Analysis of high reverse currents of 4H-SiC Schottky-barrier diodes

Abstract

Nickel (Ni), titanium (Ti), and molybdenum (Mo) 4H-silicon carbide Schottky-barrier diodes (SiC SBDs) were fabricated and used to investigate the relation between forward and reverse currents. Temperature dependence of reverse current follows a theory that includes tunneling in regard to thermionic emission, namely, temperature dependence is weak at low temperature but strong at high temperatures. On the other hand, the reverse currents of the Ni and Mo SBDs are higher than their respective currents calculated from their Schottky barrier heights (SBHs), whereas the reverse current of the Ti SBD agrees well with that calculated from its SBH. The cause of the high reverse currents was investigated from the viewpoints of low barrier patch, Gaussian distribution of barrier height (GD), thin surface barrier, and electron effective mass. The high reverse current of the Ni and Mo SBDs can be explained not in terms of a low-barrier patch, GD, or thin surface barrier but in terms of small effective masses. Investigation of crystal structures at the Schottky interface revealed a large lattice mismatch between the metals (Ni, Ti, or Mo) and SiC for the Ni and Mo SBDs. The small effective mass is possibly attributed to the large lattice mismatch, which might generate transition layers at the Schottky interface. It is concluded from these results that the lattice constant as well as the work function is an important factor in selecting the metal species as the Schottky metal for wide band-gap SBDs, for which tunneling current dominates reverse current.

The Fundamental Current Mechanisms in SiC Schottky Barrier Diodes: Physical Model, Experimental Verification and Implications

“…This result shows that, effectively, the current from the semiconductor into metal is determined by the effective mass of electrons in the metal, in agreement with experimental results showing that the effective mass is affected by the choice of metal [14,18,19].…”

Description and Verification of the Fundamental Current Mechanisms in Silicon Carbide Schottky Barrier Diodes

“…Two teams (Okino et al . 14 and Blasciuc-Dimitriu et al . 15 ) used parameters derived from the forward characteristic to describe the reverse leakage currents observed for silicon carbide (SiC) Schottky barrier diodes.…”

“…The image force permittivity may be the low or high frequency permittivity, depending on a number of material factors (for instance, does the material fully polarise in response to a carrier’s electric field within the short crossing time 11 ). For the set purpose in this paper, we will use the low frequency value, as others have done for SiC 14 .…”

Combination of thermionic emission and tunneling mechanisms to analyze the leakage current in 4H-SiC Schottky barrier diodes

“…Both models were used separately to analyze the experimental reverse leakage current of SiC and other wide-gap SBDs. Combined and not combined with barrier lowering model, some authors [6][7][8][9][10][11] described the reverse leakage current using the general model [12] of the tunneling current. At the same time, the others [13][14][15][16][17][18] used the thermionic field emission (TFE) developed by Padovani-Stratton [19] also with and without the effect of the image force barrier lowering.…”