We discuss the relationship between microstructure and luminescence efficiency for heteroepitaxial films of GaN grown on c-axis sapphire substrates by metalorganic chemical-vapor deposition. We directly characterize the correlation between threading dislocations as observed by transmission electron microscopy, surface morphology as observed by atomic force microscopy, and wavelength-resolved cathodoluminescence imaging. We show that the inhomogeneity in the luminescence intensity of these films near band edge can be accounted for by a simple model where nonradiative recombination at threading dislocations causes a deficiency of minority carriers and results in dark regions of the epilayer. An upper bound for average diffusion length is estimated to be 250 nm.

We report an experimental demonstration of an ultracompact biochemical sensor based on a two-dimensional photonic crystal microcavity. The microcavity, fabricated on a silicon-on-insulator substrate, is designed to have a resonant wavelength (lambda) near 1.5 microm. The transmission spectrum of the sensor is measured with different ambient refractive indices ranging from n = 1.0 to n = 1.5. From observation of the shift in resonant wavelength, a change in ambient refractive index of delta(n) = 0.002 is readily apparent. The correspondence between absolute refractive index and resonant wavelength agrees with numerical calculation to within 4% accuracy. The evaporation of water in a 5% glycerol mixture is also used to demonstrate the capability for in situ time-resolved sensing.

The dislocation arrangements in gallium nitride (GaN) films prepared by lateral epitaxial overgrowth (LEO) have been studied by cathodoluminescence mapping and transmission electron microscopy. A very low density of electrically active defects (<10−6 cm−2) in the laterally overgrown material is observed. Individual electrically active defects have been observed that propagate laterally from the line of stripe coalescence into the overgrown material. Additionally, by mapping wavelength-resolved luminescence in an InGaN quantum well grown on top of the overgrown material, these defects are shown to be limited to the underlying material and do not propagate normal to the surface, as in other GaN films. In the seed region, threading dislocation image widths are seen to be nearly identical in the quantum well and the underlying GaN, indicating a comparable upper limit (∼200 nm) for minority carrier diffusion length in InGaN and GaN. Additionally, it is shown that, through processing variation, these lateral defects can be avoided in LEO films and that wavelength-resolved cathodoluminescence is an excellent large-area method for rapidly and quantitatively observing variations in process development.

The heteroepitaxial growth of III-V compound semiconductors on Si would enable the integration of high-performance III-V materials with Si technology. We report epitaxial growth on (111)-oriented Si surfaces of highly aligned, single crystalline InP nanowires by chemical vapor deposition catalyzed by Au. We demonstrate laterally oriented InP nanowires bridging between vertical (111) Si surfaces formed by anisotropically etching a (110)-oriented Si substrate or the top Si layer of a silicon-on-insulator wafer. This method of connecting nanowires offers a facile way of integrating nanoscale III-V optoelectronic and photonic devices with Si.

1999). Structural and optical properties of GaN laterally overgrown on Si(111) by metalorganic chemical vapor deposition using an AlN buffer layer .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 <1100>-oriented LEO GaN stripes grown on silicon substrates are shown to have similar structural properties as LEO GaN grown on GaN/Al 2 O 3 substrates: the surface topography is characterized by continuous crystallographic steps rather than by steps terminated by screwcomponent threading dislocations; the density of threading dislocations is <10 6 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.