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Applied Surface Science (v.258, #21)
Critical issues for interfaces to p-type SiC and GaN in power devices by F. Roccaforte; A. Frazzetto; G. Greco; F. Giannazzo; P. Fiorenza; R. Lo Nigro; M. Saggio; M. Leszczyński; P. Pristawko; V. Raineri (pp. 8324-8333).
► Interfaces to p-type SiC and GaN are fundamental for the performances of power devices. ► Improvement of p-type implanted SiC morphology (capping layer) results into better Ti/Al ohmic contacts formed on it. ► Annealing of p-type implanted region can impact the 4H-SiC MOSFETs mobility, which is limited by interface traps scattering. ► Complex evolution of microstructure and Schottky barrier height in annealed Ni/Au contacts to p-GaN. ► The reduced Schottky barrier upon annealing in oxidizing atmosphere explains the lower specific contact resistance.Silicon carbide (SiC) and gallium nitride (GaN) are excellent wide band gap materials for power electronics. In spite of the significant progresses achieved in the last years, there are several issues limiting the performances of the developed devices. As an example, interfaces in SiC and GaN-based structures represent still one of the major concerns. Among them, metal/p-type SiC (or GaN) interfaces and metal-oxide-semiconductor (MOS) interfaces are fundamental building blocks for the performances of both diodes and transistors. In this context, the improvement of the related technology requires further efforts to better understand some physical aspects related to these interfaces.This paper reviews some of our recent results related to metal/semiconductor (ohmic contacts) and metal-oxide-semiconductor interfaces to p-type SiC and GaN.Firstly, the impact of the morphology of p-type implanted SiC, annealed under different conditions, on the properties of Ti/Al contacts will be discussed. The influence of different annealing conditions on the channel mobility in 4H–SiC MOSFETs will be also addressed. In the second part of the paper, the evolution of microstructure and Schottky barrier height in Ni/Au contacts to p-type GaN will be presented.All these aspects will be discussed in the present context of SiC and GaN research, considering the practical implications for devices.
Keywords: PACS; 73.40.−c, 73.40.Kp, 73.61.EySiC; GaN; Interfaces; Ohmic contacts; JBS; MOSFET; HEMT
S-termination effects for the catalytic activities of Pd on GaN(0001) surfaces by T. Konishi; Y. Ueta; M. Hirayama; N. Nishiwaki; S. Tsukamoto (pp. 8334-8337).
► A new application of S-terminated GaN surface, that is, palladium nanoparticles (PdNP) are deposited on the surface. ► The structure serves as a treatable and green chemical catalyst. ► The catalysts with or without S-termination are prepared to discuss the role of S termination in the fascinating catalytic activity. ► The catalytic activities of the samples are discussed by using the chemical conversions of repeated Mizoroki–Heck reactions. ► It was concluded that the S-termination acts as a stabilizing binder of PdNP on the surface.A S-terminated GaN(0001) substrate covered with catalytically active Pd nanoparticles (PdNP) serves as a treatable and green chemical catalyst for various cross-coupling reactions. The role of S in the formation of PdNP has been studied so far, but the effect on the catalytic activity has not been investigated. In this study, we investigate the role of S-termination during the Mizoroki–Heck reaction from the view point of the stability of PdNP and the yield in repeated reactions. PdNP are formed on both S-terminated GaN(0001) surface and non-terminated one, and their catalytic activities are compared when the quantity of PdNP is subminimal and excessive. It is found that S-termination serves as a binder of PdNP on GaN(0001) surface, resulting in the self-regulation of PdNP leaching.
Keywords: PACS; 81.16.Hc; 68.35.bj; 81.16.−cPd; GaN; S; Catalyst; Mizoroki–Heck reaction
Ab initio studies of electronic and optical properties of graphene and graphene–BN interface by C. Yelgel; G.P. Srivastava (pp. 8338-8342).
► Systematic theoretical investigation of atomic structure of graphene and its interface with boron nitride. ► Detailed analysis of electronic structure of graphene and graphene/BN. ► Ab inito calculation of surface dipole.Atomic geometry, electronic states, and optical transitions for isolated monolayer, bilayer and trilayer graphene, and graphene grown on ultra-thin layers of hexagonal boron nitride (h-BN) have been studied theoretically by using the density functional theory and the planewave pseudopotential method. For monolayer graphene, the dispersion curve near theK point is linear with Dirac electron's speed of 0.9× 106m/s. For bilayer graphene the lowest unoccupied energy band is characterised by a mixture of linear and quadratic behaviours, with a relative effective mass of 0.023. For trilayer graphene there are overlapping electron and hole bands near the Fermi level, with a relative electron effective mass of 0.0541. For a monolayer graphene on monolayer h-BN substrate, a small band gap of 57meV is established. At Brillouin zone centre, the theoretically obtained direct transition of 6.3eV for graphene is reduced to 5.7eV for graphene/h-BN. Results are also presented for the interface between graphene and a multilayer h-BN.
Keywords: Graphene; Bilayer graphene; Trilayer graphene; Graphene–BN interface; Effective mass; Density of states; Pseudopotential theory; Density functional theory
Electrical characterization of surface and interface potentials on SiC by J. Mizsei; A. Czett (pp. 8343-8348).
► Contact free vibrating capacitor measurements on the SiC surface. ► Electrostatic (corona) charge controlled surface. ► Accumulation, depletion and avalanche breakdown instead of equilibrium inversion. ► The equilibrium Q– V curve still can be measured.Contact free vibrating capacitor results have shown that the SiC surface is more stable, compared to Si, and it is possible to identify the different (Si or C) planes on SiC substrates. The surface charge density seems to be higher after compression welding process. Electrostatic (corona) charge on the surface results in accumulation and depletion, and probably avalanche breakdown instead of equilibrium inversion. However, the equilibrium Q– V curve still can be measured starting from the inversion region.Among C– V methods the capabilities of V– Q and mercury C– V have been investigated, as two major electrical measurement techniques for SiC qualification. SiC–silicon-dioxide interfaces and SiC epitaxial layers were characterized with HF/LF C– V and V– Q measurement techniques. These methods were developed basically for Si measurements, but they could easily be adapted for measuring SiC too.
Keywords: Silicon carbide; Surface voltage; Interface potential; Vibrating capacitor; SPV; C; –; V; curve; Q; –; V; curve
Growth of thin zirconium oxide films on the 6H–SiC(0001) surface by K. Idczak; P. Mazur; L. Markowski; M. Skiścim; M. Musiał (pp. 8349-8353).
► The growth of thin zirconium oxides film on 6H-SiC(0001) surface has been presented. ► Zirconium dioxide is one of the high-κ dielectric materials. ► The experiment was carried out using the methods: XPS, LEED, STM. ► The growth of ZrO2 films proceeded almost in layer-by-layer mode with some irregular islands.This is the first work which presents results of the growth of Zr on the SiC(0001) surface in the presence of oxygen by using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). The growth of ZrO2 films, STM monitored, proceeded up to a thickness of 8 ML zirconium almost in layer-by-layer mode with some irregular islands. Some paths with a changed conductance, indicating its mixed diode- and ohmic type, were also observed.After submonolayer Zr depostion and annealing the sample at 600°C, the 1×1 structure appeared indicating that the first layer grows according substrate structure and forms hexagonal zirconium. Further annealing at 1000°C and above revealed a doubled structure identified as a one stemmed from the SiC substrate and Zr adsorbate. Additionally, a new p(2×2) structure arose which is interpreted as an alternate zirconium layer. Confirmation of this thesis is found in XPS studies.
Keywords: PACS; 79.60−I; 77.55.D−; 68.37.Ef, 61.05.jhHigh-κ dielectrics; Zirconium dioxide; Silicon carbide; Semiconductor/insulator interfaces
Surface photovoltage and Auger electron spectromicroscopy studies of HfO2/SiO2/4H-SiC and HfO2/Al2O3/4H-SiC structures by A. Domanowska; M. Miczek; R. Ucka; M. Matys; B. Adamowicz; J. Żywicki; A. Taube; K. Korwin-Mikke; S. Gierałtowska; M. Sochacki (pp. 8354-8359).
► We applied contactless surface photovoltage to assess oxide/SiC interface quality. ► 5nm-thick SiO2 film seems to be better interlayer between SiC and HfO2 than Al2O3. ► Element distribution in the oxide/SiC interface was obtained from AES profiling. ► SiO2 buffer and transition silicate nanofilms were found from AES spectra analysis.The electronic and chemical properties of the interface region in the structures obtained by the passivation of epitaxial n-type 4H-SiC layers with bilayers consisting of a 5nm-thick SiO2 or Al2O3 buffer film and high- κ HfO2 layer were investigated. The main aim was to estimate the influence of the passivation approach on the interface effective charge density ( Qeff) from the surface photovoltage (SPV) method and, in addition to determine the in-depth element distribution in the interface region from the Auger electron spectroscopy (AES) combined with Ar+ ion profiling. The structure HfO2/SiO2/4H-SiC exhibited slightly superior electronic properties in terms of Qeff (in the range of −1011qcm−2).
Keywords: Silicon carbide; Surface passivation; Surface photovoltage; Interface charge; Auger electron spectroscopy; Chemical in-depth profiling
Ab-initio modeling of oxygen on the surface passivation of 3CSiC nanostructures by J.L. Cuevas; A. Trejo; M. Calvino; E. Carvajal; M. Cruz-Irisson (pp. 8360-8365).
► The electronic properties of SiC nanostructures were theoretically studied. ► The systems surface dangling bonds were passivated with H atoms and OH radicals. ► OH passivation is energetically favorable in SiC nanostructures. ► The OH saturation produces a reduction of the band gap compared to the H termination. ► In porous SiC, OH termination distorts the lattice and changes the band gap feature.In this work the effect of OH on the electronic states of H-passivated 3CSiC nanostructures, was studied by means of Density Functional Theory. We compare the electronic band structure for a [111]-oriented nanowire with total H, OH passivation and a combination of both. Also the electronic states of a porous silicon carbide case (PSiC) a C-rich pore surface in which the dangling bonds on the surface are saturated with H and OH was studied. The calculations show that the surface replacement of H with OH radicals is always energetically favorable and more stable. In all cases the OH passivation produced a similar effect than the H passivation, with electronic band gap of lower energy value than the H-terminated phase. When the OH groups are attached to C atoms, the band gap feature is changed from direct to indirect. The results indicate the possibility of band gap engineering on SiC nanostructures through the surface passivation species.
Keywords: Silicon carbide; Nanowires; Density Functional Theory; Porous semiconductors
Application of deposited by ALD HfO2 and Al2O3 layers in double-gate dielectric stacks for non-volatile semiconductor memory (NVSM) devices by Robert Mroczyński; Andrzej Taube; Sylwia Gierałtowska; Elżbieta Guziewicz; Marek Godlewski (pp. 8366-8370).
► Feasibility of application of double-gate dielectric stacks with ALD layers in NVSM was investigated. ► Significant improvement in retention at elevated temperatures was demonstrated. ► Superior memory window (extrapolated at 10 years) of flat-band voltage ( Ufb) values were obtained. ► Analysis of conduction mechanisms under negative voltage revealed F–N tunneling. ► Extracted values of barrier height ( ΦB) linearly decrease with increasing temperature.The feasibility of the application of double-gate dielectric stacks with fabricated by atomic layer deposited (ALD) HfO2 and Al2O3 layers in non-volatile semiconductor memory (NVSM) devices was investigated. Significant improvement in retention at elevated temperatures after the application of ALD high- k oxides was demonstrated. Superior memory window (extrapolated at 10 years) of flat-band voltage (Ufb) value of the order of 2.6V and 4.55V at 85°C, for stack with HfO2 and Al2O3, respectively, was obtained. Moreover, the analysis of conduction mechanisms in the investigated stacks under negative voltage revealed F–N tunneling in the range of high values of electric field intensity and lowering of barrier height with increasing temperature.
Keywords: Silicon oxynitride; Hafnium dioxide; Aluminum oxide; Electrical characterization; PECVD; ALD; Non-volatile semiconductor memories (NVSM)
High-temperature stability of c-Si surface passivation by thick PECVD Al2O3 with and without hydrogenated capping layers by Pierre Saint-Cast; Daniel Kania; René Heller; Saskia Kuehnhold; Marc Hofmann; Jochen Rentsch; Ralf Preu (pp. 8371-8376).
► We studied PECVD Al2O3 films for tow temperature processes, annealing and firing. ► Investigation on two capping layers (SiNx and SiOx) in combination with Al2O3. ► The blistering intensity depends on the Al2O3 thickness, but not on the capping. ► Characterization of the surface recombination, the interface trap and the charge. ► The Al2O3 film provides H to the interface independently from the capping.We are studying the thermal stability of thick hydrogenated amorphous aluminum oxide (Al2O3) layers (20–50nm) prepared by a high-throughput plasma-enhanced chemical-vapor-deposition (PECVD) technique for the electrical passivation of crystalline silicon surfaces. These passivation layers can be applied alone or covered by a capping layer like amorphous hydrogenated silicon nitride (SiNx) or amorphous hydrogenated silicon oxide (SiOx), also prepared by PECVD. After firing at 870°C for approximately 3s, the layers show blistering for Al2O3 of 30nm or higher, independently from the capping layer. For thinner Al2O3, no blistering can be observed even using scanning electron microscope (SEM).Very long carrier lifetimes up to 900μs was obtained in passivated p-Si (1Ωcm) wafer after annealing and firing, without observing a strong influence of the layer thickness and the capping layer. All the layer stacks, including the stacks with SiNx capping layer, show high negative charge densities in the layer (1–4×1012cm−2). Additionally, low interface defect densities (∼1011cm−2eV−1), which could be achieved with and without a hydrogenated capping layer, were measured even after firing. To explain these phenomena, hydrogen concentration depth profiles were measured by nuclear reaction analysis. These measurements have shown that, at the Al2O3–Si interface, hydrogen atomic concentration ranging 5–7% after annealing and 4% after firing are obtained independently from the capping hydrogen concentration. We conclude that PECVD Al2O3 layers of 20nm or thicker can provide enough hydrogen to passivate the interface defects, even after a high temperature step. However, the layer thickness should be limited to 30nm in order to avoid the blistering.
Keywords: Passivation; Aluminum oxide; PECVD
Theoretical analysis of semiconductor surface passivation by adsorption of alkaline-earth metals and chalcogens by G.P. Srivastava; A.Z. AlZahrani; D. Usanmaz (pp. 8377-8386).
► Ab initio theoretical studies of the electronic structure of chemisored semiconductor surfaces. ► Understanding of semiconductor passivation at atomic level. ► Detailed analysis of structural models for Ca/Si(001), Ca/Si(111), and S/GaAs(001) surfaces for sub-monolayer elemental coverages.We begin with the concept of semiconductor surface passivation by adsorption of sub-monolayer atomic coverages. We then present a theoretical analysis of structural reconstruction and passivating behaviour of semiconductor surfaces upon sub-monolayer adsorption of alkaline-earth metals (group II atoms) and chalcogens (group VI atoms). Specific results are presented from first-principles calculations for Ca adsorption on Si(001) and Si(111), and S adsorption on GaAs(001). The role of chemical species of adsorbate and surface atoms in achieving different degrees of passivation is highlighted.
Keywords: Semiconductor surface passivation; Atomic adsorption; Pseudopotential theory; Density functional theory
Electronic interface properties of silicon substrates after ozone based wet-chemical oxidation studied by SPV measurements by Heike Angermann; Klaus Wolke; Christiane Gottschalk; Ana Moldovan; Maurizio Roczen; Jens Fittkau; Martin Zimmer; Jochen Rentsch (pp. 8387-8396).
► Ultra-thin oxides were prepared on Si surfaces with O3 dissolved in ultra pure water. ► It was successfully applied to improve the wettability of textured solar substrates. ► Sequences of DIW-O3 and oxide removal in HF 1% were utilised to prepare hydrophobic substrates. ► On H-terminated Si interface state densities Dit,min≈5×1011eV−1cm−2 were achieved. ► DIW-O3 can be a low cost alternative to current wet-chemical substrate pre-treatments.The preparation of ultra-thin oxide layers on mono-crystalline silicon substrate surfaces with ozone dissolved in ultra pure water at ambient temperature was investigated as a low cost alternative to current wet-chemical cleaning and passivation processes in solar cell manufacturing. Surface photovoltage technique was applied as fast, nondestructive, and surface sensitive method, to provide detailed information about the influence of oxidation rate and substrate surface morphology on electronic properties of the oxidised silicon interfaces and subsequently prepared hydrogen terminated surfaces. Sequences of wet-chemical oxidation in ozone containing ultra pure water and subsequent oxide removal in diluted hydrofluoric acid solution could be utilised to prepare hydrophobic substrates, which are predominantly required as starting point for layer deposition and contact formation. On so prepared hydrogen-terminated substrates values of interface state densities Dit,min≈5×1011eV−1cm−2 could be achieved, comparable to values obtained on the same substrates by the standard RCA process followed by HF dip.
Keywords: Silicon solar cell substrates; Ozone; Wet-chemical oxidation; H-termination; Surface photovoltage; Interface states
Passivation of Si-based structures in HCN and KCN solutions by Emil Pinčík; Hikaru Kobayashi; Jaroslav Rusnák; Masao Takahashi; Milan Mikula; Woo Byoung Kim; Michal Kučera; Robert Brunner; Stanislav Jurečka (pp. 8397-8405).
► Confirmation of high efficiency KCN and HCN passivation procedures. ► Decrease of number of nonradiation transitions. ► Decrease of interface defect states density below level 5×1010eV−1cm−2.The contribution deals with passivation of surfaces of c-Si and 6H-SiC by formation of very thin SiO2 films in boiling HNO3 solutions and by passivation of a-Si based double and triple layer structures deposited on Corning glass and c-Si by KCN solutions. The structures are investigated by spectroscopic ellipsometry, charge version of DLTS, C–V, FTIR–DRIFT, and by photoluminescence measuremets at 6K. Newly developed 2nd generation of MOS structures prepared on c-Si with an approx. 3nm SiO2 layer gives typical density of interface defect states of 5×1010eV−1cm−2. Real part of complex refractive index of approx. 3nm thick SiO2 layers is about 1.75. Application of HCN solutions to structure approx. 3nm SiO2/Si (applied as the last technological step) leads to remarkable lowering of absorbance in wavelength region 4000cm−1–2500cm−1. This result indicates a decrease of number of non- radiation transitions in the surface region of oxide/Si structures. Such structures have also the lowest density of interface defect states (observed by Q-DLTS). Application of boiling KCN solutions considerably increases amplitudes of photoluminescence signals coming from different double and triple a-Si based layers deposited on Corning glass. We relate this effect predominantly with reduction of non-radiation transitions in excited region of amorphous structures – with passivation of corresponding defect states in a-Si structures in boiling KCN solutions.
Keywords: PACS; 78.55.Qr; 78.66.Jg; 81.16.Pr; 85.40LsSilicon; Amorphous materials; Passivation; HCN solution; KCN solution; Photoluminescence; DLTS; Spetroscopic ellipsometry; FTIR
The effect of KCN passivation on IR spectra of a-Si based structures by Martin Kopani; Milan Mikula; Naozumi Fujiwara; Masao Takahashi; Emil Pinčík (pp. 8406-8408).
► The contributions presents new results obtained on amorphous silicon based structures passivated in KCN solution. FTIR has been used as dominant research method. ► In the spectra typical features of OH group, hydrogen bridge bonding and SiOCN formation were observed. ► From these results can be drawn the binding of CN to Si through oxygen atoms.From the analysis of IR spectra of double layer structures after KCN passivation the presence of four absorption bands at 720–810cm−1 (assigned as SiC bond), 870–1060cm−1 (assigned as SiH n and SiO bonds), 1930–2200cm−1 (assigned as SiH n bonds) and absorption band around 2360cm−1 (assigned as SiNCO bond) was found. As IR spectra between 1400 and 1600cm−1 (assigned as CH, NH2) and 3200–3300cm−1 (assigned as CH and NH) under influence of KCN passivation did not change we suggest that formation of HCN, CH and NH was eliminated (polymeric HCN). From analysis of absorption bands assigned as SiH n, CN and SiNC (1950–2200cm−1) and absorption bands assigned as SiO bond (1000–1200cm−1) it is evident the different influence of passivation on samples and . In the spectra typical features of OH group, hydrogen bridge bonding and SiSiOCN formation were observed. From these results can be drawn the binding of CN to Si through oxygen atoms.
Keywords: Infrared spectroscopy; Passivation; Amorphous silicon; KCN treatment
Properties of charge states in MOS structure with ultrathin oxide layer by Stanislav Jurečka; Hikaru Kobayashi; Masao Takahashi; Taketoshi Matsumoto; Emil Pinčík (pp. 8409-8414).
► Study of space and energy quantization effects in a MOS structure with ultrathin NAOS oxide layer. ► Analysis of electrical properties of NAOS oxide layer by the STM method. ► Determination of density of interface states.The properties of charge states in metal–oxide-semiconductor (MOS) system are important for the quality of the device containing ultrathin oxide layers. In present study the MOS structures with ultrathin SiO2 layer were prepared on Si(100) substrates by using low temperature nitric acid oxidation of silicon (NAOS) method. Properties of the NAOS SiO2 layer and the charge states in the MOS structure were studied by the scanning tunneling microscopy method and by the capacitance–voltage method. Carrier confinement produces the energy and space quantization effects which remarkably influence of charge states in the MOS structure with ultrathin oxide layer. The properties of charge states in an Al/NAOS–SiO2/Si MOS structure were analyzed by solving the Schrödinger–Poisson equations and results were used in a construction of the theoretical model of the MOS capacitance with the interface states. From the comparison of theoretical capacitance model and experimental C– V curve the density of interface states were determined. The influence of fixed charge in NAOS oxide layer was not observed.
Keywords: Semiconductor; Density of states; Scanning tunneling microscopy (STM); MOS
Surface passivation function of indium-tin-oxide-based nanorod structural sensors by Tzu-Shun Lin; Ching-Ting Lee; Hisn-Ying Lee; Chih-Chien Lin (pp. 8415-8418).
► The ITO nanorods were deposited using the VLS method and the oblique-angle electron-beam deposition system. ► Various surface morphologies of ITO nanorods were used as extended-gate field-effect-transistor pH sensors. ► The sensitivity of pH sensors with 150-nm-length ITO nanorods was 53.96mV/pH. ► The surface of ITO nanorods was passivated using PEC method and examined the function of the PEC treatment. ► The sensitivity of 150-nm-length ITO nanorods pH sensors with PEC treatment was improved to 57.21mV/pH.Employing self-shadowing traits of an oblique-angle electron-beam deposition system, various indium tin oxide (ITO) nanorod arrays were deposited on a silicon substrate and used as extended-gate field-effect-transistor (EGFET) pH sensors. The length and morphology of the deposited ITO nanorod arrays could be changed and controlled under different deposition conditions. The ITO nanorod structural EGFET pH sensors exhibited high sensing performances owing to the larger sensing surface area. The sensitivity of the pH sensors with 150-nm-length ITO nanorod arrays was 53.96mV/pH. By using the photoelectrochemical treatment of the ITO nanorod arrays, the sensitivity of the pH sensors with 150-nm-length passivated ITO nanorod arrays was improved to 57.21mV/pH.
Keywords: Indium tin oxide; Nanorod array; Oblique-angle electron-beam deposition; pH sensor; Photoelectrochemical treatment
The effect of Si substrate preparation on surface morphology and surface composition of In2O3 ultrathin films deposited by rheotaxial growth and vacuum oxidation by P. Kościelniak; M. Sitarz; E. Maciak; J. Szuber (pp. 8419-8424).
► We determined the effect of Si substrate preparation on surface properties of In2O3 (IO) nanolayers deposited by RGVO method. ► Surface morphology of deposited layers was control by AFM method; all the deposited In2O3 (IO) nanolayers exhibit the granular-type surface morphology. ► Surface composition was controlled by XPS method; for the most flat one-step oxidized In2O3 nanolayers deposited on RCA Si substrate the highest contribution of elemental In was observed.In this paper, we present the results of systematic studies of the effect of Si substrate preparation on the surface morphology and surface chemistry of indium oxide nanolayers deposited by the rheotaxial growth combined with in situ oxidation under high vacuum under different oxidation regimes controlled using the atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) methods. The AFM experiments showed that Si substrates prepared by standard chemical cleaning procedure, proposed at Radio Corporation of America (RCA) and after ion bombardment cleaning are almost flat characterized by an average roughness below 0.2nm. For all the deposited indium oxide nanolayers the granular-type surface morphology of different grain sizes was observed. For the most flat one-step oxidized indium oxide (IO) nanolayers deposited on RCA Si substrate there is the highest contribution of elemental In, which is in contrary to the smallest one for the two-step oxidized IO nanolayers deposited at RCA Si substrate, as determined by XPS experiments.
Keywords: Indium oxide; Ultrathin film; RGVO method; Surface composition; Surface morphology; XPS; AFM
Photoemission studies of the surface electronic properties of L-CVD SnO2 ultra thin films by M. Kwoka; L. Ottaviano; J. Szuber (pp. 8425-8429).
► XPS core level studies allowed us to determine the variation of interface Fermi level position for L-CVD SnO2 ultrathin films after the various technological treatments. ► Valence band XPS studies showed the existence of two different bands of filled electronic states localized about 6.0eV and 3.0eV below the Fermi level, respectively. ► The variation of surface electronic properties of L-CVD SnO2 ultrathin films was assigned to the variation of their surface chemistry, including carbon contamination.This work presents the results of systematic X-ray photoelectron spectroscopy (XPS) and photoemission yield spectroscopy (PYS) studies of the surface electronic properties of L-CVD SnO2 ultrathin films submitted to various technological treatments. The interface Fermi level position in the band gap EF– Ev has been determined from XPS analysis of the Sn3d5/2 binding energy position. Such value of the Fermi level position was in a good agreement with the value estimated from the offset of XPS valence band. The variation of interface Fermi level position, after the various technological treatments, has been compared to the change of work function obtained by PYS. Valence band XPS spectra and PYS spectra point to the presence of two different bands of filled electronic states of the L-CVD SnO2 thin films. The first one was localized in the upper part of valence band at the surface at about 6.0eV below the Fermi level, whereas the second one was localized in the band gap at about 3.0eV below the Fermi level. The changes of electronic properties of the space charge layer of L-CVD SnO2 ultrathin films submitted to different technological procedures were assigned to the observed variation of their surface chemistry, including stoichiometry/nonstoichiometry and to the presence of surface carbon contamination.
Keywords: Tin dioxide; L-CVD thin films; Photoemission; Surface electronic properties; Fermi level position; Electronic band gap states