Abstract
We measured photoreflectance spectrum characteristics of InGaAs grown by MBE method on semi-insulating GaAs. The PR signal splitting of substate and epilayer was observed. The band gap energy was about 1.40 eV. It make to 8 meV difference when it is fitted by Pan's equation. The reason is stress on the interface, which is due to lattice mismatch between epilayer and substate . We became to know that reason influence crystalline on growing sample. In InGaAs epilayer, temperature dependency is low. The efficiency of photo absorption is high and activate over 200K. In this case when it is annealed at $400^{\circ}C$ below growing temperature, PR signal splitting is remarkable and crystalline is inhanced.