Substrate induced strain effects in high purity InP epilayers

Sharp line excitonic photoluminescence (PL) transitions in high purity GaAs or InP can exhibit linewidths of 50 μeV or less. In epitaxial material, such sharp transitions are very sensitive to residual strains caused by substrate effects. The effect of small changes in the substrate lattice constant on the donor bound exciton transitions in high purity nominally undoped InP epilayers was investigated. High purity InP epilayers were grown on various Fe-, As-, and S-doped (001) oriented substrates with differing degrees of lattice mismatch. For sufficiently large lattice mismatch, the resulting biaxial strain could be directly observed by high resolution X-ray diffraction. In principle, however the PL technique is much more sensitive. The techniques are complementary however, since they both probe different physical regions of the sample, and this can be important when inhomogeneous strain is present. The results provide evidence for existing j-j coupling models of the donor bound exciton in InP