Gas source molecular beam epitaxy of high quality AlxGa1-xN (0 <= x <= 1) on Si(111)

Layers of AlxGa1-xN, with 0 less than or equal to x less than or equal to 1 , were grown on Si(111) substrates by gas source molecular beam epitaxy wit h ammonia. We show that the initial formation of the Si-N-Al interlayer bet ween the Si substrate and the AIN layer, at a growth temperature of 1130-11 90 K, results in very rapid transition to two-dimensional growth mode of AI N. The transition is essential for subsequent growth of high quality GaN, A lxGa1-xN, and AlGaN/GaN superlattices. The undoped GaN layers have a backgr ound electron concentration of (2-3) x 10(16) cm(-3) and mobility up to (80 0 +/- 100) cm(2)/V s, for film thickness similar to 2 mum. The lowest elect ron concentration in AlxGa1-xN,with 0.2 < x < 0.6, similar to (2-3) x 10(16 ) cm(-3) for 0.5-0.7-mum-thick film. Cathodoluminescence and optical reflec tance spectroscopy were used to study optical properties of these AlxGa1-xN layers. We found that the band gap dependence on composition can be descri bed as E-g(x) = 3.42 + 1.21x + 1.5x(2). p-n junctions have been formed on c rack-free layers of GaN with the use of Mg dopant. Light emitting diodes wi th peak emission wavelength at 3.23 eV have been demonstrated. (C) 2001 Ame rican Vacuum Society.