Optoelectronic Devices Exploiting the Gunn Effect

[摘要] Semiconductor integrated Electro-Optic modulators which exploit the Gunn effect, have been produced in gallium arsenide. Both vertical and planar diode structures incorporating a form of optical waveguide were investigated. Optical, electrical, and Electro-Optical, design calculations were carried out for each of the proposed device designs. The vertical Gunn diode structures incorporated either a slab or a rib waveguide, whereas the planar Gunn diode structure incorporated a photoelastic waveguide. Various methods, such as the Effective Index Method, the Variational Analysis technique, and the Finite Difference method, were used to assess the propagation characteristics of the rib guide structures. The results of this assessment provided a comparison between the different techniques available, and revealed the advantages and disadvantages of each method. The propagation characteristics of the photoelastic waveguides were analysed by the Finite Difference method. A computer program was developed to analyse the electrical characteristics of the integrated devices. The program solves Poisson's equation and the Current Continuity equation under the conditions for a stable propagating dipole Gunn domain, for: an approximate velocity-field characteristic, v(E), and field independent diffusion coefficient, D; an analytical v(E) characteristic and field independent D; or an analytical v(E) and a field dependent D. The program supplies an estimate of the maximum electric field within the domain, and also of the domain length. The results for the three possible analysis situations were compared. The perturbations induced in the optical guiding characteristics, at above bandgap optical wavelengths, due to the presence of a domain, have been studied. A knowledge of the characteristics of the domain, as it propagates through the device, leads to an estimate of the magnitude of the induced optical changes, eg. in the refractive index, or in the optical absorption. A measure of the Electro-Optic interaction between the propagating domain and the guided optical wave was therefore obtained. In order to test the electrical characteristics of the vertical devices, spot contact diodes, varying in diameter from 20mum to 90mum. were fabricated. Also, for the purpose of testing both the optical and Electro-Optical properties of the vertical devices, rib guides, varying in width from 4mum to 15mum, were fabricated by optical photolithography and dry etching techniques. Unique devices incorporating a vertical Gunn diode and a rib waveguide were consequently designed and fabricated, and assessed for their modulation depth. Optical modulation, at a frequency of 24GHz, was observed in the vertical diode structure. While at a wavelength of 1.15mum modulation was solely due to the Linear Electro-Optic effect, at a wavelength of 905nm modulation was seen to be due to both the Linear Electro-Optic effect, and the Electro-Absorption effect. Estimated values of the observed Electro-Optic coefficient, r41, at wavelengths of 1.15mum and 905nm were obtained, along with an estimate of the observed Electro-Absorption coefficient, alpha, at 905nm.

[发布机构] University:University of Glasgow

[关键词] Electrical engineering, Condensed matter physics