published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

This dissertation investigates challenges associated with optics in the 10-500 wavelength size regime. For the visible spectrum, this size range (5-250um) is classified as micro-optics, but is set apart from other size ranges by a noticeable lack of suitable simulation and metrology tools. Optics of this size are gaining popularity in applications such as solid immersion lenses (SIL) and laser beam shaping, but require more research into simulation, testing, fabrication, and assembly in order to be easily integrated into commercial applications.A survey of previous work on SILs and micro-optics simulation/testing is given, including past work with gallium phosphide (GaP) microlenses. A new SIL aberration treatment is described using spherical-parent 3rd order aberrations. Agreement is shown with previous work, and the lack of hemisphere approximations gives a broader understanding of aberrations for varying SIL thicknesses. Results show that aberration reduces with lens radius, but thickness tolerances become tighter as dimensions shrink. A study of GaP intrinsic birefringence and the theoretical impact on the induced polarization signal is also given.A survey of beam propagation simulators is given and a sequential piece-wise diffraction (SPWD) simulator is developed for arbitrary optical systems that overcomes the difficulties of simulation in the 10-500 wavelength size regime. A discussion of a future extension to the work to determine reflected and transmitted field amplitudes with a non-sequential method is presented with specific discussion on the challenges of electric field surface transfer.The design and operation of a micro-interferometer is discussed and testing results from the first sub-100um diameter GaP SILs are shown. A novel method for determining the shape profile of aspheric surfaces using information from annular fringes is presented. Theoretical beam shaping applications for micro GaP lenses is also discussed with results using the SPWD method. Experimental results are also shown for a 1x1x0.3mm beam shaper package that images a laser diode beam to an approximate size of 60um at a working distance of 4mm.Finally, designs and experimental results are shown for the integration of GaP micro-optics into conventional systems as SILs or beam-shaping elements including methods and equipment for lapping and polishing GaP.

No description available.

GaN RF switches are widely used in today’s communication systems. With digital communications getting more and more popular nowadays, the need for improving the performance of involved RF switches is inevitable. Designing low ON-state resistance GaN switches are exceedingly important to improve the switch insertion loss, isolation and power loss. Moreover, considerations need to be taken into account to improve the switching speed of the involved GaN HEMTs. In this dissertation, a new GaN HEMT structure called “Tunnel MOS Heterostructure FET (TMOSHFET)” is introduced which has lower ON-state resistance and faster switching speed compared to conventional AlGaN/GaN HEMTs. In the switch ON process, the channel of this device is charged up by electron tunneling from a layer underneath the channel as opposed to typical AlGaN/GaN HEMTs in which electron injection from the source is charging up the channel. The tunneling nature of this process together with the shorter travel distance of electrons in TMOSHFET provide for a faster switching speed. In order to understand the tunneling mechanisms in TMOSHFET, the fabrication of AlGaN/GaN Schottky Barrier Diodes (SBDs) with various AlGaN thicknesses is demonstrated on Si (111) substrate. The impacts of SF6 dry etching on the trap density and trap state energy of AlGaN surface are investigated using the GP/w- w method. Various tunneling mechanisms at different biases are then characterized in samples and compared with each other. To improve the source and drain resistances in TMOSHFET, a model is generated to optimize the 2DEG density and electric field in AlGaN/GaN heterostructure based on Al mole fraction, AlGaN thickness and the thickness of SiN passivation layer and it is experimentally verified by non-contact Hall 2DEG density measurements. The spontaneous and piezoelectric polarizations together with strain relaxation have been implemented into the model, taking into account the annealing effects. From the experimental data on obtained parameters, the operation and device parameterization of the TMOSHFET is outlined and design considerations to improve the device R_(ON)-V_(BR) figure of merit are discussed.

No description available.

No description available.