Forward Biased Schottky Diodes Research Articles

Sub-Linear Current Voltage Characteristics of Schottky-Barrier Field-Effect Transistors

This article studies the sub-linearity of the output characteristics measured in Schottky-barrier metal-oxide-semiconductor field-effect transistors with simulations and experiments. It is shown that the sub-linearity is not due to the forward-biased Schottky diode at the drain contact interface but due to the drain bias impact on the source-side Schottky-barrier, resulting in an increased carrier injection with increasing drain–source voltage. The simulation results are confirmed with the measurements of fabricated dual-gate Schottky-barrier transistors.

Analysis of stress-induced inhomogeneous electroluminescence in GaN-based green LEDs grown on mesh-patterned Si (111) substrates with n-type AlGaN layer**Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFB0403105 and 2017YFB0403100) and the National Natural Science Foundation of China (Grant Nos. 11674147, 61604066, 51602141, and 11604137).

Inhomogeneous electroluminescence (EL) of InGaN green LEDs grown on mesh-patterned Si (111) substrate had been investigated. Sample with n-AlGaN inserted between the pre-strained layers and the first quantum well showed the inhomogeneous EL in the low current density range. Near-field EL emission intensity distribution images depicted that inhomogeneity in the form of premature turn-on at the periphery of the LED chip, results in stronger emission intensity at the edges. This premature turn-on effect significantly reduces the luminous efficacy and higher ideality factor value due to locally current crowding effect. Raman measurement and fluorescence microscopy results indicated that the partially relaxed in-plane stress at the edge of the window region acts as a parasitic diode with a smaller energy band gap, which is a source of edge emission. Numerical simulations showd that the tilted triangular n-AlGaN functions like a forward-biased Schottky diode, which not only impedes carrier transport, but also contributes a certain ideality factor.

Electrical and Dielectric Characterizations of Cu2ZnSnSe4/n-Si Heterojunction

Cu2ZnSnSe4 (CZTSe) thin film has been synthesized onto silicon substrates by liquid phase epitaxial growth for the first time in which Au/CZTSe/n-Si/Al heterojunction was successfully fabricated by this technique. The crystal structure and morphology of the CZTSe film were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The I-V characteristics of the CZTSe/n-Si heterojunction in the dark have been studied at different temperatures ranged from 298 to 398 K to determine the diode parameters such as the rectification ratio, series and shunt resistances (RR, Rs and Rsh resp.), the effective barrier height (ϕb) and the diode ideality factor (n). The CZTSe/n-Si heterojunction shows an excellent rectification behavior. The ideality factor n, series resistance RS, and shunt resistance RSh, were decreased with increasing the temperature. The photovoltaic constants such as VOC, JSC, fill factor and the efficiency of CZTSe/n-Si heterojunction have been calculated from the I-V characteristics under illumination. The CZTSe/n-Si heterojunction exhibits efficiency about 3.42% at room temperature. The dielectric measurements proved that the CZTSe/n-Si heterojunction device shows the behavior of two forward biased Schottky diodes.

Equivalent Circuit Model of Semiconductor Nanowire Diode by SPICE

An equivalent circuit model of nanowire diodes is introduced. Because nanowire diodes inevitably involve a metal-semiconductor-metal structure, they consist of two metal-semiconductor contacts and one resistor in between these contacts. Our equivalent circuit consists of two Schottky diodes and one resistor. The current through the reverse-biased Schottky diode is calculated from the thermionic field emission (TFE) theory and that of the forward-biased Schottky diode is obtained from the classical thermionic emission (TE) equation. Our model is integrated into the conventional circuit simulator SPICE by a sub-circuit with TFE and TE routines. The results simulated with our model by SPICE are in good agreement with various, previously reported experimental results.

Equivalent Circuit Model of Semiconductor Nanowire Diode by SPICE

An equivalent circuit model of nanowire diodes is introduced. Because nanowire diodes inevitably involve a metal-semiconductor-metal structure, they consist of two metal-semiconductor contacts and one resistor in between these contacts. Our equivalent circuit consists of two Schottky diodes and one resistor. The current through the reverse-biased Schottky diode is calculated from the thermionic field emission (TFE) theory and that of the forward-biased Schottky diode is obtained from the classical thermionic emission (TE) equation. Our model is integrated into the conventional circuit simulator SPICE by a sub-circuit with TFE and TE routines. The results simulated with our model by SPICE are in good agreement with various, previously reported experimental results.

Electrical spin injection in forward biased Schottky diodes based on InGaAs–GaAs quantum well heterostructures

The authors demonstrate efficient hole spin injection from a ferromagnetic metal (Ni) contact in a forward biased light emitting Schottky diode (LESD) fabricated on a GaAs based heterostructure with a quantum well (QW). The spin polarization of the injected holes was detected by measuring the circular polarization of the electroluminescence (EL) from the near surface InGaAs∕GaAs QW. An intermediate gold layer has been used in order to improve the spin injection efficiency. Over 40% degree of circular polarization of the EL has been observed at T=2K for the LESD structure with Au–Ni–Au Schottky contact.

Near-infrared to visible up-conversion in a forward-biased Schottky diode with a p-doped channel

Near-infrared radiation of wavelength 1.5 μm is up-converted to a visible wavelength of 818 nm by internal photoemission in a Schottky diode with a modulation p-doped channel. The near-infrared light incident upon the metal–semiconductor interface excites electrons from the metal into the semiconductor. The electrons then drift into the quantum well where they recombine radiatively, producing luminescence at the shorter wavelength of 818 nm. The intensity of the luminescence is strongly dependent on bias, and turns on at a forward bias of −0.7 V.

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.

Determination of a-Si:H Film Quality Throughfst and Sclc Techniques

ABSTRACTThe ambipolar diffusion length (L*) and the effective lifetime (τ*) in undoped a-Si:H films have been measured by the Flying Spot Technique (FST). This technique consists in measuring the decay range of charges in Schottky barriers and the potential induced by a laser beam with a constant motion rate. The data show that the FST measurements are quite suitable to determine separately the effective diffusion length and the effective lifetime of the carriers, taking into account the surface effect. The results also indicate that the photosensitivity is not the best parameter to characterize film quality. Indeed, films with high photosensitivity can present a poor lifetime and diffusion length that make them unsuitable to be used in optoelectronic devices. The results obtained by FST have been correlated with the Density of States (DOS) inferred by the Space Charge Limited Current (SCLC) measurements performed in the temperature range of 300–430 K and by the Constant Photocurrent Method (CPM) in forward biased Schottky diodes at room temperature. The dependence of the DOS on temperature shows that the SCLC technique is clearly influenced by the thermally activated carriers.

An analytical model for a vertical metal base transistor operated in the bipolar mode

A model for a vertical metal base transistor is proposed. A virtual base is created by a hole-plasma which is maintained by injection of holes from a forward biased Schottky-diode. By using a Schottky-barrier controlled plasma instead of a controlled p— n-diode, the good power handling capabilities of the BSIT can be combined with improved speed performance. This is obtained by the low base spreading resistance. The metal is placed as a buried grid between the emitter and the collector on intrinsic or weakly doped silicon. The metal is oxidized to protect the base from n + doped emitter. A possible model for the transistor is given and the current gain is calculated. The injection efficiency is discussed in consideration with the design of the base and emitter. Different designs of the transistor are discussed with respect to possible fabrication techniques.

An improved differential voltage technique for capacitance measurement

A differential voltage capacitance technique is described for measuring the capacitance of forward-biased Schottky diodes. This technique is based on the concept of an improved admittance bridge. Difficulties arising from the high conductive component were solved or minimized. Data were obtained for NiSi and PdGaAs Schottky diodes with quality factors as low as 0.001. Compared to accurate phase capacitance spectroscopy and other bridge methods, this technique is more reliable and easier to operate.

Accurate phase capacitance spectroscopy of transition metal silicon diodes

A complete understanding of Schottky barrier devices requires a knowledge of the electronic states at the metal-semiconductor interface. For this reason, a novel and accurate technique for measuring the capacitance of forward biased Schottky diodes has been developed. It is found that the measurement is extremely sensitive to the phase error and that the lock-in amplifier behaves in a nonlinear fashion at high signal current. These difficulties have been resolved to realize the interface state spectrum of a Pd/silicon Schottky barrier.

Improved Schottky capacitance spectroscopy method for the study of interface states in metal-semiconductor junctions

Schottky capacitance spectroscopy is an electrical method allowing the characterization of interface states at a metal-semiconductor junction. This method is based on the study of the capacitance of a forward biased Schottky diode as a function of bias, temperature, and frequency. The experimental procedure previously described presents the drawback of being very time consuming because of the need for low-frequency measurements. We describe here a new improved method allowing rapid and straightforward spectroscopy with high-energy resolution.

Gap states density in a-Si:H deduced from subgap optical absorption measurement on Schottky solar cells

The density of states in amorphous hydrogenated silicon is obtained by deconvolution of the optical absorption coefficient a in the full sub band-gap region. The spectral dependence of the optical absorption coefficient is measured by a constant photocurrent method (CPM) on forward-biased Schottky diodes. The spectral dependence of reflection on the semitransparent Pt electrode is determined. All assumptions used in the deconvolution of a are discussed. The difference in measured value of a (by CPM) in the region below approximately 0.9 eV compared to the measurement of α by photothermal deflection spectroscopy (PDS) is explained by an absorption process seen in PDS and not seen in CPM. This absorption is supposed to be a transition from a deep localized state to a deep localized gap state (two different charge states of the same defect). [Russian Text Ignored]

A study of interface states in metal-GaAs 〈110〉 structures by Schottky capacitance spectroscopy

A study of the capacitance of a forward biased Schottky diode as a function of bias, temperature, and frequency allows characterization of interface states at the metal-semiconductor junction. This method, called Schottky Capacitance Spectroscopy is applied to interfaces obtained by evaporating Au, Ag, or Al onto n-type cleaved GaAs 〈110〉 surfaces. We have explored the region of the semiconductor band gap about 1 eV below the conduction band minimum. There is evidence of three kinds of states. The energy levels of these states are quite reproducible while we have obtained a light dispersion of density of states and capture cross sections. Moreover, we have observed a correlation between the relative density of states C and the degradation of the I–V characteristic.

Study of metal-semiconductor interface states using Schottky capacitance spectroscopy

In a forward-biased Schottky diode, the charge of the interface states can be electrically modulated. This results in the appearance of additional capacitance whose variations with frequency, bias and temperature can be used to determine the characteristic parameters of the states (energy position, density, capture cross sections). A simple model is described, taking into account any possible charge exchanges between the interface states and the three 'reservoirs' surrounding them (conduction and valence bands of the semiconductor and conduction band of the metal). Limit cases where one or two of these exchange paths are dominant are detailed and a few typical experimental examples are given.

Conductivity of amorphous hydrogenated silicon in the planar and sandwich configurations

The temperature dependence of the conductivity of amorphous hydrogenated silicon in planar and sandwich configurations prepared under identical conditions is measured. The planar conductivity is measured on heat-dried samples; the sandwich conductivity is obtained from (i) the ohmic series resistance of forward-biased Schottky diodes and (ii) the ohmic conductivity of n+/n/n+ structures. We find that the conductivities for the two configurations compare favourably, thus ruling out any appreciable effect of space charge layers on the conductivity of the planar samples.

Determination of the density and the relaxation time of silicon-metal interfacial states

In this article a method is described for the determination of the density and the relaxation time of the Si-metal interfacial states from measurements of the admittance of a forward biased Schottky diode.