Gas source molecular beam epitaxy of high quality AlGaN on Si and sapphire (original) (raw)

Layers of Al x Ga 1Ϫx N, with 0рxр1, were grown on Si͑111͒ substrates by gas source molecular beam epitaxy with ammonia. We show that the initial formation of the SiN -Al interlayer between the Si substrate and the AlN layer, at a growth temperature of 1130-1190 K, results in very rapid transition to two-dimensional growth mode of AlN. The transition is essential for subsequent growth of high quality GaN, Al x Ga 1Ϫx N, and AlGaN/GaN superlattices. The undoped GaN layers have a background electron concentration of (2-3)ϫ10 16 cm Ϫ3 and mobility up to ͑800Ϯ100͒ cm 2 /V s, for film thickness ϳ2 m. The lowest electron concentration in Al x Ga 1Ϫx N, with 0.2ϽxϽ0.6, was ϳ(2-3)ϫ10 16 cm Ϫ3 for 0.5-0.7-m-thick film. Cathodoluminescence and optical reflectance spectroscopy were used to study optical properties of these Al x Ga 1Ϫx N layers. We found that the band gap dependence on composition can be described as E g (x)ϭ3.42ϩ1.21xϩ1.5x 2. p-n junctions have been formed on crack-free layers of GaN with the use of Mg dopant. Light emitting diodes with peak emission wavelength at 3.23 eV have been demonstrated.