Surface recombination is an important characteristic of an optoelectronic material. Although surface recombination is a limiting factor for very small devices it has not been studied intensively. We have investigated surface recombination velocity on the exposed surfaces of the AlGaN, InGaAs, and InGaAlP material systems by using absolute photoluminescence quantum efficiency measurements. Two of these three material systems have low enough surface recombination velocity to be usable in nanoscale photonic crystal light-emitting diodes.

We describe how quantum information may be transferred from photon polarization to electron spin in a semiconductor device. The transfer of quantum information relies on selection rules for optical transitions, such that two superposed photon polarizations excite two superposed spin states. Entanglement of the electron spin state with the spin state of the remaining hole is prevented by using a single, non-degenerate initial valence band. The degeneracy of the valence band is lifted by the combination of strain and a static magnetic field. We give a detailed description of a semiconductor structure that transfers photon polarization to electron spin coherently, and allows electron spins to be stored and to be made available for quantum information processing.

Antenna arrays on conventional ground planes present different deficiencies. For compact platforms, the propagation of RF surface currents results in lost power, radiation from the edges and other discontinuities. It also contributes to the strong coupling and causes blind angles and multipath interference. By building radio isolation into the ground plane of phased array antenna structures, it is possible to reduce these different disturbances. This isolation may be achieved by using corrugated surfaces. In this case, DC currents are conducted but not AC currents. Based on the previous work done on PBG structure, a new kind of surface called High Impedance Ground Plane can be used. This kind of ground plane presents the same characteristics are corrugated surfaces in all the directions. Moreover the thickness must no longer be one fourth of the wavelength and can be even much smaller. These ground planes have been applied antenna array in order to reduce the disturbances created on compact platforms. Phase measurements of two-dipole array clearly shows this reduction.

We apply the full power of modern electronic band structure engineering and\nepitaxial heterostructures to design a transistor that can sense and control a\nsingle donor electron spin. Spin resonance transistors may form the\ntechnological basis for quantum information processing. One and two qubit\noperations are performed by applying a gate bias. The bias electric field pulls\nthe electron wave function away from the dopant ion into layers of different\nalloy composition. Owing to the variation of the g-factor (Si:g=1.995,\nGe:g=1.563), this displacement changes the spin Zeeman energy, allowing\nsingle-qubit operations. By displacing the electron even further, the overlap\nwith neighboring qubits is affected, which allows two-qubit operations. Certain\nSilicon-Germanium alloys allow a qubit spacing as large as 200 nm, which is\nwell within the capabilities of current lithographic techniques. We discuss\nmanufacturing limitations and issues regarding scaling up to a large size\ncomputer.\n

Double-heterostructure GaAs/GaAlAs light-emitting diodes (LEDs) have been fabricated with the emitter regions beryllium doped to 2×1019 and 7×1019 cm−3. The 7×1019 cm−3 doped emitters have an internal quantum efficiency of 10% and an optical modulation bandwidth of 1.7 GHz. The steady-state optical output power versus the input current shows an external efficiency of 2.5 μW/mA. The 2×1019 cm−3 emitters have internal quantum efficiencies as high as 80%, but a reduced cutoff frequency. The external quantum efficiency reaches 10 μW/mA. These high-speed LEDs are produced by reducing the radiative lifetime to 100–250 ps without significantly degrading internal quantum efficiency. The current results on heavily beryllium-doped LEDs exhibit, to the best of our knowledge, the highest external efficiencies to date for such high doping and efficiencies close to that observed for lower-doped LEDs.

The bandwidth demanded for Internet traffic has been constantly growing in response to more bandwidth hungry applications such as high-resolution motion picture transmission. An optical fiber has about 10 tera-bits per second (Tbps) available bandwidth and is the ideal medium to link tomorrow's bandwidth hungry applications. The equipment purchased under this grant has permitted UCLA to purchase a number of broad-band optical components, including especially some unique code division multiplexing filters that permitted us to demonstrate optical code division multiplexing of a multi-wavelength signal source.

Antenna arrays on conventional ground planes present different deficiencies. For compact platforms, the propagation of RF surface currents results in lost power, radiation from the edges and other discontinuities. It also contributes to the strong coupling and causes blind angles and multipath interference. By building radio isolation into the ground plane of phased array antenna structures, it is possible to reduce these different disturbances. This isolation may be achieved by using corrugated surfaces. In this case, DC currents are conducted but not AC currents. Based on the previous work done on PBG structure, a new kind of surface called High Impedance Ground Plane can be used. This kind of ground plane presents the same characteristics are corrugated surfaces in all the directions. Moreover the thickness must no longer be one fourth of the wavelength and can be even much smaller. These ground planes have been applied antenna array in order to reduce the disturbances created on compact platforms. Phase measurements of two-dipole array clearly shows this reduction.

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped circuit elements, and distributed in a 2D lattice. Although it is made of continuous metal, and conducts DC currents, it does not conduct AC currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves. Furthermore, image currents induced in the surface are not phase reversed as they are on a flat metal surface.