Polarization photosensitivity of a-Si:H/c-Si heterojunctions

The photosensitivity of heterojunctions formed by depositing thin amorphous films on silicon crystalline substrates is investigated. It is found that heterojunctions exhibit polarization photosensitivity, which is observed at an oblique incidence of the linearly polarized radiation on their receiving plane. The induced photopleochroism of heterojunctions increases quadratically with an increase in the angle of incidence θ and reaches 60% for θ=80°. It is concluded that the heterojunctions obtained can be used as the broadband photodetectors of the linearly polarized radiation.     

Investigating the photosensitivity spectra of n-type GaAs-As2Se3 heterojunctions

The spectral photoresponse characteristics of heterojunctions made with n-type GaAs and amorphous films of As₂Se₃ are investigated for various thicknesses of the chalcogenide-glass semiconductor film. Expressions are obtained for calculating the following quantities: the fraction of light absorbed in the chalcogenide-glass semiconductor; the fraction of light absorbed in the GaAs, taking into account multiple reflections within the structure; and their ratio. Light absorption in the structure is analyzed, and the origin of the heterostructure photoresponse is modeled. Experimental results are found to be in agreement with the theoretical calculations. Fiz. Tekh. Poluprovodn. 33, 64–67 (January 1999)     

Effect of γ-ray radiation on photosensitivity of ZnO/CuIn3Se5 heterojunctions

The effect of γ-ray radiation (⁶⁰Co) on the photosensitivity of ZnO/CuIn₃Se₅ heterojunctions is studied. It is established that the spectral dependence of the photoconversion efficiency is retained if the heterojunctions are irradiated with γ-ray fluxes no higher than 2 × 10¹⁹ photon/cm². Dependences of the open-circuit photovoltage and the short-circuit current on the γ-photon flux are studied. It is shown that the photoelectric parameters of heterojunctions remain unchanged under irradiation with the fluxes Φ < 10¹⁷ photon/cm²; in contrast, if the flux increases in the region of Φ > 10¹⁷ photon/cm², the photocurrent decreases monotonically, while the photovoltage exhibits a maximum, after which the photovoltage returns to the initial value. The potential for using the ZnO/CuIn₃Se₅ heterojunctions under the conditions of a high background radiation is established.     

LP-MOCVD法制作n-ZnO/p-Si异质结及其电致发光研究

采用低压-金属有机化学气相沉积法(LP-MOCVD)在(100)p-Si衬底上制备未掺杂n型ZnO薄膜,并制作了相应的n-ZnO/p-Si异质结器件.通过X射线衍射(XRD)、光致发光(PL)光谱和霍尔测试分别研究了所制备薄膜的结构、光学和电学特性.得到具有较高质量的n型ZnO薄膜.在室温条件下,测得了该类异质结器件正向注入电流下可见光和近红外区域的电致发光(EL).     

p-CuAlO2/(n-, p-)Si异质结的制备与电学性质

采用化学溶液法在n型和p型Si衬底上成功制备了单相CuAlO2薄膜。薄膜的电导率-温度曲线显示,薄膜在200K-300K温度范围内呈热激活导电模式,激活能约为0.3eV。电流-电压特性测试显示,p-CuAlO2/n-Si异质结具有明显的整流特性,开启电压约为1.6V,在±3V处的整流率约为35,而p-CuAlO2/p-Si同型异质结表现出类似肖特基结的电学性质,由于p-CuAlO2导电性远低于p-Si衬底,正向电流受空间电荷限制。     

Synthesis,growth and characterization of AgInSe2 single crystals

Single crystal of the ternary semi-conductor AgInSe₂ has been grown by Bridgman technique. The AgInSe₂ crystal crystallizes in the tetragonal chalcopyrite structure. Using melt temperature oscillation method polycrystalline charge was synthesized. The synthesized charge was subjected to powder X-ray diffraction analysis. Thermal property of AgInSe₂ was analyzed using differential scanning calorimetry (DSC) technique. The melting and solidification temperature is 777 °C and 761 °C respectively. The synthesized polycrystalline charge was employed to grow AgInSe₂ single crystals. The grown crystal was confirmed by single crystal X-ray diffraction. The crystal exhibits 60% transmission in the Infrared region. The stoichiometric composition of AgInSe₂ was confirmed by Energy dispersive X-ray analysis (EDAX). The electrical properties of the crystal were studied by Hall Effect measurements and photoconductivity.     

Fabrication and photosensitivity of CdS photoresistor on silica nanopillars substrate

Silica nanopillars are used as substrate for Cadmium sulfide (CdS) photoresistor for the first time. The nanopillars substrate with the large surface ratio can increase the quantity of sensitive material and the surface of light response, which can improve the photosensitivity of the CdS photoresistor obviously. Silicon nanopillars are fabricated by Cesium Chloride (CsCl) self-assembly lithography and inductively coupled plasma (ICP) dry etching, after oxidation, the silicon nanopillars changes to silica nanopillars totally, then the 200 nm thickness CdS film is deposited on the nanopillars surface by RF magnetron sputtering using CdS ceramic target. XRD patterns of the nanopillar and planar substrates after CdS film covering indicate that all the deposited films are crystal. Photosensitivity properties of the photoresistor are tested by a home-made instrument in our group. The test results show that the nanopillar based photoresistor has the higher photosensitivity response than the planar one with different irradiance from 400 to 11,000 μW/cm². With 10,000 μW/cm² irradiance at the room temperature, the photosensitivity response for the planar sample is only 62, while the response for the nanopillar sample achieves to 137, which is more than double of the planar one. The result reveals that the nanopillars morphology can be used as substrate to increase the property of the photoresistor.     

Formation and characterization of CdS/ZnSiAs2 heterojunctions

A rectifying junction between MOCVD formed ZnSiAs₂ and evaporated CdS has been studied. Current-voltage behavior at current densities above about 1mA/cm² appears to be dominated by tunnelling. Capacitance measurements indicate an acceptor concentration in ZnSiAs₂ of 5 × 10¹⁶cm^-3, junction diffusion voltage of 1.0V and the presence of deep traps. Device series resistance could be attributed in part to compensating cross-doping. CdS/ZnSiAs₂ junctions exhibit photovoltaic response, and photovoltages above 0.5V under 5 sun illumination. ZnSiAs₂ electron affinity is estimated to be 3.9eV, and a tentative CdS/ZnSiAs₂ band diagram is presented.     

Fabrication ofn-native oxide/p-ZnTe heterojunctions by the anodic oxidation of ZnTe MBE layers

We demonstrate diode-like behavior betweenp-type ZnTe and its anodic oxide. We describe conditions in which the anodic oxidation process is selective for ZnO formation.N-type conductivity of the anodic oxide is achieved through thermal annealing, giving rise to carrier concentrations of 5 × 10¹⁸ cm^-3. The anodization and the thermal annealing parameters were correlated with Auger Electron Spectroscopy measurements. Structures of anodic oxide/ZnTe have exhibited good rectification properties after brief thermal annealing.     

Fabrication and photosensitivity of heterojunctions based on CuIn<Subscript>3</Subscript>Se<Subscript>5</Subscript> crystals

Heterojunctions based on p-CuIn₃Se₅ crystals are fabricated by magnetron sputtering of an n-ZnO:Al target and by putting naturally cleaved n-GaSe thin wafers onto polished surfaces of p-CuIn₃Se₅ wafers. The current-voltage characteristics and mechanisms of current flow in the diodes under study are analyzed. The photovoltaic effect revealed in the fabricated structures is discussed. It is shown that the fabricated photosensitive heterojunctions are promising for the development of selective analyzers of linearly polarized radiation.     

Electrical properties of thin-film semiconductor heterojunctions n-TiO2/p-CuInS2

Anisotype thin-film heterojunctions n-TiO₂/p-CuInS₂ are fabricated by spray-pyrolysis and dc reactive magnetron sputtering. The electrical and optical properties of thin CuInS₂ films deposited by spraypyrolysis in strictly controlled modes are examined. Also, the electrical properties of the Mo/CuInS₂ rear contact are studied by means of measurements by the three-probe method. The dominant charge transport mechanism in forward- and reverse-biased thin-film heterojunctions n-TiO₂/p-CuInS₂ is determined. This mechanism is well interpreted in terms of the tunneling-recombination model via surface states at the heterointerface and defects in the space-charge region.     

Fabrication technology of heterojunctions in the lattice of a 2D photonic crystal based on macroporous silicon

Design and fabrication technology of a microcavity structure based on a double heterojunction in macroporous silicon is suggested. The fabrication process of a strip of a 2D photonic crystal constituted by a finite number of lattice periods and the technique for defect formation by local opening of macropores on the substrate side, followed by filling of these macropores with a nematic liquid crystal, are considered.     

Fabrication and characterization of in situ polymerized n-polyaniline films grown on p-Si heterojunctions

This work presents a study on the fabrication and the electrical transport mechanism of the in situ polymerized n-type polyaniline (PANI) grown on p-type Si to form n-polyaniline/p-Si heterojunction devices. The current-voltage-temperature (I-V-T) characteristics of n-PANI/p-Si devices were investigated in the temperature range of 298-373 K. These devices showed good rectifying behavior and the temperature dependence of the I-V characteristics were successfully explained by the thermionic mechanism in the narrow potential range, V ? 0.4 V. The barrier height, ideality factor and the series resistance values of this structure were obtained from the forward bias I-V characteristics. The capacitance-voltage-temperature (C-V-T) characteristics of n-PANI/p-Si devices were also investigated. The barrier height values obtained from the C-V measurements were found to be higher than that obtained from the I-V measurements at various temperatures. From the capacitance-voltage-frequency (C-V-f) characteristics, it was found that the capacitance remained almost constant up to a certain values of the frequency in the lower and higher sides of the frequency scale. The higher values of capacitance at low frequencies were attributed to the excess capacitance resulting from the interface states in equilibrium with the p-Si side that can follow the AC signal.     

The electron-voltaic effect in CdS/Cu2S heterojunctions

An investigation of energy conversion in CdS/Cu₂S thin film heterojunctions has shown that the devices appear to operate differently in the photovoltaic and electron-voltaic modes, the response in the latter mode occurring mainly on the CdS side of the junction. With a view to the manufacture of compact long-life reliable microgenerators the electron-voltaic mode has been studied using 6–15 keV electrons, 75–400 keV electrons and β-emitting radioactive sources such as tritium, promethium and thallium. Greater efficiencies for electron-voltaic energy conversion were obtained when the cells were fabricated by a ‘dry’ barrier method rather than by a conventional ‘wet’ barrier technique. Tritium was found to be an ideal source for electron—voltaic energy conversion in the particular CdS/Cu₂S heterojunctions studied.     

Below bandgap emission and absorption in ZnSnP2/GaAs heterojunctions

Below bandgap emission and absorption are observed in p-ZnSnP2on n-GaAs heterojunctions. The band lineup of this heterostructure system suggests that the below bandgap transition is between the valence bands of GaAs and the conduction band of ZnSnP2at the interface. The predicted value for the interfacial gap ofE_{I} = 1.27eV compares with an experimental value of 1.31 eV.     

p-n heterojunctions

A classical kinetic emission model coupled with an assumed energy band diagram which includes the effects of a discontinuity in the electron affinity, effective mass, permittivity and the energy gap at the junction interface is used as the basis for an analysis of the static current-voltage characteristic of the abrupt p-n heterojunction. The derived characteristic is then used to determine regions of quasi-equilibrium within the depletion layer and to predict the position dependence of the quasi-Femri levels.

Two distinct modes of operation are predicted for the heterojunctions I–V characteristic: Metal-semiconductor type operation where the current is limited by the ability of the carriers to surmount the potential barrier at the junction interface and homojunction type operation where the current is limited by the ability of the carriers to diffuse away from the junction depletion region. The predicted extrapolated saturation current for the former type of operation, is in general, significantly less than that for the latter. The position dependence of the quasi-Fermi levels is also different for the two types of operation. For metal-semiconductor type operation a drop in the quasi-Fermi level across the depletion layer is expected, whereas for homodiode type operation there is a negligible variation of the quasi-Fermi level in this region.

The heterojunction I–V characteristic presented here, which differs significantly from previous models, agrees favourably with experimental data on Ge-GaAs heterojunctions reported in the literature and with others recently fabricated by the present authors.     

Fabrication and electrical characterization of n-InSb on porous Si heterojunctions prepared by liquid phase epitaxy

Thin films of InSb were grown on p-type porous silicon (PSi) (1 1 1) substrates by liquid phase epitaxy (LPE) to obtain monocrystalline InSb epilayer on a PSi substrate for low cost device applications. The structural characterization of the devices was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The X-ray diffraction measurements indicate that InSb monocrystalline epilayer was successfully grown onto PSi. The current-voltage (I-V) characteristics of n-InSb/p-PSi heterojunction devices were measured in the temperature range of 298-398 K. The measurements indicate that these heterojunctions have good rectifying characteristics. The estimated zero-bias barrier height φ_BO and the ideality factor η show strong temperature dependence. The conventional Richardson plot exhibits linear behavior in the entire temperature range indicating that the conduction seems to be predominantly due to thermionic emission mechanism. In addition, the capacitance-voltage characteristics are investigated at frequency of 1 MHz. The built-in potential of the heterojunction is determined after eliminating the effect of the capacitance effect of the interface state caused by the lattice mismatch.     

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)     

Transport properties and photosensitivity of metal/porous-silicon/c-Si structures

The current-voltage characteristics, photosensitivity, and impedance of p-type Al/porous-silicon/c-Si structures with 0.2 to 6-μm-thick porous layers of 80% porosity are studied. It is shown that at reverse and small forward bias voltages the current is determined by the potential barrier of the c-Si substrate at the isotypic porous-silicon/c-Si heterojunction. The photosensitivity is determined by the absorption of light in the c-Si substrate. The potential barrier of the metal/porous-silicon contact does not influence the photosensitivity or the currentvoltage characteristics of the structures. The experimental plots of the dependence of the impedance on applied forward bias, thickness of porous silicon layer, and frequency agree well with the theoretical dependences, if an equivalent circuit including two RC circuits connected in series and comprised of the resistance and geometric capacitance of the porous silicon layer and the resistance and capacitance of the potential barrier of the c-Si substrate is used. Fiz. Tekh. Poluprovodn. 33, 211–214 (February 1999)     

Fabrication and photoelectric properties of the ZnO-Cu(In,Ga)Se<Subscript>2</Subscript> heterojunctions

Thin-film n-ZnO:Al/p-Cu(In,Ga)Se₂ heterojunctions are fabricated by magnetron sputtering of an ZnO target, leading to a deposition of Cu(In,Ga)Se₂ films on the surface. The photoelectric properties of the fabricated heterojunctions are studied under exposure to natural and linearly polarized light. It is concluded that the resulting cadmium-free environmentally safe heterostructures can be used as high-efficiency broad-band photoconverters of natural and linearly polarized light.