X-ray investigations of GaP:N,S epitaxial layers applied in light emitting diodes

Abstract

GaP/GaP epitaxial layers doped with nitrogen and sulphur, prepared by VPE CVD method, were studied using Bond diffractometry and double crystal spectrometry. A correlation between type and concentration of dopants and temperature dependence of the lattice constants was found. The values of thermal expansion coefficient (TEC) for GaP:S suggest that the defect structure of GaP:S is similar to that of nonstoichiometric GaP crystal at lower temperatures. The presence of the N dopant does not cause any changes of TEC over the whole investigated concentration range while the lattice constant, the misfit factor and the density of misfit dislocations are strongly dependent on the N doping level. The dependence of the misfit factor on the N concentration becomes nonlinear at a high doping level. For GaP : N,S we suggest the existence of a different type of defects than for the case of undoped nonstoichiometric layers. The explanation of the degradation in photoluminencence is discussed on the basis of the results obtained.