Transmission electron microscopy and reflected high-energy electron-diffraction investigation of plastic relaxation in doped and undoped ZnSe/GaAs(001)

We report on reflected high-energy electron-diffraction and transmission electron microscopy plane-view investigation of the dislocation structure in doped and undoped ZnSe/GaAs(001) grown by molecular-beam epitaxy and metal-organic vapor-phase epitaxy. The thicknesses of the investigated layers vary between 60 and 900 nm. Several stages of dislocation formation are found which occur at distinct layer thicknesses. Frank partial dislocations (up to 500 nm), Shockley partial dislocations (between 130 and 400 nm) with a maximum density at 300 nm, and perfect 60° dislocations (above 300 nm) are observed in samples with perfectly smooth surface. The formation of Shockley partial dislocations is strongly anisotropic which might be due to the higher mobility of α-type dislocations. An increased roughness of the growing surface yields a suppression of Shockley partial dislocations and an irregular dislocation network with dislocations inclined to the 〈110〉 directions. A regular dislocation network with straight dislocations is found in Cl-doped samples.