This work is devoted to a mass spectrometric study of volatile component loss and in situ measurement of the resistance of metallized GaAs and GaP samples during heat treatment. Arsenic losses during heat treatment have been determined quantitatively with a quadrupole mass spectrometer. A relation was found between the arsenic loss and the specific contact resistance of the metallized sample. The associated activation energy was found to be similar to the case of thin film diffusion.

Volatile component loss and contact resistance of metals on GaAs and GaP during annealing

Theoretical device simulations and experimental results are presented to show that the origin of an empirical relationship between the bias voltage and transit frequency of CW longitudinal Gunn-effect devices lies in a combination of space-charge propagation effects and thermal effects. The bias current-voltage relationship is considerably altered by the particular details of the device doping profile through average accumulation or depletion effects, as well as by the temperature.

The Vf T relation of CW Gunn-effect devices

Heterojunction planar Gunn devices were first demonstrated by Khalid et al in 2007. This new design of Gunn device, or transferred electron device, was based on the well-established material system of GaAs as the oscillation media. The design did not only breakthrough the frequency record of GaAs for conventional Gunn devices, but also has several advantages over conventional Gunn devices, such as the possibility of making multiple oscillators on a single chip and compatibility with monolithic integrated circuits. However, these devices faced the challenge of producing high enough RF power for practical applications and circuit technology for integration.
This thesis describes systematic work on the design and characterisations of planar Gunn diodes and the associated millimetre-wave circuits for RF signal power enhancement. Focus has been put on improving the design of planar Gunn diodes and developing high performance integrated millimetre-wave circuits for combining multiple Gunn diodes. 
Improvement of device design has been proved to be one of the key methods to increase the signal power. By introducing additional δ-doping layers, electron concentration in the channel increases and better Gunn domain formation is achieved, therefore higher RF power and frequency are produced. Combining multiple channels in the vertical direction within devices is another effective way to increase the output signal power as well as DC-to-RF conversion efficiency. In addition, an alternative material system, i.e. In0.23Ga0.77As, has also been studied for this purpose. 
Planar passive components, such as resonators, couplers, low pass filters (LPFs), and power combiners with high performance over 100 GHz have been developed. These components can be smoothly integrated with planar Gunn diodes for compact planar Gunn oscillators, and therefore contribute to RF power enhancement. 
In addition, several new measurement techniques for characterising oscillators and passive devices have also been developed during this work and will be included in this thesis.

Design and characterisation of millimetre wave planar Gunn diodes and integrated circuits

La combustion en dessous de la surface se produit dans les transistors a effet de champ de grande puissance en GaAs, les dispositifs a transfert d'electrons planaires en GaAs polarises sous tension electrique assez elevee, et dans certains cas quand les transistors FET en GaAs et les transistors a effet de champ a dopage module en GaAs (MODFET) sont irradies par des particules alpha. Revue des modeles theoriques actuels expliquant les mecanismes physiques responsables. Les conclusions devraient aider a creer des dispositifs plus fiables grâce a leur resistance accrue a l'irradiation

Subsurface burnout mechanisms in gallium arsenide (GAAS) electronic devices

The influence of diffusion and the lateral dimensions on the growth of space-charge non-uniformities from random electron density fluctuations is calculated for a negative differential resistance material. The effect of these considerations on the performance of some transferred-electron devices is then presented. The f.m. noise performance of Gunn oscillators was overestimated by 13 dB in a previous calculation, and the allowable space charge growth in limited space-charge accumulation oscillators was underestimated. It is concluded that fully formed domains do not exist in uniform short (similar, equals 10 μm) Gunn effect devices.

Three-dimensional limitations on space-charge growth in transferred-electron devices

Observations on electrical properties of planar Gunn diodes and on failure mechanisms using Sn–Ag and In–Au contacts are reported. A conducting channel of Sn(In) is proved to be responsible for the final catastrophic failure. Excess heat is generated at the anode, where also the breakdown is observed to start. Mechanisms starting the breakdown (hole injection and combined ion drift and diffusion of impurities) are discussed.

I. Marklund

Papers

Failure mechanisms in Gunn diodes