Growth of strained ZnSe layers on GaAs substrates by pulsed laser deposition carried out in an off-axis deposition geometry

We have deposited thin layers of ZnSe on (001) oriented GaAs substrates by pulsed laser deposition at different incident laser fluence (referred to as normal geometry) and in an off-axis geometry where the plasma plume direction is at an angle of ∼ 25° away from the direction of the substrate. The crystalline quality of these layers has been studied by high-resolution X-ray diffraction measurements and Raman scattering. We find that we are in a position to deposit pseudomorphic strained layers of ZnSe on GaAs in the off-axis deposition geometry when the ZnSe layer thickness is less than the critical thickness of ZnSe on GaAs i.e. 150 nm. Secondary ion mass spectroscopy, scanning electron microscopy, photoluminescence and electrical transport measurements have also been carried out in all the ZnSe layers and the results of all the above characterizations have been compared for the normal geometry and the off-axis geometry of deposition. All the results indicate that the ZnSe layers deposited in the off-axis geometry have better crystalline quality and an improved interface as compared to the ones deposited in the normal geometry. We attribute this improvement in the overall quality of the ZnSe layers in the off-axis geometry to the reduction in the average energy of the plume particles that reach the GaAs substrate in the off-axis geometry.