Investigation of graded InxGa1−xP buffer by Raman scattering method

Abstract

The compositional changes of InxGa1−xP graded buffer inserted between GaP substrate and subsequently grown In0.36Ga0.64P homojunction LED structure were investigated by Raman spectroscopy. The indium content of InxGa1−xP interlayers was increased in eight steps with thickness of 300nm and constant compositional change ΔxIn between the steps. The properties of InxGa1−xP graded buffer along the structure cross-section have been studied by Raman back scattering method and the changes in GaP LO and TO phonons were investigated. Raman shift of 13cm−1 in GaP-like LO1 phonon was measured on beveled [100]surface for compositional change of InxGa1−xP layer in the range of 0<xIn<0.32. The measurements on the cleaved edge of the sample in [011] direction revealed a strong TO phonon at 366cm−1 and weak LO phonon peak at 405cm−1 in GaP substrate. By reaching the graded InxGa1−xP region the intensity of TO phonon decreases and appearance of considerable TO1 phonon shift up to 350cm−1 for In content xIn=0.16was observed. For upper graded layers with xIn from 0.16 to 0.24 the position of GaP-like TO1 was constant and can be ascribed to relaxation of lattice mismatched thin InxGa1−xP graded upper layers in the structure.