Investigation of extended defects in silicon carbide and gallium nitride by scanning techniques
Silicon carbide and gallium nitride are wide bandgap compound semiconductors suitable for high breakdown voltage, high power, and high frequency device applications. The major drawback is the effects of structural defects, which often limit the performance, yield, and reliability of the fabricated devices. Effective and rapid nondestructive characterization scanning techniques are required to identify and study the defects.
An electron beam-induced current (EBIC) investigation of the grown-in defects in 4H-SiC epilayers confirmed the significant effect of extended defects on Schottky diode ideality, barrier height, and reverse breakdown voltage. The device parameters degrade gradually as the number of defects visualized by EBIC increases. The defects were also observed by molten KOH etching and consist mainly of basal-plane and threading dislocations; and dislocation clusters. The EBIC images were compared with conductive atomic force microscopy (CAFM) images of leakage current associated with the dislocations.
Polytypic 3C quantum wells (double Shockley stacking faults) are spontaneously generated during thermal processing of moderately doped 4H-SiC epilayers grown on substrates with heavy n-type doping above ∼3x10 19cm-3. They intersect the wafer surface as straight lines, due to the 8∩ misorientation of the wafer from the c-axis. The electric fields, charge, and conductivity associated with these intersections were studied in detail. These intersections appear as bright lines in secondary electron images. Electrostatic force microscopy (EFM), scanning Kelvin probe microscopy (SKPM), and CAFM also produce clear images of the quantum well intersections. The results are compared to two-dimensional electrostatic simulations.
Gallium nitride epitaxial layers grown on 6H-SiC substrates were studied using the SEM, cathodoluminescence (CL), atomic force microscopy (AFM), and CAFM techniques. These layers exhibit a columnar subgrain structure, which depends on layer thickness, doping, and substrate preparation. These dependencies are investigated and explained.
Folded prismatic stacking faults formed in GaN epitaxial layers grown on 6H-SiC substrates offcut 3.5° towards the [1-210] direction were studied using CL, SEM, AFM and CAFM. Trenches due to the intersections of these faults with the surface are observed by SEM and AFM, and correlated to monochromatic CL imaging to identify luminescence features related to stair-rod dislocations and the associated lattice disconnections.
0794: Materials science