Engineering topics

Fu, Kai

Publications and source records attributed to Fu, Kai.

8 records

DOE OSTI2023

Anisotropic electrical properties of NiO x /β-Ga 2 O 3 p-n heterojunctions on (2̅01), (001), and (010) crystal orientations

Abstract NiO x / β -Ga 2 O 3 p-n heterojunctions fabricated on ( 2 ̅ 01 ) , ( 001 ) , and ( 010 ) β -Ga 2 O 3 substrates show distinctly anisotropic electrical properties. All three devices exhibited excellent rectification ≥10 9 , and turn-on voltages >2.0 V. The ( 010 ) device showed very different turn-on voltage, specific on-resistance, and reverse recovery time compared with ( 2 ̅ 01 ) and ( 001 ) devices. Moreover, it is calculated that the interface trap state densities for ( 2 ̅ 01 ) , ( 001 ) , and ( 010 ) plane devices are 4.3 × 10 10 , 7.4 × 10 10 , and 1.6 × 10 11 eV –1 cm –2 , respectively. These differences in the NiO x / β -Ga 2 O 3 heterojunctions are attributed to the different atomic configurations, the density of dangling bonds, and interface trap state densities.

Physics↗

DOE OSTI2023

Low-leakage regrown GaN p-n junctions for GaN power devices

Fabricating a regrown GaN p-n junction includes depositing a n-GaN layer on a substrate including n + -GaN, etching a surface of the n-GaN layer to yield an etched surface, depositing a p-GaN layer on the etched surface, etching a portion of the n-GaN layer and a portion of the p-GaN layer to yield a mesa opposite the substrate, and passivating a portion of the p-GaN layer around an edge of the mesa. The regrown GaN p-n junction is defined at an interface between the n-GaN layer and the p-GaN layer. The regrown GaN p-n junction includes a substrate, a n-GaN layer on the substrate having an etched surface, a p-GaN layer on the etched surface, a mesa defined by an etched portion of the n-GaN layer and an etched portion of the p-GaN layer, and a passivated portion of the p-GaN layer around an edge of the mesa.

Zhao, Yuji↗

DOE OSTI2023

Understanding the Breakdown Behavior of Ultrawide-Bandgap Boron Nitride Power Diodes Using Device Modeling

Herein, a device study using technology computer-aided design simulation to theoretically analyze the electrical performance of ultrawide-bandgap boron nitride (BN)-based vertical junction devices is performed, including h-BN Schottky diode, h-BN pn diode, and h-BN/AlN pn diode; this is also the first demonstration of the BN power devices in simulation. The material properties of BN are defined with recently reported data, and the physical mechanisms of the device performance are systematically investigated. Additionally, the h-BN junctions in this simulation shows excellent performance, especially for breakdown behaviors. Schottky diode shows a turn-on voltage of 0.6 V for Pt Schottky contact and breakdown voltages over 450 V for 5 μm, 6 × 10 15 cm –3 p-type-doped drift layer; The h-BN pn diode shows a turn-on voltage of 6 V and breakdown voltages over 3 kV with a critical electric field of 13.6 MV cm –1 for 2.5 μm, 2 × 10 16 cm –3 p-type-doped drift layer. The h-BN/AlN heterojunction pn diode shows a turn-on voltage of 5.8 V and breakdown voltage over 2 kV for 2.5 μm, 2 × 10 16 cm –3 n-type-doped AlN drift layer. Herein, an understanding of the device principles of vertical BN junctions is provided, which can serve as a reference for the future development of robust BN power electronics.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Toward high efficiency at high temperatures: Recent progress and prospects on InGaN-Based solar cells

III-nitride InGaN material is an ideal candidate for the fabrication of high performance photovoltaic (PV) solar cells, especially for high-temperature applications. Over the past decade, significant efforts have been made to improve the PV performance of InGaN-based solar cells. In this paper, we perform a comprehensive review of the recent developments in InGaN-based solar cells. The topics of discussion include theoretical modeling, material epitaxy, device engineering, and high-temperature measurement. Particularly, we highlight subjects such as substrate technology, and properties that are unique to InGaN materials such as polarization control and their positive thermal coefficient. To date, outstanding high-temperature InGaN-based solar cells with quantum efficiency approaching 80% at 450 °C have been demonstrated. In conclusion, future innovations in epitaxy science, device engineering, and integration methods are required to further advance the efficiency and expand the applications of InGaN-based solar cells.

14 SOLAR ENERGY↗

DOE OSTI2022

GaN-based threshold switching device and memory diode

A switching device including a GaN substrate; an unintentionally doped GaN layer on a first surface of the GaN substrate; a regrown unintentionally doped GaN layer on the unintentionally doped GaN layer; a regrowth interface between the unintentionally doped GaN layer and the regrown unintentionally doped GaN layer; a p-GaN layer on the regrown unintentionally doped GaN layer; a first electrode on the p-GaN layer; and a second electrode on a second surface of the GaN substrate.

Fu, Kai↗

DOE OSTI2022

GaN vertical-channel junction field-effect transistors with regrown p-GaN by metal organic chemical vapor deposition (MOCVD)

Fabricating a vertical-channel junction field-effect transistor includes forming an unintentionally doped GaN layer on a bulk GaN layer by metalorganic chemical vapor deposition, forming a Cr/SiO 2 hard mask on the unintentionally doped GaN layer, patterning a fin by electron beam lithography, defining the Cr and SiO 2 hard masks by reactive ion etching, improving a regrowth surface with inductively coupled plasma etching, removing hard mask residuals, regrowing a p-GaN layer, selectively etching the p-GaN layer, forming gate electrodes by electron beam evaporation, and forming source and drain electrodes by electron beam evaporation. The resulting vertical-channel junction field-effect transistor includes a doped GaN layer, an unintentionally doped GaN layer on the doped GaN layer, and a p-GaN regrowth layer on the unintentionally doped GaN layer. Portions of the p-GaN regrowth layer are separated by a vertical channel of the unintentionally doped GaN layer.

Zhao, Yuji↗

DOE OSTI2022

Properties and device performance of BN thin films grown on GaN by pulsed laser deposition

Wide and ultrawide-bandgap semiconductors lie at the heart of next-generation high-power, high-frequency electronics. Here, in this paper, we report the growth of ultrawide-bandgap boron nitride (BN) thin films on wide-bandgap gallium nitride (GaN) by pulsed laser deposition. Comprehensive spectroscopic (core level and valence band x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Raman) and microscopic (atomic force microscopy and scanning transmission electron microscopy) characterizations confirm the growth of BN thin films on GaN. Optically, we observed that the BN/GaN heterostructure is second-harmonic generation active. Moreover, we fabricated the BN/GaN heterostructure-based Schottky diode that demonstrates rectifying characteristics, lower turn-on voltage, and an improved breakdown capability (~234 V) as compared to GaN (~168 V), owing to the higher breakdown electrical field of BN. Our approach is an early step toward bridging the gap between wide and ultrawide-bandgap materials for potential optoelectronics as well as next-generation high-power electronics.

42 ENGINEERING↗

DOE OSTI2022

Plasma-based edge terminations for gallium nitride power devices

A p-n diode includes a first electrode, a n-GaN layer on the first electrode, a p-GaN layer on the n-GaN layer, and a second electrode on a first portion of the p-GaN layer. A region of the p-GaN layer surrounding the electrode is a passivated region. Treating a GaN power device having a p-GaN layer includes covering a portion of the p-GaN layer with a metal layer, exposing the p-GaN layer to a hydrogen plasma, and thermally annealing the p-GaN layer, thereby passivating a region of the p-GaN layer proximate the metal layer.

Zhao, Yuji↗