The adsorption of K on the n-GaAs(1 0 0) surface was investigated by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (SR–PES). The Ga3d and As3d core level was measured for clean and K adsorbed GaAs(1 0 0) surface. The adsorption of K induced chemical reaction between K and As, and the K–As reactant formed when the K coverage θ > 1 ML. The chemical reaction between K and Ga did not occur, but Ga atoms were exchanged by K atoms. From the data of band bending, the Schottky barrier is 0.70 eV. The Fermi-level pinning was not caused by defect levels. The probable reason is that the dangling bonds of surface Ga atoms were filled by the outer-shell electrons of K atoms, forming a half-filled surface state. The Fermi-level pinning was caused by this half-filled surface state.

Chemically sulfur passivation of GaAs(100) by thioacetamide ( CH 3 CSNH 2 ) has been studied using synchrotron radiation photoemission spectroscopy (SRPES), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The measurement of SRPES and AES showed that the top layer of native oxides over GaAs(100) was removed and the sulfides of Ga and As were formed after the passivation process. The thermal stability and surface structure have also been studied by annealing the passivated samples at different temperatures. We found that the surface sulfides could be removed gradually; as a result, a clean, ordered and thus Fermi level unpinning surface was finally achieved. The surface restructures with GaAs(100)–S(2×1) and 4×1 LEED patterns were observed on annealing above 260°C and at 550°C respectively.

The influence of CH 3CSNH 2 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.

First-principle calculations are performed on ZnO:VO, ZnO:VZn and ZnO:ZnI using a FP–LMTO (full potential linear muffin-tin orbital) method. The results prove that the ZnI is the dominant donor in ZnO, and VZn, a shallow acceptor, while VO is a deep donor.

A new sulfur passivation method for GaAs by using CH3CSNH2 has been developed. Its passivation mechanics have been studied. The sulfide passivation layer can prevent deposited Mg and Fe from diffusing into or reacting with GaAs substrate. It is illustrated that sulfur passivation is beneficial to the enhancement of the magnetism of Fe overlayer on GaAs surface.

We have produced epitaxial Fe overlayers on S-passivated GaAs(100) surfaces by CH3CSNH2 treatment. The correlation between magnetic properties of the overlayers and surface chemical structure of GaAs(100) surfaces was investigated by changing the annealing temperature of the surface prior to growth. The results show that the magnetization of Fe overlayers is crucially determined by the GaxS chemical bonds and by the presence of excess As after the anneals. A comparative investigation of the magnetization has been performed on both S-passivated and clean GaAs(100). It is confirmed that S-passivation on GaAs surfaces can effectively eliminate the magnetization deficiency previously attributed to interdiffusion of As into the Fe overlayer.

Synchrotron radiation photoelectron spectroscopy (SRPES) has been applied to surface analysis of indium tin oxide (ITO) thin films. Several different components of In and Sn were observed at the clean ITO surface. By comparing the chemical compositions of the film before and after vacuum annealing, the contents of In2O3-x and Sn3O4 were found to be the major factors influencing the electrical conductivity and optical transparency of the film. (C) 2000 Elsevier Science B.V. All rights reserved.

A sulfur passivation method for GaAs, CH3CSNH2 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.

Interface formation between Co and the sulfur-passivated GaAs(100) (by CH3CSNH2 treatment) has been studied by synchrotron radiation photoemission spectroscopy. Interface reaction is weak, a stable interface forms at the coverage of 0.8 nm. Ga atoms bonded with S at the surface exchange with Co atoms and cause the formation of Co-S bonding, no segregated As appears at the surface of Co overlayer, in contrast with the case of Co/GaAs(100). This indicates that S-passivation on GaAs(100) is an effective way of inhibiting the interdiffusiion of As and Ga through the coverage.

Soft X-ray synchrotron radiation photoemission (SRPES) and XPS were used to study the interaction of oxygen with Gd–Ni composite and Gd cluster films grown on Ni(110) surface. Different oxidation manners were found for the two kinds of films. Over the Gd–Ni composite film, the adsorption of oxygen resulted in the segregation and oxidation of Gd component, and chemisorbed O− and lattice oxygen were detected. For the Gd cluster film, with the increase of oxygen exposure the oxidation states of Gd were developed between the two peaks of the Gd4f double-peak at the expense of attenuation of HBE peak. Only one O1s XPS peak at 529.6 eV was detected in the range of 0–50 L exposure.

Interface formation between Co with GaAs(100) and S-passivated GaAs(100) by CH3CSNH2 treatment has been studied with synchrotron radiation photoemission. Strong interface disruption and reaction occurs between the overlayer with GaAs(100) even at low Co coverage (∼0.2 nm), while the reaction is much weaker on S/GaAs(100); a stable interface forms at a coverage of 1 nm and 0.8 nm, respectively. For S-passivated GaAs(100), Ga atoms bonded with S at the surface exchange with Co atoms and cause the formation of Co–S bonding, the amount of As bonded with Co is much less than that on GaAs(100), no segregated As appears at the surface of Co overlayer, in contrast with the case of Co/GaAs(100), indicating that S-passivation on GaAs(100) is an effective way of inhibiting the interdiffusion of As and Ga through the overlayer.

The interaction of ultrathin Mg and MgOx films with the GaAs(100) semiconductor substrate was investigated using synchrotron radiation photoemission. The results showed that strong interaction existed between Mg and GaAs leading to the formation of an interface more than 11 A, while negligible interaction and interdiffusion took place between the MgOx overlayer and the substrate. Different Mg:O-2 ratio during the deposition gave rise to the formation of MgOx with different compositions and properties. (C) 1999 Elsevier Science B.V. All rights reserved.

We have produced epitaxial Fe overlayers on sulfur-passivated GaAs(100) surfaces by CH3CSNH2 treatment, and investigated the correlation between magnetic properties of the overlayers and surface chemical structure of GaAs(100) surfaces by ferromagnetic resonance and synchrotron radiation photoemission. The surface chemical properties were modified by changing the annealing temperature of the surfaces prior to the growth. The results show that the magnetization of Fe overlayers is crucially determined by the presence of Ga–S chemical bonds and excess As after the anneals. A comparative investigation of the magnetization has been made on both S passivated and clean GaAs(100). It is confirmed that S passivation on the GaAs surface can effectively eliminate the magnetization deficiency previously attributed to interdiffusion of As into the Fe overlayer.

Ferromagnetic resonance (FMR) has been used to investigate 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 degrees 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.

An organic sulfide, CH3CSNH2 treated sulfur-passivated GaAs(100), has been studied using synchrotron radiation photo-emission spectroscopy (SRPES), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The SRPES and AES measurements show that the treatment removes the GaAs surface oxide layer and forms sulfides of Ga and As on the surface. The thermal stability and surface structure of the passivated samples at different temperatures have also been studied. We found that the surface sulfides are also gradually removed and a clean, ordered and thus Fermi level unpinning surface can finally be achieved. Surface restructuring can be observed from the GaAs(100)–S (2×1) pattern between 260 and 450°C to the (4×1) pattern without S between 460 and 550°C.

Using photoelectron spectroscopies we studied the growth process of SiC on n-Si(111) by polyimide Langmuir–Blodgett (LB) film. The polyimide pyrolyzes when heated, and leaves a skeleton of carbon atoms on the film surface, which remains the structure of LB films before pyrolysis. At about 800°C, if the polyimide LB film is thin, the substrate Si will outdiffuse quickly and form a Si layer on top of the film. At 1000°C, the Si from Si–O reacts with carbon from pyrolysis to form SiC. From the results we suggest that the LB film thickness is an important factor in the growth of good quality single crystalline SiC films.

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.

Contradictory results are obtained when Gd is deposited on S–GaP(100) and GaAs(100) substrates, respectively. The Gd4f spectra from Gd/S–GaP show single peaks with binding energy 8.3 eV at a thickness of 0.9 nm. However, the Gd4f spectra from Gd/GaAs evolve from a narrow peak into a two-featured structure with an increment of Gd. At a thickness of 2.33 nm, one feature centers at 10.3 eV binding energy, and another at 8.0 eV. We confidently exclude the contribution of contamination in these unexpected results and a new phase is supposed.

Synchrotron radiation photoelectron spectroscopy has been used to investigate III–V phosphide GaP and InP (100) surfaces treated with a neutralized (NH4)2S solution. Compared to the conventional basic (NH4)2S solution treatment, a thick sulfide layer with P–S bond and strong Ga–S (In–S) bond of high thermal stability is formed on the neutralized (NH4)2S-treated GaP (InP) (100) surfaces. The possible passivation mechanisms of the two (NH4)2S solutions to III–V phosphide surfaces are also discussed.

SiO x (x>1.5) overlayers have been in situ grown on ZnS (111) and CdTe (111) substrates. Synchrotron radiation photoemission spectroscopy has been used to measure the electronic structures and band lineups of these two heterojunctions. The valence band offsets of SiOx/ZnS(111) and SiOx/CdTe(111) derived from the measurements are 2.8±0.2 and 4.7±0.2 eV, respectively. Harrison’s “tight binding” theory is extended into the theoretical estimation of the band lineups of SiO2 related heterojunctions. The agreement between the experimental and theoretical results is good. Our result also explains the positive role of SiO2 layers in ZnS-based thin film electroluminescence devices.