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Design, Fabrication and Characterization of InAlAs/InGaAs/InAsP Composite Channel HEMTs

Liu, Dongmin

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2008, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.

InAlAs/InGaAs high electron mobility transistors (HEMTs) are among the best-performing semiconductor devices in terms of speed, noise, and high frequency gain. However, because of the small bandgap of the InGaAs channel, these devices suffer from strong impact ionization in the channel layer, which makes them not suitable for microwave power application. One effective approach to solve the problem is adding a larger band gap material under thin InGaAs to form a composite channel structure. In this type of HEMTs, under high electric field, electrons in the InGaAs can gain enough energy to transfer into the sub-channel thus exploit its advantageous properties such as a higher breakdown field and a higher saturation electron velocity. InAsP is an excellent candidate for the composite channel material. In this study, we use pseudomorphic InAsP layer beneath InGaAs main channel to form composite channel HEMTs on InP substrate to suppress the impact ionization and simultaneously achieve excellent device performance.

The composite channel HEMT layer-structure was designed based on the simulation of band structure and electron concentration distribution by solving the by solving Poisson and Schrodinger equation self-consistently. 1-D theoretical simulation shows that electrons are mainly confined in the InGaAs main channel at equilibrium and begin to transfer to InAsP sub-channel under a high drain bias. The device structure was grown on InP substrate by molecular beam epitaxy by our collaborating research group.

The composite channel devices are fabricated by a mesa-isolated HEMT process. The first fabricated 0.25 μm gate length HEMTs exhibited a peak extrinsic transconductance of 888 mS/mm, an fT of 115 GHz, and an fmax of 137 GHz. A 0.15 μm gate device showed an fT of 195 GHz. To our knowledge, these are the highest fTs reported for composite channel HEMTs on InP substrate with the same gate length. Furthermore, we present a systematic study on the gate length scaling of InGaAs/InAsP composite channel HEMTs. Devices with gate lengths of 0.15, 0.34, 0.58, 0.85 and 1.13 μm were fabricated. The dependence of direct current and microwave performance on gate length is characterized. Device characterization results showed the extrinsic transconductance increased from 498 mS/mm for 1.13 μm devices to 889 mS/mm for 0.15 μm gate devices, while the unit current gain frequency increased from 24 GHz to 195 GHz. A simple delay time analysis is employed to extract the effective carrier velocity of the composite channel.

Then we aim to improve its microwave performance by down scaling the gate length. High resolution electron beam lithography process using a ZEP/PMGI/ZEP resist stack for ultra-short T-gates was developed. A recent InGaAs/InAsP HEMTs composite channel with a gate-length of 80 nm exhibits a unity current gain cut-off frequency fT of 280 GHz. A 10 element small signal equivalent circuit model is developed for device parameter extraction. The values of circuit elements are used in an extended delay time analysis to investigate the effect of enhanced veff at short gate length. The average electron velocity under the gate is determined in the 80 nm device.

Wu Lu (Advisor)
Steven Ringel, A. (Committee Member)
Leonard Brillson, J. (Committee Member)
Tadeusz Januszkiewics (Committee Member)
194 p.

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Citations

  • Liu, D. (2008). Design, Fabrication and Characterization of InAlAs/InGaAs/InAsP Composite Channel HEMTs [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1213299848

    APA Style (7th edition)

  • Liu, Dongmin. Design, Fabrication and Characterization of InAlAs/InGaAs/InAsP Composite Channel HEMTs. 2008. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1213299848.

    MLA Style (8th edition)

  • Liu, Dongmin. "Design, Fabrication and Characterization of InAlAs/InGaAs/InAsP Composite Channel HEMTs." Doctoral dissertation, Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1213299848

    Chicago Manual of Style (17th edition)