Defects in semiconductors are a field of study that attracted solid state physicists for several decades. The complementary of different experimental techniques and the increasing links between the so called fundamental sciences and engineering led to a growing cooperation that is shown both qualitative and quantitatively by the technological development of recent years. From a solid state physicist point of view the analysisi of radiative and nonradiative recombination processes of defects in semiconductors brings about a deeper knowledge of the defects, namely, the localization of the energy levels originated by the defects, their relation with the band levels, the identification of the radiative recombination and its lifetime, the behaviour of these parameters with temperature, the response of the system to external fields, identification of the nature of the defects, etc. From a technological point of view this analysis is fundamental for the characterization of the efficiency of a semiconductor for applications. A typical example is the well known green and red light emitting diodes (LED) commercially available, where the optical characterization of the isoelectronic impurities Zn_G_a - Op and Np in GaP led to the understanding of the efficiency of the samples in electroluminescence. In this work we will study the characteristics of optically active centres in n-type GaP samples, both nominally undoped and intentionally doped, their spectral behaviour, lifetime and thermal quenching. Special attention will be given to the broad emission bands present in these samples and so far not yet studied in depth. Time resolved spectroscopy is particularly usefull in separating luminescence bands with strong overlap while cathodoluminescence in a scanning electron microscope, EPR and ODMR proove invaluable to complement the luminescence data..Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga
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