Characterization of hetero interfaces in InP/In75Ga25As/InP HFETs by means of digital signal processing of measured low frequency noise spectra

Modern HFETs exhibit very low microwave noise due to the spatial separation of the donor layer and the channel. However, these devices suffer from their low frequency (LF) noise, which limits their applicability both as mixers and as wideband amplifiers. We are interested in the characterization and localization of LF-noise sources in InP/InGaAs/InP HFETs. Because the noise contribution of the aluminium DX-centers is eliminated, we believe that the measured 1/f-noise mainly results from the InP/InGaAs hetero interfaces, especially from the lower one, caused by the less stable InP surface. Furthermore, deep traps may be located at the interfaces due to the gradual transition of the alloy composition. To detect these deep traps, the evaluation of LF-noise spectra seems to be a very promising method. Compared to DLTS; it offers several advantages, since the measurements may be performed near the thermodynamic equilibrium and the effect of gate-source voltage V, variations can be studied. Besides, DLTS is an indirect method and some deep levels detected with it may not contribute to the noise