Effect of bremsstrahlung γ-ray photons and neutrons on the parameters of indium-selenium photoconverters

The effect of Bremsstrahlung γ-ray photons and neutrons (effective energy E _eff = 8 MeV) with fluences of 10¹²–10¹³ neutron/cm² on the electrical and photoelectric parameters of layered p-n-InSe is studied for the first time. Even at the highest radiation fluence, an improvement in the current-voltage characteristics and an increase in the open-circuit voltage at an insignificant decrease in the short-circuit current are observed. Significant variations in the spectral curve of the photoresponse are not detected in general. At the same time, even the initial stage of irradiation gives rise to a pronounced degradation of the parameters of the test silicon solar cells. This fact makes it possible to recommend the photodiodes under study for use as radiation-resistant photodetectors.     

Mechanisms of anomalous photovoltage Effect in CdTe films

The method for determining the contributions of asymmetry of illumination and a difference in parameters of p-n and n-p junctions of the p-n-p structure in cadmium-telluride films to the anomalous photovoltage effect is suggested.     

Thermophotovoltaic cells based on In0.53Ga0.47As/InP heterostructures

Reflection of infrared radiation from n-InP substrates with a rear MgF₂/Au mirror is investigated in the wavelength range 1000–2200 nm. It is found that the reflectance weakly depends on substrate thickness and free-carrier concentration in the (0.1–6) × 10¹⁸ cm^?3 range. Thermophotovoltaic cells based on the InP/In_0.53Ga_0.47As lattice-matched heterostructure of p-n and n-p are fabricated by liquid-phase epitaxy and Zn and P diffusion from a gas phase. The characteristics of p-n and n-p thermophotovoltaic cells with an identical configuration of the contacts of 1 cm² area are determined. These characteristics are the open-circuit voltage U _oc = 0.465 V, the filling factor FF = 64% at the current density of 1 A/cm², and the reflectance R = 76–80% for wavelengths longer than 1.86 μm.     

Characteristic features of silicon multijunction solar cells with vertical p-n junctions

A relatively simple technology (without photolithography) based on diffusion welding and ion-plasma deposition of an insulating coating has been developed for fabricating multijunction silicon solar cells with vertical p-n junctions. The effective collection factor for such structures is independent of the wavelength of the incident light in the wavelength range λ=340–1080 nm. Fiz. Tekh. Poluprovodn. 31, 855–857 (July 1997)     

Characterization of p-n junctions under the influence of a time varying mechanical strain

This paper is concerned with the influence of time varying mechanical stress on the electrical properties of p-n junctions. A strain generator based upon a vibrating cantilever beam is described. Data obtained on silicon junctions are presented and compared to a theoretical model for the effects. The results indicate that the major effect of mechanical strain is to change the energy band structure of the semiconductor.     

Silicon photodiode with a grid <Emphasis Type="Italic">p-n</Emphasis> junction

Silicon photodiodes with a grid-structured p-region were studied. Analytical expressions for the capacitance of such photodiodes were derived. The influence of the cell sizes and diffusion length of minority carriers on the sensitivity of the silicon grid photodiode was analyzed in a spectral range of 0.6–1.0 μm. The experimental characteristics of photodiodes with a grid p-n junction with cell sizes of 50 and 110 μm are given. The factors controlling the spectral-characteristic features of these photodiodes are discussed.     

The effect of damaging radiation (<Emphasis Type="Italic">p,e, γ</Emphasis>) on photovoltaic and tunneling GaAs and GaSb <Emphasis Type="Italic">p-n</Emphasis> junctions

The properties of multiple-junction solar cells depend on the properties of the constituent photovoltaic and tunneling p-n junctions. In this study, the properties of the space-charge region for photovoltaic and tunneling p-n junctions were examined using the dark current-voltage characteristics for two semiconductors: GaSb (a narrow-gap semiconductor) and GaAs (a wide-gap semiconductor). The effects of irradiation with protons (the energy of 6.78 MeV and the maximum fluence of 3 × 10¹² cm^?2), electrons (the energy of 1 MeV and the maximum fluence of 3 × 10¹⁶ cm^?2), and γ-ray photons (the energy of 1.17–1.33 MeV and the maximum dose of 17 Mrad) on the lifetime of charge carriers in the space-charge region of photovoltaic p-n junctions and on the peak current of connecting tunneling p-n junctions were studied. The coefficients of the damage for the inverse lifetime are determined for photovoltaic p-n junctions. The coefficients of equivalence between the used types of radiation are determined; these coefficients are found to be almost independent, on the order of magnitude, of the type and material of the p-n-junction (and nearly equal for photovoltaic GaAs p-n junctions and tunneling GaAs and GaSb p-n junctions).     

Electrical and photoelectric characteristics of structures based on InSe and GaSe layered semiconductors irradiated with 12.5-MeV electrons

The effect of irradiation with 12.5-MeV electrons on the electrical and photoelectric parameters of layered photoconverters based on p-InSe-n-InSe and p-GaSe-n-InSe structures is studied. The observed variations in the current-voltage characteristics, photoresponse spectra, open-circuit voltage, and short-circuit current are caused by the formation of point defects. The absence of pronounced changes in the characteristics of the homojunctions and heterojunctions even after irradiation at the highest dose makes it possible to recommend these junctions for use in the fabrication of radiation-resistant photodetectors.     

Extension of the frequency range of the noise spectral density in silicon p-n structures irradiated with gamma-ray quanta

The possibility of intentionally shifting the high-frequency edge of plateau in the noise spectral density of silicon p-n structures to higher frequencies under irradiation with gamma-ray quanta was studied. The largest increase in the extent of the operating-frequency range was observed to amount to 2–2.5 times. As the irradiation dose increased further, the plateau width did not increase, and its boundary became less abrupt. Correlation between the variation in the effective lifetime of minority charge carriers and the width of low-frequency plateau in the noise spectral density was found. A qualitative model describing the variation in the noise spectral density with increasing irradiation dose for silicon p-n structures with microplasma channels governed by the p-n junction dimensions is suggested.     

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.     

Electromagnetic-pulse functional damage of semiconductor devices modeled using temperature gradients as boundary conditions

Attention is drawn to the problem of functional damage of nanoelements caused by high-power electromagnetic pulses. Investigations of this phenomenon have been stimulated by miniaturization of semiconductor components and the transition to nanoelectronics. A mathematical model of the nonstationary action of electromagnetic pulse on a p-n junction is developed. The temperature gradients within the junction are supposed to be linearly interrelated with coefficient β ? 1. Analytical solutions are obtained for linear, quadratic, and bell-shaped pulses. In the approach suggested, the range of the pulse parameters where the problem remains physically meaningful can be calculated for given parameters of the p-n junction. As a test example, functional damages of p-n junctions in silicon and germanium diodes are considered.     

Study of the effect of graded gap epilayers on the performance of CdxHg1−x Te photodiodes

The characteristics of the photodiodes based on Cd_xHg_1?x Te solid solutions with graded gap layers were calculated in the context of a one-dimensional diffusion-drift model. The parameters of the photodiodes were shown to be improved when the p-n junction was located in the near-surface graded gap region rather than in the central homogeneous section of the structure. The photodiodes with the n-type layer adjacent to the substrate were found to offer an advantage over the diodes with the p-layer close to the substrate in the case of illumination from the substrate side.     

Infrared Proximity Sensors Based on Photo-Induced Tunneling in van der Waals Integration

Infrared (IR) detectors based on photo-induced tunneling in van der Waals heterostructures (vdWHs) of graphene/h-BN/graphene or MoS₂/h-BN/graphene exhibit extremely low dark currents owing to a large electron barrier. However, a lack of tunneling barrier materials except for h-BN for 2D vdWHs limits their further enhancement. In this study, a broadband detection is reported with high sensitivity and fast photoresponse of IR proximity sensor by a vdW integration (2D-3D) of graphene or MoS₂, with NiO/Ni as the IR absorber and hole selective transport layer/counter electrode. The low Schottky barrier height of the reported junctions suppresses dark current with a high detectivity ≈ 10¹⁴ Jones and generates a photocurrent by transporting photo-excited carriers through a low hole barrier at a wide wavelength. Two types of integrated IR proximity sensor applications are developed: a passive sensor (MoS₂/NiO/Ni) for the near-IR (NIR) range and an active sensor (Gr/NiO/Ni) for the mid-IR (MIR) range. The former shows a broadband photoresponse to reflect the NIR, while the latter absorbs human body irradiation (2–16 µm wavelength) with a fast photoresponse of 3.5 s (rise time) and 1.8 s (fall time). The fabricated sensors utilize low power, broadband detection, high sensitivity, fast photoresponse, and large-scale area at room temperature.     

Germanium subcells for multijunction GaInP/GaInAs/Ge solar cells

Photovoltaic converters based on n-GaInP/n-p-Ge heterostructures grown by the OMVPE under different conditions of formation of the p-n junction are studied. The heterostructures are intended for use as narrow-gap subcells of the GaInP/GaInAs/Ge three-junction solar cells. It is shown that, in Ge p-tn junctions, along with the diffusion mechanism, the tunneling mechanism of the current flow exists; therefore, the two-diode electrical equivalent circuit of the Ge p-n junction is used. The diode parameters are determined for both mechanisms from the analysis of both dark and “light” current-voltage dependences. It is shown that the elimination of the component of the tunneling current allows one to increase the efficiency of the Ge subcell by ∼1% with conversion of nonconcentrated solar radiation. The influence of the tunneling current on the efficiency of the Ge-based devices can be in practice reduced to zero at photogenerated current density of ∼1.5 A/cm² due to the use of the concentrated solar radiation.     

Features of physical differentiation with respect to light absorbance in junction photovoltage spectra

Junction-photovoltage pleochroism is studied in crystalline silicon under the conditions of a conductivity anisotropy induced by a uniaxial compressive strain. Polarization modulation of light has been used: the samples are excited by linearly polarized light, with the polarizations periodically alternating with respect to the optical axis. The spectral characteristics obtained in such a way represent the polarization difference of the photovoltages, which depends on the light absorbance. A heavy dependence of the spectrum shape on the type of p-n junctions, which differ in relation to base parameters and emitter technologies, is detected. An analysis of the spectra shows that the condition of physical differentiation with respect to absorbance is satisfied only in p-n junctions with a negligible space-charge thickness.     

Numerical simulation of the physical processes in silicon semiconductor p-n junctions in the presence of the ultrashort-pulse electromagnetic radiation

The effect of the signal that is induced by the external ultrashort-pulse electromagnetic radiation on the physical processes in the silicon p-n junctions of the input semiconductor circuits of the TTL ICs is numerically simulated. It is demonstrated that the modulation of the base conductivity, avalanche generation, and thermal heating predominantly affect the current flow under such conditions. The possible types of failures of the TTL ICs in the presence of the ultrashort-pulse electromagnetic radiation are determined.     

Investigation of characteristics of InSb-based photodiode linear arrays

Electrical characteristics of eight-element InSb-based photodiode arrays were investigated at T=78–145 K. The mutual-coupling coefficients of neighboring p-n junctions were no larger than 4.3%. The sur-face of Zn-implanted p-n junctions was investigated using a scanning microscope in a secondary-electron mode and by the electron-beam induced current method. The defects of the surface under the ZnS film, as well as local inhomogeneities of the current through the p-n junctions, were revealed.     

Silicon p-n junction photodiodes sensitive to ultraviolet radiation

Experimental studies on a silicon photodiode have been carried out to achieve the performance characteristics required for applications such as spectroscopic measurements. Sheet resistance was applied as a control parameter for diffusion to obtain a shallow junction less than 1 µm in depth. For high ultraviolet responsivity, the diffusion layer, in which a built-in field is induced by the impurity gradient, was optimized for values of the sheet resistance of about 800-2000 Ω/□. The device responded in the wavelength range of 200-1000 nm,and had a responsivity of 0.065 A/W at 200 nm. In order to reduce influence of stray light in spectroscopic measurements, two types of photodiodes were fabricated with photoresponse reduced in the long-wavelength portion. A p⁺-n-p⁺device was found preferable to a p⁺-n-n⁺device. And the device structure with an extended electrode was desirable for high, reliable performance.     

Phase transformations during the Ag-In plating and bonding of vertical diode elements of multijunction solar cells

The conditions of the bonding of silicon multijunction solar cells with vertical p-n junctions using Ag-In solder are studied. The compositions of electrodeposited indium films on silicon wafers silver plated by screen printing and silver and indium films fabricated by layer-by-layer electrochemical deposition onto the surface of silicon vertical diode cells silver plated in vacuum are studied. Studying the electrochemical-deposition conditions, structure, and surface morphology of the grown layers showed that guaranteed bonding is provided by 8-min heat treatment at 400°C under the pressure of a stack of metallized silicon wafers; however, the ratio of the indium and silver layer thicknesses should not exceed 1: 3. As this condition is satisfied, the solder after wafer bonding has the InAg₃ structure (or InAg₃ with an Ag phase admixture), due to which the junction melting point exceeds 700°C, which guarantees the functioning of such solar cells under concentrated illumination.     

Reliability investigations of 850 nm silicon photodiodes under proton irradiation for space applications

This paper deals with the robustness of silicon photodiodes under proton irradiation for space applications. Our interest is focused on the impact on darkness current and noise equivalent power (NEP), which corresponds to the smaller optical signal detectable by photodiodes. The photodiodes studied were selected for their very small NEP (2 × 10^?14 W/Hz^1/2) and darkness current (50 pA at ?10 mV). Proton irradiations at 60, 100 and 150 MeV energies with fluences ranging from 10¹⁰ to 10¹¹ protons/cm² have been conducted. After irradiation, the darkness current and the NEP at 870 nm of photodiodes dramatically, respectively, increase of about 10,000% and 1000% requiring to estimate the critical dose which can be tolerated by the photodiode before reaching failure criteria and to accurately calculate the minimal shield thickness embedded around the system. Lifetime distributions are also computed in operating conditions using an electrical model based on the decrease of carriers lifetimes caused by formation of defects during irradiation.