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On the polarity determination and polarity inversion in nitrogen-polar group III-nitride layers grown on SiC
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-4902-5383
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. SweGaN AB, Olaus Magnus Vag 48A, S-58330 Linkoping, Sweden.
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2022 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 131, no 5, article id 055701Article in journal (Refereed) Published
Abstract [en]

We investigate the interfaces and polarity domains at the atomic scale in epitaxial AlN and GaN/AlN grown by hot-wall metal organic chemical vapor epitaxy on the carbon face of SiC. X-ray diffraction, potassium hydroxide (KOH) wet chemical etching, and scanning transmission electron microscopy combined provide an in-depth understanding of polarity evolution with the film thickness, which is crucial to optimize growth. The AlN grown in a 3D mode is found to exhibit N-polar pyramid-type structures at the AlN-SiC interface. However, a mixed N-polar and Al-polar region with Al-polarity domination along with inverted pyramid-type structures evolve with increasing film thickness. We identify inclined inversion domain boundaries and propose that incorporation of oxygen on the & lang;40-41 & rang; facets of the N-polar pyramids causes the polarity inversion. We find that mixed-polar AlN is common and easily etched and remains undetected by solely relying on KOH etching. Atomic scale electron microscopy is, therefore, needed to accurately determine the polarity. The polarity of GaN grown on mixed-polar AlN is further shown to undergo complex evolution with the film thickness, which is discussed in the light of growth mechanisms and polarity determination methods.

Place, publisher, year, edition, pages
AIP Publishing , 2022. Vol. 131, no 5, article id 055701
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-182951DOI: 10.1063/5.0074010ISI: 000749890900001OAI: oai:DiVA.org:liu-182951DiVA, id: diva2:1638001
Note

Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA)Vinnova [2016-05190]; Linkoeping University; Chalmers University of Technology; ABB; EricssonEricsson; Epiluvac; FMV; Gotmic; Hexagem; On Semiconductor; Saab; SweGaN; UMS; Swedish Research Council VRSwedish Research Council [2016-00889]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [RIF14-055, RIF 14-0074, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkping University, Faculty Grant SFO Mat LiU [2009-00971]

Available from: 2022-02-15 Created: 2022-02-15 Last updated: 2023-12-28
In thesis
1. Hot-wall MOCVD of N-polar group-III nitride materials and high electron mobility transistor structures
Open this publication in new window or tab >>Hot-wall MOCVD of N-polar group-III nitride materials and high electron mobility transistor structures
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Group III-Nitride semiconductors: indium nitride (InN), gallium nitride (GaN), aluminum nitride (AlN) and their alloys continue to attract significant scientific interest due to their unique properties and diverse applications in photonic and electronic applications. Group-III nitrides have direct bandgaps which cover the entire spectral range from the infrared (InN) to the ultraviolet (GaN) and to the deep ultraviolet (AlN). This makes III-nitride materials suitable for high-efficient and energy-saving optoelectronic devices, such as light-emitting diodes (LEDs) and laser diodes (LDs). The Nobel Prize in Physics 2014 was awarded for the invention of efficient GaN blue LEDs, which further accelerated the research in the field of group III-nitride materials. GaN and related alloys are also suitable for high-temperature, high-power and high-frequency electronic devices with performance that cannot be delivered by other semiconductor technologies such as silicon (Si) and gallium arsenide (GaAs). For example, GaN-based high electron mobility transistors (HEMTs) have been widely adopted for radio frequency (RF) communication and power amplifiers, high-voltage power switches in radars, satellites, and wireless base stations for 5G.

Recently, nitrogen (N)-polar group-III nitrides have drawn much attention due to their advantages over their metal-polar counterparts in e.g. HEMTs. These include feasibility to fabricate ohmic contacts with low resistance, an enhanced carrier confinement with a natural back barrier, and improved device scalability. Despite intensive research, the growth of micrometer-thick high-quality N-polar GaN based materials remains challenging. One of the major problems to develop device-quality N-polar nitrides is the high surface roughness, which results from the formation of hexagonal hillocks or step-bunching. Another significant hurdle is the unintentional polarity inversion, which reduces the crystalline quality and prohibits device fabrication. 

This thesis focuses on the development of N-polar AlN and GaN heterostructures on SiC substrates for HEMT RF applications. The overall aim is to exploit the advantages of the hot-wall MOCVD concept to grow high-quality N-polar HEMT structures for higher operational frequencies and improved device performance. In order to achieve this goal, special effort is dedicated to understanding the effects of growth conditions and substrate orientation on the structural properties and polarity of AlN, GaN and AlGaN grown by hot-wall MOCVD. N-polar AlN nucleation layers (NLs) with layer by layer growth mode and step-flow growth mode can be achieved on on-axis and 4­ off-axis SiC (000¯1), respectively, by carefully controlling V/III ratio and growth temperature. Utilizing scanning transmission electron microscopy (STEM) we have established a comprehensive picture of the atomic arrangements, local polarity and polarity evolution in AlN, GaN/AlN and AlGaN/GaN/AlN in the cases of low-temperature and high-temperature AlN NLs both for on-axis and off-axis substrates. We have shown that the typically employed methods for polarity determination using potassium hydroxide wet etching could not provide conclusive results in the case of mixed-polar AlN as Al-polar domains may be easily over-etched and remain undetected. Atomic scale electron microscopy is therefore needed to accurately determine the polarity. A polarity control strategy has been developed by variation of thermodynamic Al supersaturation and substrates offcut angles in order to achieve desired growth mode and polarity. We further have developed growth strategy and have optimized the epitaxial process for N-polar GaN by multiple-step temperature processes on three types of C-face SiC substrates with different offcut angles. A highquality N-polar AlGaN/GaN/AlN heterostructure has been demonstrated. A 2DEG carrier density up to 1013 cm−2 have been demonstrated for N-polar HEMT structure. 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2022. p. 66
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2239
Keywords
Nitrogen-polar, MOCVD, III-nitride, GaN, AlN, C-face SiC, HEMTs
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-187141 (URN)10.3384/9789179293918 (DOI)978-91-7929-390-1 (ISBN)978-91-7929-391-8 (ISBN)
Public defence
2022-09-08, Nobel (BL32), B-huset, Campus Valla, Linköping, 13:30 (English)
Opponent
Supervisors
Funder
Vinnova, 2016 - 05190Linköpings universitetSwedish Research Council, 2016 - 00889Swedish Foundation for Strategic Research, FL12-0181; RIF14-055; EM16-0024
Note

Additional funding agencies:

Chalmers University of technology; ABB; Ericsson; Epiluvac; FMV; Gotmic; On Semiconductor; Saab; SweGaN; UMS; Volvo Cars; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No.2009- 00971.

Available from: 2022-08-05 Created: 2022-08-05 Last updated: 2023-12-28Bibliographically approved

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