Structural and electrical properties of ZnSe laser diodes optimized by transmission electron microscopy, reflection high energy electron diffraction, X-ray diffraction and C-V profiling

Abstract

The properties of ZnSe and ZnS x Se 1− x epilayers grown by molecular beam epitaxy deposited either directly on GaAs substrates or on GaAs buffer layers are compared with each other. The superior structural quality of the latter one is confirmed by reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Under optimized conditions nearly lattice matched ZnS x Se 1− x epilayers with full width at half maximum (FWHM) values down to 23 arc sec were achieved. The dependence on the type of dopant of the dislocation density and the depth of penetration related to the GaAs/ZnSe interface is discussed by cross-sectional TEM images. At the GaAs:Si/ZnSe:Cl interface a high-impedance layer was found and investigated by C−V profiling (CVP) and Van der Pauw (VdP) measurements for different initial growth conditions and for various ZnSe carrier concentrations. In addition the dislocations at the ZnSe/ZnS x Se 1− x interfaces were studied by TEM. Finally, we were able to improve the structural quality of the active area of blue green laser diodes by a special design of layer thicknesses.