The effect of (NH4)2Sx passivation on the (311)A GaAs surface and its use in AlGaAs/GaAs heterostructure devices (original) (raw)
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Investigation of neutralized (NH[sub 4])[sub 2]S solution passivation of GaAs (100) surfaces
Applied Physics Letters, 1997
Synchrotron radiation photoelectron spectroscopy combined with scanning electron microscopy ͑SEM͒ and gravimetry has been used to study GaAs ͑100͒ surfaces treated with a neutralized ͑NH 4 ͒ 2 S solution. Compared to the conventional basic ͑NH 4 ͒ 2 S solution treatment, a thick Ga sulfide layer and strong Ga-S bond were formed on the GaAs surface after dipping GaAs wafers in a neutralized ͑NH 4 ͒ 2 S solution. Gravimetric data show that the etching rate of GaAs in the neutralized ͑NH 4 ͒ 2 S solution is about 15% slower than that in the conventional ͑NH 4 ͒ 2 S solution. From SEM observation, fewer etching pits with smaller sizes were found on the neutralized ͑NH 4 ͒ 2 S-treated GaAs surface. © 1997 American Institute of Physics. ͓S0003-6951͑97͒01247-3͔
2019
Sulfur interaction with GaAs can reduce the harmful effect of surface states on recombination attributes. Apart from surface passivation, study of sulfur bonding on GaAs is also important for developing novel molecular electronics and molecular spintronics devices, where a molecular channel can be connected to at least one GaAs surface via thiol functional group. Excess thiol functional groups that are not involved in making molecular device channels can serve as the passivants to quench surface states. However, the primary challenge lies in increasing the stability and effectiveness of the sulfur passivated GaAs. We have investigated the effect of single and double step surface passivation of n-GaAs(100) by using the sulfide and fluoride ions. Our single-step passivation involved the use of sulfide and fluoride ions individually. However, the two kinds of double-step passivations were performed by treating the n-GaAs surface. In the first approach GaAs surface was firstly treated w...
XPS study of surface chemistry of epiready GaAs(100) surface after (NH4)2Sx passivation
Vacuum, 2006
The results of systematic XPS studies of wet sulfide passivation capabilities to remove the native oxides and excess arsenic at the epiready GaAs(1 0 0) native surfaces are presented. Different procedures of dipping an epitaxy-ready sample (at room and elevated temperatures) in an ammonium polysulfide (NH 4) 2 S x solution combined with a UHV flash annealing were used. The surface chemistry after each processing step was investigated by the inspection of the XPS As3d and Ga3d spectra taken using an enhanced surface sensitivity mode. The analysis revealed that the procedure of sulfidation itself removes native oxides and that both AsS and GaS bondings are created, and when combined with subsequent UHV annealing, diminishes excess As efficiently. Moreover, the results are in agreement with our previous work on the surface Fermi level position of (NH 4) 2 S x-treated samples.
Sulphide passivation of GaAs: the role of the sulphur chemical activity
Semiconductor Science and Technology, 1998
The passivation of n-GaAs in different sulphur containing solutions in which sulphur chemical activity was varied, i.e. solutions of sodium and ammonium sulphides in water and alcohols, as well as a solution of sulphur monochloride in carbon tetrachloride, was studied by photoluminescence and Raman spectroscopy. The increase of the sulphur chemical activity in the passivating solution results in an increase of the photoluminescence intensity and in a decrease of the surface barrier of the passivated semiconductor.
Effects of Surface Passivation on Twin-Free GaAs Nanosheets
Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30-to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 Â 10 5 to 2.7 Â 10 4 cm/s with passivation.
Journal of Applied Physics, 2010
The interactions of oxygen atoms on the GaAs͑001͒-2͑2 ϫ 4͒ surface and the passivation of oxidized GaAs͑001͒-2͑2 ϫ 4͒ surface were studied by density functional theory. The results indicate that oxygen atoms adsorbed at back-bond sites satisfy the bond saturation conditions and do not induce surface gap states. However, due to the oxygen replacement of an As dimer atom at a trough site or row site, the As-As bond is broken, and gap states are produced leading to the Fermi level pinning because of unsaturated As dangling bonds. Atomic H, Cl, S, F, and the molecular species GaO were examined to passivate the unsaturated As dangling bond. The results show that H, Cl, F, and GaO can remove such gap states. It is also found that the interaction of S with the unsaturated As dangling bond does not remove the gap states, and new gap states are generated upon single S adsorption. A higher S coverage forms S-S dimer pairs which passivate two unsaturated As atoms, and removes the As-induced gap states.
Solvent effect on the properties of sulfur passivated GaAs
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
Photoluminescence and x‐ray photoelectron spectroscopy have been used to study the solvent effect on surface properties of GaAs passivated in different sulfide solutions. It has been found that sulfur passivation could be made more efficient by decreasing the solution dielectric constant through the use of various alcohols as solvents. Specifically, the band edge photoluminescence intensity is much higher, the total amount of oxides is lower, and sulfur coverage is higher compared with a GaAs surface treated in an aqueous sulfide solution. The role of the solvent in sulfur passivation is discussed. © 1996 American Vacuum Society
Passivation of GaAs Nanocrystals by Chemical Functionalization
Journal of the American Chemical Society, 2008
The effective use of nanocrystalline semiconductors requires control of the chemical and electrical properties of their surfaces. We describe herein a chemical functionalization procedure to passivate surface states on GaAs nanocrystals. Cl-terminated GaAs nanocrystals have been produced by anisotropic etching of oxide-covered GaAs nanocrystals with 6 M HCl(aq). The Cl-terminated GaAs nanocrystals were then functionalized by reaction with hydrazine or sodium hydrosulfide. X-ray photoelectron spectroscopic measurements revealed that the surfaces of the Cl-, hydrazine-, and sulfide-treated nanocrystals were As-rich, due to significant amounts of As 0 . However, no As 0 was observed in the photoelectron spectra after the hydrazine-terminated nanocrystals were annealed at 350°C under vacuum. After the anneal, the N 1s peak of hydrazine-exposed GaAs nanocrystals shifted to 3.2 eV lower binding energy. This shift was accompanied by the appearance of a Ga 3d peak shifted 1.4 eV from the bulk value, consistent with the hypothesis that a gallium oxynitride capping layer had been formed on the nanocrystals during the annealing process. The band gap photoluminescence (PL) was weak from the Cl-and hydrazine-or sulfide-terminated nanocrystals, but the annealed nanocrystals displayed strongly enhanced band-edge PL, indicating that the surface states of GaAs nanocrystals were effectively passivated by this two-step, wet chemical treatment.