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Etudes spectroscopiques du dopage dans les matériaux II-VI pour les détecteurs infrarouge et les cellules photovoltaïques

Abstract : This thesis work presents optical and electrical characteristics of dopants in HgCdTe, CdZnTe and CdS layers. These 3 materials II-VI have mutual interest to be used in detection devices, for infrared light detection with HgCdTe and CdZnTe or for visible light detection in the case of CdS. Optical characterization of these II-VI layers was carried out with photoluminescence and was correlated with electrical measurements realized by temperature dependant Hall effect. First, a study of intrinsic doping with mercury vacancies and of extrinsic doping with arsenic in HgCdTe layer, the active layer in infrared detectors, was carried out. To do so, optical measurements by photoluminescence (on an experiment set up in the laboratory during the first thesis year which allows to work from low temperatures to room temperature between 1µm and 12 µm in IR) on HgCdTe layers grown by liquid phase epitaxy (LPE) with different compositions were managed. Correlation between these optical measurements with electrical measurements by temperature dependent Hall measurements led to identify activation energies of the 2 mercury vacancy acceptor levels and to show U-negativity phenomenon of mercury vacancy in HgCdTe. Moreover, comparison between PL spectra of As doped samples during molecular beam epitaxial (MBE) growth with measurements carried out by X-ray absorption (EXAFS) allowed to observe optical recombination associated to the different arsenic complexes formed before and after activation annealing . Besides, a modelling work about alloy disorder phenomenon in HgCdTe was managed. More precisely, a model based on a Gaussian statistic associated to alloy fluctuations around a mean gap and a Boltzmann statistic was developed in order to fit absorption spectra first, then to fit photoluminescence spectra. This model allowed us to fit closely photoluminescence and absorption spectra, taking into account alloy disorder of the material. Thus, we found that spectra fitting with Gaussian functions as usually done in literature allows to find right energy intervals between emission peaks, so right ionization energies. Secondly, also in infrared detection case, our work dealt with the study of CdZnTe substrate used for HgCdTe epitaxy. Comparison of PL spectra with growth parameters were carried out. More particularly, a study on a specific area of samples which show IR ray absorption was realized in order to understand the origin. Last, we took interest in CdS layer, II-VI material intrinsically doped (n-type) used as transparent window and forming p-n junction with CdTe in solar cells, visible light detectors. In this part, we studied consequences of different deposition method, sublimation or chemical bath of CdS layer on a glass substrate, by comparing photoluminescence spectra obtained and thermal treatments carried out after deposition. These measurements were correlated with solar cells efficiency.
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Gemain Frédérique. Etudes spectroscopiques du dopage dans les matériaux II-VI pour les détecteurs infrarouge et les cellules photovoltaïques. Optique / photonique. Université Joseph-Fourier - Grenoble I, 2012. Français. ⟨tel-00796028⟩

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