We report the observation of visible photoluminescence in the amorphous SixC1−x(H) alloy system. The spectrum consists of two bands one of which shifts linearly with x. For x=0.4 the principle luminescence maximum lies at 2.1 eV.
Photoluminescence of amorphous silicon is measured in the range from 77 K to room temperature. The temperature dependence of the three bands, of which the total luminescence spectrum consists, could be determined seperately. It is found that all three of them decrease a t high temperature with approximately the same activation energy of 0.13 eV. This decrease sets in a t different temperatures for the different bands. The three bands are interpreted as transitions within electron-hole pairs consisting of more or less deeply trapped carriers. The activated decrease a t high temperature is explained by thermally activated dissociation of these pairs. The electronhole pair concept also explains why photoconductivity decreases about twice as fast as luminescence when the substrate temperature is lowered.Die Photolumineszenz von amorphem Silizium wird zwischen 77 K und Zimmertemperatur gemessen. Die Temperaturabhiingigkeit der drei Banden, aus denen das gesamte Lumineszenzspektrum besteht, kann dabei getrennt bestimmt werden. Alle drei Banden nehmen bei hoher Temperatur mit ungefahr der gleichen Aktivierungsenergie von 0,13 eV ab. Dieser Abfall setzt fur die verschiedenen Banden bei verschiedenen Temperaturen ein. Die drei Banden werden als Ubergange innerhalb von Elektron-Loch-Paaren gedeutet, wobei die Elektronen oder Locher in verschieden tiefen Haftstellen sitzen. Der aktivierte Abfall der Lumineszenz bei hoher Temperatur wird durch thermisch aktivierte Dissoziation dieser Paare erkliirt. Dieses Konzept erkliirt auch, warum die Photoleitung doppelt so schnell abnimmt wie die Lumineszenz, wenn die Substrattemperatur erniedrigt wird.
FIRST and SOFIA are both future infrared observatories with 3m class main mirrors having sophisticated instrumentation aboard. The present design of the FIRST imaging spectrometer PACS requires two large far-infrared photoconductor arrays of 25x16 pixels each, the baseline material is stressed and unstressed Ge:Ga. A gallium arsenide photoconductive detector which is sensitive in the far infrared (FIR) wavelength range from about 60 .tm to 300 m might offer the advantage of extending considerably the long wavelength cut-off of presently available photodetectors. FIRGA is an ESA sponsored detector development program on this matter involving international partners. The aim is a monolithic 4x32 demonstrator array module with associated cryogenic read-out electronics. Recent progress in material research has led to the production of Te-doped n-type GaAs layers using liquid phase epitaxy (LPE). We prepared sample detectors from those materials and investigated their electrical and infrared characteristics. First measurements indicate that GaAs has in principle considerable potential as a FIR photon detector. Theoretical modeling of GaAs detectors (bulk type and blocked impurity conduction band devices) can help with the detector design and allows the prediction of response transients as a function of detector parameters. Present development activities are mainly concentrating on material research, i.e. the production of GaAs:Te with improved FIR characteristics. Results of the current tests and measurements are reported. The FIRGA study is intended to prepare the technology for large two dimensional GaAs detector arrays for far infrared astronomy.
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