Light-intensity and temperature dependence of trap-dangling bond recombination in hydrogenated microcrystalline silicon
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Light-intensity and temperature dependence of trap-dangling bond recombination in hydrogenated microcrystalline silicon Christoph Boehme and Klaus Lips Hahn-Meitner-Institut, Kekuléstrasse 5, 12489 Berlin, Germany ABSTRACT A quantitative study of the trap-dangling bond tunneling recombination in hydrogenated microcrystalline silicon (µc-Si:H) is presented. The transition coefficients were measured at various light exposures and temperatures between T = 10 K and T = 140 K using time-domain measurements of spin-dependent recombination (TSR). TSR is a new characterization method related to electrically detected magnetic resonance (EDMR). It combines the advantages of pulsed electron spin resonance with that of EDMR. In contrast to previous models, the experimental results can only be interpreted if the interaction between the spins of the trap and the dangling bonds as well as triplet recombination is considered.
INTRODUCTION The understanding of the nature of electron-hole-recombination in disordered semiconductors such as amorphous or microcrystalline silicon depends on the availability of experimental methods that allow a distinct observation of recombination mechanisms. In the past, electron spin resonance (ESR) has been utilized for the selective excitation of a given paramagnetic defect in order to influence recombination [1-4]. This method, which is often referred to as electrically detected magnetic resonance (EDMR), is based on the measurement of an ESR-induced enhancement of the recombination rate between paramagnetic states that is detected by photoconductivity measurements. EDMR is performed as an adiabatic field-sweep experiment where the sample is exposed to a continuous microwave radiation. Resonant current changes are then indicative of a defects electronic activity. Although EDMR is able to identify the states participating in recombination, it fails to reveal quantitative information about the recombination probability. Therefore, a new approach has been developed in recent years, the time-domain measurement of spin-dependent recombination (TSR) [5]. The principle of TSR is similar to that of EDMR, however, instead of a continous radiation, a mircowave burst is used in order to quickly alter the spin state occupation of a recombining pair (e.g. from triplet to singlet). This burst has to be sufficiently strong and short such that the induced changes are faster than the recombination time or any other incoherent process, e.g. spin-lattice relaxation. In that case, the photoconductivity response to such a microwave pulse contains all the information on the recombination probability. As shown before [5], TSR is able to resolve the dynamics of trap-dangling bond tunneling recombination (CE-db) of hydrogenated microcrystalline silicon (µc-Si:H). From the TSR transient of this transition, dissociation and recombination times could be gained, providing that the interaction between the CE and the db states are negligible. Subject of this study is the investigation of the light-intensity dependence as well as
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