Gas source molecular beam epitaxy of high quality AlxGa1−xN (0⩽x⩽1) on Si(111)

Layers of ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N},$ with $\text{0⩽x⩽1,}$ were grown on Si(111) substrates by gas source molecular beam epitaxy with ammonia. We show that the initial formation of the Si–N–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, ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N},$ and AlGaN/GaN superlattices. The undoped GaN layers have a background electron concentration of ${\text{(2–3)×10}}^{16}\hspace{0.5em}{\mathrm{cm}}^{\mathrm{-3}}$ and mobility up to (800±100) cm²/V s, for film thickness ∼2 μm. The lowest electron concentration in ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N},$ with $\text{0.2<x<0.6,}$ was ${\text{∼(2–3)×10}}^{16}\hspace{0.5em}{\mathrm{cm}}^{\mathrm{-3}}$ for 0.5–0.7-μm-thick film. Cathodoluminescence and optical reflectance spectroscopy were used to study optical properties of these ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ layers. We found that the band gap dependence on composition can be described as $E_g{\text{(x)=3.42+1.21x+1.5x}}^2.$ 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.