University of Zagreb. Faculty of Science. Department of Physics.
Abstract
Zračenje poluvodičkih materijala brzim ionima nužno proizvodi defekte u kristalnoj strukturi u vidu vakancija i intersticija. Najveća gustoća defekata se opaža pri kraju dosega brzog iona u materijalu. Unutar tih lokaliziranih područja s visokim koncentracijama defekata može doći do rekombinacije ili formiranja kompleksnih defekata. Inicijalne kaskadne rekombinacije u pikosekundnim vremenskim prozorima su dobro proučene. Ipak, promatranje procesa smanjenja broja defekata nastalih ionizacijskim zračenjem u poluvodičima na duljim vremenskim skalama je još dosta otvoreno i manje razjašnjeno, te je upravo to bila tema ovog rada. Ispitivali smo dvije vrste detektora: Si PIN diode i 4H-SiC Schottky diode. Diode su ozračivane ionskim snopovima različitih karakteristika, a za proučavanje utjecaja nastalih električki aktivnih defekata na mobilnost nosioca naboja korištena je metoda IBIC mikroskopije. Kod silicija je uočeno značajno napuštanje nečistoća na sobnoj temperaturi u vremenskom periodu jednog dana, dok u SiC nema takvog efekta zbog šireg energijskog procijepa u ovom materijalu. Korištenjem pulsnog ionskog snopa pokušali smo proučiti vjerojatnosti rekombinacije defekata u milisekundnim vremenima. Rekombinacije koje se odvijaju za vrijeme pauza pulsnog snopa nisu proizvele statistički značajan utjecaj na učinkovitost skupljanja naboja, vjerojatno zbog nedovoljne gustoće ionskih oštećenja formiranih prilikom ozračivanja. Za SiC proučen je i utjecaj temperature na napuštanje oštećenja lokalno uvedenih ionizirajućim zračenjem. Rezultati su interpretirani na temelju postojećih DLTS mjerenja, kojima su se karakterizirali energijski nivoi u poluvodiču koji odgovaraju centrima uhvata nosioca naboja.Irradiating semiconductor material with fast ions creates defects in crystal lattice, namely vacancies and interstitials. The highest defect concentration is observed near the end of the range of high energy ions in the material. Within these localized volumes, where defect concentration is increased, defect recombination or complex defects formation is possible. Initial recombination cascades, which occur during the first picosecond time frames, are well studied. But, processes that are responsible for reducing the number of defects, produced during ionizing radiation of semiconductors, during longer time scales, are not so clarified, so these were the main subject of our study. Two detector materials were examined: Si PIN diodes and 4H-SiC Schottky diodes. Detectors were irradiated using ion beams of different properties. In order to study the influence of the created electrically active defects on the charge carrier’s mobility, IBIC method was utilized. For silicon, significant defect annealing was observed (at room temperature conditions) on time scales of one day, while no such effect was recorded in SiC due to the wide band-gap in this material. By using a pulsed ion beam, we tried to study defect recombination in the millisecond time frames. Recombinations which occur during pulsed beam pauses have not produced a statistically significant influence on the charge collection efficiency, probably because the density of the created damage events was insufficient. Also, for SiC detector, effect of the temperature on defect mobility (induced by locally damaging ions) was investigated. Results have been interpreted based on existing DLTS measurements, which have been used to characterize energy levels in the semiconductor that are responsible for trapping the charge carriers
