Impurity-free vacancy diffusion (IFVD) induced quantum well intermixing (QWI) of red light diode laser wafer using silicon dioxide (SiO2) encapsulation is explored. The wafer has an active region of two 5 nm-thick GaInP quantum wells and three 8 nm-thick AlGaInP barriers. The 250 nm SiO2 dielectric layer is prepared through electron beam evaporation method. The QWI is induced by rapid thermal annealing for 60 s at different temperatures. Blue shifts and full width at half maximum (FWHM) are obtained through photoluminescence tests. A maximum blue shift of 29.5 nm is obtained at 900 °C annealing temperature and an optimal FWHM of 43 nm by the IFVD-induced QWI is noted at 750 ℃.