CONTENTS & ABSTRACTS
InEnglish. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Engineering
Volume 10 No. 3September 2004
Special issue on electronics:wide band-gap semiconductor structures, measurement and processing of sensor signals BEC 2004
Guesteditorial; 155–156
Mart Min
Comparisonof photon recycling effect in GaAs and GaN structures;157–172
Enn Velmre and Andres Udal
Abstract. Extending earlier studiesof photon recycling effect in GaAs, estimations are found for a new promisingwide band-gap semiconductor GaN. Relying on available data, approximately oneorder higher radiative recombination coefficient and absorption coefficientsthan in GaAs and equal or greater Urbach energies than in GaAs are valid forGaN. The distance-dependent radiative recombination transfer functions areintroduced and studied for typical charge carrier distribution cases. In spiteof high absorption rates of GaN, the estimations show approximately one orderof magnitude higher photon recycling efficiency than in the case of GaAs. Bynumerical simulations, the possibility of appearance of the S-shape forward I/Vcharacteristics of p-i-n structures due to strong photonrecycling is shown.
Key words: photon recycling,recombination radiation reabsorption, Gallium arsenide, Gallium aitride,radiative recombination transfer function, one-dimensional drift-diffusionsimulations, p-i-n structures.
Comparisonof the dynamic behaviour of complementary 6H- and 4H-SiC Schottky structuresusing numerical simulation; 173–178
Toomas Rang and Raido Kurel
Abstract. In this paper we compare,using numerical simulation, the dynamic behaviour of complementary Schottkystructures based on 6H- and 4H-SiC substrates. Clear differences in thebehaviour of these two Schottky structures at different temperatures has beenestablished. The calculations show that the turn-off time is about the same forboth Schottky structures, but it varies with the temperature about 1.5 times.
Key words: SiC, Schottkystructures, turn-off time, high temperature behaviour, numerical simulation.
Interpretationof some physical parameters of SiC Schottky interfaces manufactured bydiffusion welding technology; 179–184
Toomas Rang, Oleg Korolkov, and Jevgeni Ljutov
Abstract. The goal of this paper isto show some new problems introduced by the diffusion welding technology forSiC Schottky structures concerning the current transport through themetal–semiconductor interface using classical thermionic-diffusion theory. Theexperimental results show clearly that the classical Schottky current modelparameters like Richardson coefficient, on-state series resistance and idealityfactor differ from their usual values. The calculations show that the currenttransport, based on classical description of the ideal Schottky interface, doesnot give a true picture of the situation at the interface. Namely, during themanufacturing process, between the metal and semiconductor appears an extrathin silica layer, which, we guess, has an influence on the electricalcharactersitics of the device.
Key words: SiC, diffusionwelding technology, current transport, Schottky interface.
Improvementof lock-in signal processing for applications in measurement of electricalbioimpedance; 185–197
Toomas Parve and Raul Land
Abstract. Improvement of the switching mode lock-in signal processing,based on narrowing of the pulse of the half wave of the rectangular formsignal, is discussed. The solution is aimed to the diminishing of the phasorerrors caused by the sensitivity of the switching mode lock-in signalconverters to the odd higher harmonics of the input signal. This improvement istechnically realizable without significant increasing of circuit complexity andenergy consumption. The method is foreseen for electrical bioimpedancemeasurement units used in implantable and portable medical devices for makingmedical measurements in vivo.
Key words: lock-in signal processing, measurement errors, electricalbioimpedance, implantable medical devices.
Theoreticaldevelopment and computer simulation of a bioimpedance measurement system;198–208
Toivo Paavle
Abstract. In this paper,theoretical conceptions of a novel bioimpedance measurement system (MS) arediscussed. The proposed MS couples the lock-in measurement principles and amethod of undersampling in digital signal processing. The MS is a mixed-signalsystem incorporating an analogue phase-locked loop (PLL) as the source ofreference signal, demodulators for amplitude and phase demodulation, and adigital signal processor. It is shown that using a single PLL, simultaneousdemodulation of two signals with different frequencies is possible. Thetheoretical conceptions of lock-in measurement and efficiency of the whole MShave been verified by means of special computer simulators, structures of whichare presented. The results of this work can be considered as a preliminarystudy for the practical design.
Key words: bioimpedance,biomodulation, lock-in measurement, phase-locked loop, undersampling,signal-domain model, phase-domain model.
Transientsin adaptive Fourier analysers; 209–226
Ants Ronk and Ülle Voolaine
Abstract. In the paper severaldifferent modifications of an adaptive Fourier analyser are consideredpresenting simulation results on transients of the analyser’s fundamentalfrequency and output signal. The results permit to compare convergenceproperties of these modifications and to choose and optimize a propermodification for different applications, including such an extension of theanalyser, which processes composite signals consisting of several periodicsignals of different waveforms and (not harmonically related) frequencies.
Key words: adaptive filters,observers, spectral analysis, waveform analysis, frequency estimation,transient processes.
Instructionsto authors; 227–230
CopyrightTransfer Agreement; 231
