Defect Selective Etching of Bulk Hexagonal Boron Nitride (hBN)

Hexagonal boron nitride (hBN) is a wide-bandgap semiconductor material with potential applications in neutron detection, ultraviolet light emission, and nanophotonics. In this study, defect selective etching (DSE) was developed to measure the density of dislocations in hBN single crystals grown using a high temperature Ni-Cr flux method. DSE is a simple, rapid, and effective method for determining dislocation types and density. The objective of this research project is to evaluate the quality of the hBN crystal by determining the dislocation density with DSE and to calculate activation energy of etch rate. Bulk hBN crystals mechanically extracted from the Ni-Cr surface were etched in a molten KOH/NaOH eutectic mixture between 425°C and 525°C. With etching, hexagonal etch pits formed where dislocations intersect the crystal surface. Four types of etch pits were observed and categorized: inversed hexagon pyramid pits, inversed truncated hexagonal pits, a combination of the above, and shallow hexagon prism pits. The typical etch pit density is 4.8×10⁷ cm^-2, and the optimal etching condition was 450°C for 1 minute to produce separated etch pits that could be easily seen by scanning electron microscope. From an Arrhenius plot of the log of the etch rate (as measured from the pit sizes) versus the inverse temperature, the activation energy was estimated to be 17 kJ/mol, which is typical of a kinetically controlled reaction.