Showing papers in "Semiconductor Science and Technology in 1989"

Valence band engineering in strained-layer structures

Abstract: It is now possible to grow high-quality strained-layer superlattices, in which individual layers are composed of semiconductor materials which would normally have significantly different lattice constants. Strained structures open new possibilities for band-structure engineering and applications, but place even higher demands on crystal growth techniques. The authors first describe some of the growth that has been achieved and the theoretical and experimental limits on good quality growth. They then discuss in detail the electronic structure of strained quantum wells, and in particular the possibility of valence band engineering in strained layers. Axial strain splits the degeneracy of the light- and heavy-hole zone centre states, accessing a range of subband structures, including the possibility of the highest band being light-hole-like, and of holes with electron-like zone centre masses. The authors next describe the experimental evidence confirming such subband structures. This strain-based band engineering suggests new device applications, including high hole mobility transistors and low threshold current, long-wavelength lasers. The authors review what has been achieved in respect of the main proposed device applications to date. Strained layers are also of interest for the new materials combinations which they allow. They briefly overview some of the materials-based advantages, and conclude that strained layers will continue to attract significant attention.

MOS interface states: overview and physicochemical perspective

Abstract: The metal-oxide-semiconductor transistor has become the dominant device for very large-scale integrated circuits. The performance and reliability of an MOS device are heavily influenced by the quality and properties of the interface between the oxide and the Si region directly beneath. Inherent, process-related, and operationally and environmentally generated interface states or traps are exceedingly harmful or disabling when present. Although controlled successfully by semiempirical design, fabrication and operational regimens, ever-smaller device size-approaching the scale in which a single trap can be important-makes further extension of knowledge on the basic physical and chemical aspects of interface states essential for confident technological progress. In addition, Si/SiO2 interface states continue to merit research in their own right. This paper briefly highlights selected topics from past and present interface-state research and describes some essential physical and chemical properties.

Chemical bath deposition of CuxS thin films and their prospective large area applications

Abstract: CuxS thin films with a wide range of sheet resistances (rSquare Operator ) and optical transmittance (T%), indicating different composition x, have been obtained from chemical baths constituted from copper(II) chloride, triethanolamine and thiourea at appropriate pH (10-12). Depending on the deposition parameters, a range of combination of rSquare Operator approximately=30 Omega to 1 M Omega and T% (500 nm) approximately=1 to 65 and a range of colour of reflected daylight (golden yellow, purple, blue, green, etc.) can be obtained. The films have been found to be stable with respect to electrical and optical properties on storage under ambient. Various possible large area applications such as in architectural glazing, photothermal and photovoltaic conversions are discussed.

An overview of radiation-induced interface traps in MOS structures

Abstract: The authors focus on radiation-induced interface traps, describing first how they fit into the overall radiation response of metal-oxide-semiconductor structures. Detailed measurements of the time, field and temperature dependences of the build-up of radiation-induced interface traps indicate three processes by which the build-up occurs. The largest of these is the slow two-stage process described by McLean and co-workers (1989) which is rate-limited by the hopping transport of hydrogen ions. Two other faster processes also contribute small interface trap build-ups in gate oxides. The processes seem to be controlled by hole transport to the Si/SiO2 interface and by neutral hydrogen diffusion respectively. They also discuss several models which fall into three classes, corresponding roughly to the three processes observed experimentally. Other topics discussed briefly are dose dependence, field oxide effects, chemical and processing dependences and scaling effects.

Individual defects at the Si:SiO2 interface

Abstract: In micron-sized MOSFETS, the alternate capture and emission of carriers at individual Si-SiO2 interface defects generates discrete switching in the source-drain resistance. The resistance changes are observed in the drain current as random telegraph signals, or as stepped transients after a strong perturbation of the trap occupation. The study of individual defects in MOSFETS has provided a powerful means of investigating the capture and emission kinetics of interface traps, has demonstrated the defect origins of low-frequency (1/f) noise in MOSFETS, and has provided new insight into the nature of defects at the Si:SiO2 interface.

Interface trap transformation in radiation or hot-electron damaged MOS structures

Abstract: The interface traps created by ionising radiation or hot-electron injection in MOS capacitors have been found to undergo significant changes with time over an extended period (many months). Immediately after radiation or hot-electron damage, an interface trap peak above the midgap ( approximately Ev+0.75 eV) invariably appears. This peak (designated peak 1), along with its background, would continuously change with time after damage, and the detailed time-dependent behaviour depends on the surface orientation of the Si substrate, processing history, gate bias and sample temperature. For samples made on (100) substrates, three separable regimes have been observed: (i) latent generation (peak 1 and its background increase with time), (ii) defect transformation (peak 1 gradually converts into peak 2 below the midgap, resulting in a double-peak interface trap distribution), and (iii) room-temperature annealing (the overall density of interface traps decreases with time). The focus of this paper is on the defect transformation process. For samples made on (111) samples, on the other hand, the most salient feature is the gradual shift of the energy position of peak 1 toward the valence band, and eventually a single-peak residing below the midgap is observed. In contrast to the (100) results, no discernible double-peak distribution has been found in (111) samples. Results on (110) samples are qualitatively similar to those on (111) samples, while (311) samples are similar to (100) samples. The various experimental parameters that affect the defect transformation process in both (100) and (111) samples will be discussed. While the (100) results are too complex to be explained satisfactorily based on existing theories at the present time, the (111) results will be interpreted in terms of the atomic relaxation of the dangling-bond defect at the (111)Si/SiO2 interface.

Diamond electronic devices-a critical appraisal

Abstract: The electronic properties of diamond with particular emphasis on current research into the production of semiconducting films by chemical vapour deposition are reviewed. It is stressed that no method of producing n-type diamond having a conductivity appropriate to device applications has been developed to date. An analysis of the temperature-dependence of the hole mobility for six natural semiconducting diamonds indicates that the room-temperature value is very sensitive to the presence of ionised impurities, and reemphasises the fact that the mobility decreases very rapidly with increasing temperature. A number of diamond electronic devices that have been fabricated, or proposed, are examined in the light of these properties. The survey suggests that claims made for the devices are, in general, optimistic, and that few, if any, are likely to be commercially successful.

Observation and control of the amphoteric behaviour of Si-doped InSb grown on GaAs by MBE

Abstract: The MBE growth and doping of heteroepitaxial layers of InSb on GaAs (100) are investigated. The layers are assessed by low-field Hall and magnetoresistivity measurements and high-field Shubnikov-de Haas studies together with infrared transmission, and TEM. The mechanism for silicon incorporation is investigated as a function of growth temperature. At low growth temperatures ( approximately=340 degrees C) silicon acts only as a donor and can produce electron concentrations up to 3*1018 cm-3 with 77 K mobilities identical to those found with bulk material. Although higher concentrations than 3*1018 cm-3 can be achieved; auto-compensation appears to occur in those samples. The 77 K mobilities achieved for less heavily doped samples (>40000 cm2 V-1 s-1 for n=1.2*1017 cm-3 for samples grown at 340 degrees C) are the highest low-temperature mobilities yet reported for n-type InSb films of approximately=1 mu m thickness grown on GaAs. However, higher growth temperatures ( approximately=420 degrees C) combined with constant silicon flux are found to simultaneously decrease electron concentration and mobility measured at 77 K although the structural quality as assessed by TEM remains unchanged. Analysis of the observed behaviour in terms of the Brooks-Herring model of ionised impurity scattering, modified for nonparabolicity, suggests that silicon is acting amphoterically with compensation ratios (NA/ND) reaching 0.5 at the higher temperatures. The effect of the interface between GaAs and InSb (lattice mismatch=14%) on the electrical properties is studied by introducing doping slabs of thickness approximately=1300 AA at various distances (d) between the interface (d=0 mu m) and the surface (d approximately=1.5 mu m) of the epilayer. A series of peaks not periodic in reciprocal field (1/B) are found at low fields with B parallel to the slabs and are interpreted as arising from the diamagnetic depopulation of the large number of subbands occupied as a result of the considerable thickness of the slabs. Be doping at 2*1019 cm-3 was demonstrated and, as with silicon, the bulk mobility corresponding to this hole concentration was achieved.

General characteristics of thermally cycled tin oxide gas sensors

Abstract: The response, measured as conductance, of thermally cycled tin oxide gas sensors was studied to determine the potential inherent in this technique with respect to increased selectivity and sensitivity. It was found that the range of cycle temperature as well as the period of the cycle had a critical effect on the amount of information that could be extracted from the conductance versus time curves. Significantly different conductance curve shapes were seen for such gases as propane, carbon monoxide and ethanol when an offset sinusoidal waveform was used to drive the sensor heater. The effect of varying the concentration of the reducing gas was examined both to check the effect on selectivity between gases and to determine the functional relationship between conductance and gas concentration as related to the time in the cycle period. It was found that the conductance change at the low-temperature section of the thermal cycle can vary at a rate faster than linear for low concentrations, and because the clear air conductance is very low in these sections the thermally cycled sensor is extremely sensitive to reducing gas.

Optimisation of (Al,Ga)As/GaAs two-dimensional electron gas structures for low carrier densities and ultrahigh mobilities at low temperatures

Abstract: The authors have grown (Al,Ga)As/GaAs two-dimensional electron gas (2DEG) structures with lightly doped regions of (Al,Ga)As and superlattices in the undoped GaAs. Using this technique, they have obtained ultralow density (2*1010 cm-2), high-mobility samples where phonon scattering at 4 K is the dominant factor in limiting the mobility; reducing the measurement temperature to below 1.5 K gives mobilities of up to 107 cm2 V-1 s-1.

A diffusion-reaction model of electrical conduction in tin oxide gas sensors

Abstract: The recent advent of integrated gas sensors and advances in pattern recognition techniques have heralded a renewed interest in the electrical characteristics of porous thick semiconductor layers. A linear diffusion-reaction model is considered here that may be used to characterise the transient and steady-state response of several metal-semiconductor-metal devices. This approach differs from that of chemical kinematics which is widely adopted and focuses upon the relationship between electrical conductance and the geometrical structure of the device. The theoretical transient response is derived for several MSM device configurations and compared with experimental data on SnO2 gas sensors. There is reasonable agreement with the model predictions at low gas concentrations. Consequently, the electrical conductivity of thick porous tin oxide gas sensors is diffusion-limited as the reaction rate is fast compared with the diffusion rate. However, further work is needed to address nonlinear adsorption processes and to consider a diffusion-reaction process where the reaction rate is slow compared with physical diffusion.

Characterisation of Si III and Si IV, metastable forms of silicon at ambient pressure

Abstract: Two crystalline phases of silicon: Si III (BCC) and Si IV (hexagonal diamond) are known to be metastable at ambient. Pure, single phase, microcrystalline samples of both varieties may be prepared by high-pressure synthesis above 18 GPa at 300 K. The authors report on high-resolution electron microscopy, kinetics of the temperature driven phase-change from Si III to Si IV, and Raman scattering measurements performed on these samples. Results are compared with those obtained by other characterisation methods and/or published in earlier works.

Hot phonons in high-field transport

Abstract: The effect of hot-phonon production on the steady-state high-field transport properties of electrons in bulk and quasi-2D semiconductors is discussed within the framework of a simple theoretical model in which Cerenkov effects and phonon drift are assumed to be negligible. The model also assumes a single spherical parabolic band for the electrons whose distribution is a displaced Maxwellian, with scattering confined to polar optical phonons, restricted to interface modes in a deep square quantum well in the quasi-2D case. A finite phonon lifetime of 7 ps is shown to reduce the energy relaxation rate and to increase the momentum relaxation rate. The result is to lower the mobility and to delay runaway to higher fields, these effects increasing with the electron density. It is pointed out that nondrifting hot phonons tend to quench intervalley and real-space-transfer NDRS and to reduce the drift velocity for a given field. It is shown that, in general, the effective energy relaxation time is field dependent.

Versatile solar control characteristics of chemically deposited PbS-CuxS thin film combinations

Abstract: Solar control characteristics of chemically deposited PbS and CuxS thin films in the glass-PbS-CuxS structure are reported. This combination offers pleasing colours: bluish, greenish, greenish-yellow etc in reflected daylight and low NIR transmittance-not possible with PbS-only coatings, while providing a high-enough NIR solar reflectance-not achievable with CuxS-only coatings. A 15 min air bake at 150 degrees C has been found to reduce the sheet resistance of the CuxS films by two to three orders of magnitude, which in turn drastically decreases the integrated NIR transmittance, T*(IR), of the PbS-CuxS combination (typically from 46% to 14%), while retaining the integrated transmittance, T*(vis), and the integrated reflectance, R*(vis), in the visible region to within 14-30% and 15-20% respectively for the various PbS-CuxS combinations. The major advantage of the PbS-CuxS thin film combinations as solar control coatings is that by controlling the thicknesses of the individual films a range of combinations of T*(vis), R*(vis), T*(IR), R*(IR) and colour in reflected daylight is achievable. This makes them very versatile for architectural glazing applications to suit different space conditioning, illumination level and cosmetic requirements.

Hydrogen passivation of shallow acceptors in p-type InP

Abstract: Undoped GaInAs/zinc-doped InP structures grown by metal-organic chemical vapour deposition have been exposed to a RF hydrogen or deuterium plasma. Secondary ion mass spectrometry experiments show deuterium diffusion in both materials and the existence of a hydrogen-acceptor pairing effect in the p-type InP layer. After hydrogenation, the InP layer becomes highly resistive as a result of a strong passivation of acceptors by hydrogen. Hall effect and conductivity measurements performed on a lightly thermally reactivated InP layer indicate that the hole mobility is significantly higher than in the non-hydrogenated InP layer. This increase is attributed to a decrease of the ionised acceptor concentration under hydrogenation and is consistent with the existence of a pairing between the proton and the ionised acceptor giving rise to neutral Zn-H complexes. The relative thermal stability of Zn-H complexes in InP:Zn if compared to GaAs:Zn can be interpreted with the help of the microscopic model of these complexes, hydrogen being more tightly bonded to a phosphorus than to an arsenic atom.

Estimation of percentage relaxation in Si/Si1-xGex strained-layer superlattices

Abstract: A series of Si/Si1-xGex strained-layer superlattice structures has been studied by X-ray double-crystal diffractometry, Raman spectroscopy and transmission electron microscopy. The periodicity of the superlattices, the alloy composition and the degree of relaxation have been measured. The precisions of the three techniques are discussed and the results critically compared.

Post-growth diffusion of Si in delta -doped GaAs grown by MBE

Abstract: A GaAs layer grown by MBE at a substrate temperature of 520 degrees C and containing three delta -doped planes with Si concentrations of 0.4, 1 and 4*1013 atoms/cm2 has been post-growth annealed in a furnace, up to temperatures of 648 degrees C. Secondary ion mass spectroscopy (SIMS) and capacitance voltage (cv) measurements have been carried out to measure profile-broadening. The most lightly doped plane gave a near-Gaussian diffusion profile with a diffusion coefficient comparable with literature values for simple diffusion of isolated SiGa atoms. The more heavily doped planes exhibit a complex profile shape with two components, a proportion of the atoms being confined to the original plane, together with an almost square-shaped profile of fast-diffusing atoms. Comparison of the CV and SIMS data suggests that formation of Si islands is taking place during deposition of the delta -doped plane, giving electrically inactive atoms which can subsequently diffuse into the surrounding GaAs during heat-treatment. This model is supported by preliminary local vibrational mode measurements which have been made on a set of multiplane samples.

Spectroscopic evidence for hydrogen-phosphorus pairing in zinc-doped InP containing hydrogen

Abstract: A sharp IR line is observed in the low-temperature absorption spectrum of p-type InP doped with zinc when it has been passivated with hydrogen or deuterium. Because of the spectral characteristics of the line, it is attributed to the vibration of hydrogen or deuterium bonded to P atoms that are first neighbours of zinc acceptors. This consistently provides the same picture of the passivating complexes as in GaAs by replacing the As atom by the P atom. It is further argued that the microscopic structure of the acceptor complexes observed in germanium doped with zinc or beryllium when grown in a hydrogen atmosphere can be similarly explained by the formation of a Ge-H bond on the first neighbour of the Zn atom, leaving the acceptor atom tri-coordinated and neutralising one of the two holes. This explains the production of single acceptor complexes with trigonal symmetry whose electronic spectra have been analysed some time ago.

Electron velocity in GaAs: bulk and selectively doped heterostructures

Abstract: The paper describes measurements of the velocity of electrons at electric fields up to 9 kV cm-1 in GaAs and in GaAs/AlGaAs heterostructures. In order to avoid charge and field domain formation, this experiment uses a sinusoidally varying electric field with frequency of 35 GHz. The results of these measurements indicate that negative differential mobility is present in not only the undoped GaAs, but also in the heavily doped GaAs and in the selectively doped heterostructures. These results imply that such a measurement is necessary to correctly determine the velocity-field characteristics of electrons in this electric field range. The experimental results further indicate that in the case of the selectively doped heterostructures, the electrons have peak velocities lower than those found in undoped bulk GaAs and that the peak occurs at a lower electric field. At room temperature, this effect is primarily due both to the effective lowering of the Gamma -L energy difference which results in a more efficient k-space transfer of electrons and to real-space transfer of electrons into the AlGaAs. At 77 K, these mechanisms are still active; additionally, the two-dimensionality of the electrons results in an enhanced scattering of the electrons with the polar optical phonons. In the case of doped GaAs, because of the significantly increased ionised impurity scattering, the peak velocity is also lower than that found in undoped GaAs, but the peak occurs at higher electric fields.

Near-ideal solar control characteristics of CuxS thin films

Abstract: CUxS thin films, deposited from chemical baths on glass substrates and air-annealed at 150 degrees C and then given a polymer protective coating, have been found to offer optical transmission and reflection characteristics near to ideal solar control characteristics. The transmission spectra in the visible region resembles the phototopic vision spectra, with an integrated transmittance of approximately=30%-providing a greenish-yellow illumination of the interior under daylight. The low integrated visible reflectance of approximately=9% prevents glare and the mild bluish-purple colour in reflected daylight improves cosmetic appearance. Due to the low sheet resistance of the films approximately=30 Omega Square Operator -1, the integrated infrared transmittance is very low, approximately=10% and the integrated infrared reflectance is acceptably high, 25%. The total optical and thermal transmittance into the interior through the CuxS coated glazing is in the 30-35% range, assuring substantial saving in the cooling costs when these glazings are employed in regions with a generally warm climate. Various possibilities in the commercial production of the coatings are suggested.

Valence subband structure and optical gain of GaAs-AlGaAs (111) quantum wells

Abstract: The authors use the envelope function method to calculate the hole confinement energies and valence subband dispersion energies of (111) GaAs-AlGaAs quantum wells of varying widths. The heavy-hole mass is significantly larger along (111) than along the conventional (001) growth direction. This increases the number of heavy-hole confined states for a given well width. Away from the zone centre, the subband dispersion shows less mixing between heavy- and light-hole bands than for (001) growth and, in thin wells, the highest subband has a low in-plane effective mass over a greater energy range ( approximately 25 meV for a 50 AA well). It has recently been shown that (111) GaAs-AlGaAs quantum well lasers can have a lower threshold current density than equivalent (001) lasers. They perform laser gain calculations which show that this reduced threshold current density can be explained by the enhanced light-hole behaviour at the valence band maximum of (111) quantum wells. No theoretical evidence is found to support an increased in-plane heavy-hole mass or enhanced optical matrix element, as have been deduced from recent experiments on (111) quantum well structures.

A photoemission study of passivated silicon surfaces produced by etching in solutions of HF

Abstract: Hydrogen-terminated silicon surfaces produced by etching in solutions of HF have been studied using photoelectron spectroscopy and LEED. They have been found to be remarkably free from contamination, locally ordered and electrically passivated. The hydrogen may be removed from the (100) surface by annealing in UHV at (520+or-10) degrees C. At that temperature, the initial (1*1) structure of the surface changes to a two domain (2*1) reconstruction and the Fermi level becomes pinned by surface states. The relationship between residual contamination and etching parameters such as time, concentration and crystallographic orientation of the sample has been examined, together with the degradation of the hydride surface with exposure to various environments. This has shown that the contamination levels of the surface are sensitive to etching procedure, but with suitable care, a 5% non-aqueous HF solution provides the optimum etch.

Electron paramagnetic resonance studies of Si-SiO2 interface defects

Abstract: This paper contains a review of electron paramagnetic resonance studies on Pb-type centres at the Si-SiO2 interface. It includes a synopsis of studies on the atomic structure of Pb defects and the chemical kinetics whereby Pb centres are passivated with H2.

Far-infrared spectroscopic identification of D- states in GaAs, InP and InSb

Abstract: D- states (i.e. the states formed by a neutral donor, D0, binding an extra electron), D0 interexcited state transitions (i.e. n to m where the principal quantum numbers n, m are greater than 1) and cyclotron resonance are all observed simultaneously in the far-infrared spectrum of n-GaAs and n-InP. This observation constitutes the first unambiguous identification of D- states in a compound semiconductor. D- states have been observed in seven GaAs and two InP samples. A chemical shift is observed, but no central cell splitting is found even at the largest available fields (i.e. 24 T). D- states are studied under a variety of experimental conditions such as hydrostatic pressure, temperature and electric field bias. The application of hydrostatic pressure strongly enhances the D- intensity in VPE InP, but not in VPE GaAs. Effects attributable to the formation of D- complexes occur in GaAs when the temperature is reduced to 2 K. The intensity of the D- transition increases markedly with increasing electric field bias. Divergence between theory and experiment is evident when the dimensionless magnetic field parameter, gamma , exceeds unity, indicating the inadequacy of existing variational calculations in this regime. D- triplet and singlet transitions are tentatively identified in n-InSb.

Defect dynamics and wear-out in thin silicon oxides

Abstract: The authors describe the results of a study of discrete, low-frequency fluctuations in the current through very thin insulator ( approximately 20 AA), small-area (1-2500 mu m2) metal-oxide-semiconductor tunnel diodes. Findings suggest that the discrete nature of the fluctuations arises from the activated transitions of oxide defects, either localised or extended, between a number of accessible metastable configurations, each of which has associated with it a different net trapped charge. Inelastic interactions between the fluctuating defects and the diode tunnel current can result in random energy input to the defects, which can effectively heat them above the bulk oxide temperature. At sufficiently high device biases, these interactions, coupled with interactions between the defects themselves, are strong enough that they can result in the creation of additional oxide defects, and thus lead to the gradual wear-out or deterioration of the oxide. A study of the complex fluctuations which arise during thin oxide wear-out and their effects on diode characteristics reveals that after an initial period of Si-SiO2 interface defect creation, the oxide wear-out proceeds by the diffusion of defects into the oxide. These moving defects appear to be closely associated with hole traps in the oxide. A number of the characteristics of very thin oxide wear-out can also be seen or inferred in measurements on thicker oxides, suggesting that the studies of very thin oxide diodes are providing a particularly detailed picture of the early stages of trap state formation, wear-out and breakdown in tunnel oxides in general.

Hot-electron energy relaxation rates in GaAs/GaAlAs quantum wells

Abstract: Experimental results of high-field parallel transport in GaAs/GaAlAs multiple quantum wells are presented. The experiments make use of steady-state photoluminescence spectroscopy and Hall effect measurements in the hot-electron regime. In a nominally undoped sample with n=1.55*1010 cm-2 per well, the effective energy relaxation time is constant and tau eff=127 fs. In a modulation-doped degenerate sample with n=1.38*1012 cm-2 per well, however, tau eff is found to be an order of magnitude longer and to vary somewhat with the electron temperature. The results are compared with a simple analytical model based on the production of hot phonons.

Magneto-optical and transport studies of ultrahigh mobility films of InAs grown on GaAs by molecular beam epitaxy

Abstract: InAs layers of very high electrical quality are grown on GaAs substrates by molecular beam epitaxy (MBE). The observation of sharp cyclotron resonance and donor lines (linewidths approximately=1 cm-1) in far-infrared magneto-optical studies suggest that the low-temperature mobilities in the bulk of the films are in the range 200 000-300 000 cm2 V-1 s-1 with an electron concentration of approximately=2*1014 cm-3. A strong but broad cyclotron resonance line and the Shubnikov-de Haas effect are observed from a two-dimensional electron gas (2DEG) at the surface or GaAs interface (nS approximately=1*1012 cm-2 and mu s approximately=20 000 cm2 V-1 s-1). As a consequence of parallel conduction from the low mobility layer the Hall mobility measured from a 5 mu m thick sample is 80 000 cm2 V-1 s-1 at 77 K and that in a 2 mu m sample is only 30 000 cm2 V-1 s-1. The width of bulk cyclotron resonance and impurity lines depend only weakly on thickness and consequently scattering from dislocations generated by the misfit at the GaAs/InAs interface is not thought to affect the bulk mobility strongly down to film thicknesses of 1 mu m. The parallel conduction from the 2DEG also produces a large magnetoresistance. Please note - the first author name has been corrected from Homes to Holmes

The .Si identical to Si3 defect at various (111)Si/SiO2 and (111)Si/Si3N4 interfaces

Abstract: The low-temperature (2

Vibronic states of silicon-silicon dioxide interface traps

Abstract: Ionic vibrational properties of trap systems present at the silicon-silicon dioxide interface are expected to influence measured data and their interpretation. Similar to the case of deep bulk impurities in semiconductors, these traps require a model, where the eigenenergies of the total defect system, including the captured electrons and the vibrating ion, is taken into account in optical investigations. For thermally governed processes, the same particle picture can be brought into a thermodynamical description, to make more detailed information on interface states possible. Differences between optical threshold energies and thermally obtained energy quantities, Gibbs free energies and enthalpies, together with thermally activated carrier capture and entropy changes during carrier transitions are expected when ionic relaxations are present at the interface. Experimental results, published in the literature, are examined in the light of this model. A number of data exist, which indicate that important parts of a detailed understanding of the silicon dioxide-silicon interface states are lost when treated as bare electronic systems.

Spin splitting of the electron subbands in the electrostatic interface potential on HgCdTe

Abstract: The authors determine the electric-field-induced spin splitting of the electron subbands on the surface of narrow gap HgCdTe from measurements of the oscillatory magnetoconductivity and cyclotron resonance. The coalescence and crossing of the Landau levels in the Shubnikov-de Haas oscillations is analysed in terms of the model developed by Bychkov and Rashba (extended to include nonparabolicity). Together with the resonance data it allows them to obtain the dispersion E0+or-(k/sub ///) of the electrically spin-split ground state subband. The experiments provide for the first time a number to be compared with sophisticated subband calculations.