Showing papers in "Semiconductor Science and Technology in 2000"
TL;DR: In this paper, a review of recent achievements in the fabrication of diode lasers for the near-infrared range on GaAs substrates is presented, including material growth, optical properties and laser characteristics.
Abstract: The present paper reviews recent achievements in the fabrication of diode lasers for the near-infrared range on GaAs substrates. 1.3??m light emitters are currently widely used in fibre-optic communication systems. GaAs-based devices are potentially advantageous compared to their InGaAsP counterparts in several aspects, such as improvement of thermal stability, possibility to grow vertical-cavity surface-emitting lasers in a single growth run and the use of large-area high-quality inexpensive GaAs substrates. Three main approaches have been suggested so far to achieve the 1.3??m emission from structures grown on GaAs substrates. They are InGaAs and GaAsSb quantum wells, GaInAsN quantum wells and InAs/GaAs quantum dots. In the present paper we discuss all these approaches including material growth, optical properties and laser characteristics. The results obtained by these methods are compared and their potential advantages discussed.
171 citations
IBM1
TL;DR: In this paper, the authors examine the limit of gate oxide scaling from a reliability point of view, and explore the relative importance of characteristic breakdown time and Weibull slope in lifetime projection, and the possibilities of extending gate oxide beyond the currently predicted limit.
Abstract: In this article, we critically examine the limit of gate oxide scaling from a reliability point of view. The thickness dependence of the characteristic breakdown time (charge) and Weibull slope as well as the temperature dependence of oxide breakdown are measured with emphasis on accuracy. The failure modes of soft and hard breakdown events and their impact on device characteristics are reviewed. Using a two-dimensional reliability analysis, we explore the relative importance of characteristic breakdown time and Weibull slope in lifetime projection, and the possibilities of extending gate oxide beyond the currently predicted limit.
146 citations
TL;DR: In this paper, a Gaussian line shape gain model with a constant intraband relaxation time gives good agreement with experimental gain spectra and the inclusion of k-dependent intrband relaxation time yields slightly improved agreement.
Abstract: Momentum-dependent and independent intraband relaxation time effects on a non-Markovian (Gaussian line shape) many-body optical gain spectrum are presented. Our theoretical results are compared with experimental data as well as those obtained from a many-body gain model with a conventional Lorentzian line shape function. We show that a Gaussian line shape gain model with a constant intraband relaxation time gives good agreement with experimental gain spectra and the inclusion of k -dependent intraband relaxation time yields slightly improved agreement. In the case of a Lorentzian line shape function, it is found that the inclusion of the k -dependent carrier-carrier scattering in the intraband relaxation time is important to obtain good agreement with the experiment. This is because the Gaussian line shape function is steeper than the Lorentzian for a constant intraband relaxation time. The Gaussian line shape function with a constant intraband relaxation time requires less computational time than that with a k -dependent intraband relaxation time; therefore, it is an efficient model for comparison with experimental data.
117 citations
TL;DR: In this article, the authors reviewed the properties that are exploited by the latest generation of detectors, and those which are less well understood, such as grain boundaries and priming effects.
Abstract: Diamond's many extreme properties, such as its radiation and corrosion resistance, large bandgap, high electron and hole mobility, make it an attractive semiconductor for UV and particle detectors. This paper reviews the properties that are exploited by the latest generation of detectors, such as the radiation hardness and detection mechanisms, and those which are less well understood, such as grain boundaries and priming effects. The UV and particle detectors and dosimeters that have been reported in the last few years are described and briefly assessed.
93 citations
TL;DR: In this paper, it is shown that the log-normal distribution is inadequate to describe the tBD-statistics; only the Weibull distribution can be used to describe tBDstatistics, and it is concluded that a ln(tBD)-Vg-dependence is well suited to extrapolate high voltage tBD data to low voltage.
Abstract: Gate oxide reliability is an essential factor in qualifying CMOS technologies. An accurate and consistent methodology for determining ultrathin oxide reliability is therefore needed. In this paper, the crucial steps of this methodology are analysed. First it is demonstrated that soft and hard breakdown show an identical distribution and therefore extrapolation, from the test voltage to a voltage where the soft to hard breakdown prevalence ratio is different, is allowed. Secondly, the log-normal distribution is shown to be inadequate to describe the tBD-statistics; only the Weibull distribution can be used. Thirdly, based on stress-induced leakage current measurements, it is concluded that a ln(tBD)-Vg-dependence is well suited to extrapolate high voltage tBD-data to low voltage. It is demonstrated that in the 1 to 2 V range, the gate voltage shows no threshold value below which the oxide degradation is reduced or altered. A detailed analysis in the oxide thickness range 2 to 5 nm is presented showing that oxide reliability might become a major showstopper for the further downscaling of CMOS technology. Possible flaws in the reliability prediction methodology are discussed and guidelines for future research are indicated.
92 citations
TL;DR: In this article, the authors used photoluminescence (PL) spectroscopy on multicrystalline silicon (mc-Si) wafers to investigate the defect distribution affecting the efficiency of solar cells.
Abstract: Scanning photoluminescence (PL) spectroscopy was performed on as-grown and processed multicrystalline silicon (mc-Si) wafers to investigate the defect distribution affecting the efficiency of solar cells. In highly inhomogeneous mc-Si prepared by (i) edge-defined film-fed growth or (ii) a block-casting technique, regions of a wafer with enhanced recombination activity and reduced minority carrier lifetime exhibit an intensive `defect' PL band at room temperature with the maximum at about 0.8 eV. By comparing PL mapping with the distribution of dislocations, we present experimental evidence that the 0.8 eV band corresponds to electrically active dislocation networks. This was confirmed using low-temperature PL spectroscopy, which revealed a characteristic quartet of the dislocation D-lines. One of these dislocation lines, D1, can be tracked as temperature increases and linked to the `defect' band. Strong linear polarization of the 0.8 eV PL band corresponds to a preferential localization of defects in regions with a high level of elastic stress measured with scanning infrared polariscopy. The origin of the 0.8 eV PL band is attributed to dislocations contaminated with impurity precipitates.
89 citations
TL;DR: In this paper, spray pyrolysis technique has been employed to prepare uniform, large-area thin-film coatings of PbS on glass and on fluorine-doped tin oxide (FTO) conducting substrates at various substrate temperatures.
Abstract: The spray pyrolysis technique has been employed to prepare uniform, large-area thin-film coatings of PbS on glass and on fluorine-doped tin oxide (FTO) conducting substrates at various substrate temperatures. Growth of polycrystalline PbS films occurred at a lower temperature (T-S = 275 degrees C) on conducting substrate than on glass (T-S = 325 degrees C) and oriented growth of polycrystalline cubic PbS occurred on FTO substrates. Characterization of the films has been carried out using x-ray diffraction, scanning electron microscopy and electrical resistivity studies. The optical transmittance spectra of these films have been taken for a wavelength range of 400-2500 nm. The films are found to be n type and their conductivities are of the order of 10(-4) (Omega cm)(-1). The lattice parameter value is presented. The average crystallite size of the films is of the order of 10(3) Angstrom and the average grain size is of the order of 10(4) Angstrom. Solar control properties of spray pyrolytically deposited PbS thin films have been investigated.
87 citations
TL;DR: In this paper, a 1.6-nm oxide with a soft breakdown criterion was used to evaluate the reliability of a 10-year lifetime with a 100-ppm failure rate for 1.3-V operation at 100°C.
Abstract: The important components of reliability projection are investigated. Acceleration parameters are obtained for a 1.6 nm oxide with a soft breakdown criterion. Based on the physical percolation model, the voltage scaling factor for time to breakdown is found to increase with lower voltage, explaining the experimental observation of 6.7 ± 0.4 dec V-1 for the 1.6 nm oxide. The distribution of breakdown times is shown to be sensitive to thickness variation across the test wafer, and a Weibull slope of 1.38 ± 0.1 was obtained. The temperature dependence of the time to breakdown was found to be non-Arrhenius and to have a slope of 0.02 dec °C-1. Using these parameters, the 1.6 nm oxide was found to have a 10 year lifetime with a 100 ppm failure rate for 1.3 V operation at 100 °C. Our understanding of soft breakdown is described as well as an investigation of device operation after soft breakdown, which may further improve the reliability projection.
78 citations
TL;DR: In this paper, the authors show that the increase in direct tunnelling leakage leads to more hole injection and trapping in the SiO2, and the enhanced dielectric degradation rate with tox reduction can be explained on the basis of an intrinsic molecular model where hole capture serves to catalyze Si-O bond breakage.
Abstract: SiO2 films, at constant electric field, show a significant reduction in time-dependent dielectric breakdown (TDDB) performance when the thickness tox is scaled below 4.0 nm. This reduction in TDDB performance is coincident with and scales with the increase in direct tunnelling (DT) leakage through these hyper-thin oxide films. Assuming that the increase in DT leakage leads to more hole injection and trapping in the SiO2, the enhanced dielectric degradation rate with tox reduction can be explained on the basis of an intrinsic molecular model where hole capture serves to catalyze Si-O bond breakage.
77 citations
TL;DR: In this article, a comparative analysis is made of laser diodes based on Stranski-Krastanow (SK) and sub-monolayer (SML) InAs/GaAs quantum dots, emitting at about 940nm.
Abstract: A comparative analysis is made of laser diodes based on Stranski-Krastanow (SK) and sub-monolayer (SML) InAs/GaAs quantum dots, emitting at about 940 nm. Owing to the better uniformity of sub-monolayer quantum dots, the SML QD laser surpasses the SK QD one in power characteristics. A maximum output power of 3.9 W and a peak power conversion efficiency of 59% have been achieved for SML QD 100 µm wide lasers at 10 °C.
76 citations
TL;DR: A theoretical analysis and computer simulation of the threshold current density jth and characteristic temperature T0 of multiple quantum well lasers (MQWLs) are presented in this paper, together with the spontaneous radiative recombination, the Auger recombination and the lateral diffusive leakage of carriers from the active region are included into the model.
Abstract: A theoretical analysis and computer simulation of the threshold current density jth and characteristic temperature T0 of multiple quantum well lasers (MQWLs) are presented. Together with the spontaneous radiative recombination, the Auger recombination and the lateral diffusive leakage of carriers from the active region are included into the model. A first-principle calculation of the Auger recombination current is performed. It is shown that the lateral diffusive leakage current is controlled by the radiative and Auger currents. When calculating the carrier densities, the electrons in the barrier regions are properly taken into account. Redistribution of electrons over the active region is shown to increase the threshold current considerably. The dependences of jth and T0 on temperature, number of QWs, cavity length and lateral size are discussed in detail. The effect of lattice and carrier heating on jth and T0 is investigated and shown to be essential at high temperature.
TL;DR: In this article, the performance of a multi-couple thermoelectric device as a generator is investigated and the general expressions of two important performance parameters, the efficiency and power output, are given.
Abstract: The performance of a multi-couple thermoelectric device as a generator is investigated. The general expressions of two important performance parameters, the efficiency and power output, are given. The -K characteristic curves of a thermoelectric generator are presented for some differently constrained conditions, where is the efficiency of the thermoelectric system and K is the total thermal conductance of the multi-couple thermoelectric device. The maximum efficiency of the system is calculated. The structure parameters of the device are optimized. The effect of the thermal conductances between the thermoelectric device and the external heat reservoirs on the performance of the system is expounded by using some representative numerical examples. The results obtained here will be useful for a more detailed investigation and for the optimal design of real thermoelectric generators.
TL;DR: In this article, a wet etching method for GaN and AlxGa1-xN, based on aqueous solutions of KOH, is presented, and a detailed analysis of the etching rate dependence with temperature and concentration is described.
Abstract: A wet etching method for GaN and AlxGa1-xN, based on aqueous solutions of KOH, is presented. A detailed analysis of the etching rate dependence with temperature and concentration is described. This etching has been used for the fabrication of high optical quality pyramidal nanostructures in wurtzite N-face GaN grown on AlN-buffered Si(111) substrates by molecular beam epitaxy. These nanostructures have been studied by high-resolution transmission and scanning electron microscopy and their optical quality has been analysed by low-temperature photoluminescence (PL) measurements. The pyramids are parallel to the basal plane and limited by {111} planes and its presence improves the overall PL response of the sample. The relationship between the polarity of GaN and the characteristics of the AlN buffer has also been analysed.
TL;DR: In this article, a-and b-type thin In2O3:Sn thin films were obtained when the films were deposited at the substrate temperature of 793 K and 753 K, respectively.
Abstract: Tin doped indium oxide (In2O3:Sn) or indium tin oxide (ITO) thin films have been successfully deposited by the low cost spray-pyrolysis method. Low sheet resistance and high mobility films were obtained when the films were deposited at the substrate temperature of 793 K. The direct optical bandgaps for the films deposited at 793 (a) and 753 K (b) were found to be 3.46 and 3.40 eV, respectively. Similarly, the indirect bandgaps for a- and b-type films were found to be 3.0 and 2.75 eV, respectively. The Burstein-Moss shift was observed in the films. The refractive index (n) and extinction coefficient (k) were found to be in the range of 2.1 to 1.1 and 0.6 to 0.01, respectively. The various scattering mechanisms such as lattice, ionized impurity, neutral impurity, grain boundary and alloy scattering due to variation of theoretical mobilities with temperature are discussed, in order to compare experimental results. In the lattice scattering mechanism, the quantum size effect phenomena were employed to estimate the energy dilation (EI). The a-type films exhibited SnO2 as secondary phase whereas b-type films showed single phase In2O3:Sn with high sheet resistance. The lattice constants were found to be 10.16 and 10.09 A for a- and b-type films, respectively.
TL;DR: In this article, the influence of the ratio of Al to Ti on the contact resistivity, thermal stability and surface morphology of the Al/Ti/n-GaN ohmic contact was revealed.
Abstract: The Al/Ti/n-GaN ohmic contact and multilayer variations on this contact are widely used because of the low contact resistivities they provide to n-GaN. However, there are few reports that reveal the influence of the atomic ratio of Al to Ti on the contact resistivity, thermal stability and surface morphology of the contacts. This study reveals that the ratio of Al to Ti strongly influences all of these characteristics. All contacts in this study had atomic ratios of Al to Ti higher than 1. Those contacts with ratios of Al to Ti less than 3 required higher annealing temperatures or longer annealing times to reach comparable contact resistivities compared to the more Al-rich contacts. On the other hand, the less Al-rich contacts provided several advantages. They exhibited smooth surface morphologies even after they were annealed at temperatures near 1000 °C, and they suffered much less severe degradation during long-term aging at 600 °C. These findings are explained by differences in the phases formed after annealing.
TL;DR: In this paper, Annealing of InGaAs quantum dots (QDs) fabricated by metal-organic chemical vapour deposition and covered with a very thin GaAs cap layer completely eliminates large dislocated inGaAs clusters and remarkably improves the optical properties of the structures.
Abstract: Annealing of InGaAs quantum dots (QDs) fabricated by metal-organic chemical vapour deposition and covered with a very thin GaAs cap layer completely eliminates large dislocated InGaAs clusters and remarkably improves the optical properties of the structures. A modal gain of ~4 cm-1 is achieved in the 1.35 µm range. The elimination of defects allows the stacking of QDs emitting at 1.3 µm without deterioration of their optical and structural properties and reduces the QD density in the upper sheets.
TL;DR: In this article, the authors reported measurements of photoluminescence and time decay on three MOVPE-grown InGaN/GaN multiple quantum well structures with 13% In in the wells and well widths Lz = 1.25, 2.5 and 5.0 nm.
Abstract: We report measurements of photoluminescence, photoluminescence excitation spectroscopy and photoluminescence time decay on three MOVPE-grown InGaN/GaN multiple quantum well structures with 13% In in the wells and well widths Lz = 1.25, 2.5 and 5.0 nm. The PL spectra are dominated by single emission peaks, together with phonon sidebands spaced by a GaN LO phonon energy (92 meV). The peak energies are red-shifted with respect to energies calculated for exciton recombination in square quantum wells and the wide well sample also shows a significant Stokes shift between emission and absorption. Recombination lifetimes measured at 6 K are energy dependent, increasing as the photon energy is scanned downwards through the emission line. They also depend strongly on well width. On the low energy side of the 5 nm well emission line we measure lifetimes as long as 100 ns. Raising the temperature from 6 to 300 K results in a strong reduction of emission intensity for all samples and reduction of the lifetimes, though by a much smaller factor. The peak positions shift slightly to lower energy but by far less than the shift in the band edge. We consider three different theoretical models in an attempt to interpret this data, an exponential tail state model, a model of localization due to In/Ga segregation within the wells and the quantum confined Stark effect model. The QCSE model appears able to explain most of the data reasonably well, though there is evidence to suggest that, in addition, some degree of localization occurs.
TL;DR: In this article, the strain state, film and surface morphology of SiGe virtual substrates grown by gas-source molecular beam epitaxy (use of disilane and germane) were studied.
Abstract: We have studied the strain state, film and surface morphology of SiGe virtual substrates grown by gas-source molecular beam epitaxy (use of disilane and germane). The macroscopic strain relaxation and the Ge composition of these virtual substrates have been estimated in high resolution x-ray diffraction, using either omega-2 theta scans or reciprocal space maps around the (004) and (224) orders. Typically, linearly graded Si0.67 Ge0.33 virtual substrates 2.5 µm thick are 97% relaxed. From transmission electron microscopy, we confirm that the misfit dislocations generated to relax the lattice mismatch between Si and SiGe are mostly confined inside the graded layer. The surface roughness of the relaxed SiGe virtual substrates increases significantly as the Ge concentration and/or the growth temperature exceeds 20%/600 °C. At 550 °C, we find for the technologically important Ge concentration of 30% a surface root mean square roughness of 12 nm, with an undulation wavelength for the cross-hatch of the order of one micron.
TL;DR: In this paper, a brief review of the electronic and transport properties of carbon nanotubes is given from a theoretical point of view, including a giant Aharonov-Bohm effect on the bandgap and a Landau-level formation in magnetic fields.
Abstract: A brief review is given of electronic and transport properties of carbon nanotubes mainly from a theoretical point of view. The topics include a giant Aharonov-Bohm effect on the bandgap and a Landau-level formation in magnetic fields, absence of backward scattering except for scatterers with a potential range smaller than the lattice constant, a conductance quantization in the presence of short-range and strong scatterers such as lattice vacancies and transport across junctions between nanotubes with different diameters.
TL;DR: In this paper, a doubling Nd:YVO4 laser with a pulse energy of 18.5 µJ and a repetition frequency of 20 µJ was used to crystallize amorphous silicon films.
Abstract: We crystallize amorphous silicon films by a frequency doubled Nd:YVO4 laser with a pulse energy of 18.5 µJ and a repetition frequency of 20 kHz. A sequential lateral solidification process yields polycrystalline silicon with grains longer than the channel of thin-film transistors. The resulting electron field effect mobility of 410 cm2 V-1 s-1 shows the superiority of our process compared with excimer laser crystallization. A calculation results in a possible throughput of 35 cm2 s-1 for our laser crystallization process if one used a laser with a pulse energy of 1.25 mJ and a repetition frequency of 100 kHz.
TL;DR: In this paper, the authors investigated the relationship between the hydrostatic strain, the uniaxial strain and the intrinsic chemical effect of Ge and C on the band offsets of Si(001) substrate.
Abstract: The band offsets for strained Si1-x-yGexCy layers grown on Si(001) substrate and for strained Si1-xGex layers grown on fully relaxed Si1-zGez virtual substrates are estimated. The hydrostatic strain, the uniaxial strain and the intrinsic chemical effect of Ge and C are considered separately. Unknown material parameters relative to the latter effect are chosen to give the best agreement with the available experimental results for Si1-xGex and Si1-yCy layers on Si. As a general trend concerning carrier confinement opportunities, it is found that a compressive strain is required to obtain a sizeable valence band offset, while a tensile strain is needed to obtain a conduction band discontinuity. In most cases the strain is responsible for a bandgap narrowing with respect to that of the substrate. The obtained results are in very good agreement with available experimental determinations of band offsets and bandgap changes for ternary alloys on Si(001).
TL;DR: In this paper, the magnitude of the electron density induced by spontaneous and piezoelectric polarization in a polar heterostructure is studied. But the model is restricted to the case of pure material and the induced electrons derive from ''ambient' doping associated with surface states and surface ions.
Abstract: Models for the magnitude of the electron density induced by spontaneous and piezoelectric polarization in a polar heterostructure are given. In the case of pure material the induced electrons derive from `ambient' doping associated with surface states and surface ions. Where the donor density is large enough depletion will contribute to the electron gas.
TL;DR: In this article, the authors calculated the measured tunnel current based on multiple scattering theory and showed that the threshold voltage and the transconductance fluctuations will be problematic when the gate oxide thickness is scaled down to about 0.8 nm.
Abstract: The statistical distribution of the direct tunnel leakage current through the ultrathin gate oxides of MOSFETs induces significant fluctuations in the threshold voltage and the transconductance when the gate oxide tunnel resistance becomes comparable to the gate poly-Si resistance. By calculating the measured tunnel current based on multiple scattering theory, it is shown that the threshold voltage and the transconductance fluctuations will be problematic when the gate oxide thickness is scaled down to about 0.8 nm.
TL;DR: In this article, the post-breakdown resistance (Rbd) distribution of ultra-thin SiO2 is discussed on the basis of the experimental results of the post breakdown resistance distribution.
Abstract: The dielectric breakdown mechanism of ultra-thin SiO2 is discussed on the basis of the experimental results of the post-breakdown resistance (Rbd) distribution. We have noticed that the Rbd of SiO2 in MOS devices is strongly related to the SiO2 breakdown characteristics such as the polarity dependence, the oxide field dependence or the oxidation process dependence of Qbd. In this paper, we discuss the dielectric breakdown mechanism of SiO2 from the viewpoint of the statistical correlation between the Rbd distribution, the Qbd distribution and the discharging energy at the SiO2 breakdown, by changing the stress polarity, the stress field, the oxide thickness and the oxidation process. In the case of hard breakdown, it has been clarified that the Rbd distribution for substrate electron injection is clearly different from that for gate electron injection. We have also found that, irrespective of the stress current density, the gate oxide thickness, the stressing polarity and the oxidation process, Rbd can be uniquely correlated to the discharging energy at dielectric breakdown, in the case of hard breakdown. Furthermore, it has been clarified that the Rbd does not depend on the energy dissipation at soft breakdown.
TL;DR: In this article, the potential of silicon oxynitride, a gradient index material, for the fabrication of integrated optical devices has been presented, and advances in the growth of SiON for application to integrated optics have been summarized.
Abstract: The passivation of silicon by low temperature processed dielectrics, particularly SiN, has recently received a great deal of attention for applications in photovoltaics technology. Low surface recombination velocity is a key issue for ongoing improvements of a large variety of silicon based microelectronic devices. This review discusses the various deposition techniques and also gives recent results of nitride passivation. Issues such as the impact of deposition parameters, thermal stability, interface traps and surface recombination velocity measurements are described. The benefits achieved by the passivation process on the photovoltaic device performance are also discussed. The potential of silicon oxynitride, a gradient index material, for the fabrication of integrated optical devices has been presented. Advances in the growth of SiON for application to integrated optics have been summarized. Based on optimized SiON technology the review reports on special purpose wave-guiding structures such as microcavity resonators, electrooptic modulators, polarization splitters and second harmonic generation devices. SiON technology offers a silicon-compatible technology, a waveguiding structure with high dielectric-index contrast, a low optical loss <0.15 dB cm-1, in the 1550 nm telecommunication window and a negligible polarization dependence.
TL;DR: By varying oxygen partial pressure during deposition, epitaxial yittria-stabilized zirconia thin films were grown on natively oxidized silicon wafer by the pulsed laser deposition technique as discussed by the authors.
Abstract: By varying oxygen partial pressure during deposition, epitaxial yittria-stabilized zirconia thin films were grown on natively oxidized silicon wafer by the pulsed laser deposition technique. The commensurate crystalline interface was attributed to the lower partial pressure at the initial deposition stage, where the amorphous interfacial oxide is eliminated by the metal Zr (or Y) ions reacting with native silicon oxide on the surface of the silicon substrate. The partial pressure effect on the origin of re-growth of amorphous interfacial oxide is discussed. The results demonstrate that the commensurate crystalline oxide can be obtained by an appropriate deposition process, which sheds light on the fabrication of high-quality crystalline thin films on Si wafers to promote the application of silicon-based electronic technology.
TL;DR: In this article, structural and optical properties of thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties, and the depositions were carried out at substrate temperatures in the range 65-295 °C.
Abstract: Structural and optical properties of thin films CuInS2 grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The depositions were carried out at substrate temperatures in the range 65-295 °C. We obtain CuInS2 layers with high structural quality by growing at Ts 140 °C with the presence of an amorphous component and at Ts 240 °C with formation of In and Cu7 In4 as minority phases. From the optical transmission and reflection an optical absorption coefficient of 3 × 104 -105 cm-1 for 200 °C. Analysis of the absorption coefficient data revealed the existence of several energy gaps, direct and forbidden direct gaps. The direct gaps lie between 1.38 and 2.20 eV and the forbidden direct gaps are in the 0.61-1.97 eV range. The effect of the substrate temperatures on the grain size and surface roughness has been studied. It has been shown that the substrate temperatures Ts 140 °C and Ts 240 °C yield maxima of the grain size and minima of the surface roughness.
TL;DR: In this paper, the authors investigated the effect of donor and acceptor centers on the defect production rate in silicon-doped n-GaN and showed that the defect model of all native defects immobile at room temperature is not true.
Abstract: Radiation-induced point defects and their annealing in silicon-doped n-GaN have been investigated by means of Hall effect measurements and Raman spectroscopy. Correlated compensation effects due to simultaneous introduction of donor and acceptor centres are observed in irradiated n-GaN. The defect production rate is dependent on the dopant concentration. This means that the model of all native defects immobile at room temperature is not true. The behaviour of radiation-induced defects upon heating is complicated, exhibiting two prominent stages of reverse annealing. The presence of radiation defects is still observable after annealing to T = 750 °C.
TL;DR: In this article, the electronic structure of heterojunctions between II-VI semiconductors (CdS, CdTe) and layered transition metal dichalcogenide (MoTe2, WSe2) was investigated by soft x-ray photoelectron spectroscopy.
Abstract: The electronic structure of heterojunctions between II-VI semiconductors (CdS, CdTe) and layered transition metal dichalcogenide semiconductors (MoTe2, WSe2) were investigated by soft x-ray photoelectron spectroscopy. The interfaces were formed sequentially by molecular beam epitaxy (MBE) of the II-VI semiconductors on van der Waals (0001)-surfaces of layered compound single crystals. The II-VI semiconductors grow with their polar hexagonal axis ([111] for CdTe, [0001] for CdS) parallel to the non-polar substrate [0001]-axis, without evidence for lattice distortions as prooved by TEM and LEED. Band offsets were determined from soft x-ray photoelectron spectra. Large substrate independent interface dipoles of 1.2 eV for CdS and 0.8 eV for CdTe were determined. The deviation of experimental band offsets from the electron affinity rule prediction is described by a simple model which takes the polarity of the grown interfaces into account.
TL;DR: In this article, thin films of tetragonal lead monoxide have been prepared from spray pyrolytic decomposition of an aqueous solution of lead nitrate, and the absorption coefficients of the films have been determined from transmittance measurements in the 400-1200 nm region.
Abstract: Thin films of tetragonal lead monoxide have been prepared from spray pyrolytic decomposition of an aqueous solution of lead nitrate. The spray pyrolysis set-up developed for this study is also described briefly. From the structural investigations it has been found that the films generally grow with some admixture of monoclinic PbO1.57 phase. The absorption coefficients of the films have been determined from transmittance measurements in the 400-1200 nm region. From an analysis of the room temperature optical absorption data, a direct transition band gap of 1.9 eV has been obtained for α-PbO.