Ⅲ-Ⅴ nitrides are promising direct transition semiconductor materials used for the application in both optoelectronic and electronic devices. Recently Si is viewed as one of the most promising substrates for the GaN epitaxy because of its high quality

large size

low cost and a well-known existing device technology. However

due to the large difference in lattice constant and thermal expansion coefficient

it is rather difficult to grow highquality single crystalline GaN on Si. Hexagonal GaN layers were grown on Si(111) substrates using high-temperature-grown AlN as buffer (layer) by a vertical MOCVD reactor. After the Si(111) substrate was annealed under H

2

ambient at 1 100℃ for 10 min to clean the surface

a thin AlN buffer layer was deposited at 1 060℃ for 8 min

about 20 nm thick. After AlN growth

GaN with excessive Ga HT-GaN layer and with LT-GaN layer were grown at (1060℃)

(about) 0.6 μm thick.The growth and characteristics of the GaN layers were investigated by using X-ray diffraction(DCXRD)

scanning electron microscope(SEM)

atomic force microscope(AFM) and room temperature photoluminescence spectrum(RT PL). These results indicate that the crystalline quality and morphology of GaN with excessive Ga HT-GaN layer is much better than that with LT-GaN layer. High-resolution X-ray diffraction exhibited a GaN(0002) and (10

1

-2) spectra with full-width at half-maximum(FWHM) as low as 698 and 842 acrsec. A very strong band-edge emission peak at 361 nm(3.4 eV) is observed

with a FWHM of only 44.6 meV and no yellow (luminescence) exists.