Crystals

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7 pages, 1057 KiB

Open AccessEditor’s ChoiceCommunication

Efficient Activation and High Mobility of Ion-Implanted Silicon for Next-Generation GaN Devices

by Alan G. Jacobs, Boris N. Feigelson, Joseph A. Spencer, Marko J. Tadjer, Jennifer K. Hite, Karl D. Hobart and Travis J. Anderson

Crystals 2023, 13(5), 736; https://doi.org/10.3390/cryst13050736 - 27 Apr 2023

Cited by 3 | Viewed by 2079

Abstract

Selective area doping via ion implantation is crucial to the implementation of most modern devices and the provision of reasonable device design latitude for optimization. Herein, we report highly effective silicon ion implant activation in GaN via Symmetrical Multicycle Rapid Thermal Annealing (SMRTA) [...] Read more.

Selective area doping via ion implantation is crucial to the implementation of most modern devices and the provision of reasonable device design latitude for optimization. Herein, we report highly effective silicon ion implant activation in GaN via Symmetrical Multicycle Rapid Thermal Annealing (SMRTA) at peak temperatures of 1450 to 1530 °C, producing a mobility of up to 137 cm²/Vs at 300K with a 57% activation efficiency for a 300 nm thick 1 × 10¹⁹ cm⁻³ box implant profile. Doping activation efficiency and mobility improved alongside peak annealing temperature, while the deleterious degradation of the as-grown material electrical properties was only evident at the highest temperatures. This demonstrates efficient dopant activation while simultaneously maintaining low levels of unintentional doping and thus a high blocking voltage potential of the drift layers for high-voltage, high-power devices. Furthermore, efficient activation with high mobility has been achieved with GaN on sapphire, which is known for having relatively high defect densities but also for offering significant commercial potential due to the availability of cheap, large-area, and robust substrates for devices. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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10 pages, 3112 KiB

Open AccessArticle

High Current Density Trench CAVET on Bulk GaN Substrates with Low-Temperature GaN Suppressing Mg Diffusion

by Xinyi Wen, Kwang Jae Lee, Yusuke Nakazato, Jaeyi Chun and Srabanti Chowdhury

Crystals 2023, 13(4), 709; https://doi.org/10.3390/cryst13040709 - 21 Apr 2023

Cited by 3 | Viewed by 2686

Abstract

We report that, for the first time, a low-temperature GaN (LT-GaN) layer prepared by metal–organic chemical vapor deposition (MOCVD) regrowth was used as a Mg stopping layer (MSL) for a GaN trench current–aperture vertical electron transistor (CAVET) with p-GaN as a carrier blocking [...] Read more.

We report that, for the first time, a low-temperature GaN (LT-GaN) layer prepared by metal–organic chemical vapor deposition (MOCVD) regrowth was used as a Mg stopping layer (MSL) for a GaN trench current–aperture vertical electron transistor (CAVET) with p-GaN as a carrier blocking layer (CBL). Inserting LT-GaN on top of the p-GaN effectively suppresses Mg out-diffusion into the regrown AlGaN/GaN channel, contributing to the high current capability of GaN vertical devices with a p-GaN CBL. With different MOCVD growth conditions, MSLs inserted in trench CAVETs were comprehensively investigated for the influence of MSL regrowth temperature and thickness on device performance. With the best on-state current performance obtained in this study, the trench CAVET with a 100 nm thick MSL regrown at 750 °C shows a high drain current of 3.2 kA/cm² and a low on-state resistance of 1.2 mΩ∙cm². The secondary ion mass spectrometry (SIMS) depth profiles show that the trench CAVET with the 100 nm thick MSL regrown at 750 °C has a dramatically decreased Mg diffusion decay rate (~39 nm/decade) in AlGaN/GaN channel, compared to that of the CAVET without a MSL (~104 nm/decade). In developing GaN vertical devices embedded with a Mg-doped p-type layer, the LT-GaN as the MSL demonstrates a promising approach to effectively isolate Mg from the subsequently grown layers. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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13 pages, 5164 KiB

Open AccessEditor’s ChoiceArticle

Properties of ScAlMgO₄ as Substrate for Nitride Semiconductors

by Takashi Matsuoka, Hitoshi Morioka, Satoshi Semboshi, Yukihiko Okada, Kazuya Yamamura, Shigeyuki Kuboya, Hiroshi Okamoto and Tsuguo Fukuda

Crystals 2023, 13(3), 449; https://doi.org/10.3390/cryst13030449 - 4 Mar 2023

Cited by 5 | Viewed by 2121

Abstract

SCAM has been expected to be a suitable substrate for GaN blue-light-emitting-diodes (LEDs) and high-power high electron mobility transistors (HEMTs) because of its lower lattice mismatch to GaN than that of the widely used sapphire. Considering both potential device applications, the crystal lattice [...] Read more.

SCAM has been expected to be a suitable substrate for GaN blue-light-emitting-diodes (LEDs) and high-power high electron mobility transistors (HEMTs) because of its lower lattice mismatch to GaN than that of the widely used sapphire. Considering both potential device applications, the crystal lattice and optical properties of SCAM substrates were investigated on selected high quality samples. As lattice parameters, the thermal expansion coefficient as well as the lattice constant were extrapolated from room temperature to 2000 °C by using a high temperature X-ray diffraction (XRD) system with the heating unit on a sample stage. The thermal conductance, which is also important for growing bulk SCAM crystals and the operation of devices on the SCAM substrate, was measured. Raman scattering measurements were carried out to better understand crystal lattice characteristics. It was clearly confirmed that prepared SCAM crystals were of high quality. Similar to sapphire, SCAM has the high transparency over the wide wavelength range from ultraviolet to mid-infrared. The refractive index, important for the design of any optical devices, was measured. From these results, it can be said that SCAM is a suitable substrate for nitride devices, especially LEDs and solar cells. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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9 pages, 3721 KiB

Open AccessArticle

Progress in Near-Equilibrium Ammonothermal (NEAT) Growth of GaN Substrates for GaN-on-GaN Semiconductor Devices

by Tadao Hashimoto, Edward R. Letts and Daryl Key

Crystals 2022, 12(8), 1085; https://doi.org/10.3390/cryst12081085 - 3 Aug 2022

Cited by 9 | Viewed by 2334

Abstract

This paper reviews the near-equilibrium ammonothermal (NEAT) growth of bulk gallium nitride (GaN) crystals and reports the evaluation of 2″ GaN substrates and 100 mmbulk GaN crystal grown in our pilot production reactor. Recent progress in oxygen reduction enabled growing NEAT GaN substrates [...] Read more.

This paper reviews the near-equilibrium ammonothermal (NEAT) growth of bulk gallium nitride (GaN) crystals and reports the evaluation of 2″ GaN substrates and 100 mmbulk GaN crystal grown in our pilot production reactor. Recent progress in oxygen reduction enabled growing NEAT GaN substrates with lower residual oxygen, coloration, and optical absorption. The oxygen concentration was approximately 2 × 10¹⁸ cm⁻², and the optical absorption coefficient was 1.3 cm⁻¹ at 450 nm. Maps of full-width half maximum (FWHM) of X-ray diffraction rocking curveswere generated for grown crystals and finished wafers. The X-ray rocking curve maps confirmed high-quality and uniform microstructure across the entire surface of the bulk crystals and substrates. The average FWHM of the 50 best bulk crystals from the recent batch was 28 ± 4 arcsec for the 002 diffraction and 34 ± 5 arcsec for the 201 diffraction, with an average radius of curvature of 20 m. X-ray topography measured on both sides of the bulk crystals implied that the density of dislocations wasreduced by one order of magnitude during the NEAT growth. A typical NEAT GaN substrate shows dislocation density of about 2 × 10⁵ cm⁻². Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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Review

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17 pages, 3227 KiB

Open AccessEditor’s ChoiceReview

Progress in Ammonothermal Crystal Growth of Gallium Nitride from 2017–2023: Process, Defects and Devices

by Nathan Stoddard and Siddha Pimputkar

Crystals 2023, 13(7), 1004; https://doi.org/10.3390/cryst13071004 - 23 Jun 2023

Cited by 9 | Viewed by 2667

Abstract

Gallium nitride continues to be a material of intense interest for the ongoing advancement of electronic and optoelectronic devices. While the bulk of today’s markets for low-performance devices is still met with silicon and blue/UV LEDs derived from metal–organic chemical vapor deposition gallium [...] Read more.

Gallium nitride continues to be a material of intense interest for the ongoing advancement of electronic and optoelectronic devices. While the bulk of today’s markets for low-performance devices is still met with silicon and blue/UV LEDs derived from metal–organic chemical vapor deposition gallium nitride grown on foreign substrates such as sapphire and silicon carbide, the best performance values consistently come from devices built on bulk-grown gallium nitride from native seeds. The most prominent and promising of the bulk growth methods is the ammonothermal method of high-pressure solution growth. The state-of-the-art from the last five years in ammonothermal gallium nitride technology is herein reviewed within the general categories of growth technology, characterization and defects as well as device performance. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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17 pages, 5183 KiB

Open AccessReview

The Fabrication of GaN Nanostructures Using Cost-Effective Methods for Application in Water Splitting

by Xin Xi, Lixia Zhao, Tuo Li, Xiaodong Li and Chao Yang

Crystals 2023, 13(6), 873; https://doi.org/10.3390/cryst13060873 - 26 May 2023

Cited by 3 | Viewed by 1878

Abstract

The adjustable bandgap, single crystal structure, and strong chemical inertness of GaN materials make them excellent candidates for water splitting applications. The fabrication of GaN nanostructures can enhance their water splitting performance by increasing their surface area, improving photon absorption, and accelerating photocatalytic [...] Read more.

The adjustable bandgap, single crystal structure, and strong chemical inertness of GaN materials make them excellent candidates for water splitting applications. The fabrication of GaN nanostructures can enhance their water splitting performance by increasing their surface area, improving photon absorption, and accelerating photocatalytic reactions. Developing cost-effective methods to fabricate GaN nanostructures is crucial to promote the development of GaN-based materials in water splitting applications. In this review, we introduce the main cost-effective techniques for the fabrication of GaN nanostructures and highlight future development directions. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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12 pages, 6056 KiB

Open AccessReview

A Review of Homoepitaxy of III-Nitride Semiconductors by Metal Organic Chemical Vapor Deposition and the Effects on Vertical Devices

by Jennifer K. Hite

Crystals 2023, 13(3), 387; https://doi.org/10.3390/cryst13030387 - 24 Feb 2023

Cited by 3 | Viewed by 2306

Abstract

This paper reviews some of the basic issues in homoepitaxial growth of III-nitrides to enable a vertical device technology. It focuses on the use of metal organic chemical vapor deposition (MOCVD) to grow GaN and explores the effects of the native substrate characteristics [...] Read more.

This paper reviews some of the basic issues in homoepitaxial growth of III-nitrides to enable a vertical device technology. It focuses on the use of metal organic chemical vapor deposition (MOCVD) to grow GaN and explores the effects of the native substrate characteristics on material quality, interface composition, and device performance. A review of theoretical work understanding dopants in the ultra-wide III-nitride semiconductors, AlN and BN, is also included for future efforts expanding the technology into those materials. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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23 pages, 7139 KiB

Open AccessReview

Characterization of Defects in GaN: Optical and Magnetic Resonance Techniques

by Jaime A. Freitas, Jr., James C. Culbertson and Evan R. Glaser

Crystals 2022, 12(9), 1294; https://doi.org/10.3390/cryst12091294 - 14 Sep 2022

Cited by 2 | Viewed by 2861

Abstract

GaN and its alloys with InN and AlN are of technological importance for a variety of optical, electronic, and optoelectronic devices due to its high thermal conductivity, wide band gap, high breakdown voltage and high saturation velocity. GaN-based devices now provide superior performance [...] Read more.

GaN and its alloys with InN and AlN are of technological importance for a variety of optical, electronic, and optoelectronic devices due to its high thermal conductivity, wide band gap, high breakdown voltage and high saturation velocity. GaN-based devices now provide superior performance for a variety of high power, high frequency, high temperature, and optical applications. The major roadblock for the full realization of Nitride semiconductor potential is still the availability of affordable large-area and high-quality native substrates with controlled electrical properties. Despite the impressive accomplishments recently achieved by techniques such as hydride vapor phase epitaxy and ammonothermal for GaN growth, much more must be attained before establishing a fully satisfactory bulk growth method for this material. Recent results suggest that ammonothermal GaN wafers can be successfully used as seeds to grow thick freestanding GaN wafers by hydride vapor phase epitaxy. A brief review of defect-sensitive optical and paramagnetic spectroscopy techniques employed to evaluate structural, optical, and electronic properties of the state-of-the-art bulk and thick-film (quasi-bulk) Nitride substrates and homoepitaxial films is presented. Defects control the performance of devices and feeding back knowledge of defects to growth efforts is key to advancing technology. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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10 pages, 1467 KiB

Open AccessReview

Vacancy Defects in Bulk and Quasi-Bulk GaN Crystals

by Filip Tuomisto

Crystals 2022, 12(8), 1112; https://doi.org/10.3390/cryst12081112 - 9 Aug 2022

Cited by 3 | Viewed by 2123

Abstract

In-grown vacancy defects in bulk and quasi-bulk GaN crystals have been extensively studied with positron annihilation spectroscopy. High concentrations of Ga-vacancy-related defects are found irrespective of the growth method used in crystals with a high O contamination or intentional O doping, and they [...] Read more.

In-grown vacancy defects in bulk and quasi-bulk GaN crystals have been extensively studied with positron annihilation spectroscopy. High concentrations of Ga-vacancy-related defects are found irrespective of the growth method used in crystals with a high O contamination or intentional O doping, and they act as the dominant compensating native defect for n-type conductivity. Low-temperature crystal growth also leads to high concentrations of Ga-vacancy-related defects. Ga vacancies are present in the crystals as a part of the different types of complexes with O, H, and/or V_N, depending on the growth conditions. Full article

(This article belongs to the Special Issue Research in GaN-based Materials and Devices)

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