CHARGE-TRANSFER BETWEEN IN AND GA IN INGAAS-BASED ALLOYS

It was suggested that the phonon anomalies observed in the InxGa1-xAs system arise from coupling between the GaAs and the InAs-like modes, c ausing charge transfer from the In to the Ga ion. It is shown here tha t the above conclusion is nicely demonstrated in the quaternary alloy InyAlxGa1-x-yAs lattice matched to InP. While the AlAs-like mode behav es regularly when varying x, similarly to that mode in the AlxGa1-xAs system, the GaAs and the InAs-like modes show marked differences in in tensity and in their oscillator strengths. This is particularly impres sive, since the In content is held fix. It is claimed that larger GaAs ionicity in the alloy is the main contributor to the charge transfer, particularly at large Ga content.