Showing papers on "Depletion region published in 1996"

Determination of defect distributions from admittance measurements and application to Cu(In,Ga)Se2 based heterojunctions

Abstract: A method to deduce energy distributions of defects in the band gap of a semiconductor by measuring the complex admittance of a junction is proposed. It consists of calculating the derivative of the junction capacitance with respect to the angular frequency of the ac signal corrected by a factor taking into account the band bending and the drop of the ac signal over the space charge region of the junction. Numerical modeling demonstrates that defect distributions in energy can be reconstructed by this method with high accuracy. Defect distributions of polycrystalline Cu(In,Ga)Se2 thin films are determined by this method from temperature dependent admittance measurements on heterojunctions of Cu(In,Ga)Se2 with ZnO that are used as efficient thin film solar cells.

Development of transient current and charge techniques for the measurement of effective net concentration of ionized charges (Neff) in the space charge region of p-n junction detectors☆

Abstract: Transient current and charge techniques (TCT/TChT) have been developed as alternatives to the standard C-V measurements for measurements of the effective net concentration of ionized charges (Neff) in the space charge region (SCR) of Si p-n junction detectors, especially for heavily irradiated detectors. This paper contains the physical background of the techniques, modeling of current and charge pulse response, and applications of the methods to the characterizations of silicon planar detectors designed for high energy physics.

High efficiency and fast modulation of Er‐doped light emitting Si diodes

Abstract: We demonstrate that the electrical excitation of Er ions incorporated within the depletion layer of a p+−n+ Si diode allows one to simultaneously obtain efficient pumping of rare earth ions and a fast turnoff time of the electroluminescence signal. In fact it is found that during pumping, under reverse bias at the breakdown, a high internal quantum efficiency (10−4) can be achieved since the Er ions are excited with a cross section of 6×10−17 cm2 and exhibit a decay lifetime of 100 μs at room temperature. On the other hand, when the diode is turned off, the electroluminescence signal dies off in less than 10 μs (a limit set by the time response of the adopted detector). These results are explained by observing that fast nonradiative decay of the excited Er ions can occur by Auger transfer of the energy to a free electron or to an electron bound to an Er‐related level in the bandgap. These processes are inhibited within the depletion layer and only set in when, at the turnoff, the excited Er ions are sudde...

Ultrafast, dual-depletion region, InGaAs/InP p-i-n detector

Abstract: The design of a new kind of photodetector, the dual-depletion region p-i-n photodetector, is presented. This vertical detector has a parasitic capacitance and transit time that can be controlled semi-independently. This eases the classical tradeoff between these two speed limiting factors, allowing the design of large, fast detectors. A theoretical analysis of the transit time effect and the capacitance effect is made. This analysis is then used to compute optimum design parameters.

Trenched field effect transistor with PN depletion barrier

Abstract: A trenched MOSFET in its on-state conducts current through an accumulation region and through an inverted depletion barrier layer located along the trench sidewalls. Blocking is achieved by gate control depletion of the adjacent region and by the depletion barrier layer (having the appearance of "ears" in a cross sectional view and being of opposite doping type to the adjacent region) which extends laterally from the trench sidewalls into the drift region. This MOSFET has superior on-state specific resistance to that of prior art trenched MOSFETs and also has good performance in terms of on state resistance, while having superior blocking characteristics to those of prior art trenched MOSFETs. The improvement in the blocking characteristic is provided by the depletion barrier layer which is a semiconductor doped region. In the blocking state, the depletion barrier layer is fully or almost fully depleted to prevent parasitic bipolar conduction. The shape and extent of the depletion barrier layer may be varied and more than one depletion barrier layer may be present.

SOI FET design to reduce transient bipolar current

Abstract: Producing a gap between a source and/or drain region of a silicon-on-insulator (SOI) field effect transistor which is less than the thickness of a depletion region normally surrounding the source and/or drain region, preferably at zero volts bias, permits gain of a parasitic bipolar transistor formed therewith to be transiently reduced and the effective base-emitter junction capacitance to be transiently increased during only modes of operation in which the parasitic bipolar conduction dominates normal operation of the field effect transistor. Such transient reduction of gain coupled with a transient reduction of high frequency response reduces the parasitic bipolar current spike to a degree greater than previously achievable and is fully compatible with other techniques of reducing such current spike. As applied to an SOICMOS SRAM, the transistor structure including such a gap is effective in suppressing half-select write disturb effects while maintaining the benefits of excess charge storage and floating body effects in the transistor.

The bias-dependence change of barrier height of Schottky diodes under forward bias by including the series resistance effect

Abstract: Schottky barrier height shifts depending on the interfacial layer as well as a change of the interface state charge with the forward bias while considering the presence of bulk (semiconductor) series resistance are discussed both theoretically and experimentally. It has been concluded that the barrier height shift or increase in Schottky diodes is mainly due to the potential change across the interfacial layer and the occupation of the interface states as a result of the applied forward voltage. One assumes that the barrier height is controlled by the density distribution of the interface states in equilibrium with the semiconductor and the applied voltage. In nonideal Schottky diodes, the values of the voltage drops across the interfacial layer, the depletion layer and the bulk resistance are given in terms of the bias dependent ideality factor, n, different from those in literature. These values are determined by a formula obtained for Vi and Vs by means of change of the interface charge with bias.

A new model for generation-recombination in silicon depletion regions after neutron irradiation

Abstract: Deep level transient spectroscopy has been used to investigate defects in high resistivity silicon diodes after neutron irradiation. Three defects have been correlated with the leakage current. The leakage current in the diodes is found to be a factor of 50 to 600 greater than expected from standard Shockley-Read-Hall (SRH) theory for the observed defect-concentrations. The results can be explained by an enhancement factor due to intercentre transfer of charge between defects in close proximity to each other. It is proposed that a possible mechanism for this process is rapid, direct transfer between a deep donor state and a deep acceptor state. An unidentified defect is observed at E/sub C/-0.45/spl plusmn/0.02 eV which anneals at /spl sim/700/spl deg/C. This defect is correlated to excess leakage current in both diodes and charge coupled devices.

Band‐gap engineering in CdS/Cu(In,Ga)Se2 solar cells

Abstract: Using a numerical device simulation program, the band‐gap engineering in CdS/Cu(In,Ga)Se2 solar cells is examined. The device physics of different design concepts is analysed. Normal band‐gap grading improves performance, especially due to the additional quasi‐electric field, and the analysis showed that the best results are achieved if the grading extends from the highest band‐gap value at the back up to the space charge region. The double grading concept does not yield further improvement, because the front grading—even if located in the space charge region—repels the minority carriers (electrons) away from the CdS interface, and consequently, the fill factor drops significantly. Notch structures in the base also exhibit lower performance than the uniform band‐gap base due to the lower open‐circuit voltage and poorer fill factor. Therefore, the best results are achieved by a normal grading in a Cu(In,Ga)Se2 base from the edge of the space charge region to the back contact.

Low-frequency noise in UHV/CVD epitaxial Si and SiGe bipolar transistors

Abstract: In this work a comprehensive investigation of low-frequency noise in ultrahigh vacuum/chemical vapor deposition (UHV/CVD) Si and SiGe bipolar transistors is presented. The magnitude of the noise of SiGe transistors is found to be comparable to the Si devices for the identical profile, geometry, and bias. A comparison with different technologies demonstrates that the SiGe devices have excellent noise properties compared to AlGaAs/GaAs heterojunction bipolar transistors (HBT's) and conventional Si bipolar junction transistors (BJT's). Results from different bias configurations show that the 1/f base noise source is dominant in these devices. The combination of a 1/Area dependence on geometry and near quadratic dependence on base current indicates that the 1/f noise sources are homogeneously distributed over the entire emitter area and are probably located at the polysilicon-Si interface. Generation/recombination (Gm) noise and random telegraph signal (RTS) noise was observed in selected Si and SiGe devices. The bias dependence and temperature measurements suggest that these G/R centers are located in the base-emitter space charge region. The activation energies of the G/R traps participating in these noise processes were found to be within 250 meV of the conduction and valence band edges.

Interpretation and use of Mott–Schottky plots at the semiconductor/electrolyte interface

Abstract: The Poisson Boltzmann equation is solved for a semiconductor without making the usual assumption of no majority carriers in the depletion layer. The capacative behaviour of the semiconductor is combined with that of the Helmholtz layer to provide a complete description of the potential distribution in the electrolyte and in the semiconductor for all applied potentials including accumulation, the flat band transition and depletion. Calculations show that good linear Mott–Schottky plots are obtained in the depletion region even when 90% of the potential is across the Helmholtz layer. A procedure is described which uses the curvature of the Mott–Schottky plot in the region of the flat band potential to determine the ratio of the semiconductor capacitance to that of the Helmholtz layer. This allows one to determine experimentally the amount of band bending in any system. The procedure is illustrated with data for tin-doped indium oxide. Reasonable values are obtained for the doping density, the Helmholtz capacitance and the true flat band potential.

Study of the charge collection efficiency of CdZnTe radiation detectors

Abstract: The charge collection efficiency of CdZnTe radiation detectors with two different configurations: aSchottky diode detector and aresistive detector are compared. The average charge collection efficiencies for three different directions of irradiation (negative electrode, positive electrode and perpendicular to the electric field) are calculated. The mobility-lifetime product of the CdZnTe substrates is evaluated from the dependence of the measured spectra upon detector bias voltage. The measurement of the average charge collection efficiency is based on monitoring the shift of the peak channel with bias voltage in an experimental setup which is well calibrated. Two types of radiation are used:gamma photons from several radioactive sources andalpha particles from an241Am source. The models for the evaluation of mobility-lifetime product from the measured data for the two types of detector configurations as well as for the two types of radiation sources, are compared and discussed. The CdZnTe (Zn = 10%) substrates under study are obtained commercially and are grown by the high pressure Bridgeman method. The mobility-lifetime products and specific resistivity of the two types of detectors are evaluated and compared. A lower resistivity material has a narrower depletion region and behaves like a thinner detector thus exhibiting better collection efficiencies. Therefore, medium resistivity material which is completely inadequate for resistive detectors can still yield high performance Schottky detectors. The preferred direction of irradiation, i.e. from the negative electrode, is possible only in the case of n-type material which is reverse biased by negative voltages applied to the Schottky gate. The mobility-lifetime products that are derived on both the resistive detector (with specific resistivity of ≈1.1010 ω.cm) and the Schottky diode (with specific resistivity of ≈1.106 Ω.cm) are μnτn ≈-4.10−4 cm2V−1 and μpτp≅ 8.10−5 cm2V−1.

High voltage termination with buried field-shaping region

Abstract: A semiconductor device structure and method are presented for increasing a breakdown voltage of a junction between a substrate of first conductivity type and a device region. The structure includes a region of second conductivity type in the substrate completely buried in the substrate below and separated from the device region. The region of second conductivity type is located a predetermined distance away from the device region. The distance is sufficient to permit a depletion region to form between the region of second conductivity type and the device region, when a first voltage is applied between the device region and the substrate. The distance also is determined to produce a radius of curvature of the depletion region, when a second voltage that is larger than the first voltage is applied between the device region and the substrate, that is larger than a radius of curvature of the depletion region about the device region that would be formed if the region of second conductivity type were not present. Traditional field shaping regions spaced from the device region at a surface of the substrate and spaced from the region of second conductivity type may be used in conjunction with the buried ring, if desired.

Thermally poled silica glass: Laser induced pressure pulse probe of charge distribution

Abstract: Charge distributions in thermally poled silica glass are mapped by using laser induced pressure pulse technique. The experimental results may be explained through postulating the formation of both real space charge layers and dipole polarization inside the depletion region.

Origin of dielectric relaxation observed for Ba0.5Sr0.5TiO3 thin-film capacitor

Abstract: In order to identify the origin of dielectric relaxation of Pt/Ba1-x Srx TiO3/Pt thin-film capacitors, effects of post-annealing in oxygen ambient on their electrical properties were investigated. From comparison of the electrical properties of as-deposited and post-annealed capacitors, it is concluded that electrons from oxygen vacancies in the interfacial depletion region are the origin of the phenomenon.

LDD buried channel field effect semiconductor device and manufacturing method

Abstract: An LDD-structured field-effect semiconductor device that can eliminate fluctuations in the threshold voltage caused by variations in the position of higher-density diffusion layers, thereby suppressing variations in the threshold voltage to a lower level. The junction depth of each of the lower-density diffusion layers in contact with a substrate is greater than the depth of a depletion layer at the place corresponding to a portion of the channel region contacting the source region. This prevents a change in the positional relationship between diffusion layers serving as, what are referred to as "pocket layers", and the depletion layer adjacent to the source, even though the position of the higher-density diffusion layers is varied in the longitudinal direction of the channel due to variations in the width of a spacer. Thus, there are no fluctuations in the quantity of impurities contained in the pocket layers within the depletion layer adjacent to the source, which would otherwise influence the threshold voltage.

Electrical characterization of n‐amorphous/p‐crystalline silicon heterojunctions

Abstract: n‐type amorphous silicon on p‐type crystalline silicon heterojunction diodes were fabricated and electrically characterized. The a‐Si:H film was deposited by plasma enhanced chemical vapor deposition. Electrical properties were investigated by capacitance–voltage and current–voltage measurements at different temperatures. The capacitance–voltage results confirm an abrupt heterojunction. Current–voltage characteristics show good rectifying properties (50000:1 at ±0.5 V). A detailed analysis of transport mechanisms was developed in order to establish a unified model of conduction. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage (V<0.4 V), the current is determined by recombination at the amorphous side of the space charge region, while at higher voltages (V≳0.6 V), the current becomes space charge limited.

Influence of iodine on the electrical and photoelectrical properties of zinc phthalocyanine thin film devices

Abstract: The electrical and photovoltaic properties of the zinc phthalocyanine (ZnPc) and I 2 doped ZnPc thin films, sandwiched between indium tin oxide (ITO) and Al electrodes, were investigated. Doping with iodine brings adequate changes in the characteristics of the device. The devices constitute a metal-insulator-semiconductor (MIS) structure, in which depletion layer is formed in ZnPc, near Al-Al 2 O 3 /ZnPc. The depletion layer width and potential barrier height decrease with I 2 doping. The charge transport phenomenon at higher voltage range appears to be space charge limited conduction (SCLC), in the presence of the discrete trapping level. The position of Fermi level shifts toward the valence band edge, which indicates that I 2 doping increases the P-type conductivity. Various electrical and photovoltaic parameters were determined from the J-V and C-V analysis. The influence of the I 2 doping has been discussed in detail.

Recessed gate field effect transistor

Abstract: A semiconductor device includes a compound semiconductor body having a recess, the recess having a bottom and a hollow, and a refractory metal gate electrode having a lower portion within the hollow. The compound semiconductor body includes a compound semiconductor substrate; a channel layer including a compound semiconductor of a first conductivity type, the channel layer being located on the substrate between the gate electrode and the substrate; first active layers of the compound semiconductor and of the first conductivity type located on regions of the substrate in the recess where the channel layer is not present; and second active layers of the compound semiconductor and of the first conductivity type located on regions of the substrate in the recess where the channel layer is not present; and second active layers of the compound semiconductor of the first conductivity type located on regions of the substrate sandwiching the recess. Therefore, the controllable region in the channel layer is not adversely affected by a depletion layer produced at the interface between the first active layers and a passivation film, whereby an unwanted reduction in the control speed in the channel layer due to the charging and discharging of carriers in traps at the interface is avoided.

Improved modeling of grain boundary recombination in bulk and p‐n junction regions of polycrystalline silicon solar cells

Abstract: This article provides a theoretical investigation of recombination at grain boundaries in both bulk and p‐n junction regions of silicon solar cells. Previous models of grain boundaries and grain boundary properties are reviewed. A two dimensional numerical model of grain boundary recombination is presented. This numerical model is compared to existing analytical models of grain boundary recombination within both bulk and p‐n junction regions of silicon solar cells. This analysis shows that, under some conditions, existing models poorly predict the recombination current at grain boundaries. Within bulk regions of a device, the effective surface recombination velocity at grain boundaries is overestimated in cases where the region around the grain boundary is not fully depleted of majority carriers. For vertical grain boundaries (columnar grains), existing models are shown to underestimate the recombination current within p‐n junction depletion regions. This current has an ideality factor of about 1.8. An improved analytical model for grain boundary recombination within the p‐n junction depletion region is presented. This model considers the effect of the grain boundary charge on the electric field within the p‐n junction depletion region. The grain boundary charge reduces the p‐n junction electric field, at the grain boundary, enhancing recombination in this region. This model is in agreement with the numerical results over a wide range of grain boundary recombination rates. In extreme cases, however, the region of enhanced, high ideality factor recombination can extend well outside the p‐n junction depletion region. This leads to a breakdown of analytical models for both bulk and p‐n junction recombination, necessitating the use of the numerical model.

Characterization of polysilicon-gate depletion in MOS structures

Abstract: This paper presents a new technique to characterize the depletion capacitance and (active) impurity concentration of gate polysilicon in MOS transistors. The method has been validated by means of 2-D simulation; experimental results obtained with state-of-the-art n-channel 0.5 micrometer transistors are presented.

Polycrystalline heterojunction solar cells: A device perspective

Abstract: Analysis of high efficiency, thin film, small grain, polycrystalline. heterojunction CdTe and CuInSe 2 based solar cells can help explain the high quantum efficiencies and the resulting short circuit current (J SC ) as well as the forward diode current that controls the open circuit voltage (V OC - This analysis shows that minority carrier recombination at the metallurgical interface and at grain boundaries is greatly reduced by the proper doping of the window and absorber layers thereby increasing J SC . Additional analysis and measurements show that the V OC in present state of the art solar cells is controlled by the magnitude of the forward diode current which appears to be caused by recombination in the space charge region of the absorber layer. This also shows that ally quantitative modeling of these devices which relates the device performance to the bulk electronic properties of the material should consider the additional geometric dimension introduced by the polycrystallinity because of grain boundary effects.

Self-powered device

Abstract: The invention provides a self-powered device having at least one substrate (102), at least one radioactive power source formed over the substrate, and integrated circuits (110) formed over the substrate. The radioactive power source includes a first active layer (103) of a first conductivity type, and a second active layer (104) of a second conductivity type. The first and second active layers form a depletion layer. A tritium containing layer (106) is provided which supplies beta particles that penetrates the depletion layer generating electron-hole pairs. The electron-hole pairs are swept by the electric field in the depletion layer producing an electric current.

Influence of Surface Defects on the Characteristics of GaN Schottky Diodes

Abstract: We have studied the fabrication of Pt/Au Schottky diodes on n-type GaN. We show that the electrical characteristics of the diodes are strongly dependent on the surface chemical treatment before the metal deposition. Lowest leakage currents were obtained by the use of a HC1 solution. We also show that annealing the diode at a moderate temperature (400°C) leads to reduced reverse currents. In order to explain these results, we measured the density of deep levels in the Schottky diode depletion region before and after the annealing process. We did not observe any significant difference in the bulk density of defects due to the anneal. We also studied the temperature dependence of the reverse currents and found a low activation energy. Our results are interpreted in terms of electrical defects at the metal-GaN surface.

The electrical properties of junctions between aluminium and doped polypyrrole

Abstract: Polypyrrole (PPy) doped with small anions like or large polymeric anions such as poly(styrenesulphonate) forms a conducting organic solid. The electrical properties of metal contacts to this material were evaluated by current - voltage characteristics and impedance spectroscopy measurements. The I - V characteristics of the -doped device was symmetrical but non-ohmic, while that of the -doped diode was rectifying. The complex impedance spectra of -doped structures showed two partially overlapping semi-circles, which revealed the existence of two distinct regions at the metal/doped PPy junctions. They were modelled by an equivalent circuit consisting of two parallel RC circuits in series representing a thin insulating interfacial layer and a depletion region. The impedance spectra of -doped devices manifested a single semi-circle whose diameter depended on the bias voltage. In this case, the thin interfacial non-conducting layer was absent.

On the electronic interaction between additives and semiconducting oxide gas sensors

Abstract: A model for the electronic interaction between additives and semiconducting oxide gas sensors is presented. The model is based on the depletion layer that is created due to the metal–semiconductor contact forced by the presence of a metallic additive. This depletion layer corresponds to an active grain size that is smaller than the geometrical one. Thus, the work function of the metal is connected to the change of sensor characteristics. Moreover, the dependence of the sensitivity on the amount of the deposited additive is explained on the same basis. Experimental results are presented in the case of tin oxide thin film gas sensors with Pd, Pt, and Ni in the presence of zero grade air and carbon monoxide. The experimental results are in excellent qualitative agreement with the proposed model.

Capacitance of semiconductor-electrolyte junction and its frequency dependence

Abstract: The frequency dependent capacitance of semiconductor-electrolyte junction and its relationship to the surface roughness of the semiconductor and the ions in the electrolyte are discussed. Due to very low mobility of the ions, the observed capacitance can be dominated by the Helmholtz double-layer of the electrolyte rather than the space charge layer of the semiconductor. The capacitance will also depend on the frequency. This, often observed power-law frequency dependence of capacitance is ascribed to the contribution of constant phase angle impedance. The power-law exponent can easily be related to the fractal dimension if the semiconductor surface can be described by fractal geometry.