Electrical Properties of the Multilayer Structures Based on Ultrathin Diamond-Like Carbon Films
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ABSTRACT The electrical characteristics of multilayer structures based on amorphous ultrathin diamondlike carbon films were investigated including dynamic and quasi-static current-voltage characteristics, capacitance-voltage characteristics, deep level transient spectra. The effect of illumination and temperature on these characteristics was also investigated. For the multilayer structures composed of lower band gap amorphous carbon layers separated with higher band gap ones, there were observed well-defined regions of negative differential resistance and sharp 20fold changes in capacitance at definite voltages. Activation energies, capture cross sections, and locations of trapping centers were defined. The effects observed are discussed in terms of trapassisted tunneling and, also, in terms of resonant tunneling between energy levels in superlattices and charge filling of the quantum wells and trapping centers. INTRODUCTION Abeles and Tiedje (1983) were the first to produce periodic multilayers (superlattices) of amorphous material (Si and related alloys) [1]. The observed peculiarities in the optical and electrical characteristics of these amorphous superlattices were explained in terms of quantum size effects. In 1987 Miyazaki, Ihara and Hirose observed negative-differential-resistance (NDR) in amorphous double-barrier structures, which could be explained in terms of resonant tunneling [2]. Later, it was shown that the phase compositions and, consequently, the optical and mobility band gap of diamond-like carbon (DLC) films can be varied over a wide range by changing the conditions under which they are deposited [3-7]. This enables one to made superlattice structures using only amorphous DLC films with different band gaps. The NDR effect for the amorphous superlattices using DLC multilayers were described for the first time in [4, 9]. The quantum size effect was considered as one of the possible models to describe the bumps in current-voltage characteristics of the structures investigated. However, some authors disputed resonant tunneling as the possible mechanism for the samples based on amorphous silicon and ascribed the observed features to a combination of alternative effects such as charge limited currents, a multiple-hopping transport mechanism, and trap-assisted tunneling processes [10, 11]. It seems that there is the same ambiguity in the explanation of the real conduction mechanism for amorphous DLC superlattices. Therefore, the peculiarities in carrier transport through of the amorphous DLC superlattices are questionable and need additional studies. In this work, we report new data on the electrical characteristics of amorphous carbon superlattices including dynamic and quasi-static current-voltage characteristics, capacitancevoltage characteristics, deep level transient spectra, and the effect of the illumination and 845
Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
temperature on these characteristics. Activation energies, capture cross sections, and locations of trap states
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