Hot Probe Technique Research Articles

Hot probe technique for thin films Seebeck coefficient measurement

A new experimental method using a 50 μm diameter hand fabricated hot probe of Pt90/10Rh alloy is proposed as a tool to measure the Seebeck coefficient of thin films deposited onto electrically insulated substrates. A thermal model for heat transfer inside the probe and to the sample was developed to simulate the corresponding temperature distributions. Simulations showed that the ratio of the temperature rise in the contact point to the average temperature of the probe evolves basically independent on electrical current and film-substrate properties. Moreover, the values of contact radius and thermal contact resistance should not be necessary known, but only the pairs which are best fitting the probe thermal resistance in contact with the film-substrate. This brings a great simplification in respect with certain AFM based hot probe methods for which is necessary to determine these two parameters by calibration of the two substrates with known thermal conductivity. The values can be further used to evaluate the Seebeck coefficient of the sample with a macroscopic probe, within 1 % precision. By variance to the classical measuring methods, which resort to a heater-heat sink ensemble instrumented with thermocouples, heated metallic rods with built-in thermocouples or microfabricated structures, the proposed method is fast, reliable and of higher spatial resolution. The method was validated by measuring the Seebeck coefficient on CdS, Bi and Cr thin films reference samples, respectively.

Growth of Cu2ZnSnS4 Thin Film Solar Cells Using Chemical Synthesis

Objectives: Cu2ZnSnS4 thin film solar cell is fabricated by using the chemical spray pyrolysis method. Method: CZTS thin films were successfully deposited by employing the eco-friendly and cost-effective chemical spray pyrolysis method. X-ray diffraction (XRD) and Raman spectroscopy are used to investigate the structural properties of the prepared samples. The surface morphology of the deposited films is studied using a scanning electron microscope. An energy dispersive spectrometer is used to know the chemical compositions of the deposited films. A double beam spectrophotometer is used to study the optical characteristics of these films. The hot probe technique is used to confirm the nature of the conductivity of the deposited films. Findings: The XRD spectra of the thin films reveal the polycrystalline nature with the kesterite structure of the thin films. The optical band gap is found to be 1.52 eV and the absorption coefficient value of these films is found to be  104 cm-1. The nature of conductivity is identified to be p-type. Finally, Cu2ZnSnS4 thin film solar cell is fabricated with the substrate configuration glass/Mo/CZTS/CdS/Ag which exhibited an open circuit voltage and short circuit current of 156 mV and 1.82 mA/cm2 respectively. Novelty: The growth of Cu2ZnSnS4 thin films is studied by varying the distance between the spray nozzle and glass substrate from 25 to 35 cm in steps of 5 cm and maintaining all other parameters as constant. Finally, the Cu2ZnSnS4 thin film solar cell is prepared in a substrate as well as a superstrate configuration. Keywords: Thin films; Absorber layers; Spray technique; Solar cell; Cu2ZnSnS4

Synthesis and Characterization of High-Efficiency Halide Perovskite Nanomaterials for Light-Absorbing Applications.

Inorganic perovskite materials are possible candidates for conversion of solar energy to electrical energy due to their high absorption coefficient. Perovskite solar cells (PSCs) introduced a new type of device structure that has attention due to better efficiencies and interest in PSCs that has been increasing in recent years. Halide perovskite materials such as CsPbIBr2 show remarkable optical and structural performance with their better physical properties. Perovskite solar cells are a possible candidate to replace conventional silicon solar panels. In the present study, CsPbIBr2 perovskite materials' thin films were prepared for light-absorbing application. Five thin films were deposited on the glass substrates by subsequent spin-coating of CsI and PbBr2 solutions, subsequently annealed at different temperature values (as-deposited, 100, 150, 200 and 250 °C) to get CsPbIBr2 thin films with a better crystal structure. Structural characterizations were made by using X-ray diffraction. CsPbIBr2 thin films were found to be polycrystalline in nature. With increasing annealing temperature, the crystallinity was improved, and the crystalline size was increased. Optical properties were studied by using transmission data, and by increasing annealing temperature, a small variation in optical band gap energy was observed in the range of 1.70-1.83 eV. The conductivity of CsPbIBr2 thin films was determined by a hot probe technique and was found to have little fluctuating response toward p-type conductivity, which may be due to intrinsic defects or presence of CsI phase, but a stable intrinsic nature was observed. The obtained physical properties of CsPbIBr2 thin films suggest them as a suitable candidate as a light-harvesting layer. These thin films could be an especially good partner with Si or other lower band gap energy materials in tandem solar cells (TSC). CsPbIBr2 material will harvest light having energy of ∼1.7 eV or higher, while a lower energy part of the solar spectrum will be absorbed in the partner part of the TSC.

Structural, optoelectrical analysis, and optical properties of indium-doped Al2O3 thin films synthesized by spray pyrolysis

In this study, thin films of aluminium oxide (Al2O3) and indium-doped Al2O3 with doping ratios of 0%, 5%, 7.5%, and 10% were prepared by spray pyrolysis technique at 350 °C. The phase compositions of the Al2O3 and indium-doped Al2O3 films were determined using x-ray diffraction analysis. The structural parameters of the studied films, such as the strain function (ε), crystallite size (D), and dislocation density (δ) were evaluated. The transmittance and reflectance spectra of the prepared films were analysed to evaluate the optical and optoelectrical parameters, including the optical free-carrier concentration (Nopt), optical conductivity (σopt), absorption coefficient (α), optical dielectric constants (ε1 and ε2), and energy gap (Eg). The optical results indicate that the investigated films exhibited direct optical transitions. The nonlinear optical constants of the sprayed films were determined using the Miller equations. The hot-probe technique was used to determine the majority of carriers in the investigated films. Electrons were the majority carriers in the indium-doped Al2O3 films. The high optical transparency and the tendency of being an n-type semiconductor make indium-doped Al2O3 thin films suitable for producing a novel window layer for thin-film solar cells.

New salicylaldehyde azine esters: Structural, aggregation induced fluorescence, electrochemical and theoretical studies

The establishment of high-tech products relying on organic optoelectronics is focused towards latest strategies for improving the processability and performance. In the present study, two esters of salicylaldehyde azine SAE-F and SAE-NF were synthesized and their structural characterization were performed using FT-IR, 1H and 13C NMR, UV–visible spectroscopy, mass spectrometry and single crystal-XRD technique. The bathochromic shift observed in luminescence measurements from solution to aggregate/solid state, solvent based fluorescence studies, SEM and DLS measurements confirmed the fluorescence emission from the SAE-F aggregates. The DSC data indicated the phase transitions, and the TGA measurements confirmed the thermal stability of SAE-F to withstand temperatures up to 225 °C. The morphological characterization revealed formation of homogeneous pin-hole free uniform films of SAEF. Cyclic voltammetry was used to estimate the HOMO and LUMO energy levels which were found to be −5.46 eV and −3.05 eV respectively with a band gap of 2.41 eV. The p-type semi-conductivity of SAE-F was established using hot probe technique. The dielectric measurements were carried out to measure dielectric constant and ac conductivity at different frequency ranges. The electronic data obtained based on Density Functional Theory calculations were in conformity with the experimental results. Successful fabrication of a diode and the recorded current-voltage characteristics clearly advocated SAE-F to be an excellent candidate for electro-optical devices.

Pure SnSe, In and Sb doped SnSe single crystals – Growth, structural, surface morphology and optical bandgap study

The pure SnSe is a potential material for technological applications due to its favourable electrical, optical, thermal, etc. properties. To make SnSe more suitable for varied applications needs tailoring of properties. In this work, an effort has been made to modify the properties of SnSe by doping with group III (indium) and V (antimony) elements of the periodic table. The pure SnSe, indium (In) and antimony (Sb) doped SnSe single crystals are grown by direct vapour transport technique. Two concentrations of 5% and 10% are employed for doping. The chemical compositions of the grown crystals are confirmed by X-ray energy dispersive and electron probe micro analysis techniques. The X-ray diffraction analysis substantiated the orthorhombic SnSe phase of all grown single crystals. The surface morphology study of the as-grown single crystal surfaces showed the crystal growth to have occurred by layer growth mechanism. The hot point probe technique analysis showed all crystals to be p-type semiconducting in nature. The optical absorption spectra of all as-grown samples showed sharp absorption near 846 nm wavelength. The modification of the optical bandgaps by incorporation of In3+ and Sb3+ ions within SnSe is studied. The obtained results are discussed in details.

Hot probe measurements on neutron irradiated, isotope enriched ZnO nanorods

We report on neutron transmutation doping (NTD) of isotopically (64Zn) enriched ZnO nanorods to produce material with holes as the majority mobile carrier. Nanorods of ZnO enriched with 64Zn were synthesised and the abundance of 64Zn in these samples is ∼ 71%, compared to the natural abundance of ∼ 49 %. The enriched material was irradiated with thermal neutrons which converts some 64Zn to 65Zn. The 65Zn decays to 65Cu with a half-life of 244 days and the Cu can act as an acceptor dopant. After 690 days, a hot probe technique was used to determine the majority charge carriers in non-irradiated and neutron irradiated nanorod samples. Non-irradiated samples were measured to be to have electrons as the majority mobile carrier and the irradiated samples were measured to have holes as the majority mobile carrier.

Fluorescent aromatic symmetrical azines: Synthesis and appraisal of their photophysical and electrochemical properties

There is an immense push for the development of innovative, convenient and high-performance organic electronics. In this study, we present the synthesis of two azines and the exploration of their photophysical, surface morphological, electrochemical and electroluminescence properties for application in organic electronic devices. A diphenol substituted azine, 2,2'-[hydrazine-1,2-diylidenedimethylylidene]diphenol was synthesized by refluxing ethanolic solution of hydrazine hydrate with ethyl 2-oxo-2H-chromene-3-carboxylate. It was then converted into an azine spacer incorporated new tetrazo dye, bis–[2-(iminomethyl)-4-(phenyl diazenyl)phenol] by coupling with benzenediazonium chloride. The structures of the symmetrical azines were confirmed by FT-IR, NMR and mass spectroscopic techniques. Both the azines in thin film states exhibited deep yellow photoluminescence on UV excitation at 570 nm. The HOMO and LUMO energy levels assessed by cyclic voltammetry measurements, conformed to the electrochemical band gap energies of 4.41–4.55 eV. The p-type conductivity of the azines were confirmed by hot probe technique. The transport properties of both the azines were investigated by fabricating a bi-layer device. The successful construction of diodes with azines suggest that they could play a significant role as organic materials in the construction of electronic devices.

Phosphorus doping of diamond-like carbon films by radio frequency CVD-cum-evaporation technique

Diamond-like carbon (DLC) films have been deposited by cracking methane gas in radio frequency plasma. Phosphorus was incorporated in DLC films by simultaneously evaporating phosphorus during the synthesis of DLC with methane gas by using capacitatively coupled plasma chemical vapour deposition (CVD) technique. The films were characterized by FESEM, XRD, XPS and Raman studies. The band gap of the pristine DLC films was found to be ~2.61eV and it decreased from 2.61eV to 2.31eV with increased incorporation of P in the DLC films. Raman studies indicated the presence of two broad peaks located at ~1360–1396cm−1 (D-line) and ~1542–1548cm−1 (G-line). The peak positions of the D-lines shifted in towards lower wave number with increased incorporation of phosphorus in them. This indicated that the DLC films became sp2 rich with increased incorporation of phosphorus. Electrical resistivity measurements have been carried out. The films were n-type as indicated by hot-probe technique. The values of electrical resistivity of the undoped and doped DLC films were 2.0×102Ω-cm and 0.7×102Ω-cm, respectively. Value of carrier concentrations (Nd) obtained were 2.5×1015cm−3 and 2.2×1016cm−3 for undoped and phosphorus doped DLC film with 3.4 at.% P in DLC, respectively.

Structural and optical properties of the ZnS/GaSe heterojunctions

In the current work, the ZnS/GaSe thin film heterojunction interfaces are experimentally designed and characterized by means of x-ray diffraction, scanning electron microscopy, energy dispersion spectroscopy and optical spectroscopy techniques. The heterojunction is observed to exhibit physical nature of formation with an induced crystallization of GaSe by the ZnS substrate. For this heterojunction, the hot probe technique suggested the formation of a p-ZnS/n-GaSe interface. In addition, the designed energy band diagram of the heterojunction which was actualized with the help of the optical spectrophotometric data analysis revealed a respective conduction and valence band offsets of 0.67 and 0.73 eV. On the other hand, the dielectric dispersion analysis and modeling which was studied in the frequency range of 270–1000 THz, have shown that the interfacing of the ZnS with GaSe strongly affects the properties of ZnS as it reduces the number of free carriers, shifts down the plasmon frequency, increases the charge carrier scattering time and results in higher values of drift mobility at Terahertz frequencies.

Optical and electrical characterization of BixSe1−x thin films

Abstract Bulk samples of the BixSe1-x system with (x = 0, 5, and 10) were prepared using conventional melt quenching technique. Thin films were then deposited by thermal evaporation technique under high vacuum conditions from the prepared bulk samples. Effect of Bi substitution on surface morphology, electrical and optical properties of BixSe1-x thin films was studied. X-ray diffraction studies showed the formation of nanocrystalline clusters at Bi concentration x = 10. Formation of these clusters resulted in a rough surface which was confirmed by AFM measurements. The film surface was smooth, with RMS roughness of 0.0124 nm for Bi5Se95. For Bi10Se90, the RMS roughness increased to 3.93 nm indicating the formation of Bi2Se3 clusters. A simple hot probe technique showed a transition from p-type to n-type due to Bi incorporation. Charge transport mechanisms were investigated by temperature dependent DC electrical conductivity measurements in the temperature range of 209 K to 313 K. Electrical activation energy (ΔE) of the films with different Bi concentrations was found to exhibit a notable change at the p to n transition. At low temperature, the conduction was in reasonable agreement with Mott’s condition of variable range hopping. Mott parameters and the density of localized states near Fermi level were evaluated and correlated with the structural changes resulting from Bi addition. In addition, a red shift of the optical absorption edge of the films under study caused by Bi-Se substitution was observed. Slight changes in the optical parameters were observed with the γ-irradiation. Addition of Bi atoms could be used to tailor the structural, electrical and optical properties of chalcogenide materials such as junctionless photovoltaic devices.

Effect of substrate temperature on the structural and electrical properties of spray deposited lead sulfide thin films

Lead sulfide (PbS) thin films were prepared by chemical spray pyrolysis method using lead acetate and thiourea as precursors of Pb+2 and S-2 ions. X-ray diffraction (XRD) technique, scanning electron microscope (SEM) and EDAX analysis were used for structural, morphological and compositional characterization. XRD analysis shows that the films are cubic in nature with a preferred orientation along (2 0 0). EDAX analysis shows that films deposited at 150°C are sulfur rich. An increase in the substrate temperature results in a decrease in the sulfur content of the prepared film. It has been observed that thin films deposited at or above 225°C are smooth & uniform morphologically. Beyond a substrate temperature of 275°C, the films become discontinuous and non-uniform. However, the films are sulfur rich, even at 275°C. Electrical conductivity of prepared thin films have been measured using silver contacts in coplanar geometry. Films are n - type as confirmed by hot probe technique. The electrical conductivity at room temperature (25°C) was in the order of 10-4 Ω-1cm-1 and was found to increase with increase in temperature showing the semiconducting nature of the films with the band gap of 0.39 eV.

Hot probe measurements of n-type conduction in Sb-doped ZnO microwires

The charge carriers type in antimony-doped ZnO (ZnO:Sb) microwires was studied using the hot probe technique. The wires were grown by a simple thermal evaporation method. Contrary to the expected p-type behavior reported for Sb doped ZnO thin films and nanowires, our hot probe measurements of representative single Sb-doped ZnO wires show a stable n-type behavior. The hot probe technique is a simple and efficient way to determine the charge carrier type from thermoelectric measurements on a single semiconductor wire and could offer an alternative to Hall effect measurements. The technique relies on creating a temperature gradient across the wire (i.e., heating one side of the wire relative to the other) and monitoring the resulting open-circuit voltage between the two ends. We also performed Energy Dispersive X-ray Spectroscopy measurements to identify and monitor the elemental composition in these ZnO:Sb wires.

Annealing Effects on the Structural and Optical Properties of Thermally Deposited Tin Antimony Sulfide Thin Films

We report the deposition and characterization of tin antimony sulfide thin films on a soda glass substrate by a thermal evaporation technique. The thin films were annealed in argon gas at 150, 175, and 300 °C inside glass ampoules. The structural and optical properties of the deposited and annealed films are investigated. X-ray diffraction (XRD) patterns show that the films are polycrystalline in structure. Photoconductivity plot revealed good response in the NIR and visible regions, while the films show no transmittance below 700 nm. The absorption coefficient was of the order of 106 cm−1. Optical band gaps were also evaluated and a decrease in band gap was observed due to annealing. Hot point probe technique was employed for type of conductivity.

Novel Electrical Characterization of Thin 3C-SiC Films on Si Substrates

Thin semiconductor films provide many functional uses in the fields of electronics, sensors, optics, and microelectro-mechanical systems (MEMS). A prime example is the case of thin film 3C-Silicon Carbide epitaxially grown on standard silicon wafers. The required SiC layer thickness for these applications ranges from a few nanometers to a few microns, and process conditions that control film stress, doping type and concentration, crystal orientation, and surface roughness need to be developed along with accurate physical and electrical characterization techniques. In this paper, we present two novel variations on established measurement techniques. Firstly, the hotprobe technique is used as a simple, non-destructive method to monitor film doping and crystal quality based on the open circuit voltage and short circuit currents. Results are presented for both ntype and p-type films grown on (100) and (111) silicon orientations, and supported by transmission electron micrographs and X-ray diffraction data. Secondly, a technique based on the four point resistivity measurement is used to determine film resistivity while eliminating the errors introduced by substrate leakage.

Apparatus for measuring Seebeck coefficient and electrical resistivity of small dimension samples using infrared microscope as temperature sensor

An apparatus for measuring the Seebeck coefficient (α) and electrical resistivity (ρ) was designed to operate under an infrared microscope. A unique feature of this apparatus is its capability of measuring α and ρ of small-dimension (sub-millimeter) samples without the need for microfabrication. An essential part of this apparatus is a four-probe assembly that has one heated probe, which combines the hot probe technique with the Van der Pauw method for "simultaneous" measurements of the Seebeck coefficient and electrical resistivity. The repeatability of the apparatus was investigated over a temperature range of 40 °C-100 °C using a nickel plate as a standard reference. The results show that the apparatus has an uncertainty of ±4.9% for Seebeck coefficient and ±5.0% for electrical resistivity. The standard deviation of the apparatus against a nickel reference sample is -2.43 μVK(-1) (-12.5%) for the Seebeck coefficient and -0.4 μΩ cm (-4.6%) for the electrical resistivity, respectively.

Hot-probe method for evaluation of majority charged carriers concentration in semiconductor thin films

Physical properties of thin films significantly differ from those of bulk materials. Also, these properties are influenced from the technological parameters of the films deposition technique. Therefore, characterization methods for evaluation of thin film properties become of high importance. A novel approach to the well-known "Hot-Probe" method is proposed and applied in our work. The conventional Hot Probe characterization method enables only the definition of a semiconductor type, P or N, by identifying the majority of the charged carriers. According to the new Hot Probe technique, one can measure and calculate the impurities concentration and charged carriers dynamic parameters. Feasibility proof of the upgraded Hot Probe method was done in Si and Ge bulk, and in thin film semiconductor samples of In2O3 and VO2.

Growth of 3C–SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C–SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C–SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH 4 and C 2H 2. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.

Annealing temperature effect on the structural, optical and electrical properties of ZnS thin films

Zinc sulfide thin films were prepared on glass substrates at room temperature using a chemical bath deposition method. The obtained films were annealed at temperatures ranging from 100 to 500°C in steps of 100°C for 1h. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray analysis (EDX), optical absorption spectra, and electrical measurements. X-ray diffraction analysis indicates that the deposited films have an amorphous structure, but after being annealed at 500°C, they change to slightly polycrystalline. The optical constants such as the refractive index (nr), the extinction coefficient (k), and the real (ε1) and imaginary (ε2) parts of the dielectric constant are calculated depending on the annealing temperature. Aside from the ohmic characteristics of the I–V curve, a nonlinear I–V curve owing to the Schottky contact is also found, and the barrier heights (ϕbn) for Au/n-ZnS and In/n-ZnS heterojunctions are calculated. The conductivity type was identified by the hot-probe technique.

Characterization of Tin disulphide thin films prepared at different substrate temperature using spray pyrolysis technique

Thin films of tin disulphide on glass substrates were prepared by spray pyrolysis technique using precursor solutions of SnCl2·2H2O and n–n dimethyl thiourea at different substrate temperatures varied in the range 348–423 K. Using the hot probe technique the type of conductivity is found to be n type. X ray diffraction analysis revealed the polycrystalline nature with increasing crystallinity with respect to substrate temperature. The preferential orientation growth of SnS2 compound having hexagonal structure along (002) plane increased with the substrate temperature. The size of the tin disulphide crystallites with nano dimension were determined using the Full Width Half Maximum values of the Bragg peaks and found to increase with the substrate temperature. The surface morphology had been observed on the surface of these films using scanning electron microscope. The optical absorption and transmittance spectra have been recorded for these films in the wavelength range 400–800 nm. Thickness of these films was found using surface roughness profilometer. The absorption coefficient (α) was determined for all the films. Direct band gap values were found to exist in all the films deposited at different substrate temperatures. The value of room temperature resistivity in dark decreased from 5.95 × 103 Ω cm for the amorphous film deposited at low temperature (348 K) to 2.22 × 103 Ω cm for the polycrystalline film deposited at high temperature (423 K) whereas the resistivity values in light decreased from 1.48 × 103 to 0.55 × 103 Ω cm respectively, which is determined using the four probe method. Activation energy of these thin films was determined by Arrhenius plot.