Showing papers on "Depletion region published in 1991"

Mechanism of carrier transport in highly efficient solar cells having indium tin oxide/Si junctions

Abstract: The carrier transport mechanism of the Si solar cells having n‐Si/indium tin oxide (ITO) junctions has been studied by use of the current‐voltage and capacitance‐voltage measurements and x‐ray photoelectron spectroscopy. An 11‐A‐thick nonstoichiometric Si oxide layer is formed when ITO is deposited by spray pyrolysis on a Si electrode etched with hydrofluoric acid. In this case, the tunneling probability of majority carriers through the oxide layer is high, and the thermionic emission current over the energy barrier in Si takes a dominant part of the dark current. On the other hand, for a Si electrode where a Si oxide layer is intentionally interposed between ITO and Si, the thermionic emission current is suppressed, and trap‐assisted multistep tunneling through the depletion layer becomes dominant. By making a mat‐structure treatment on the Si surface, a solar energy conversion efficiency of 13% and the photocurrent density of 42.5 mA cm−2 were attained under AM 1 100 mW cm−2 illumination.

The effects of CdCl2 on the electronic properties of molecular‐beam epitaxially grown CdTe/CdS heterojunction solar cells

Abstract: Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl2 dip followed by a 400 °C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl2‐induced improvement in cell performance along with possible performance‐limiting defects resulting from this process in molecular‐beam epitaxy‐grown polycrystalline CdTe/CdS solar cells. Current density‐voltage‐temperature (J‐V‐T) analysis revealed that the CdCl2 treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl2 treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7×10−7 A/cm2 to 2.6×10−9 A/cm2 and, (c) an i...

Multiplication noise in uniform avalanche diodes

Abstract: A general expression is derived from which the spectral density of the noise generated in a uniformly multiplying p-n junction can be calculated for any distribution of injected carriers. The analysis is limited to the white noise part of the noise spectrum only, and to diodes having large potential drops across the multiplying region of the depletion layer. It is shown for the special case in which \beta = k\alpha , where k is a constant and α and β are the ionization coefficients of electrons and holes, respectively, that the noise spectral density is given by 2eI_{in}M^{3}[1 + (\frac{1 - k}{k})(\frac{M - 1}{M})^{2}] where M is the current multiplication factor and I in the injected current, if the only carriers injected into the depletion layer are holes, and by 2eI_{in}M^{3}[1 - (1 - k)(\frac{M - 1}{M})^{2}] if the only injected carriers are electrons. An expression is also derived for the noise power which will be delivered to an external load for the limit M \rightarrow \infin .

Photovoltaic properties of iodine-doped magnesium tetraphenylporphyrin sandwich cells. II, Properties of illuminated cells

Abstract: The photovoltaic characteristics of optimized iodine‐doped thin‐film sandwich cells of the structure Al/Al2O3/magnesium tetraphenylporphyrin/Au, fabricated and tested under high vacuum, are reported. The action spectra of the short‐circuit photocurrent show that only light absorbed near the Al‐Al2O3 electrode, to a depth of ∼70 nm in the porphyrin layer, is effective in producing charge carriers, consistent with the presence of a depletion region at this contact. Comparison of observed and modeled action spectra indicate an underlying enhancement of carrier generation which increases with increasing excitation energy above ∼2 eV. The photovoltaic efficiency increases with decreasing porphyrin thickness between 200 and 100 nm. Maximum values of ηwh=1×10−3 %, η’e=7×10−2 % and φe=4.3 % are obtained for a 100‐nm thick film. For the thinner cells, the photocurrent varies linearly with light intensity up to 106 mW/cm2, indicating that little recombination of charge carriers occurs during transport to the electr...

Surface and perimeter recombination in GaAs diodes: an experimental and theoretical investigation

Abstract: Surface and perimeter recombination in GaAs heteroface diodes was studied experimentally and by two-dimensional numerical simulation including Fermi-level pinning. Perimeter and bulk current components were experimentally extracted, and the numerical model was used to study the origin of perimeter current in these devices. Under moderate bias, perimeter recombination occurs primarily within the junction depletion region, but as the bias is increased the perimeter outside of the junction depletion region becomes increasingly important. A bias dependence of the perimeter current ideality factor was observed both experimentally and theoretically and attributed to the perimeter recombination of injected carriers diffusing to the perimeter from the bulk regions. Fermi-level pinning was shown to increase the effective surface-recombination velocity, but conduction along the surface channel plays little role in these devices. The results demonstrate that a simple numerical treatment of Fermi-level pinning and surface recombination can accurately account for surface and perimeter recombination in GaAs homojunction diodes. >

Conduction mechanism in PtSi/Si Schottky diodes.

Abstract: The conduction mechanism in PtSi/Si Schottky diodes has been studied in the temperature range of 80 to 300 K. Above 100 K the forward current-voltage (I-V) characteristic of the diodes is highly ideal and obeys the thermionic-emission theory including image-force lowering of the barrier. Certain diodes show a deviation from this behavior, which is due to carrier recombination in the depletion region. Factors that contribute to carrier recombination are a small area-to-periphery ratio and a thick silicide layer. Carrier recombination is also responsible for the soft behavior of the reverse I-V characteristic. The temperature dependence of the barrier height and the bias-independent position of the quasi-Fermi-level at the interface are shown to be associated with a high density of interface states. The activation energy found for the current transport at low temperatures suggests that these states are due to substitutional Pt atoms on the Si lattice.

He2+ and H+ dynamics in the subsolar magnetosheath and plasma depletion layer

Abstract: A magnetosheath interval monitored by a pair of close upstream spacecraft is analyzed. Composition measurements are used to determine separately many of the properties of H(+) and He(2+) in the magnetosheath, plasma depletion layer, and accelerated flow layer. Magnetosheath ion densities and density ratios are well correlated with those in the upstream and on average the He(2+)/H(+) temperature ratio remains constant across the shock. Temperatures decrease and anisotropies increase as the magnetosheath plasma is lost parallel to the magnetic field in the depletion layer. Compared to the magnetosheath, there is a 20-30-percent enhancement in the depletion layer He(2+)/H(+) density ratio and an enhancement in the depletion layer temperature ratio. By monitoring upstream conditions, a methodology is developed for studying the plasma depletion layer and magnetosheath separately.

Contactless technique for measuring epitaxial dopant concentration profiles in semiconductor wafers

Abstract: The dopant concentration of a semiconductor wafer is determined using a contactless technique First, a temporary P-N junction is formed in the surface of the semiconductor wafer using corona discharge Then, the area of the junction is measured, and the depletion region is deepened, again by corona discharge The depletion region is collapsed using light, and as the depletion region collapses, the surface potential is measured as a function of time The charge which drains as the depletion layer collapses is directly proportional to the change in time Since the total charge is known from the original corona discharge used to establish the depletion layer, as are the unit area and the surface voltage, the dopant profile is directly calculatable as a function of the surface voltage and the charge per unit area

Semiconductor schottky device with pn regions

Abstract: A semiconductor device has a first diode having a pn junction and a second diode having a combination of a Schottky barrier and a pn junction in a current-passing direction provided side by side in a direction perpendicular to the current-passing direction. When a forward current with a current density JF is passed into the second diodes, the relation ##EQU1## is established in a forward voltage VF range of 0.1 (V) to 0.3 (V), where k represents the Boltzmann constant, T represents the absolute temperature, and q represents the quantity of electron charges. The first diode is constituted by a first semiconductor region of one conductive type and a second semiconductor region of the other conductive type provided so as to be adjacent to the first semiconductor region to form a pn junction, so as to be in ohmic contact with one main electrode, and so as to have an impurity concentration higher than that of the first semiconductor region, and the second diode is constituted by the first semiconductor region of the one conductive type and a third semiconductor region of the other conductive type provided so as to be adjacent to the first semiconductor region to form a pn junction, so as to be in contact through a Schottky barrier with the one main electrode, and so as to have an impurity concentration higher than the first semiconductor region.

Scanning tunneling microscopy of photoexcited carriers at the Si(001) surface

Abstract: A scanning tunneling microscope is used to probe changes in the surface potential created by photoexcited carriers. At small tunneling currents, the dependence of surface photovoltage on laser intensity agrees with a model based on the transport of majority carriers through the depletion layer. At larger values of the tunneling current, charging of the surface by the current modifies the surface photovoltage because of changes in band bending near the probe tip. Spatial variations in the surface photovoltage are observed on a length scale comparable to the width of the depletion layer. Variations on an atomic scale are also observed and are interpreted as an increase in surface charging at specific defects on the Si(001) surface.

Semiconductor device of band-to-band tunneling type

Abstract: A semiconductor device of band-to-band tunneling type including a silicon substrate, a first gate electrode formed by a highly doped surface region of the silicon substrate, a first silicon oxide film formed on a surface of the surface region, a silicon thin film formed on the first silicon oxide film, a second silicon oxide film formed on a surface of the thin silicon film, and a second gate electrode formed by a metal film applied on a surface of the second silicon oxide film. In the thin silicon film, there are formed P and N type regions side by side to constitute a PN junction. When a gate bias voltage is applied across the first and second gate electrodes, a band bend having a large height and inclination in a direction perpendicular to the thin silicon film is produced in the depletion region in the vicinity of the PN junction. Minority carriers brought up from the valence band into the conduction band by tunneling due to the band bend are conducted through the PN junction under the influence of a reverse bias voltage applied across the PN junction. The band bend can be made large at will by increasing the gate bias voltage, so that it is possible to obtain a large tunneling current.

Direct measurements of polymer depletion layers by neutron reflectivity.

Abstract: We present results of direct measurements of polymer depletion layers at the liquid/air interface using neutron reflectivity. The systems studied are semidilute solutions of polystyrene in toluene using polymers of different molecular weights. The thickness of the depletion layer d is found to be of the order of the correlation length ξ of the polymer in the bulk solution

p‐n junction diode made of semiconducting diamond films

Abstract: A diamond p‐n junction diode fabricated by the chemical vapor deposition technique, shows distinct rectification characteristics. From the electron beam induced current measurement, the existence of a depletion region or a space‐charge region around the interface between the n‐ and p‐type semiconducting diamond layers was identified.

Modeling of Minority -Carrier Surface Recombination Velocity at Low-High Junction of

Abstract: Modeling of recombination velocity of minority carriers at the p-p+ low-high junction end of the p-base region of n+-p-p+ silicon diodes has been carried out by taking the minority-carrier recombi- nation effects in the space-charge region (SCR) of the low-high (I-h) junction into account. Solving Poisson's equation in the SCR numeri- cally, it has been revealed that the SCR is composed of an accumula- tion layer on the p side and a depletion layer on the p+ side. Generally, the depletion layer is very thin as compared with the accumulation layer and the built-in potential across the depletion layer never exceeds the thermal voltage, i.e., kT/q. Further, the minority-carrier recom- bination in this layer is also insignificant. For most I-h junction-based silicon devices, in practice, the minority-carrier recombination in the accumulation layer controls the value of the effective minority-carrier recombination velocity (&) at the back surface of the p-base region and the influence of the recombination in the heavily doped p+ region is less significant. A new expression for the Se, has been derived in terms of material parameters (such as the doping concentration, mi- nority-carrier lifetime, and diffusion coefficient of the two regions) which is in excellent agreement with the experimentally measured val- ues of back surface recombination velocity for nf-p-p+ and p+-n-n+ solar cells reported in literature.

Modeling of minority-carrier surface recombination velocity at low-high junction of an n/sup +/-p-p/sup +/ silicon diode

Abstract: Modeling of recombination velocity of minority carriers at the p-p/sup +/ low-high junction end of the p-base region of n/sup +/-p-p/sup +/ silicon diodes is carried out by taking the minority-carrier recombination effects in the space-charge region (SCR) of the low-high (L-H) junction into account. Solving Poisson's equation in the SCR numerically revealed that the SCR is composed of an accumulation layer on the p side and a depletion layer on the p/sup +/ side. Generally, the depletion layer is very thin as compared with the accumulation layer, and the built-in potential across the depletion layer never exceeds the thermal voltage, i.e. kT/q. Further, the minority-carrier recombination in this layer is also insignificant. For most L-H junction-based silicon devices, in practice, the minority-carrier recombination in the accumulation layer controls the value of the effective minority-carrier recombination velocity (S/sub eff/) at the back surface of the p-base region and the influence of the recombination in the heavily doped p/sup +/ region is less significant. >

A study of slow‐mode structures in the dayside magnetosheath

Abstract: Recent observations indicate that a region of enhanced plasma pressure and decreased magnetic field intensity frequently occurs in front of the plasma depletion layer at the dayside magnetopause (Song et al., 1990). This inverse relationship is characteristic of a slow-mode wave. This phenomenon was simulated with a two-dimensional incompressible MHD simulation code. When a normal component of the interplanetary magnetic field is present (Bx not equal to 0), the total magnetic field intensity tends to decrease in front of the depletion layer due to the bending of the magnetic field lines, and the plasma pressure is enhanced in this region. On the other hand, when Bx = 0, this slow-mode structure is not present in the simulation and only the plasma depletion layer is observed.

Nonlinear transmission line

Abstract: The present invention comprises a novel semiconductor device which further comprises a nonlinear transmission-line structure. The semiconductor device is that of a very long narrow voltage-dependent capacitor, such as a semiconductor diode or MOS capacitor, where the anode and cathode electrodes comprise the conductors of a transmission line and the depletion region comprises the dielectric of the transmission line. An input signal is applied at one end of the long, narrow structure. Such signal application results in the launch of a traveling wave traveling along the transmission-line structure. At the far end of the transmission-line structure, the signal is coupled out and applied to a load. The temporal and spatial modulation of the depletion capacitance of the semiconductor device as the traveling wave travels along the transmission-line structure results in temporal compression of the input signal. Input signals of comparatively slow transition time therefore have their transition time reduced such that the transition time of the output signal is much faster than that of the input signal. Output signals exhibiting picosecond transition times may be obtained from input signals exhibiting nanosecond transition times. Further, since the nonlinear transmission line according to the present invention may incorporate many of the properties of conventional semiconductor devices, but in a novel configuration, comparatively high-voltage nonlinear transmission lines according the present invention may be fabricated to provide correspondingly high-voltage, or high-current, output signals.

Manufacture of semiconductor device

Abstract: PURPOSE:To contrive the improvement of the operating speed of a transistor and the improvement of the reliability of the transistor by a method wherein the formation of an impurity region and a concentration distribution in the impurity region are specified CONSTITUTION:As an N-type layer 4 is formed and a channel region, through which source and drain currents are made to flow, is formed into a low-concentration N-type, the speed of an electron transfer can be increased As a P-type layer 3 of an impurity concentration higher than that of a P-type Si substrate 1 is formed under the layer 4, the spread of a depletion layer at a time when a voltage is applied between a source and a drain is little and a punch-through voltage can be increased As a low- concentration N-type layer 10 is formed in the vicinity of the drain, a current path becomes more distant from the interface between the Si substrate and an SiO2 film and even if hot carriers are generated, a probability that the hot carriers are injected in the interface, an SiO2 film 5 or a polycrystalline Si gate electrode 7 is reduced Therefore, a fluctuation in the denaturation of a transistor is inhibited As a low- concentration N-type layer 11 is provided on the outside of a high-concentration N-type layer 12, the P-N junction capacitances between the source and drain and the substrate are reduced and the improvement of the switching speed of the transistor is contrived

Transient photoluminescence decay study of minority carrier lifetime in GaAs heteroface solar cell structures

Abstract: Transient photoluminescence decay has been studied theoretically and experimentally as a technique for the investigation of GaAs solar cell materials and solar cell structures. The time-dependent continuity equation was solved using two variable boundary conditions modelling the interface between the emitter and hetero-window layer (AlGaAs) and between the emitter and space charge region, respectively. The solution was found with help of the Fourier transform method and the method of residues. There results an analytical expression for the time dependent photoluminescence (PL) intensity. The influence of various solar cell parameters on this photoluminescence transient has been studied in detail. An experimental investigation of transient PL decay was performed using a synchronously pumped mode locked and cavity dumped Nd:YAG/dye laser system for excitation and an optical sampling oscilloscope as the detector. GaAs wafers with and without surface passivation have been measured as well as hetero-window pn-structures and processed solar cells. A fit of the theoretical PL transients to the measured transients allows surface and bulk recombination parameters to be determined.

Pore Formation and Propagation Mechanism in Porus Silicon

Abstract: This paper presents a model of the microporous silicon formation process which is based on hole depletion due to quantum confinement in the porous structure. This model is compared with the formation of larger porous structures (meso-, macroporous) where hole depletion is generated by a space charge region.

Solid state image sensor having high charge transfer efficiency

Abstract: A solid state image sensor comprises a p-type semiconductor region, an n-type photoelectric conversion region formed in a surface region of the semiconductor region, an n-type charge transfer region formed in the surface of the semiconductor region separately from the photoelectric conversion region, and an electric charge read-out gate region formed between the photoelectric conversion region and the charge transfer region. A p + thin surface layer region if formed to cover a surface of the photoelectric conversion region excluding an end portion adjacent to the electric charge read-out gate region. A gate electrode is formed above the electric charge read-out gate region. The end portion of the photoelectric conversion region not covered by the thin surface layer region, has a short length sufficient to make a potential well formed in the portion shallow under influence of potentials of the p + thin surface layer region and the electric charge read-out gate region. Preferably, this end portion of the photoelectric conversion region is formed of a surface region having a low impurity concentration.

Effects of poly depletion on the estimate of thin dielectric lifetime

Abstract: Poly-gate depletion during the accelerated time-dependent breakdown (TDDB) test of single-doping-type capacitors (both electrodes of the doping type) results in an overestimate of dielectric lifetime at operation voltage. Simple high-field data extrapolation fails to take into account the voltage-dependent poly band bending. A three-orders-of-magnitude overestimate of lifetime at 5 V for 68-AA oxide equivalent poly/poly capacitors was found. After correcting for the poly depletion effects, the slope of the TDDB projection line decreases by 18%. The effects can be minimized by performing TDDB testing below the top poly inversion voltage. Fermi-Dirac statistics quantitatively explained the phenomenon. Calculated maximum allowable TDDB voltages for different gate doping and oxide thickness are presented as guidelines for test design. >

Capacitance-voltage characteristics of microwave Schottky diodes

Abstract: Based on an analytical solution of Poisson's equation, the authors calculate/capacitances of metal circular dots and metal stripes on the surface of a doped semiconductor material. When the dimensions of the dot or stripe are much larger than the depletion region, the results are reduced to the conventional formula for a parallel-plate capacitor. In the opposite limit, the overall capacitance is determined by the edge effect. This edge capacitance is proportional to the device periphery, with the coefficient of proportionality dependent on the shape of the metal. The parallel-plate component of the device capacitance is modulated by the applied voltage; the edge component is nearly independent of the applied voltage. Hence, the largest capacitance modulation is achieved in devices with the smallest ratio of the device periphery over the device area, which has the smallest edge effect. The measured capacitances of small round GaAs Schottky barrier diodes are in reasonable agreement with calculated results. >

Thermal dissociation energy of the Si-H complex in n-type GaAs

Abstract: The thermal dissociation kinetics of the hydrogen‐donor complex in n‐type GaAs:Si were determined from bias‐temperature anneals on hydrogenated Schottky‐barrier diodes. The anneal kinetics are approximately first order and yield a thermal dissociation energy for the Si‐H complex of 1.2±0.1 eV. Depth redistribution of the Si‐H complexes both within the depletion layer of biased diodes and in the field‐free region of unbiased diodes suggests that hydrogen in n‐type GaAs can migrate as a negatively charged species.

Heterostructure bipolar transistor

Abstract: Improved heterojunction bipolar transistor (HBT) are disclosed. Inventive devices can attain high cut-off frequency (fT), exemplarily 80 GHz or higher, and high DC current gain (β), exemplarily 25 or higher. The devices exhibit lateral scaling, permitting reduction in emitter stripe width without unacceptable decrease in β. Exemplarily the stripe width is 1 μm or less. The inventive HBTs are hot electron devices, with the hot electrons in the base region being spatially confined such that relatively few electrons reach the surface of the extrinsic base region. The relatively low bulk and surface recombination rate in the base of inventive HBTs is an important aspect of the invention and makes possible devices having relatively high β and low power consumption. Appropriate choice of base material, namely, a semiconductor material having relatively low intrinsic surface recombination velocity, can result in further reduction of surface recombination, as can, for instance, the use of an appropriate non-alloyed metal base contact. Appropriate choice of collector material can result in improved ballistic transport through the collector depletion region, and novel selection criteria are disclosed. InP, InAs, and In0.53 Ga0.47 As are exemplary materials that meet these criteria. Use of a highly doped collector contact region, with dopant level within a relatively narrow concentration range, can also lead to improved device behavior, as can the use of a compound emitter that comprises one or more appropriately placed thin undoped heteroepitaxial layers.

Semiconductor integrated circuit device

Abstract: PURPOSE:To prevent a current from flowing through a depletion layer development region of a complementary logical circuit without lowering of integration even if a high voltage is supplied from the outside in a state of high impedance by inserting a step-up circuit between the depletion layer development region of a first transistor and a first power supply of an output buffer circuit. CONSTITUTION:In a semiconductor integrated circuit device having a plurality of output buffer circuits, each output buffer circuit has a first transistor 1 of a first conductivity type and a second transistor 2 of a second conductivity type which are inserted one by one in series between a first power supply VDD1 to supply a relatively high voltage and a second power supply VSS to supply a relatively low voltage. An output terminal 5 is connected to a connecting part of the first and second transistors 1, 2. In at least a part of the plurality of output buffer circuits, a step-up circuit 30 is inserted between a depletion layer development region 15 of the first transistor 1 and the first power supply VDD1 to thereby supply a voltage which is higher than the first power supply VDD1 to the depletion layer development region 15.

Semiconductor laser device

Abstract: PURPOSE:To enable light intensity of a laser beam to be monitored easily by providing an electrode for applying voltage to a pn junction at a current block layer. CONSTITUTION:When a laser beam of a transparent semiconductor laser for a clad layer 5 is absorbed by a current block layer 6, an electron hole pair is generated due to light absorption of the block layer 6 and diffused minority carriers enable a depletion layer to be drifted near a junction surface with a clad layer 5, thus allowing current in inverse direction for the pn junction to flow. Then, with an electrode 12 formed at the current block layer 6, it is possible to determine the intensity of light by monitoring the current in inverse direction.

A model for the degradation of Ga(Al)As single-quantum-well lasers

Abstract: The degradation during cw operation or under electron beam bombardment of the graded index separate‐confining heterostructure laser devices grown on Si and on GaAs substrates was investigated. The induced current and the cathodoluminescence modes of a scanning electron microscope were used to observe the cleaved face of these devices as a function of the stage of degradation. Our findings strongly suggest that the degradation starts owing to a mechanism of donor annihilation and complex formation within the space‐charge region of the device. Two different methods allowing the evaluation of the donor concentration within the depletion zone were developed. One method is based on the measurement of the direct bias necessary to recover the initial microscopic characteristics of a damaged device. The other one relies on a numerical calculation of the partition of nonequilibrium carriers which takes into account the detailed structure of the device. This calculation is based on a three‐dimensional analytical fu...