Formation of two-dimensional electron gas and enhancement of electron mobility by Zn polar ZnMgO/ZnO heterostructures

H. Tampo; H. Shibata; K. Matsubara; A. Yamada; P. Fons; M. Yamagata; H. Kanie; S. Niki

doi:10.1117/12.714044

20 February 2007 Formation of two-dimensional electron gas and enhancement of electron mobility by Zn polar ZnMgO/ZnO heterostructures

H. Tampo, H. Shibata, K. Matsubara, A. Yamada, P. Fons, M. Yamagata, H. Kanie, S. Niki

Author Affiliations +

Proceedings Volume 6474, Zinc Oxide Materials and Devices II; 64740J (2007) https://doi.org/10.1117/12.714044
Event: Integrated Optoelectronic Devices 2007, 2007, San Jose, California, United States

Abstract

A two-dimensional electron gas (2DEG) was observed in Zn polar ZnMgO/ZnO (ZnMgO on ZnO) heterostructures grown by radical source molecular beam epitaxy. Reflection high energy electron diffraction patterns taken during the growth of the ZnMgO layer remained streaky; x-ray diffraction measurements showed no evidence of phase separation for up 44 % Mg composition. These results shows that the high quality ZnMgO layers up to 44 % Mg composition were obtained without phase separation. The electron mobility of the ZnMgO/ZnO heterostructures dramatically increased with increasing Mg composition and the electron mobility (&mgr;~250 cm²/Vs) at RT reached a value more than twice that of an undoped ZnO layer (&mgr;~100 cm²/Vs) due to the 2DEG formation. The carrier concentration in turn reached values as high as ~1x10¹³ cm^-2 and remained nearly constant regardless of Mg composition. Strong confinement of electrons at the ZnMgO/ZnO interface was confirmed by C-V measurements with a concentration of over 4x10¹⁹ cm^-3. Temperature-dependent Hall measurements of ZnMgO/ZnO heterostructures also exhibited properties associated with well defined heterostructures. The Hall mobility increased monotonically with decreasing temperature, reaching a value of 2750 cm²/Vs at 4 K. Zn polar "ZnMgO on ZnO" structures are easy to adapt to a top-gate device. These results open new possibilities for high electron mobility transistors (HEMTs) based upon ZnO based materials.

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H. Tampo, H. Shibata, K. Matsubara, A. Yamada, P. Fons, M. Yamagata, H. Kanie, and S. Niki "Formation of two-dimensional electron gas and enhancement of electron mobility by Zn polar ZnMgO/ZnO heterostructures", Proc. SPIE 6474, Zinc Oxide Materials and Devices II, 64740J (20 February 2007); https://doi.org/10.1117/12.714044

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KEYWORDS

Heterojunctions

Zinc oxide

Magnesium

Zinc

Field effect transistors

Dielectric polarization

Sapphire

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