High Performance InAlAs/InAs/InGaAs Pseudomorphic High Electron Mobility Transistors
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1108-A09-02
High Performance InAlAs/InAs/InGaAs Pseudomorphic High Electron Mobility Transistors. Nobuhito Wakimura, Yugo Nakagawa, Hirohisa Taguchi, Tsutomu Iida, and Yoshifumi Takanashi
Department of Materials Science and Technology, Faculty of Industrial Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 ABSTRACT High electron mobility transistors (HEMTs) with a pseudomorphically strained InAs channel (InAs-PHEMTs) were fabricated, and their high frequency characteristics were estimated by measuring the S-parameters. For a VDS of 1.4 V and VGS of 0.3 V, InAs-PHEMTs showed an excellent intrinsic cut-off frequency (fT, int.) as high as 90 GHz regardless of their longer LG (0.7 µm). Since fT is known to be inversely proportional to LG to the first approximation, fT, int. of our InAs-PHEMTs may reach 630 GHz if their LG is reduced to 0.1 µm. Moreover, we calculated the InAs-PHEMTs’ energy state and potential profile by selfconsistently solving the Schrödinger and Poisson equations. In solving the Schrödinger equation, the energy-dependent effective mass was employed to take into account the strong nonparabolicity of InAs conduction-band based on the k ⋅ p perturbation theory by E. O. Kane. It was clarified that most electrons are confined to the InAs layer. On the contrary, if the nonparabolicity is not taken into account, electrons will spread over the InGaAs channel layer. INTRODUCTION High electron mobility transistors (HEMTs) made using an InAlAs/InGaAs material system have attracted much attention because of their high-speed operation and their applicability to high-speed integrated circuits (ICs) [1, 2]. HEMTs with strained InGaAs channels exhibit a current cut-off frequency (fT) in excess of 500 GHz [3]. HEMTs with a pseudomorphically strained InAs channel (InAs-PHEMTs) are expected to operate at a still higher frequency [4]. This is because the electron mobility of InAs (33000 cm-2/V-s) is much higher than that of InGaAs (16000 cm-2/V-s). In addition, it is possible to enhance the density of two-dimensional electron gas (2DEG) due to a large conduction band discontinuity. Recently, these HEMTs have been shown to operate as a high-speed optical receiver [5, 6]. In this work, we investigated the intrinsic transit-time of InAs-PHEMTs, in which electrons transit through the InAs channel beneath the gate region. Moreover, we calculated the InAsPHEMT’s energy state and potential profile by self-consistently solving the Schrödinger and Poisson equations. In solving the Schrödinger equation, the energy-dependent effective mass was employed to take into account the strong non-parabolicity of the InAs conduction-band based on the k ⋅ p perturbation theory by E. O. Kane[7]. EXPERIMENT Sample Structure
Figure 1 illustrates the structure of the InAs-PHEMT we investigated. Epitaxial structures were grown on Fe-doped semi-insulating InP substrates using molecular beam epitaxy. Since a lower growth temperature is required to grow strained layers, we grew the pseudomorphic HEMTs at a
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