The high-frequency application of double-barrier resonant tunnelling diodes
The aim of this Thesis was to try to develop an understanding of the growth and fabrication of Double Barrier Resonant Tunnelling (DBRT) diodes, in order to enhance their properties at millimetre wave frequencies (ie. above 35GHz). Chapter 1 introduces the DBRT diode and outlines some of its applications while Chapter 2 describes aspects of device fabrication. Chapter 3 discusses the solid-state and quantum mechanical aspects which determine the DBRT's current-voltage characteristics and Chapter 4 describes an extensive parametric study relating the device properties to the high frequency behaviour. Chapter 5 covers the applications of DBRT devices at high frequencies and presents some of the results achieved so far. Besides the primary objective of studying the properties which determine the high frequency application of DBRT devices (via. the characterization of an extensive range of structures grown for the project), the other goal was to try to improve upon the results of other workers in terms of generating power and to improve the efficiency of up and down conversion at millimetre wave frequencies. Perhaps the most promising application of DBRT devices is as self-oscillating mixers (SOM) which can also provide conversion gain (due to the wide bandwidth of the negative differential resistance) at the intermediate frequency. This is of great importance since it negates the need to generate a local oscillator signal and dispenses with complicated image rejection mixer arrangements (for superheterodyne mixing) and amplification stages, which are very difficult to build and are expensive at millimetre wave frequencies. Whilst working in collaboration with staff at the University of Leeds, department of Electronic and Electrical Engineering a SOM was fabricated on microstrip which gave a modest gain at around 10GHz. Similarly a DBRT diode was operated in waveguide at 106GHz and provided -9.8dBm of power as measured on a spectrum analyzer. Both of these results represent (to the authors knowledge) the best results currently seen for DBRT devices in the UK and Europe.