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Although an increasing volume of x-ray photoemission spectroscopic (XPS) data has been accumulated on boron and boron-rich compounds because of their unusual properties, including a unique three-center, two-electron bonding configuration, their common nonmetallic nature has been overlooked. Typically, the measured energy-state data are not clarified by surface Fermi level positions of these nonmetallic samples, which compromises the scientific contents of the data. In the present study, we revisited the XPS studies of sputter-cleaned β-rhombohedral boron (βr-B), the oxidized surface of βr-B, B6O pellet, and polished B2O3, to illustrate the impact and resolution of this scientific issue. These samples were chosen because βr-B is the most thermodynamically stable polytype of pure boron, B2O3 is its fully oxidized form, and B6O is the best known superhard family member of boron-rich compounds. From our XPS measurements, including those from a sputter-cleaned gold as a metal reference, we deduced that our βr-B had a surface Fermi level located at 0.7±0.1 eV from its valence-band maximum (VBM) (referred as EFL) and a binding energy for its B 1s core level at 187.2 eV from VBM (Eb,VBM). The latter attribute, unlike typical XPS binding energy data that are referenced to a sample-dependent Fermi level (Eb,FL), is immune from any uncertainties and variations arising from sample doping and surface charging. For bulk B2O3, we found an Eb,VBM for its B 1s core level at 190.5 eV and an Eb,FL at 193.6 eV. For our βr-B subjected to a surface oxidation treatment, an overlayer structure of ∼1.2 nm B2O3/∼2 nm B2O/B was found. By comparing the data from this sample and those from βr-B and bulk B2O3, we infer that the oxide overlayer carried some negative fixed charge and this induced on the semiconducting βr-B sample an upward surface band bending of ∼0.6 eV. As for our B6O sample, we found an EFL of ∼1.7 eV and two different chemical states having Eb,VBM of 185.4 and 187.2 eV, with the former belonging to boron with no oxygen neighbor and the latter to boron with an oxygen neighbor. The methodology in this work is universally applicable to all nonmetallic samples.

Sulfur ions with well-controlled kinetic energy were used to introduce additional energy for passivating the InP (100) surface. 50 eV S+ bombardment resulted in the formation of a single In–S species on InP surface and assisted the InP (100) surface to form an ordered (1×1) structure. Further annealing removed the damage introduced during the ion bombardment and resulted in a sharp (1×1) low-energy electron diffraction (LEED) pattern. The treatment was extended to repair Ar+ damaged InP (100) surface. When InP (100) samples were damaged by 200 eV Ar+ bombardment followed by 50 eV S+ treatment and annealing, we could obtain an InP surface with (1×1) LEED pattern and with low surface states.

S+ ions with well-controlled kinetic energy were used to bombard n- and p-type GaAs (100) surfaces. 50 eV S+ bombardment formed a maximum of 1.5 monolayers of sulfide on a GaAs (100) surface and did not change the nonordered surface to an ordered surface. After the bombardment, the surface Fermi levels for both sulfur ion-bombarded n- and p-type samples were moved towards the midgap. After the samples were further annealed at 400 °C, the surface Fermi level of n- and p-type samples gave a separation larger than that of the samples after the UV/O3 and HF treatment. A sharp (1×1) low-energy electron diffraction pattern was observed and the sulfide coverage was about one monolayer. Under such well-controlled conditions, effective surface passivation by reducing surface states and formation of an ordered surface structure can be achieved.

Time-resolved binding energy (BE) changes of the In 3d5/2 level of heavily doped n-InP (100) (S-doped with a carrier density of 2.4 × 1017 cm−3) and p-InP (100) (Zn-doped with a carrier density of 3.9 × 1018 cm−3) after cleaving in UHV were measured by XPS. Also presented are spectra of survey, In 3d5/2 and P 2p levels after the BE stopped shifting. Measurements were carried out on the in situ cleaved (110) facets. The results show nearly flat band surface as cleaved in UHV. The subsequent binding energy changes reflected the Fermi level shift in the band gap relative to the valence band maximum induced by surface states which are believed to be a consequence of surface lattice relaxation after cleavage. The accurate BE of the as cleaved P 2p level can be obtained via interpolation according to the BE changes of In 3d5/2.

The dynamical process of surface band bending induced by ion bombardment as a function of ion fluence and energy has been studied with a special low energy ion beam system and an x-ray photoelectron spectrometer. It was found that 10 and 100 eV Ar+ bombardment of n- and p-InP (110) samples, which were prepared in ultrahigh vacuum by in situ cleavage of InP (100) bars, moved their surface Fermi levels to a common pinning position 0.95 eV above the valence-band maximum. The observed surface band bending was attributed to the displacement damage in the near-surface region induced by the ion bombardment. A quantitative analysis of the band bending data as a function of ion fluence showed that for the 10 eV Ar+ bombardment the formation of ionized surface states at a density of about 1×1012/cm2 in the band gap of InP was induced by an ion fluence of 5×1016/cm2. As expected, an increase of bombardment energy from 10 to 100 eV greatly raised the formation probability of surface defects. The results imply that ve...

X-ray photoelectron spectroscopy measurements of amorphous carbon nitride films have been performed. The samples were prepared by magnetic filtered plasma deposition, and cleaned by Ar+ ion sputtering before analysis to eliminate the surface contamination. The spectra include standard survey scans and high resolution scans of the photoelectron peaks of C, N, and O atoms. These spectra were collected using a monochromatic Mg Kα x-ray source operated at 300 W (20 mA, 15 kV). The survey scans were collected using an 80 eV pass energy, while high resolution scans were recorded using a 20 eV pass energy. By deconvolution of the XPS spectra, it was found that the XPS C 1s and N 1s signals could be deconvoluted into three and two Gaussian peaks, respectively. A plausible suggestion on the assignments of XPS peaks to C3N4, CNx, and ta-C phases was discussed. The relative abundance of CN bonds, calculated from the area of the respective C 1s Guassian peaks divided by the total area of the C 1s spectra, was determi...

A surface etching effect was observed using polysulfide solution for the passivation of III–V semiconductors. The etching rate was found to be 2 A/min on InP (100). The etching effect increased surface roughness, which enhanced the adsorption of adventitious hydrocarbons and water from the ambient. Such an etching effect was not observed on the samples treated by a gas-phase polysulfide treatment. The surfaces of these samples also showed less adventitious hydrocarbons and water after exposure to the ambient. The presence of sulfide on the surface reduced the sticking coefficient of the adventitious hydrocarbons and water.

V. A. Gritsenko,1,2,* J. B. Xu,2,3, R. W. M. Kwok,2,4 Y. H. Ng,2,4 and I. H. Wilson2,3 1Institute of Semiconductor Physics, 630090, Novosibirsk, Russia 2Materials Science and Technology Research Centre, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong 3Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, New Territory, Hong Kong 4Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territory, Hong Kong (Received 4 May 1998)

Ion beam synthesis of silicon carbide (SiC) layers was performed by metal vapor vacuum arc implantation. Subsequent furnace annealing was carried out in nitrogen at various temperatures to form stoichiometric SiC layers. The implanted layers were characterized by various techniques. Rutherford backscattering spectrometry analysis revealed the carbon distribution and formation of the SiC layers. Fourier transform infrared spectroscopy spectra showed absorption peaks produced by the amorphous and β-phase crystalline SiC layers. The crystallinity was increased by high temperature annealing. The dependence of the surface morphology and dynamics of the crystallization on annealing temperature and time was studied by atomic force microscopy (AFM) for the first time. At about 900 °C, nanocrystalline SiC was formed on the sample surface and contained columnar grains with a full width of half maximum of tens of nanometers and a height of 10 nm. A conducting AFM was used to study the electrical properties of the formed SiC layer on the nanometer scale.

Development of high quality ultrathin dielectric films of thickness less than 100 A has become an important research subject due to the scaling down of semiconductor devices. In the present study, samples with 20–100 A SiO2 on silicon were prepared by dry oxidation, and subsequently subjected to rapid thermal nitridation (RTN) using NH3 in the temperature range of 800–1200 °C. X-ray photoelectron spectroscopy and surface charge spectroscopy were applied to study the nitrogen distribution in the dielectric layers, the changes in the interface state density, Dit, and the dielectric breakdown field strength due to the nitrogen incorporation. It was found that nitrogen was mainly incorporated to the dielectric at the dielectric/Si interface without any consumption of silicon in the substrate during RTN. In the study of the electrical properties, we found that RTN led to a slight decrease in Dit and an increase in the breakdown field strength.

The structural and chemical changes of the GaAs(110) surface induced by sequential processes of UV/O3 exposure, HF etching, and gas‐phase polysulfide passivation were investigated by x‐ray photoelectron spectroscopy (XPS), low‐energy electron diffraction (LEED), and thermal desorption. Prior to any annealing, no samples showed any LEED patterns, and XPS indicated the presence of both As–S and Ga–S bonds. When the polysulfide‐passivated surface was annealed to 400 °C, a sharp oblique LEED pattern started to emerge, which was accompanied by the desorption of S–As species. At the same time, XPS indicated that only a single type of sulfide (S–Ga) remained on the surface. Further annealing of the sample to 600 °C resulted in a complete removal of sulfur species from the surface and the appearance of a (2×1) LEED pattern. In contrast, no LEED pattern was observed from samples that had only been subjected to UV/O3 treatment and HF etching up to an anneal temperature of 600 °C, thus indicating the absence of any ...

In the present study, a modified charge neutralizer was used to generate both the negative and positive surface potentials at the dielectric surface for the surface charge spectroscopy (SCS). A stable surface potential and a uniform potential area can be easily achieved. The SCS results of plasma enhanced chemical vapor deposition SiO2/Si samples without annealing and thermal SiO2/Si samples with and without annealing in forming gas (4%H2 in N2) are used to demonstrate the applicability of the SCS analysis.

The effects of a gas‐phase polysulfide treatment on InP were studied by x‐ray absorption near‐edge structures (XANES) of both the sulfur L‐edge and K‐edge, and by x‐ray photoelectron spectroscopy (XPS). Some passivated InP samples were encapsulated with about 4 nm of remote plasma deposited silicon nitride, and the chemical structure of the sulfur atoms at the interface was again determined by angle dependent K‐edge XANES. Both XPS and L‐edge XANES confirmed the presence of indium to sulfide bonding on the surface exposed to gas‐phase polysulfide, and XPS confirmed the presence of more than one sulfide species. The angle dependence in K‐edge XANES indicated that most of the surface sulfur atoms had their sigma bonds oriented along the (110) azimuth with a polar tilt angle of about 40°–60°. It is thus plausible that these sulfur atoms terminated the indium atoms on InP (100) in the form of In–S–In bridging bonds along the (110) azimuth. Vacuum annealing was found to cause desorption of some surface sulfide...

Deep‐level bulk and interface defect states in InP metal/insulator/semiconductor diodes have been investigated using capacitance‐voltage measurements and deep‐level transient spectroscopy. The InP surfaces were cleaned with an ultraviolet light/ozone/HF process followed by an optional polysulfide passivation and then capped with a layer of silicon nitride produced by remote plasma‐enhanced chemical‐vapor deposition. Polysulfide treatment reduced the bulk trap concentrations produced during contact annealing, reducing a bulk trap at 0.33 eV below the measurement limits and reducing a 0.45 eV trap to a concentration of 5×1013 cm−3. The density of interface states close to the conduction‐band edge also decreased with the polysulfide treatment.

A novel technique, surface charge spectroscopy (SCS), has been developed for measuring interface state density at a dielectric-semiconductor interface in conjunction with x-ray photoelectron spectroscopy (XPS). In this technique, a thin dielectric layer with thickness up to 15 nm, is deposited on a semiconductor substrate. The surface Fermi level (EFs) of the semiconductor and the surface potential of the dielectric are measured using XPS, the latter of which can be varied by charging the dielectric with electrons from a low energy electron flood gun commonly equipped inside an XPS system. The interface state distribution in the band gap of the sample is then extracted from the relationship between the EFs and the dielectric surface potential with a simple space-charage calculation similar to the conventional capacitance-voltage technique. Experimental data on SiO2/Si and SiNx/InP samples are shown in the article to illustrate the applicability of SCS.

Releasing the Fermi‐level pinning of InP by gas phase polysulfide exposure has recently been demonstrated by surface charge spectroscopy [Lau et al., Surf. Sci. 271, 579 (1992)]. The present article reports a study of capacitance–voltage (C–V) measurements on metal–insulator–semiconductor (MIS) diodes fabricated using a process which includes this polysulfide passivation. The effectiveness of this passivation technique in reducing interface trap densities (Dit) was confirmed. The optimized MIS fabrication procedure involved (a) surface cleaning and polysulfide exposure; (b) immediate deposition of silicon nitride by remote plasma chemical vapor deposition (RPCVD); and (c) deposition of aluminum and annealing at 500 °C for 15 min in forming gas. The C–V results gave a Dit of 5×1010 cm−2 eV−1 via the Terman analysis and 5×1011 cm2 eV−1 via the high–low frequency method. The MIS properties were unchanged after a two months air exposure and a one week 110 °C heating in air. It was also found that the replacement of aluminum with Ti/Pt/Au, and of RPCVD with plasma enhanced chemical vapor deposition all led to higher Dit values.

Surface chemistry, and surface Fermi level (EFs) changes on InP, as a result of exposure to several sulfur compounds, and of subsequent heating were studied by x‐ray photoelectron spectroscopy. It was found that after p‐InP samples were exposed to a mixture of hydrogen sulfide and polysulfide, heating at 200–300 °C induced a strong type‐inversion of the semiconductor surface. However, subsequent heating at 400 °C returned EFs towards the valence band maximum (VBM). From many repeated experiments, EFs was found to be changed in the range of 0.5–1.2 eV (referenced to VBM). Further studies on exposure to other sulfur compounds including hydrogen sulfide, sulfur, and sulfur dioxide showed that the large range of EFs movement correlated only with polysulfide. The overall spectral results suggest that adsorption of hydrogen polysulfide reduced surface states in the band gap of InP and led to the formation of donor states near the conduction band minimum of InP upon heating at 200–300 °C. Further heating at 400 ...

The use of an ultrathin amorphous silicon layer at the interface between silicon nitride and InP has been studied. The objective was to reduce the interface state density of the dielectric‐semiconductor structure. Amorphous silicon and silicon nitride were deposited sequentially in the same remote plasma chemical vapor deposition chamber with a base pressure in ultrahigh vacuum. Less than 2 nm of amorphous silicon was deposited on InP by decomposing silane in a remote plasma. Three different plasmas, argon, helium, and hydrogen were tried. Silicon nitride was deposited by reacting silane with atomic nitrogen from a remote nitrogen plasma. Most of the processing steps were monitored by x‐ray photoelectron spectroscopy (XPS) with sample transfer in ultrahigh vacuum. The degree of Fermi level pinning of InP at the resultant interface was studied by surface charge spectroscopy (SCS). It was found that the deposition of amorphous silicon in the nanometer thickness range could be readily controlled. The amount ...

A 10 A ultraviolet/ozone grown oxide was used as an atomic diffusion barrier in a Ge/GaAs heterostructure. Good thermal stability of the oxide layer has been demonstrated by the appearance of dendritic crystallization [K. M. Lui, K. P. Chik, and J. B. Xu, J. Appl. Phys. 81, 7757 (1997)], induced by in situ thermal pulse annealing, of the Ge overlayer. In this work, an abrupt heterointerface was revealed by aligned Rutherford backscattering spectroscopy after annealing and compared with a control with no barrier at the interface where considerable diffusion had taken place. Current–voltage measurement indicated good rectifying properties of the oxide barrier heterojunction.

A remarkably low turn-on field of about 1 V/μm has been observed in electron field emission from planar SiC/Si heterostructures formed by high dose C implantation into Si using a metal vapor vacuum arc ion source. An implant energy of 35 keV was used to a dose of 1.0×1018 ions/cm2 with subsequent annealing in nitrogen at 1200 °C for 2 h. X-ray photoelectron spectroscopy showed that a thin surface stoichiometric SiC layer, with a thickness of about 150 nm, had been formed. Atomic force microscopy showed that there are densely distributed small protrusions formed on the surface. The formation of a thin surface stoichiometric SiC layer and the formation of densely distributed small protrusions on the surface are believed to be the two factors responsible for the efficient electron field emission.

Gas phase polysulfide passivation of InP was studied and used to improve the electrical properties of metal-insulator-semiconductor structures and metal-insulator-semiconductor field effect transistors (MISFETs). The gas phase polysulfide treatment was used successfully to reduce the interface state density of silicon nitride/InP. MISFETs with a slow drain current drift were fabricated. The results indicate that both depletion mode and accumulation-depletion mode InP MISFETs can be fabricated with a useful drain current. >

Planar SiC/Si heterostructures were formed by high dose carbon implantation using a metal vapor vacuum arc ion source. The variations of the field emission properties with the implant dose and annealing conditions were studied. A remarkably low turn-on field of 1 V//spl mu/m was observed from a sample implanted at 35 keV to a dose of 1.0/spl times/10/sup 18/ cm/sup -2/ with subsequent annealing in nitrogen at 1200/spl deg/C for 2 h. The chemical composition depth profiles were determined from X-ray photoelectron spectroscopy and the surface morphology was observed by atomic force microscopy. The formation of a thin surface stoichiometric SiC layer and the formation of densely distributed small protrusions on the surface are believed to be the two factors responsible for the efficient electron field emission.

Ultrathin silicon nitride films on Si(100) have been studied using x‐ray photoelectron spectroscopy, medium energy ion scattering, Raman spectroscopy, and variable‐energy positron annihilation spectroscopy. Films ∼10‐nm‐thick were prepared by remote microwave plasma chemical vapor deposition. A compressive stress of about 0.4 GPa was found by measuring the Raman shift of the fifth‐harmonic LO mode of the silicon substrate. The film properties, however, changed significantly upon vacuum annealing. Annealing at 100 °C for 1 h resulted in an increase of nitrogen concentration near the film surface, probably because of nitrogen surface segregation. Annealing at 100–500 °C also released film induced stress and a complete stress release was achieved by annealing at 500 °C for 1 h. Positron annihilation results showed that vacuum annealing only affected the film but not the substrate.

Planar SiC/Si heterostructures were formed by high dose carbon implantation using a metal vapor vacuum arc ion source. The variations of the field emission properties with the implant dose and annealing conditions were studied. A remarkably low turn-on field of IV/μm was observed from a sample implanted at 35 keV to a dose of 1.0×1018 cm−2 with subsequent annealing in nitrogen at 1200°C for 2h. The chemical composition depth profiles were determined from x-ray photoelectron spectroscopy and the surface morphology was observed by atomic force microscopy. The formation of a thin surface stoichiometric SiC layer and the formation of densely distributed small protrusions on the surface are believed to be the two factors responsible for the efficient electron field emission.

Buried SiC layers were synthesized by carbon implantation into silicon with a metal vapor vacuum arc ion source under various implantation and annealing conditions. The infrared absorption spectra of these samples were deconvoluted into two or three gaussian components depending on the preparation conditions. One component peaked at around 700 cm-1was assigned to amorphous SiC (a-SiC). The other two components, both peaked at 795 cm-1 but with different values of full width at half maximum (FWHM), were attributed to β-SiC. The one with a larger (smaller) FWHM corresponds to β-SiC of smaller (larger) grains. With this deconvolution scheme, the fraction of various SiC phases in these samples were determined. It was found that for the as-implanted samples there are critical energies and doses at which the crystalline SiC fraction increases abruptly. This was attributed to the ion beam induced crystallization (IBIC) effect. It was also shown that the IBIC effect leads to strong dependence of the β-SiC fraction on the order of implantation for samples synthesized by double-energy implantation. Analysis of the evolution of the β-SiC fraction with annealing time indicated that the crystallization process in these SiC layers could well be described by the classical random nucleation and growth theory.

Ion beam synthesis of SiC/Si heterostructures was performed by MIEVVA (metal vapor vacuum arc) implantation under various implantation and annealing conditions. The implanted SiC/Si heterostructures were characterized by various techniques. Carbon redistribution in overstoichiometrically implanted samples during annealing to form a stoichiometric SiC layer has been observed for the first time. The FTIR spectra were found to be composed of two components, one attributed to amorphous SiC and the other to ß-SiC. It was also found that there are critical dose and critical energy at which the crystalline fraction increases abruptly. Other results on electrical and optical characterization are also presented and discussed.

The structural and chemical changes induced by the annealing of InP which has been exposed to gas-phase polysulfide, a known passivation method for the reduction of surface states for InP, were investigated using in situ low-energy electron diffraction (LEED), thermal desorption spectrometry, and x-ray photoelectron spectroscopy (XPS). A diffused InP (1×1) LEED pattern was observed on InP which had been exposed to ultraviolet/O3 followed by etching with a 1:30 HF solution. The (1×1) LEED pattern became sharper after the gas-phase polysulfide exposure and the subsequent annealing. The sharpest pattern was obtained after annealing at 400 °C. Accompanying these structural changes were the desorptions of species containing H and S at 300 °C and the species containing H, S, and P at 400 °C. XPS analyses showed that during the structural changes, the multiple sulfide species on the as-exposed surface were converted to a single relatively stable In–S species as a result of appropriate annealing. Similar chemical changes of sulfide species were obtained at the SiNx/InP interface. The results suggest that sulfide assisted the reordering of the InP surface, thus leading to the reduction in interface state densities which were determined by capacitance–voltage measurements.

Ultrathin SiO2 dielectric layers of thickness less than 100Å on silicon substrates have been prepared by dry oxidation and rapid thermal nitirdation (RTN). In this study, X-ray photoelectron spectroscopy and surface charge spectroscopy had been applied to study the nitrogen distribution in the dielectric layers and the change in the interface state density (Dit) due to the nitrogen incorporation. It is found that most of the incorporated nitrogen is located near the dielectric/Si interface and the nitrogen content increases with the RTN temperature. For the electrical properties, we found that the Dit, after RTN slightly decreases and the breakdown field strength deduced from the dielectric surface potential was enhanced by the incorporation of nitrogen.

Properties of ultrathin (— lOnm) silicon nitride films on single crystal Si, InP and GaAs have been studied using Raman spectroscopy, medium energy ion scattering (MEIS), variable-energy positron annihilation spectroscopy and x-ray photoelectron spectroscopy (XPS). The silicon nitride films were prepared by remote microwave plasma chemical vapour deposition (RPCVD). The results showed that oxidation of the film due to air exposure was restricted to the near surface with an oxygen penetration depth no greater than 2 nm. The residual stress in the as-grown films was substrate-dependent. For films on Si (100), the film induced residual stress was compressive with a value of 0.5GPa. Annealing at 500°C for 60 minutes resulted in a complete release of the residual stress. Vacuum annealing at a temperature below 500° C also led to changes of the electrical properties in the films but not the substrate.

The magnetic properties and structure evolution of CoxC1−x (x=44, 65, 71 at. %) nanocomposite films prepared by pulsed filtered vacuum arc deposition were studied. The as-deposited films consist of amorphous Co clusters in a-C and are soft ferromagnets. The low coercivity in the amorphous films is due to the very low anisotropy of the amorphous Co clusters. After annealing in vacuum at 350 °C for 1 h, the Co clusters crystallize and these films become magnetically harder. The magnetic hardening is attributed to the enhanced magnetic anisotropy of the nanocrystals. Their saturation magnetization reduces slightly. This is attributed to the reduction of the density of states at the Fermi level caused by the crystallization of the amorphous Co clusters.

BNx films with N content varying from 2 to 40 at. % were deposited by dual ion beam deposition. The films are solid admixtures of a B-rich phase composed of icosahedral atomic clusters, and a graphite-like boron nitride phase. The fraction of the B-rich phase drops, while that of the graphite-like boron nitride phase grows with increasing N content. The hardness of the films first rises, reaches a maximum value of 18.8 GPa at a N content of 20.2 at. %, and falls with further increase in N content. This rise is explained by assuming that some N atoms are located interstitially at the sites surrounded by icosahedral clusters, such that the hardness of the material is enhanced as a result of additional cross-linking of the network by the N atoms. However, the overall N contents are not sufficient to ensure the two phases to have the ideal stoichiometry of B4N and hexagonal BN (h-BN) structures, so that the B-rich phase in the film does not exhibit the theoretical strongest possible cross-linking that has bee...