Strained epilayers effectively reduce plasma-induced fluorine damage in P-HEMTs

We intentionally inserted several strained epilayers, namely In_0.5Ga_0.5As, InAs, and InSb, as fluorine-trapping barriers in a conventional pseudomorphic high electron mobility transistor (P-HEMT) structure and investigated their effectiveness against plasma-induced fluorine damage using Hall measurements and secondary ion mass spectrometry (SIMS) analysis. The strained barriers effectively diminished plasma-induced fluorine incorporation into deeper layers than the δ-doped layer and improved the carrier density and electron mobility compared with those of the conventional P-HEMT. In particular, when the most strained InSb barrier was inserted into the P-HEMT using post-thermal annealing, the carrier density and electron mobility remarkably recovered to 85% and 97% of their respective values before processing because of diminished fluorine incorporation and reduction of incorporated fluorine from the channel layer to the upper layers. This confirms that highly strained barriers are very effective at suppressing plasma-induced fluorine damage in P-HEMTs.