MEASUREMENTS BY X-RAY TOPOGRAPHY OF THE CRITICAL THICKNESS OF ZNSE GROWN ON GAAS

The initial stages of relaxation in ZnSe layers grown by molecular bea m epitaxy on vertical-gradient-freeze Bridgeman GaAs substrates have b een studied using synchrotron-generated X-ray topography. We have dete cted the formation of the very first strain-relieving misfit dislocati ons in the ZnSe layers in a layer of thickness 100 nm while no disloca tions are found in a layer of 95 nm thickness. The critical thickness for this material system is therefore estimated to be around 97 nm, wh ich is markedly lower than the widely accepted value of 150 nm. These data are used to infer the maximum critical thickness of ZnCdSe quantu m wells possible in II-VI laser diodes. (C) 1998 Elsevier Science B.V. All rights reserved.