Table of contents

The distribution of the lattice temperature in a semiconductor plate is described for the case when one of the plate surfaces is illuminated by strongly absorbed light. It is shown that the temperature of the illuminated surface and the average temperature of the sample became lower than the temperature of the surrounding medium when the diffusion flux of carriers drags phonons and certain boundary conditions are used.

Indium tin oxide (250 nm) and Ni(5 nm)/Au(10 nm) films were successfully deposited onto both glass substrates and p-GaN epitaxial layers. The normalized transmittance of the as-deposited ITO film was 90.6% at 450 nm, which was much larger than that of Ni/Au film. The transmittance of the RF sputtered ITO film could be increased to 97.8% with in situ annealing. In situ annealing of ITO films would also improve the electrical properties of ITO on p-GaN. Nitride-based light-emitting diodes (LEDs) were also fabricated. It was found that the 20 mA forward voltage was 3.16 V, 5.74 V and 4.28 V for the LEDs with Ni/Au, as-deposited ITO and in situ annealed ITO p-contact layer, respectively.

Recently, some peculiarities of current–voltage (I–V) curves of inhomogeneous diodes at low temperatures, which appear not to be in accordance with the concept of thermionic theory, have been discussed in the literature. We have recalculated some of the published results by a direct numerical iteration of I–V curves without an approximation of the apparent barrier height. We have confirmed that the discrepancy connected with the saturation current can be removed by lowering the integration limit for the apparent barrier calculation. It is further shown that the currently used formula for the apparent barrier height with integration limits −∞ and ∞ may lead to an unphysical negative apparent barrier height. We have also shown that the crossing of low-temperature I–V curves with higher-temperature curves is not the result of the difference in ideality factors for single curves but it is caused by the different apparent barrier heights at different temperatures. The ideality factor of these inhomogeneous diodes remains unity, just as the ideality factor of single diode patches creating the diode, and there is no need to generate I–V curves with artificially deteriorated ideality factors at lower temperatures.

Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.

In this paper we explore the application of scanning capacitance microscopy (SCM) for studying focussed ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots, and by comparison of topographical and SCM data. Further, we investigate how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analysed by SCM in cross-sectional geometry.

In this paper, we demonstrate the etching of chromium (Cr) film on quartz through a surface reaction induced by an electron beam and enhanced with XeF₂ gas. We have studied the influences of the electron beam energy, the gas flow rate and the specimen composition on the etch rate. The electron beam energy has significant influence on the etch rate. The etch rate made by an electron beam of 20 keV is five times higher compared to that made by a beam of 10 keV. The XeF₂ gas flow rate shows little effect on the etch rate when the gas pressure is higher than 2 × 10⁻⁶ Torr. The structure and grain size of the Cr film did not show any apparent change under exposure to XeF₂ or when irradiated by an electron beam, while the composition of Cr has a significant effect on the etch process. The material removal of Cr induced by an electron beam means that it can be applied to the direct fabrication of microstructures on Cr films and that it solves the contamination problem in Cr mask repair.

We report on the studies of steady-state high-field drift velocity in GaN/AlGaN HEMT structures. The results are compared with a model taking into account the effect of hot phonon production on the high-field transport of electrons. In the theoretical model Cerenkov effects and phonon drift are assumed to be negligible. Experimental results show that the drift velocity saturates at v_d = 1.0 × 10⁷ cm s⁻¹ at electric fields in excess of F ≈ 7.5 kV cm⁻¹ at T_L = 77 K. Theoretical calculations indicate that the enhanced scattering rate due to the production of non-drifting hot phonons reduces the drift velocity. The reduction in the drift velocity increases with increasing population of non-drifting non-equilibrium phonons.

Reflectometry using a white light source has been applied to in situ monitoring of metal organic vapour phase epitaxy of InGaN alloy structures on GaN buffer layers. Both InGaN epilayers 60–350 nm in thickness and InGaN/GaN multi-quantum-well (MQW) structures with periods of order 10 nm were studied. The InGaN epilayers have indium mole fractions between 0.105 and 0.240, determined principally by the growth temperature. The standard method of deriving film growth rates from in situ reflectance data is a useful predictor of InGaN epilayer thicknesses, and monitoring at wavelengths of 600 or 800 nm minimizes complications caused by absorption and scattering. For a set of seven InGaN epilayers, the average agreement between reflectance-derived thicknesses and estimates based on Rutherford backscattering is within 5%. Uncertainties in these measurements arise from the significant surface roughness of the films, an imprecise knowledge of optical constants and apparent short-term fluctuations in growth rates. Growth rates obtained from in situ monitoring of InGaN epilayers and GaN grown under the same conditions as MQW barriers can be used to successfully predict layer thicknesses in actual QW structures. We illustrate this methodology by comparing predicted layer thicknesses in 10- and 18-period MQW structures with results from conventional ex situ characterization, using transmission electron microscopy and x-ray diffraction.

We study the influences of band splitting and band anisotropy on the statistics of free holes and on the electrical transport in p-type GaN. Published experimental results for the hole effective mass span a wide range, m_h = 0.3–2.2m_o. Based on theoretical data, we determine reliable values for the pertinent effective masses. We also examine the distribution of free holes among three closely spaced valence bands. Around room temperature, the density-of-states effective mass is calculated to be m_h3ds = 1.25m_o. Depending on the direction of electrical current, the roles of different valence bands are distinctive. The holes from the A-band prevail in the transversal direction. However, the holes from the C-band dominate the transport along the c-direction, although their relative concentration is the smallest. This effect could play a role in optoelectronic devices.

We report a series of studies on GaSb/InAs superlattices, pseudomorphically strained to GaSb buffer layers. These heterostructures have recently been grown using molecular beam epitaxy for very long wavelength infrared photodetectors. We calculated the valence band alignment with the widely used model solid theory and evaluated the electronic band structure by employing an empirical pseudopotential (EP) scheme. The absorption coefficient was subsequently calculated at the far-infrared range of the spectrum, using density matrix theory. This approach predicted optical cut-off wavelengths, showing poor agreement with values obtained from absolute spectral responsivity measurements. Variation of the bond types at the interfaces (InSb- or GaAs-like, or a combination) led to significant changes in the cut-offs and absorption magnitude. However, no combination of interface bonds gave rise to results which were consistent with the experimental cut-offs. Addressing the band offset, we employed a recently published, interface-specific model as an alternative to the model solid theory-derived value. Including this model in our EP scheme, we obtained good agreement with experiment for a superlattice containing an InSb-like bond at each heterojunction, the configuration which had been fabricated in the photodetectors.

Using a model reduction method, a formula for the ideality factor of a pn junction as a function of the diffusion and generation terms of its reverse current is derived. Using this formula a method for separate computation of these two currents for a pn junction is presented. The validity of the method is investigated using computer simulations for an assumed diode with known ideality factor and total leakage current. Experimental results for two commercially available diodes validate the proposed technique.

We have investigated the temperature dependence of the transport parameters of Sn-doped InSe at different pressures, up to 2.5 GPa. A noticeable change in the temperature dependence of all the transport parameters has been observed above 1.2 GPa. This fact is explained by assuming the transformation of Sn shallow donors into deep donors at a hydrostatic pressure of 1.1 GPa, and by taking into account the transfer of electrons from the absolute minimum to higher energy minima in the conduction band. At ambient pressure, the position of the Sn deep level is estimated to lie 75 ± 20 meV above the absolute conduction-band minimum.

Intercollisional dynamics of hole spin, when free holes are subjected to an external electric field, is considered. Coherent evolution of spin projections and the population in valence bands is presented for dc and harmonic fields. Spin operators in the band representation are found and it is shown that there appears an uncertainty related with band degeneracy. The results obtained may be useful in the simulation of simultaneous spin and charge transport in p-type semiconductors, for example, by the Monte Carlo method.

This paper reports on a complementary investigation of the structural and opto-electronic characteristics of top-emitting organic light-emitting diodes (OLEDs). The key point of such a procedure is the deposition of the indium tin oxide (ITO) transparent top electrode onto the organic films structure. This was achieved by RF sputtering under soft enough conditions so as to avoid any deterioration of the underlying organic layers (room temperature deposition, low plasma power density and minimal bombardment effect) as much as possible. The electrical and optical properties of ITO as a function of the deposition conditions are described first. Hall effect measurements show that ITO films can be grown at room temperature with a high mobility (40 cm² V⁻¹ s⁻¹) and a carrier density exceeding 5 × 10²⁰ cm⁻³. The surface roughness as a function of the plasma conditions was determined by AFM and can be as low as 1.2 nm. Hole only silicon/Al/poly(N-vinylcarbazole) (PVK)/poly(3,4)ethylenedioxythiophene (PEDOT)/sputtered ITO diodes were processed and characterized both structurally (high resolution TEM in cross section) and electrically. An excellent agreement between the interfacial ITO/PEDOT structure and the hole injection performance was evidenced. Glass/ITO/PEDOT/PVK/Alq/BCP/ITO top-emitting OLED were processed and characterized.

In this paper, a profound study of the subsurface damage induced by backgrinding Si wafers is presented. It is shown that a thin amorphous layer (30–80 nm) is generated during backgrinding. Below the amorphous layer, there is a polycrystalline zone. Its thickness (about 0.5 μm) is obtained from Raman spectroscopy measurements. Below that layer, there is a strained crystalline zone. Its stress can be roughly calculated from warpage measurements of the wafer. The stress is also measured directly by Raman spectroscopy. A new analytical model is established to study the stress propagation with depth. The model fits the Raman spectroscopy measurements very well. The measurements show that the stress is reduced to zero after dry etching of the wafers.

The emission of episide down bonded InAsSbP/In(Ga)As/n⁺-InAs and graded InAsSb(P) light-emitting diodes (LEDs) with λ_max = 3.3–5.5 μm has been modified with an 'internal' Fabry–Perot cavity or bandpass filter attached to the LED with an optical glue. Positive and negative emission with the full width at half-maximum close to that of the filter (8–20 meV) have been obtained in the 20–50 °C temperature range.

In this work, we extend the temperature–entropy formulation to multi-stage thermoelectric coolers. With reference to commercially available thermoelectric materials, temperature–entropy diagrams are constructed to facilitate understanding the effects of electric current(s) and/or ratios of the number of thermocouples between stages on devices' performance. The temperature dependence of material properties is taken into consideration.

We report on the performance of a fabricated organic light-emitting device employing the electrophosphorescent material, fac tris(2-phenylpyridine) iridium (Ir(ppy)₃), doped into the new polyimide type of polymer, aromatic polyimide host. The luminance and the external quantum efficiency of the host emitter can be improved to ∼50000 cd m⁻² and ∼7%, respectively, by doping the host with Ir(ppy)₃. The photoluminescence (PL) and electroluminescence (EL) have been investigated. The EL spectra shift with the changes of the concentration of Ir(ppy)₃. Bright green emission was observed from the EL devices. The current–voltage (I–V) characteristics suggest that, when the voltage is higher than the turn-on voltage, the current of the doped cell is higher than that of the undoped cell at the same voltage, indicating that the doping has an effect on the I–V characteristics.

A study of the optimization of the detectivity of a mid-infrared double heterostructure photovoltaic detector is proposed. Simple approximate analytic expressions for the dark current are compared with full numerical calculations, and give physical insight into the mechanisms dominating the dark current. The analysis is performed step by step in different structures, from a simple p–n junction to the full double heterostructure. The influence of temperature, barrier band gap energy in a double heterostructure and doping density in the active region, on diffusion and generation–recombination mechanisms is analysed. It is finally shown how the performances of a double heterostructure photovoltaic detector can be improved by a controlled doping of the active region, especially at low temperature.

In this paper, we discuss the use of a semiconductor multiple quantum well (MQW) electron wave filter for multi-channel communication applications. This bandpass-type electron wave energy filter, made of GaAs and Ga_0.55Al_0.45As, is designed for different numbers of layers and cavities for a pass wavelength of 10 nm. We report on the calculated values of the design parameters, such as the passband wavelength, 3-dB bandwidth, quality factor and passband loss for the electron wave filter. The design parameters are also evaluated for a tunable MQW electron wave filter when varying the angle at which the electron wave is incident on the input layer of the filter.

Recent studies have indicated that the final wave vector k_f of the electron is exactly the same as the initial wave vector k_i for electrons tunnelling through a parallel magnetic-barrier structure, where double δ-function magnetic fields point in the same direction. In contrast to the anti-parallel magnetic-barrier configuration, we have found that the parallel magnetic-barrier configuration as well as identical initial and final wave vectors cannot concur. We have derived the correct formula of the transmission and have shown that the spectra of both the transmission and the conductance are quite different from published results. Numerical results further confirm that spin filtering in the magnetic-electric barrier is relatively weak because the intrinsic Zeeman term between the electronic spin and the inhomogeneous magnetic field is local and it strength is small for the GaAs system.

We have grown nanocrystalline ZnSe thin films on GaAs(100) substrates by pulsed laser deposition using a KrF excimer laser. Atomic force microscopy shows that the ZnSe thin films grown on GaAs(100) at 10⁻¹ Torr are flat and dense and are composed of crystallites with an average roughness of 1–2 nm. X-ray diffraction results indicate that crystallites of these ZnSe thin films are of (100) crystalline orientation with an average size of about 10–30 nm. X-ray photoelectron spectroscopy indicates that the as-deposited thin films contain 5–7% [N], and nitrogen with N–Zn bondings includes about 40–60% of the total contained nitrogen. Photoluminescence measurements show a donor-to-acceptor pair recombination emission, which reveals the activation of [N] atoms as shallow acceptors in nanocrystalline ZnSe.

Fourier transform infrared absorption measurements have been performed on thin films of GaAs_1−xN_x grown by metalorganic chemical vapour deposition or molecular beam epitaxy on semi-insulating GaAs substrates. The local vibrational mode absorption due to N_As is used to assess the substitutional nitrogen fraction. Based on a comparison with secondary ion mass spectroscopy and x-ray diffraction analysis, the calibration factor for the integrated absorption is derived. Quantitative determination of substitutional nitrogen is possible up to x ≈ 0.05, in epitaxial layers of thicknesses down to 10–100 nm.

The role of the free surface in determining the equilibrium position of misfit dislocations in thin epitaxial films is considered. When the film is elastically stiffer than the substrate, the core of the dislocation is predicted to lie at some distance from the interface in the softer substrate. On the other hand, when the film is softer than the substrate, the core of the dislocation is always predicted to lie close to the interface.

Dye-sensitized photoelectrochemical cells based on nanocrystalline films of TiO₂ yield energy conversion efficiencies ∼10%. The efficiencies of similar cells with films of other oxide materials (SnO₂, ZnO) are well below the above value. However, the cells made from SnO₂–ZnO composite films give efficiencies comparable to TiO₂ cells. Two types of composite systems with SnO₂ and ZnO are possible. In the first type, SnO₂ crystallites are covered with an ultra-thin (<1 nm) outer shell of ZnO₂ and in the second type, the film comprises SnO₂ crystallites (∼10 nm) with a thin ZnO outer shell and larger ZnO particles (∼100 nm). The short-circuit photocurrent and efficiency of these cells are ∼17 mA cm⁻², 19 mA cm⁻² and 7%, 8% respectively. This paper explains in detail how a thin shell of ZnO on SnO₂ could effectively counteract recombinations of electrons with acceptors in the electrolyte (e.g., I₃⁻) and increase the efficiency although SnO₂ and ZnO are individually not good materials for dye-sensitized photoelectrochemical cells. In the second type, larger ZnO crystallites reduce the rate of geminate recombinations, in addition to the effect of the outer shell.

DC characteristics of interesting In_0.49Ga_0.51P-channel heterostructure field-effect transistors (HFETs) with different gate metals, e.g., Pt, Pd and Au, have been studied and demonstrated. A very thin and fresh oxide layer is introduced to increase the gate turn-on and breakdown voltages and reduce the gate leakage current. It is found that, metal-oxide-semiconductor field-effect transistors show higher barrier height, turn-on voltage, breakdown voltage, off-state voltage, output current and transconductance than metal-semiconductor field-effect transistors. In addition, the barrier height and turn-on voltage are increased with the increasing metal work function. However, the breakdown voltage is decreased with the increasing metal work function. All studied devices show good performances of high breakdown voltage, high output drain saturation and flat and wide transconductance operation regimes. The temperature-dependent behaviours are also studied. It is known from experimental results that In_0.49Ga_0.51P HFETs show good potentiality in high-temperature electronics applications.

Type-II superlattices are very attractive as tuning regions in tunable laser diodes exploiting the free-carrier plasma effect. Due to the confining of the electrons and holes in different layers, the recombination of the electron–hole pairs is drastically suppressed. As a result, the carrier density, and hence the tuning efficiency for type-II superlattices, is enhanced by more than an order of magnitude in the small current regime as compared to bulk tuning regions. However, with increasing carrier density the recombination rate increases because of the stronger penetration of the electron and hole wavefunctions into the corresponding barriers. For high carrier densities, the capability of type-II superlattices depends critically on design parameters such as as layer thickness, band offset and strain. Our calculations show that, for an optimized type-II superlattice, the tuning range can be significantly enhanced by more than a factor of 3 for a given current.

The electronic states of Si slabs contained within SiO₂ barriers and placed in strong electric fields have been calculated using tight-binding theory. The SiO₂ barriers resolve the problem of dangling bonds and surface termination in a simple and unobtrusive manner, and also relate to actual nanostructures. Two critical fields are identified from the calculations. The electronic density of states (DOS) change very slowly until the first critical field F_c1 begins to be reached. This first critical field at 7 MV cm⁻¹ corresponds to the onset of the silicon-bandgap ionization, in excellent agreement with the vacuum emission experiments. The second critical field F_c2 is revealed by the clear fragmentation of the density of states into Wannier–Stark ladders. Our theoretical methods apply directly to Si/SiO₂ and other superlattice structures as well. The field-dependent DOS results presented here are relevant to theories of electroluminescent devices, high-field hot-electron transport as well as to opto-electronic switching devices.

Mössbauer spectroscopy on the ⁶⁷Ga(⁶⁷Zn), ¹¹⁹Sn and ^129mTe(¹²⁹I) isotopes has shown that no modifications of the local symmetry of lattice sites, electronic structure of atoms and intensity of electron–phonon interaction are revealed for Pb_1−xSn_xTe solid solutions in the gapless state at 80 and295 K.

Various parameters in the structural features of the Sb_xGe_28−xSe₇₂ glassy system are studied as a function of average coordination number ⟨r⟩ in the light of recently proposed models for network glasses. The relation between the chemical ordered covalent network model and the constraint theory on the structural features is studied. The overall mean energy ⟨E⟩ of a covalent network for a ternary Sb–Ge–Se chacogenide system has been determined. In amorphous materials, there are non-random structural elements that have the behaviour of a simple chemical ordering. In addition, two topological effects are discussed, the floppy to rigid transition and the structural transition, which resulted in the Sb_xGe_28−xSe₇₂ glassy system and induced some changes in chemical ordering.

The infrared transmission spectrum was measured in the wavenumber region 500–200 cm⁻¹ at room temperature. The results are interpreted in terms of the vibrations of the isolated molecular units in such a way as to preserve fourfold and twofold coordination for germanium and chalcogen atoms, respectively. The infrared features are assigned to Ge–Se bonds in GeSe₄ tetrahedral units and Sb–Se bonds in pyramidal molecules. On the other hand, the results explain that a structural model, based on the random covalent network model assuming tetra-coordinated Ge, tri-coordinated Sb and di-coordinated Se, confirms the information obtained from infrared spectroscopy.

Hot electron luminescence (HEL) from p-doped GaAs and quantum wells shows a series of peaks corresponding to discrete LO-phonon losses. Much of the width of the zero-phonon loss peak arises directly from the initial-state valence band warping, so the HEL energies within the peak can be associated with specific k-directions. The degree of linear polarization (DoLP) varies over the width of the peak, so different k-directions can be identified with different polarizations. We present measurements of this polarization anisotropy for a series of quantum wells, together with model calculations in the diagonal approximation that the acceptor wavefunction is dominated by heavy hole states along the ⟨11⟩ directions, and in the spherical approximation that other directions contribute substantially. The data allow the diagonal approximation to be discarded. In contrast to the case for bulk material, the DoLP increases strongly with the initial photoexcitation energy. Previous calculations, averaging the DoLP over the HEL peak, underestimate this by a factor of nearly two. We show that the DoLP anisotropy requires comparison with calculations along high symmetry directions to obtain good agreement with the data.

We have studied in reduced-pressure chemical vapour deposition the influence of the growth temperature on the interstitial–substitutional carbon incorporation ratio in SiGeC using dichlorosilane as the Si gas precursor. X-ray diffraction and secondary ion mass spectrometry were used in order to determine the substitutional and the total (interstitial + substitutional) carbon concentrations in the layers. Si/Si_1−yC_y tensile-strained heterostructures were grown at 650 °C. The highest substitutional carbon concentration incorporated is around 0.75% (with a large amount of interstitial C atoms (also 0.75%), however). Low Ge concentration Si_1−x−yGe_xC_y layers have also been grown. We have managed through the increase of the SiCH₆ mass flow to tailor the Si_1−x−yGe_xC_y layer strain from compressive to tensile. The highest substitutional carbon concentrations obtained are 1.82% (0.95%) for growth temperatures of 600 °C (650 °C). Finally, compressively strained high Ge concentration Si_1−x−yGe_xC_y layers with up to 3.20% (2.49% and 1.41%) in substitutional carbon atoms were grown at 550 °C (600 °C and 650 °C). The growth temperature does not seem to impact upon the total carbon concentration C_T in these layers. Its dependence on the F(SiCH₆)/(F(SiH₂Cl₂) + F(GeH₄)) mass flows ratio is indeed rather well fitted using the following relationship: C_T^1.4/(1 − C_T) = q(F(SiCH₆)/(F(SiH₂Cl₂) + F(GeH₄)), with q in between 0.38 and 0.34 for the 550–650 °C temperature range. However, the more the temperature increases, the more the substitutional/interstitial carbon incorporation ratio is reduced.

We present a novel method for determining semiconductor parameters such as diffusion length L, lifetime τ and surface recombination velocity S of minority carriers by employing scanning electron microscopy (SEM). This new method is applicable to both electron beam induced current (EBIC) and surface electron beam induced voltage (SEBIV) modes in SEM. The quantitative descriptions for EBIC and SEBIV signals are derived. The parameters L, S and τ can be directly extracted from the expressions for EBIC or SEBIV signals and their relaxation characteristics in experiment. As an example, the values of L, S and τ for n–p junction and p-Si crystal are determined by using the novel method in EBIC or SEBIV mode. The carrier diffusion length of a p-Si crystal is determined to be 8.74 μm in SEBIV mode. It is very close to the normal diffusion length of 7.41 μm of this sample. The novel method is proved to be very helpful for the quantitative characterization of semiconductor materials and devices. Especially, the SEBIV mode in SEM shows great potential for investigating semiconductor structures nondestructively.

We present a novel way to determine the type of dominant carrier photoexcited from deep traps in a photorefractive semiconductor. A numerical analysis of a picosecond free-carrier grating dynamics has revealed an excitation intensity dependent grating diffusive decay time τ_D as well as effective carrier diffusion coefficient D, when the intensity varied in the range below that required to create a bipolar carrier plasma. According to the numerical analysis, an increase or decrease of effective diffusion coefficient D with excitation can be used as a criterion to distinguish the type of photogenerated carrier. We have verified this method experimentally by measuring dependences of effective D versus excitation density in a number of vanadium-doped and shallow-impurity codoped CdTe and ZnCdTe crystals, using for excitation a picosecond YAG:Nd laser (hν = 1.17 eV). The results were found to be in good agreement with predictions, based on carrier transport peculiarities in photorefractive crystals, and correlated well with the secondary ion mass spectroscopy data for each crystal.

We derive parametrized equations using variational calculation for energy levels and the spatial extension of Wannier excitons in two-dimensional quantum wells with an arbitrary shape of the confining potential. The formulation is performed in the framework of the effective mass approximation, two-band model and taking into account both mass mismatch and dielectric mismatch. According to the new formulation, qualitative and general features of excitons are deduced. Illustrations are given for GaAlAs–GaAs–GaAlAs and CdMnTe–CdTe–CdMnTe systems for both rectangular and parabolic quantum wells as well as for the 2s exciton state. The comparison with existing data displays good agreement. An application of the model is given for an exciton in a parabolic quantum well under a constant electric field.

The low temperature photoluminescence properties of InAs/InP self-assembled quantum dots are investigated in magnetic fields up to 17 T. The zero field spectrum exhibits a number of inhomogeneously broadened peaks similar to the highly excited spectrum of InAs/GaAs quantum dots in which emission from excited states can be observed. However, for InAs/InP dots, application of a magnetic field in the Faraday configuration reveals only weak diamagnetic shifts, thus proving that the transitions originate from zero angular momentum states consistent with ground state emission from distinct families of islands present in the sample. The diamagnetic shift is observed to increase as the thickness of the island family increases. Calculations performed assuming a flat disc geometry show that the latter effect can be accounted for by the change in carrier effective mass as the dot thickness increases.

We demonstrate a novel method of determining the thickness and Ge concentration in multilayer SiGe heterojunctions using an optical microscope. The sample preparation is a two-step process: first the layer structure is bevelled under a shallow angle to enlarge the width of the layers, followed by a wet thermal oxidation step at low temperatures. Differences in the oxide thickness, due to the dependence of oxidation rate on Ge composition, result in colour differences in the layers that are visible under an optical microscope. The Ge concentration is calibrated using XRD results, and the measured layer thickness is compared to TEM results.

In this paper, we investigate oxidation-induced stacking faults (OSFs) and related grown-in oxygen precipitates of nitrogen-doped Czochralski (NCZ) silicon. The samples were oxidized at 1150 °C or were annealed under different conditions. It was found that OSFs with different densities in the NCZ silicon distributed not only in the OSF-ring region, but also in the inner region of the ring. Furthermore, the OSF ring was extended by nitrogen doping. In addition, the investigation of oxygen precipitates indicates that nitrogen changes the size and density distribution of grown-in oxygen precipitates in the OSF-ring and void regions of the NCZ silicon during crystal growth, and therefore the OSF behaviour is changed. Based on the experimental facts, in particular we discuss the mechanism of nitrogen affecting the distribution of OSFs in different regions.