Multiple Transit Region Gunn Diode

The thesis examines the DC and RF performance of double transit region Gunn diodes (DTGD) grown by molecular beam epitaxy (MBE) for possible application in the automotive industry. DC and RF measurements are described and evidence prcscntcd to support the contention that coherent domain nucleation is occurring in the double transit devices. A single transit, digitally doped Gunn diode grown by metalorganic vapour phase epitaxy (MOVPE) was also investigated and is shown to be able to produce coherent RF oscillations. Monte Carlo simulations showed no adverse effects from the digitally doped region to the formation of GUlln domain. This is further supported using a simple model to show the effects of a digital doping region on the electric field profile. Knowledge of the temperature dependence of gallium arsenide ionisation coefficients would provide a better understanding of the breakdown mechanism in DTGDs. DTGDs are vulnerable to breakdown due to thermal stress, which is further exacerbated by the impact ionisation process. These coefficients can be inferred from multiplication and excess noise factor measurements. A noise measurements system is described, and is shown to be able to measure from a photoccurent of 0.22 llA onwards, the lowest reported so far. The system was modified using the bootstrap technique, and is shown to be able to measure devices of differing capacitance and can be adapted for measurements in a cryostat, thus allowing the temperature characterisation of excess noise factors to be made.EThOS - Electronic Theses Online ServiceGBUnited Kingdo