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Mg-doping and free-hole properties of hot-wall MOCVD GaN
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. (Centre for III-nitride technology (C3NiT); Terahertz Materials Analysis Center - THeMAC)ORCID iD: 0000-0003-4902-5383
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. (Centre for III-nitride technology (C3NiT))ORCID iD: 0000-0002-7042-2351
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Iceland, Iceland. (Centre for III-nitride technology (C3NiT))
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. (Centre for III-nitride technology (C3NiT))
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2022 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 131, no 18, article id 185704Article in journal (Refereed) Published
Abstract [en]

The hot-wall metal-organic chemical vapor deposition (MOCVD), previously shown to enable superior III-nitride material quality and high performance devices, has been explored for Mg doping of GaN. We have investigated the Mg incorporation in a wide doping range ( 2.45 x 10( 18) cm(-3) up to 1.10 x 10(20) cm(-3)) and demonstrate GaN:Mg with low background impurity concentrations under optimized growth conditions. Dopant and impurity levels are discussed in view of Ga supersaturation, which provides a unified concept to explain the complexity of growth conditions impact on Mg acceptor incorporation and compensation. The results are analyzed in relation to the extended defects, revealed by scanning transmission electron microscopy, x-ray diffraction, and surface morphology, and in correlation with the electrical properties obtained by Hall effect and capacitance-voltage (C-V) measurements. This allows to establish a comprehensive picture of GaN:Mg growth by hot-wall MOCVD providing guidance for growth parameters optimization depending on the targeted application. We show that substantially lower H concentration as compared to Mg acceptors can be achieved in GaN:Mg without any in situ or post-growth annealing resulting in p-type conductivity in as-grown material. State-of-the-art p-GaN layers with a low resistivity and a high free-hole density (0.77 omega cm and 8.4 x 10( 17) cm(-3), respectively) are obtained after post-growth annealing demonstrating the viability of hot-wall MOCVD for growth of power electronic device structures. (C)2022 Author(s).

Place, publisher, year, edition, pages
AIP Publishing , 2022. Vol. 131, no 18, article id 185704
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-185485DOI: 10.1063/5.0089406ISI: 000796003000002OAI: oai:DiVA.org:liu-185485DiVA, id: diva2:1662720
Note

Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program [2016-05190]; Linkoping University; Chalmers University of Technology; Ericsson; Epiluvac; FMV; Gotmic; Hexagem; Hitachi Energy; On Semiconductor; Saab; SweGaN; UMS; Swedish Research Council VR [2016-00889]; Swedish Foundation for Strategic Research [RIF14-055, RIF14-0074, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; KAW Foundation

Available from: 2022-06-01 Created: 2022-06-01 Last updated: 2024-03-01
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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