Showing papers on "Depletion region published in 1982"

Alpha-particle-induced field and enhanced collection of carriers

Abstract: A simple physical model explains all the characteristics of the newly discovered funnelling phenomenon. An alpha strike results in significant field in the quasi-neutral regions to a depth that is equal to 1 + µ _{n} /µ _{p} times the depletion region width of an n+/p junction. This and the predicted current waveform agree with experiments and simulation results. The model also predicts the effects of the angle of alpha incidence, and that p+/n junctions should exhibit weaker funnelling phenomenon.

Optical response time of In0.53Ga0.47As/InP avalanche photodiodes

Abstract: Heterojunction In0.53Ga0.47As/InP avalanche photodiodes have recently been observed to have a response to long‐wavelength optical pulses which contains both fast and slow components. We present evidence that the slow response is limited by charge pile‐up at the semiconductor heterointerface. We find that the speed of response depends on the degree of compositional grading in the heterointerface region. The response time can be significantly reduced for compositional grading lengths of greater than 600 A depending on the doping and depletion region width in the In0.53Ga0.47As layer.

Electron and hole impact ionization coefficients in InP determined by photomultiplication measurements

Abstract: The electron and hole ionization coefficients α and β in (100) InP have been determined through analysis of photomultiplication data on p+‐n and n+‐p junctions grown by liquid phase epitaxy (LPE). A special device structure is described which allows reproducible thinning of the substrate in order to achieve pure carrier injection from either side of the p‐n junction. By fabricating wafers with depletion layer doping levels from 1.2×1015 to 1.2×1017 cm−3, α and β have been determined over a wider range of electric fields than previously reported. The ratio of β/α decreases from 4.0 to 1.3 as the electric field is increased from 2.4 to 7.7×105 V/cm.

Junction field-effect transistor controlled by merged depletion regions

Abstract: A new method of semiconductor operation has been conceived, developed and applied to produce a revolutionary new semiconductor design. The method is that of merging depletion regions for purposes of operation, isolation and control of channel current in a junction field-effect transistor. Using this method depletion regions are made to merge with suitable biasing in an intervening layer interposed between the gate and channel of a junction field-effect device and the interaction of the depletion regions is used for isolation and coupling to alter the associated depletion region in the channel of the junction field-effect device. A number of embodiments are disclosed of the new junction field-effect transistor controlled by merged depletion regions. In each embodiment a channel of one conductivity type material is formed in a semiconductor body of opposite type material. A gate region of the same conductivity type material as the channel is placed near enough to the channel so that when the gate junction is reversed bias, the gate depletion region merges with the channel junction depletion region in the intervening layer. When the two depletion regions have merged, the gate controls the channel current in a manner similar to conventional devices. Because the output and input and control connections are of the same conductivity type material, no metal contacts or interconnections are required. The lack of need for metal interconnects makes the device better suited to integrated circuits than any other device. In addition, the depletion regions surrounding the gate and channel isolate the gate and channel from other semiconductor regions of the same conductivity type and thus isolation regions are not required for the junction field-effect transistor controlled by mergers depletion regions. Consequently, use of the invention can result in the densest form of logic available today. Such devices hold the promise of improved performance in almost every semiconductor device application and can be used in almost every application where MOS and junction field-effect devices are now used.

Semiconductor Photoelectrochemical Solar Cells

Abstract: The total band bending or potential drop at the electrode-electrolyte interface is across the space charge layer in the semiconductor plus that across the Helmoltz layer in the electrolyte. The latter is negligible. The band bending at the electrode-electrolyte interface changes on illumination, as for p-n junctions, and can be used for constructing solar cells. Such solar cells are termed 'photoelectrochemical solar cells'. The charge transfer from semiconductor to electrolyte can take place such that under different conditions it can either reduce or oxidise the species in the electrolyte depending upon the redox reaction (Esub(F, redox)) energy value with respect to Esub(c) and Esub(v) at the edge. Generally, the enhanced charge transfer under illumination results in a voltage. However, if the redox species is H/sub 2/O/O/sub 2/, the electrolysis of water takes place. Such cells are known as photoelectrolysis cells. These cells have low efficiency of approx. equal to 1% and hence not economically viable at present. However, an efficiency approx. equal to 10 to 14% has been attained in electrochemical photovoltaic solar cells within four years since the first report by Gerischer. This seems encouraging and competitive to conventional photovoltaic solar cells.

Space charge layers created by coronae at ground level below thunderclouds: Measurements and modeling

Abstract: High electric fields created by thunderclouds at ground level are enhanced by the irregularities of the surface. This causes corona discharges to occur. The generated ions, when they are not blown away, form a space charge layer which reduces the magnitude of the electric field at ground level. During the LANDES 79 experiment (south western France), electric field soundings have been performed. The sensor is a balloon-borne double field-mill device designed for measuring the vertical and horizontal components of the external electric field. At several occasions, a strong vertical field increase with height was detected in the lower part of the sounding. This reveals the existence of important space charge layers near the ground. Space charge density profiles are deduced from electric field soundings. They display density values running from 2 to 7 nC m−3, distributed over shallow layers. A numerical model taking into account ion capture by the neutral aerosol particles leads to theoretical charge density profiles which display features close to those of the experimental profiles. Computation shows that the initial number of neutral aerosol particles has a drastic effect on both density maximum values and layer depths. According to aerosol density, charge density values run from 0.6 nC m−3 (in clean air) up to 3.1 nC m−3 (high aerosol density).

A mechanism of degradation in leakage currents through ZnO varistors

Abstract: Thermally stimulated currents through ZnO varistors subjected to the voltage stresses, dc, and square‐wave voltages are analyzed on the base of carrier trappings in the depletion layers of ZnO grains. The analysis indicates that the field ionization of trapped carriers in a reverse‐biased depletion layer plays an important role in the degradation phenomena, thereby suggesting that the current increase with time under the dc and ac stresses is due to the same origin. An Arrhenius relation to predict the life of varistors and a dependence of leakage current Jc on time t, ln Jc ∝t1/2, are derived from a carrier trapping model.

Degradation mechanism of zinc oxide varistors under dc bias

Abstract: The degradation mechanism of ZnO varistors under dc bias is investigated from the viewpoint of the time dependence of leakage current under dc biasing, the voltage‐current characteristics, and the thermally stimulated current and dielectric properties before and after dc biasing test. The experimental results are analyzed on the basis of the Schottky barriers which control current transport in varistors at the grain boundary regions. The increase in leakage current is expressed as J = A exp (Bt0.3) ( J is the leakage current; A and B are constants, and t the biasing time) and is attributed to the deformation of the Schottky barriers. The deformation corresponds to the lowering of the barrier height and decrease in the depletion width. This is due to the uneven distribution of positive charges caused by the migration of donor ions. In case of the degradation of varistors under long term dc bias, the deformation is mainly due to decrease in the depletion width. Taking into account the electric field due to positive charges and the skew of Fermi level, etc., the asymmetrical deformation can be also explained as a phenomenon due to surplus positive charges, formed in the reverse‐biased depletion layer.

On the response behavior of fast photoconductive optical planar and coaxial semiconductor detectors

Abstract: Fast optical detectors use photoconductive effects in semiconducting channels or thin films. The behavior of those planar and coaxial detectors is reviewed. It is shown that p-type and n-type materials show different behavior in respect to bandwidth and gain. The strong influence of the contacts is clarified and the surface recombination is taken into account. The bandwidth of those detectors is evaluated and the gain and gain bandwidth product are given in terms of the geometry and material data. Furthermore, the influence of deep levels and of a depletion layer along the surface is considered, which considerably affect the static characteristics as well as the pulse response. Regarding these effects, the different behavior of GaAs- and Ga 0.47 In 0.53 As-conductive photodetectors is demonstrated.

Electronic structure of Na x W O 3 : A photoemission study covering the entire concentration range

Abstract: Angle-resolved and angle-integrated ultraviolet-photoemission-spectroscopy (UPS) investigations have been carried out over the entire concentration range $0lxl1$ of the sodium-tungsten-bronze system ${\mathrm{Na}}_{x}\mathrm{W}{\mathrm{O}}_{3}$. The results indicate that the rigid-band model used by several authors fails to explain the $x$ dependence of the electronic structure. For the metallic samples with $x\ensuremath{\ge}0.3$, the top of the valence band and the bottom of the conduction band remain at 3 and 1 eV, respectively, and the width of the occupied part of the conduction band is independent of $x$. The peak amplitude at the Fermi level varies linearly with $x$ and does not follow the predicted dependence. A detailed comparison is made between the experimental results and the band-structure calculation of Kopp et al. Both the width of the valence band and the separation between the valence and conduction bands are too small in the calculation. Angle-resolved UPS measurements reveal a peak in the gap region for the metallic samples which disperses from 2.1 eV for ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{\ensuremath{\parallel}}=0 \mathrm{to} 1.2$ eV for ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{\ensuremath{\parallel}}$ along $\ensuremath{\Gamma}\ensuremath{-}M$. This feature is assigned to a surface state. The failure to detect localized gap states for the semiconducting samples is explained by band bending and a charge depletion layer caused by oxygen acceptor states at the surface. The fact that the work function $\ensuremath{\varphi}$ decreases linearly with increasing $x$ indicates that there is no surface depletion of sodium as has been claimed earlier.

Theory of photocurrent in semiconductor‐electrolyte junction solar cells

Abstract: Expressions are derived for the current‐voltage characteristics of semiconductor‐electrolyte junctions. Charge transfer kinetics, surface recombination, recombination in the quasineutral region and in the depletion region as well as the effect of the incident illumination on the minority carrier distribution in the semiconductor are included in the model. It is shown that surface transfer velocity for minority carriers is a very important parameter that determines the photocurrent of the cell. The dependence of the photoresponse on the light intensity is shown to be a diagnostic tool in determining the efficiency of charge transfer at the surface.

Theoretical basis for field calculations on multi-dimensional reverse biased semiconductor devices

Abstract: In this report the theory and the computational methods used to perform numerical field calculations on reverse biased two-dimensional (or three-dimensional with circular symmetry) structures are fully described and completely justified. Finite difference methods are used to approximate Poisson's equation and, together with a depletion region logic, solutions to semiconductor field problems are obtained without the need to solve the complete set of device equations. Two unique aspects of the methods are the depletion logic and the approach taken to handle dielectric interfaces.

Effects of grain boundaries on the current-voltage characteristics of polycrystalline silicon solar cells

Abstract: The current components associated with the grain boundaries of diffused p/n junction polysilicon solar cells made on n- and p-type Wacker substrates are analyzed and experimentally identified. New electrical methods for determining the presence or absence of preferential diffusion along the grain boundaries and for determining the average doping density of preferentially diffused regions along the grain boundaries are described. For p-type substrates, these methods revealed preferential phosphorus diffusion along grain boundaries; no preferential boron diffusion along grain boundaries was observed. The recombination current components were analyzed for the cells in which preferential diffusion occurred. The analysis shows that the dominant current component at small bias levels (0-300 mV) is the recombination current at the grain boundaries within the p/n junction space-charge region. At higher bias levels ( V \simeq V_{OC} \simeq 500-600 mV), both this current component and the current component due to recombination at that part of the grain boundary below the preferentially diffused region are important. The grain-boundary shunt resistance does not contribute a significant current component. It is shown that the preferential diffusion makes negligible the recombination current injected into the sidewall of the preferentially diffused region. This is consistent with a model in which the phosphorus diffusion significantly lowers the surface recombination velocity at the grain boundaries and in which the retarding built-in electric field further decreases the recombination current.

Depletion layer studies and carrier photogeneration in doped merocyanine photovoltaic cells

Abstract: The capacitance and photocurrent of Al/Cl2‐doped merocyanine/Au thin film photovoltaic cells have been studied as a function of applied voltage bias. The capacitance data indicated that a Schottky barrier had formed between the Al and organic dye. The barrier width, built‐in potential, and carrier concentration were 23 nm, 1.05 V, and 1018 cm−3, respectively. Photocurrent measurements at different excitation wavelengths strongly suggest that carrier photogeneration is a bulk phenomenon. Combining these observations with a study of the effects of doping with molecular chlorine, we propose that carriers are generated by electron transfer from a thermalized exciton to a dopant site. The dopant is thought to be adsorbed in the dye layer as the acceptor half of a weak charge transfer complex. A quantum yield of 11.2% at 632.8 nm based on light absorbed by a 30‐nm thick merocyanine film was measured for the chlorine‐doped cell.

The camel diode as photodetector with high internal gain

Abstract: The camel diode is a three layer majority carrier device with an interior layer sufficiently thin so that it is depleted of carriers at all values of bias voltage. The current flow is controlled by a potential barrier in the bulk of the semiconductor, the height of which can be controlled by free carriers trapped in the potential minimum. They will be generated optically within the space charge layer and the adjacent diffusion region. Basic theoretical considerations and first experimental results, which exhibit a gain of values of up to 500, are presented.

Electroluminescenee in Polyethylene Terephthalate (PET) I. Impulse Voltage

Abstract: Electroluminescence was observed in PET when an impulse voltage was applied. The electroluminescence depended on the electrode material of the cathode and showed only a weak temperature dependence and a superlinear dependence on the electric field. The spectrum of the electroluminescence was identical with that of the photoluminescence originating from PET molecules. Considering these results, the following mechanism was concluded to be responsible for the electroluminescence in PET. Electrons injected from the cathode by tunneling through the interfacial barrier are accelerated by the electric field to sufficiently high energy to excite or ionize PET molecules. They finally lose their energy and become trapped, forming a space charge layer. The electroluminescence occurs when the excited PET molecules are deactivated into their ground states. The generation and dissipation of the space charge is discussed in this paper, and analysis of the electroluminescence is shown to be useful for understanding the dynamic behavior of the space charge in polymers.

Electret semiconductor solar cell

Abstract: An induced junction solar cell includes a silicon semiconductor wafer with an aluminum ohmic contact layer on one surface, a thin oxide layer on the other surface, a grid-type aluminum contact on the oxide layer and an electret, i.e. charged outer polymer layer covering the grid-type contact and exposed oxide layer. The electric field of trapped charges in the electret penetrate the semiconductor and separate photogenerated carriers. Minority carriers are extracted through a rectifying grid-type contact to permit a build-up of potential and a barrier for majority carriers.

Three terminal semiconductor laser

Abstract: A semiconductor laser includes an anode region of a first conductivity type made of a highly doped region, an active layer adjacent the anode region, a channel region made of a high-resistivity region and adjacent the active layer, a cathode region of a second conductivity type at one end of the channel region which is made of a highly doped region, and a gate region that surrounds at least part of said channel region and which is made of a highly doped region of the first conductivity type. The anode region and channel region have a wider band gap than that of the active layer.

Insulated-gate field-effect transistor

Abstract: PURPOSE:To enable to obtain the high withstand voltage of an insulated gate field effect transistor by a method wherein a low impurity concentration layer and a high impurity concentration layer are formed by performing diffusion of a source region or a base region two times. CONSTITUTION:Deep diffusion is performed at low surface concentration to form the first source region layer 13a coming in contact with the base region 2, and shallow diffusion is performed after formation of the layer 13a at high surface concentration sufficiently higher than the former to form the second source region layer 13b coming in contact with the layer 13a. By forming the source region like this, diffusion impurity concentration at the base region 2, especially at the part near the surface of the substrate is reduced according to the distance from the edge of a diffusion hole. As a result, because the total quantity of impurities of the region 2 is increased, and extension of a depletion layer to the base layer to be generated when a drain voltage is applied is reduced, enhancement of the withstand voltage can be attained. Moreover by shortening channel length still more, mutual conductance can be enlarged, and formation of the transistor as to have large current capacity can be attained.

Variable capacitance device

Abstract: Variable capacitance device consisting of a semiconductor substrate having a first conductivity type semiconductor layer, at least one second conductivity type semiconductor region formed in a surface portion of said first conductivity type semiconductor layer, and a barrier for generating a depletion layer formed on the surface opposite to said surface portion of said first conductivity type semiconductor layer, in which a capacitance reading-out section is disposed on said at least one second conductivity type semiconductor region. A depletion layer control section is disposed on said surface opposite to said surface portion; and said depletion layer control section is reversely biased so that said depletion layer extends from said barrier to a junction portion between said first conductivity type semiconductor layer and said at least one second conductivity type semiconductor region, whereby a capacitance variation results at said capacitance reading-out section in response to variation of the reverse bias voltage.

Thermal filling effects in capacitance experiments on deep levels in semiconductors

Abstract: The interpretation of capacitance studies of deep levels in semiconductors is complicated by the presence of a Debye tail of free carriers, thermally excited from the bulk into the depletion region. The concentration of these carriers varies spatially within the depletion region and so produces a variation in the rate constant for capture by deep traps. Unless this effect is taken into account wrong values of concentration of the centre being studied will be obtained. A further consequence is that capacitance transients are in general not exponential functions of time, although in favourable cases an exponential function may be a good approximation. In the general case unreliable time constants may be deduced if capture effects are not eliminated in the reduction of data; this may be difficult to do satisfactorily when measuring initial rates of change of capacitance.

Insulated gate field effect transistor

Abstract: An insulated gate field effect transistor has a well region formed in a surface region of a semiconductor sub-strate of a first conductivity type which has an opening in a part thereof. The well region has a second conductivity type. A source region and a drain region of the first conductivity type oppose the opening of the well region interposed therebetween. A gate electrode is disposed on the substrate surface between the source and drain regions through a gate insulating film. The potentials of the substrate and the well region are fixed so that the junction between the substrate and the well region may be reverse-biased. The transistor is thus operated under the state in which the whole or a part of the well opening is made a depletion layer. The result is a device having a constant current characteristic and a reduced body effect relative to prior designs, and hence a device well suited to use in a monolithic logic integrated circuit.

Method of making a field effect transistor with modified Schottky barrier depletion region

Abstract: A method of making a field effect transistor with a modified metal semiconductor Schottky barrier depletion region wherein a GaAs semiconductive active layer on a semiinsulating substrate is supplied with a pair of ohmic contacts and with a gate or barrier electrode between the ohmic contacts and spaced therefrom so that below the surface of the active layer upon which the barrier electrode and ohmic contacts are supplied, an electron-depletion region is formed between each ohmic contact and the gate or barrier electrode. According to the invention, this surface region is treated by bombardment with nitrogen or by the application of a layer thereto to modify the depth of the depletion region so that this depth beneath the treated surface region will differ from that beneath the gate or barrier electrode.

High voltage resistance element

Abstract: A resistance element capable of withstanding a high voltage is formed through impurity diffusion in a single crystal island (1) of a semiconductor integrated circuit substrate. The resistance element includes a resistive region (2; 16) formed in an exposed surface of the single crystal island (1) and folded reciprocatively by at least one and a half turns in a planar zigzag-like pattern. The pitch at which the resistive region is folded is decreased as viewed in the direction in which extension of depletion layer formed within the single crystal island upon application of a voltage between two ends of the resistive region is decreased.

Field effect transistor

Abstract: PURPOSE:To improve voltage withstanding capabilibities by elevating the voltage triggering an avalanche multiplication phenomenon along a boundary layer by a method wherein the contact length between a depletion layer and a buffer layer is made larger for the purpose of maintaining low the electric field intensity along the boundary between the active layer and the buffer layer. CONSTITUTION:A GaAs buffer layer 2 is stacked on a GaAs substrate 1, then is covered with an N type GaAS active layer 3'. The central part of the surface of an active layer 3' is provided with a gate electrode 4 on the both sides of which a source electrode 5 and a drain electrode 6 are formed flanking the electrode 4. The thickness of the active layer 3' is not uniform, thicker at the drain side and growing gradually thinner toward the source side. The length of the depletion layer 7, generated below the gate electrode, with which said layer 7 contacts the buffer layer 2, or the length l of the effective buffer part 8', becomes longer, resulting in a voltage drop reducing the voltage applied to the boundary between the layers 3' and 2. In consequently, the layer 2 is provided with higher withstanding capabilities and will be broken down only when higher drain voltages are applied thereto.