Sulfur Passivation Research Articles

Deep levels reduction in (NH 4) 2S treated and annealed GaAs epilayer on Si substrate

The surface properties of GaAs/Si after ex-situ treatment with (NH 4) 2S solution were investigated by photoluminescence (PL) and X-ray photoelectron spectroscopy. The As 3d and Ga 3d core level studies show that the surface is free of native oxides. A 4.5-fold increase in the PL intensity was observed on undoped GaAs/Si surface after sulfur passivation. This treatment improves the electronic properties of the surface as seen from the increase in PL intensity. After the treatment, the films were annealed at 350 and 450°C in nitrogen atmosphere. Then the films are studied with deep level transient spectroscopy measurements employing metal–insulator–semiconductor structures. Two deep levels at 0.44 and 0.73 eV below the conduction-band edge are found in the as-grown, S passivated and annealed samples. In (NH 4) 2S treated and 450°C annealed sample the trap concentration has reduced nearly half order of magnitude.

INFLUENCE OF CH3CSNH2 PASSIVATION ON INTERFACE DIFFUSION BETWEEN FERROMAGNETIC METALS AND GaAs

The influence of CH3CSNH2 passivation on diffusion at interface between ferromagnetic metals and GaAs has been studied. The experimental results show that sulfur passivation can change the chemical environment of As element , prevent As from diffusing into ferromagnetic metal overlayer, weaken the reaction of As with ferromagnetic metals and enhance the magnetism of the interface. Furthermore, we discussed the reason that S passivation can prevent As atoms diffusion.

Preparation of highly transparent superconductor-semiconductor contacts

In this report we present a procedure to fabricate highly transmissive superconducting Nb-In0.77Ga0.23As contacts. A combination of a sulphur passivation of the etched semiconductor prior to the deposition of Nb and an annealing step is used. To quantitatively classify the transparency of the contacts, transport measurements of the differential conductance are carried out at 300 mK and compared with a model given by Blonder, Tinkham, and Klapwijk [Phys. Rev. B 25, 4515 (1981)]. The procedure yields almost ideal superconductor-semiconductor contacts. Additionally, a high reproducibility of the contact transparency is achieved. The results are interpreted in terms of diffusion of In in both the niobium and the In0.77Ga0.23As.

Sulfur passivation of Ga2O3 (Gd2O3)/GaAs metal–oxide–semiconductor structures

The properties of Ga2O3 films evaporated on unpassivated and passivated GaAs surfaces using a Gd3Ga5O12 source were studied. The properties of unpassivated (passivated) films were a strong (weak) function of substrate temperature with best results obtained at a substrate temperature of about 100 °C. The thermal stability of films evaporated at a substrate temperature of 100 °C was studied as well. The passivated films showed a better thermal stability. The bonds formed at the surface layer of passivated GaAs were used to explain the results.

Analysis of sulfide layer on gallium arsenide using X-ray photoelectron spectroscopy

The increasing use of the III–V compound semiconductors in electronic devices has created a pressing need to develop a good passivant to reproducibly control their surface properties. Ultrathin sulfur passivation of GaAs stabilizes its surface or interface very well and reduces the interface states density. However, the passivated surface exhibits a substantial degradation due to the exposure to air after passivation. In this study, the effect of growing a thick non-degradable sulfide layer by non-aqueous ammonium polysulfide anodization on the GaAs surface was investigated using X-ray photoelectron spectroscopy (XPS). The surface chemistry of this amorphous sulfide layer indicated a relationship between the atomic structure and the property of the interface state. The depth profile of the passivation layer revealed that the structure of the thick sulfide/GaAs interface includes a Ga 2S 3 rich layer on the surface and homogeneous distribution of GaS, Ga 2S 3, As 2S 5 and GaAs in the bulk of the insulator layer.

A novel sulfur-passivation method and magnetic overlayers on passivated III–V semiconductor surface

A sulfur passivation method for GaAs, CH 3CSNH 2 treatment has been developed. It is quite effective for removing the surface oxide layer and forming the sulfide passivation layer on GaAs surface, with sulfur atoms bound with Ga and As atoms. After being annealed, a stable sulfur passivation layer is formed. The enhancement of PL intensity reveals the reduction of surface non-radiative recombination and the density of surface states. Moreover, the investigation has been made for the role of S-passivation on interfacial interaction between magnetic overlayer and GaAs. The interdiffusion of As, Ga into overlayer is effectively inhibited, and the magnetization of Fe overlayers is enhanced. In addition, a relationship has been found between the surface chemical structure of the substrates and the magnetic property of overlayers.

Effective sulfur passivation of an n-type GaN surface by an alcohol-based sulfide solution

The sulfur passivation of an n-GaN surface was investigated by employing an aqueous (NH4)2S solution and (NH4)2S+t-C4H9OH solution. Photoluminescence and Auger electron spectroscopy revealed that treatment with (NH4)2S+t-C4H9OH results in a more effective passivation of the n-GaN surface than that with (NH4)2S due to a higher chemical reactivity of sulfur species in the former solution. The (NH4)2S+t-C4H9OH-treated sample shows a stronger photoluminescence intensity by a factor of 2.5 with respect to an untreated sample. In addition, improved Ohmic characteristics of the sample are evident from current–voltage measurements. This result can be attributed to the effective removal of an insulating layer on the n-GaN surface.

Thermal Stability of Indium Tin Oxide/n-GaAs Heterostructures with and without Sulfur Passivation

Thermally evaporated ITO/n-GaAs contacts with and without sulfur passivation are studied. It is determined that passivation improves the thermal stability (up to 700 °C annealing temperature) of contacts. This improvement is due to formation of thermally stable S-S, S-As, and S-Ga bonds at GaAs surface layer.

Thermal Stability of Indium Tin Oxide/n-GaAs Heterostructures with and without Sulfur Passivation

Thermal Stability of Indium Tin Oxide/n-GaAs Heterostructures with and without Sulfur Passivation

Thermal Stability of Indium Tin Oxide/n-GaAs Heterostructures with and without Sulfur Passivation

Thermal Stability of Indium Tin Oxide/n-GaAs Heterostructures with and without Sulfur Passivation

Comments on Surface Studies and Surface Alteration of CuInSe2 Polycrystalline Thin Films

The effects of surface alteration on CuInSe2 thin films by KCN etching and subsequent (NH4)2Sx sulfur passivation as well as the formation of higher bandgap CuIn(S,Se)2 layer were investigated. After these chemical treatments, no oxygen uptake was observed and a significant number of sulfur atoms were found to diffuse into the Sb-incoporated CuInSe2 thin films to form a stable and higher bandgap CuIn(S,Se)2 layer. A model is proposed to explain how Sb atoms in CuInSe2 thin films can create a pathway for fast replacement of Se by S atoms. Also, Cu segregation from Cu-rich CuInSe2 thin films was directly verified for the first time by the experiments of angular dependence of x-ray fluorescence.

Texturized interface as a basis of surface-barrier heterostructure for solar cells application

Simulation of the photocurrent of surface-barrier structures (SBS) with texturized interface has been performed on the basis of obtained theoretical expression for internal quantum efficiency of homogeneous SBS and the model of parallelly connected diodes. The role of various sources of recombination losses (in the semiconductor, at the interface and due to the emission of majority carriers into the metal) in solar energy convertors has been analyzed. The complex method of characterization of SBS with texturized interface is proposed that includes an analysis of optical, electric and photoelectric characteristics. The possibility to increase the photosensitivity of the Au/GaAs SBS due to texturization and sulfur passivation of the interface for two types of microrelief (dendritic and quasigrating) obtained by wet anisotropic etching has been investigated. The morphology and statistical geometric characteristics of the interface were investigated by atomic force microscopy (AFM). The obtained results allowed to determine the change of optical and electronic (recombination) parameters of the interface caused by the used processing (texturization, passivation).

A new method to enhance the magnetism of Fe overlayer on GaAs(100): sulfur passivation using CH 3 CSNH 2

Ferromagnetic resonance (FMR) has been used to investigat the magnetism of Fe overlayer on S-passivated GaAs(100) pretreated by CH3CSNH2. Comparing with the magnetism of Fe overlayer on clean GaAs(100), we find that sulfur passivation can prevent As diffusion into Fe overlayer and weaken the interaction of As and Fe. It results in enhancing the magnetism of Fe overlayer on GaAs(100). We also investigate the effects of the pre-annealing of S- passivated GaAs(100) substrate on the magnetism of Fe overlayers. The results show that the maximum effective magnetization can be obtained at annealing temperature of 400 °C. According to the experimental results of synchrotron radiation photoemission, it can be explained by the change of chemical composition and surface structure of the passivation layer on GaAs(100) surface after the annealing.

Influence of sulfur on the Sb–GaAs(001) interface

The modification of clean GaAs(100) surfaces by in situ deposition of molecular sulfur was investigated by soft X-ray photoemission spectroscopy. Upon sulfur treatment of the clean GaAs(001) sample at 500°C in ultra-high vacuum the formation of an approximately 0.3 nm thick gallium sulfide-like compound is observed that exhibits a (2×1) LEED pattern. Owing to the sulfur modification on n-GaAs a reduction of the band bending by 0.44 eV is achieved, whereas the band bending on p-GaAs is increased by 0.12 eV. Antimony was deposited onto these sulfur-modified surfaces from a Knudsen cell. This was found not to react with the gallium sulfide layer on the surface. At approximately 1.8 nm antimony coverage the position of the Fermi level above the valence band maximum amounts to 1.05 eV and 0.66 eV for n- and p-doped samples respectively, which is higher than the Fermi level position observed for the unmodified Sb–GaAs(001) Schottky contact (0.75 eV and 0.50 eV). The change in barrier height due to the sulfur passivation is attributed to a sulfur-induced interface dipole.

Interface formation and interaction of Fe overlayer on S-passivated GaAs(100)

We have studied the interface formation and electronic structure of an Fe overlayer deposited on S-passivated GaAs(100). In the first stage of deposition, Fe clusters were formed near S atoms. Compared to Fe/GaAs(100), the sulfur passivation weakens the reaction between As and Fe. It is beneficial to the magnetism at the interface. A magnetic ordering feature could be found at higher coverage due to large exchange splitting.

Sulfur Passivation of InP/InGaAs Metal‐Semiconductor‐Metal Photodetectors

In this paper, we report on the fabrication of high‐performance metal‐semiconductor‐metal photodetectors (MSM‐PDs) using sulfur passivation of the InP surface. Sulfur passivation resulted in a more reliable and reproducible performance, more consistency from device to device, and improved aging stability. The InGaAs MSM‐PDs (2 × 2 μm) have a dark current of about 200 ± 10 nA (at 10 V), a low capacitance of 200 ± 10 fF, a breakdown voltage of about 20 V, a fairly high responsivity of 0.75 ± 0.05 A/W, and a full width at half‐maximum of the temporal response (at λ = 1.3 μm) of 8.5 ± 0.2 ps, which corresponds to a 3 dB frequency of 20 GHz. In addition to the significantly reduced dark current, the field dependence of the photocurrent is also substantially minimized after passivation. Improvement of MSM‐PD performance by sulfur passivation is attributed to the increase of the Schottky barrier height and the reduction of surface and/or interface states. © 1999 The Electrochemical Society. All rights reserved.

The influence of sulfur on the In/GaAs(100) interface formation

The In adsorption on sulfur modified GaAs(100) surfaces was studied using high resolution soft X-ray photoemission spectroscopy (SXPS). The sulfur passivation was performed in UHV by annealing the GaAs(100) substrates in a flux of sulfur atoms. This leads to a (2×1) reconstructed gallium sulfide like layer at the surface. Due to the sulfur treatment the position of the Fermi level relative to the conduction band minimum (CBM) is reduced by approximately 0.46 and 0.36 eV on p- and n-type GaAs, respectively. Onto these sulfur modified surfaces indium is deposited from a Knudsen cell. From the core level emission spectra it is concluded that no alloying between gallium and indium takes place. The indium only reacts with the sulfur layer on the top, represented by a reacted component in the core level spectra, while the contribution of metallic indium clusters dominates the spectra at higher indium coverages. At approximately 4 nm indium coverage, the position of the Fermi level above the valence band maximum amounts to 1.1 and 0.8 eV for n- and p-doped samples respectively, which is higher than the Fermi level observed for the unmodified In/GaAs(100) Schottky contact (0.75 and 0.50 eV). The change in barrier height due to the sulfur passivation is attributed to a sulfur-induced interface dipole.

Sulphur passivation of dry-etched AlGaAs laserfacets

The effects are reported of sulphur treatment in Na2S and (NH4)2S solutions for the passivation of AlGaAs laser facets, etched using Cl2-based chemically-assisted-ion-beam-etching. Compared to untreated lasers, a 37% average improvement in the catastrophic optical mirror damage threshold is measured on sulphur-treated broad-area CAIBE lasers.

An in-situ study of structure and magnetic properties of Fe films on the sulphur passivated Ge(100) surface at 150°C

Ultra-thin Fe films have been grown on the sulphur passivated Ge(100) surface at 150°C. The growth, structure and the magnetic properties of the thin films were studied with LEED, AES, angle resolved AES and in-situ magneto-optical Kerr effect measurements. For the first five monolayers of Fe, no long-range order was observed . However, angle resolved AES data suggest that local order occurs with a small fraction of the Fe atoms adsorbed on bcc sites. For thicker Fe films, the growth becomes ordered. A comparison of the present study and with a previous study of the growth of Fe on sputter cleaned Ge(100)(2×1) surface, shows that sulphur passivation effectively prevents Fe–Ge intermixing. During the Fe deposition process, most of the sulphur atoms migrate to the growing surface, thus acting as surfactants. The presence of sulphur at the surface also affects the growth and magnetic properties of the thin films.

Oxidation and Carbon Contamination in GaAs (100) Wet Treatments

ABSTRACTOxidation and carbon contamination of n-type GaAs (100) surfaces have been investigated by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) for a variety of cleaning and etching pretreatment procedures prior to immersion in either (NH4)2S, Na2S aqueous solutions or S2Cl2 solution in dichloromethane. The study has shown that sulfur passivation removes surface oxide and minimize carbon contamination for surfaces treated in (NH4)2S and S2Cl2 solutions. A significant oxygen and carbon contamination in the anodic passivation of GaAs (100) in (NH4)2Sx aqueous solution have been quantitatively measured. In addition, pretreatment in basic solutions have shown minimal oxygen and carbon level in comparison with the acidic solutions. Surface pretreatment carried out ex-situ has shown a higher risk of surface contamination prior to sulfur passivation.