Low Frequency Dispersion in InP HEMTs

Abstract

The InAlAs/InGaAs/InP HEMT is the state-of-the-art technology for design of ultralow noise amplifiers for radio astronomy and deep space communication. One of the reasons that make this technology very attractive is the outstanding cut-off frequency fT and maximum frequency of oscillation fmax. However, a low frequency dispersion problem has been found for InP HEMTs working at very low temperature. This is a concern for receivers working in cryogenic condition to achieve better noise performance. No study has been published on this phenomenon before. In this thesis, a full study of low frequency dispersion in InP HEMTs is presented. The study is based on different measurement techniques including DC, RF and pulse characterization as well as analyzing spectrum measurements. Moreover, this thesis is focused on the influence of the temperature and device structure on the low frequency dispersion problem. Three mechanisms, traps, odd mode oscillation and impact ionization, have been found closely associated with the observation of low frequency dispersion in InP HEMTs.