Dislocation-enhanced diffusion in heteroepitaxial GaInP/InP:S

We characterize sulfur diffusion from heavily doped (n~10¹⁹ cm^-3) InP:S (001) substrates into nominally undoped Ga _xIn_1-xP (0⩽x⩽0.2) epilayers during growth by low-pressure MOCVD. The composition, relaxation and dislocation density of the samples have been studied by high resolution X-ray diffraction and in-depth doping profiles have been obtained using a C-V electrochemical profiler. The analysis of these profiles shows that as the Ga content of these thick (~1 μm) samples is increased, a rapid enhancement of the sulfur diffusion from the substrate is observed. This enhancement is a consequence of the generation of an increasing number of dislocations initially caused by the mismatch. The structural defects act as pipes inside which the diffusion coefficient (D_d) of sulfur atoms is calculated to be 6 orders of magnitude higher than that of the undislocated material (D_l). Value of D_l~2×10^-17 cm²/s at the growth temperature of 640°C have been deduced