Haiou LI, Chak-wah TANG, Kevin J. CHEN, and Kei May LAU
Electronic and Computer Engineering Department
Hong Kong University of Science and Technology,
Clear Water Bay, Hong Kong SAR.
Keywords: GaAs, MHEMT, E/D-mode, CF4 Plasma Treatment
Enhancement-mode metamorphic InAlAs/InGaAs HEMTs grown by MOCVD on GaAs substrates have been fabricated using CF4 plasma treatment. Shifting of the threshold voltage from negative (depletion mode) to zero (enhancement mode) can be adjusted with process parameters. The plasma process provides a side benefit of reducing the leakage current of the device up to two orders of magnitudes. Depletion-mode and enhancement-mode devices fabricated from the same epi-wafer are compared, both with reasonably good device performance. Transistors with 1.5µm gate length exhibited transconductance up to 315mS/mm and current gain cut off frequency (fT) of 17.9GHz and maximum available gain (fmax) of 80GHz. Confirmed by atomic force microscope (AFM) measurements, thickness reduction of the InAlAs layer treated by CF4 Plasma is less than 1nm.