Showing papers on "Depletion region published in 1972"

A feedback method for investigating carrier distributions in semiconductors

Abstract: The capacitance-voltage relationships of abrupt reverse-biased p-n junctions have long been used to investigate semiconductor doping distributions. Such investigations usually employ accurate point by point C-V measurements or else RF harmonic generation to provide the required detailed connection between a small change in junction voltage and the associated quantity of charge flowing around the external circuit. The method described here differs in that a feedback loop is used in such a way as to provide a controlled motion of the low-field boundary of the depletion layer. This motion can be one of two kinds, either that of a constant amplitude modulation of the depletion layer width or else a motion corresponding to a constant amplitude modulation of the electric field. In the former case the information obtained corresponds to the carrier density N(x) , while in the latter it is its reciprocal. In practice this approach provides a number of advantages. Among these is the ability to mount the sample at the end of coaxial cables of essentially arbitrary length. This has allowed such applications as on-line profiling during accelerator implantations and profiling devices in cryostats to obtain information on free-carrier concentrations as a function of temperature. In the present paper the basis of the method and its implementation are outlined and some representative results are given.

Thermally Stimulated Capacitance (TSCAP) in p‐n Junctions

Abstract: High‐frequency small‐signal capacitances of semiconductor junction vs temperature, from the initial conditions of filled and emptied traps in the junction depletion region, are used to determine the trap concentration and the thermal activation energies of trapped electrons and holes. Illustrations are given for silicon N + P diodes doped with gold impurity or irradiated with 1‐MeV electrons, showing the room‐temperature annealing for the latter.

Comments on the conduction mechanism in Schottky diodes

Abstract: The diffusion and thermionic emission theories of conduction in Schottky diodes are compared in terms of the behaviour of the quasi-Fermi levels for electrons. It is shown by an analysis of published experimental data that, for medium- and high-mobility semiconductors, the quasi-Fermi level is essentially flat throughout the depletion region under forward bias, in accordance with the thermionic emission theory. Under reverse bias the electron quasi-Fermi level is flat through most of the depletion region but rises as it approaches the metal, in agreement with the theoretical calculations of Crowell and Beguwala. The hole quasi-Fermi level remains horizontal through the depletion region at a value coincident with the Fermi level in the metal.

Variable capacitance device

Abstract: This specification discloses variable capacitance devices which vary their capacitances under the influence of DC bias voltages or radiations. One embodiment comprises a PN junction diode, a dielectric thin film deposited on the surface of said junction diode at which the junction terminates and a conducting electrode deposited on the dielectric thin film, in which the area of an equivalent plate electrode formed in said junction diode is varied by changing the thickness of a depletion region. In another embodiment, a nonlinear resistance layer deposited on the dielectric thin film is employed. As a DC voltage as applied to the nonlinear resistance layer is increased, the lateral conductivity of the nonlinear resistance layer increases and the area of the equivalent plate electrode facing the conducting electrode is increased. A further embodiment employs a thin film transistor or a MIS transistor to vary the area of the equivalent plate electrode provided therein.

Performance of GaAs Surface-Barrier Detectors Made from High-Purity Gallium Arsenide

Abstract: Gallium arsenide surface barrier diodes have been fabricated from high purity level materials. These devices have an Au surface barrier having a depletion layer thickness of from 70?mto 1 mm and an area of from 3mm2-27mm2. These devices have been operated as ?-particles, / s-ray, and ?-ray spectrometers and detectors. The best energy resolutions taken with a GaAs detector made from liquid phase epitaxial GaAs wafer were 20keV (fwhm) and 8 keV for 5.486 MeV ?-particles from 241Am and 115 keV conversion electrons from 57Co at room temperature, respectively. For room temperature applications, a simple charge sensitive preamplifier was constructed using two FETs and one OP amp. The combination of a encapsulated GaAs detector and two small semiconductor thermoelements (electrical cooling device) was studied to make a simple X-or ?-ray spectrometer. A special tiny GaAs detector was also fabricated as in vivo s-ray counting detector in biomedical applications. The energy per electron-hole pair (?) in GaAs was measured at 4.35 + 0.02 eV for ?-particles with a linear variation with bandgap energy (Eg) of 2.53 over a temperature range of 1950°K to 330°K, and 4.57 eV for conversion electrons (115keV) at 300°K, respectively. The ? vs Eg relationship was also investigated for Ge, Si, GaAs and CdTe using experimental values and led to ? = 2. 596 Eg + 0.714 (eV) with correlation coefficient of 0.999 at 300°K. The related problems for intrinsic material constant (?) are discussed for several semiconductor materials.

Photocapacitance Effects at a Cu2S–CdS Heterojunction

Abstract: The influence of trapped charge on the photovoltaic properties of an efficient Cu2S-CdS single-crystal heterojunction has been studied by a photocapacitance technique. For the nonheat-treated cell, a persistent increment in capacitance as high as 70% of the dark capacitance remained after illumination of the junction by band-gap light at 100 K. The additional capacitance is due to holes trapped in deep levels in the CdS depletion region near the interface. The trapped holes enhanced the 100 K photocurrent spectrum uniformly by a factor of 3 before heat treatment. After a 200 C heat treatment in air, the maximum trapped charge at 100 K enhanced the photocurrent by two orders of magnitude. The results are interpreted in terms of the tunneling through a conduction band spike of electrons photoexcited in the Cu2S.

Electroluminescence in reverse-biassed zinc selenide Schottky diodes

Abstract: Schottky diodes consisting of a metal layer in contact with an n-type ZnSe crystal are electroluminescent when biassed in the reverse direction. Electrons tunnel from the metal into the semiconductor, are accelerated in the depletion layer field and then impact-ionize luminescent centres. Experiments confirming each of these mechanisms are described. A simple theory is propounded to give a quantitative understanding of the processes and of the performance of the diodes as light sources.

Vertical channel junction field-effect transistors and method of manufacture

Abstract: The disclosed junction field-effect transistor (FET) has a precisely controlled gate configuration which enables either high power operation or high frequency operation or both. The FET is manufactured by steps including the growing of a first epitaxial layer having a predetermined crystallographic orientation on a substrate to form a drain. Next, a first anisotropic etch of the epitaxial layer provides "U"-shaped grooves with flat bottoms, therein through which a gate is diffused having internal side walls of uniform depth that define the source-to-drain channel. A second epitaxial layer is then grown on the surface of the first epitaxial layer and of the gate to provide a source. A second anisotropic etch exposes a portion of the gate, which also forms an etch stop, to facilitate electrical contact thereto. Current flowing through the channel is controlled in response to an input signal applied between the gate and source which adjusts the thickness of a depletion region extending into the channel.

Background energy level spectroscopy in GaP using thermal release of trapped space charge in Schottky barriers

Abstract: The energy distribution and concentration of electrically active background impurities in GaP have been investigated by observing the current when space charge trapped at these impurities is thermally released within the depletion region of a Schottky barrier formed on the semiconductor. Large‐area Schottky barriers are used for these measurements in order that small concentrations of impurities may be detected. The measurements have been carried out for both liquid‐encapsulated‐Czochralski (LEC)‐ and liquid‐phase‐epitaxial (LPE)‐grown material using n‐type wafers. In LEC GaP, at least seven electrically active background levels are detectable and these exist at concentrations between 1 × 1015−3 × 1016 cm−3, while in LPE GaP only three or four are detectable and these exist in much smaller concentrations of about 1014 cm−3.

A theoretical investigation on the generation current in silicon p-n junctions under reverse bias

Abstract: In a reverse-biased p-n junction, the current component arising from carrier generation in the depletion layer has been up to now considered proportional to the depletion layer width W. As the junction capacitance varies inversely with W, the current-capacitance product should be constant with the applied voltage whenever the reverse current is essentially a generation current. There is experimental evidence, however, that this is not so. In the present paper it is shown that an important cause of such a discrepancy is the considerable difference existing between the depletion layer width and the width Wi of the region in which the generation function reaches its maximum value. In fact, the generation current is proportional to Wi rather than to W and the current-capacitance product must be expected to vary as the ratio W i W , which is all but constant with the applied voltage. A simple model is proposed for evaluation of the generation current effective width Wi, which has been explicitly computed as a function of the applied reverse voltage and of the doping profile in cases of abrupt and linearly-graded junctions.

Field effect semiconductor device having an unsaturated triode vacuum tube characteristi

Abstract: A field effect transistor comprises a semiconductor channel, a source and a drain electrode formed at the opposite ends of the channel and a gate electrode provided on the side of the channel. The channel has a small impurity density and therefore the depletion layer extending from the gate goes deep into the channel to substantially close the conductive portion of the channel even in the absence of a gate voltage. The drain current will not flow where the drain voltage is below a certain threshold voltage, and will flow where the drain volage is above the threshold voltage exhibiting a linear resistance characteristic. This drain-current to drain-voltage characteristic simulates the anode-current to anode-voltage characteristic of the triode vacuum tube very closely.

Frequency Response of Gold Impurity Centers in the Depletion Layer of Reverse‐Biased Silicon p+n Junctions

Abstract: The frequency dependence of ΔV/Δ(Crf−2), which is closely related to the space‐charge density of a reverse‐biased p+n junction containing deep impurities, is discussed by using Goodman's model. In order to measure the variation of ΔV/Δ(Crf−2) with frequency, a special technique has been developed. The experimental result on a gold‐doped silicon p+n junction shows that frequency dispersion of gold acceptors is well explained by assuming a single deep level, whose charging and discharging time constant is 8.0 × 10−4 sec at room temperature. A value of 1.25 × 103 sec−1 is obtained for the thermal emission rate of electrons from the gold acceptors, which agrees well with the data obtained from the photo and dark junction current and capacitance experiments. This result differs from that determined by capture rate measurements. The disagreement is removed by taking into account an electron capture process through the excited states of the gold acceptors under non‐equilibrium conditions.

Photocapacitance studies of deep‐double‐electron‐trap oxygen in gallium phosphide

Abstract: Transitions of the deep O donor in a GaP p‐n junction are studied by photocapacitance. It is found that the O donor may deeply trap either one or two electrons. The four optical absorption cross sections are measured for the two states, and from this information the O concentration profile is determined. The concentration ranges from (4 ± 1) × 1014 cm−3 on the n side to (1.5 ± 0.2) × 1016 cm−3 on the p side of the junction depletion layer. It is believed that these measurements represent the first direct determination of the concentration of O donors in GaP.

Peripheral and diffused layer effects on doping profiles

Abstract: The impurity profile of an epitaxial layer has been determined from the capacitance-voltage ( C-V ) characteristics of a diffused p-n junction. The C-V characteristics were corrected for peripheral and diffused layer effects. Peripheral capacitance corrections account for the lateral spread of the space-charge region, whose periphery is assumed to be cylindrical. Diffused layer corrections account for the penetration of the space-charge region into the diffused layer, assumed to be Gaussian. The importance of these corrections can be estimated from graphs that cover a wide range of practical diffusion conditions and junction diameters. The sensitivity of profiles to the assumed Gaussian diffusion are examined. Finally, the corrections are applied to an experimental junction and the results are presented from a computer printout. The Appendix includes graphs for determining the space-charge width of a Gaussian-diffused silicon junction, given the diffused layer sheet resistance, junction depth, and background concentration.

High-frequency fall-off of Impatt diode efficiency

Abstract: Large-signal operation of Si and GaAs abrupt junction Impatt diodes is studied with a Read type analysis. Modifications are made to the existing Read type analysis to take into account a finite width of the avalanche region. Read's original assumption of a constant total particle current in the avalanche region is kept. A series of diodes with varying space charge layer widths are analyzed at typical operating conditions respectively. It is found, under many simplifying assumptions, that oscillation efficiency of the Si p+n abrupt junction diode remains essentially the same up to about 100 GHz and starts to degrade appreciably beyond that. The cause is the saturation of ionization rates at high electric field. The GaAs diode is found to perform better up to 50 GHz but become comparable beyond 100 GHz. Experimental data in the literature indicate that the tunnel current has practically no effect even in the 0·1 μm Si diode, which is the narrowest studied. This seems to be the case with the GaAs diode too.

Photovoltaic effect and space charge capacitance of amorphous semiconductor-metal contacts

Abstract: The space charge region of contacts to amorphous semiconductors were studied by measuring at various temperatures (i) the photovoltage as a function of light intensity and wavelength and (ii) the space charge capacitance as a function of frequency. Semitransparent electrodes of Au, Sb, Al, SnO 2 , and nichrome were used. For all except Sb the illuminated metal electrode has negative polarity. The photovoltage incrases first linearly with photon flux and then logarithmically. Capacitance measurements suggest the presence of “blocking” barriers for holes. The width is about several hundred Angstrom. The chalcogenide alloy used was Ge 16 As 35 Te 28 S 21 .

Experimental Study of the Space‐Charge Layer in Silver Halide Crystals

Abstract: Using equations developed in a previous paper the properties of surface layers in silver halide crystals have been studied by measuring their low‐frequency dielectric constant. It was found that the subsurface space charge depends strongly upon the nature of the material in contact with the crystal surface. Experimental results on the variations of the dielectric constant measured at 1 kcycle/sec as a function of an applied voltage are also reported and a model for the interpretation of these results is provided.

Signal storage device

Abstract: A solid-state device consisting of an interface between a semiconductor material and an insulator material, such as in a metal-oxide-semiconductor (MOS) sandwich, serves to store electric charge when an electron beam penetrates the insulator material. The stored charge effects the size of a depletion region in the semiconductor material adjacent the interface and, subsequently, when an electron beam penetrates the depletion region and creates electrons in the semiconductor conduction band and corresponding holes in the semiconductor valence band, the built-in field in the depletion region sweeps the electrons and holes in opposite directions causing a substantial transient electron-hole current, which can be registered by an external current detector. Thus, the same area of the insulatorsemiconductor interface (or the MOS sandwich) serves to store an electric charge when conditioned in one manner by an electron beam and produces an output current pulse indicative of the stored charge when conditioned in another manner by an electron beam and the area of the interface which is involved need be no greater than approximately the cross-section area of the electron beam.

Nature of current and of forward-bias electroluminescence excess noise in GaAs-diodes

Abstract: The excess fluctuations of the direct current and of the forward-bias electroluminescence intensity in GaAs-diodes have been investigated. The diodes of two types have been studied: the samples doped by non-amphoteric impurities (type I diodes) and the samples doped by non-amphoteric together with amphoteric impurities (type II diodes). The current noise in type I samples as well as in the wide current range in type II samples is shown to be generated in the space charge region of diodes. These noises are as a matter of fact the fluctuations of the excess component of the whole current which is likely to pass through some ‘peculiar’ regions of p - n -junctions rather than through the whole area. The current noise observed in type II diodes at sufficiently large currents is due to the fluctuations of the resistance of the compensation region of the diode or due to the fluctuations of its contact resistance. The excess electroluminescence noise in all diodes investigated has been found to be connected with the above-mentioned fluctuations of the excess component of the whole current and in the type II samples the over-barrier electron flow responsible for the electroluminescence passing probably through the same ‘peculiar’ regions of p - n -junction as the excess current does.

A solid state variable delay line using reversed biased pn junctions

Abstract: An electronically variable delay line including a wafer of silicon on one side of which a thin insulating layer is deposited. A highly conducting ground plane contacts the silicon wafer on its remaining side while a highly conducting microstrip line contacts the insulating layer. The microstrip line contacts the silicon wafer through small holes etched in the insulating layer at predetermined intervals. At these holes, P-N junctions are formed. The P-N junctions are reverse biased so as to vary the effective thickness of the insulating layer to vary the delay time by creating a depletion layer within the silicon wafer which acts as an effective insulator.

Neutron Damage in GaP Light‐Emitting Diodes

Abstract: The effects of neutron damage on the red and green light output at 300 °K of GaP lightemitting diodes have been examined. The results indicate that the diodes are not sensitive to neutron irradiation in those voltage regions where the radiative current is due to spacecharge recombination in the depletion layer. As a consequence of this, it is shown that the response of the diodes to neutron irradiation can be used to elucidate the radiative currentflow mechanisms in these devices.

On the wide-range bias dependence of transistor d.c. and small-signal current gain factors.

Abstract: Critical reappraisal of the bias dependence of the dc and small-signal ac current gain factors of planar bipolar transistors over a wide range of currents. This is based on a straightforward consideration of the three basic components of the dc base current arising due to emitter-to-base injected minority carrier transport, base-to-emitter carrier injection, and emitter-base surface depletion layer recombination effects. Experimental results on representative n-p-n and p-n-p silicon devices are given which support most of the analytical findings.

Metal-insulator-semiconductor structures having reduced junction capacitance and method of fabrication

Abstract: Metal-insulator-semiconductor structures characterized by reduced junction capacitance and methods of fabrication are disclosed. A substantially intrinsic region beneath the junction is formed by implanting selected ions. The ion implantation does not produce lateral diffusion of conventionally formed junctions, and therefore breakdown and packing density are not changed. The substantially intrinsic region does, however, increase the space charge region of the adjacent junction, thus reducing the effective capacitance. In the preferred method of fabrication, ions are implanted using the same mask employed in forming the p-n junction.

High performance fet

Abstract: A field effect transistor having improved mobility and including an impurity doped surface channel portion containing a controlled amount of impurity opposite to that in the substrate. The devices of the invention are characterized by the provision of a metallurgical junction formed within the normal maximum depletion depth from the insulator-semiconductor interface of a field effect transistor. The built-in electric field, or space charge region, of the junction extends to the interface providing an enhancement mode device. The preferred embodiment includes a step-junction although structures having graded junctions are also disclosed.

The rectifying contact of gold on etched CdTe single crystals

Abstract: An investigation was made of the fundamental electrical properties of diodes prepared by the precipitation of gold on mechanically polished and chemically etched surfaces of n-type CdTe monocrystals. The forward I–U characteristics measured in the temperature range from 210 to 300 K can be explained by Schottky's theory of metal–semiconductor junction with recombination in the space charge region. The reverse I–U characteristics are in good agreement with Schottky's theory at room temperature only. At lower temperatures a strong increase of the current with increasing voltage was observed. This effect may be explained by the current tunnelling through the high resistivity layer formed between the metal and the semiconductor. [Russian Text Ignored].

Comparison of theoretical and experimental values of the capacitance of diffused junctions

Abstract: Using computer calculations, the exact values of the C−3‐vs‐U intercept with the U axis are calculated for diffused junctions. These theoretical intercepts are 0.125 V lower than the classical values obtained from Shockley's theory. This difference is due to three factors: the variation of the diffusion voltage, the nonzero electric field at the boundaries of the depletion region, and the contribution of electrons and holes. The exact values also disagree with the experimental results. It is shown that this discrepancy depends on the diffusion parameters and that it may be caused by two effects: irregularities in the diffusion profile around the metallurgical junction and incomplete ionization of impurities.

Depletion-Layer Transduction of Surface Waves on Piezoelectric Semiconductor

Abstract: Effective generation and detection of surface elastic waves on semiconducting GaAs are achieved by using the depletion-layer which avoids the screening of piezoelectric fields by free carriers A pair of interdigital transducers is constructed by evaporating Au on the (111) plane of GaAs, resulting in the formation of the Schottky barrier under the electrodes of the transducers The surface wave of 25 MHz is propagated along the direction Applying the dc bias voltage to the Schottky barrier, the signal level is increased up to 30 dB A fairly good agreement is obtained between an analysis and the experiments

Thermoelectromagnetic energy conversion system

Abstract: A thermoelectromagnetic energy conversion system includes a p-n semiconductor junction having a space charge region on either side thereof and a magnet providing a magnetic flux through the space charge region in a direction parallel to the junction, and a source of thermal energy. Electrical contact may be made to two end regions of the junction which are spaced apart in a longitudinal direction perpendicular to the flux direction and centrally located dielectric regions on either side of the depletion region permit electrical communication between the end regions only through the depletion region. As electrons and holes which are thermally generated within the space charge region drift toward the edges thereof, the magnetic flux provides a longitudinally directed force on the mobile carriers which establishes a voltage potential between the two end regions.