Surface Barrier Diodes Research Articles

Biplanar Epitaxial AlN/SiC/(n, p)SiC Structures for High-Temperature Functional Electronic Devices

We investigate the possibility of integration of epitaxial SiC and AlN technologies using opposite faces of the common SiC substrate (AlN epitaxy is performed at the final stage), preserving the initial quality of the preliminarily prepared SiC layers. In particular, we study the influence of AlN heteroepitaxy and accompanying elastic stresses on the redistribution of a doping impurity in SiC layers, as well as the transformation of the local values of the breakdown voltage of barrier diodes, which is associated with this process. As the diagnostic procedure in studying possible negative consequences of durable growth (about 3 h, 60 μm), we have measured reverse branches of the current–voltage characteristics of surface-barrier diode matrices of the Au–SiC type, which have intentionally been formed before and immediately after AlN epitaxy and then removed after the appropriate measuring procedure. Statistical processing of the breakdown voltages (including the calculation of histograms) shows that the variation of mean values and dispersion for the n- as well as p-layers is insignificant.

PROSPECTS OF USING SURFACE AND BARRIER CdTe-DIODES IN SOLAR ENERGY

The paper discusses the advantages and disadvantages of the most used today semiconductor materials of different structural perfection (single crystals, polycrystalline and amorphous) to create solar cells. The main attention is paid to the study of the possibilities of using surface-barrier diodes (SBD) as photoconverters based on single-crystal cadmium telluride. A number of technological methods for modifying n-CdTe substrates are analyzed, which lead to a significant improvement in the electrical and photoelectric parameters and characteristics of SBD. It has been established that the treatment of substrates in an aqueous suspension of alkali metal salts causes the potential barrier ϕ0 height and the open circuit voltage of diodes Vo c based on them to increase by about 1.8 times compared with similar parameters of SBD on the base substrates. Annealing of the latter under certain conditions in air leads to the formation of a surface nanostructure, as a result of which not only almost a twofold increase is observed ϕ0 and Vo c , but also a significant expansion of the photosensitivity Sω spectrum of diodes based on unmodified substrates. It was established that the surface recombination rate of SBD on the basis of substrates with surface nanostructures is two and one orders of magnitude lower than in structures based on basic substrates and treated in suspension of alkali metal salts, respectively.It is shown that the photoconversion efficiency of SBD based on substrates with surface nanostructure (CdTe:O2 ) reaches 13% at 300 K in AM2 lighting conditions. The use of technologies used in the creation of surface-barrier solar cells based on cadmium film telluride is discussed.

Comparative study of fabrication and characterization of Al-ZnO based Schottky barrier diodes using Pd and Au metal contacts

This work shows a comparative study of two types of surface barrier diodes (SBDs). RF magnetron sputtering was used to fabricate Al doped ZnO films (Al0.02Zn0.98O) at two different temperatures (100 and 300 °C) and then the structural and optical properties of these thin films were obtained and analyzed using SEM, AFM, XRD, EDX and UV–Vis spectroscopy. Then the heterojunction layers Pd/Al-ZnO/p-Si (SBD1) & Au/Al-ZnO/p-Si (SBD2) were prepared using these Al-ZnO films (developed at both the temperatures). Optical and electrical properties and the effect of temperature on ideality factor, barrier potential and carrier concentration of both the SBDs were also studied.

Influence of Isotropic Pressure on the Current–Voltage Characteristics of Surface-Barrier Diodes Sb–p-Si〈Mn〉–Au

The influence of hydrostatic pressure on the current–voltage characteristics of surface-barrier diode structures of the Sb–p-Si〈Mn〉–Au type are investigated. The potential-barrier height and the baric coefficient of its variation are found to be eϕδ = 0.75 eV and δ =–1.54 × 10–11 eV/Pa, respectively.

Влияние изотропного давления на вольт-амперную характеристику поверхностно-барьерных диодов Sb-p-Si<Mn>-Au

AbstractThe influence of hydrostatic pressure on the current–voltage characteristics of surface-barrier diode structures of the Sb– p -Si〈Mn〉–Au type are investigated. The potential-barrier height and the baric coefficient of its variation are found to be e ϕ_δ = 0.75 eV and δ =–1.54 × 10^–11 eV/Pa, respectively.

Absolute spectral characterization of silicon barrier diode: Application to soft X-ray fusion diagnostics at Tore Supra

This paper presents an experimental protocol for absolute calibration of photo-detectors. Spectral characterization is achieved by a methodology that unlike the usual line emissions-based method, hinges on the Bremsstrahlung radiation of a Soft X-Ray (SXR) tube only. Although the proposed methodology can be applied virtually to any detector, the application presented in this paper is based on Tore Supra's SXR diagnostics, which uses Silicon Surface Barrier Diodes. The spectral response of these n-p junctions had previously been estimated on a purely empirical basis. This time, a series of second-order effects, like the spatial distribution of the source radiated power or multi-channel analyser non linearity, are taken into account to achieve accurate measurements. Consequently, a parameterised physical model is fitted to experimental results and the existence of an unexpected dead layer (at least 5 μm thick) is evidenced. This contribution also echoes a more general on-going effort in favour of long-term quality of passive radiation measurements on Tokamaks.

Unexpected current lowering by a low work-function metal contact: Mg/SI–GaAs

The low-bias current–voltage characteristics of surface barrier diodes, based on semi-insulating GaAs (SI–GaAs) with different contact metals and area, are reported and analyzed in order to demonstrate the possibility of tuning their low-bias transport characteristics. Novel applications of SI–GaAs emerge for devices with low-current at low-bias requirements, as follows from the possibility of current lowering by as much as two orders of magnitude, achieved by manipulation of the contact metallization and the contact area. The lowest current is observed in the structure with small Mg top and large-area Ti/Pt bottom contact. Since the observed behavior contradicts the conventional ohmic bulk limited and thermionic emission transport models, alternative explanations are discussed. The strong blocking ability of the low-work function Mg contact was attributed to the downwards band-bending, formation of a quasi-degenerate interface region accumulating charge carriers, and the corresponding lowering of the bulk SI–GaAs free carrier concentration.

Mechanisms of current flow in Au-CdTe contacts with a modified surface

The reverse current-voltage characteristics of surface-barrier diodes based on n-CdTe with a surface modified by treating in an aqueous solution of alkali metal salts have been investigated. The reverse current is found to have a tunneling nature at low biases and be caused by avalanche multiplication of carriers as a result of impact ionization at high biases.

Feasibility Study of a Monolithic Silicon Telescope for BNCT Applications

A monolithic silicon telescope, consisting of a thin ΔE stage (of ~2 μm in thickness) coupled to a residual-energy stage E (thickness 500 μm), was studied and tested for measuring the boron concentration in biological samples for boron neutron capture therapy (BNCT). At the Laboratorio di Energia Nucleare Applicata BNCT facility, Pavia, Italy, this information is derived by placing the tissue sample in front of a surface barrier diode and by irradiating the system with neutrons generated in the thermal column of the TRIGA Mark II reactor. The boron concentration is estimated through the measurement of the energy deposited in the detector by the products of the 10B(n,α)7Li reaction. However, the low-energy part of the measured spectra is typically distorted by secondary electrons produced by photon background and by protons generated via the 14N(n,p)14C reaction in tissue. This work discusses the possibility of using a different silicon device, namely, the monolithic silicon telescope, for improving the accuracy of the method by exploiting its particle discrimination capabilities. A device with a sensitive area of 1 mm2 was irradiated (in vacuo) bare, faced both with a certified boron implanted silicon wafer and with a thin sample of rat lung loaded with boron. The preliminary results showed that (a) alpha particles and lithium ions produced by neutron capture on boron are well identified, (b) the events due to protons generated in tissue by neutron capture on nitrogen can be well discriminated, and (c) the presence of nitrogen inside the detector dead layer gives rise to an additional contribution of protons from neutron absorption. These preliminary studies gave confidence about the possibility of improving the accuracy for the assessment of the 10B concentration in biological samples for BNCT.

Mechanism of forward current transport in modified-surface Au-CdTe photodiodes

Current-voltage characteristics of surface-barrier diodes based on n-CdTe substrates treated in aqueous solutions of alkali metal salts were studied. It was found that the forward current is controlled by recombination processes in the space-charge region and the above-barrier carrier transport.

Characterization of detection efficiency as function of energy for soft x-ray detectors

A new technique has been especially developed for determining the detection efficiency of the silicon surface barrier diodes used for tomography reconstructions at Tore Supra, as function of the energy of the x-ray photons, in the range of 4-25 keV. The response of these diodes has been studied for different bias voltages (0-120 V), with a portable x-ray electronic tube and a cooled Si-p-i-n diode, working in photon counting mode, for the absolute calibration.

Electrical Properties of Surface-Barrier Diodes Based on the CdTe Crystals with Modified Surface

Electrical Properties of Surface-Barrier Diodes Based on the CdTe Crystals with Modified Surface

Potential of using the Cd0.8Hg0.2Te alloy in solar cells

Surface-barrier diodes based on the CdxHg1−x Te alloy (x ∼ 0.8) sensitive in the wavelength range 0.3–1.1 μm, which were obtained by etching (bombardment) of the surface of the p-type crystal with argon ions, are studied. Using the measured spectral absorption and reflection curves, as well as the parameters of the diode structure, which were found from electrical characteristics, the spectra of photoelectric quantum efficiency of diodes are calculated. The results of the calculation of photoelectric parameters of the Gd0.8Hg0.2Te-based diodes are given in comparison with the CdTe-based and Si-based solar cells. For the AM1.5 solar irradiation conditions, the open-circuit voltage and short-circuit current, as well as values of limiting efficiency, are determined.

Electrical performance of CdHgTe photodiodes for 1.30 and 1.55 μm

Hg1−x CdxTe-based (x ≈ 0.64 and 0.71) surface-barrier diodes that are photosensitive at 1.30 and 1.55 μm are investigated. The parameters governing the photoelectric performance of the diodes—the concentration of majority carriers, position of the Fermi level in the substrate, contact potential, width of the space-charge region, and effective lifetime of carriers—are found. The electric characteristics measured at temperatures of 268–340 K testify the generation-recombination mechanism of charge transfer. At elevated reverse biases, high-field effects come into play.

Specific features of the physical properties of a modified CdTe surface

Specific features of the optoelectronic properties of CdTe substrates with a modified layer and surface-barrier diodes based on them are revealed and explained by quantum confinement effects in the nanocrystalline structure of the modified layer. The formation of the modified layer is confirmed by study of its surface using atomic-force microscopy and is attributed to the processes of self-organization, which is dominant under specific annealing conditions.

On the mechanism of current passage in metal/p-CuInSe2 structures

Mechanisms of current passage and the temperature dependence of the current-voltage characteristics in Schottky diodes produced by vacuum evaporation of indium on p-CuInSe2 single crystals are discussed. High values of the open-circuit voltage and short-circuit current in these surface-barrier diodes, as well as a high reproducibility of these parameters, suggest that such an inexpensive and rather simple technology is promising for efficient conversion of solar radiation.

Surface barrier diode based on zinc selenide with a passivating zinc oxide film

We propose a method of fabricating surface barrier diodes with overlapped metal junction, which provides for a significant decrease in the reverse currents and an increase in the breakdown voltage.

Electrical properties of surface-barrier diodes based on CdZnTe

Diode structures obtained by vacuum sputtering deposition of Al onto the surface of p-Cd1−xZnxTe (x=0.05) single crystals were studied. In the context of the Sah-Noyce-Shockley model for generation and recombination of charge carriers, a quantitative description of the diodes’ electrical characteristics is attained.

Analytical, optical and electrophysical investigations of TiB x–GaAs interface

The results of analytical (Auger electron spectroscopy, secondary ion mass spectrometry), photoluminescence, spectral ellipsometry and electrophysical investigations of the TiB x –GaAs Schottky contacts are presented. The contacts were obtained by magnetron sputtering and then were thermally annealed in hydrogen atmosphere at T= 400°C, 600°C and 800°C. It was shown that decay of the Ga x B 1− x As phase in a transition layer at the interface during thermal annealing decreases its optical conductivity and causes degradation of the surface-barrier diodes.

Tangential x-ray imaging system for analysis of the small-scale modes in the T-10 tokamak

A toroidally viewing x-ray imaging system is used in the T-10 tokamak for reconstruction of the small-scale plasma perturbations (high-m modes). The imaging system is based on the matrix array of the silicon surface-barrier diodes with a two-dimensional Soller collimator and an automatic positioning system. An additional hard x-ray detector and magnetic probe are placed inside the tokamak vessel for measurements of the nonthermal emission and fast magnetic field perturbations. Initial experiments in T-10 indicated improved sensitivity of the system for identification of the small-scale plasma perturbations prior the density limit disruptions.