Low-field current transport mechanisms in rf magnetron sputter deposited boron carbide (B5C)/p-type crystalline silicon junctions in the dark

Measurements of the forward and reverse currents in an undoped rf magnetron sputter deposited boron carbide (B5C)/p-type Si( 111) junction have been made in the dark in the temperature range 120-300 K at low-bias voltages (0-0.3 V). A diode-like behaviour of the junction current has been observed in this low-bias region at all temperatures but with a rather large reverse (leakage) current I-R, particularly at high temperatures (I-R approximate to 2 muA at V = -0.3 V and T = 290 K). The forward 'voltage factor' A (T) was found to decrease with increasing temperature as A(T) approximate to q/etak(B)T, with relatively high values of the 'ideality factor' eta (about 3.5-4), probably due to the existence of an interfacial layer. The temperature dependence of the measured junction current (forward and reverse) flowing at low bias voltages and of the forward 'current factor' I-0F can be described satisfactorily by a model of the tunnelling of thermally excited carriers, including tunnelling via impurity localized levels, of the form I(T) proportional to exp [-C/T-1/3] over the entire temperature range studied (120-300 K). A high density of 'localized' energy states as large as 10(18) cm(-3) eV(-1) was estimated, which can be attributed in part to 'extrinsic' interface states that could have been formed throughout the fabrication procedures of the rf sputter deposited B5C/p-crystalline silicon junction studied. Another possible cause of such large concentration of 'localized' states is the 'intrinsic' interface states produced by the lattice mismatch between the polycrystalline boron carbide and crystalline silicon semiconductors as well as of the high intrinsic defect concentration caused by structural imperfections that often exist in boron carbide compounds.