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 m ade 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/eta k(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 a t low bias voltages and of the forward 'current factor' I-0F can be describ ed satisfactorily by a model of the tunnelling of thermally excited carrier s, including tunnelling via impurity localized levels, of the form I(T) pro portional 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' int erface states that could have been formed throughout the fabrication proced ures 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 betwee n 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.