Heterostructure Diodes for Millimeter Wave Power Generation

Abstract: This thesis deals with two types of heterostructure diodes namely the Resonant Tunneling Diode (RTD) and the Single barrier varactor diode (SBV). The RTD is a device for high frequency generation either as a negative reistance oscillators or as a multiplier. Different means to reach high frequencies are outlined. They involve design procedures for the epitaxial layer as well as for the quantum well structure. Suggestions for new material combinations such as AlSb barrier on an InAs substrate are made. It is noted that the velocity of the electrons is one key parameter in reaching the highest frequencies. A method for determining the peak velocity in epitaxial semiconductor structures using a simple current voltage measurement technique on micro bridges is described.

Fundamental frequency oscillations as high as 120 GHz with an output power of 10 mW and third harmonic oscillations at 174 GHz with an output power of 1 µW have been reached for a RTD. For multipliers using the same diode we have achieved an output power of 0.8 mW for a tripler at 250 GHz at an efficiency of 1% in good agreement with theory.

The SBV diode has been investigated as a multiplier both experimentally and theoretically. Multiplier results for a tripler to 250 GHz reaching 5% efficiency and more than 2 mW output power are presented. These results are comparable to a state of the art Schottky barrier diodes.

An accurate method for on-wafer characterisation of high frequency diodes is presented. The method is demonstrated on single barrier varactor diodes and resonant tunneling diodes. In particular, the heterojunction capacitance of a resonant interband tunneling diode is determined.