Edge modes in finite-size systems with different edge terminals

We investigate the behavior of edge modes in the presence of different edge terminations and long-range(LR)hopping.Here,we mainly focus on such model crystals with two different types of structures(type I:“…-P-Q-P-Q-…”and type II:“…=P-Q=P-Q=…”),where P and Q represent crystal lines(CLs),while the symbols“-”and“=”denote the distance between the nearest neighbor(NN)CLs.Based on the lattice model Hamiltonian with LR hopping,the existence of edge modes is determined analytically by using the transfer matrix method(TMM)when different edge terminals are taken into consideration.Our findings are consistent with the numerical results obtained by the exact diagonalization method.We also notice that edge modes can exhibit different behaviors under different edge terminals.Our result is helpful in solving novel edge modes in honeycomb crystalline graphene and transition metal dichalcogenides with different edge terminals.

Investigation on Breakdown Characteristics of Various Surface Terminal Structures for GaN-Based Vertical P-i-N Diodes

GaN-based vertical P-i-N diode with mesa edge terminal structure due to electric field crowding effect, the breakdown voltage of the device is significantly reduced. This work investigates three terminal structures, including deeply etched, bevel, and stepped-mesas terminal structures, to suppress electric field crowding effects at the device and junction edges. Deeply-etched mesa terminal yields a breakdown voltage of 1205 V, i.e., 89% of the ideal voltage. The bevel-mesa terminal achieves about 89% of the ideal breakdown voltage, while the step-mesa terminal is less effective in mitigating electric field crowding, at about 32% of the ideal voltage. This work can provide an important reference for the design of high-power, high-voltage GaN-based P-i-N power devices, finding a terminal protection structure suitable for GaNPiN diodes to further enhance the breakdown performance of the device and to unleash the full potential of GaN semiconductor materials.

A landscape of β-Ga_(2)O_(3) Schottky power diodes

β-Ga_(2)O_(3) Schottky barrier diodes have undergone rapid progress in research and development for power electronic applications.This paper reviews state-of-the-art β-Ga_(2)O_(3) rectifier technologies,including advanced diode architectures that have enabled lower reverse leakage current via the reduced-surface-field effect.Characteristic device properties including onresistance,breakdown voltage,rectification ratio,dynamic switching,and nonideal effects are summarized for the different devices.Notable results on the high-temperature resilience of β-Ga_(2)O_(3) Schottky diodes,together with the enabling thermal packaging solutions,are also presented.

Hybrid-anode structure designed for a high-performance quasi-vertical GaN Schottky barrier diode

A quasi-vertical Ga N Schottky barrier diode with a hybrid anode structure is proposed to trade off the on-resistance and the breakdown voltage.By inserting a Si N dielectric between the anode metal with a relatively small length,it suppresses the electric field crowding effect without presenting an obvious effect on the forward characteristics.The enhanced breakdown voltage is ascribed to the charge-coupling effect between the insulation dielectric layer and Ga N.On the other hand,the current density is decreased beneath the dielectric layer with the increasing length of the Si N,resulting in a high on-resistance.Furthermore,the introduction of the field plate on the side wall forms an metal-oxide-semiconductor(MOS)channel and decreases the series resistance,but also shows an obvious electric field crowding effect at the bottom of the mesa due to the quasi-vertical structure.

Determination of band alignment between GaO_(x)and boron doped diamond for a selective-area-doped termination structure

An n-GaO_(x)thin film is deposited on a single-crystal boron-doped diamond by RF magnetron sputtering to form the pn heterojunction.The n-Ga Ox thin film presents a small surface roughness and a large optical band gap of 4.85 e V.In addition,the band alignment is measured using x-ray photoelectron spectroscopy to evaluate the heterojunction properties.The GaO_(x)/diamond heterojunction shows a type-Ⅱstaggered band configuration,where the valence and conduction band offsets are 1.28 e V and 1.93 e V,respectively.These results confirm the feasibility of the use of n-GaO_(x)as a termination structure for diamond power devices.

Physical mechanism of field modulation effects in ion implanted edge termination of vertical GaN Schottky barrier diodes

In this study,the physical properties of F ion-implanted GaN were thoroughly studied,and the related electric-field modulation mechanisms in ion-implanted edge termination were revealed.Transmission electron microscopy re.sults indicate that the ion-implanted region maintains a single-crystal structure even with the implantation of high-energy F ions,indicating that the high resistivity of the edge termination region is not induced by amorphization.Alternately,ion implantation-induced deep levels could compensate the electrons and lead to a highly resistive layer In addition to the bulk ffect,the direct bombardment of high-energy F ions resulted in a rough and nitrogen-deficient surface,which was confirmed via atomic force microscopy(AFM)and X-ray photoelectron spectroscopy,The implanted surface with a large density of nitrogen vacancies can accommodate electrons,and it is more conductive than the bulk in the implanted region,which is validated via spreading resistance profiling and conductive AFM measurements.Under reverse bias,the implanted surface can spread the potential in the lateral direction,whereas the acceptor traps capture electrons acting as space charges,shifting the peak electric field into the bulk region in the vertical direction.As a result,the Schottky barrier diode terminated with high-energy F ion-implanted regions exhibits a breakdown voltage of over 1.2 kv.

Development of 10 kV 4H-SiC JBS diode with FGR termination

The design, fabrication, and electrical characteristics of the 4H-SiC JBS diode with a breakdown voltage higher than 10 kV are presented. 60 floating guard rings have been used in the fabrication. Numerical simulations have been performed to select the doping level and thickness of the drift layer and the effectiveness of the edge termination technique. The n-type epilayer is 100 μm in thickness with a doping of 6 × 10^14 cm^-3. The on-state voltage was 2.7 V at JF = 13 A/cm^2.

1.4 kV 4H-SiC PiN diode with a robust non-uniform floating guard ring termination

This paper presents the design and fabrication of an effective, robust and process-tolerant floating guard ring termination on high voltage 4H-SiC PiN diodes. Different design factors were studied by numerical simulations and evaluated by device fabrication and measurement. The device fabrication was based on a 12 μm thick drift layer with an N-type doping concentration of 8 × 10^15 cm^-3. P^＋ regions in the termination structure and anode layer were formed by multiple aluminum implantations. The fabricated devices present a highest breakdown voltage of 1.4 kV, which is higher than the simulated value. For the fabricated 15 diodes in one chip, all of them exceeded the breakdown voltage of 1 kV and six of them reached the desired breakdown value of 1.2 kV.