Search

Microcrystalline gallium phosphide (GaP)/Si multilayer structures grown on GaP substrates using combination of plasma enhanced atomic layer deposition (PE-ALD) for GaP and plasma-enhanced chemical vapor deposition for Si layers deposition are studied by three main space charge capacitance techniques: capacitance versus voltage (C-V) profiling, admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS), which have been used on Schottky barriers formed on the GaP/Si multilayer structures. C-V profiling qualitatively demonstrates an electron accumulation in the Si/GaP wells. However, quantitative determination of the concentration and spatial position of its maximum is limited by the strong frequency dependence of the capacitance caused by electron capture/emission processes in/from the Si/GaP wells. These processes lead to signatures in AS and DLTS with activation energies equal to 0.39 ± 0.05 and 0.28 ± 0.05 eV, respectively, that are linked to the energy barrier at the GaP/Si interface. It is shown that the value obtained by AS (0.39 ± 0.05 eV) is related to the response from Si/GaP wells located in the quasi-neutral region of the Schottky barrier, and it corresponds to the conduction band offset at the GaP/Si interface, while DLTS rather probes wells located in the space charge region closer to the Schottky interface where the internal electric field yields to a lowering of the effective barrier in the Si/GaP wells. Two additional signatures were detected by DLTS, which are identified as defect levels in GaP. The first one is associated to the SiGa + VP complex, while the second was already detected in single microcrystalline GaP layers grown by PE-ALD.

The article is based on an important characterization task to accurately evaluate the properties of the layers, their interfaces with c-Si, and to select the best candidates to integrate them into a c-Si-based solar cell. The work has shown that GaP could be doped with n-type doping, thus providing a selective contact for the electrons, and has a significant valence band offset with c-Si, making it an excellent candidate as a selective contact, without requiring an additional ITO layer.

This work is devoted to the study of the deposition of a-Si:H by the PECVD method in continuous and pulsed regime on test structures in the form of trenches with a high aspect ratio. The thicknesses of the layers obtained in these modes were investigated by the method of scanning electron microscopy. It was shown that the layers obtained in the pulsed mode, as compared with the continuous one, have better conformity.

In this work last results on optimization of (p)a-Si:H/p-Si ohmic contact made by PECVD method are presented. A strong effect of growth temperature and trimethylboron flow on charge carriers transport was demonstrated. An optimized (p)a-Si:H layer also was successfully applied as an emitter layer to a heterojunction solar cell fabrication where a measured open circuit voltage of 0.65 V was obtained.

In this work the properties of the BP/Si heterojunction interface were investigated by capacitance methods, the deep levels transient spectroscopy method and admittance spectroscopy. Admittance spectroscopy did not detect any defects, but the deep level transient spectroscopy showed response with activation energy of 0.33 eV and capture cross-section σn=(1-10)·10-19 cm2 and defect concentration (NT) is in the order of 1013 cm-3. This defect level is a trap for electron with position of 0.33 eV below the conduction band in region near the BP/Si interface.

This article is devoted to the formation and study of the properties of amorphous gallium phosphide layers obtained by plasma-chemical deposition at a temperature of 250 °C. The optical and structural properties of the obtained layers on fused silica and silicon substrates were investigated. The possibility of the formation of a homogeneous amorphous gallium phosphide with a smooth surface at a low temperature and low power of RF plasma was shown.

The formation of p-type GaP by plasma-enhanced atomic layer deposition at a temperature of 380 °C has been studied. The incorporation of Zn impurity was detected by the method of glow discharge optical emission spectroscopy (GDOES). Strong band bending was confirmed by electrical measurements performed for the p-n homojunctions formed by deposition of p-GaP on the surface of n-type GaP substrates, which indicates the acceptor behavior of the impurity. It has been shown that p-type GaP deposited by PE-ALD can be used to form photovoltaic converters.

III-V nanowires (NWs) are a promising technology for piezotronic and nanooptoelctronic applications. In this work, we investigate the processes of fabricating a structure with InP NW arrays on a silicon substrate for piezotronic applications. The coating of the NW array with a polymer and the fabrication of a transparent electrical contact to NWs is studied. The piezoelectric effect for the structures with a nonzero piezoelectric modulus d 33 is demonstrated in an oil environment at voltage amplitudes of about 100 mV. The experimental electromechanical coupling is about 0.049, which is close to the theoretical estimate of 0.053.

This article is concerned with plasma-enhanced atomic layer deposition of GaPN in the form of a GaP/GaN digital alloy at 380°C on a silicon substrate. It was found that the GaP/GaN digital alloy has a uniform structure without significant mechanical stresses and defects at the interface with the substrate. EDX and Raman scattering study confirmed deposition of a monolithic GaPN crystalline material with a total nitrogen content of 7.8%.

The author analyzes the main tools for promoting scientific articles that are used most often by the editorial board of the Computer Optics journal to promote the publication in international scientometric databases and popularize the ideas of science. It is noted that the use of these tools allowed the publication to increase significantly the “portfolio” of articles, the number of articles published per year, including the articles in English, increase significantly the citation of journal articles in other scientific publications, as well as expand the geographical spread of authors.

Arrays of silicon nanowires were fabricated by dry etching in the ICP mode in a mixture of SF6/O2 gases at a temperature of-140 °C. Defects located near the wafer surface with E a =0.30 eV, σ=(1–10)×10−14 cm2 and E a =0.68–0.74 eV, σ=1×10−15 cm2 were detected by admittance spectroscopy and deep-level transient spectroscopy. An increase in the dry etching time from 3.5 min (for the 1st sample) to 4.5 min (for the 2nd sample) leads to an rise of their concentration, but additional stage of wet etching in 4% KOH during 30 s leads to a vanish of the response from the first sample (N T ˂1011 cm−3), while for the second sample the defect concentration becomes in two times lower.

In this work an application of selective contacts p-Si/MoOx for evaluation of silicon surface degradation is shown. Using a method of I-V measurements the effect of silicon surface degradation during SiO2 magnetron deposition was demonstrated.

Periodic nanoheterostructures GaP/Si grown by PE-ALD with argon plasma treatment on GaP wafers were studied by capacitance methods. The response from silicon quantum well was clearly observed by capacitance-voltage characteristics as peak on profile of concentration of free charge carriers in sample GaP (50 cycles)/Si (22 s) with 7 wells. It is explained by higher doping of GaP layers due to higher total time of silane flow in growth process unlike samples with smaller numbers of silicon wells or lower time of silicon deposition. Further, response from defect level was observed with capture cross-section (1–10)×10−15 cm−2, and its energetic level decreases from 0.51 eV to 0.39 eV under conduction band with increasing of total time of silane flow.

The work is devoted to the study of electrical properties of InGaN nanostructures with branched morphology (NSs) on p-type Si substrates. It was found that the IV curves between InGaN NSs and p-Si are close to linear, which could indicate a tunneling conductivity. Such unique structures as InGaN NSs on p-Si can be used as building blocks for water splitting devices and tandem solar cells.

The features of the formation of a SiO2 hard mask using dry etching and nanosphere lithography are considered in the paper. A series of experiments was carried out using a variation of plasma etching parameters such as ICP and RF power, pressure as well as a substrate temperature. As a result, optimal parameters were found to obtain both good selectivity and high etching rate.

In this paper, we study the effect of the height and diameter of vertically aligned silicon structures on their optical properties. Structures with different geometry were formed using nanosphere lithography and dry etching. Nanosphere lithography was realized with 0.9 and 2 μm latex spheres. The etching process was carried out through a formed mask (template) composed of 0.9 and 2 μm latex spheres, respectively. The diameter of the spheres and the etching time determined the size of the formed structures and their optical properties. A significant reduction of the total reflection with height as well as blue shift of the minimum with diameter decrease were observed.

In this article the temperature dependences of selective contacts based on MoOx were studied. The p-Si/MoOx/Al structure was fabricated. Current-voltage and capacitance-voltage characteristics in the temperature range from 80 to 300K were measured. Band diagram was also calculated to reveal potential barriers location and its influence on charge carrier transport.

The work is devoted to exploration of arrays of vertical aligned silicon nanowires (SiNWs) obtained by cryogenic dry etching in ICP mode with height of 4.5-5.5 μm and aspect ratio of 7. It was shown that geometry of nanowires has crucial influence on rate of wet etching in KOH since it is higher for 3D objects than for planar wafer, and the diameter should be the same along the nanowire for controlled wet etching. Wet etching in 4% KOH solution during 30 s allowed to save array of uniformity vertical aligned SiNWs with height of 4 μm and diameter of 500 nm. Such treatment reduced concentration of defects detected by deep-level transient spectroscopy, particularly, it drops as minimum in two times for deep level with £0=0.68-0.74 eV placed near to surface of wafer.

An approach for epitaxial growth of GaP layer on Si substrate at low temperature (380°C) by plasma-enhanced atomic layer deposition (PEALD) is explored. A significant improvement of the crystalline properties of the GaP layers was obtained using additional in-situ Ar plasma treatment. The epitaxial growth for the first 20-30 nm of GaP on the Si substrate could be achieved according to transmission electron microscopy. Moreover, use of in-situ Ar plasma treatment during PEALD process allows one to increase the growth rate per cycle from 0.9±0.1 A/cycle to 1.9±0.1 A/cycle and reduce RMS roughness from 3.76 nm to 1.88 nm. The effect of Ar plasma treatment on the electronic properties of the GaP/Si interface is studied by deep level transient spectroscopy (DLTS). A defect level at (0.33±0.03) eV below the conduction band is observed in the underlayer of Si for the GaP/Si structure grown under Ar plasma treatment. However, the defect response observed by DLTS vanishes after rapid thermal annealing at 500 oC in nitrogen ambient.

The effect of hydrogen plasma treatment on the electrical and optical properties of GaN NWs/Si based vertical hetero structures synthesized by the method of plasma molecular beam epitaxy is studied. The effect of treatment has been carefully studied by variation of the passivation duration. Measurements of the electron beam-induced current (EBIC) technique showed the absence of potential barriers between the active parts of the diode and the contacts, which indicates the ohmic behavior of the latter. The current - voltage characteristics show that hydrogen can efficiently passivate recombination centers at the GaN NWs/Si heterointerface. It is established that the optimal passivation duration, providing improved electrical properties, is 10 minutes in the adopted passivation modes. It is shown that a longer treatment causes a deterioration in electrical properties.

The work is devoted to studying the influence of an additional step of argon plasma treatment on the quality of the GaP/n-Si isotype heterojunction grown by plasma-enhanced atomic-layer deposition (PE-ALD). Deep-level transient spectroscopy measurements demonstrated that argon plasma leads to the formation of defects with a high concentration in silicon wafers, unlike the PE-ALD mode without a step of hydrogen or argon plasma treatment. In addition, GaP layers obtained by PE-ALD have defects with an activation energy of 0.40 eV and 0.62 eV for processes with and without argon plasma treatment, respectively.

The experimental and modelling results of the investigation of photovoltaic properties of the InP nanowires grown on p-Si substrate are presented. It is shown that InP 2D-layer between nanowires on Si is II-type heterojanction. The resulting structure exhibits an open-circuit voltage (Voc) of 0,37 V, a short-circuit current density (Jsc) of 10.6 mA/cm2, a fill factor (FF) of 0.61 and efficiency of 2.4% at 1 sun. The InP/p-Si structure can be applied as prototype for solar cells or the photosensitive component in an integrated circuit based on silicon technology.

Nowadays, classical silicon solar cell achieved efficiencies close to theoretical limit and new design of silicon solar cell is required. Vertically aligned silicon solar cells seems to be a promising design of future silicon multijunction solar cells. These structures can be produce with dry etching technics. However, dry etching requires high quality mask. Mask can be archived with classical photolithography, but photolithography is multistep process and cannot be used in mass production of solar cells, because of the price. Nanosphere lithography is a powerful one-step method to produce periodic mask on silicon, but polystyrene spheres does not have enough selectivity in silicon etching process. Etching depth in silicon that can be archived in cryo process with 900 nm polystyrene sphere is about 3 μm. For deep silicon etching, we have to use hard mask. In this paper, we investigated nanosphere lithography on 500 nm thick PECVD deposed silicon oxide on silicon. Influence of isopropyl content in nanosphere solution were investigated. The effect of process conditions is discussed in the paper.

I-V characteristics of silicon wafer with Schottky contacts were investigated to find out influence of dry plasma etching on defects emerging in the structure. Wafer was divided into two pieces, one of them has affected to cryogenic etching using SF6/O2 (in ratio 5:1) and a pressure 5 mTor for two minutes. The second part of the wafer was used as a reference. It was founded, that for the same contact diameters, etched samples demonstrate higher slope of the I-V curve at the direct voltage. A similar effect was observed in the case of the existence of a defective near-surface region, where carrier recombination is enhanced, which results a significant increase in the direct current.

The effect of ITO magnetron deposition on carrier lifetime in silicon was demonstrated. The method of 2D photoluminescence decay time measurements revealed the lifetime degradation in silicon after magnetron deposition of thin ITO film which is used for top contact in modern solar cells.

The authors analyze the process of passing an article from the moment it is received by the editors to publication in the scientific journal Computer Optics, which has three main sections: 1) diffractive optics, optical information technologies; 2) image processing, pattern recognition; 3) numerical methods and data analysis. It is noted that due to the effective organization and precise regulation of the editorial and publishing process, the journal has gained credibility, being indexed in the international scientometric databases Scopus and Web of Science (ESCI).

The role of chemical pre-treatment on silicon surface quality and texturing uniformity was investigated. It was shown that for better uniformity of texturing the initial silicon surface of as-cut slurry sawed wafer should be treated to clean up from organic and metal contaminations followed by the organic solvent traces removing and saw damaged silicon layer etching. Additional measurements of photoluminescence decay confirmed high quality and uniformity of textured wafers passivated by a-Si:H.

Nickel oxide (NiO) thin films were deposited by an RF magnetron sputtering process in different atmospheres: one with a mixture of nitrogen and argon, and another with oxygen and argon. The structural, optical and electrical properties of NiO films were investigated using the spectroscopy, atomic-force microscopy and resistivity measurements. The dependencies of the film properties on atmosphere composition were studied. Optimization of the NiO thin film properties was carried out for further fabrication of effective hole transport layers for perovskite solar cells.

The work is devoted to development of the post-growth technology for direct study of the top subcell based on p-i-n junction with the GaPAs i-layer in the double-junction solar cell grown on silicon wafer. It allowed to more precisely measure quantum efficiency (QE) of the top subcell without additional IR-illumination for saturation of the bottom subcell in wafer. In result, measured QE of mesa-structure shows more reliable results without artefacts in spectra.

The influence of zinc oxide seed layers on morphological and electrophysical properties of ZnO nanorods was studied. Sublayers were obtained via spin-coating and magnetron sputtering methods. Nanorods were produces via low-temperature hydrothermal synthesis in the presence of anionic and zwitterionic surface-active substances. Characterization of the obtained coatings was carried out using scanning electron microscopy and atomic-force microscopy methods.

The structural and optical properties of Cu2O thin films grown by magnetron sputtering under elevated substrate temperatures were investigated. All samples show clear XRD patterns and photoconductivity response. An influence of Ar/O2 ratio and sputtering power on Cu2O structural properties was demonstrated. A ZnO/Cu2O-based solar cell was grown by magnetron sputtering at a temperature of 450 °C. An open circuit voltage of the solar cell is 80 mV.

Titanium nitride is a promising material due to its low resistivity, high hardness and chemical inertness. Titanium nitride (TiN) can be applied as an ohmic contact for n-GaN and rectifying contact for p-GaN and also as a part of perovskite solar cell. A technology of TiN low temperature reactive rf-magnetron sputtering has been developed. Electrical and optical properties of titanium nitride were studied as a function of the rf-power and gas mixture composition. Reflectance and transmittance spectra were measured. Cross-section and surface SEM image were obtained. 250 nm thin films of TiN with a resistivity of 23.6 μOm cm were obtained by rf-magnetron sputtering at low temperature.

International audience; Single-junction InGaNAs solar cells were grown by MBE with active layers based on a GaAsN/InAs superlattice. Dependence of defect formation on thickness of InGaNAs was explored in the study. Thickness increase from 900 nm to 1200 nm leads to defect formation with two activation energies of 0.20 eV and 0.50 eV but the value of quantum efficiency stays almost the same. Further thickness increase up to 1600 nm leads to the increase of defect concentration in the InGaNAs active layer. These defects are non-radiative recombination centres because a significant decrease of solar cell quantum efficiency was observed. The existence of a critical thickness for defect-free growth of InGaNAs based on GaAsN/InAs superlattice is proposed. 1. Introduction In 2015 multi-junction solar cells (MJ SC) based on III-V compounds with a record efficiency of 46% were fabricated [1]. Triple-junction SC based on the GaInP (1.85 eV) / GaAs (1.42 eV) / Ge (0.7 eV) system are used in industry for space applications where the key factors are efficiency and resistance to radiation. But its concentrator efficiency has almost reached the theoretical limit (46%) and now its value is more than 40% [2]. Fortunately, according to theoretical estimations an additional subcell with energy bandgap of 1 eV could increase the SC efficiency up to 52% [3]. However, such subcell should be lattice-matched to Ge and GaAs wafers. Ga1-xInxNyAs1-y with a small content of nitrogen is one of the most promising alloys to reach this goal. Such III-V-N alloys (GaPNAs, InGaNAs etc.) with nitrogen content less than 5% are called dilute nitrides. It has been shown that the small addition of nitrogen leads to large bowing parameters for the bandgap in quaternary Ga1-xInxNyAs1-y alloys: already few percent of nitrogen reduces the bandgap by hundreds of meV [4] and a value of 1 eV can be achieved. Furthermore, these layers can be epitaxially grown on Ge and GaAs wafers when y=0.35x. Various groups [3, 5-8] studied InGaNAs layers grown by epitaxy, but the quality is not sufficient for fabrication of high-efficiency solar cells. The low lifetime of charge carriers is the most crucial issue in dilute nitrides. The main reason is the high concentration of non-radiative recombination centers in active layers. In MOCVD (metal-organic chemical-vapor deposition) it comes from the background doping of carbon and hydrogen during the process. On the other hand, MBE (molecular-beam epitaxy) allows one to avoid these problems and enables to control the flow of nitrogen more precisely. However, a lower process

The temperature dependence of the electrical conductivity in Cu2O thin films grown by magnetron sputtering at room temperature under different rf-power was investigated. Calculated activation energy of the conductivity for copper oxide (I) films linearly increases with increase in sputtering power reflecting an increasing in concentration of gap states.

InGaN/GaN nanorod structure for light emission diode fabricated by the reactive plasma etching through the self-assembled Ni nano-cluster mask is presented. Fabricated array structure, presented in the form of truncated cones with average diameter height and period of nanorods is 250±50 nm, 430nm and 650±50 nm, respectively. The side angle of single structure about 80o. EL spectrum has maximum at 460 nm.

Modeling of photovoltaic properties of multi-junction solar cells integrated on a Si substrate with an array of GaN nanowires as a top emitter has been carried out. Very good antireflection properties of the structure are demonstrated theoretically: the calculated reflectance is lower than 3% for both GaN nanowires/Si and GaN nanowires on GaPN/Si cells. According to our simulations, basic GaN nanowires on Si cell with optimised parameters (doping and NWs morphology) provides energy conversion efficiency of 20%. The approach demonstrates high potential of the GaPN(As)-based multi-junction lattice matched with Si solar cells using an array of GaN nanowires as a top emitter.

Method of manufacturing substrates for self-catalyst/free-catalyst ordered growth of the nanowires has been developed. Experiments show the possibility of autocatalytic growth of ordered GaAs NWs on the substrates produced during the research.

In this letter we investigate photovoltaic properties of GaN nanowires (NWs) – Si substrate heterostructure obtained by molecular beam epitaxy (MBE). Antireflection properties of the NW array were studied theoretically and experimentally to show an order of magnitude enhancement in antireflection comparing to the pure Si surface (2.5% vs. 33.8%). In order to determine optimal morphology and doping levels of the structure with maximum possible efficiency we simulated it's properties using a finite difference method. The carried out simulation showed that a maximum efficiency should be 20%.

The photoluminescence (PL) of ZnO thin films grown by magnetron sputtering at room temperature has been observed. The PL spectra were measured using an instrument from Accent Optical Technologies with a solid state UV laser (λ = 266 nm) as the pumping source and at the temperature of 300 K. Samples grown at sputtering power of 100-200 W show a strong photoluminescence (PL) at wavelength of 377 nm and its intensity shows non-linear dependence with magnetron power. At values of sputtering power less then 100 W PL signal was not observed. A correlation between PL, XRD intensity and ZnO grain size was shown.

Indium Tin Oxide (ITO) thin films were grown at room temperature (RT) in oxygen-free environment by rf-magnetron sputtering on glass and Si(100)-substrates. The effects of argon pressure, sputtering power and film thickness on the electrical and optical properties of ITO films were investigated. For a 100 nm thick ITO films grown at RT in argon pressure 1.95·10−3 mbar and sputtering power of 50 W, the transmittance was near 90% at 480 nm and resistance was 5.4·10−4 Ohm·cm. It has been shown that the sputtering power plays an important role in electric properties of ITO films. SEM images of these samples show smooth surface with sharp substrate/ITO interface.