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Showing papers in "Semiconductor Science and Technology in 1988"


Journal ArticleDOI
TL;DR: It is shown that the algorithm is capable of modelling layer by layer growth of AsGa, and based on using conditional probabilities to select the sites at which events occur, this has the advantage of being economic on computer time.
Abstract: A new algorithm is proposed for Monte Carlo simulation of MBE growth. The algorithm is based on using conditional probabilities to select the sites at which events occur. This has the advantage of being economic on computer time, the time per event scaling as the square root of the number of sites in the system. It is shown that the algorithm is capable of modelling layer by layer growth of AsGa.

171 citations


Journal ArticleDOI
TL;DR: In this article, the photo-to-dark conductivity ratio up to 109 and photoconductivity up to 3 Omega -1 cm-1 for white illumination approximately 300 W m-2 can be prepared from chemical baths containing thiourea and triethanolamine complex of cadmium ions.
Abstract: Cadmium sulphide thin films showing photo-to-dark conductivity ratio up to 109 and photoconductivity up to 3 Omega -1 cm-1 for white illumination approximately 300 W m-2 can be prepared from chemical baths containing thiourea and triethanolamine complex of cadmium ions. The photocurrent decay time depends on the bath temperature and the duration of storage and it ranges from a few seconds to 104 s per decade. The optical transmission of the films also varies significantly: from about 10% to 70-80% (above the band-gap absorption), depending on the deposition conditions. The high activation energy approximately=1 eV for dark conductivity as well as the high photosensitivity suggest the nearly stoichiometric nature of the films. The implications of these characteristics in various opto-electronic applications are discussed.

93 citations


Journal ArticleDOI
TL;DR: In this paper, the saturation of the free-electron concentration at high doping densities in delta -doped GaAs is studied by Shubnikov-de Haas measurements under hydrostatic pressure.
Abstract: The saturation of the free-electron concentration at high doping densities in delta -doped GaAs is studied by Shubnikov-de Haas measurements under hydrostatic pressure. Saturation occurs as soon as the depth of the Hartree potential is large enough to make the energy of the DX centre line up with the Fermi energy. The ultimate limit of the low-temperature equilibrium free-electron concentration in truly delta -doped GaAs is estimated to be 5.5*1012 cm-2 for Si donors. For realistic samples grown at Ts=500 degrees C the electron concentration is saturated at 7*1012 cm-2 due to the occupation of DX centres in a doping sheet, of finite thickness ( approximately=30 AA). For samples grown at higher temperatures (Ts=600 degrees C) autocompensation can occur prior to the population of the DX centre. Increases in mobility with increasing pressure observed in the Shubnikov-de Haas measurements for the i=0 sub-band provide additional evidence for a movement of the donors away from the original doping plane.

88 citations


Journal ArticleDOI
TL;DR: In this paper, high quality homo- and hetero-epitaxial GaSb has been grown from TMGa and TMSb using atmospheric pressure metal-organic vapour phase epitaxy (MOVPE).
Abstract: High-quality homo- and hetero-epitaxial GaSb has been grown from TMGa and TMSb using atmospheric pressure metal-organic vapour-phase epitaxy (MOVPE). Unintentionally doped material was p-type. At 295 K it had a carrier concentration of around 3.0*1016 cm-3 and a corresponding Hall mobility in the range of 670 to 1000 cm2 V-1 s-1. Growth parameters were carefully correlated with surface morphology, electrical quality and photoluminescence data to establish the growth window for this material.

81 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used SIMS profiling optimized for high depth resolution to investigate Si atomic plane or delta ( delta )-doping of GaAs during MBE, and found that post-growth diffusion occurs at the growth temperature with a diffusion coefficient estimated to be 9*10-17 cm2 s-1 at a substrate temperature of 550 degrees C.
Abstract: Si atomic plane or delta ( delta )-doping of GaAs during MBE has been investigated using SIMS profiling optimised for high depth resolution. For layers in which almost all the Si atoms act as donors, post-growth diffusion occurs at the growth temperature with a diffusion coefficient estimated to be 9*10-17 cm2 s-1 at a substrate temperature of 550 degrees C. At temperatures greater than about 550 degrees C, a marked preferential migration towards the surface is observed, which may be due to surface segregation or possibly enhanced diffusion.

70 citations


Journal ArticleDOI
TL;DR: In this paper, a simple method is described for calculating electronic states in narrow semiconducting wires near threshold, where there are few electrons in the system and the potential in which the electrons move can be found purely from electrostatics.
Abstract: A simple method is described for calculating electronic states in narrow semiconducting wires near threshold, where there are few electrons in the system and the potential in which the electrons move can be found purely from electrostatics. The pinning of the chemical potential on the surface of GaAs and (Al,Ga)As means that the surface can be treated as an equipotential, a great simplification that permits analytic solutions. The method is applied to wires fabricated by several techniques, either in epitaxial or modulation-doped layers. The width of the wavefunction can be reduced to about 20 nm in a typical shallow-etched wire or one 'squeezed' under a split gate. Energy levels for motion parallel to the interface are about 10 meV apart while those for motion normal to the interface are separated by about 40 meV. These relative scales are similar to those calculated by Laux and Stern (1986, 1988) for narrow channels in silicon. Confinement can be improved by putting the electrons closer to the surface. Comparison with the numerical work of Laux, Frank and Stern (1988) on squeezed wires in GaAs shows some differences which are traced to the appearance of an inversion layer of holes when there is a large negative bias on the gate. It is possible to define a depletion width for a two-dimensional electron gas with this method, as half the width of a deep etched mesa at the point where electrons just appear. Agreement with the experiments of Choi, Tsui and Alavi (1987) is acceptable, but highlights the problem of defining a unique depletion width in a two-dimensional system.

62 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the room temperature Raman spectrum from porous films on silicon substrates and interpreted this as due to the amorphous component in the film, although a similar spectrum may be obtained from the interface region between the silicon pores and their oxide.
Abstract: The authors have measured the room temperature Raman spectrum from porous films on silicon substrates. Data from films on degenerate substrates showed a Raman peak at the frequency expected for bulk silicon together with a peak shifted to lower frequencies. This was interpreted in terms of material having, in general, two different dimensions. Raman spectra from films on nondegenerate substrates show, in addition to the single crystalline peak, a broad wing extending to low frequencies. They have interpreted this as due to the amorphous component in the film, although a similar spectrum may be obtained from the interface region between the silicon pores and their oxide.

57 citations


Journal ArticleDOI
TL;DR: In this article, a characterisation study of single epitaxial layers of GaSb grown by the technique of molecular beam epitaxy (MBE) was performed, where both optical and electrical properties of this material were determined by low-temperature photo-luminescence and Hall effect techniques respectively.
Abstract: The authors report a characterisation study of single epitaxial layers of GaSb grown by the technique of molecular beam epitaxy (MBE). Both optical and electrical properties of this material are determined by low-temperature photo-luminescence and Hall effect techniques respectively, and compared with previous work on bulk GaSb grown by other methods. Optically detected cyclotron resonance (ODCR) measurements are reported for the first time in this material in order to determine conduction band electron effective masses and carrier momentum relaxation times. Deduced electron mobilities obtained by this novel technique are of the order of 105 cm2V-1s-1 and are in close agreement with theory.

55 citations


Journal ArticleDOI
TL;DR: In this article, the absorption properties of the system were quantitatively described by considering the system as a multi-layer dielectric stack, and it was shown that strong absorption is obtained provided that a large optical electrical field perpendicular to the quantum wells is generated.
Abstract: The observation of resonant inter-sub-band absorption in AlxGa1-xAs/GaAs single quantum wells using a total internal reflection geometry is reported. It is shown that strong absorption is obtained provided that a large optical electrical field perpendicular to the quantum wells is generated. Such conditions occur when the well is close to the reflecting boundary and reflection occurs at a semiconductor/metal interface, but not when reflection occurs at a semiconductor/vacuum interface. The optical properties of the whole structure can be quantitatively described by considering the system as a multi-layer dielectric stack.

53 citations


Journal ArticleDOI
TL;DR: In this article, an asymmetric resonant-tunnelling structure based on n-GaAs/(AlGa)As, incorporating a thin emitter barrier and a thick collector barrier, was observed to have intrinsic bistability.
Abstract: Intrinsic bistability is observed in an asymmetric resonant-tunnelling structure based on n-GaAs/(AlGa)As, incorporating a thin emitter barrier and a thick collector barrier. The resonant charge build-up in the quantum well which gives rise to the bistability is monitored by the Landau level structure in the magneto-capacitance.

52 citations


Journal ArticleDOI
TL;DR: In this paper, the 0 to 1 inter-sub-band electronic transition in (100) GaAs/Al 0.35Ga0.65As multi-quantum well structures as a function of temperature between 4.2 K and room temperature was studied.
Abstract: The 0 to 1 inter-sub-band electronic transition is studied in (100) GaAs/Al0.35Ga0.65As multi-quantum well structures as a function of temperature between 4.2 K and room temperature. Samples doped in the barrier or in the well are compared. A lineshape calculation allows the authors to separate the broadening of a single energy state from the intrinsic broadening caused by the different sub-band dispersions. Qualitatively different behaviour is found for modulation doped and well doped samples.

Journal ArticleDOI
P. S. Nandhra1, R C Newman1, R Murray1, B Pajot1, J Chevallier1, R B Beall1, J J Harris1 
TL;DR: In this paper, the dipole moment of the Be0 line at 482.1 cm-1 was determined and the strength of this line decreased during electron irradiation and it was inferred that Be impurities form complexes with intrinsic defects.
Abstract: Infrared absorption measurements have been made of the localised vibrational modes (LVM) of 9BeGa acceptors in GaAs grown by MBE for as-grown, electron-irradiated and hydrogen-passivated samples. The dipole moment has been determined for the Be0 line at 482.1 cm-1. The strength of this line decreased during electron irradiation and it is inferred that Be impurities form complexes with intrinsic defects. In passivated samples H-Be complexes form and stretching modes from H and D are found at 2037 and 1471 cm-1 respectively. Surprisingly the width of the former line is some three times greater than that of the latter. Only one mode of the complexes Be has been found at 555.7 cm-1. The hydrogen is believed to occupy a bond centre position between the Be atom and a nearest neighbour As atom. A comparison is made with H-Zn complexes.

Journal ArticleDOI
TL;DR: In this article, Czochralski silicon samples have been heated at temperatures between 350-450 degrees C in a hydrogen plasma, and donors were generated at about five times the rate found after furnace annealing, even if the ambient is hydrogen gas.
Abstract: Czochralski silicon samples have been heated at temperatures between 350-450 degrees C in a hydrogen plasma. Thermal donors are generated at about five times the rate found after furnace annealing, even if the ambient is hydrogen gas. The final donor concentration is comparable for the two types of processing. There is no significant evidence for hydrogen passivation effects and donors are not produced in plasma treated FZ silicon. Heating samples in an argon plasma does not enhance the rate of donor formation. Possible mechanisms for the enhancement are outlined briefly.

Journal ArticleDOI
TL;DR: In this article, annealing effects in Si/Ge strained layer superlattices (SLS) are studied by Raman scattering, where spectra from optical and folded acoustic phonons are recorded after each temperature treatment.
Abstract: Annealing effects in Si/Ge strained layer superlattices (SLS) are studied by Raman scattering. Spectra from optical and folded acoustic phonons are recorded after each temperature treatment. Above 600 degrees C the Ge LO phonon shifts to lower frequencies and the Si-Ge alloy mode gains in intensity due to diffusion of Si into the Ge layers. The Si mode remains unchanged up to annealing temperatures of about 800 degrees C. The intensity ratios of folded LA phonons are also sensitive to the annealing process. Their frequencies shift only slightly. Raman spectroscopy allows the authors to separate a different interdiffusion process of species in adjacent layers.

Journal ArticleDOI
TL;DR: A broad overview of the possible applications of Rapid Thermal Processing (RTP) techniques is given in this article, where three main modes of RTP, the adiabatic, thermal flux and isothermal modes, are compared in terms of heat flow, physical processes and suitability for various applications in the field of silicon semiconductor processing.
Abstract: The authors give a broad overview of some of the possible (and actual) applications of rapid thermal processing (RTP) techniques. Pioneering work done in the field of RTP is described, and a large number of references (about 90) are given. Because of the very wide range of possible applications the detail in which each is discussed may not be in direct relation to their importance for commercial or research purposes. The three main modes of RTP, the adiabatic, thermal flux and isothermal modes are described and contrasted in terms of heat flow, physical processes and suitability for various applications in the field of silicon semiconductor processing. The main types of equipment utilised for RTP research studies are briefly described, ranging from pulsed and CW laser and electron beam sources to radiant heat sources such as graphite plate and lamp systems. Three examples of the application of RTP to silicon semiconductor processing are described in some detail, with comparisons to conventional processing techniques made where relevant. The use of isothermal annealing systems for the activation of ion-implanted dopants is described and reviewed. The possible advantages of RTP are given, and the place of such technology in modern CMOS processing are briefly summarised. The formation of silicon-on-insulator structures using RTP techniques is described and compared with the competing technologies of oxygen implantation and porous silicon. Finally, the wide-ranging, new field of in situ multi-stage processing (or limited reaction processing) is briefly described, and possible applications discussed. This final section covers a subject in which much interest at the research level is presently focused.

Journal ArticleDOI
TL;DR: In this paper, a thin layer of dye sandwiched between p-CuCNS deposited on a copper substrate and n-SnO2 coated transparent glass was found to yield photocurrents resulting from light absorption in the dye.
Abstract: A thin layer of dye sandwiched between p-CuCNS deposited on a copper substrate and n-SnO2 coated transparent glass was found to yield photocurrents resulting from light absorption in the dye. The mechanism of photocurrent generation is discussed.

Journal ArticleDOI
TL;DR: In this article, a photoluminescence study at low temperatures of Si-doped AlxGa1-xAs (0
Abstract: A photoluminescence study at low temperatures of Si-doped AlxGa1-xAs (0

Journal ArticleDOI
TL;DR: In this article, the effect of conduction band non-parabolicity on inter-sub-band absorption in doped semiconductor quantum wells was theoretically treated and an analytical expression for the absorption at zero temperature was derived.
Abstract: The authors have theoretically treated the effect of conduction band non-parabolicity on inter-sub-band absorption in doped semiconductor quantum wells. The authors have derived an analytical expression for the absorption at zero temperature. The absorption peak is shifted to lower energies and the peak height is reduced by non-parabolicity. These effects are small for GaAs-based quantum wells, but may be detrimental to InGaAs quantum wells.

Journal ArticleDOI
TL;DR: In this article, photoluminescence studies of Ga1-xInxAs/Al1-yInyAs quantum wells nominally lattice matched to InP are reported.
Abstract: Photoluminescence studies of Ga1-xInxAs/Al1-yInyAs quantum wells nominally lattice matched to InP are reported. The photoluminescence from two samples each having six quantum wells of thicknesses ranging from about 6 to 122 AA is studied in detail. The main emission peak associated with each quantum well is attributed to excitonic recombination. The emission from the 6 AA quantum well at 897.3 nm is found to have a peak width of only 18 meV at 4.2 K. Temperature dependence studies show that at 4.2 K the excitons are localised at potential fluctuations in the quantum wells. Impurity-related emission is also observed from some of the quantum wells.

Journal ArticleDOI
TL;DR: In this paper, large oscillations of the current in non-degenerate n-type GaAs/AlGaAs quantum wells have been observed under a range of conditions below room temperature.
Abstract: Large oscillations of the current in non-degenerate n-type GaAs/AlGaAs quantum wells have been observed under a range of conditions below room temperature. In the case of low electron concentration in a MQW sample the oscillations were damped and the period corresponded to the transit time for transversely polarised acoustic waves. Accompanying oscillations of photoluminescence are also observed, and the electron temperature is seen to drop with time. In the case of a degenerate single-quantum-well sample the oscillations were continuous and the period was a factor about eight shorter than the acoustic transit time. All samples were cut and contacted such that current flowed along a (110) direction.

Journal ArticleDOI
TL;DR: In this paper, the effect of broadening on the capacitance transient and on deep-level transient spectroscopy (DLTS) analysis of traps is examined and the authors illustrate their analysis by considering both simulated and actual experimental situations.
Abstract: A deep trap in the fundamental gap of a semiconductor has a sharp (delta function) character. In a semiconductor alloy the presence of disorder introduces a distribution of trap activation energies. The authors have undertaken a detailed analytical and numerical exercise to examine the effect of such broadening on the capacitance transient and on deep-level transient spectroscopy (DLTS) analysis of traps. In general the standard DLTS analysis introduces negligible error except in cases of severe broadening where it overestimates the activation energy. They illustrate their analysis by considering both simulated and actual experimental situations.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results on the band-structure effects in single-barrier tunnelling, calculated using a new scattering matrix method, and show that the transmission amplitude may be divided into two regions.
Abstract: The authors present the results on the band-structure effects in single-barrier tunnelling, calculated using a new scattering matrix method. Their results show that the transmission amplitude may be divided into two regions. The first is for electron energies in the band gap of the barrier material, where the transmission is found to be a single state property, with the Gamma state dominant. The appropriate barrier height, regardless of the direct/indirect nature of the barrier band gap, is the Gamma - Gamma band offset. The tunnelling behaviour is therefore single state like. The other regime is for electrons with energies above the barrier material's conduction band edge where, for indirect band-gap barriers, a sharp transition to an X dominated behaviour is observed. Coupling between the barrier Gamma and the X states are found in thin barriers and X well resonances are obtained. The single barrier transmission in this regime is therefore a multistate property.

Journal ArticleDOI
TL;DR: In this article, the effect of anisotropic parabolic energy bands and indirect parabolic bands (conduction and valence band extrema at different points in wavevector space) on the transition probability per unit time for impact ionisation is investigated.
Abstract: The effect of anisotropic parabolic energy bands and of indirect parabolic energy bands (conduction and valence band extrema at different points in wavevector space) on the transition probability per unit time for impact ionisation is investigated. The resulting direction-dependent threshold energy is described by introducing a threshold ellipsoid. It is found that for the 'lucky-drift' model for impact ionisation in an electric field the transition probability rate which is applicable increases from zero above the energy threshold with a cubic power for anisotropic or indirect parabolic bands, or, in special circumstances a 5/2 power compared with the more usual square law of the Keldysh result for direct isotropic parabolic band structures.

Journal ArticleDOI
TL;DR: In this paper, the photoluminescence spectra from ZnSe-ZnTe superlattices are explained by a very simple model in which excitons are formed from holes tightly localised in single znSe layers and from electrons in large orbits extending over several layers of both types.
Abstract: The photoluminescence spectra from ZnSe-ZnTe superlattices are shown to be explained by a very simple model in which excitons are formed from holes tightly localised in single ZnSe layers and from electrons in large orbits extending over several layers of both types. The results suggest that the conduction band offset is insufficiently large to localise the electrons. The holes are trapped by tellurium iso-electronic centres and, since tellurium can act as an iso-electronic trap in several II-VI compounds, this new type of excitonic behavior in superlattices may have important device implications.

Journal ArticleDOI
TL;DR: In this article, it was shown that the retention of only one further term provides an analytic approximation that is quantitatively useful over a much wider range of cases of interest, assuming that the contributions from the motion of second and further neighbours of the impurity are negligible.
Abstract: The 'rigid-well' approximation for the local vibrational mode frequency of a light impurity in a crystal in which only the impurity itself is regarded as moving may be regarded as the leading term in an expansion in powers of the ratio of the impurity mass to the host mass or masses. It is found that the retention of only one further term provides an analytic approximation that is quantitatively useful over a much wider range of cases of interest. This approximation assumes a particularly simple form if the contributions from the motion of second and further neighbours of the impurity are negligible. Various applications are presented.

Journal ArticleDOI
TL;DR: In this paper, high quality Al0.48In0.52As layers with specular morphology and narrowest reported X-ray linewidths of 24 seconds of arc have been grown on InP substrates by LP MOVPE at temperatures of 680-710 degrees C.
Abstract: High quality Al0.48In0.52As layers with specular morphology and narrowest reported X-ray linewidths of 24 seconds of arc have been grown on InP substrates by LP MOVPE at temperatures of 680-710 degrees C. Background carrier concentrations were in the range 8*1515-4*1016 cm-3 with room temperature mobilities as high as 1900 cm2 V-1 s-1 for growth under optimum conditions. Doping in the range 1017-2*1018 cm-3 was achieved using a H2S/H2 mixture. Improvements in structural and electrical quality were concurrent with successful Schottky barrier measurements where barrier heights of up to phi B=0.73 eV were obtained from C-V measurements on diodes using evaporated PtAu. These results have important implications in the development of Ga0.47In0.53As/Al0.48As HEMTS and InP-based opto-electronic devices.

Journal ArticleDOI
TL;DR: In this paper, the first growth of superlattices in the wurtzite CdS/CdSe system was reported, which were grown by metalorganic chemical vapour deposition on GaAs (111) substrates.
Abstract: The authors report the first growth of superlattices in the wurtzite CdS/CdSe system. The superlattices were grown by metal-organic chemical vapour deposition on GaAs (111) substrates. Transmission electron microscopy shows the superlattices to be of good quality with abrupt interfaces. The layers were purely hexagonal with no twinning. Low-temperature photoluminescence of the superlattices was studied for various layer thicknesses. All the structures showed a broad intense near-infrared emission which shifts to higher energy for the thinnest layers. In addition, thicker layers showed a narrower red emission at 690 nm. The photoluminescence spectra provide preliminary evidence that the structure is of type II.

Journal ArticleDOI
TL;DR: In this paper, the properties of these defects in undoped and doped alloys are reviewed and the properties can be consistently explained by involving the interaction of the defects with indirect L and X minima.
Abstract: The electrical properties of the AlxGa1-xAs alloys for x>or=0.24 are dominated by deep donors which appear in undoped and doped crystals. The corresponding defects, which are now more commonly known as D-X centres, also behave as electron traps. The properties of these defects in undoped and doped alloys are reviewed. Results of Hall, transient capacitance, deep-level transient spectroscopy and thermally stimulated capacitance measurements on crystals grown by liquid phase epitaxy and molecular beam epitaxy are presented and discussed. The deep levels have a constant thermal activation energy of 0.21 eV in the direct band-gap region, while in the same composition range the defect binding energy, as determined from Hall measurements, increases monotonically. Beyond the crossover region, the thermal activation energy and binding energy assume similar values and both decrease monotonically with increase of x. These energy values and the electron capture properties of the defects can be consistently explained by involving the interaction of the defects with indirect L and X minima. Defects with similar properties are also identified in other alloy systems in which the L and X conduction minima are lowest in energy.

Journal ArticleDOI
TL;DR: In this paper, the results of photoluminescence excitation spectroscopy are shown to depend strongly on carrier mobilities when, at a given distance from the surface, an escape mechanism exists, i.e. a possibility for carriers to escape from the active layer after moving through it.
Abstract: In GaAs/AlxGa1-xAs superlattices, GaAs and AlGaAs epitaxial layers, the results of photoluminescence excitation spectroscopy are shown to depend strongly on carrier mobilities when, at a given distance from the surface, an escape mechanism exists, i.e. a possibility for carriers to escape from the active layer after moving through it. When there is no escape mechanism close enough to the surface, excitation spectra are roughly flat apart from the excitonic resonances. When an escape mechanism is present at a distance of around 1 mu m from the surface, if the mobility is high enough as in GaAs and superlattices with periods smaller than about 70 AA (for x approximately 0.3 and nearly equal well and barrier widths), the excitation spectra exhibit a decreasing high-energy tail; on the contrary in AlGaAs and superlattices with greater periods the excitation spectra have the same shape as in similar samples without an escape mechanism. Superlattices with small periods constitute better structures than equivalent AlGaAs layers for device applications.

Journal ArticleDOI
TL;DR: In this paper, the use of a metal-organic precursor molecule (dimethyl indium ditertiarybutyl phosphine) for the co-evaporated growth of epitaxial indium phosphide by metalorganic molecular beam epitaxy was reported.
Abstract: The authors report preliminary results on the use of a novel metal-organic precursor molecule-dimethyl indium ditertiarybutyl phosphine-for the co-evaporated growth of epitaxial indium phosphide by metal-organic molecular beam epitaxy. It is shown that indium-rich growth occurs at all substrate temperatures studied but that stoichiometric growth is only possible at 480 degrees C with simultaneous incident flux of dissociated phosphine.