InP-InAlAs and InGaP-InAlAs mixed spacers to reduce the gate leakage current in InAlAs/InGaAs/InP HEMTs

In this work, we propose a comparative study of the behaviour of three HEMT structures at high reverse bias: a reference structure (S1) with a conventional InAlAs spacer, the second with an InP/InAlAs mixed spacer (S2) and the third with an In/sub 0.5/Ga/sub 0.5/P/InAlAs (S3) mixed spacer. We show a drastic decrease of the gate leakage current for the mixed spacer HEMTs, thanks to the large valence band offset between InP (or InGaP) and InGaAs. Moreover, Low Frequency Noise (LFN) measurements were performed to investigate the defect distribution in the three structures. These help us to distinguish between the transport mechanisms which govern the gate leakage current.