Abstract
Dc/ac transport characteristic of PECVD grown hydrogenated amorphous silicon carbide (a-SiCx:H) thin film was investigated in MIS (metal/insulator/semiconductor) structure by dc current/voltage (I/V) at different temperature (T), ac admittance vs. temperature at constant gate bias voltages and deep level transient spectroscopy (DLTS), respectively. According to I-V-T analysis, two main regimes exhibited. At low electric field, apparent Ohm’s law dominated with Arrhenius type thermal activation energy (EA) around 0.4 eV in both forward and reverse directions. At high field, on the contrary, space charge limited (SCL) current mechanism was eventual. The current transport mechanisms and its temperature/frequency dependence were interpreted by a thermally activated hopping processes across the localized states within a-SiCx:H thin film since 0.4 eV as EA was not high enough for intrinsic band conduction. Instead, transport of charge carriers took place in two steps; first a carrier is thermally excited to an empty energy level from an occupied state then multi-step tunnelling or hopping starts over. Therefore, the two steps mechanisms manifested as single activation energy, differing only through capture cross sections. In turn, two steps in capacitance together with conductance peaks in C-(G)-T while convoluted DLTS signal associated with such events in the measurements.
Highlights
Both tunability of energy band gap from 1.9 - 3.2 eV with different carbon content (x) [1] and n-/p- type dopability by appropriate doping gases [1] lead an opportunity of amorphous hydrogenated silicon carbide (a-SiCx:H) films to be used in solar cell technology and light-emitting diodes (LED’s)
Dc/ac transport characteristic of plasma enhanced chemical vapor deposition (PECVD) grown hydrogenated amorphous silicon carbide (a-SiCx:H) thin film was investigated in MIS structure by dc current/voltage (I/V) at different temperature (T), ac admittance vs. temperature at constant gate bias voltages and deep level transient spectroscopy (DLTS), respectively
In former, owing to the excellent surface passivation of crystalline silicon (c-Si) and large area deposition capability, a-SiCx:H films are used in silicon solar cell applications
Summary
Both tunability of energy band gap from 1.9 - 3.2 eV with different carbon content (x) [1] and n-/p- type dopability by appropriate doping gases [1] lead an opportunity of amorphous hydrogenated silicon carbide (a-SiCx:H) films to be used in solar cell technology and light-emitting diodes (LED’s). Recent works have shown that Si-rich a-SiCx:H films with low power regime possesses brilliant electronic surface passivation in silicon heterojunction solar cells [2,3,4,5,6,7,8]. Transport and/or recombination issues, limits the efficiency of LED’s in which carriers might flow through either localized or extended states via hopping [11] in a-SiCx:H films Within this context, since carrier injection issue and nature/amount of localized density of states (DOS) distribution are tightly bound with each other, d.c. and a.c. conductivities seem to be convenient techniques for characterizing electrical features of the a-SiCx:H film within a metal/insulator/semiconductor structure. UV- VIS spectroscopy (Perkin Elmer Lambda 2S) supplied the optical energy gap and refractive index as 2.67 eV and 2.15, respectively, d.c and ac electrical measurements were performed by an electrometer (Keithley 6517), an impedance analyser (HP 4192 A), and DLTS (Semilab DLS 82 E), respectively
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