Non-metastable recombination induced reactions involving hydrogen in SiC.
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Non-metastable recombination induced reactions involving hydrogen in SiC. Yaroslav Koshka, Bharat Krishnan, Michael S. Mazzola. Department of Electrical & Computer Engineering, Mississippi State University, Box 9571, Mississippi State, MS 39762, USA ABSTRACT A brief survey of some of the recent results of recombination-induced defect reactions involving hydrogen in 4H and 6H-SiC is given. A variety of outcomes of such reactions have been observed in hydrogenated 4H and 6H-SiC polytypes under optical excitation at reduced temperature. A few different non-metastable hydrogen-defect complexes can form, including hydrogen complexes with Al and B acceptors, hydrogen complex with Si vacancy, as well as some other non-identified complexes. Electrical measurements indicated strong recombinationinduced passivation of the electrical activity of aluminum and boron acceptors in SiC. This passivation resulted in the reduction of the net free hole concentration and even inversion of the conductivity type. It is suggested that optical excitation causes a long-range migration of hydrogen followed by its capture in one or another kind of defect complexes. Further insight in the formation of specific complexes as a result of recombination-induced defect reactions is provided by thermal admittance spectroscopy. Energy gap levels in the regions that remained ptype after hydrogenation as well as in the regions where the conductivity was inverted by the recombination-induced passivation are investigated. INTRODUCTION Defect migration and defect reactions enhanced or induced by carrier capture and recombination fascinated semiconductor researchers for many years (see for example Ref.1-3). Associated phenomena are particularly complex and diverse in wide band-gap semiconductors [4]. Electronic mechanism of enhanced defect migration has also been reported for hydrogen. Such phenomena were observed for example in hydrogenated amorphous silicon (α-Si:H) [5]. The first evidence of recombination-enhanced defect reactions (REDRs) in SiC was obtained by Dean and Choyke for a hydrogen complex with Si vacancies (VSi-H) [6]. Excitation of SiC samples with above band-gap light at low temperature resulted in metastable quenching of the VSi-H photoluminescence (PL). The corresponding REDR was attributed to a transition between a stable and a metastable configuration of the hydrogen-defect complex [6,7]. Nonmetastable REDRs in SiC not related to hydrogen were also reported. Recombination-induced generation and growth of stacking faults was found in forward-biased SiC pn diodes [8]. Our recent results indicated that electronic mechanism can produce athermal migration of hydrogen in p-type 4H and 6H-SiC polytypes. Athermal migration of hydrogen at low temperatures (15 K) resulted in the formation of a variety of non-metastable complexes with defects and impurities [9-11]. The process named recombination-induced passivation (RIP) exhibited complex temperature behavior, with the efficiency of the new complex formation getting significantly reduced w
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