High-Temperature Electron Transport Properties in AlGaN/GaN Heterostructure Field Effect Transistors
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High-Temperature Electron Transport Properties in AlGaN/GaN Heterostructure Field Effect Transistors
Narihiko Maeda, Tadashi Saitoh, Kotaro Tsubaki, Toshio Nishida and Naoki Kobayashi NTT Basic Research Laboratories, Physical Science Laboratory, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa, 243-0198, Japan
Electron transport properties in the Al0.15Ga0.85N/GaN heterostructure field effect transistors (HFETs) have been examined from room temperature up to 400oC. The temperature dependencies of the two-dimensional electron gas (2DEG) mobility have been systematically measured for the samples with different 2DEG densities. The 2DEG mobility has decreased with increasing the temperature, however, its decrease ratio has been no longer large above 300oC. Moreover, the 2DEG mobility has found to be less dependent on the 2DEG density at higher temperatures. These observed features indicate that the 2DEG mobility above room temperature is limited by longitudinal optical (LO) phonon scattering, as is expected by theoretical prediction. The observed 2DEG mobilities at 400oC were as high as from 100 to 120 cm2/Vs, directly providing the evidence for suitability of the HFET of this material system for high-temperature applications. The temperature dependence of the transconductance (gm) of a HFET device has also been examined up to 400oC. It has been revealed that the temperature dependence of gm has basically the same features as those of the 2DEG mobility in the corresponding temperature region.
INTRODUCTION
AlGaN/GaN heterostructure field effect transistors (HFETs) have recently been attracting much attention because of their promising uses for high-voltage, high-power, and high-temperature microwave applications [1-11]. Since possible high-temperature applications are among advantages of the nitride-based devices over GaAs-based and Si devices; along with intensive investigations on device performance at room temperature [1-6], high-temperature device performance has also been demonstrated [7-11]. To understand and improve device performances at high-temperatures, inevitably required is an understanding of electron transport properties in the high-temperature region. In this paper, we systematically examine high-temperature electron transport properties in AlGaN/GaN HFETs and in their constituent materials of both GaN and AlGaN layers. We also present calculated results of the electron occupations in the sub-band structure in the AlGaN/GaN HFET at high temperatures. We further fabricate an AlGaN/GaN HFET, and examine the temperature dependence of the transconductance (gm). EXPERIMENTAL DETAILS AND DISCUSSIONS
High-Temperature Electron Transport in GaN and AlGaN
We have examined electron transport properties in GaN and AlGaN single-layers above room temperature, before examining those in the AlGaN/GaN HFET. We have grown Si-doped GaN and Al0.15Ga0.85N samples on SiC substrates by low pressure Metal Organic Vapor Phase Epitaxy (MOVPE) technique at 300 Torr. The sample structures are as follows: Si-doped GaN 1 µm /AlN(10
