Study of stress/strain and structural defects at Cu/GaN interface

Cu films with different thicknesses were deposited on GaN wafers with different doping states. Several techniques were employed to study element, dislocation density and stress/strain at Cu/GaN interfaces. The stress decreased with the increase of Cu thickness in the three undoped GaN layers. In the undoped GaN, screw dislocations with a Burger's vector of 1/2< 0001 > and edge dislocations with a Burger's vector of 1/3<1120 > were produced. The SFs in the Mg doped GaN were type I1 basal-plane SFs with a ABABCBC stacking in the [0002] direction and a total displacement vector 1/6< 2023 >. The 50 nm Cu/Si-doped GaN had the biggest stress (0.48 GPa) and the largest screw dislocation density (7.01 x 107cm (-2)) among the five Cu/GaN samples. Dislocation movement and stress relaxation were restrained by Si atoms. In the Si-doped GaN, abundant positive and negative strain ex-tremes in [0002] direction far from the border line were due to the generation of dislocations. One reason for the existence of interfacial stress was the difference of thermal expansion coefficients between Cu and GaN. The Cu/ GaN interfaces were mainly semi-coherent. The lattice mismatch between Cu and GaN did not generate abundant dislocations near the interface line and thus the strain was preserved.