Schottky barriers for (0001), (0001bar), (11bar00), and (12bar10) crystallographic faces of four hydrogen and 6 hydrogen silicon carbide measured by current-voltage, capacitance-voltage and internal photoemission methods.

摘要

The Schottky barrier is the essential characteristic of any metal-semiconductor diode. The goals of this research were: (1) to determine Schottky barrier heights of metal-semiconductor diodes for four crystallographic faces ((0001), (0001¯), (11¯00), and (12¯10)) of 6H and 4H silicon carbide (SiC), (2) to compare reliability of theoretical models used to describe experimental data obtained by Current-Voltage (I-V), Capacitance-Voltage (C-V), and Internal Photoemission (IPE) experimental techniques. Schottky contacts were fabricated and the barrier heights measured for the four different crystallographic faces of homoepitaxial layers of 6H and 4H-SiC specially prepared for this research. SiC epilayers grown on each crystallographic face were characterized using atomic force microscopy and low temperature photoluminescence. Pt, Mo, and Ti were used for fabrication of thin metal Schottky contacts. Metal films on all four SiC faces were characterized with X-ray diffraction for Pt and Mo. I-V, C-V, and IPE techniques were used to obtain the Schottky barrier heights. A model based on a spatially inhomogeneous Schottky barrier height was used to analyze both I-V and IPE data. To the best of our knowledge, this is the first time that the model was applied to Internal Photoemission measurements. The results demonstrate that use of the model of a spatial distribution (Gaussian form) of barrier heights: (1) reduces differences between the values of the mean Schottky barrier heights obtained by different experimental techniques and (2) allows one to compare the barrier heights of different contacts measured by I-V even if their ideality factors obtained by the conventional method are different. The 6H and 4H silicon carbide Schottky barriers show a dependence on the crystallographic orientation. The highest barrier height was observed for the (0001¯) face, the lowest for the (0001) face. The barrier heights for the two non-basal faces are close to the value for the (0001¯) face for Mo and between those for the (0001¯) and (0001) faces for Ti and Pt. The dependence of the Schottky barrier height on the metal work function is almost linear for 4H SiC but is not linear for 6H SiC. A simple surface double layer model is proposed to describe the experimental findings.