AlGaN/InGaN Heterostructure Field Effect Transistors Grown on Sapphire by Metal-Organic Chemical Vapor Deposition
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AlGaN/InGaN Heterostructure Field Effect Transistors Grown on Sapphire by Metal-Organic Chemical Vapor Deposition Chang-Cheng Chuo, Chia-Min Kan, Jen-Inn Chyi, Tzer-En Nee, Chia-Ming Lee, and Chin-Kun Peng* Department of Electrical Engineering, National Central University, Chung-Li, Taiwan, 32054, R.O.C. *Procomp Informatics, Science-Based Industrial Park, Hsinchu, Taiwan 300, R.O.C.
ABSTRACT AlGaN/InGaN heterostructure field effect transistors were grown on sapphire by metalorganic chemical vapor deposition. Transmission electron microscopy shows that there are no additional dislocations induced by inserting the InGaN channel while a variation of strain field across the channel is observed. The transistors exhibit good pinch-off characteristics with a threshold voltage of about –2.9 V and a saturation current density of 0.55 A/mm. At room temperature, a peak transconductance of 132 (mS/mm) was obtained for a 1.0 µm-device. Current gain cutoff frequency fT of 9.4 GHz and maximum oscillation frequency fmax of 28.2 GHz were measured for the 1.0 µm-device. As the temperature is increased to 300 oC, the transconductance decreases to 50 mS/mm accompanied by a reduction of saturation current density of 0.24 A/mm due to the enhanced carrier scattering, gate leakage, and drain-source resistance.
INTRODUCTION AlGaN/GaN heterostructure field effect transistors (HFETs) have recently attracted much attention because of their promising uses for high-voltage, high-power, and high-temperature microwave applications [1-4]. In nitride heterostructures with wurtzite crystal structures in (0001) orientation, there exist large spontaneous and strain-induced piezoelectric effects that largely influence the electrical properties in the heterostructures [5]. In the AlGaN/GaN HFETs with lattice strain, positive polarization charges are generated at the heterointerface and alter the potential profiles so that higher density of two-dimensional electron gas (2DEG) is induced in the GaN channel [6]. For conventional GaAs- or InP-based materials, AlGaAs/InGaAs and InAlAs/InGaAs pseudomorphic high electron mobility transistors (PHEMT) are much attractive G11.11.1
due to superior electron transport properties, such as higher electron mobility, higher peak electron velocity, and higher electron density [7]. Hence, introducing a pesuodomorphic InGaN channel in the AlGaN/GaN HFET is also expected to improve the device performance. By this way, the capacity for two-dimensional electron gas (2DEG) density is expected to increase in InGaN DH-FETs as the result of the enhanced piezoelectric effect and the enlarged conduction-band discontinuity at the AlGaN/InGaN heterointerface. In this study, AlGaN/InGaN/GaN DH-FET is realized and characterized. Temperature dependence on the saturation current and transconductance is also investigated.
EXPERIMENTAL DETAILS The DH-FET structure used for this study was grown on a 2-inch c-plane sapphire substrate in an AIX 200/4 low-pressure metalorganic chemical vapor deposition (MOCVD) system. The precursors were
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