Interfacial dislocations in TiN/GaN thin films

Thin films of stoichiometric cubic TiN for ohmic contact formation are dire ctly deposited, by rf magnetron sputtering at room temperature, on (0001) s urfaces of GaN epilayers grown on c-plane sapphire, Chemical etching and in situ dry etching of the free GaN surface allows an epitaxial growth of the deposited TiN films as revealed by high resolution electron microscopy obs ervations. Taking into account the experimentally determined orientation re lationship of the two structures, (0001) GaN parallel to (111) TiN, [1(1) o ver bar 20] GaN parallel to [1(1) over bar 0] TiN, families of dislocations are expected in the interface plane to accommodate the misfit (similar to5 .8%) with a spacing of 4.5 nm. The mathematical formulation of the circuit mapping technique is used to analyse the misfit dislocation content on HREM images since it allows the exact determination of the Burgers vector. This gives 1/2[0(0)over bar 1>] TiN or 1/3[1(2) over bar 10] GaN. A demistep of height c(GaN)/2 is observed at the TiN/GaN interface interface and from th ere a (1(1) over bar 2) twin emanates into the TiN layer. It appears that s uch demisteps have an important role in mediating the columnar growth of th e TiN material.