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Tuning composition in graded AlGaN channel HEMTs toward improved linearity for low-noise radio-frequency amplifiers
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. (Center for III-Nitride Technology, C3NiT-Janzén)ORCID iD: 0000-0003-4902-5383
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. (Center for III-Nitride Technology, C3NiT-Janzén)ORCID iD: 0000-0002-0399-8369
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden. (Center for III-Nitride Technology, C3NiT-Janzén; THeMAC)ORCID iD: 0000-0001-7344-1518
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. (Center for III-Nitride Technology, C3NiT-Janzén; THeMAC)ORCID iD: 0000-0002-8827-7404
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2023 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 122, no 15, article id 153501Article in journal (Refereed) Published
Abstract [en]

Compositionally graded channel AlGaN/GaN high electron mobility transistors (HEMTs) offer a promising route to improve device linearity, which is necessary for low-noise radio-frequency amplifiers. In this work, we demonstrate different grading profiles of a 10-nm-thick AlxGa1-xN channel from x = 0 to x = 0.1 using hot-wall metal-organic chemical vapor deposition (MOCVD). The growth process is developed by optimizing the channel grading and the channel-to-barrier transition. For this purpose, the Al-profiles and the interface sharpness, as determined from scanning transmission electron microscopy combined with energy-dispersive x-ray spectroscopy, are correlated with specific MOCVD process parameters. The results are linked to the channel properties (electron density, electron mobility, and sheet resistance) obtained by contactless Hall and terahertz optical Hall effect measurements coupled with simulations from solving self-consistently Poisson and Schrodinger equations. The impact of incorporating a thin AlN interlayer between the graded channel and the barrier layer on the HEMT properties is investigated and discussed. The optimized graded channel HEMT structure is found to have similarly high electron density (similar to 9 x 10(12) cm(-2)) as the non-graded conventional structure, though the mobility drops from similar to 2360 cm(2)/V s in the conventional to similar to 960 cm(2)/V s in the graded structure. The transconductance g(m) of the linearly graded channel HEMTs is shown to be flatter with smaller g(m) and g(m) as compared to the conventional non-graded channel HEMT implying improved device linearity. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Place, publisher, year, edition, pages
AIP Publishing , 2023. Vol. 122, no 15, article id 153501
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-193705DOI: 10.1063/5.0141517ISI: 000967612400009OAI: oai:DiVA.org:liu-193705DiVA, id: diva2:1756995
Note

Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA); Lund University; Linkoeping University; Chalmers University of Technology [2022-03139]; Ericsson; Epiluvac; FMV; Gotmic; Hexagem; Hitachi Energy; On Semiconductor; Region Skane SAAB; SweGaN; Volvo Cars; UMS; Swedish Research Council VR; Swedish Foundation for Strategic Research; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University; KAW Foundation [2016-00889, 2022-04812]; Swedish Research Council and the Foundation [RIF14-055, EM16-0024, STP19-0008]; [2009-00971]; [2021-00171]; [RIF21-0026]

Available from: 2023-05-15 Created: 2023-05-15 Last updated: 2023-12-28
In thesis
1. Hot-wall MOCVD for advanced GaN HEMT structures and improved p-type doping
Open this publication in new window or tab >>Hot-wall MOCVD for advanced GaN HEMT structures and improved p-type doping
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The transition to energy efficient smart grid and wireless communication with improved capacity require the development and optimization of next generation semiconductor technologies and electronic device components. Indium nitride (InN), gallium nitride (GaN) and aluminum nitride (AlN) compounds and their alloys are direct bandgap semiconductors with bandgap energies ranging from 0.7 to 6.0 eV, facilitating their utilization in optoelectronics and photonics. The GaN-based blue light-emitting diodes (LEDs) have enabled efficient and energy saving lighting, for which the Nobel Prize in Physics 2014 was awarded. GaN and AlN have high critical electric fields, high saturation carrier velocities and high thermal conductivities, which make them promising candidates for replacing silicon (Si) in next-generation power devices. The polarization-induced two-dimensional electron gas (2DEG), formed at the interface of AlGaN and GaN has enabled GaN-based high electron mobility transistors (HEMTs). These devices are suitable for high-power (HP) switching, power amplification and high-frequency (HF) applications in the millimeter-wave range up to THz frequencies. As such, HEMTs are suitable for next-generation 5G and 6G communication systems, radars, satellites, and a plethora of other related applications.

Despite the immense efforts in the field, several material related issues still hinder the full exploitation of the unique properties of GaN-based semiconductors in HF and HP electronic applications. These limitations and challenges are related among others to: i) poor efficiency of p-type doping in GaN, ii) lack of linearity in AlGaN/GaN HEMTs used in low-noise RF amplifiers and, iii) MOCVD growth related difficulties in achieving ultra-thin and high Alcontent AlGaN barrier layers with compositionally sharp Al profiles in AlGaN/GaN HEMTs for HF applications.

In this PhD thesis, we address the abovementioned issues by exploiting the hot-wall MOCVD combined with extensive material characterization. Main results can be grouped as follows:

i) state-of-art p-GaN with room-temperature free-hole concentrations in the low 1018 cm-3 range and mobilities of ~10 cm2/Vs has been developed via in-situ doping. A comprehensive understanding of the growth process and its limiting factors, as related to magnesium (Mg), hydrogen (H) and carbon (C) incorporation in GaN is established. Further improvement of p-type doping in as-grown GaN:Mg is achieved by using GaN/AlN/4H-SiC templates and/or by modifying the gas environment in the growth reactor through the introduction of high amounts of hydrogen (H2) in the process. Using advanced scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) we have established an improved comprehensive model of the pyramidal inversion domain defects (PIDs) in relation to the ambient matrix. First experimental evidence that Mg is present at all interfaces between PID and matrix allows for more accurate evaluation of Mg segregated at the PID, necessary for understanding the main limiting factor for p-type conductivity in GaN against alternative compensating donor or passivation sources.

ii) Compositionally graded AlGaN channel layers in AlGaN/(Al)GaN HEMTs with various types of compositional grading have been developed, and graded channel devices were compared with conventional AlGaN/GaN HEMT indicating improved linearity. The first large signal measurements in Europe of a graded channel AlGaN/GaN HEMT has been carried out demonstrating improved linearity figure of merit IM3 by 10 dB compared to conventional Fe-doped GaN buffer devices. These results are showing state-of-the-art performance and pave the way for novel highly linear GaN receivers.

iii) Ultrathin (sub-10nm) and high Al-content (>50%) AlGaN barrier GaN HEMT structures have been developed with 2DEG carrier densities ~1.1×1013 cm-2 and mobilities ~1700 cm2/Vs. Advanced characterization with atomic precision involving STEM and energy dispersive X-ray spectroscopy (EDS), has allowed experimental determination of the Al profiles and has revealed deviations from the nominally intended structures. Such deviations are found also in different source materials including commercial HEMT epistructures grown by MOCVD. The implications of the Al-profile deviations are critically analyzed in terms of 2DEG properties and device fabrication and performance. The capabilities and the limitations of MOCVD processes, related to growth of compositionally sharp and ultrathin high-Al-content AlGaN layers on GaN have been evaluated and their prospects in HF have been assessed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2023. p. 80
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2333
Keywords
Hot-wall MOCVD, III-nitrides, p-type GaN, HEMTs, Linearity, High-Al barrier
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-197324 (URN)10.3384/9789180752800 (DOI)9789180752794 (ISBN)9789180752800 (ISBN)
Public defence
2023-10-05, Nobel BL32, B Building, Campus Valla, Linköping, 10:00 (English)
Opponent
Supervisors
Note

Funding agencies: The Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program Grant No. 2016-05190 and 2022-03139, Linköping University, Chalmers University of Technology, Ericsson, Epiluvac, FMV, Gotmic, Hexagem, Hitachi Energy, On Semiconductor, Region Skåne, Saab, SweGaN, UMS, and Volvo cars. We further acknowledge support from the Swedish Research Council VR under Award No. 2016-00889 and 2022-04812, Swedish Foundation for Strategic Research under Grants No. RIF14-055 and No. EM16-0024, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No. 2009-00971. The KAW Foundation is also acknowledged for support of the Linköping Electron Microscopy Laboratory.

Available from: 2023-08-31 Created: 2023-08-31 Last updated: 2024-03-01Bibliographically approved

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