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Dynamic testing of solar cells
Šneidr, Radim ; Hégr, Ondřej (referee) ; Boušek, Jaroslav (advisor)
The content of this thesis is the validation of the method of dynamic testing of solar photovoltaic cells. Testing methods for determining the parameters of the photovoltaic cell replacement scheme has been verified through testing a set of crystalline silicon photovoltaic cells. To accelerate the diffusion capacity measurement and to improve reproducibility of the measurement we propose new method of determining the time constant for diffusion capacitance using a combination of two short pulses. For this method of measurement new scheme for dynamic tester timing has been proposed and implemented.
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The Noise Spectroscopy of Radiation Detectors Based on the CdTe
Zajaček, Jiří ; Štourač, Ladislav (referee) ; Hájek, Karel (referee) ; Grmela, Lubomír (advisor)
The main object of this work is noise spectroscopy of CdTe radiation detectors (-rays and X–rays) and CdTe samples. The study of stochastic phenomenon and tracing redundant low-frequency noise in semiconductor materials require long-term measurements in time domain and evaluate suitable power spectral densities (PSD) with logarithmic divided frequency axes. We have used the means of time-frequency analysis derived from the discrete wavelet transform (DWT) and we have designed the effective algorithm for PSD estimation, which is comparable with an original analog method. CdTe single crystal with Au contacts we can imagine as a series connection of two Schottky diodes with a resistor between them. The bulk resistance at constant temperature and other constant parameters changes due to the carrier concentration changing only. The p-type CdTe sample shows metal behavior with every temperature changes. Semiconductor properties of the sample begin to dominate just after some period of time. This behavior is caused by the hole mobility changing. The voltage noise spectral density of 1/f noise depends on the quantity of free carriers in the sample. All the studied samples have very high value of low frequency noise, much higher than it should have been according to Hooge’s formula. The excess value of low frequency noise is caused by the low carrier concentration within the depleted region.
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The Noise Spectroscopy of Radiation Detectors Based on the CdTe
Zajaček, Jiří ; Štourač, Ladislav (referee) ; Hájek, Karel (referee) ; Grmela, Lubomír (advisor)
The main object of this work is noise spectroscopy of CdTe radiation detectors (-rays and X–rays) and CdTe samples. The study of stochastic phenomenon and tracing redundant low-frequency noise in semiconductor materials require long-term measurements in time domain and evaluate suitable power spectral densities (PSD) with logarithmic divided frequency axes. We have used the means of time-frequency analysis derived from the discrete wavelet transform (DWT) and we have designed the effective algorithm for PSD estimation, which is comparable with an original analog method. CdTe single crystal with Au contacts we can imagine as a series connection of two Schottky diodes with a resistor between them. The bulk resistance at constant temperature and other constant parameters changes due to the carrier concentration changing only. The p-type CdTe sample shows metal behavior with every temperature changes. Semiconductor properties of the sample begin to dominate just after some period of time. This behavior is caused by the hole mobility changing. The voltage noise spectral density of 1/f noise depends on the quantity of free carriers in the sample. All the studied samples have very high value of low frequency noise, much higher than it should have been according to Hooge’s formula. The excess value of low frequency noise is caused by the low carrier concentration within the depleted region.
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Radiation Detectors Noise Spectroscopy
Andreev, Alexey ; Grmela, Lubomír (advisor)
Kadmium telurid je velmi důležitý materiál jak základního, tak i aplikovaného výzkumu. Je to dáno zejména jeho výhodnými elektronickými, optickými a strukturními vlastnostmi, které ho předurčují pro náročné technické aplikace. Dnes se hlavně používá pro jeho vysoké rozlišení k detekci a X-záření. Hlavní výhodou detektorů na bázi CdTe je, že nepotřebují chlazení a mohou spolehlivě fungovat i při pokojové teplotě. To způsobuje efektivnější interakce fotonů než je tomu u Si nebo jiných polovodičových materiálů. Obsahem této práce byla analýza a interpretace výsledků získaných studiem šumových a transportních charakteristik CdTe vzorků. Měření ukázaly že odpor homogenní části CdTe krystalů mírně klesá při připojení elektrického pole na vzorku. Při změně teploty navíc dochází k odlišné reakci u CdTe typu p a n. Právě těmto efektům je v práci věnována pozornost. Pomocí šumové spektroskopie bylo zjištěno, že při nízkých frekvencích je u vzorků dominantní šum typu 1/f, zatímco při vyšších frekvencích je sledován generačně-rekombinační šum a tepelný šum. Všechny měřené vzorky vykazovaly mnohem vyšší hodnotu šumu na nízkých frekvencích než udává Hoogeova rovnice. Byly nalezeny a popsány zdroje nadbytečného šumu.
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Dynamic testing of solar cells
Šneidr, Radim ; Hégr, Ondřej (referee) ; Boušek, Jaroslav (advisor)
The content of this thesis is the validation of the method of dynamic testing of solar photovoltaic cells. Testing methods for determining the parameters of the photovoltaic cell replacement scheme has been verified through testing a set of crystalline silicon photovoltaic cells. To accelerate the diffusion capacity measurement and to improve reproducibility of the measurement we propose new method of determining the time constant for diffusion capacitance using a combination of two short pulses. For this method of measurement new scheme for dynamic tester timing has been proposed and implemented.
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