Tin dioxide (SnO 2 ) thin films, as a candidate for realizing next-generation electrical and optical devices, were grown on 2-inch diameter m -plane sapphire substrates by mist chemical vapour deposition at atmospheric pressure. The SnO 2 thin films were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffraction (XRD) in θ–2θ and φ scanning modes, and electron backscatter diffraction (EBSD). Although the SEM and AFM images showed a relatively rough surface morphology, it was found from the XRD and EBSD measurements that SnO 2 films were epitaxially grown on the substrates under optimised growth condition. Epitaxial growth of SnO 2 thin film growth at three typical areas on the substrate was confirmed by the EBSD measurements. It is likely that the single crystalline SnO 2 (001) thin film was formed across the 2-inch sapphire substrate. Finally, the second SnO 2 layer was overgrown on the above single crystalline SnO 2 thin film, which functioned as a buffer layer. This method which drastically improved surface roughness of the second SnO 2 layer.
The punctual character and random nature of the impurity positions in depletion regions lead to inhomogeneities that can significantly affect the potential intergranular barriers at polycrystalline semiconductors and, in general, of potential barriers at any semiconductor interface. This would reflect in Arrhenius plots for the electrical conductivity that become curved due to fluctuations of the intergranular barrier heights. Experimental results for polycrystalline tin oxide can be fitted assuming thermionic emission conduction at grain boundaries with a Gaussian distribution of barrier height fluctuations. However, resorting to a computational numerical model, we found that spatial fluctuations in barrier heights due to the discreteness of the donors and their statistical distribution at the depletion region differ from a Gaussian distribution. The type of obtained fluctuations, considering thermionic emission conduction, cannot explain the Arrhenius plots for the electrical conductivity found experimentally, especially at low temperature. Conversely, the tunneling contribution to conduction, without resorting to fluctuations, presents the observed trends.
Selective doping of a Zn impurity at the group III site in a Cu(In, Ga)Se 2 (CIGS) film was performed by the doping of Zn at the first stage of the three-stage method. The p -type CIGS:Zn film was obtained, which is in contrast to the n -type CIGS:Zn film obtained by the Zn impurity doping at the second and third-stages. Based on excitation intensity dependence of photoluminescence (PL) at low-temperature, the change in the acceptor level was observed. The enhancement of carrier concentration as a result of Zn-doping in the p -type CIGS:Zn film was observed. The CIGS:Zn solar cells exhibited η of 14.5% and V oc of 0.658 V, which are higher than that of the corresponding solar cells using the undoped CIGS films
To image the variation of surface potential in semiconductors, energy selective secondary electron detector, named fountain detector (FD), was developed. Two types of grids, planar and spherical, were designed and the superiority of latter was demonstrated. The p–n junction of 4H-SiC was observed using spherical FD and the image was much clear than that using conventional detector.
For the first time the samples, cut from the same wafer of crystals of float‐zone silicon, n−FZ−Si(P) and n−FZ−Si(Bi), were subjected to irradiation with 0.9‐MeV electrons and 15‐MeV protons at RT for studying them by low‐temperature positron annihilation lifetime spectroscopy. Measurements of Hall effect have been used for the materials characterization. The discussion is focused on the open vacancy volume (Vop) of the thermally stable group‐V‐impurity‐vacancy complexes comprising the phosphorus atoms; the bismuth‐related vacancy complexes are briefly considered. The data of positron probing of PV pairs (E‐centers), divacancies, and the thermally stable defects in the irradiated n−FZ−Si(P) materials are compared. Beyond a reliable detecting of the defect‐related positron annihilation lifetime in the course of isochronal annealing at ∼ 500 °C, the recovery of concentration of phosphorus‐related shallow donor states continues up to ∼650–700 °C. The open vacancy volumes Vop to be characterized by long positron lifetimes Δτ2 ∼271–289 ps in (gr.‐V‐atom)–Vop complexes are compared with theoretical data available for the vacancies, τ(V1), and divacancies, τ(V2). The extended semi‐vacancies, 2Vs‐ext, and relaxed vacancies, 2Vinw, are proposed as the open volume Vop in (gr.‐V‐atom)–Vop complexes. It is argued that at high annealing temperature the defect Ps–Vop–Ps is decomposed.
Nanogratings (NGs) on the surface of the top Si layer of a Si/SiO 2 / substrate device structure were prepared using laser interference lithography. Electron transport, photoluminescence, and Raman scattering were then studied on the plain Si and NG Si structures to see the effect of NG introduction. As a result of NG‐introduction and very likely G‐doping maintenance, all samples studied in this work displayed a 2 to 3 order of magnitude reduction in resistivity for NG Si. The Hall coefficient indicated that electrons are main charge carriers that is also expected for exactly G‐doping. Plain Si layer did not show any photoluminescence either for 532 nm (2.38 eV) or 325 nm (3.81 eV) laser excitation. A broad photoluminescence band, composed of a number of almost equidistant peaks was observed on NG Si layer between the photon energies 1.5 and 3.5 eV. Both Stocks and anti‐Stocks components for 522.65 cm −1 phonons at room temperature were observed in the Raman spectra of NG Si layer. Estimated from the ratio between the intensities of Stocks and anti‐Stocks components, the drop (if any) in phonon gas temperature below ambient (295 K) does not exceed 3 K.
Light emitting diodes with an active defect‐rich region produced by oxygen implantation and a subsequent multistep annealing of silicon wafers were investigated by means of transmission electron microscopy, SIMS, capacitance voltage, deep level transient spectroscopy, electroluminescence (EL), and cathodoluminescence (CL) techniques. The properties of two groups of n‐based samples with and without thermal pre‐treatment at 1000 °C for 15 min were compared regarding their defect structure, defects electrical activity, luminescent spectra as well as the impact of prolonged intense electron irradiation. The observed difference in the properties of such groups was explained by a difference in the density and oxygen content of oxygen‐related defects. A significant distinction between EL and CL spectra at low excitation levels was found and interpreted to be due to particular defect kinds in near‐surface and the deepest layers of the implanted region. The blue shift of EL spectra upon excitation increase reported previously is explained by the increase of penetration depth of the holes and specific depth distribution of the defects of different kinds.
The low‐temperature data of Hall‐effect measurements on p‐type InP doped with Cd, Zn, or Mg reported by Benzaquen et al., which exhibit the characteristic of nearest‐neighbor hoping conduction in an impurity band, have been analyzed within the two‐band model including the valence band and the impurity band. It is shown that the temperature‐dependent Hall‐effect data can be well fitted by assuming the hopping drift mobility expressed as μib = μib0(T0/T)3/2exp(−T0/T) and the hopping Hall factor expressed as Aib = (kBT/J)exp(−T0H/T) on the basis of a small‐polaron theory. Especially, Hall‐effect sign anomaly observed at low temperature in Mg‐doped InP is well reproduced by assuming a negative Hall effect for hoping conduction. The sign of the Hall coefficient for hoping conduction is discussed in connection with the overlap between the upper and the lower impurity Hubbard bands.
Coupled optical/electrical simulations have been performed on solar cells consisting in arrays of p-i-n radial nanowires based on crystalline p-type silicon (c-Si) core/hydrogenated amorphous silicon (a-Si:H) shell heterojunctions. Three-dimensional (3D) optical calculations based on rigorous coupled wave analysis (RCWA) are firstly performed and then coupled to a semiconductor device simulator that exploits the radial symmetry of the nanowires. By varying either the doping concentration of the c-Si core, or the work function of the Al-doped ZnO (AZO) back contact we can separate and originally highlight the contribution to the cells performance of the nanowires themselves (the radial cell) from the planar part in between the nanowires (the planar cell). We show that the short-circuit current density (J(sc)) only depends on the doping of the c-Si core indicating that it is mainly influenced by the radial cell. On the contrary the open-circuit voltage (V-oc) is strongly affected by the back contact conditions (AZO work function), revealing an important impact of the interspacing between the nanowires on the characteristics of the entire nanowire array. We explain this strong influence of the back contact conditions by the fact that it determines the band-bending in the a-Si:H absorber shell touching the AZO, i.e. in the planar part. Therefore, it directly impacts the potential drop (V-bi) in the same area. For low AZO work functions, the dark current density (J(dark)) is increased in the planar region, where V-bi is lower, which degrades the V-oc of the entire cell.
The low‐temperature data of Hall‐effect measurements on uncompensated P‐doped n ‐Si samples with different P concentrations N D reported in literature have been analyzed on the basis of an impurity‐Hubbard‐band model. In the model, the drift mobility and the Hall factor of nearest‐neighbor hopping in the top Hubbard band are assumed to be expressed as μ 2 = μ 20 ( E 2 / k B T ) 3/2 exp(− E 2 / k B T ) and A H 2 = ( k B T / J H 2 )exp( K H 2 E 2 / k B T ), respectively, according to the small‐polaron model, while those of variable‐range hopping in the bottom Hubbard band are assumed to be expressed as μ 3 = μ 30 ( T ES / T ) 1/3 exp[−( T ES / T ) 1/2 ] and A H 3 = A H 30 ( T ES / T ) 2/3 exp[(1− ) ( T ES / T ) 1/2 ] according to the Efros‐Shklovskii model. With the critical concentration of N c = 3.52 × 10 18 cm −3 for the metal‐insulator transition, the deduced values of T ES have been proved to obey the relation of T ES = T 00 (1− N D / N c ) p with p = 2.9 and T 00 = 11 000 K. In addition, the Coulomb gap has been proved to obey the relation of Δ CG = Δ CG 0 (1− N D / N c ) n with n = 2.5 and Δ CG 0 = 30 meV.
The cross‐plane thermal conductivity of WSe2 is investigated using reverse nonequilibrium molecular dynamics (RNEMD) and a recently developed Stillinger‐Weber potential. It is found that the cross‐plane thermal conductivity of WSe2 is strongly size dependent and saturates around 80 layers. Moreover, it is shown that even at 1000 K, ordered crystalline WSe2 does not reach the phonon glass‐like limit in the cross‐plane direction.
The binary compound SnS consists of elements that are non-toxic, inexpensive, and abundant in the Earth's crust. It is a p-type semiconductor with a band gap energy of 1.3 eV and an absorption coefficient of 10 4 cm −1 , and is therefore a potential candidate for use as a solar cell absorber material. In this study, SLG/Mo/SnS/CdS/ZnO:Al/Al and SLG/Mo/SnS/ZnO/ZnO:Al/Al SnS thin-film solar cells with different buffer layers were fabricated using a co-evaporation method. The dependence of the photovoltaic properties of the SnS thin-film solar cells with CdS or ZnO as the buffer layer was investigated. We demonstrate that the device with a ZnO buffer layer exhibited higher conversion efficiency and short-circuit current density compared to the device with a CdS buffer layer.
Impact of various irradiation (Ar and He ions, high energy electrons) on microhardness and indentation of monocrystalline Si 0,98 Ge 0,02 alloy is studied. Samples of Si and SiGe alloy are obtained by Czochralski (CZ) method in the [111] direction in the atmosphere of high purity Ar. High energy electron irradiation with fluence of ∼10 12 cm −2 is conducted at the Clinac 2100iX. Ar and He ion implantation is performed on modernized “VEZUVI-3M” plant. It is shown that for all types of irradiation the microhardness and indentation modulus versus load are characterized by reverse indentation size effect (ISE). With the increase of fluences of Ar and He ions, the maximum value of the effect increases. At high values of loading force impact on the indenter the mechanical characteristics slowly decrease. Impact of isochronous thermal annealing on mechanical properties of high energy electron irradiated samples is studied. Non-monotonic changes of microhardness and indentation modulus are revealed in the temperature range of 200–260 °C. It is proposed that such changes are caused by radiation defects transformation.
We report on the first demonstration of the atomic layer deposition (ALD) based three dimensional (3D) integrated ZnO thin film transistors (TFTs) on rigid substrates. Devices exhibit high on-off ratio (similar to 10(6)) and high effective mobility (similar to 11.8 cm(2)V(-1) s(-1)). It has also been demonstrated that the steps of fabrication result in readily stable electrical characteristics in TFTs, eliminating the need for post-production steps. These results mark the potential of our fabrication method for the semiconducting metal oxide-based vertical-integrated circuits requiring high packing density and high functionality.
In this work, we report the fabrication of indium tin oxide free organic solar cells and demonstrate the ability of niobium doped titanium dioxide (TNO) layers produced by sol-gel as feasible alternative electrode. The conductivity of the TNO was tailored by changing the layer thickness and the post-annealing conditions. Later, the crystal structure was revealed by X-ray diffraction. The post-annealing treatments were performed in a rapid thermal processing furnace under different gas atmospheres, temperatures and times. The conductivity of the samples was measured using a four-point set-up and the transparency through a UV-VIS spectrophotometer. A good sheet resistance of 181 Omega/square is achieved when the electrode was heated in an N-2/H-2 atmosphere mixture at 1000 degrees C for 10 min. TNO based organic solar cells were manufactured and their performance was evaluated by current-voltage measurements. A power conversion efficiency of 0.71% was attained. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cu (In, Ga) Se 2 (CIGS) solar cells were irradiated with 60, 100, and 250 keV electrons to reveal the characteristics of radiation induced defects. Electrons with less than 200 keV energy cannot generate any displacement defects in CIGS materials. In addition, a low amount of the electrons can improve the roll‐over behavior in current‐voltage characteristics of CIGS solar cells. However, the deterioration of the electrical performance in CIGS solar cells irradiated with a high amount of electrons was observed. The deterioration rate on the cells irradiated with lower‐energy electrons was higher than that induced by electrons with higher‐energy. The degradation curve of J SC based on the ionizing dose estimated from the ionizing energy loss model does not depend on the energy of electrons. Therefore, it implies that the electrons can degrade CIGS solar cells due to the ionization effect.
In this paper, we report on the phenomenon of nanostructure self‐formation on the surface of Cu(In,Ga)Se 2 (CIGS) thin films during inductively coupled argon plasma treatment with its duration varied from 10 to 120 s. The initial films were grown on glass substrates using the selenization technique. During the CIGS film surface treatment in the high‐density low‐pressure radio‐frequency inductively coupled argon plasma there took place a formation of arrays of uniform vertical nanostructures, which shape with increasing processing duration changed from nanocones to nanorods and back to nanocones. A model of the nanotip plasma‐assisted self‐formation associated with the implementation of micromasking and vapor–liquid–solid mechanisms involving metallic In‐Ga (In‐Ga‐Cu) liquid alloy droplets is proposed.
Investigations of stress distributions and material quality across a 75‐mm wafer consisting of device‐quality GaN integrated with a diamond substrate are presented. Stress in the GaN are mapped both over the full wafer and across the layer along the growth direction. Ultraviolet (UV) and visible micro‐Raman and UV photoluminescence (PL) spectroscopy from both sides of the wafer reveal an unexpected gradient between the tensile stress at the free GaN surface (∼0.86–0.90 GPa) and the GaN/diamond interface (∼0.05–0.23 GPa). The stresses obtained exhibit good cross‐wafer uniformity. The stress gradient is understood through variations in the material along the growth direction of the layers due to the presence of threading dislocations which result in local stress relaxation. Transmission electron microscopy confirms the presence of extended defects to be greater near the interface with diamond, corresponding to the initial GaN growth regime, and diminished toward the surface where transistors would be fabricated in a full device technology. Finite element (FE) simulations describing the observed stress dependence along with TEM imaging of the GaN cross‐section support the relaxation interpretation.
