Theory of switching in p-n-insulator (tunnel)-metal devices: Part I: Punchthrough mode

The four-layered structure (M-I(leaky)-n-p⁺) is found to exhibit a current-controlled negative resistance region in its I-V characteristics. In this paper, a quantitative physical model of the device in the punch-through mode is presented. The negative resistance behaviour is due to a positive feedback mechanism between the tunnel MIS and the n-p⁺ junction parts of the device. The effect of the device parameters on its I-V characteristics is studied.     

<Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Si-<Emphasis Type="Italic">n</Emphasis>-CdF<Subscript>2</Subscript> heterojunctions

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p⁺-n junctions and p⁺-Si-n-CdF₂ heterostructures on an n-CdF₂ crystal surface. Forward portions of the I–V characteristics of the p⁺-n junctions and p⁺-Si-n-CdF₂ heterojunctions reveal the CdF₂ band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p⁺-Si-n-CdF₂ heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.     

Drift of the breakdown voltage in p-n junctions in silicon (walk-out)

A quantitative model for the time behaviour of the walk-out phenomenon in planar p-n junctions is given. The injection of hot carriers into SiO₂ and subsequent trapping of part of them is assumed to be the origin of the walk-out. The model is found to be in reasonable agreement with the experimental results on both p⁺?n and n⁺?p junctions. The parameters in the model are discussed in relation with the experiments.     

Statistical analysis of shallow p–n junction leakage increase using XTEM results probabilities

The reverse current increase for CoSi₂ silicided Si n⁺p shallow junctions is investigated, with particular interest for the diffusion component (I_d), being the fundamental lower limit. The non-uniformity of the CoSi₂ layer is shown to enhance I_d even without the presence of a catastrophic spiking defect. The n⁺ emitter thinning due to the Co reaction with Si enhances I_d by a reduction of the Gummel number. Here it is shown that, in addition, local silicide thickness variations cause a more than linear increase of I_d. A more general method for analysis of the physical variables (the average junction depth x_j and I_d) is shown, based on thickness statistical fluctuations, which are derived from cross-sectional transmission electron microscopy (XTEM) observations. It is applied for junctions with 50–200 nm mean depths.     

The effect of current suppression in the pn−n+ diode of integrated injection logic

The j-V characteristics of the pn^?n⁺ diode are derived by combining the different current components in the n^? region of the diode for various bias voltages. For infinitly fast recombination, the expression for the current density as a function of bias reduces to that of a conventional one-dimensional theory. For finite recombination, however, the expression deviates significantly from the usual expression. In fact, contrary to what would be expected from the conventional theory, the current increases as the width of the neutral n^? region increases for a constant bias. Finally the results of the analysis of the pn^?n + diode are applied to an analysis of the current gain in the integrated injection logic (I²L) device. A qualitative discussion of the current gain for the lateral pnp transistor and for that of the vertical npn transistor is given.     

Silicon p−n insulator-metal (p-n-I-M) devices

Silicon p-n-I-M devices with thin insulating layers ($\text{thicknesses}\text{? 30}\text{A}\text{?}$), named MTIS devices, have been developed. The two terminal device shows an S-shaped negative resistance characteristics similar to a Schockley diode (or p-n-p-n diode). Typically the threshold and sustaining voltages are 10 ～ 15 and 1.3 ～ 2 volts, respectively. The former however can be controlled by optical illumination. Turn-on time including delay is less than 2 nsec and turn-off time ? 1 nsec or less. A thyristor-like device with its third terminal connected to the n-layer shows switching operation controllable by this terminal. A monolithic linear array of p-n-I-M diodes with 30 μm spacing operates as a shift register through coupling of adjacent diodes. Life of the two terminal devices recorded at present is over 1.5 × 10⁴ hr. These devices can be applied to low power and high-speed electrical switching and also to optical switching and integrated logic circuits.     

Fabrication and study of p-n structures with crystalline inclusions in the space-charge region

A new model of connecting elements for monolithic multijunction solar cells based on III–V compounds is proposed, in which p-n junctions with crystalline inclusions of a foreign semiconductor material in the space-charge region are used instead of p ⁺⁺-n ⁺⁺ tunnel junctions. The study shows that the introduction of crystalline inclusions to the space-charge region of the p-n junction in a GaSb-based structure allows current densities of ～50 A/cm² at an ohmic loss of ～0.01 Ω cm². The obtained characteristics of the connecting elements with crystalline inclusions show their applicability to multijunction solar cells for concentrated light conversion.     

Contact potential of p-Al0.5Ga0.5As/n-GaAs structures

The built-in potential of Al_0.5Ga_0.5As (10¹⁸ cm^?3) gates on n-type (10¹⁷ cm^?3) GaAs channel layers in the case of heterojunction normally-off FETs has been measured via C-V and forward I-V methods. A built-in potential of 1.39 eV from C-V measurements and 1.36 eV from forward I-V characteristics which compare well with the theory (1.4 eV) have been deduced. The ideality coefficient is found to be 1.56.     

Effect of neutron irradiation on the structure of silicon p-n junctions of voltage limiters

Changes in capacitance-voltage characteristics of p-n junctions with a linear or close-to-linear uncompensated charge distribution under neutron irradiation are analyzed. It is confirmed that an intrinsic conductivity region is formed near the p-n junction due to such exposure. Empirical formulas are derived which describe the dependence of the sizes of this region and the effective concentration gradient of uncompensated charge on the neutron fluence in a wide range of initial (before neutron irradiation) concentration gradients (from 3 × 10¹⁸ to 2 × 10²⁰ cm^?4) and initial silicon resistivities (from 0.3 to 2 Ω cm).     

High-temperature behavior of GaAs junctions prepared by different techniques

Since high-temperature materials and devices could be useful for a number of applications, four investigations were conducted regarding the fabrication of GaAs layers and/or of p-n junctions. The junctions were obtained by diffusion, by iso- and hetero-epitaxial vapor growth and by ion implantation of GaAs wafers. The results of these studies are described and the temperature behavior of the reverse leakage current is compared. At 300°C and 1V or 2V bias, high-temperature diffusion results in leakage current densities of typically 2 × 10⁻¹ A/cm² while ion implantation yields 1.5 × 10⁻³ A/cm² and the vapor growth techniques lead to intermediate j_R values. The effects of the various fabrication techniques on the temperature characteristics of the junctions are discussed.     

Characterization of aluminum/LPCVD polysilicon Schottky barrier diodes

The I-V characteristics of aluminum Schottky diodes made on LPCVD deposited polysilicon with a wide range of doping concentration (8.5 × 10¹⁵−1.7 × 10²⁰ cm⁻³) have been investigated. Diodes with ideality factor n = 1.12 at room temperature were obtained with doping concentration ≤ 8.5 × 10¹⁶ cm⁻³. In contrast to large grain polysilicon, uniform I-V characteristics can be obtained across the wafer on fine grain LPCVD polysilicon. A barrier height of qφ_B0.73 eV at 300 K was consistently determined from both the I-V measurements and the specific contact resistance measurements. The contact resistance of aluminum/polysilicon contacts is well described by present theory except in the intermediate doping range.     

1/f noise in n+-p-n microwave transistors

1/f noise measurements in the base current and the collector current of NEC 57807 n⁺-p-n microwave transistors show that the noise is not of the mobility fluctuation type, since the current dependence of S_IR(f) and S_IC(f) differs from the theoretical predictions. The low collector current 1/f noise makes it doubtful whether the mobility fluctuation concept is applicable in this case.     

Electrical characterization of p+/n shallow junctions obtained by boron implantation into preamorphized silicon

Electrical characteristics of p⁺/n diodes obtained by boron implantation into amorphous silicon layers formed by a prior implantation of Si⁺ ions are presented. The absence of channeling phenomena (preamorphization), the low boron implantation energy (10–20 keV), and the post-implantation low temperature anneal (600–1000°C) or rapid anneal (electron beam) allow to obtain very shallow junctions (0.1–0.3 μm). Particular attention is given to analyse effects on the reverse diode current from dislocation loops which are formed at the amorphous-crystalline interface during annealing. If the dislocation loops are outside of the space charge region, the diodes show a low leakage current (∼ 1 nA/cm² at - 1 v), but the reverse current increases strongly when this residual damage falls into the depleted n-region. Experimental I–V characteristics are in excellent agreement with a numerical simulation, which takes into account a strong lifetime degration associated with the dislocation loops.     

Mechanism of dislocation-governed charge transport in schottky diodes based on gallium nitride

A mechanism of charge transport in Au-TiB _x -n-GaN Schottky diodes with a space charge region considerably exceeding the de Broglie wavelength in GaN is studied. Analysis of temperature dependences of current-voltage (I–V) characteristics of forward-biased Schottky barriers showed that, in the temperature range 80–380 K, the charge transport is performed by tunneling along dislocations intersecting the space charge region. Estimation of dislocation density ρ by the I–V characteristics, in accordance with a model of tunneling along the dislocation line, gives the value ρ ≈ 1.7 × 10⁷ cm^?2, which is close in magnitude to the dislocation density measured by X-ray diffractometry.     

High-resistance HTS SNS edge junctions

HTS SFQ digital circuit applications require high resistance HTS Josephson junctions. We have investigated the factors affecting the resistance of SNS edge junctions which use Co-doped Y-Ba-Cu-O as the normal metal layer. Several parameters are found to have a surprisingly large effect on device resistance, including edge angle, base electrode material, and deposition conditions of the normal metal and counterelectrode. Controlling these factors has enabled the fabrication of high-quality, high-resistance (≈1 Ω) SNS edge junctions with 1-σ I_c spreads down to 10% and critical currents and I_cR_n products suitable for SFQ digital applications.     

Leakage currents over the Surface of CdHgTe-based photodiodes

The leakage current I _p over the surface of Cd_xHg_1−x Te-based photodiodes that have a cutoff wavelength of the photosensitivity spectrum of λ=9.8–11.6 μm and are fabricated by implanting Zn⁺⁺ ions into the p-type solid solution is investigated. The surface character of the I _p current is indicated by a coordinate shift of the peak in the sensitivity profile of n ⁺-p junctions, which is measured in a scanning mode by the beam of a CO₂ laser with a wavelength of 10.6 μm, with an increase in voltage U across the photodiode and the shift of spectral characteristics to shorter wavelengths with increasing U. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 7, 2004, pp. 890–895. Original Russian Text Copyright ? 2004 by Biryulin, Turinov, Yakimov.     

Electrical properties of CuInSe2 single crystals

Various bulk electrical properties and device characteristics have been measured. It has been shown that the majority carrier type is dependent on crystal stoichiometry. Mobilities of 660 cm²/V sec and 30 cm²/V sec have been measured for n-and p-type samples, respectively. Rectifying contacts and p-n junctions have been investigated by small signal analysis and the associated doping levels and equilibrium band diagrams have been determined. Photovoltage measurements on rectifying contacts have shown that the band-gap has a value of 0.95 ± 0.01eV.     

A simplified theory of the p-i-n diode

A simplified theory of the p-i-n diode is developed for the case of heavy injection in the base, and light injection in the end regions. The current I is taken as the fundamental parameter. The carrier densities n₁ and n₂ at the base boundaries are given directly as functions of the current I by means of simple approximate expressions. The approximation improves with increasing base width and increasing current. It is always within 15% of the correct value for base widths of about 2 diffusion lengths or higher. The accuracy is much better still on the voltage drop across the device, as calculated from the approximate equations for the carrier densities within the base.     

Self-Action of Intense Millimeter Waves in Waveguides with Integrated P-I-N Structures

The nonlinear interaction of high power millimeter (mm) electromagnetic waves with silicon integral p-i-n structures placed in a metal waveguide is theoretically investigated. The level of double injection of charge carriers due to detection of high intensity millimeter wave electric field in p-i-n structures is estimated. A mathematical model of the mutual influence of electromagnetic waves and injected charge carriers in the active region of p-i-n structures is formulated. A numerical solution of the nonlinear Helmholtz equation supplemented by proper boundary conditions on the active region boundary is obtained. The effect of high-power electromagnetic waves leads to an excessive injection of carriers into the active region of the semiconductor between p⁺-i, n⁺-i injection junctions and redistribution of the electric field in the structure. The reflection and transmission coefficients vary rapidly with the change in the input amplitude of the electromagnetic wave. This leads to bistability of these coefficients. The bistability is more pronounced in the low-frequency part of the mm range.     

Correlation impedance in transistors at high injection

It is shown that the correlation impedance R_cor of a p⁺-n-p transistor at high injection and low frequencies is given as $\text{R}{}_{\mathrm{<mtext>cor</mtext>}}\text{= 2(}\text{μ}{}_{\mathrm{<mtext>p</mtext>}}\text{μ}{}_{\mathrm{n}}\text{)(}\text{k}\text{T}\text{q}\text{I}{}_{\mathrm{<mtext>Ep</mtext>}}\text{)}$, which is small for silicon transistors. For n⁺-p-n transistors under the same conditions $\text{R}{}_{\mathrm{<mtext>cor</mtext>}}\text{= 2(}\text{μ}{}_{\mathrm{n}}\text{μ}{}_{\mathrm{p}}\text{)(}\text{k}\text{T}\text{q}\text{I}{}_{\mathrm{<mtext>EP</mtext>}}\text{)}$, which is large for silicon transistors. This strong asymmetry between p⁺-n-p and n⁺-p-n silicon transistors should be measurable.