Phase composition of CuInSe2 in different annealing process

CuInSe₂ was synthesized by a low cost, non-vacuum hydrothermal solution method using copper chloride, indium chloride and Se powder as raw materials. The reaction schemes of CuInSe₂ in different annealing processes were investigated by in-situ X-ray diffraction measurements. Its phase composition, crystal structure and morphology properties of CuInSe₂ were studied. The results show that CuInSe₂ has chalcopyrite crystal structure and it remains stable below the temperature of 773 K, but it decomposes to CuSe and InSe at temperature above 773 K in vacuum annealing. While in oxygen annealing, CuInSe₂ is oxidized to CuO, In₂O₃ and SeO₂ at the temperature of 523 K. Therefore, the temperature of selenization or annealing must be lower than 773 K in order to reduce the amount of CuSe and InSe in large production scale. The results were demonstrated by energy dispersive spectrometer as well. The process of its reaction mechanism was discussed based on the experimental data.     

Majority and minority carrier traps in monocrystalline CulnSe2

Electron and hole traps in Bridgman-grown monocrystalline CuInSe₂ were investigated by carrying out deep level transient spectroscopy measurements on homojunctions, Al-CuInSe₂ (p-type), and Au-CuInSe₂ (n-type) Schottky junctions. Three hole trap levels and two electron trap levels were observed on these devices. Effects of oxygen and etching on the electron trap level at 182 ±15 meV from the conduction band edge were specifically studied. It was found that the election trap densities in the homojunctions prepared using the CuInSe₂ samples treated in NH₂NH₂ solution, which absorbes oxygen atoms in the samples, were larger than the electron trap densities in the homojunctions prepared using untreated samples. Moreover, the electron trap densities in the homojunctions after prolonged heat treatment in O₂ were less than that without prolonged heat treatment. The results thus suggested that oxygen atoms in CuInSe₂ can reduce the electron trap density of p-type CuInSe₂. The effects of chemical etching on these electron traps were also studied. The excess indium atoms in the CuInSe₂ were considered to affect the electron traps.     

Investigation of post-thermal annealing on material properties of Cu-In-Zn-Se thin films

The Cu-In-Zn-Se thin film was synthesized by changing the contribution of In in chalcopyrite CuInSe2 with Zn.The XRD spectra of the films showed the characteristic diffraction peaks in a good agreement with the quaternary Cu-In-Zn-Se compound.They were in the polycrystalline nature without any post-thermal process,and the main orientation was found to be in the (112) direction with tetragonal crystalline structure.With increasing annealing temperature,the peak intensities in preferred orientation became more pronounced and grain sizes were in increasing behavior from 6.0 to 25.0 nm.The samples had almost the same atomic composition of Cu0.5In0.5ZnSe2.However,EDS results of the deposited films indicated that there was Se re-evaporation and/or segregation with the annealing in the structure of the film.According to the optical analysis,the transmittance values of the films increased with the annealing temperature.The absorption coefficient of the films was calculated as around 105 cm-1 in the visible region.Moreover,optical band gap values were found to be changing in between 2.12 and 2.28 eV depending on annealing temperature.The temperature-dependent dark-and photo-conductivity measurements were carried out to investigate the electrical characteristics of the films.     

Influence of N2 and O2 annealing treatment on the optical bandgap of polycrystalline Ga2O3:Cu films

Cu-doped Ga₂O₃ thin films were deposited by electron beam evaporation with subsequent annealing at 1000 °C in N₂ and O₂ for 1 h. The influence of the annealing atmosphere on the crystal structure, surface morphology and optical properties of Ga₂O₃:Cu films was investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and transmittance and photoluminescence (PL) spectroscopy. The optical bandgap deduced from the absorption spectrum was greater for the O₂ annealed than for N₂ annealed samples. In both cases the bandgap was wider than for bulk β-Ga₂O₃. The grain size and surface roughness were sensitive to the annealing atmosphere. Results confirmed that the annealed samples were polycrystalline β-Ga₂O₃ with some amorphous phase. We hypothesize that annealing in oxygen led to recrystallization of the Ga₂O₃:Cu film. Annealing treatment improved the crystal quality of Ga₂O₃:Cu films and the PL intensity of the samples increased.     

Synthesis of CuInSe2 monodisperse nanoparticles and the nanorings shape evolution via a green solution reaction route

High-quality CuInSe₂ nanoparticles were successfully synthesized through a green, simple, low-cost route using environmentally friendly N-oleoylmorpholine as a new solvent of Se powder and oleylamine as capping ligand. The as-synthesized nanoparticles were characterized by X-ray diffraction, TEM, HRTEM, and energy dispersive X-ray spectroscopy. The experimental results revealed that the as-prepared CuInSe₂ nanoparticles with chalcopyrite tetragonal structure have an average size about 8 nm. The facile and green synthesis strategy was also used to synthesize hexagonal shaped CuInSe₂ nanorings by altering the synthesis parameters. Possible shape evolution and crystals growth mechanisms have been suggested for the formation of spherical shaped CuInSe₂ nanoparticles and hexagonal shaped CuInSe₂ nanorings, respectively.     

Lattice vibrations of sequentially evaporated CuInSe2 by Raman microspectrometry

Copper Indium Diselenide (CuInSe₂) thin films of different atomic concentrations were prepared using sequential elemental evaporation. Raman analysis has been carried out to determine the structure and the different vibration modes of CuInSe₂ thin film. The analysis reveals that CuInSe₂ films possess chalcopyrite structure with preferential orientation along (112) plane. Vibration modes such as A₁, B₁, B₂ and E were observed in the Raman spectra. It has been observed that the intensity of the A₁ mode is directly proportional to the crystallinity. Also it has been noted that, the intensity of all the vibration modes are varied with respect to the compositions. The Raman spectra of the CuInSe₂ films were interpreted and incorporated with XRD and EDAX.     

Photoluminescence Studies of CuInS2-CuInSe2 Alloy Crystals

Photoluminescence spectra are presented for single crystals of CuInS₂, CuInSe₂ and CuInS_2ySe_2-2y alloys. The PL spectrum of stoichiometric CuInSe₂ is dominated by free exciton emission of 9 meV FWHM at 1.03 eV, but structure at 090, 0.94 and 0.97 eV is observed due to transitions involving residual native defect states. For pure CuInS₂ broad deep luminescence bands are obtained that involve several deep native defect states, e.g. donors at 45 and 160 meV below the CBE and acceptors at 85 meV above the VBE. These defects persist in S-rich CuInS₂/CuInSe₂ alloys, but excitonic emission is observed, in addition to the deep luminescence. Surprisingly CuInS_2ySe_2-2y crystals at y ≳ l are totally dominated by free exciton emission. This result shows that an increase of at least 20% over the bandgap of CuInSe₂ and excellent crystal quality can be achieved by partial substitution of Se by S.     

Optical spectroscopy of excitonic states in CuInSe2

Optical properties of structurally perfect CuInSe₂ single crystals were studied in the temperature range of 4.2–300 K with the use of photoluminescence, optical absorption, optical reflection, and wavelength-modulated optical reflection (WMOR). The intense lines of free excitons A (～1.0414 eV) and B (～1.0449 eV) with a half-width of ～0.7 meV at 4.2 K are found to be related to two extrema of valence band split by a crystal field. The excitons emission line C (～1.2779 eV) in WMOR spectra are related to a lower valence band split-off by spin-orbit interaction. Within the context of the quasi-cubic Hopfield model, the parameters of valence band splitting Δ_CF=5.2 meV and Δ_SO=234.7 meV defined by the crystal and spin-orbit interaction, respectively, are calculated. In the region of the fundamental absorption edge, the lines of bound excitons are found with a half-width ～0.3 meV that is indicative of a high quality of grown CuInSe₂ crystals.     

Synthesis and crystal growth of copper indium diselenide from the melt

A technique for in situ synthesis and crystal growth of CuInSe₂ from the melt in an open crucible is described. Cylindrical ingots 55 mm in diameter and weighing up to 200 g exhibited single-crystal grains up to 90 mm₂ in area after slowly cooling in the synthesis crucible. A B₂O₃ liquid encapsulant was used in conjunction with argon gas at 50 to 70 atmospheres pressure to suppress vaporization of the constituents. Liquid encapsulated Czochralski growth was also demonstrated. Electrical and compositional properties of the crystals are presented.     

RTA effects on the formation process of embedded luminescent Si nanocrystals in SiO2

It is well known that Si ion implantation into SiO₂ and subsequent high temperature anneals induce the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of rapid thermal annealing to enhance the photoluminescence as well as those to induce low temperature formation of luminescent Si nanocrystals have been investigated. Ion implantation was used to synthesize specimens of SiO₂ containing supersaturated Si with different concentrations. The implanted samples were rapidly annealed only for a few minutes. After that, in some cases before that, the samples were annealed for a few hours using a conventional tube furnace to induce Si precipitation. Photoluminescence spectra were measured at various stages of anneal processes. The luminescence intensity is strongly enhanced with a rapid thermal annealing prior to a conventional furnace anneal. The luminescence intensity, however, decreases when rapid thermal annealing follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Enhancement is found to be typical for low dose samples. Moreover, the visible photoluminescence is found to be observed even after conventional furnace anneal below 1000 °C, only for rapidly thermal annealed samples. Based on our experimental results, we discuss the mechanism for the enhancement of the photoluminescence, together with the mechanism for the initial formation process of Si nanocrystals.     

The annealing of Cd1−xZnxTe in CdZn vapors

As-grown CdZnTe usually contains defects, such as twins, subgrain boundaries, dislocations, and Te precipitates. It is always important to anneal CdZnTe slices in Cd vapor to eliminate these defects, especially Te precipitates. The exchange of Zn atoms between the slices and the vapor plays an important role during the annealing process. In this paper, the effects of Zn partial pressure on the properties of the annealed slices are studied carefully by measuring the concentration profiles, the infrared (IR) transmission spectra, and the x-ray rocking curves. It was found that a surface layer with different compositions and possibly different structure from the bulk crystal formed during the annealing of CdZnTe samples in the saturated Zn vapor. The accumulation of excess Te in the surface layer helps to increase the IR permeability of the bulk crystal greatly. To improve the crystallization quality, a lower Zn-pressure annealing should be used following the high Zn-pressure annealing. The diffusion of Zn in the bulk crystal has also been analyzed at the temperatures of 700°C and 500°C. Calculations determined that D_Zn (700°C)=4.02 × 10⁻¹² cm²s⁻¹ and D_Zn (500°C)=1.22 × 10⁻¹³ cm²s⁻¹.     

Fe and Ti implants in In0.52Al0.48As

Single (200 keV) and multiple energy Fe implants in n-type and Ti implants in p-type material were performed in In_0.52Al_0.48As at both room temperature and 200°C. For the Fe implants, the secondary ion mass spectrometry profiles showed a severe out-diffusion for all rapid thermal annealing schemes used, independent of the implantation temperature. The Fe implant peaks observed after annealing, at 0.8Rp, Rp+ΔRp and 2Rp (where Rp and ΔRp are range and straggle, respectively) depth locations in other In-based compounds like InP and InGaAs were not observed here. On the contrary, Ti implants showed only a slight in- and out-diffusion for both room temperature and 200°C implants as in the case of InP and InGaAs. The Rutherford backscattering measurements on the annealed samples implanted at 200°C showed a crystal quality similar to that of the virgin material. The resistivity of all the samples after annealing was higher than 10⁶ Ω-cm.     

Low Resistance Contacts to p-CulnSe2 and p-CdTe Crystals

Room temperature formation of ohmic contacts by electroplating gold on chemically treated surfaces of p-CuInSe₂ and p-CdTe single crystals is reported. The effect of Br₂/methanol and KOH+KCN+H₂O treatments prior to plating was analyzed in the case of CuInSe₂. It is shown that the former treatment yields better ohmic contacts, with lower contact resistance, than the latter. While annealing these contacts made them highly non-ohmic, the method gives reasonably ohmic contacts on surfaces, that were purposely oxidized prior to contact preparation. In the case of p-CdTe stable, low resistance ohmic contacts were obtained at room temperature by electrochemical diffusion of Hg from solution, prior to gold plating. The treatment forms a highly degenerated p^+- HgCdTe layer. The contacts, which have a very low contact to bulk resistivity ratio, were further improved by vacuum annealing.     

Study of the fluctuation conductivity in YBCO thin film with low transition temperatures

An insulating YBa₂Cu₃O_7-δ (YBCO) thin film was grown by inverted cylindrical magnetron (ICM) sputtering and under nitrogen cooling instead of oxygen in situ annealing. This insulating film went through different annealing processes in flowing oxygen, each time with increasing annealing temperature. The resistivity as a function of temperature was measured after each annealing. The fluctuation conductivity σ^′(T) is determined from the resistivity data and an analysis of the possible mechanisms for scattering of the fluctuating pairs is presented in this work. The crystal structure of the film through these different steps is also reported.     

Elevated-Temperature Annealing Effects on AlGaN/GaN Heterostructures

The effect of high-temperature annealing of undoped AlGaN/GaN heterostructures on different substrates was systematically studied between 1100°C and 1230°C. An AlN spacer layer was found to add stability to structures on sapphire substrates. AlGaN/GaN heterostructures on SiC substrates demonstrated excellent robustness for the temperature range studied, maintaining their mobility, sheet resistance, and sheet concentration values, even after annealing. A silicon nitride, SiN _x , capping layer was found to assist in minimizing surface roughness during annealing and maintaining the electrical characteristics of the heterostructures. AlGaN/GaN heterostructures on SiC substrates showed a 20% decrease in mobility for uncapped samples compared with SiN _x -capped samples.     

Photosensitivity of thin-film structures based on (CuInSe2)x(2ZnSe)1−x solid solutions

Polycrystalline (CuInSe₂)_x(2ZnSe)_1−x films (x=0.6–1.0) with p-type conductivity and a thickness of 0.5–0.9 μm were obtained by pulsed laser evaporation. It is shown that a chalcopyrite-sphalerite transition occurs in the above system for x=0.7. The obtained films were used to fabricate the photosensitive structure of the In/p-(CuInSe₂)_x(2ZnSe)_1−x and InSe(GaSe)/(CuInSe₂)_x(2ZnSe)_1−x types. Spectral dependences of photovoltaic-conversion quantum efficiency were studied, and the photosensitivity of the structures in relation to the type of energy barrier and the composition was analyzed. It is concluded that the structures under consideration can be used as broadband photovoltaic converters. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 5, 2000, pp. 576–581. Original Russian Text Copyright ? 2000 by V. Rud’, Yu. Rud’, Bekimbetov, Gremenok, Bodnar’, Rusak.     

Effects of Annealing on Structural and Electrical Properties of CuInSe<Subscript>2</Subscript> Thin Films Prepared by Hybrid Sputtering/Evaporation Processes

CuInSe₂ (CIS)-based absorber layers have been fabricated on soda-lime glass substrates by co-sputtering Cu/In and evaporating Se. The effects of annealing in the Se environment on the structural and electrical properties of the CIS layers were studied. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to investigate the surface morphology and crystal structures of the CIS films, respectively. XRD patterns showed that the CIS films had a single chalcopyrite structure with preferential (112) orientation. The asymmetry of the Se 3d x-ray photoelectron spectroscopy (XPS) peak for the as-grown films and a separated peak for the annealed films are indications of the existence of two different valence states in the two kinds of CIS films. The electrical properties of the CIS films were studied by the four-probe method and Hall measurements. The results showed that the as-grown films had lower carrier mobility than the annealed films. However, the as-grown films had higher carrier concentration.     

Phase transition of Cu2O to CuO nanocrystals by selective laser heating

In this paper, we reported the preparation of CuO nanocrystals by microwave irradiation method. With the aid of suitable surfactants, CuO nanoparticles of uniform size and shape were successfully prepared. The as-prepared nano-products were characterized by different techniques such as Xray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM), which all confirmed the good quality of the product. However, Raman spectra showed some peaks, which were attributed to impurity phases such as Cu₂O or Cu(OH)₂. Post annealing the samples by laser is a good method to convert these phases into pure CuO. Phase transition was observed in situ by Raman spectroscopy. After laser treatment process, Raman spectra of the samples showed that the nano-product is single phase and the crystal quality of CuO nanocrystal was improved clearly.     

Comparison of p–n junction formed by BF2 and B implantation in silicon microstrip detector with low and high thermal budget: impact of fluorine on electrical characteristics

The influence of crystal damage on the electrical properties and the doping profile of the implanted p⁺–n junction has been studied at different annealing temperatures using process simulator TMA-SUPREM4. This was done by carrying out two different implantations; one with implantation dose of 10¹⁵ BF₂⁺ ions/cm² at an energy of 80 keV and other with 10¹⁵ B⁺ ions/cm² at 17.93 keV. Substrate orientation 1 1 1 of phosphorus-doped n-type Si wafers of resistivity 4 kΩ cm and tilt 7° was used, and isochronally annealing was performed in N₂ ambient for 180 min in temperature range between 400°C and 1350°C. The diode properties were analysed in terms of junction depth, sheet resistance. It has been found that for low thermal budget annealing, boron diffusion depth is insensitive to the variation in annealing temperature for BF₂⁺-implanted devices, whereas, boron diffusion depth increases continuously for B⁺-implanted devices. In BF₂⁺-implanted devices, fluorine diffusion improves the breakdown voltage of the silicon microstrip detector for annealing temperature upto 900°C.For high thermal budget annealing, it has been shown that the electrical characteristics of BF₂⁺-implanted devices is similar to that obtained in B⁺-implanted devices.     

Optimization of Annealing Process for Improved InGaN Solar Cell Performance

We report enhanced performance of InGaN solar cells grown by metalorganic chemical vapor deposition through optimization of the annealing of the epitaxial wafer before device fabrication. We varied the annealing environment gas mixtures as well as temperatures to obtain the optimized annealing condition. It was found that the major improvement of the nitride solar cell efficiency after annealing is in the increase of the V _oc. In addition, annealing at the reasonably moderate temperature of 550°C in O₂ environment results in the highest-efficiency InGaN solar cell devices compared with devices annealed at different temperatures and in different gas environments.