Correlation between the infrared reflectance and microstructure of thin gallium nitride films grown on silicon substrates

Thin gallium nitride (GaN) films grown on silicon substrates are studied by infrared reflectance (IR) spectroscopy and scanning electron microscopy (SEM). For different samples, a variation of the reststrahlen band is observed. Through a theoretical analysis using a proposed three-component effective medium model, this variation of IR spectra is attributed to the polycrystalline nature of GaN grown on silicon, as revealed by SEM measurements. A correlation between the shape of the reststrahlen band and the microstructure of the GaN film is found. It shows that IR can offer a versatile means to characterize the quality of GaN on silicon.