P.M. Nikolić

Photoacoustic frequency transmission technique: Electronic deformation mechanism in semiconductors

A quantitative analysis of the electronic deformation (electronic strain) contribution to the photoacoustic signal in semiconductor samples was done. The photoacoustic (PA) effect was investigated as a function of the modulation frequency in a transmission detection configuration. The theoretical model for this configuration was given for the thermal and elastic processes besides the carrier transport characteristic and the relation for electronic elastic deformation was derived by the theory of the elastic thin plate vibrations. Analysis showed that the electronic deformation mechanisms can have an important infleucne on the PA signal in the frequency range typical for gas-microphone detection. The experimental photoacoustic data for Si samples were measured and they exhibited a satisfactory agreement with the theoretical model.

Investigation of carrier transport processes in semiconductors by the photoacoustic frequency transmission method

The development of various methods for the investigation of transport phenomena in solids has attracted much attention. The pho- toacoustic method is a valuable tool in the study of various processes in semiconductors and electronic devices. Especially for the characteriza- tion of thermal and carrier transport processes in semiconductors, the transmission detection configuration is available for many applications. That the photoacoustic frequency transmission technique as a valuable tool in the study of carrier transport processes of the semiconductor is shown. The photoacoustic spectra of wide bandgap semiconductors (Si- wafers, Ge and GaAs), narrow bandgap semiconductors (InSb, PtSb2) and thin amorphous semiconductor (GeSe) films are measured as a function of modulation frequency.

Photoacoustic frequency heat‐transmission technique: Thermal and carrier transport parameters measurements in silicon

Photoacoustic frequency heat‐transmission technique is used to study thermal and carrier transport properties in low‐doped silicon wafers. Amplitude and phase photoacoustic signals as a function of modulation frequency of incident optical beam are measured using different experimental conditions. The thermal diffusivity, coefficient of excess carrier diffusion, carrier lifetime, and the surface recombination velocity were determined by comparing experimental results and calculated theoretical photoacoustic signals. The suitability of the photoacoustic frequency heat‐transmission technique as a contactless diagnostic method is assessed in comparison with the more conventional photothermal deflection and photothermal modulated reflection techniques.

Photoacoustic investigation of thermal and transport properties of amorphous GeSe thin films

In this work the possibility of simultaneous determination of thermal and transport properties of thin films using a photoacoustic method was investigated. The properties of amorphous GeSe thin films, which were evaporated on quartz substrata, were examined by measuring their amplitude and phase photoacoustic spectra as a function of the modulated optical laser beam frequency. The measurements were performed in a specially constructed photoacoustic cell which enabled excitation of the sample on one side and detection of the acoustic response on the other. Thermal diffusivity and transport properties (diffusivity coefficient, recombination time, and the surface recombination velocity) of the GeSe thin films were determined by comparing of the experimental results and the calculated theoretical photoacoustic spectra.

Thermal diffusivity of NTC layers obtained with photoacoustic technique

The thermal diffusivity of thick film NTC layers based on a metal oxide powder mixture was measured at room temperature by the photoacoustic (PA) technique. The powder mixture was composed of MnO (60 percent), CoO (32 percent) and Fe2O3 (8 percent), which were ball milled to nanometer particle size. NTC layers of different thicknesses were made by sequentional screen‐printing followed by drying and co‐firing at 850, 900 and 1,000°C in a hybrid conveyor furnace. The experimental PA phase and amplitude diagrams were numerically analyzed and the thermal diffusivity and electron transport parameters were calculated. An increase of thermal diffusivity with sintering temperature was observed. The fractal structure model was in agreement with the experimental data for modulation frequencies in which the sample behaved as thermally thick.

Thermal and electronic transport properties of single crystal PtSb2 obtained by the photoacoustic method

Single crystal PtSb2 ingots were synthesized using the Bridgman technique. Electronic transport properties and thermal diffusivity of PtSb2 sample were determined using the photoacoustic (PA) method with transmission detection configuration. The excess carrier lifetime, the recombination velocity and thermal diffusivity were determined by comparing the experimental results and theoretical photoacoustic signals.

Resistivity Versus Geometry Relation In Bulk - Sintered And Thick Film MnCoFe - Oxide Thermistors

A relation between the electrical resistivity and geometry in bulk (pressed and sintered) and thick film NTC thermistors was determined. A powder mixture consisting of MnO, CoO and Fe2O3 called NTC-3K3 (EI Ferrites) was used for the realization of classical NTC disc shape thermistors sintered at 1200°C /30 min. After that, a thick film NTC thermistor paste was composed using the same powder (0.9 μm particle size on average), 4% of Bi2O3 and an organic vehicle (NTC-3K3-95 /2 EI Iritel). Different thick film thermistor geometry’s were printed of NTC paste on alumina and sintered at 850°C/10 min. PdAg paste was printed on both sintered-bulk and thick film thermistors. Their resistivity vs. geometry was compared. NTC coefficient B was determined on NTC - R (T) curves as B=4200 K. The range of the resistivity values obtained varied for planar shapes from 100 Ω to 10 MΩ, and for classical disc types from 2–200 kΩ

A Thermal Sensor for Water Using Self-Heated NTC Thick-Film Segmented Thermistors

A simple thermal (heat loss) sensor system was designed in a small plastic tube housing using a negative thermal coefficient (NTC) thick-film thermistor as a self-heating sensor. The voltage power supply [range constant voltage (RCV)-range constant voltage] uses the measured input water temperature to select the applied voltage in steps (up and down) in order to enable operation of the sensor at optimal sensitivity for different water temperatures. The input water temperature was measured using a “cold” NTC thick-film segmented thermistor. The measured calibration curves were modeled. Additional calculated curves were interpolated between the experimental curves in fine steps to cover each temperature of input water and can be used for determining the water volume flow rate or water velocity. The realized prototype flow meter inertia, stability, repeatability, and tolerance were measured and analyzed. The proposed intelligent RCV thermal flow meter system will include a smart power supply with range-constant-voltages (auto-range), a simple acquisition card and custom designed flow meter software.

A photoacoustic investigation of transport properties and thermal diffusivity of InSb single crystals

Thermal and electronic transport properties of low-doped single crystal InSb were determined for the first time and analyzed using a photoacoustic frequency heat transmission technique. The thermal diffusivity, excess carrier lifetime, front and rear side recombination velocity and electronic diffusivity were determined by comparing experimental results and theoretical photoacoustic signals.

Combined FTIR and SEM-EDS study of Bi2O3 doped ZnO-SnO2 ceramics

The effects of Bi2O3 addition on the phase composition, microstructure and optical properties of ZnO–SnO2 ceramics were investigated. Starting powders of ZnO and SnO2 were mixed in the molar ratio 2:1. After adding Bi2O3 (1.0 mol.%) this mixture was mechanically activated for 10 min in a planetary ball mill, uniaxially pressed and sintered at 1300°C for 2 h. Far‐infrared reflection spectra were measured (100–1000 cm–1). To investigate the occurred differences in FTIR spectra, the Bi2O3‐doped sample was examined more carefully with a Perkin–Elmer FTIR spectrometer (Perkin Elmer, Waltham, MA, USA) connected with a Perkin–Elmer FTIR microscope and itemized points of interest were also studied with SEM‐EDS.