Search

The power-dependent wavelength shift of photonic coupling resonances of a two-dimensional photonic crystal waveguide by reflection geometry pump-probe measurements are studied. Initial experimental results for further optimisation of the optical-switching process by the use of resonant pumping to either photonic band structure modes or buried quantum wells.

Multiple vertically stacked GaAs/A1xGa1-xAs quantum wire laser diodes were formed using metal organic vapor phase epitaxy on GaAs substrates.

Space charge effects control carrier escape from single quantum well p-i-n structures between the temperatures 80 and 150 K. The parameters x and y have been observed to exhibit thermal activation in this temperature range. The parameters also do not involve carrier populations, since both are the product and quotient of carrier depletion lifetimes, respectively. These findings indicate that it is possible to conduct ab initio calculations of escape lifetimes, tunneling and thermionic emission.

Quantum-well intermixing (QWI) using the impurity-free vacancy disordering (IFVD) technique is a simple and versatile method of controlling the bandgap of the QW after growth, especially in GaAs-A1GaAs structures. The IFVD effects in p-i-n and n-i-p GaAs-A1GaAs QS structures are examined, and it is demonstrated that a variation of the IFVD technique can be used in the control of bandgap energy.

The impact of the dislocation line density caused by the relaxation of strain in GaAs/In(sub x)Ga(sub 1-x)As multiquantum wells where x=0.155-0.23 was examined. There was a strong correlation between the dark line density, seen by cathodoluminescence, before processing of the wafers into photodiode devices, and the subsequent low forward bias dark current densities of the devices. Comparison of the correlation between the reverse bias current density and dark line density, showed that forward bias current density has greater variation.

Analysis of the dc electrical characteristics of AlGaInP/GaAs heterojunction bipolar transistors developed using metalorganic vapor phase epitaxy method shows that the transistors display near-ideal characteristics with the collector and base current ideality factors having unit value. Base bulk recombination current serves as the current-gain controlling process in the transistors. The common-emitter dc current gain value of 4 times 10 to the power of 3 amps per sq cm and a minority electron diffusion length of 1.1 micrometer are the maximum values measured in a transistor with 440 ohms per sq of base sheet resistance.

Photoluminescence and photoreflectance measurements in partially intermixed GaAs/AlGaAs double quantum wells show that increases in annealing temperatures cause the ground-state optical transitions to shift to high energy levels. Integration of the high energy level spectral features to form broad peaks confirms the occurrence of strong intermixing. Variations in the shapes of square wells and the resulting subband convergence at specific energies account for the shift in spectral features.

Capacitance measurements which were a function of bias in GaAs double barrier structures at low and high pressure regimes revealed evidence of electron redistribution. The Fermi level, due to the variation of capacitance with bias, attached to the lowest X level in each well at low bias. At larger bias, the collector well was depleted.

Illumination causes a permanent reduction of dark conductivity in AlGaAs/GaAs heterostructures. Photon energies between 0.7 and 1.15 electrovolts at a temperature of 200 Kelvin produces this reduction. Such a phenomenon occurring in modulation-doped heterostructures reduce the efficiency of such structures. These structures are widely used as basic components in high-speed electronic circuits.

The spectral response of a quantum well solar cell was characterized using a model. The model accurately predicted the spectral response of a wide variety of cell types ranging from conventional p-n junctions in GaAs and AlGa1-xAs to various geometries of quantum solar cell. It was shown that much larger short-circuit currents can be possible with more sophisticated cell structures.

Arrhenius behavior was detected in dc photocurrent variations with temperature and bias from GaAs-AlxGa1-xAs single quantum wells present in p-i-n diodes. An activation energy determined by the field was observed close to the hole well depth. The assumption used here was that the rapidly escaping carriers determine the recombination rate, and that their carriers are light-hole driven processes.

A study on the GaAs-GaAlAs multiple quantum-well hetero-nipi waveguides is presented. It shows the measured optical nonlinearities of Multiple quantum-well hetero-nipi waveguides caused by the proliferation and recombination of photogenerated carriers. It also discusses the nonlinearity at normal waveguide intensity and absorption degree as a function of the optical power and the width of the multiple quantum-well hetero-nipi zone.