bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐Pressure chemical vapour deposition of tantalum pentoxide films for ulsi devices using tantalum pentaethoxide as precursor
Authors: Treichel H. , Mitwalsky A. , Sandler N. P. , Tribula D. , Kern W. , Lane A. P.
Published: May 2005

A laminar flow low‐pressure chemical vapour deposition (LPCVD) system (LAM IntegrityTM) has been used to deposit tantalum pentoxide (Ta2O5) from Ta(OEt)5 films in the presence of oxygen (O2) at 470 °C at a typical deposition rate of 4 nm min−1. Uniformities of <1.5% (SD 1σ) over a 150 mm silicon substrate were obtained. The layers were annealed under different conditions. It was discovered that the films did not change their stoichiometry as determined by Rutherford backscattering (RBS). The as‐deposited films were amorphous but became crystalline (β‐Ta2O5) at temperatures > 700 °C. The transmission electron microscopy (TEM) results on crystallisation behaviour were supported by X‐ray diffraction data. The electrical properties of the Ta2O5 films have been characterised using MIS (metal/insulator/silicon) capacitor structures. Leakage values of <10−6 A cm−2 at 6 MV cm−1 equivalent applied electric field and breakdown strengths of >7 MV cm−1 at 1.6 μA were obtained for annealed layers. Compound dielectric constants (native silicon oxide thickness of about 2.5 nm plus Ta2O5 of various thicknesses) between 14 and >30 have been measured. The electrical properties reveal the potential use of Ta2O5 as a storage capacitor dielectric in 64 and 256 Mbit DRAM (dynamic random access memory) devices.
The pyrolytic LCVD of high‐purity gold tracks from alkyl (trialkylphosphine) gold(I) complexes
Authors: Davidson J. L. , John P. , Milne D. K. , Roberts P. G. , Jubber M. G. , Wilson J. I. B.
Published: May 2005

The pyrolytic LCVD of high‐purity gold tracks from the organogold(I) complex MeAuPMe3 is reported. The tracks were deposited onto (100) n‐type single‐crystal silicon with a thermally grown oxide layer (3000 Å), single‐crystal GaAs with an intact native oxide layer and polycrystalline diamond films upon (100) silicon using the output from an argon ion laser (Coherent Innova 100‐10) at 514.5 nm. Deposits were grown at a range of scan speeds from 0 to 200 μm s−1 and characterised by SEM, SIMS, LIMA and scanning profilometry. Electrical resistivities as low as 7.04 μΩ cm, within a factor of three of that of bulk gold, were achieved at scan speeds below 156.3 μm s−1. These are consistent with deposit purities of better than 99% (LIMA) without the need for a post‐deposition annealing step.

The relationship between power density, beam residence time and deposition rate was measured. The morphology of the deposit from the onset of detectable nucleation through to the formation of continuous tracks was analysed by SEM micrographs of deposits grown at successively increasing power densities. The nucleation process was found to be substrate‐dependent. Changes in deposit morphology with power density and scan speed were observed. These include periodicity in track width and at high power densities the development of ‘volcano’‐shaped profiles.

The formation of a phosphorus‐based interfacial layer, exclusive to laser deposition upon GaAs, is evidence for a reaction between the PMe3 and GaAs.
A modified plasma source for controlled layer thickness synthesis in laser pulse vapour deposition (LPVD)
Authors: Dietsch R. , Mai H. , Pompe W. , Völlmar S.
Published: May 2005

The conventional thin film deposition equipment of LPVD has been modified for the preparation of nanometre‐layer stacks of uniform thickness at reduced target/substrate separation. Therefore the planar target was replaced by a cylindrical one and the target motion regime has been modified.

During thin film deposition a substrate translation is preferred instead of the usual rotation technique. With this arrangement the emission characteristic of the plasma source can be computer controlled and tailored via a stepper‐motor‐driven manipulator for the desired layer thickness profile across an extended substrate. Thus, for example, a homogeneous film thickness is obtained even for lower target/substrate distances, and an appropriate deposition rate can be maintained.

First applications of the equipment are explained and compared with typical results of the conventional technique.
Low‐temperature plasma‐assisted processes for fabrication of SiO2/Si heterostructures
Authors: Lucovsky Gerald
Published: May 2005

In the conventional high‐temperature thermal oxidation and rapid thermal oxidation processes used to fabricate commercial SiO2/Si structures at ∼850–1050°C, the SiO2/Si interface and the bulk oxide are formed at the same time. We have developed a low‐temperature process for the formation of SiO2/Si structures at 200–300°C that separately controls and optimizes the properties of the SiO2/Si interface and the bulk SiO2. This has been accomplished by separating interface formation by plasma‐associated oxidation from bulk oxide plasma‐assisted deposition. The oxidation step (i) removes residual C contamination from the Si surface, (ii) prevents N incorporation at the interface from the O atom source gas N2O and (iii) forms an oxide layer ∼0.6 nm thick and an SiO2/Si interface with a trap density, Dit ≈(1–4) × 1010 cm−2 eV−1. This type of process has also been extended to the deposition of multilayer oxide–nitride–oxide dielectrics.
Laser‐induced deposition of aluminium on gallium arsenide from trimethylamine alane
Authors: Bourée J. E. , Tonneau D. , Sayah A. , Frugier T. , Boulahia A. , Mencaraglia D. , Siffre J. M.
Published: May 2005

Aluminium microstructures (dots or strips) have been photodeposited on GaAs substrates via the decomposition of a solid precursor, the 2:1 hydride adduct of Al, called trimethylamine alane (TMAA).

The dissociation of TMAA, the vapour pressure of which can be varied between 0.4 and 1 mbar by dilution in hydrogen carrier gas, has been achieved via a pyrolytic process using a CW Ar+ laser operating in the visible range (488–514 nm). This decomposition reaction occurs at laser powers higher than 0.3 W, i.e. at laser‐induced temperatures higher than 130°C, and leads to the formation of high‐purity aluminium strips as observed from Auger electron spectroscopy (AES) and energy‐dispersive X‐ray analysis (EDX) data. The deposition rates are in the range 50–1400 Å s−1. The minimum of line resistivity measured versus scanning speed and laser power is 6.5 μΩ cm.

The photolytic decomposition of TMAA has been performed at room temperature within the laser spot area using a CW UV laser (intracavity frequency doubler emitting at 257 nm). The formation of aluminium clusters has been observed at very low deposition rates (20 Å s−1). However, these tiny clusters react quickly with oxygen and are transformed into alumina clusters.

All these results have been tentatively explained on the basis of the surface reactivity of H2 and TMAA regarding GaAs or Al, as obtained by other workers through surface science techniques and mass spectrometry.
Laser cleaning: Laser‐induced removal of particles from surfaces
Authors: Zapka W. , Ziemlich W. , Leung W. P. , Tam A. C.
Published: May 2005

Pulsed‐laser‐induced removal of particles from surfaces is a new cleaning technique. This laser cleaning can be performed on dry surfaces as well as on wet surfaces with a micron‐thick liquid film during pulsed laser irradiation to provide enhanced removal efficiency. Using the latter technique, to be called ‘steam laser cleaning’ here, we are able to remove epoxy, alumina, silicon or gold particles with diameters in the range 0.1–10 μm from silicon and other surfaces.
Damage of STM tips during nanofabrication
Authors: Yokoi N. , Namba S. , Takai M.
Published: May 2005

The STM tip shape was found to change when nanofabrication using a scanning tunnelling microscope (STM) was attempted by applying voltage pulses between the tip and the sample. This change, which is considered to be caused by the voltage pulses, was studied systematically to investigate the thermal contribution to nanofabrication using STM tips. The tips become easily damaged as the pulse amplitude and pulse width increase or the tunnelling gap decreases. Thermal reaction, including thermochemical reaction, is considered to play an important role in such nanofabrication.
Pulsed laser deposition of some II–VI compounds and alloys
Authors: Aydinli Atilla , Compaan Alvin D.
Published: May 2005

Pulsed laser deposition (PLD) of materials is a growing field with applications to many systems. With many materials, however, a major problem is particulate formation due to splashing of molten droplets or ablation of solid clusters from the target. For the case of II–VI semiconductors we have found that careful selection of the laser power density and appropriate mastering of the beam could reduce particulate formation to a negligible level even with the use of pressed targets. In this work we have deposited a number of II–VI semiconductors and their alloys, using XeCl and Nd:YAG lasers, from pressed and bulk targets onto various substrates in high vacuum. The ternaries of ZnTe and ZnSe as well as of ZnTe and CdTe were studied in detail. We determined the optimum growth temperatures and deposition rates for the growth of optical quality films. X‐ray diffraction, optical absorption, energy‐dispersive X‐ray analysis and Raman scattering were used to characterise these films or grain size and orientation, optical band gap and alloy effects on photon bands.
Excimer laser micromachining
Authors: Ihlemann J. , Schmidt H. , Wolff‐Rottke B.
Published: May 2005

The machining of several materials such as polymers, metals and ceramics using excimer lasers (193, 248 and 308 nm) was investigated. By photoablation, micrometer resolution can be achieved for polymers if the wavelength and fluence are chosen properly. High‐definition processing of metals is complicated by the occurrence of surface melting. An interaction between the ablation plume and the walls of the laser‐drilled holes leads to hole widening in the case of polymers at high fluences. For small structures (<100 μm) all materials investigated show a size‐dependent ablation rate. This effect has to be taken into account if a precise ablation depth is required for a pattern with structures of different sizes.
Ceramic thin films deposited on Si(100) by laser ablation: Application as buffer layers for YBa2Cu3O7 films
Authors: Sánchez F. , Varela M. , Queralt X. , Carcía‐Cuenca M. V. , Palau J. , Aguiar R. , Morenza J. L.
Published: May 2005

Ceramic thin films of yttria‐stabilised zirconia (YSZ), SrTiO3(STO) and CeO2 have been deposited on Si(100) substrates by laser ablation. The films have been characterized by X‐ray diffractometry, field emission scanning electron microscopy and secondary ion mass spectrometry (SIMS). The effects of the oxygen partial pressure during deposition and the substrate temperature were studied. All the films have preferential orientation: (h00) and (hh0) for STO and (hhh) for CeO2 and YSZ. The films show a low density of particulates and a very smooth surface. SIMS profiles indicate a low interdiffusion between film and silicon. One of the applications of these materials is their use as a buffer layer for the growth of YBCO on silicon. Because both materials are highly reactive, it is necessary to put a barrier between YBCO and silicon. For this purpose we used the ceramic films previously deposited in order to obtain superconducting YBCO films. The deposited YBCO films present good superconducting properties with zero resistance at temperatures between 80 and 85 K.
Redox reactions on modified bilayer lipid membranes for biosensing device
Authors: Krysiński Pawel
Published: May 2005

Suitably modified bilayer lipid membranes (BLMs) offer exceptionally good opportunities for probing the electric field effects on charge transfer and redox reactions in biosensor and molecular electronics research and development. This work presents an attempt to form an ultrathin electron‐conducting matrix for a biosensing redox device on the basis of a BLM modified with tetracyano‐p‐quinodimethane (TCNQ), a well‐known compound forming charge transfer complexes of ‘organic metal’ behavior. The rationale behind the choice of membrane modifier was the reports of its unusual rectifying current–voltage characteristics when incorporated into BLMs alone or as part of an σ‐bridged donor–acceptor molecule of C16H33–Q3CNQ (Z‐β‐(1‐hexadecyl‐4‐quinolinium)‐α‐cyano‐4‐styryldicyano methanide) deposited in the form of a Langmuir–Blodgett film.
The photovoltage signals of bacteriorhodopsin in Langmuir–Blodgett films with different molecular orientations
Authors: Ikonen Marjo , Sharonov Alexey , Tkachenko Nikolai , Lemmetyinen Helge
Published: May 2005

The photoresponse of bacteriorhodopsin (bR) has been studied in Langmuir–Blodgett (LB) films bR was deposited by vertical dipping as x‐ or z‐type monolayers and as z‐type multi layers between stearic acid LB films. The electrodes used were a transparent vacuum‐deposited ITO on a quartz substrate and an InGa metal alloy. The signals were observed from samples containing a single bR layer or five bR layers both at room humidity and in water‐saturated conditions. The photoelectric signals of x‐ and z‐type monolayers had opposite polarities and both had two exponential kinetics on a microsecond time scale with time constants of about 10 and 70 μs. The amplitude of the fast negative component of the signal of a bR monolayer was 0.4 mV, in the opposite direction to that in which protons were pumped. The amplitude due to five layers was five times as high as that due to a monolayer. The ratio between the amplitudes of the fast negative component and the slow positive part of the signal, in the proton‐pumping direction, was 1:3. The photoresponse signal saturated with a light intensity of about 1.7 mJ cm−2, which is equivalent to a photon density of 0.5 Å−2. The activation energy of the bR photovoltage was 75 ± 5 kJ mol−1 in the temperature range between 17 and 35°C.
A study of the effect of in situ doping on the crystallinity of LPCVD polysilicon
Authors: Hitchman Michael L. , Jones Cameron W. , Zhao Junfu , Shamlian Sarkis
Published: May 2005

Results are presented for the degree of crystallinity, determined by Raman spectroscopy, of in situ B‐doped LPCVD polysilicon as a function of deposition temperature. The results are compared with those reported in the literature for P‐doped polysilicon and it is found that for B doping full crystallinity of the layer is achieved at a significantly lower deposition temperature than is required for P doping. An attempt to understand this effect is made in terms of a quantitative model which allows an estimation of values for silicon self‐diffusivity and which is in accord with the experimental observations.
Modification of the dark and photoconductivity and the optical transmittance of solution‐grown CdS thin films
Authors: Sebastian P. J. , Sanchez A. , Nair P. K.
Published: May 2005

Very interesting behaviour is shown by chemically deposited CdS thin films for optoelectronic applications after air and vacuum (10−5 Torr) annealing. Vacuum annealing of samples at about 100°C caused the dark conductivity to improve by five orders of magnitude. The dark and photoconductivity of air‐annealed (at around 200°C) samples increased by seven and two orders of magnitude respectively. Air‐annealed (at 350°C for about 2 min) samples exhibited a very quick photoresponse (<2 s for two decades of photocurrent decay) with σp/σd ≈ 105 for a bias of 10 V, which may be exploited for photodetector applications. Air or vacuum annealing of samples for a minimum of 10–15 min caused the optical transmittance above the band edge to increase by 10%–15% and annealing the sample at 200°C caused the absorption edge to shift towards the longer‐wavelength region compared with the as‐prepared and 100 and 350°C annealed films.
Evidence for solid state electronic conductivity in mixtures of a porphyrin and its two‐electron oxidation product
Authors: Milgrom Lionel R. , Hill Jonathan P. , Bone Stephen
Published: May 2005

Conductivity measurements demonstrate that in the presence of toluenesulphonic acid, 1:1 mixtures of mesotetrakis(3,5‐di‐t‐butyl‐4‐hydroxyphenyl)porphyrin and its two‐electron oxidation product give materials whose degree of semiconductivity is dependent on the toluenesulphonic acid concentration in the solid.
On the electro‐optic properties of single crystals of sodium, potassium and rubidium acid phthalates
Authors: Miniewicz Andrzej , Bartkiewicz Stanislaw
Published: May 2005

The linear electro‐optic (Pockels) effect in a series of alkali metal acid phthalate crystals has been studied. Single electro‐optic coefficients r and r for sodium (NaAP), potassium (KAP) and rubidium (RbAP) acid phthalates have been measured by employing the modified Mach–Zehnder interferometric technique. The best electro‐optic crystal in this series is RbAP with r = 9.10 × 10−12 m V−1, r = 3.05 × 10−12 m V−1 and a sizable figure of merit for electro‐optic phase retardation, comparable with that of KDP. The dispersion properties of the electro‐optic coefficients for KAP are discussed in detail.
A comparative investigation of the oxidation of silicon using H2/O2, TCA/O2 and HCl/O2 mixtures
Authors: Ahmed W. , Ahmed E. , Armour D. G.
Published: May 2005

The oxidation of single‐crystal silicon wafers has been investigated using an industrial thermal oxidation system. The growth characteristics and electrical properties of the oxides resulting from pure hydrogen/oxygen (H2/O2), trichloroethane/oxygen (TCA/O2) and hydrogen chlorid/oxygen (HCl/O2) mixtures have been investigated and compared. The addition of both HCl and TCA to oxygen produces higher growth rates and improved electrical characteristics. It is shown that the oxidation rate for TCA/O2 is approximately 30%–40% higher than for HCl/O2 and that comparable electrical properties can be readily obtained. A TCA/O2 ratio of 1 mol% gives the optimum process for VLSI applications, though 3 mol% HCl/O2 gives comparable results. It is suggested that the overall mechanisms governing the processes are similar. However, the TCA process is a safer and cleaner alternative because it generates HCl in situ in the oxidation chamber.
Neural network fitting and prediction of polarisability tensors for aromatic hydrocarbons
Authors: Munn R. W. , Munn N. S.
Published: May 2005

A standard back‐propagation neural network is used to correct input semi‐empirical molecular orbital calculations of polarisability tensors to fit experimental data for aromatic hydrocarbons. The method readily yields the correct component normal to the molecular plane but is restricted by a small training set. The network is also used to predict polarisability components for structures input as the pattern of rings fused to a central benzene ring. Semi‐quantitative predictions are obtained depending on the size and method of presentation of the training set.
Laser activation and metallisation of oxide ceramics
Authors: Shafeev G. A.
Published: May 2005

UV excimer laser irradiation of oxides such as SrTiO3, PbTi1 − xZrxO3 (PZT) and Al2O3 results in the formation of colour centres. These colour centres mediate catalytic activity for electroless plating from Cu and Ni solutions. The adherence of the metal deposits to the as‐sintered ceramic surfaces is excellent.
Structure of 2‐(iminocoumar‐3‐yl)‐4‐(coumar‐3‐yl)‐thiazole, C2lHl4N2O3S
Authors: Baumer V. N. , Ponomaryov O. A. , Novikov A. I. , Lakin E. E. , Kuznetsov V. P.
Published: May 2005

We have determined the structure of 2‐(iminocouma‐3‐yl)‐4‐(coumar‐3‐yl)‐thiazole, C21H14N2O3S, Mr=372.4, λ = 0.71073 Å, monoclinic, space group P21/n, a = 9.472(2) Å, b = 11.284(2) Å, c = 15.821(3) Å, β = 86.50(2)°, V = 1687.9(6) Å3, Z = 4, Dx = 1.465 Mg m−3, μ(Mo Kα) = 0.207 mm−1, F(000) = 768, S = 1.91, R = 3.82%, wR = 3.26% for 1251 observed reflections (F > 6σF). In the observed conformation of the molecule the imino group forms an intramolecular H…S bond of length 2.26 Å and the carbonyl oxygen makes a short contact with the hydrogen atom of the thiazolyl cycle. The molecule is planar. In the crystal structure a particular disorder of about 20% of molecules is observed with respect to the pseudo‐mirror plane which is perpendicular to the molecular plane and passes through the thiazolyl N atom and the middle of the SCH bond. The disagreement found between the observed conformation and that predicted by molecular mechanics calculations is explained by the tendency of the molecule to have the lowest value of dipole moment due to minimisation of the electrostatic contribution to the energy.
Electroluminescence from phenylenevinylene‐based polymer blends
Authors: Vestweber H. , Oberski J. , Greiner A. , Heitz W. , Mahrt R. F. , Bässler H.
Published: May 2005

The electroluminescent behaviour of films of poly(phenylphenylenevinylene) (PPPV), of PPPV blended with polystyrene (PS) and of PS doped with oligo(phenylenevinylene) sandwiched between indium–tin oxide (ITO) and Al contacts has been investigated. Polymer blending increases the relative quantum efficiency by up to two orders of magnitude. Studying the cell performance under application of rectangular voltage pulses as a function of temperature indicates that (i) hole injection at the ITO contact occurs by tunnelling, (ii) tunnel injection of electrons at the cathode is promoted by a space charge field across an interfacial Al2O3 layers and (iii) leakage of holes through the cathodic barrier is the main loss mechanism for holes.
The kinetics of charges in dry bacteriorhodopsin Langmuir–Blodgett films—an analysis and comparison of electrical and optical signals
Authors: Ikonen Marjo , Sharonov Alexey Yu. , Tkachenko Nikolai V. , Lemmetyinen Helge
Published: May 2005

The decay of the M intermediate and the recovery kinetics of bacteriorhodopsin (bR) were detected optically in dry and wet bR Langmuir–Blodgett (LB) films and electrically in dry films. From the electrical signals the kinetics of the proton motion was distinguished from the cell function and it was found to be equal to that determined optically for the M intermediate decay. The rate‐determining step for the recovery rate of bR was found to be the M state.
Visible fluorescence on IR excitation of polar dimethylaminobenzylidene 1,3‐indandione crystals
Authors: Valkunas L. , Juodzbalis D. , Urbas A. , Gruodis A. , Durandin A. D. , Silinsh E. A. , Klimkans A. , Larsson S.
Published: May 2005

A novel non‐linear fluorescence (NLF) effect in polar dimethylaminobenzylidene 1,3‐indandione (DMABI) crystals is presented and discussed. A single crystal or vacuum‐evaporated layer of DMABI excited in the IR region at 1064 nm (by a Q‐switched YAG laser) emits red light in the visible region of the spectrum at 600–740 nm depending on the DMABI crystalline modification. This anti‐Stokes luminescence shows a quadratic dependence on the exciting light intensity which transforms to a linear dependence at very high excitation intensities. The observed NLF effect under IR excitation is determined by optical transitions into intermolecular charge transfer (CT) states. It has been suggested that the photoexcited singlet 1CT excitations may either interact in a quadratic singlet–singlet (1CT + 1CT) annihilation reaction or, more probably, form long‐lived triplet 3CT excitons via a hyperfine interaction effect which may subsequently annihilate in a similar bimolecular fusion reaction (3CT + 3CT). In both cases the excited molecular singlet state S1 is formed and thus the NLF effect is due to singlet–singlet or triplet–triplet fusion of CT excitons. A detailed energy diagram and kinetic description of the model are presented. Quantum chemical calculations of the electronic structure of the DMABI molecule illustrate the dipolar nature of its ground and excited states.
A photolithographic technique for patterning spin‐coated polyaniline films
Authors: Di Bartolomeo C. , Barker P. , Petty M. C. , Adams P. , Monkman A. P.
Published: May 2005

Solvent‐cast polyaniline films have been deposited by spin coating and photolithographic techniques used to pattern the films to a resolution of 15–20 μm. This approach is then used successfully to deposit the polymer on the gate areas of an array of silicon field effect transistors.
Polyalkylthiophene thin films and their characterisation with transmission spectroscopy
Authors: Heinämäki A.
Published: May 2005

Polyalkylthiophene thin films have been prepared to enable the characterisation of the films with transmission spectroscopy and profilometry for the first time. The optical properties of the films as a function of annealing temperature are discussed. The changes in absorption with time are related to thermochromism.
Relationship between microscopic and macroscopic structures of organic thin films for SHG
Authors: Voigt‐Martin I. G. , Zhou E. , Simon P. , Garbella R. W. , Yan D. , Paulus W. , Ringsdorf H.
Published: May 2005

The experiments described in this paper were undertaken in order to obtain information about the relationship between the structure and non‐linear optical properties (second‐harmonic generation) of organic thin films. For this purpose, two closely related dyes, diones and tetrones, were compared, both of which are shown to have large hyperpolarisabilities. Their microscopic properties are investigated by conformational analysis and electron diffraction. It could be shown that detailed knowledge about the structure and the adjacent neighbour packing can be obtained from conformational analysis and electron diffraction in order to understand the non‐linear optical properties of the two dyes.
Group 2 element and related compounds as chemical vapour deposition precursors for high‐temperature superconducting metal oxides
Authors: Barron Andrew R. , Rees William S.
Published: May 2005

The advent of high‐temperature superconducting metal oxides (SMOs) has prompted an increasing number of studies aimed at the development of new routes to their syntheses, in particular in the form of thin films. The preferred method in this regard has been that of chemical vapour deposition (CVD); however, significant difficulties have been associated with the efficacy of commercial precursors for the group 2 metals, in particular those of the bis(β‐diketonates) of barium, whose co‐ordinative unsaturation leads to cluster formation. The development of alternative β‐diketonate precursor systems has focused upon the synthesis of stable Lewis acid‐base complexes by either inter‐ or intramolecular stabilisation. The results of these studies are described herein, along with a review of the research to date on non‐β‐diketonate derivatives of the group 2 metals, including organometallic, halide, amide, carboxylate and alkoxide compounds. On the basis of the results to date, a series of goals for the synthesis of the ideal precursor are discussed.
The influence of chlorine on the optical properties of monoclinic lead phthalocyanine thin films
Authors: Krier A. , Abass A. K. , Collins R. A.
Published: May 2005

The optical transmittance and absorption of thin films of monoclinic lead phthalocyanine have been studied as a function of exposure to chlorine and air. The effect of chlorine on the refractive index and dielectric constant of freshly prepared films was estimated from reflectivity data in the photon energy range 2.1–2.6 eV. Responsivity and recovery from gaseous exposure were studied with regard to the applicability of lead phthalocyanine to the fabrication of an optical chlorine sensor.
Formation of silicon nitride films by remote plasma‐enhanced chemical vapour deposition
Authors: Alexandrov Sergei E. , Hitchman Michael L. , Shamlian Sarkis
Published: May 2005

In this paper we describe the growth of silicon nitride from nitrogen and silane for the first time by capacitively coupled remote PECVD. We report on the effect of process parameters on the composition and properties of the deposited films and we show that by adjustment of these parameters it is possible to produce high‐quality material which could be of interest for electronic applications. Of particular note is that the growth rate is about one order of magnitude higher than any previously reported for nitride growth with remote PECVD using molecular nitrogen as the nitrogen source. We also discuss the mechanism of growth and propose that electron excitation of nitrogen and silane occurs in the gas phase, producing SiHx species which are adsorbed on the growing surface. The nitrogen is then incorporated into the layer by heterogeneous reaction.
In‐Situ mechanistic studies of the reaction of trimethylgallium and phosphine in zeolite H‐Y
Authors: Anderson M. W. , Logothetis G. K. , Pemble M. E. , Taylor A. G. , Wallace N. C. , Yates H. M.
Published: May 2005

Coherent anti‐Stokes Raman scattering (CARS) has been utilised to monitor the decomposition of trimethylgallium (TMGa) on the reactive internal surface of the protonated form of zeolite Y under metal organic chemical vapour deposition (MOCVD) conditions designed to produce GaP deposits that exhibit quantum‐size effects. The CARS data clearly reveal the facile room temperature decomposition of TMGa in the zeolite, as evidenced by the detection of increasing levels of methane with increasing reaction time. In addition, the zeolite samples were analysed by solid state nuclear magnetic resonance with magic angle spinning (MAS NMR) before reaction, after reaction of TMGa and after subsequent reaction with phosphine at 300°C. These data reveal that TMGa reacts with acid sites in the zeolite 12‐rings, resulting in species containing methyl groups. Subsequent exposure to phosphine removes these methyl group protons, leaving various, as yet not fully characterised, phosphorus species. Exposure to phosphine does not appear to regenerate the acid sites on the zeolite.
Controlling the interface between II–VI and III–V semiconductors
Authors: Zahn Dietrich R. T.
Published: May 2005

This paper describes ways in which the interface between II–VI and III–V semiconductors can be controlled so as to suppress or alter commonly observed interfacial reactions. This will be done using CdTe/InSb and CdS/InP heterostructures as examples. In the case of CdTe/InSb a modification of the interfacial properties is achieved by a variation in the II/VI ratio offered to the surface during growth, while the influence of Sb interlayers is studied for CdS on InP. Information on the interface properties is obtained from Raman spectroscopy. While structural and electronic properties of the II–VI layer can be deduced from the scattering intensities of its characteristic vibrational modes, the formation of interfacial compounds is observed by the appearance of scattering intensity in a different spectral range, which is consistent with the formation of III2VI3 compounds. The potential of Raman spectroscopy for on‐line in situ monitoring of growth processes will be displayed.
Phase transition from the cubic to the hexagonal modification in thin CdS films on InP(110)
Authors: Zahn D. R. T. , Kudlek G. , Rossow U. , Hoffmann A. , Broser I. , Richter W.
Published: May 2005

CdS films were prepared by molecular beam epitaxial growth on clean cleaved InP(110) substrates. Films with thicknesses in the 200 nm range were studied by optical techniques: spectroscopic ellipsometry, reflection and photoluminescence. The film thickness and the dielectric function of the films are evaluated from the ellipsometry data. The feature in the imaginary part of the film dielectric function which is induced by the E1 interband transition in CdS is found to be extremely sensitive to the crystal modification. A splitting of this feature occurring at approximately 200 nm indicates a phase transition in the thin films from the cubic to the hexagonal modification. This is confirmed by reflection measurements which show two series of reflection loops for both modifications for film thickness exceeding 200 nm. The energy positions of the free excitons of the hexagonal and cubic modifications are derived. In addition, the band gap for the cubic modification is determined for the first time. The photoluminescence spectra also reveal cubic and hexagonal contribution of donor–acceptor pair recombinations. From the excitonic transitions attempts are made to identify the main impurities in the layers.
High‐density and optical non‐linearity effects in epitaxially grown ZnTe layers
Authors: Wagner H. P. , Festner S. , Stanzl H. , Kudlek G. , Presser N.
Published: May 2005

We investigated the high‐density luminescence and non‐linear transmission of ZnTe layers grown by metal‐organic vapour phase epitaxy (MOVPE). For the high‐density luminescence we compared ZnTe layers on (001) GaAs substrate with free‐standing ZnTe layers of equal thickness. At high excitation intensities a strong luminescence P band appears a few meV below the free exciton energy which is assigned to resonant exciton‐scattering processes. A second strong luminescence N band occurs only in free‐standing layers. It shows a remarkable red shift with increasing intensity and becomes the dominant emission for an excitation intensity Iexc > 1.5 MW cm−2. This lower‐energy band was interpreted as electron–hole plasma recombination.

The optical non‐linearity of thin ZnTe layers in the excitonic region was investigated by pump‐and‐probe experiments at 2 K and room temperature (RT). For these experiments we used two different pump energies, one above (at 2 K and RT) and one below (at 2 K) the band gap energy. In all cases a red shift and a large non‐linear decrease in the excitonic absorption with increasing pump intensity was observed. The experimental results can be explained by many‐body effects of exciton screening.
Dynamics of impurity‐related optical switching in CdS near the band edge
Authors: Schmolke R. , Schöll E. , Nägele M. , Gutowski J.
Published: May 2005

We present a dynamic theory related to experiments on the induced transmission of doped CdS crystals under pulsed laser excitation at 2 K at frequencies just below the band gap. Numerical simulations of the optical switching front which describes the non‐linear spatio‐temporal dynamics of the switching process from low to high transmittivity and back are performed for two different two‐level models. These are associated with two different bleaching mechanisms of the acceptor–conduction band transition.
Gain and dynamics of excitons in MOVPE‐grown ZnSe/ZnSxSe1 − x heterostructures
Authors: Umlauff M. , Kalt H. , Langbein W. , Wind O. , Geyzers K. P. , Heuken M.
Published: May 2005

Optically pumped stimulated emission in ZnSe/ZnSxSe1 − x heterostructures grown by MOVPE has been observed up to 170 K. Gain measurements have been performed using the variable stripe length method. The underlying gain mechanism at 25 K is atributed to an excitonexciton scattering process. Photoluminescence excitation spectra and the temporal evolution of the luminescence indicate a transfer process from the ZnSxSe1 − x barrier into the ZnSe active layer.
Peculiarities of the quantisation of the energy spectrum of gapless semiconductors in a magnetic field under space confinement
Authors: Germanenko A. V. , Minkov G. M. , Rumyantsev E. L. , Rut O. E.
Published: May 2005

An exact solution for the zero boundary condition of the problem of carriers in spatially confined gapless semiconductors in a magnetic field is presented. Three cases are analysed: (i) the semiconductor occupies a half‐space and the magnetic field orientatin is H ⟂ n (n is the surface normal); (ii) and (iii) a film of a gapless semiconductor at two orientations of the magnetic field, i.e. H ⟂ n and H | n respectively. It is shown that since the energy spectrum of gapless semiconductors is formed by strong relativistic spin–orbit interaction, significant peculiarities of the quantisation of the electron energy spectrum occur in all cases considered. Experiments to check the results obtained are discussed.
Anisotropy of dissolution and microrelief of II–VI semiconductor compound surfaces
Authors: Yablonskii G. P.
Published: May 2005

The shape, crystallographic orientation and size of microrelief elements of various surfaces of CdS, ZnSe and ZnO monocrystals after chemical etching have been studied. When illuminated with a focused laser beam, the microrelief creates a symmetric light pattern, or light figures, on the opposite surface whose shape corresponds to the crystal symmetry.

The effects of the dissoltion rate and etching time on the form, size and angles of the microrelief elements in the temperature interval from 263 to 333 K were investigated. During etching, laser light was also used to convert the process of selective etching into a polishing process. To elucidate the relationship between the crystallographic orientation of the microrelief elements and the dissolution anisotropy, mean etching rates were determined and polar diagrams of resistance to dissolution were constructed for {1120} and {0001} by the Gross method. The relation between the kinetics of dissolution and the structure of the chemical bonds is discussed.

The light figures formed by the surface microrelief enabled us to carry out the approximate orientation of semiconductor planes and solid samples. In the early stages of dissolution one may determine the density and distribution of the microscopic etch pits. The microrelief created on the side surfaces and the ‘fully reflected’ mirrors of II–VI semiconductor lasers pumped by electron beam or optical radiation promote the multiple enhancement of laser power and efficiency.
Stimulated emission in ZnSxSe1 − x/ZnSe heterostructures grown by MOVPE
Authors: Nägele M. , Weckendrup D. , Neukirch U. , Gutowski J. , Geyzers K. P. , Heuken M.
Published: May 2005

Non‐linear and stimulated emission of ZnSxSe1 − x/ZnSe multilayer structures grown by MOVPE on GaAs is investigated by means of high‐density excitation spectroscopy using a high‐resolution pulsed excimer‐dye laser system as well as a picosecond titanium–sapphire laser for time‐resolved measurements. Heterostructures with ZnSe layers or single and multiple quantum wells were grown in which the ZnSe layer widths were varied between 1 nm (strong quantum confinement) and 500 nm (quasi‐bulk situation). The sulphur concentration in the ZnSxSe1 − x buffer, barrier and cap layers was chosen between x = 0.045 and x = 0.74 in order to find the most promising compromise with regard to maximum band offset to ZnSe for most efficient carrier confinement and suitable waveguiding properties depending on variation in the refractive index, and to highest structural quality of the actively emitting ZnSe layers. Stimulated emission is found to occur in all samples, being brightest in the sample with the lowest sulphur concentration in the cap and barrier layers. Its dynamical properties point to a probable interpretation in terms of electron–hole plasma creation, which, however, may not be the basic process in narrow‐quantum wells or strongly structurally disturbed samples.
Experimental and theoretical aspects of electrical characteristics of Au/ZnSe/GaAs heterostructures
Authors: Martinez R. , Schmeits M. , Evrard R.
Published: May 2005

We present results of a theoretical and experimental study of AuZnSeGaAs heterostructures. In the theoretical part we report the band diagrams, charge densities and static I–V curves obtained from a detailed numerical analysis. In the experimental part we give the results for the static I–V curves and frequency‐dependent admittance and impedance at different bias voltages for an AuZnSeGaAs heterostructure with a ZnSe layer of 2.75 μm thickness. An explicit analysis of the data shows that the system can be represented by an equivalent circuit of two RC elements in series corresponding to the ZnSeGaAs and AuSe heterojunctions.
Luminescence dynamics of CdSe quantum dots
Authors: Wind O. , Kalt H. , Woggon U. , Klingshirn C.
Published: May 2005

We present results of time‐resolved luminescence measurements of CdSe quantum dots embedded in glass with radii around 20 Å using intense picosecond excitation resonant into the first excited hole state of a photodarkened sample. Distinct luminescence bands with different spectral widths and positions are found. Their decay on nano‐ and subnanosecond time scales reflects three different relaxation processes. The fastest luminescence component is discussed in terms of the direct recombination of the excited electron–hole pair, the slower components as being due to the recombination from surface‐related states.
Origin of the stokes shift in semiconductor quantum wells
Authors: Hagston W. E. , Harrison P. , Stirner T.
Published: May 2005

Excitonic energy levels have been calculated in CdTe quantum wells with Cd1−xMnxTe barriers. It has been shown that the introduction of small‐scale (relative to the exciton Bohr radius) interface disorder, which either preserves or breaks the inversion symmetry, can produce appreciable Stokes shifts between optical absorption and emission and that the associated line‐widths can remain narrow. A criterion for the existence of high‐quality interfaces, based on optical spectra, is described.
Laser processes in wide gap II–VI semiconductors
Authors: Klingshirn C.
Published: May 2005

After a brief historical remark about the evolution of scientific interest in wide gap II–VI compounds, we review the various laser processes which have been identified in bulk materials and thin layers during the last 25 years. We then proceed to quantum wells and superlattices and stress the differences from III–V compounds. We finish by considering the exploitation of specific properties of widegap II–VI compounds for light‐emitting and laser diodes.
The role of ZnS in ZnS/SrS:Ce,Cl multilayered TFEL devices
Authors: Velthaus K. O. , Mauch R. H. , Schock H. W.
Published: May 2005

Different ZnS/SrS:Ce,Cl multilayered electroluminescent devices have been prepared by a multisource deposition method. The highest luminance achieved in this investigation is 1540 cd m−2 at 1 kHz using a stack of nine alternating layers of ZnS and SrS:Ce,Cl; the highest luminance in the blue exceeds 14 cd m−2 at 60 Hz, 50 μs pulse excitation. The influence of the ZnS thickness on device performance and stability has been investigated. The electrical and optical behaviour of standard and multilayered devices in time‐resolved measurements is compared.
Dynamical aspects of free exciton–magnetic polaron formation in CdTe–Cd1 − xMnxTe quantum wells
Authors: Goodwin J. P. , Hagston W. E. , Harrison P. , Stirner T.
Published: May 2005

Calculations of the energies of magnetic polarons formed by free excitons localised in non‐magnetic CdTe wells next to magnetic Cd1 − xMnxTe barriers are presented. A comparison with recent time‐resolved spectroscopy results allows insight to the physical aspects governing the dynamics of the formation of the polarons. It is shown that the experimentally measured energy shift is not the polaron energy itself but the difference between this and the change in the exciton binding energy. The latter is calculated within the envelope function approximation and by employing a variational technique. The polaron energy calculation uses a modified version of an approach described by Wolff.

The results show that static polaron calculations are not generally reliable and that the exciton–magnetic polaron has to be viewed as a dynamically evolving complex. It is initially energetically favourable for the exciton–magnetic polaron complex to increase its spatial localisation, since the gains in polarisation energy exceed the loss in exciton binding energy. However, thermodynamic considerations suggest that in general saturation of the magnetic ions will not occur.
Spin‐polarised tunnelling current in metal–insulator–gapless semiconductor structures in a magnetic field
Authors: Germanenko A. V. , Kruzhaev V. V. , Minkov G. M. , Rumyantsev E. L. , Rut O. E.
Published: May 2005

Experimental investigations of tunnelling conductivity oscillations of metal–insulator–gapless semiconductor structures are performed. For the orientation of the magnetic field H | n (n is normal to the structure plane) a splitting of the oscillation maxima of the tunnelling conductivity due to the spin splitting of the Landau levels is observed. It is revealed that when the magnetic field turns away from this direction the amplitudes of the low‐bias maxima decrease monotonously, and at H ⟂ n oscillations corresponding to tunnelling into one spin state only are observed. A theoretical analysis shows that this is caused by an unusual behaviour of the electron wavefunctions near the surface of gapless semiconductors in an applied magnetic field.
Photoluminescence and efficiency of Ce3+ in SrS powders
Authors: Hüttl B. , Müller G. O. , Mach R. , Fouassier C. , Benalloul P.
Published: May 2005

The luminescence efficiency of SrS: Ce powders in the doping range from 0.01 to 1.0 at.% was investigated by photoluminescence decay studies. The radiative decay time of Ce3+ in SrS was determined to be 27 ns. The onset of concentration quenching at concentrations higher than about 0.7 at.% has been obtained. The photoluminescence spectrum of Ce3+ exhibits two emission bands as a consequence of the ground state splitting. The Huang–Rhys factor of the 5d‐4f transition was estimated to be about 6. The inhomogeneous broadening of the emission band of samples with higher doping level has been investigated by site‐selective and time‐resolved spectroscopy.
Free exciton absorption in zinc selenide
Authors: Zheng Jia‐Zhen , Allen J. W.
Published: May 2005

We have measured the absorption spectrum of the n = 1 free exciton in ZnSe from 4.2 to 190 K. By fitting to a Lorentzian, we have found the exciton peak energy, width and oscillator strength. The values are compared with published ones, which were mainly obtained by less direct methods. The importance of the electron–hole interaction in radiative processes in ZnSe is emphasised.
Homogeneious linewidth and relaxation of excited hole states in II–VI quantum dots
Authors: Woggon U. , Gaponenko S. V. , Uhrig A. , Langbein W. , Klingshirn C.
Published: May 2005

By use of differential absorption spectroscopy at different temperatures we investigate the homogeneous line broadening of small CdSxSe1 − x quantum dots embedded in glass. Our experiments show the strong correlation between the precipitation stages and characteristics optical parameters such as the saturation intensity and the longitudinal and transverse relaxation times. In samples grown in the diffusion‐controlled regime to avoid coalescence, we find after strong laser excitation for the first time spectrally narrow holes in the non‐linear differential absorption spectra. These sharp non‐linear resonances with a halfwidth Γ of only 10 meV at T = 20 K allow us to investigate the energetic distance of the lowest hole levels and the temperature dependence of the line broadening. The different contributions of LO phonon coupling and temperature‐independent scattering to the homogeneous linewidth will be analysed. The relaxation from the excited hole states has been investigated by exciting in the higher‐energy hole states and measuring the resulting change in the ground state absorption.