Abstract :
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.