RAMAN-STUDY OF THE NITRIDED GAAS THIN-LAYERS

The properties of the nitrided GaAs thin layers have been investigated by using Raman spectroscopy. The nitrided GaAs thin layers were prepa red by irradiating electron-cyclotron resonance (ECR) nitrogen plasma at various substrate temperatures from room temperature to 600 degrees C. Raman measurements have shown that not only are the longitudinal-o ptical (LO) and transverse-optical (TO) phonon modes shifted down in f requency, but also the LO-TO splitting decreases as the nitridation te mperature increases. It is believed that the origin of the frequency s hifts is the changes in effective charge and the strain effects due to defects included in the nitrided GaAs thin layers. The bandwidth for the LO-phonon mode for the sample nitrided at 600 degrees C is the lar gest, which means that the nitridation at high temperature causes more disordered surface structure. We have estimated several physical para meters in the nitrided GaAs thin layers, such as the fraction of defec ts, the strains, and the correlation length from the measured Raman sp ectra. [S0163-1829(98)05719-1].