Electrical properties of anisotype n-CdO/p-Si heterojunctions

An n-CdO/p-Si heterojunction is fabricated by the deposition of a thin cadmium-oxide film with n-type conductivity onto a polished polycrystalline p-Si wafer by the spray-pyrolysis technique. The I-V characteristics of the heterostructure are measured at different temperatures. It is established that the current through the investigated heterostructure at the forward bias 3kT/e < V < 0.5 V is formed by tunneling-recombination processes with the participation of surface states at the CdO/Si interface and at V > 0.5 V, by tunneling through the space-charge region. The dominant mechanisms of current transport at reverse bias are the Frenkel-Pull emission and tunneling with the participation of energy levels formed by surface states.     

Electrical properties of anisotype heterojunctions n-CdZnO/p-CdTe

Anisotype surface-barrier n-Cd_0.5Zn_0.5O/p-CdTe heterojunctions are fabricated by the high-frequency sputtering of a Cd_0.5Zn_0.5O alloy film onto a freshly cleaved single-crystal CdTe surface. The main electrical properties of the heterojunctions are studied and the dominant mechanisms of charge transport are established, namely, the multistage tunnel-recombination mechanism under forward bias, Frenkel-Pool emission, and tunneling under forward bias. The influence of the surface electrically active states at the heterojunction interface is analyzed and their surface concentration is evaluated: N _ss ?? 10¹⁴ cm^?2.     

Electrical and photoelectric properties of anisotype n-TiN/p-Si heterojunctions

Photosensitive n-TiN/p-Si heterojunctions are fabricated by the reactive magnetron sputtering of a thin titanium-nitride film with n-type conductivity onto polished polycrystalline p-Si wafers. The I–V characteristics of the heterostructures are measured at different temperatures. The temperature dependences of the potential-barrier height and series resistance of the n-TiN/p-Si heterojunction are studied. The dominant mechanisms of current transport through the heterojunction in the cases of forward and reverse bias are established. The heterostructures generate the open-circuit voltage V _oc = 0.4 V and the short-circuit current I _sc = 1.36 mA/cm² under illumination with a power density of 80 mW/cm².     

Specific features of the recombination loss of the photocurrent in n-TiN/p-Si anisotype heterojunctions

Photosensitive n-TiN/p-Si heterostructures are fabricated by reactive magnetron sputtering. The heterostructures generate an open-circuit voltage of V _oc = 0.4 V and a short-circuit current of I _sc = 1.36 mA/cm² under illumination at 80 mW/cm². An analysis of the light current-voltage characteristic and quantum-yield spectrum demonstrate that the poor photoelectric parameters are due to recombination in the base region of the heterojunction and to the formation of a high-resistivity SiO₂ layer on the surface of polycrystalline silicon, which fails to provide high-quality passivation of surface states.     

Photoelectric properties of isotype and anisotype Si/GaN:O heterojunctions

Results of a comprehensive study of electrical and photoelectric properties of isotype (p-Si/p-GaN:O) and anisotype n-Si/p-GaN:O) heterojunctions are reported. The structures were fabricated by chemical vapor deposition of thin films of GaN:O solid solutions on silicon substrates by pyrolytic decomposition of gallium monoammine chloride in the presence of water vapor. Total and spectral photosensitivity and photoresponse kinetics in the current mode under forward and reverse biases, current-voltage characteristics, and saturation open-circuit photovoltage were studied. It was found that in both kinds of heterojunctions the charge distribution near the contacts is mainly governed by carrier capture into interface states (with density estimated to be ～10¹⁴–10¹⁵ cm^?2) with the formation of depletion layers on both sides of the interface. Photosensitivity mechanisms are analyzed for anisotype and isotype heterojunctions. It is shown that the differential nature of the photoresponse kinetics is related to the recharging of interface states, and the strong rise in the photoresponse signal of a biased anisotype heterojunction is attributed to the phototransistor effect. The proposed energy band models of the heterojunctions consistently describe the observed effects.     

Electrical and photoelectric properties of n-CdO-p-InSe anisotype heterojunctions

Anisotype n-CdO-p-InSe heterojunctions are for the first time fabricated on the basis of layered InSe crystals. The temperature dependences of the current-voltage characteristics of the heterojunctions are studied and the mechanisms of charge transport across the barrier under forward and reverse biases are determined. The spectral range of photosensitivity of the heterojunctions is determined.     

Theory for nonequilibrium behavior of anisotype graded heterojunctions

An analysis for the terminal behavior and capacitance of anisotype graded heterojunctions is presented. A closed form expression for the I–V characteristics is derived using the depletion approximation and the rigid band model. The expression is valid for uniform nondegenerate doping and low-level injection. The transition region is modeled to extend beyond the space-charge region with a constant bandgap gradient. Variations of the dielectric constant, carrier lifetime and mobility are ignored. The nonsaturating nature of the reverse current is demonstrated. The effects of variations of bandgap and electron affinity on the I–V characteristics and junction capacitance are discussed. Numerical results for a graded nGe-pGaAs device are given.     

Temperature dependence of the photoluminescence energy of CdTe/ZnTe heterostructures

The photoluminescence (PL) energy was calculated for the heterostructure CdTe/ZnTe, where the emission is based on quantum confinement. This system was studied because it yields a high-intensity emission, covering a wide range of the visible spectrum wavelengths. Our calculations obtained the energy of the fundamental state for electrons and holes, as well as the PL energy using both the Varshni and Manoogian–Woolley formalisms taking into consideration the effects of strain. The Varshni and M–W formalisms for the study of the band gap energy as a function of the temperature differ for high- and low-temperature values. This is because the M–W model takes into account the thermal dilatation and electron–phonon interaction through the U and V parameters. The calculations used quantum wells based on the CdTe/ZnTe heterostructure with different thicknesses (number of monolayers) and involved analyzing the dependence on the thickness and barrier height. The aims of this study were analyzing how the shift occurs in the emission color while increasing of the quantum-well width, and studying the temperature dependence of two different formalisms. The PL energy as a function of the quantum well thickness presents an inflection point at around five monolayers, which is in agreement with reports regarding the critical thickness of heterostructure CdTe/ZnTe. This inflection point is modified when the strain in the heterostructure is taken into account.     

Experimental manifestations of correlated hopping in the temperature dependences of the conductivity of doped CdTe

The behavior of hopping transport in the region of the crossover from Mott conduction to conduction among Coulomb-gap states is investigated in doped CdTe crystals. Inconsistencies are discovered in individual parameters (the localization radius and the dielectric constant) estimated from the behavior of the conductivity on different sides of the crossover. These inconsistencies are explained within a simplified model that takes into account the role of assisting hops. Fiz. Tekh. Poluprovodn. 32, 703–707 (June 1998)     

Temperature dependence of the electrical parameters of frozen sand at low frequencies

The permittivity of moist sand is measured at frequencies of 120 Hz and 1, 10, and 100 kHz in the temperature range +20 to-150°C. It is found that the loss tangent is close to unity at the critical temperature at which through conduction vanishes. In the case of conduction of frozen sand, it is discovered that the sand demonstrates a permittivity hysteresis if a quasi-static electric field is applied.     

Temperature dependence of electrical parameters of SMD ferrite components for EMI suppression

This paper presents how electrical characteristics of ferrite EMI suppressors depend on the operating frequency and temperature. These multi-layer surface-mounted components consist of conductive platinum layer embedded in the middle of nickel-zinc ferrite monolithic structure. In order to analyze variation of performances with temperature changes, a simulation tool has been developed to predict behavior of the SMD ferrite components for EMI suppression. Results for the impedance and inductance as a function of frequency in the temperature range from +25 °C to +120 °C are presented. Proposed EMI suppressors were experimentally tested in the frequency range 1 MHz-1 GHz using an Agilent 4191A RF Impedance analyzer. The calculated results were in very good agreement with the measured ones.     

温度循环下CdS/CdTe太阳电池稳定性的研究

对CdS/CdTe太阳电池在温度循环下的稳定性进行了研究,测定了其I-V特性曲线,并与室温下的电池作了比较.结果表明:经温度循环后电池的转换效率、填充因子和短路电流密度都有不同程度的下降,而用ZnTe作背接触层的电池稳定性有所改善.     

Features of the mechanism of electrical conductivity of semiinsulating CdTe crystals

Temperature dependence of electrical characteristics of p-CdTe semi4nsulating single-crystals are studied, and substantial features of their electrical conductivity not described in available publications are revealed. The activation energy of the p-type conduction material close to the intrinsic one can be both lower and higher than the half-width of the band gap of semi conductor. The results of the analysis of statistics of electrons and holes based on the electroneutrality equation showed that the observed features of electrical properties of the material can be interpreted based on the specific features of compensation processes. The procedure of determining the ionization energy and degree of compensation of acceptors responsible for electrical conductivity of the material is suggested. It is shown that, in the limits of climatic temperature variations, inversion of the conduction type can be observed, and, as a consequence, the Schottky contact can disappear in the CdTe-based detector of the X-ay and γ radiation.     

Temperature and magnetic-field dependences of the thermoelectric power of electronic indium antimonide

The thermoelectric power of electronic indium antimonide with n = 2 × 10¹⁴ cm^?3 in a transverse magnetic field as high as 7 kOe is studied in the temperature range from 4.8 to 120 K. The thermoelectric power is found to be independent of field at a temperature close to 56 K.     

In-situ ellipsometric measurements of the MBE growth of CdTe/HgTe and CdTe/ZnTe superlattices

Phase modulated ellipsometric data recorded during molecular beam epitaxial growth of CdTe/HgTe and CdTe/ZnTe superlattices on (100) and (211)B oriented Cd_0.96Zn_0.04Te and GaAs substrates are presented. The measurements provide a continuous monitor of the growth process, thickness, growth rate, compositional data, and evidence of interdiffusion in CdTe/HgTe superlattices at elevated temperatures. The thickness measurements are independent of growth kinetics and surface orientation and agree well with those obtained from x-ray diffraction and reflection high energy electron diffraction. Ellipsometry shows that the incorporation of Hg in CdTe is significantly higher on (100) oriented surfaces than on (211)B oriented surfaces. Fine structure in the data from CdTe/ZnTe superlattices may be associated with a surface reconstruction during deposition of each CdTe layer. The experimental results for CdTe/HgTe superlattices compare well with results of thin film multi-layer calculations. The general applicability of ellipsometry as an in-situ analytical technique for epitaxial growth of a range of semiconductor superlattices is discussed.     

Photoelectric properties of n-CdS/p-InP heterojunctions

The polarization method for studying photoactive absorption is used to investigate the photoconversion processes in CdS/InP heterojunctions as a function of the orientation of the indium phosphide substrate. The results of these investigations demonstrate the sensitivity of the photoelectric processes to several factors, including the crystallographic orientation of the p-type InP substrate and the optical quality of the CdS layer. The induced photopleochroism coefficient of these heterojunctions increases proportionally to the square of the angle of incidence (P _I ∼Θ²). Such CdS/InP heterojunctions can be employed as polarization-photosensitive devices. Fiz. Tekh. Poluprovodn. 32, 72–77 (January 1998)     

Structural and electrical properties of the Ge x Si1−x /Si heterojunctions obtained by the method of direct bonding

The results of studying the structural and electrical properties of structures produced by the method of direct bonding of Ge _x Si_1?x and Si wafers are reported. The wafers were cut from the crystals grown by the Czochralski method. Continuity of the interface and the crystal-lattice defects were studied by X-ray methods using synchrotron radiation and by scanning electron microscopy. Measurements of the forward and reverse current-voltage characteristics of the p-Ge _x Si_1?x /n-Si diodes made it possible to assess the effect of the crystallattice defects on the electrical properties of heterojunctions. Satisfactory electrical parameters suggest that the technology of direct bonding is promising for the fabrication of large-area Ge _x Si_1?x /Si heterojunctions.     

Temperature dependences of electroluminescent characteristics inthe devices fabricated with novel triphenylamine derivatives

In this paper, we investigated the temperature dependences of the electroluminescent (EL) characteristics of two-layer devices fabricated using four hole-transporting materials based on triphenylamine, and a typical emitting material, tris (8-quinolinolato) aluminum. The thermal stability of the organic EL devices is clearly seen to depend on the glass transition temperature (T_g) of the hole-transporting material. The EL device with a pentamer of triphenylamine exhibits uniform light emission in a continuous operation up to 155°C without breakdown. A lowering of the “turn-on voltage” for light emission and an increase of luminous efficiency with increasing temperature are found in the devices. Excellent durability of continuous operation is also achieved at high temperatures. Our results indicate that the linear linkage of triphenylamine provides the high T_g material and the high device performance at high temperatures