High thermal stability AlGaAs/InGaAs enhancement-mode pHEMT using iridium buried-gate technology

Hsien Chin Chiu*, Chih Wei Yang, Chao Hung Chen, Che Kai Lin, Cheng Shun Wang, Jeffrey S. Fu

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

1 Scopus citations


The dc, flicker noise, power, and temperature dependence of AlGaAs/InGaAs enhancement-mode pseudomorphic high electron mobility transistors (E-pHEMTs) were investigated using iridium (Ir) buried-gate technology. Although the conventional platinum (Pt)-buried gate has a high metal work function, which is beneficial for increasing the Schottky barrier height of the E-pHEMT, the high rate of intermixing of the Pt-GaAs interface owing to the effect of the continuous production of Pt As2 on the device influenced the threshold voltage (Vth) and transconductance (gm) at high temperatures or over the long-term operation. Variations in these parameters make Pt-gate E-pHEMT-related circuits impractical. Furthermore, a Pt As 2 interlayer produced a serious gate leakage current and unstable Schottky barrier height. This study presents the Ir-GaAs Schottky contact because Ir, buried in GaAs, absorbs surface oxygen atoms, forming Ir O 2 after annealing at 200°C. Thermally stable Ir O2 inhibited the overdiffusion of Ir at high temperatures and simultaneously suppressed device flicker noise. The Vth of Ir/Ti/Au Schottky gate E-pHEMT was 0.238 V and this value shifted to 0.244 V after annealing at 200°C. However, the Vth shifted from 0.084 to 0.231 V after annealing of the Pt/Ti/Au Schottky gate E-pHEMT because the Pt sunk into a deeper channel. The slope of the curve of power gain cutoff frequency (f max) as a function of temperature was -1.5× 10-2 GHz/°C for an Ir/Ti/Au-gate E-pHEMT; it was -6.9× 10-2 GHz/°C for a Pt/Ti/Au-gate E-pHEMT. The slight variation in the dc and radio-frequency characteristics of the Ir/Ti/Au-gate E-pHEMT at temperatures from 0 to 150°C revealed that the Ir-GaAs interface has great potential for high power transistors.

Original languageEnglish
Pages (from-to)H877-H880
JournalJournal of the Electrochemical Society
Issue number12
StatePublished - 2009


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