An AlxGa1−xN/GaN two-dimensional electron gas structure with x = 0.13 deposited by molecular beam epitaxy on a GaN layer grown by organometallic vapor phase epitaxy on a sapphire substrate was characterized. Hall effect measurements gave a sheet electron concentration of 5.1×1012 cm−2 and a mobility of 1.9 × 104 cm2/Vs at 10 K. Mobility spectrum analysis showed single-carrier transport and negligible parallel conduction at low temperatures. The sheet carrier concentrations determined from Shubnikov-de Haas magnetoresistance oscillations were in good agreement with the Hall data. The electron effective mass was determined to be 0.215±0.006 m0 based on the temperature dependence of the amplitude of Shubnikov-de Haas oscillations. The quantum lifetime was about one-fifth of the transport lifetime of 2.3 × 10−12 s.

We demonstrate a two-step process wherein the lateral epitaxial growth (LEO) of GaN from <100>-oriented stripes is initiated at a low V/III ratio to produce smooth, vertical <110> sidewalls, and where the V/III ratio is subsequently raised in order to increase the lateral growth rate. We find that the formation of the <101> facets is inhibited using this two-step process, and that it is possible to maintain the <110> sidewalls while achieving a large lateral growth rate. The ratio of lateral to vertical growth rate has been increased by up to factor of 2.6 using this approach relative to identical growth conditions without the initiation at low V/III ratio. The effect of lateral growth rate on the structural properties of the stripes is discussed.

An AlxGa1-xN/GaN two-dimensional electron gas structure with x = 0.13 deposited by molecular beam epitaxy on a GaN layer grown by organometallic vapor phase epitaxy on a sapphire substrate was characterized. Hall effect measurements gave a sheet electron concentration of 5.1×1012 cm-2 and a mobility of 1.9 × 104 cm2/Vs at 10 K. Mobility spectrum analysis showed single-carrier transport and negligible parallel conduction at low temperatures. The sheet carrier concentrations determined from Shubnikov-de Haas magnetoresistance oscillations were in good agreement with the Hall data. The electron effective mass was determined to be 0.215±0.006 m0 based on the temperature dependence of the amplitude of Shubnikov-de Haas oscillations. The quantum lifetime was about one-fifth of the transport lifetime of 2.3 × 10-12 s.

Lateral epitaxial overgrowth (LEO) on Si(111) substrates using an AlN buffer layer is demonstrated and characterized using scanning electron microscopy, atomic force microscopy, transmission electron microscopy, x-ray diffraction, photoluminescence spectroscopy, and cathodoluminescence imaging. The <100>-oriented LEO GaN stripes grown on silicon substrates are shown to have similar structural properties as LEO GaN grown on GaN/Al2O3 substrates: the surface topography is characterized by continuous crystallographic steps rather than by steps terminated by screw-component threading dislocations; the density of threading dislocations is <106 cm−2; the LEO regions exhibit crystallographic tilt (0.7-4.7°) relative to the seed region. The AlN buffer thickness affects the stripe morphology and, in turn, the microstructure of the LEO GaN. The issues of chemical compability and thermal expansion mismatch are discussed.

Extended defect reduction at the surface of GaN grown by lateral epitaxial overgrowth (LEO) on large-area GaN/Al2O3 wafers by low pressure MOCVD is demonstrated by atomic force microscopy. The overgrown GaN has a rectangular cross section with smooth (0001) and {110} facets. The density of mixed character threading dislocations at the surface of the LEO GaN is reduced by at least 3-4 orders of magnitude from that of bulk GaN. Dislocation-free GaN surfaces exhibit an anisotropic step structure that is attributed to the orientation dependence of the dangling bond density at the step edges.

We demonstrate a two-step process wherein the lateral epitaxial growth (LEO) of GaN from <1010>-oriented stripes is initiated at a low V/II1 ratio to produce smooth, vertical {1120} sidewalls, and where the V/III ratio is subsequently raised in order to increase the lateral growth rate. We find that the formation of the {1101} facets is inhibited using this two-step process, and that it is possible to maintain the {1120} sidewalls while achieving a large lateral growth rate. The ratio of lateral to vertical growth rate has been increased by up to factor of 2.6 using this approach relative to identical growth conditions without the initiation at low V/III ratio. The effect of lateral growth rate on the structural properties of the stripes is discussed.

We have integrated nanometer-sized ErAs islands in GaAs, resulting in a nano-composite of paramagnetic particles in a semiconductor. Negative giant magnetoresistance of up to four orders of magnitude is observed at low temperatures. We can control the density and size of the ErAs islands, making this an ideal system to investigate transport in magnetic nano-structures.