Showing papers on "Depletion region published in 1985"

Anomalous leakage current in LPCVD PolySilicon MOSFET's

Abstract: The anomalous leakage current I L in LPCVD polysilicon MOSFET's is attributed to field emission via grain-boundary traps in the (front) surface depletion region at the drain, and an analytic model that describes the strong dependences of I L on the gate and drain voltages is developed. The model predictions are consistent with measured current-voltage characteristics. Physical insight afforded by the model implies device design modifications to control and reduce I L , and indicates when the back-surface leakage component is significant.

Variation of lateral doping—A new concept to avoid high voltage breakdown of planar junctions

Abstract: In this paper a new concept for high voltage planar junctions is presented The necessary widening of the space charge region at the end of the junction is obtained by implantation through small openings in the oxide mask and subsequent drive-in, leading to a controlled smeared-out dopant distribution Experimental results show the validity of the concept

Electroluminescence in ZnO varistors: Evidence for hole contributions to the breakdown mechanism

Abstract: The previously postulated production of holes during the electrical breakdown of varistors has been directly verified. In some compositions band‐gap (3.2 eV) luminescence from the recombination of these holes with free electrons has been observed. The intensity of this luminescence is greater in varistor compositions exhibiting higher nonlinearity coefficients. It is also proportional to the square of the current which implies hole creation by impact ionization in the depletion region near the grain boundaries. This study used varistors of relatively simple chemical composition.

Erasable, programmable read-only memory device

Abstract: An erasable, programmable read-only memory device comprises a plurality of memory cells of channel injection type. First and second impurity regions used as source and drain have different configurations such that when the same level of voltages are applied to first and second impurity regions, respectively, the intensity of electric field near the channel region in the depletion layer between the second impurity region and the substrate is weaker than that in the depletion layer between the first impurity region and the substrate. In the writing operation, a higher voltage in absolute value is applied to the first impurity region and channel current flows in one direction. Therefore, hot electrons can be effectively injected into the floating gate near the first impurity region. On the other hand in the reading operation, a higher voltage in absolute value is applied to the second impurity region and channel current flows in the opposite direction. The voltage in the reading operation is lower in absolute value than the voltage in the writing operation. According to such a device, the unintentional injection writing phenomenon in the reading operation can be suppressed.

Low‐resistance nonalloyed ohmic contacts to Si‐doped molecular beam epitaxial GaAs

Abstract: We have found evidence that the surface depletion charge density in molecular beam epitaxial n‐GaAs doped heavily with Si approaches the Si concentration. In situ metallization of the as‐grown surface of GaAs uniformly doped with Si at 1×1020 cm−3 yields a specific contact resistivity of 1.3 μΩ cm2, indicating a space‐charge density about equal to the silicon density despite a measured bulk electron density of 4×1018 cm−3. This contact resistivity is among the lowest for nonalloyed ohmic contacts to n‐GaAs. We attribute the large discrepancy between surface space‐charge density and bulk electron density to the amphoteric behavior of silicon in GaAs. Surface Fermi‐level pinning and arsenic stabilization create a surface depletion region where donor site selection predominates, whereas the extrinsic electron density in the bulk causes self‐compensation.

Electric field dependence of hydrogen neutralization of shallow‐acceptor impurities in single‐crystal silicon

Abstract: An electric field applied to p‐type single‐crystal silicon during hydrogenation dramatically affects the neutralization of shallow‐acceptor impurities (e.g., boron). This is demonstrated with capacitance‐voltage and secondary‐ion mass spectrometry measurements on n+‐p junction diodes that were reverse biased during exposure to monatomic deuterium at elevated temperatures. The results reveal that there is no neutralization within the field‐induced space‐charge layer, which extends from the metallurgical p‐n junction into the p‐type material. Rather, deuterium‐boron pairing occurs in the electrically neutral material beginning at the edge of the depletion layer. Consequently, the distribution of deuterium (hydrogen) is also altered by the applied field. The effect of an electric field on hydrogen‐boron pairing in p‐type silicon is discussed in terms of the role of free holes in the chemical reaction and possible charge states of the diffusing hydrogen atoms.

Analysis of Trapping and Recombination Effects in Photoelectrochemical Processes at Semiconductor Electrodes: Investigations at n-GaAs

Abstract: Fast impedance measurements have shown that reliable flatband potentials of GaAs can only be obtained using high scan rates. Illumination leads to a shift of energy bands at the interface which is interpreted by hole trapping in surface states. A recombination conductance determined by impedance measurements is used to characterize the recombination of minority carriers injected by light or a redox system. A semiquantitative model is discussed according to which the recombination occurs mainly in the space charge region of the semiconductor.

Frequency response of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption "grading" and multiplication regions

Abstract: We have measured the frequency response of InP/ InGaAsP/InGaAs photodiodes with separate absorption, "grading," and multiplication regions (SAGM-APD's) for a wide range ( 2 \leq M_{0} \leq 35 ) of dc gains. The results are explained in terms of a theoretical model which incorporates the transit time of carriers through the depletion region, the RC time constant, the accumulation of holes at the valence band discontinuity of the heterojunction interfaces, and the gain-bandwidth limit.

Transient capacitance spectroscopy in heavily compensated semiconductors

Abstract: We have developed the theory of the capacitance transient of a junction in the case where the usual approximation, namely that the defect concentration N T is not negligible compared to the free carrier concentration, is not fulfilled. We show that the correct analysis of this transient by the so-called Deep Level Transient Spectroscopy technique must take into account the fact that, during the transient, the width of the space charge region varies. The validity of the expressions obtained for the shift of the signature (variation of the emission rate vs temperature) and for the concentration N t is verified by comparison with experimental results obtained for electron induced defects in n -GaAs.

Optical Effects on the Static and Dynamic Characteristics of a GaAs MESFET (Short Paper)

Abstract: In this paper, we describe the effect of light on the S-parameters of a GaAs MESFET. The photon energy is greater than the gap bandwidth of the semiconductor. The photoconductive and photovoltaic dc phenomena in the channel and in the depletion layer are theoretically analyzed with a unidimensional model to describe the light effect on the dc transconductance g/sub m/. The comparison between the dc transconductance, without and under illumination, and the theoretical model shows a very close agreement.

Field-enhanced emission and capture in polysilicon pn junctions☆

Abstract: Large electric fields present in polysilicon pn junctions result in field enhancement of the emission and capture rates of traps in the depletion region. We used numerical integration to evaluate the enhanced emission rate and found that the field dependence of the emission rate could be approximated by a simple analytic expression. Calculation of the junction currents in forward and reverse bias were in qualitative agreement with measurements. However, the predicted magnitudes of the currents were considerably lower than those measured at low temperatures. This may be a consequence of interaction between traps, which results in a higher emission rate than predicted by the simple theory.

Potential barriers in HgCdTe heterojunctions

Abstract: The graded energy gap heterojunction in HgCdTe is analyzed using a highly accurate computer model that solves the one‐dimensional semiconductor equations. Results are shown in the form of energy band diagrams which illustrate several important features expected to be encountered in these heterojunctions. In particular, our calculations demonstrate the existence of potential energy barriers to minority carrier transport in the conduction band of wide‐gap‐n on narrow‐gap‐p structures and in the valence band of wide‐gap‐p on narrow‐gap‐n structures. Also demonstrated are cases where these barriers are eliminated. The physics of barrier formation is discussed in terms of the internal force fields due to the electrostatic potential gradient in the depletion region of the p‐n junction and the gradient of electron affinity in the graded gap region of the heterojunction. Results obtained from computer simulations were found to be in qualitative agreement with previous experimental data on HgCdTe heterojunctions.

MOSFET which reduces the short-channel effect

Abstract: Disclosed herein is a MOS-type field-effect transistor in which a semiconductor region having the same type of conductivity as the substrate and an impurity concentration higher than that of the substrate is formed under the channel so as to come at both ends thereof into contact with the source and drain regions. The semiconductor region restricts the extension of depletion layer from the source and drain regions, and restricts the short-channel effect. The junction capacity is small between the semiconductor region and the source and drain regions.

n-MoSe2/p-WSe2 heterojunctions

Abstract: The preparation of n‐MoSe2/p‐WSe2 heterojunctions by epitaxial growth of WSe2 (Eg=1.16 eV) on MoSe2 (Eg=1.06 eV) substrates is reported. The two semiconductors are nearly lattice matched along their hexagonal (001) base plane with Δa/a=0.25%. Diode capacitance‐voltage measurements show that the band edges of MoSe2 and WSe2 are aligned within ∼0.1 eV. The diode forward current at room temperature is carried by recombination in the depletion region.

Raman scattering determination of free‐carrier concentration and surface space‐charge layer in 〈100〉 n‐GaAs

Abstract: We have used Raman scattering as a nondestructive, contactless method for determining not only the free‐carrier concentration N but also the width of the space‐charge layer in 〈100〉 n‐GaAs with 4×1017 cm−3≤N≤1×1019 cm−3 using as an excitation several different wavelengths of an Ar+ laser. By comparing the intensity at different wavelengths of the uncoupled longitudinal optic phonon mode originating in the space‐charge layer with the signal from a piece of undoped 〈100〉 material, it is possible to experimentally evaluate the width of the depletion layer Ls. We find that there is very good agreement between the experimental values and those obtained from a generalized theory for both degenerate and nondegenerate materials. Thus, these experimental results demonstrate that for 〈100〉 III‐V semiconductors, Raman scattering can be used as a contactless method to determine the width of the space‐charge region for carrier concentrations up to 1×1019 cm−3.

Origin of 1/f noise observed in Hg0.7Cd0.3Te variable area photodiode arrays

Abstract: The origin of 1/f noise in Hg0.7Cd0.3Te photodiodes is investigated with variable area n+–p junction photodiode arrays. From the geometrical dependences, it is found that both G–R current and 1/f noise in these diodes originate dominantly at the surface depletion region. Also, the 1/f noise power is found to be proportional to the reverse bias voltage for 0.01

Schottky-Barrier Profiling Techniques in Semiconductors - Gate Current and Parasitic Resistance Effects

Abstract: The theory for obtaining mobility and carrier concentration profiles by the Hall‐effect, magnetoresistance, and capacitance‐conductance methods is developed in the relaxation‐time approximation. This theory is then applied to semiconductors in which a Schottky barrier is used to control a depletion region. Particular emphasis is given to field‐effect transistor structures which are ideally suited for geometric magnetoresistance measurements. A unique feature of the present model is the correction for finite gate (Schottky‐barrier) current, which can be very important under forward‐gate‐bias conditions. The ability to use forward‐bias makes the near‐surface region more accessible. Also, parasitic resistance effects are treated. We apply these results to GaAs conducting layers formed by direct implantation of 4×1012/cm2, 100‐keV Si ions into Cr‐doped GaAs.

Semiconductor radiation detector

Abstract: A semiconductor device for detecting incident gamma-radiation wherein the output from the device is relatively independent of the energy of the incident radiation The device includes a semiconductor substrate having a depletion layer formed therein by an applied voltage The depletion layer is shaped such that it includes a plurality of elongated projections within a plane parallel to the surface of the substrate The minimum distance between the edge of the substrate and the outer extent of the depletion layer is substantially equal to the average range of mobility of secondary electrons created by the gamma rays having the highest energy of the gamma-rays to be detected The device further includes means for counting the current pulses generated in the depletion layer by secondary electrons created by the incident gamma rays

Complementary thin-film transistor

Abstract: PURPOSE:To simply obtain a complementary device having uniform characteristics which is individually excellent by a method wherein a channel is formed using an Si film containing no impurities, the Si thin film of source and drain is formed in P or N type, and a P-channel or N-channel thin film FET is provided CONSTITUTION:Si thin films 302 and 303 containing no impurities are provided on an insulated substrate 301 in an isolated manner, a gate insulating film 304 is coated thereon, and a gate electrode 305 is attached P-thin films 308 and 309 are formed by performing B-ion implantation using the resist 304 as a mask, and N type thin films 312 and 315 are formed by implanting As ions using a resist 305 as a mask Lastly, an insulating film 314 is coated, an aperture is provided, electrodes 315-318 are attached and the titled transistor is formed According to this constitution, as a channel consists of an Si thin film containing no impurities, OFF current is low, and P- and N-channel elements with a conductive type source and drain can be obtained in a simple manner Also, as the thin film is thinner than the maximum width of a depletion layer, Vth is reduced, ON current is increased, a high speed operation can be performed, the characteristics of both FETs are markedly improved, and the difference in characteristics can be reduced

Determination of space charge layer parameters on InSb(110) by electron energy loss spectroscopy

Abstract: The coupled surface phonon (Fuchs–Kliewer)/plasmon polaritons are studied by means of high resolution electron energy loss spectroscopy (HRELS) on cleaved, clean and oxygen‐covered InSb(110) surfaces. Intensities and energetic positions of the losses can accurately be described by a layer model in which a surface layer with negligible carrier concentration is assumed. For the oxygen‐covered surface this layer is identified as a depletion space charge layer. Thickness and band bending of this depletion layer are determined.

Band-gap narrowing in the space-charge region of heavily doped silicon diodes

Abstract: The densities of states of the valence and conduction bands have been calculated in the space-charge region of a heavily doped linearly graded p - n junction silicon diode. Both the donor and acceptor densities were chosen to be equal to 6.2 × 10 18 cm −3 . The results showed the emergence of band tails which penetrated deeply into the energy gap and accounted for the band-gap narrowing observed in such a diode by analysis of capacitance vs voltage measurements of the built-in voltage.

Semiconductor device having an annular region for improved voltage characteristics

Abstract: The breakdown voltage of a p-n junction operated under reverse bias in at least one mode of operation of a semiconductor device is increased by providing at least one annular region forming an auxiliary p-n junction within the spread of a depletion layer from the reverse-biased junction. A passivating dielectric layer with an overlying electrically resistive layer extends over the semiconductor body surface between the active device region forming the p-n junction and a surrounding region of the body portion located beyond the (outer) annular region. The resistive layer is connected to these regions but is insulated from the annular regions by the dielectric layer. A stable high breakdown voltage can be obtained by providing the resistive layer with conductive connection means at the or each annular area which overlies the annular region(s). The conductive connection means, which may be for example annular metal areas or annular highly-doped parts of the resistive layer, is more highly conductive than the resistance of adjacent parts of the resistive layer and provides an electrical connection between these adjacent parts so that a potential variation which corresponds approximately with that along the underlying semiconductor body surface (including the annular regions) can be obtained along the resistive layer.

Computed response of the space charge layer created by corona at ground level to external electric field variations beneath a thundercloud

Abstract: The present numerical simulation deals with ion creation by corona at ground level and their evolution between the ground and the thundercloud. The study starts from a previous model in which the external electric field was constant in time. As an extension, the new model includes several types of variation of the external electric field responsible for ion creation. The following phenomena are taken into account: (1) ion creation of both polarities (bipolar medium), (2) capture of small ions by neutral aerosol particles as well as by other ions of opposite polarity, and (3) influence of turbulent diffusion. The model provides the transient response of the space charge to two types of variation of the electric field created by a thundercloud: the rapid variation due to a lightning stroke and the slow recovery which occurs during regeneration. Time and space evolution of the various parameters are deduced from the computation: small and large ion concentrations, space charge density, and electric field. The different results reveal the tremendous influence of the space charge on the electric field variation at ground level, especially after a lightning stroke. Pulses of corona current higher than 20 nA m−2 following 20 kV m−1 field steps can create such a high ion concentration that the surface electric field can be rapidly reduced to a value close to the corona threshold regardless of the intensity aloft. Electric field profiles plotted after a lightning stroke often show opposite polarities of the electric field at ground level and aloft.

Doping effects in reactive plasma etching of heavily doped silicon

Abstract: Etch rates of heavily doped silicon films (n and p type) and undoped polycrystalline silicon film were studied during plasma etching and also during reaction ion etching in a CF4/O2 plasma. The etch rate of undoped Si was lower than the n+‐Si etch rate, but higher than the p+‐Si etch rate, when the rf inductive heating by the eddy current was minimized by using thermal backing to the water‐cooled electrode. This doping effect may be explained by the opposite polarity of the space charge present in the depletion layer of n+‐Si and p+‐Si during reactive plasma etching.

Edge channel FET

Abstract: Edge channel FET structural geometry and processing are disclosed. A plurality of mesa stacked horizontal layers are provided including source and drain semiconductor layers (74, 76) separated by an insulator layer (75) and having exposed edges (78, 80) at a generally vertical side (83) of the mesa. A generally vertical semiconductor layer (84) extends along the side of the mesa over the exposed source and drain layer edges and forms a channel (93). A gate layer (91, 92) on the channel controls depletion region spreading in the channel layer to control conduction therethrough between the source and drain layers. Channel length is extremely small, as low as 0.1 micron. Ohmic contacts (87, 90) to the source and drain layers are defined several microns away from the conducting channel, resulting in considerable reduction in fabrication complexity, as well as improved reliability. Fabrication and alignment of the gate to the active channel layer is simplified.

A deep-depletion CCD imager for soft X-ray, visible, and near-infrared sensing

Abstract: A high-resolution 512 × 96 element buried-channel charge-coupled (CCD) imager was designed and fabricated on 1-5 kΩ . cm p-type 〈100〉 uncompensated float-zone silicon substrates for soft X-ray (1-10 keV), and near-infrared (0.75-1 µm) sensing. The large depletion layer width (>50 µm) resulting from the high substrate resistivity minimizes minority-carrier generation in the neutral bulk region and thus modulation transfer function (MTF) degradation due to lateral minority-carrier diffusion effects. A unique design approach was used to integrate both high- and low-resistivity regions on the same chip for deep-depletion CCD's and MOS transistor peripheral circuitry, respectively. The low-resistivity region prevents transistor punchthrough caused by the very low substrate doping. Present fabrication technology eliminates previous problems associated with high-resistivity silicon processing, namely, resistivity degradation, saturating dark signal at room temperatures, reduction in full-well capacity, and wafer breakage. Typical dark signal and transfer efficiency of the imager at 25°C are 4 nA/cm2and 0.99997, respectively. Experimental results demonstrate MTF improvements over conventional CCD imagers in the near-infrared and X-ray regions.

Theoretical calculations of Debye length, built-in potential and depletion layer width versus dopant density in a heavily doped p-n junction diode

Abstract: Theoretical calculations of Debye length, built-in potential, depletion layer width and capacitance as a function of dopant density in a heavily doped p - n junction diode are described in this paper. The heavy doping effects such as carrier degeneracy, dopant density-dependent dielectric constant and bandgap narrowing are accounted for by using the empirical approximation for the reduced Fermi-energy given by[1] and the dopant density dependent dielectric constant given by[2], as well as the bandgap narrowing model proposed by[3]. The results show that: (1) bandgap narrowing and carrier degeneracy have important effects on the junction built-in potential; (2) carrier degeneracy and dopant density-dependent dielectric constant are important to Debye length for the abrupt junction case, and (3) the dopant density-dependent dielectric constant is a key parameter which strongly affects the values of depletion layer width and depletion capacitance. These findings are important for modeling of heavily doped p - n junction devices in the VLSI applications.

RF plasma annealing of implanted MIS structures

Abstract: Low-pressure rf plasma treatment of the MIS structures is shown to anneal the ion-implantation- induced defects in the semiconductor. In the course of such an annealing the sample temperature doesn't exceed 230 °C. In the case of prolonged rf plasma treatment of the initial MIS structures (about 30 min in the experiments) surface traps in the lower half of the silicon band gap appear. When the implanted MIS structures are treated for 30 min, the defects in the upper half of silicon band gap are completely annealed but the traps distributed in the space charge region of the semiconductor with levels in the lower half of band gap remain. The recombination-enhanced annealing of deep traps is supposed to be responsible for the observed processes. This annealing is stimulated by X-ray and high-energy uv photon absorption in silicon and by a simultaneous applying an ac electric field to the MIS structure. [Russian Text Ignored].

On electron tunneling in the metal-insulator-semiconductor systems including various electron effective masses

Abstract: It is shown that in some cases of the metal‐insulator‐semiconductor systems the electron tunnel current may be expressed in the form of one‐dimensional integral with modified ‘‘supply function’’ even if the effective mass is not the same in each region of the system. The proposed formula together with description of the semiconductor space charge region (which is not considered in the paper) may be used for modeling of the electron tunnel current‐voltage characteristics, e.g., of the metal–SiO2–Si〈100〉 tunnel diodes. The considerations are based on the electron total energy and transverse wave‐vector conservation assumptions.