Ga-C bonds following reaction with CH(3)MgCl. In addition, 4-fluorophenyl groups were attached and detected after reaction with C(6)H(4)FMgBr, further confirming the susceptibility of Cl-terminated GaN(0001) to surface alkylation. However, the measured hydrophobicities of alkyl-terminated GaAs(111)A and GaN(0001) were markedly distinct, indicating differences in the resultant surface layers. The results presented here, in conjunction with previous studies on GaP, show that atop Ga atoms at these crystallographically related surfaces can be deliberately functionalized and protected through Ga-C surface bonds that do not involve thiol/sulfide chemistry or gas-phase pretreatments.

Wet-Chemical Approaches for Atomic Layer Etching of Semiconductors: Surface Chemistry, Oxide Removal and Reoxidation of InAs (100)

“…18,19 For GaAs (111) the importance of Cl was also shown. 20,21 The strong effect of the anion on the etching behavior formed the basis of a dissolution model we developed. A schematic overview of the chemical etching mechanism for InAs in HCl/H 2 O 2 solution is given in Figure 2.…”

“…Prior to each experiment, the O 3 /H 2 O treated wafer was immersed for 60 minutes in 2 M HCl solution resulting in a (predominantly) Cl-terminated surface (see references. [21][22][23][24][25] The air-grown oxide was dissolved in 2 M HCl solution and the composition of the etchant was analyzed by ICP-MS. Figure 5a shows the measured In and As concentration as function of air exposure time. Both elemental concentrations gradually increase with increasing time.…”

In situ functionalization of gallium nitride powder with a porphyrin dye

“…Of these semiconducting materials, gallium nitride (GaN), a III-V material with a band gap of 3.4 eV, is of significant interest. 1 The surface modification of GaN has been used to develop field effect transistors with a myriad of surface treatments, such as recognition peptides, 2 attached thiols, 3 and alkyl groups, 4 nucleic acids binders, such as olefins, 5 1-alkenes, 6 atomic layer deposition thin films, 7 and alkylphosphonic acids 8 for unique properties. The chemisorption of multiple molecules (haloanilines, 9 aniline, 10 pyrroline, 11 water, 12 and fluorine 13 ) on GaN surfaces has traditionally been studied within controlled environments.…”

Optimized Process and Tool Design for GaN Chemical Mechanical Planarization

“…12,13 Since the pure chemical dissolution rate of GaN is negligible, the mechanical removal provided by the submicron size abrasive particles was noted to be very critical for GaN removal after a chemically modified layer is formed on the surface. [12][13][14][15] The preliminary investigations held by using silica based slurries and KOH or NaOH based pH adjustment have shown improved polishing rates as well as surface quality post material removal. A removal rate of 17 nm/h (2.83 Å/min) was reached with 0.1 nm of average surface roughness (Ra) after 40 hours of polishing.…”

“…The removal mechanism on the N-side GaN is also very well described as formation of nitrogen terminated layer with one negatively charged dangling bond on each nitrogen atom, adsorption of hydroxide ions, formation of oxides and dissolution and removal of the oxides. 14,15 Again by using silica-based slurry, the material removal rates were reported to vary from 400 to 1100 nm/h (66.7 to 183.3 Å/min) and the surface roughness values within 0.4-1.1 nm range (RMS-root mean square) were reached.…”