Enhanced Electron Mobility in AlGaN/InGaN/AlGaN Double-Heterostructures by Piezoelectric Effect. Maeda, N., Saitoh, T., Tsubaki, K., Nishida, T., & Kobayashi, N. 1999. Issue: 7B Publication Title: Japanese Journal of Applied Physics Volume: 38
abstract   bibtex   
A striking effect of piezoelectric electron confinement on transport properites has been observed for the first time in nitride double-heterostructures. The two-dimensional electron gas mobility has shown to be drastically enhanced in the AlGaN/GaN/AlGaN double-heterostructure, compared with that in the conventional AlGaN/GaN single-heterostructure. The observed mobility enhancement results from the piezoelectrically enhanced electron confinement in the double-heterostructure. The electron transport properties in the AlGaN/InGaN/AlGaN double-heterostructure have also been examined for the first time. The increased capacity for the two-dimensional electron gas density has been observed in addition to the enhanced electron mobility. The AlGaN/(In)GaN/AlGaN double-heterostructures are promising for field effect transistor applications because of their superior electron transport properties. KEYWORDS: AlGaN/InGaN/AlGaN double-heterostructure, AlGaN/GaN/AlGaN double-heterostructure, field effect transistor, two-dimensional electron gas, piezoelectric effect, MOVPE L 799 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. 1-7) Improving device performances requires an understanding of how we can increase the mobility and the density of the two-dimensional electron gas (2DEG) in this material system. Desirable designs of heterostructures should be investigated for superior transport properties. In nitride heterostructures with wurtzite crystal structures in (0001) orientation, there exists large piezoelectric effect that largely influences the electrical properties in the heterostructures. 8-15) In the AlGaN/GaN HFETs with lattice strain, positive piezoelectric charges are generated at the heterointerface and greatly alter the potential profiles so that higher densities of the two-dimensional electron gas (2DEG) are induced in the GaN channel. Hence, in designing AlGaN/GaN HFETs, keeping heterostructures with lattice strain, i.e., without lattice relaxation, is crucial for obtaining high 2DEG densities. 15) In this letter, we show how we can increase the 2DEG mobility by means of the piezoelectric effect. We can generally expect that the 2DEG mobility could be altered if the electron confinement is altered by the change in the electric field in the channel, because the electron confinement could influence, for example, the screening effect against the ionized impurity scattering, which plays an important role in determining the 2DEG mobility. In nitride HFETs, the electron confinement in the channel is expected to be stronger in the double-heterostructure field effect transistors (DH-FETs) than in conventional single-heterostructure field effect transistors (SH-FETs), because the piezoelectric field should be enhanced in the DH-FET channel due to both positive and negative piezo-electric charges at the two heterointerfaces. Hence, the 2DEG mobility in DH-FETs could be larger than that in SH-FETs. Figures 1(a) and 1(b) illustrate the potential profiles and distributions of 2DEG expected in (a) AlGaN/GaN SH-FET and (b) AlGaN/GaN/AlGaN DH-FET. The lattice strain is assumed to exist at every heterointerface, so that positive and negative piezoelectric charges are generated at heterointer-faces, as shown in Figs. 1(a) and 1(b). Since electrons in the DH-FET channel (Fig. 1(b)) are repulsed by the negative (MOVPE) at 300 Torr. In all samples, only the surface-side 300 Å Al 0.15 Ga 0.85 N barrier layers were uniformly doped with piezoelectric charges at the substrate-side heterointerface, the 2DEG distribution width in DH-FET is expected to be smaller than that in SH-FET (Fig. 1(a)). In order to find a way to increase 2DEG mobilities in nitride HFETs, we have examined what influence the strong electron confinement in DH-FET has on the transport properties: we have fabricated both conventional AlGaN/GaN SH-FETs and AlGaN/GaN/AlGaN DH-FETs, and have compared their electrical properties. We have also extended our study to the application of the InGaN channel to DH-FETs for exploiting the enhanced piezoelec-tric effect and the enlarged conduction-band discontinuity at the AlGaN/InGaN heterointerface. The sample structures are shown in Fig. 2, for (a) conventional GaN SH-FET, and (b) GaN (or InGaN) DH-FET. The layer structures in (a) SH-FET and (b) DH-FET consist of (a) Al 0.15 Ga 0.85 N (300 Å)/GaN (1 µm) and (b) Al 0.15 Ga 0.85 N (300 Å)/(In)GaN (200 Å)/Al 0.15 Ga 0.85 N (1000 Å) layers, which are the substantial layers in each HFET. The samples were grown on SiC(0001) substrates using AlN buffer layers, by metalorganic vapor-phase epitaxy Fig. 1. Potential profiles and 2DEG distributions in (a) GaN SH-FET and (b) GaN (or InGaN) DH-FET. SH and DH denote the single -heterostructure and the double-heterostructure, respectively. The 2DEG distribution width in (b) is narrower than that in (a), because electrons in (b) are repulsed by the negative piezoelectric charges at the sub-strate-side heterointerface.
@article{maeda_enhanced_1999,
	title = {Enhanced {Electron} {Mobility} in {AlGaN}/{InGaN}/{AlGaN} {Double}-{Heterostructures} by {Piezoelectric} {Effect}},
	abstract = {A striking effect of piezoelectric electron confinement on transport properites has been observed for the first time in nitride double-heterostructures. The two-dimensional electron gas mobility has shown to be drastically enhanced in the AlGaN/GaN/AlGaN double-heterostructure, compared with that in the conventional AlGaN/GaN single-heterostructure. The observed mobility enhancement results from the piezoelectrically enhanced electron confinement in the double-heterostructure. The electron transport properties in the AlGaN/InGaN/AlGaN double-heterostructure have also been examined for the first time. The increased capacity for the two-dimensional electron gas density has been observed in addition to the enhanced electron mobility. The AlGaN/(In)GaN/AlGaN double-heterostructures are promising for field effect transistor applications because of their superior electron transport properties. KEYWORDS: AlGaN/InGaN/AlGaN double-heterostructure, AlGaN/GaN/AlGaN double-heterostructure, field effect transistor, two-dimensional electron gas, piezoelectric effect, MOVPE L 799 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. 1-7) Improving device performances requires an understanding of how we can increase the mobility and the density of the two-dimensional electron gas (2DEG) in this material system. Desirable designs of heterostructures should be investigated for superior transport properties. In nitride heterostructures with wurtzite crystal structures in (0001) orientation, there exists large piezoelectric effect that largely influences the electrical properties in the heterostructures. 8-15) In the AlGaN/GaN HFETs with lattice strain, positive piezoelectric charges are generated at the heterointerface and greatly alter the potential profiles so that higher densities of the two-dimensional electron gas (2DEG) are induced in the GaN channel. Hence, in designing AlGaN/GaN HFETs, keeping heterostructures with lattice strain, i.e., without lattice relaxation, is crucial for obtaining high 2DEG densities. 15) In this letter, we show how we can increase the 2DEG mobility by means of the piezoelectric effect. We can generally expect that the 2DEG mobility could be altered if the electron confinement is altered by the change in the electric field in the channel, because the electron confinement could influence, for example, the screening effect against the ionized impurity scattering, which plays an important role in determining the 2DEG mobility. In nitride HFETs, the electron confinement in the channel is expected to be stronger in the double-heterostructure field effect transistors (DH-FETs) than in conventional single-heterostructure field effect transistors (SH-FETs), because the piezoelectric field should be enhanced in the DH-FET channel due to both positive and negative piezo-electric charges at the two heterointerfaces. Hence, the 2DEG mobility in DH-FETs could be larger than that in SH-FETs. Figures 1(a) and 1(b) illustrate the potential profiles and distributions of 2DEG expected in (a) AlGaN/GaN SH-FET and (b) AlGaN/GaN/AlGaN DH-FET. The lattice strain is assumed to exist at every heterointerface, so that positive and negative piezoelectric charges are generated at heterointer-faces, as shown in Figs. 1(a) and 1(b). Since electrons in the DH-FET channel (Fig. 1(b)) are repulsed by the negative (MOVPE) at 300 Torr. In all samples, only the surface-side 300 Å Al 0.15 Ga 0.85 N barrier layers were uniformly doped with piezoelectric charges at the substrate-side heterointerface, the 2DEG distribution width in DH-FET is expected to be smaller than that in SH-FET (Fig. 1(a)). In order to find a way to increase 2DEG mobilities in nitride HFETs, we have examined what influence the strong electron confinement in DH-FET has on the transport properties: we have fabricated both conventional AlGaN/GaN SH-FETs and AlGaN/GaN/AlGaN DH-FETs, and have compared their electrical properties. We have also extended our study to the application of the InGaN channel to DH-FETs for exploiting the enhanced piezoelec-tric effect and the enlarged conduction-band discontinuity at the AlGaN/InGaN heterointerface. The sample structures are shown in Fig. 2, for (a) conventional GaN SH-FET, and (b) GaN (or InGaN) DH-FET. The layer structures in (a) SH-FET and (b) DH-FET consist of (a) Al 0.15 Ga 0.85 N (300 Å)/GaN (1 µm) and (b) Al 0.15 Ga 0.85 N (300 Å)/(In)GaN (200 Å)/Al 0.15 Ga 0.85 N (1000 Å) layers, which are the substantial layers in each HFET. The samples were grown on SiC(0001) substrates using AlN buffer layers, by metalorganic vapor-phase epitaxy Fig. 1. Potential profiles and 2DEG distributions in (a) GaN SH-FET and (b) GaN (or InGaN) DH-FET. SH and DH denote the single -heterostructure and the double-heterostructure, respectively. The 2DEG distribution width in (b) is narrower than that in (a), because electrons in (b) are repulsed by the negative piezoelectric charges at the sub-strate-side heterointerface.},
	author = {Maeda, Narihiko and Saitoh, Tadashi and Tsubaki, Kotaro and Nishida, Toshio and Kobayashi, Naoki},
	year = {1999},
	note = {Issue: 7B
Publication Title: Japanese Journal of Applied Physics
Volume: 38},
}
Downloads: 0
About
Documentation
Keywords
Search
Users
Terms and Conditions of Use
Privacy Policy
Sitemap
© BibBase.org 2021