Surface-barrier Structures Research Articles

Spray deposited heavy doped indium oxide film as an efficient hole supplier in silicon light-emitting diodes

The role of a spray deposited tin-doped indium oxide film (ITO) in forward-biased surface-barrier structures fabricated on silicon, from which an efficient radiation emission is obtained, is explained in this work. Such structures present the properties of an induced p–n junction. To achieve a high injection of holes from the p-inversion layer into the n-type silicon substrate, the tin-doped indium oxide film must be a good supplier of holes to maintain this inversion layer. An efficient delivery of holes is possible only if the conduction band of the degenerate n-type tin-doped indium oxide film contains a sufficient number of unoccupied energetic states below the Fermi level that is not less than the surface concentration of holes at the inversion layer. Under such a condition, electrons from the silicon valence band can occupy these empty energetic levels, leaving an equal number of empty energetic states (holes) in the silicon valence band. Our calculations demonstrate the legitimacy of our model for structures with heavily doped indium oxide. The applicability of this model to other high barrier metal–semiconductor contacts is also shown.

Growth and Properties of CuGa3Te5 Single Crystals and In/p-CuGa3Te5 Surface-Barrier Structures

CuGa3Te5 single crystals were grown by the Bridgman method, and their composition, melting point, lattice parameters, and band gap were determined. The crystals were used to fabricate the first photosensitive In/p-CuGa3Te5 surface-barrier structures, which were characterized by photoelectric measurements. The results suggest that such structures are potentially attractive as broadband visible-light detectors.

Thermal–Field Forward Current in GaN-Based Surface-Barrier Structures

The voltage and temperature dependences of the capacitance and forward current in surface-barrier Ni-n-GaN structures are experimentally studied. The results are compared with the Padovani-Stratton thermofield emission theory. It is established that, in a temperature range of 250–410 K, the forward current of the Ni-n-GaN surface-barrier structures (the electron density in GaN is ∼1017 cm−3) is caused by a thermofield emission of electrons, whose energy is ∼0.1 eV below the potential-barrier top.

Nanoindentation as a Tool for Formation of Thin Film-Based Barrier Structures

AbstractA2B6 semiconductors and their solid solutions (ZnSe, ZnTe, CdTe, ZnCdHgTe) are matter of choice for near- and far-infrared optoelectronics. The importance of maximally reduced degree of defectness for these materials is not subjected to discussion. However, preparation of high quality barrier structures based on these compounds by means of MBE, laser technology or liquid phase technique is not always successful due to lattice parameters mismatch. At the same time, good selection of a proper buffer layer may also pose some unavoidable problems. From this point of view the nanoindentation as a tool of defect engineering can be effective for fabrication of surface barrier structures. The first experimental results and numerical simulation of experimental data obtained under investigation of nanoindentation effect on electric characteristics (in particular, current – voltage (I-V) and capacitance – voltage (C-V)) of ZnCdHgTe thin films and ZnCdHgTe/Cd(Zn)Te heterostructures at the room temperature are presented.

Photoelectric Properties of Surface-Barrier Structures Based on Zn[sub 2 – 2x]Cu[sub x]In[sub x]Se[sub 2] Films Obtained by Selenization

p-Zn2−2xCuxInxSe2 (ZCIS) polycrystalline films 1–2 ¼m thick have been obtained by selenization. Photosensitive surface-barrier In/p-ZCIS structures are fabricated based on the films. The spectra of relative quantum efficiency of the structures obtained by selenization of the initial ZnSe/(Cu-In) and (Zn-Cu-In) films are examined. The optical band gap of the Zn2−2xCuxInxSe2 films is determined. Conclusions are reached on the prospects for the use of the obtained films as broadband photoconverters of natural optical radiation.

Photosensitivity of surface barrier structures based on Cu(In,Ga)Se2 films grown by codeposition in vacuum

Polycrystalline Cu(In,Ga)Se2 (CIGS) films with various ratios of Cu, In, and Ga were grown by codeposition of all elements in vacuum. The X-ray diffraction study showed that the films are single-phase and possess a chalcopyrite structure with predominant [112] orientation. The films exhibited a mirror smooth surface and had a close-packed structure composed of crystallites with clear faceting and a transverse size of 0.1–0.3 μm. Related surface barrier structures of the (In,Ag)/Cu(In,Ga)Se2 type were obtained and their spectra of the quantum efficiency of photoconversion were studied. The obtained structures can be used for optimization of the CIGS film technology.

Electrochemical synthesis of thin CdS films

Thin cadmium sulfide (CdS) films have been electrochemically synthesized on metal substrates and the related photosensitive surface barrier structures have been obtained. The proposed method can be used in the technology of thin-film photoelectric converters with large areas.

Growth and Properties of CdGa2S4Single Crystals

CdGa2S4 single crystals were grown by the Bridgman–Stockbarger method and chemical vapor transport, and their composition, structure, morphology, and transport properties were studied. The crystals were used for the first time to produce In/CdGa2S4 surface-barrier structures and H2O/CdGa2S4 photoelectrochemical cells. The photoelectric properties of these devices were investigated in unpolarized and linearly polarized light.

Ultraviolet radiation photodetectors based on structures consisting of a metal and a wide-bandgap semiconductor

Recently, much attention has been given to measuring and monitoring ultraviolet radiation from the Sun and artificial sources. Detectors based on various wide-bandgap surface-barrier structures, which are characterized by a linear dependence of the photocurrent on incident power density in the range of 10−2–103 W/m2 and can record various kinds of ultraviolet radiation, are described. For example, GaP detectors with a UFS-6 filter have a spectral photosensitivity range corresponding to that of solar ultraviolet radiation on the Earth’s surface. The spectral sensitivity of 4H-SiC surface-barrier photodetectors corresponds to the spectral curve of the bactericidal effect produced by ultraviolet radiation. A model has been developed for explaining the process of short-wavelength photoelectric conversion. According to this model, photogenerated electrons and holes can unite into hot excitons, being thus excluded from the photoelectric conversion process. The rise in quantum efficiency with increasing temperature, which has been established experimentally for photodetectors based on Schottky barriers, is attributed to the capture of photogenerated carriers by traps arising from fluctuations of the conduction and valence band edges, with subsequent thermal release of these carriers. These fluctuations are related to imperfections in the surface layer of the semiconductor, which is confirmed by the temperature independence of the quantum efficiency of photodetectors based on p-n structures.

Fabrication and properties of ZnFe2S4 single crystals and structures based on them

A new class of ternary semiconductor compounds has been proposed and synthesized. ZnFe2S4 single crystals, which belong to this class, have been grown for the first time; and their structural, electrical, and optical properties have been investigated. The first photosensitive structures have been fabricated, and their photoelectric characteristics have been studied. A conclusion was made that heterostructures and surface-barrier structures based on ZnFe2S4 single crystals are promising for practical applications.

Photosensitive structures based on CdGa2Se4 single crystals

Photosensitive structures based on CdGa2Se4 single crystals have been fabricated for the first time: In/CdGa2Se4 surface-barrier structures and InSe/CdGa2Se4 heterostructures. The current-voltage characteristics and the quantum efficiency spectra of these structures were studied. The polarization photosensitivity of In/CdGa2Se4 structures were found. The photosensitivity is discussed taking into account the photoactive absorption in CdGa2Se4 crystals in the impurity-related and intrinsic spectral ranges. A conclusion has been made that CdGa2Se4 single crystals are promising for commercial applications in photoelectric converters of unpolarized and linearly polarized light.

Generation-recombination centers in CdTe:V

Generation-recombination currents in surface-barrier structures based on vanadium-doped CdTe are investigated. The level depth and the capture cross section of the centers responsible for the most efficient generation-recombination processes in the samples examined are determined.

Special features of formation and characteristics of Ni/21R-SiC Schottky diodes

The Ni/n-21R-SiC(0001) and $$Ni/n - 21R - SiC(000\bar 1)$$ surface-barrier structures formed on 21R-SiC crystals doped to a concentration of (1–2)×1018 cm−3 and grown by the Lely method were investigated prior to and after rapid thermal annealing (RTA) in vacuum (10−2 Pa) in the temperature range of 450–1100°C. Using X-ray diffraction analysis and Auger analysis, it is shown that cubic NiSi2 and orthorhombic δ-Ni2Si and NiSi silicides coexist with pure Ni in starting samples. The RTA brings about a polymorphic transformation of these phases, which causes the transformation of a barrier contact to a rectifying one independently of the SiC face type, even at T≳600°C. The physicochemical mechanisms of degradation of these barrier structures are discussed.

Fabrication and properties of photosensitive structures based on ZnIn2S4 single crystals

Photosensitive structures based on single crystals of the ZnIn2S4 ternary compound were fabricated and studied for the first time. The optoelectronic properties of this compound and corresponding structures were analyzed using the results of measurements of the optical-absorption spectra of ZnIn2S4 crystals, steady-state current-voltage characteristics, and photosensitivity of the structures at T=300 K. It is concluded that surface-barrier structures and heterojunctions based on ZnIn2S4 can be used as wide-band photodetectors of natural optical radiation.

Electrical properties of UV detectors based on zinc selenide with modified surface barrier

The paper presents technological methods for preparation and treatment of the surface-barrier structures, allowing to improve significantly the electrical characteristics of the sensors based on zinc selenide. The possible mechanisms of the phenomena observed are discussed in details.

New values of the Ag-n-GaP potential barrier

Surface-barrier structures of the Ag-GaP type based on high-quality epitaxial n-GaP layers with n=(0.5–30)×1016 cm−3 were studied. It was found that the potential barrier height depends on the method of surface treatment prior to the metal deposition and correlates with the structural nonideality coefficient and the intermediate layer thickness. For high-quality structures with a reverse current below 10−14 A, the barrier height is ϕ=1.55±0.04 eV. For structures with a relatively thick intermediate layer, the barrier may reach up to ϕ=1.7±0.07 eV. The dependence of the barrier height on the method of the GaP surface treatment is related to the absence of rigid pinning of the Fermi level on the GaP surface.

Analysis of thin film surface barrier solar cells with a microrelief interface

The influence of a microrelief interface between a thin conductive film (emitter) and a semiconductor substrate (absorber) on the optical and recombination losses in surface barrier solar cells is analyzed. Equations for the calculation of monochromatic light transmission through a thin absorbing film with one or two rough surfaces, on an absorbing substrate, are presented. For a weakly texturized interface and a normal direction of the incident light, the influence of the microroughness is taken into account by the formulae obtained. A model of patches with microsurfaces parallel to the structure surface and ones inclined to it at a certain angle (the most probable statistically) was used to describe the experimental results. Au/GaAs surface barrier structures with interface microrelief of a quasigrating or a dendritic type, obtained by chemical anisotropic etching of GaAs, were investigated. The geometric and statistical parameters of the microrelief were determined by atomic force microscopy techniques. The recombination parameters of the textured interfaces were determined from the experimental spectra of the external quantum efficiency, taking into consideration the calculated spectra of light transmittance. A comparison of the internal quantum efficiency spectra with the calculated ones allows a determination of the electronic parameters of the interface. Both the photoconversion parameters under AM0 simulated illumination and the tolerance for 60Co γ-irradiation, obtained for structures with various interface microrelief morphologies, allowed identification of microrelief of the quasigrating type as more suitable for solar cell applications.

A Semi-Infinite Superconductor with Monotonous Tc Variation

The modified London equation for an inhomogeneous superconductor is used to study the magnetic field behavior as well as the surface barrier structure of semi-infinite type-II superconductors with monotonous T c variation. We developed a time dependent modified London equation for an inhomogeneous superconductor, and extented this model to study the effects of the surface barrier on the double critical state model of the system. Analytical expressions for the penetrating field, the flux line fields, the superheating field and the effective penetration depth are obtained.

The ultraviolet radiation detectors based on wide-bandgap Schottky barrier structures

Recently, much attention has been given to measure and control ultraviolet radiation (UVR) from the Sun and artificial sources. We present photodetectors based on different wide-bandgap surface-barrier structures, which exhibit linear photocurrent-radiant flux characteristics in the range 10 −2–10 3 W/m 2 and can register different types of UVR. The use of light filter UFS-6 with GaP photodetector results in a spectral photosensitivity range corresponding to the Sun UV radiation if observed on Earth. The spectral sensitivity range of the photodetectors based on 4H-SiC is near the spectrum of relative effectiveness of various wavelengths in bactericidal UVR. The photosensitivity of the surface-barrier photodetectors based on wide-bandgap semiconductors exhibits the essential decline in the short-wavelength UVR region (5–6 eV), which is the region of intrinsic absorption of the semiconductor. We propose a hot exciton model, according to which the hot excitons can form in the process of the photoelectroconversion in the short-wavelength UVR region because of Brillouin zone structure peculiarities. Thus, photocarriers, forming hot excitons, do not take part in the next photoelectric conversion process and the quantum efficiency decreases.

Photocurrent multiplication in ITO/SiO x/Si optical sensors

A visible/near-infrared optical sensor based on an ITO/SiO x /n-Si structure with internal gain is presented. This surface-barrier structure was fabricated by a low-temperature processing technique. The interface properties and carrier transport were investigated from dark current–voltage and capacitance–voltage characteristics. Examination of the multiplication properties was performed under different light excitation and reverse bias conditions. The spectral and pulse response characteristics are analyzed. The current amplification mechanism is interpreted by the control of electron current by the space charge of photogenerated holes near the SiO x /Si interface. The optical sensor output characteristics and device applications are discussed.