Browsing by Author "Luong, Tien Tung"

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BUFFER-OPTIMIZED IMPROVEMENT IN RF LOSS OF ALGAN/GAN HEMTS ON 4-INCH SILICON (111)
(2017-01-01)
Luong, Tien Tung
;
Lumbantoruan, Franky
;
Chen, Yen-Yu
;
Ho, Yen-Teng
;
Lin, Yueh-Chin
The effect of different buffer layers on the RF losses of GaN-based high-mobility-transistors (HEMTs) on Si substrate has been studied. It is found that the electron inversion layer induced by the residual tensile stress in AlN buffer is responsible for a dominant loss factor. It is first time such mechanisms of the RF loss of GaN/Si is discussed. It is proven that using a thin high-low-high temperature (HLH) AlN buffer reducing the tensile stress in AlN consequently reduces the RF loss.
Phase separation-suppressed and strain-modulated improvement of crystalline quality of AlGaN epitaxial layer grown by MOCVD
(2018-04-01)
Luong, Tien Tung
;
Ho, Yen-Teng
;
Wong, Yuen-Yee
;
Chang, Shane
;
Chang, Edward-Yi
High crystalline quality AIGaN films were grown on GaN templates by metalorganic chemical vapor deposition (MOCVD). Inhomogeneous distributions of Al compositions in both the vertical and lateral growth direction caused by the strong gas-phase pre-reaction occurring between Al precursors and NH3 were suppressed by optimizing the growth conditions. The residual strain in AIGaN/GaN induced by lattice mismatch, which results in the degradation of crystallinity, was modulated by varying thickness of a high temperature (HT) AIN interlayer (IL) inserted between AIGaN and GaN layers. Both the crystalline quality and Al-incorporation into the AIGaN are influenced by the residual strain related to the AIN IL thickness. Lastly, the understanding of the AIGaN growth and of the strain modification was employed to grow an AIGaN/GaN HEMT structure showing good electrical characteristics and uniformity. (C) 2017 Elsevier Ltd. All rights reserved.
RF loss mechanisms in GaN-based high-electron-mobility-transistor on silicon: Role of an inversion channel at the AlN/Si interface
(2017-07-01)
Luong, Tien Tung
;
Lumbantoruan, Franky
;
Chen, Yen-Yu
;
Ho, Yen-Teng
;
Weng, You-Chen
One of the epitaxial issues pertaining to the growth of AlGaN/GaN HEMTs on Si is the decrease of parasitic losses that can adversely impact the RF device performances. We characterized the microwave losses in coplanar waveguides (CPWs) on GaN-based high-electron-mobility-transistors (HEMTs) and their buffer layers on Silicon substrate, up to 40GHz. The RF losses depend not only on the crystalline quality but also on the residual tensile stress in AlN buffer, as well as its thickness. The mechanism of interfacial lossy channel induced by the piezoelectric field is discussed. Adopting a thin high-low-high temperature (HLH) AlN buffer can help to reduce the tensile stress leading to a reduction of RF losses. We suggest that a thinner p-type AlN and/or p-AlGaN-on-thin AlN near the interface can suppress the electron interfacial lossy channel, which helps the GaN-HEMT-on-HR Si to remain in a high frequency range and at high-temperature operation. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Threading dislocation reduction in three-dimensionally grown GaN islands on Si (111) substrate with AlN/AlGaN buffer layers
(2017-09-14)
Chang, Shane
;
Wei, Lin Lung
;
Luong, Tien Tung
;
Chang, Ching
;
Chang, Li
Three-dimensional GaN island growth without any masks was first introduced under high pressure in metalorganic chemical vapor deposition after the growth of AlN and AlGaN buffer layers on Si ( 111) substrate, followed by two-dimensional GaN growth to form a continuous GaN film with improvement of the crystalline quality and surface smoothness. X-ray diffraction and cross-sectional scanning transmission electron microscopy analyses show that a high-quality GaN film can be achieved by bending of edge threading dislocations (TDs) and the formation of dislocation half-loops. It is observed that most of edge TDs bend 90 degrees from the growth direction along c-axis, whereas mixed TDs bend about 30 degrees towards the inclined sidewall facets of the islands. Consequently, a 1.2 mu m thick GaN epitaxial film with a low threading dislocation density of 2.5 x 10 8 cm(-2) and a smooth surface of 0. 38 nm roughness can be achieved on Si substrate. Published by AIP Publishing.