Abstract:We have studied the formation of sulfide layers on the GaAs͑100͒ c(8ϫ2) gallium rich surface through thermal and photoinduced ͑193 nm͒ decomposition of H 2 S. H 2 S was adsorbed on the sample at 90-95 K. The sulfide layer desorbs as Ga 2 S beginning at 740 K. For thermal sulfide layer formation, it was found that more sulfur could be built up on the surface by repeated cycles of H 2 S exposure at low temperature followed by heating to 600 K. Several such cycles gave a sulfide layer saturating at about one mono… Show more
“…23,24 In addition, phosphorus hydrides (PH and PH 2 ) may decompose at high temperatures and the resulting H atoms may desorb from the surface in the form of molecular H 2 or react with neighboring HS on the In atom to cause a recombinative desorption of H 2 S (b). 34,35 The chemisorbed sulfur species may desorb at elevated temperatures. As shown in Figure 6, the In 4d intensity on the high binding energy side decreases with an increase of the sample temperature.…”
Section: Resultsmentioning
confidence: 99%
“…The gradual loss of P was thought to be replaced with S to form the InS compound of one monolayer. It was also demonstrated that hydrogen can preferentially etch phosphorus atoms from the InP surface to form an In-rich surface with the presence of In clusters. , In addition, phosphorus hydrides (PH and PH 2 ) may decompose at high temperatures and the resulting H atoms may desorb from the surface in the form of molecular H 2 or react with neighboring HS on the In atom to cause a recombinative desorption of H 2 S (b). , 4 Soft X-ray photoelectron spectra of S 2p, collected from the InP surface exposed to 3.0 L of H 2 S at 100 K followed by annealing the sample to the indicated temperatures. 5 Soft X-ray photoelectron spectra of P 2p from the InP(100) surface exposed to 3.0 L of H 2 S at 100 K followed by annealing the sample to the indicated temperatures.…”
The adsorption and thermal reaction of H 2 S on the InP(100) surface is studied by synchrotron radiation (SR) soft X-ray photoelectron spectroscopy. In addition to molecular adsorption, H 2 S decomposes to form the dissociative species of S, HS, and H on the surface at 100 K. The S atom of the sulfide species preferentially bonds to the In atom, and the H atom generated by the H 2 S dissociation bonds to the P atom. H 2 S molecules may physisorb on the surface in the form of an icelike multilayer/cluster at low temperatures, even at low coverages. The irradiation of SR white light can induce an alternative reaction of H 2 S with the InP surface to form a thicker sulfur layer than that obtained by thermal deposition. The resulting sulfur layer may provide chemical protection for the InP substrate from further reaction.
“…23,24 In addition, phosphorus hydrides (PH and PH 2 ) may decompose at high temperatures and the resulting H atoms may desorb from the surface in the form of molecular H 2 or react with neighboring HS on the In atom to cause a recombinative desorption of H 2 S (b). 34,35 The chemisorbed sulfur species may desorb at elevated temperatures. As shown in Figure 6, the In 4d intensity on the high binding energy side decreases with an increase of the sample temperature.…”
Section: Resultsmentioning
confidence: 99%
“…The gradual loss of P was thought to be replaced with S to form the InS compound of one monolayer. It was also demonstrated that hydrogen can preferentially etch phosphorus atoms from the InP surface to form an In-rich surface with the presence of In clusters. , In addition, phosphorus hydrides (PH and PH 2 ) may decompose at high temperatures and the resulting H atoms may desorb from the surface in the form of molecular H 2 or react with neighboring HS on the In atom to cause a recombinative desorption of H 2 S (b). , 4 Soft X-ray photoelectron spectra of S 2p, collected from the InP surface exposed to 3.0 L of H 2 S at 100 K followed by annealing the sample to the indicated temperatures. 5 Soft X-ray photoelectron spectra of P 2p from the InP(100) surface exposed to 3.0 L of H 2 S at 100 K followed by annealing the sample to the indicated temperatures.…”
The adsorption and thermal reaction of H 2 S on the InP(100) surface is studied by synchrotron radiation (SR) soft X-ray photoelectron spectroscopy. In addition to molecular adsorption, H 2 S decomposes to form the dissociative species of S, HS, and H on the surface at 100 K. The S atom of the sulfide species preferentially bonds to the In atom, and the H atom generated by the H 2 S dissociation bonds to the P atom. H 2 S molecules may physisorb on the surface in the form of an icelike multilayer/cluster at low temperatures, even at low coverages. The irradiation of SR white light can induce an alternative reaction of H 2 S with the InP surface to form a thicker sulfur layer than that obtained by thermal deposition. The resulting sulfur layer may provide chemical protection for the InP substrate from further reaction.
“…To get a rough estimate of the overlayer thickness we analyzed the overlayer/substrate intensities in XPS spectra, using the exponential attenuation of the substrate signal: , where d ol is the overlayer thickness, λ ol the corresponding electron mean free path, θ the electron take-off angle, relative to the plane of the surface, I sub ( d ol ) the substrate intensity in presence of the overlayer, and I sub (0) the substrate intensity when no overlayer is present. This analysis assumes that all of the material screens electrons equally, depending only on the overlayer thickness.…”
Control of the work function of GaAs single crystals, under
ambient conditions, was achieved by chemisorption
of a series of benzoic acid derivatives with varying dipole moments.
Quantitative Fourier transform infrared
spectroscopy shows that the benzoic acid derivatives bind as
carboxylates, via coordination to oxidized Ga
or As atoms, with a surface coverage of about one layer and a binding
constant of 2.1 104 M-1 for
benzoic
acid. Contact potential difference measurements reveal that
molecules affect the work function by changing
the electron affinity while band bending is not affected significantly.
The direction of the electron affinity
changes depends on the direction of the dipole moments, and the extent
of the change increases linearly with
the dipole's magnitude. Investigation of the surface composition
by X-ray photoelectron spectroscopy shows
that the etched surface, onto which the molecules adsorb, is covered by
an oxide layer. This may prevent the
molecules from affecting band bending.
“…However, with all these advantages, GaAs has a serious problem: it suffers from a surface effect known as Fermi-level pinning. Extensive work dealing with the passivation of GaAs surfaces has been carried out. − Sandroff et. al.…”
Section: Introductionmentioning
confidence: 99%
“…It was found that using H 2 S gives a treated surface that is more stable in air or water . Recently the passivation of the GaAs surface involving gas phase sulfur compounds has attracted considerable attention. , As part of our attempt to passivate GaAs by gas phase sulfur deposition, the photochemistry of adsorbed OCS on GaAs has been studied.…”
Adsorption of OCS on GaAs(100) has been investigated using
temperature-programmed desorption and
photoinduced desorption/dissociation spectroscopy. It was observed
that OCS molecularly adsorbs on
GaAs(100) and thermally desorbs at 160 K. Adsorbed OCS molecules
either dissociate into gaseous CO,
leaving S adsorbed on GaAs(100), or desorb as molecular OCS under
irradiation of λ = 300 ∼ 770 nm. The
photodissociation cross section is about 5.0 ×
10-19 cm2 at 300 nm, which is
about 2 orders of magnitude
higher than that for gaseous OCS at 250 nm and even 10 times greater
compared with that for OCS on
Ag(111) at 254 nm. It drops rapidly as the wavelength
increases and becomes undetectable at about 480 nm.
In addition, the photodesorption cross section was found to be
about 8.4 × 10-20 cm2 at 300 nm
with a
threshold at about 770 nm. We also observed that the
photodissociation cross section is strongly dependent
on the coverage of OCS on GaAs(100), changing from 2.0 ×
10-18 cm2 for 0.03 L OCS on
GaAs(100) at 320
nm to 3.6 × 10-19 cm2 for 3.3 L
OCS. A 2.4 eV red shift of threshold photon energy for
photodissociation
of OCS on GaAs(100) was observed in our experiment relative to
gaseous OCS. Our results support the
interaction of photogenerated carriers with adsorbed OCS in the
photochemical processes. The observed
difference in the threshold energies for photodissociation and
photodesorption is possibly attributable to the
different final states involved.
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