Forward-biased Diode Research Articles

Selective epitaxial growth of strained SiGe/Si for optoelectronic devices

Two aspects of the selective epitaxial growth of Si and Si 1− x Ge x will be discussed. First the facet formation as dependent on the oxide wall orientation and the lateral size of oxide openings. Besides the often cited {111}, {113} and {110} planes additional planes were observed, the {119} and the {0 1 12} planes. Second, the reduction of misfit dislocation density by reducing the area of the pads allows strained Si 1− x Ge x layers to grow much thicker than the critical thickness. As an application for the latter the electroluminescence of forward biased PIN diodes with strained Si 0.80Ge 0.20/Si(001) will be discussed as being dependent on the thickness of the SiGe layer. It was found that in thicker strained samples the band edge electroluminescence persists up to room temperature. Quantitative modelling of the electroluminescence could explain the temperature and SiGe thickness dependence of the electroluminescence.

Compensation of the temperature-dependent offset drift of a Hall sensor

We present a method to cancel the offset of a Hall sensor and compensate its temperature-dependent drift. We adapt and improve a compensation technique based on a correction using the input voltage. A more accurate compensation for the temperature drift is obtained by an offset calibration at two different temperatures. To decrease the calibration time, we propose a procedure for fast heating of the sensor. It consists of forcing a current pulse through a p-n junction of the sensor. Since the resistance of a forward-biased diode is small, this principle is compatible with low-voltage applications. After correction, the resulting offset is less than two percent of the initial offset over the temperature range −10 to +60°C. The corresponding residual equivalent offset is lower than 250 μT.

Stationary equations for charge carriers in semiconductors including electron-hole scattering

Under high-injection conditions, carrier transport through the semiconductor device is strongly affected by carrier-carrier interaction such as electron-hole scattering. An extended drift-diffusion model with drag current terms is presented, which can be motivated by the analysis of the Boltzmann equations incorporating electron-hole collision operators. In this paper an existence and uniqueness result for Holder continuous weak solutions of the quasilinear system of—a priori degenerate—elliptic equations is proved. Numerical simulations of a forward biased pn-junction diode show that the electron-hole scattering lead to a diminution of the total current compared to the current without electron-hole collision terms. Finally, a formula for the total current depending on the applied voltage and the scattering parameter is derived from asymptotic analysis.

Feedback stability of charge amplifiers with continuous reset through forward-biased diode junctions

A low noise charge sensitive amplifier that does not require a feedback resistor nor an additional reset device has recently been proposed and successfully tested in several spectroscopy systems. The discharge of the leakage and signal current from the detector is performed continuously through the forward-biased gate to channel junction of the input JFET or, in general, through a diode shunting the preamplifier input. Up to now this forward-biased FET charge amplifier (FBFA) has been used only with detectors having currents limited to a few tens of pA. Recent applications of the FBPA for larger area detectors operating at room temperature with leakage current up to few nA reveals that the original feedback configuration of the FBFA is no longer stable and can show low frequency oscillations. In this work the double feedback loop of the FBFA and its stability is analyzed in detail, and a solution to the mentioned problem is found. The acceptable limit of the input current value in the original configuration of the amplifier is analytically determined, and a new configuration of the singularities of the loop gain, which guarantees stability of the FBFA response at higher input current, is proposed. Experimental tests are presented that show the critical condition of the original FBFA configuration and verify the feasibly of the new proposed solution.

Asymptotic Analysis of a Semiconductor Model Based on Fermi-Dirac Statistics

The quasi-hydrodynamic carrier transport equations for semiconductors extended to Fermi–Dirac statistics are considered. It is shown that in the high injection case, these equations reduce to a drift-diffusion model with non-linear diffusion terms. The limiting procedure is proved rigorously and error estimates are shown. We compute numerically static voltage–current characteristics of a forward biased pn-junction diode and compare the curves with the corresponding characteristics obtained from the standard drift-diffusion model based on Boltzmann statistics. It turns out that there exists a so-called threshold voltage at which the behaviour of the characteristic changes. Under high injection conditions, the dependence of the current on the bias appears to be approximately polynomial. The characteristics are studied analytically for a unipolar device.

Charge-sensitive amplifier front-end with an nJFET and a forward-biased reset diode

A new configuration of a resistorless charge sensitive preamplifier with an nJFET as an input device was tested. The DC level of the input of the amplifier was kept constant by a slightly forward-biased np junction connected between the input of the amplifier and ground. A noise level of 22 root mean square (r.m.s.) electrons is measured at 295 K and 15 r.m.s. electrons at 253 K. The dynamic behavior of the amplifier is investigated with different leakage current conditions. The technological benefits and the suitability of the front-end connection for room temperature detectors, particularly multianode drift chambers, are highlighted.

A fin line diode switch with coupled strip conductors

AbstractA design method and experimental results of a new‐type fin line diode switch using coupled strip conductors as matching elements are described. A diode and the strip conductor electromagnetically coupled with fin line are connected in shunt. By introducing coupled conductors, the forward biased diode impedance can be made low but the reverse biased diode impedance is high; so the broad band characteristic of the fin line switch with only one diode can be realized. In this switch, in order to get the greatest bandwidth, the parameters of the microstrip line switch consist of the strip conductor, the dielectric substrate, and fin conductors are uniquely determined. The validity of the design method is verified by measuring the experimental single and two‐stage SPST switches at W‐band.

STATIC CHARACTERISTICS OF MOS-CONTROLLED THYRISTORS — ANALYSIS, SIMULATION, AND EXPERIMENTAL RESULTS

An equation for the iK-vAK static forward characteristic of an MOS-controlled thyristor (MCT) is derived using a four-transistor equivalent model of the device. The Ebers–Moll large-signal model is used for n-p-n and p-n-p bipolar transistors. The equation is similar to that for forward-biased diodes. The equivalent saturation current of the MCT is a function of both the saturation currents and the forward and reverse current gains of the n-p-n and p-n-p transistors. Effects of these parameters on the MCT equivalent saturation current are investigated. Voltages and currents of all transistors that form the MCT equivalent model are simulated using SPICE to explain the behavior of the device in the forward-biased region. Finally, the experimental iK-vAK characteristics are presented. The calculated and measured iK-vAK characteristics were in good agreement. The measured ON-voltage drop was 1.6 V at a cathode current of 200 A and a temperature of 300 K. MCTs are especially useful power devices for electric car applications.

Numerical Approximation of a Drift‐Diffusion Model for Semiconductors with Nonlinear Diffusion

AbstractDiese Arbeit beschäftigt sich mit der numerischen Approximation des transienten, eindimensionalen Drift‐Diffusions‐Modells, das aus einer Poisson‐Gleichung für das elektrische Potential und zwei nichtlinearen Zustandsgleichungen für die Leiterdichten besteht. Die nichtlinearen Diffusionsterme sind so geartet, daß die parabolischen Gleichungen degeneriert sind. Wir zeigen, daß die Gleichungen transiente Lösungen erlauben, für die die Leiterdichten lokal verschwinden.Nachdem wir uns ein Existenz‐ und Eindeutigkeitsresultat ins Gedächtnis gerufen und die Regularität der Lösungen bewiesen haben, diskretisieren wir die Gleichungen mittels der Methode der exponentiellen Anpassung und geben Beispiele von Vakuumlösungen an. Wir zeigen numerisch, daß Vakuumlösungen auch dann auftreten, wenn eine physikalisch sinnvolle PN‐Übergangsdiode betrachtet wird. Infolge des Vakuumeffekts ändert sich das Wachstum der statischen Strom‐Spannungs‐Charakteristik für eine Durchlaßvorspannungs‐Diode an der sogenannten Schwellenspannung. Im hohen Einschuß‐Regime der Durchlaßvorspannungs‐Diode erweist sich das Wachstum der Charakteristik als polynomial.

Resonant forward-biased guard-ring diodes for suppression of substrate noise in mixed-mode CMOS circuits

Substrate noise is a serious concern and a limitation in mixed-mode, analogue-digital, CMOS integrated circuits. The use of forward-biased n+p– guard-ring diodes which resonate with substrate lead inductance is demonstrated by simulations to be effective in reducing this substrate noise by an order of magnitude.

Pressure-dependent operation in poly(3-alkylthiophene) field-effect transistors and Schottky diodes

We have studied charge transport in thin film of poly(3-alkylthiophenes) by measuring polymeric field-effect transistors and Schottky diodes under hydrostatic pressure. The field-effect mobility and conductivity were found to increase with increasing pressure below 2 kbar saturating above 2 kbar to a value of about 1.5–2.0 times the ambient pressure value. A roughly similar increase in the forward biased diode current was observed. The estimated compressibilities are in reasonable agreement with the results of other recent studies.

Novel variable gallium arsenide capacitors

The development of a new type of variable semiconductor capacitor is reported. Its essence is a monolithic (or hybrid) GaAs structure consisting of a reverse biased, high voltage, low reverse current Schottky diode connected in series (back-to-back) to a forward biased PiN diode. The PiN diode has an i layer with a net doping concentration (Nd-Na)i of less than 5×1011 cm−3 and a width of between 3 and 70 μm. The principle of operation is based mainly on control of the PiN diode diffusion capacitance by the reverse Schottky diode current. This current can be changed by structural design or by light. Experimental parameters of a light controlled capacitor include Cmax/Cmin ratios of 20 at ∼1 V and 4–5 at 35 V and a ΔC/ΔV slope of ∼2000 pF/V.

A novel fabrication process and analytical model for Pt/GaAs Schottky barrier mixer diodes

A new fabrication process for small-area honeycomb structured GaAs Schottky barrier diodes is described. This fabrication process is based on the anodic pulse etching technique of GaAs in combination with an electrolytic in situ Pt deposition. The presented diodes exhibit nearly ideal I/V and noise characteristics. An analytical model has been developed to self-consistently model the fabricated near-ideal Schottky barrier diodes. The analytical model includes the effects of a current dependent recombination velocity, an accurate derivation of the spreading resistance for epitaxial diodes, a n-n + junction voltage dependent on the diode current and a bias dependent barrier height. A closed-form expression for the recombination current in the depletion region is given. This model, compared to the simple thermionic model is able to determine technology dependent parameters such as the bias dependent series resistance and junction capacitance as well as the current dependent noise temperature. These are the most important diode parameters which define the diode mixing performance. Although the simple thermionic model also fits the measured data very well, it is shown that the physical parameters of the Schottky diodes, determined by this approach, are inaccurate. The novel analytical model gives new insight into the physical understanding of forward biased epitaxial Schottky diodes with small junction areas.

Effect of mechanical stress on current-voltage characteristics of thin film polycrystalline diamond Schottky diodes

Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament-assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current-voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diamond Schottky diodes not only are very stress sensitive but also have good linearity. This study shows polycrystalline diamond Schottky diodes have potential as mechanical sensors.

Study of Zener Diodes by Sem-DVC

AbstractA Scanning Electron Microscopy method called Dark Voltage Contrast (DVC) was applied for the first time to investigate on a microscale, the narrow depletion region of a Zener diode. Zener diodes were fabricated by the Sprague Semiconductor Corp. using conventional boron diffusion into a n-type wafer with phosphorus.Zener diodes were chosen because of the presence of a shallow p-n junction and for the ability of Zeners to work in the breakdown regime where the dynamics of the current might influence the field distribution in the p-n junction. The samples were examined in the SEM with a beam current below 50 pA to minimize injection of electrons into the depletion region.Reverse and forward biased diodes were examined and potential distribution information was obtained, using Dark Voltage Contrast software. Doping information and C-V measurements were used to double check DVC depletion region measurements.The main results of these studies include measurements of electrical field for three regimes of operation: forward, reverse, and breakdown, with almost ideal field distribution in some Zeners, and fluctuations in others. The field irregularities are related to the defects in the junction area. However the amount of charge build-up appears to depend on the current flow in the dynamic regime for the breakdown. The typical measurements of depletion region width were Wf=.14 μm when forward biased, Wr=0.35 μm at 3-4 volts when reverse biased and Wbr=0.44 gm for 6 v of breakdown. This data helps to reconstruct the diffusion profile.

A new ESD protection concept for VLSI CMOS circuits avoiding circuit stress

ESD protection concepts have to guarantee the required ESD hardness considering possible stress paths between every two pins of a circuit. It was found that all commonly used protection circuit concepts cause a circuit stress for a part of the relevant stress combinations. In these cases, the discharge is not shunted effectively by the protection circuits. Overvoltages appear at output and input transistors, parasitic elements or internal circuit parts. The last effect was found to be caused by forward biased diode structures which divert the discharge current to the supply lines. To avoid stress or damage of the circuit, each path between inputs/outputs and supply lines has to be protected effectively. A new type of protection concept is presented which prevents circuit stress.

Two-step debonding of hydrogen from boron acceptors in silicon

Previous work has demonstrated that B⋅H pairs in silicon thermally dissociate obeying simple first-order kinetics if they are located in a region depleted of majority carriers. B⋅H debonding in equilibrium, however, is a slower, more complex process. We have investigated the dissociation of B⋅H pairs under a variety of equilibrium and nonequilibrium conditions and have demonstrated that the dissociation process is strongly influenced by the local concentration of majority and minority carriers. In particular, we show that injection of minority carriers can markedly accelerate the dissociation process. A model is proposed which suggests that hydrogen released from an acceptor, while initially positive, must always be neutralized before escape is possible. This picture correctly describes the time dependence of debonding in both equilibrium and forward-biased diodes.

Reply to ‘‘Comment on ‘Negative capacitance at metal-semiconductor interfaces’ ’’ [J. Appl. Phys. 70, 1090 (1991)

The origin of the excess admittance at a forward-biased Schottky diode invokes a controversy among research workers. Werner commented on our papers [J. Appl. Phys. 70, 1090 (1991)], in which he believes that the excess admittance is caused by minority-carrier extraction at defective back contacts rather than charge capture and emission at interface states. This reply answers the questions raised by Werner et al. [Phys. Rev. Lett. 60, 53 (1988)] and points out that the minority-carrier effect cannot account for the experimental observations.

A novel substrate hot electron and hole injection structure with a double-implanted buried-channel MOSFET

Summary form only given. Substrate hot electron and hole injection into the same gate insulator is achieved with a double ion-implanted buried-channel n-channel MOSFET device. Under the gate, the impurity profile is n-on-n/sup +/ on a p substrate. The n-on-n/sup +/ buried channel, which is formed by implanting the phosphorus ions twice (first, deep heavy implant and, second, shallow and light implant), makes it possible to inject hot electrons in the accumulation region and hot holes in the inversion region of the device operation. For the case of electron injection, a forward-biased diode adjacent to the stressed device supplies the electrons into the junction space-charge layer between n/sup +/ and p bulk (source and drain are grounded and bulk is held at a large negative voltage). For the case of hot hole injection, the gate is biased to provide a hole inversion layers at the interface. >

Gallium Arsenide Electroluminescent P-N Junctions Made by Close-Spaced Vapor Transport Epitaxy

Epitaxial gallium arsenide p-n junctions have been prepared using close-spaced vapor transport to grow an n-type layer on a p+ substrate. The diodes obtained show two well-defined conduction mechanisms. Using deep level transient spectroscopy a level located at Ec–Et=0.74 eV having a concentration around 1014 cm-3 has been detected in the n region. Forward biased diodes show room temperature electroluminescence peaking at 1.4 eV.