SIDEGATING-INDUCED NEGATIVE DIFFERENTIAL RESISTANCE IN MBE-GROWN INASALSB HFETS/

We report sidegating measurements on mesa-isolated InAs/AlSb-based het erojunction field effect transistors (HFETs) grown on GaAs semi-insula ting substrates with thick strain-relaxed AlSb buffer layers. We find that the AlGaSb/AlSb buffer layers provide adequate inter-device isola tion for low sidegate voltages \V-SG\ < 5 V. For sidegate electrode vo ltages of +/-20 V, the substrate leakage current remains lower than 10 0 nA for a sidegate separation of only 4 mu m from the active channel. For large positive sidegate voltages, a marked sidegating-induced neg ative differential resistance (SINDR) appears in the drain characteris tics. The peculiar frequency and temperature dependencies of the SINDR effect indicate that the negative differential resistance is caused b y a transient occupation of deep level centers by holes injected into the buffer layers from the sidegate electrode. In contrast, large nega tive sidegate voltages have a negligible impact on the HFET drain char acteristics. The present results illustrate the importance of buffer l ayers in InAs/AlSb HFETs and call for a deep level transient spectrosc opy characterization of deep centers in InAs/AlSb HFET buffer layers.