Vapor-liquid-solid epitaxy process has been developed to synthesize high quality semiconductor nanowire arrays. The nanowires generally are single crystalline and have diameters of 10-200 nm and aspect ratios of 10-100. There is much current interest in the optical properties of these semiconductor nanowires, as the cylindrical geometry and strong two-dimensional confinement of electrons, holes, and photons makes them particularly attractive as potential building blocks for nanoscale electronics and optoelectronics devices. We recently reported the first study of laser action and nonlinear optical mixing in individual zinc oxide (ZnO) and GaN nanowires, demonstrating the potential of these structures as room temperature nanoscopic coherent light sources and frequency converters. These efforts further led to the demonstration of ZnO nanoribbon laser as well as GaN-based quantum wire lasers.
Quasi one-dimensional nanostructures are unique probes of cavity quantum electrodynamics because they are capable of exhibiting photonic and/or electronic confinement in two dimensions. The near-cylindrical geometry and sharp end facets of zinc oxide (ZnO) nanowires enable the realization of active nanoscale optical cavities that exhibit UV/blue photoluminescence (PL) waveguiding and lasing action at room temperature under appropriate optical pumping conditions. Study of individual nanostructures is crucial for isolating geometry-dependent effects, and here it is achieved through both near- and far-field microscopies. The polarization of the emitted PL or lasing from individual nanostructures characterizes the coupling of the spontaneous emission to cavity modes, depending both on the wavelength of the emitted light and the nature of the emitting species (i.e., excitons and intrinsic defects in various charge states). In addition, the spectral evolution of the lasing/PL as a function of the pump fluence indicates both exciton and electron-hole plasma dynamics. Variations of size, geometry, and material on the prototypical cylindrical ZnO nanowire lead to further observation of unique photonic and/or carrier confinement effects in novel nanostructures.
One-dimensional nanostructures hold the promise of becoming critical elements for next generation nanoscale electronic and photonic devices. While significant efforts have been devoted to the development of nanotube or nanowire based transistors, little has been done on their photonic counterpart. Here we summarize our recent efforts on one-dimensional crystalline nanostructures, in particular, the zinc oxide (ZnO) nanowires grown on a sapphire substrate. ZnO is a wide bandgap (3.37 eV) compound semiconductor that is especially suitable for blue and ultraviolet (UV) optoelectronic applications. Room-temperature optical energy conversion and stimulated UV light emission from ZnO nanowires are emphasized, along with a discussion of potential applications of nanoscale lasers.
A novel vapor-liquid-solid epitaxy (VLSE) process has been developed to synthesize high-density semiconductor nanowire arrays. The nanowires generally are single crystalline and have diameters of 10-200 nm and aspect ratios of 10-100. The areal density of the array can be readily approach 1010 cm-2. Results based on Si and ZnO nanowire systems are reported here.
The carrier lifetime, mobility, and drift velocity are the important parameters of photoconductors. Normally, several independent tests such as conductivity, Hall effect, and decay of photoconductivity, etc., are used to measure these parameters separately. Pc decay sometimes becomes size limited, however, quite a lot of device configurations have small dimensions. Particularly, at low temperature pc decay may be nonexponential, that leads to some errors in the measurement. We applied the photo-mixing technique to measure the transport parameters. When a multimode laser beam is incident upon the photoconductor sample, the carrier generation rate of the sample will contain frequency components made up of the sum, difference, harmonics, and dc components of the incident frequencies as a bias is applied to the sample. We have generalized the theory of photo-mixing for the case of an unmode-locked multimode laser light incident upon a semiconductor. The results yield the photocurrent as a sum of a dc and an ac part.
Conference Committee Involvement (3)
Nanostructure Integration Techniques for Manufacturable Devices, Circuits, and Systems: Interfaces, Interconnects, and Nanosystems
23 October 2005 | Boston, MA, United States
Complex Mediums V: Light and Complexity
4 August 2004 | Denver, Colorado, United States
Complex Mediums IV: Beyond Linear Isotropic Dielectrics
4 August 2003 | San Diego, California, United States
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