GaN Schottky Barrier Diodes Research Articles

Studies on the Thermal Stability of Ni/n–GaN and Pt/n–GaN Schottky Barrier Diodes

High temperature annealing of Ni and Pt Schottky diodes on n-GaN has been investigated. Ni/n–GaN and Pt/n–GaN Schottky diodes were fabricated using ultra high vacuum and annealed at various temperatures (200 °C−700 °C) using rapid thermal anneal system. It was observed that in case of Ni/GaN diodes, the Schottky barrier height increases for 200 °C and then decreases with increase in annealing temperature. For Pt/GaN diodes, the barrier height found to decrease with increase in annealing temperature. The observed variation of barrier height and ideality factor is discussed on the basis of interfacial chemical reactions between metal and semiconductor.

Franz–Keldysh effect in n-type GaN Schottky barrier diode under high reverse bias voltage

The photocurrent of GaN vertical Schottky barrier diodes was investigated under sub-bandgap wavelength light irradiation. Under a low reverse bias voltage, the photocurrent is induced by internal photoemission, while under a high reverse bias voltage, the photocurrent increases significantly with the bias voltage. This is due to sub-bandgap optical absorption in a depletion region due to the Franz–Keldysh effect. The voltage and wavelength dependences of the photocurrent are successfully explained quantitatively.

DLTS analysis of high resistive edge termination technique‐induced defects in GaN‐based Schottky barrier diodes

Efficient edge terminations are fundamental for power electronic devices. High resistive edge termination technique obtained by ion implantation is a possible solution for GaN Schottky barrier diodes (SBD), but may induce defects detrimental to the devices. In this work, two sets of GaN SBDs, with or without a high resistive guard ring edge termination, were investigated by deep levels transient spectroscopy (DLTS). The corresponding DLTS spectra of devices with guard ring were compared to those of as‐fabricated devices (without). Four deep traps at 0.13, 0.26, 0.35, and 0.51 eV were observed below the conduction band in as‐fabricated structures while the ones with guard ring exhibit two additional levels at 0.47 and 0.80 eV and a strong enhancement in DLTS peaks magnitude. Further investigations showed that the additional traps detected in SBD devices with guard ring were consistent with ion implantation‐induced damages. These observations highlight the impact of high resistive edge termination technique on our devices and raise the need of optimization of such crucial structure for the improvement of GaN‐based Schottky barrier diode.

Improved performance in vertical GaN Schottky diode assisted by AlGaN tunneling barrier

In a vertical GaN Schottky barrier diode, the free electron concentration n in the 6-μm-thick drift layer was found to greatly impact the diode reverse leakage current, which increased from 2.1 × 10−7 A to 3.9 × 10−4 A as n increased from 7.5 × 1014 cm−3 to 6.3 × 1015 cm−3 at a reverse bias of 100 V. By capping the drift layer with an ultrathin 5-nm graded AlGaN layer, reverse leakage was reduced by more than three orders of magnitude with the same n in the drift layer. We attribute this to the increased Schottky barrier height with the AlGaN at the surface. Meanwhile, the polarization field within the graded AlGaN effectively shortened the depletion depth, which led to the formation of tunneling current at a relatively small forward bias. The turn-on voltage in the vertical Schottky diodes was reduced from 0.77 V to 0.67 V—an advantage in reducing conduction loss in power switching applications.

High-voltage vertical GaN Schottky diode enabled by low-carbon metal-organic chemical vapor deposition growth

Vertical GaN Schottky barrier diode (SBD) structures were grown by metal-organic chemical vapor deposition on free-standing GaN substrates. The carbon doping effect on SBD performance was studied by adjusting the growth conditions and spanning the carbon doping concentration between ≤3 × 1015 cm−3 and 3 × 1019 cm−3. Using the optimized growth conditions that resulted in the lowest carbon incorporation, a vertical GaN SBD with a 6-μm drift layer was fabricated. A low turn-on voltage of 0.77 V with a breakdown voltage over 800 V was obtained from the device.

The ESD protection characteristic and low-frequency noise analysis of GaN Schottky barrier diode with fluorine-based plasma treatment

In this work, the electrostatic discharge (ESD) protection of Schottky diode with fluorine-based plasma treatment is proven by transmission-line pulse (TLP) measurement. And the low-frequency noise (LFN) is used to determine the activation energy (Ea) of a GaN Schottky diode with plasma treatment. This experiment compares the Schottky diode with CF4 and CHF3 plasma treatment, respectively with a standard Schottky diode to determine the characteristics and to assess the low-frequency noise and the ESD protection ability.

Improved Vertical GaN Schottky Diodes with Ion Implanted Junction Termination Extension

The realization of selectively implanted p-type regions in GaN as well as an understanding of processing effects that cause carrier type conversion are key enabling steps for vertical GaN devices. Here, GaN Schottky barrier diodes (SBDs) with edge termination formed by either a field plate or junction termination extension (JTE) achieved by ion implanted and symmetric multicycle rapid thermal annealing (SMRTA) are presented. The devices with JTE exhibited substantially reduced leakage currents and improved turn-on characteristics. This is attributed to the elimination of the plasma process steps associated with the deposition and patterning of the field oxide layer required in a field plate process. The breakdown characteristics were studied by electroluminescence imaging, and is indicative of avalanche behavior. The realization of vertical GaN devices with low reverse leakage and ion implanted termination regions represents a key step for future power electronic devices.

0.34 <inline-formula> <tex-math notation="LaTeX">$\text{V}_{\mathrm {T}}$ </tex-math> </inline-formula> AlGaN/GaN-on-Si Large Schottky Barrier Diode With Recessed Dual Anode Metal

A large GaN-Schottky barrier diode (SBD) with a recessed dual anode metal is proposed to achieve improved the forward characteristics without a degradation of the reverse performances. Using optimized dry etch condition for a large device, the electrical characteristics of the device are demonstrated when applying the recessed dual anode metal and changing the recess depths. The device size and channel width are 4 mm2 and 63 mm, respectively. The 16-nm recessed dual anode metal SBD has a turn- on voltage of 0.34 V, a breakdown voltage of 802 V, and a reverse leakage current of $1.82~\mu \text{A}$ /mm at −15 V. The packaged SBD exhibits a forward current of 6.2 A at 2 V and a reverse recovery charge of 11.54 nC.

50 A vertical GaN Schottky barrier diode on a free-standing GaN substrate with blocking voltage of 790 V

This paper reports on vertical GaN Schottky barrier diodes (SBDs) fabricated on a free-standing GaN substrate with different sizes of Schottky electrode. The fabricated SBDs with 3 × 3 mm2 Schottky electrodes exhibited both a forward current of 50 A and a blocking voltage of 790 V. To our knowledge, the characteristics of operation with a simultaneous high forward current and high blocking voltage are reported for the first time for vertical GaN SBDs on free-standing GaN substrates. The dependence of these characteristics on the Schottky electrode size is also reported in detail.

Bias-Enhanced Visible-Rejection of GaN Schottky Barrier Ultraviolet Photodetectors

The bias-enhanced performance of visible-blind ultraviolet (UV) detection of GaN Schottky barrier diodes has been studied. The UV response of the Schottky diodes was found to be vastly amplified at elevated reverse bias, leading to the observation of the voltage-dependent gain arising from the defect-induced Schottky barrier lowering effect. In contrast, the visible light response of the GaN Schottky diodes shows insignificant voltage dependence because of the dominance of the internal photoemission absorption. Thus, the visible rejection ratio, defined as the responsivity of UV over visible range, can be greatly enhanced at high operating bias for the UV detectors based on the GaN Schottky barrier diodes. The observation has been supported by both experimental results and simulation data, and has been utilized to minimize the interference between the monolithically integrated GaN photodetectors and power light-emitting diodes (LEDs) in the present study of LED communication.

GaN Schottky Barrier Diode With TiN Electrode for Microwave Rectification

GaN Schottky barrier diodes (SBDs) with low turn-on voltage are developed for microwave rectification. The diodes with reactively-sputtered TiN electrodes have a lower turn-on voltage compared with the diodes with Ni electrode, while the on-resistance, the reverse leakage current, and the reverse breakdown characteristics are comparable to each other. Theoretically, the SBDs with TiN electrodes can enhance the efficiency of a rectenna circuit at 2.45 GHz from 84% to 89% when the turn-on voltage decreases from 1.0 to 0.5 V.

High-voltage AlGaN/GaN Schottky barrier diodes on silicon using a post-process O2 treatment

High-voltage AlGaN/GaN Schottky barrier diodes (SBDs) were fabricated using on a silicon (111) substrate, and a post-process O2 treatment was carried out to reduce the leakage current and increase the breakdown voltage. Time-of-flight secondary ion mass spectroscopy revealed that, following the post-process O2 treatment, oxygen diffused into an AlGaN barrier and AlO was generated. A significant suppression of the leakage current (of approximately 6 orders of magnitude) occurred in the buffer isolation structures following the O2 treatment. Our method also resulted in suppression of the surface leakage current through the mesa-etched surface. A virgin GaN SBD exhibited a leakage current of 1.76×10−2A/cm2, whereas the equivalent O2-treated device had a leakage current of 1.75×10−4A/cm2 (the anode–cathode distance was LAC=10μm, and the applied bias was −100V). This reduction in the leakage current was caused by surface passivation at the anode and cathode. The post-process O2 treatment also increased the breakdown voltage from Vb=808V to Vb=1590V for a device with LAC=10μm. GaN SBDs with and without the post-process O2 treatment exhibited low specific on-resistance of Ron,sp=2.51mΩcm2 and Ron,sp=2.48mΩcm2, respectively, with LAC=10μm. Devices with the post-process O2 treatment exhibited a figure of merit of Vb2/Ron,sp=1006MW/cm2, whereas devices without the O2 treatment exhibited a figure of merit of Vb2/Ron,sp=263MW/cm2. These high-voltage GaN SBDs employing the post-process O2 treatment are suitable for applications including DC–DC converters, inverters, and power factor correction circuits, where high voltage operation is required with low leakage currents.

Wrap around field plate technique for GaN Schottky barrier diodes

AbstractIn this paper, we propose a wrap around field termination technique for a vertical Schottky barrier diode fabricated on a free standing GaN substrate. Unlike conventional field plate designs, in the wrap around structure the field plate surrounds the active device area. This allows for better control of the electric field distribution, and reduces field-crowding. 2D finite element simulations using ATLAS show a uniform field distribution across the device. Calculations show that the Ron increases relative to the conventional field plate. A break down voltage of 1300V was predicted for a 5um thick epilayer.

Numerical Determination of Schottky Barrier Height of Nickel/n-Type Gallium Nitride Diodes Formed on Free-standing Substrates

To validate the condition for applying thermionic emission (TE) theory when depletion-layer width is larger than carrier mean free path, Schottky barrier height qΦB of reported nickel/n-type gallium-nitride diodes was numerically determined. The forward-current/voltage characteristics of diodes on free-standing substrates were precisely reproduced by qΦB of 0.98 eV. Although this qΦB is consistent with the reported value (0.99 eV) determined from capacitance-voltage measurement, it is 0.05 eV higher than the reported value (0.93 eV) determined from TE theory. This discrepancy indicates that qΦB of GaN Schottky barrier diodes needs to be determined not by analytically but by numerically fitting the experimental data.

GaN Schottky Barrier Diodes with High-Resistivity Edge Termination Formed by Boron Implantation

Edge termination is one of the key technologies for fabricating high voltage Schottky barrier diodes (SBDs), which could effectively reduce the peak electric field along the Schottky contact edge and enhance the breakdown voltage. We adopt a high-resistivity ring structure as the edge termination for planar GaN SBDs. The edge termination is formed by self-aligned boron implantation on the edge of devices to form a highly damaged layer. In the implant dose and energy ranges studied experimentally, the GaN SBDs show improved blocking characteristics in terms of reverse leakage current and breakdown voltage at higher implant dose or implant energy. Meanwhile, the forward turn-on characteristics of the GaN SBDs exhibit no apparent change.

Analysis of electrical properties and deep level defects in undoped GaN Schottky barrier diode

Electrical and deep level defects have been investigated in GaN Schottky barrier diode (SBD) in the temperature ranging from 125K to 425K. The study was carried out by combined current density–voltage (J–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) characterization techniques. It is found that the ideality factor n of the diode decreases and the corresponding Schottky barrier height (SBH) increases with increasing temperature, which indicates the barrier in-homogeneity at metal/semiconductor interface. Thermionic emission with Gaussian distribution of SBHs is thought to be responsible for the electrical behavior of the diode over the temperature region. The possible explanation for this discrepancy in the estimated SBHs from J–V and C–V is presented. The DLTS measurement has revealed two deep level traps in GaN with activation energies Ec−0.23eV and Ec−0.45eV having different capture cross-sections. In addition, we observed that the reverse leakage current in GaN SBD above 275K is due to Frenkel–Poole emission (FPE). The estimated emission barrier height by FPE model is about ~0.25eV. Hence, the reverse leakage current is due to the emission of electrons from the trap state near the metal–semiconductor interface into a continuum of states, associated with conductive dislocations.

Effects of post-oxidation on leakage current of high-voltage AlGaN/GaN Schottky barrier diodes on Si(1 1 1) substrates

The effects of post-oxidation on the leakage current of high-voltage AlGaN/GaN Schottky barrier diodes (SBDs) on Si(111) substrates were investigated. Auger electron spectroscopy was used to study post-oxidation mechanisms. The group-III oxides, AlOx or GaOx, were formed as indicated the oxygen on the AlGaN layer after post-oxidation. The formation of group-III oxides resulted in passivation. The diffusion of Ni into the AlGaN layer was also detected owing to the post-oxidation annealing shallow states near the Schottky contact. When post-oxidation was performed at 600°C, all Ni at the Schottky contact was combined with oxygen. This high post-oxidation temperature was therefore unsuitable because the Schottky interface changed from Ni/AlGaN to Au/AlGaN. Leakage current until breakdown was considerably decreased after post-oxidation at 500°C. The breakdown voltage of GaN SBD was increased from 351 to 524V at a drift length of 20μm by the post-oxidation. The figure-of-merit (BV2/Ron,sp) of identical device was also improved from 29.6 to 53.1 by the post-oxidation. Our results suggest that post-oxidation is suitable for GaN power switch fabrication.

차세대 전력 스위치용 1.5 kV급 GaN 쇼트키 장벽 다이오드

The O₂ annealing technique has considerably suppressed the leakage current of GaN power devices, but this forms NiO at Ni-based Schottky contact with increasing on-resistance. The purpose of the present study was to fabricate 1.5 ㎸ GaN Schottky barrier diodes by improving O₂-annealing process and GaN buffer. The proposed O₂ annealing performed after alloying ohmic contacts in order to avoid NiO construction. The ohmic contact resistance (R<SUB>C</SUB>) was degraded from 0.43 to 3.42 Ω-㎜ after O₂ annealing at 800 ℃. We can decrease RC by lowering temperature of O₂ annealing. The isolation resistance of test structure which indicated the surface and buffer leakage current was significantly increased from 2.43×10? to 1.32×10<SUP>13</SUP> Ω due to O₂ annealing. The improvement of isolation resistance can be caused by formation of group-Ⅲ oxides on the surface. The leakage current of GaN Schottky barrier diode was also suppressed from 2.38×10<SUP>-5</SUP> to 1.68×10<SUP>-7</SUP> A/mm at ?100 V by O₂ annealing. The GaN Schottky barrier diodes achieved the high breakdown voltage of 700, 1400, and 1530 V at the anode-cathode distance of 5, 10, and 20 ㎛, respectively. The optimized O₂ annealing and 4 ㎛-thick C-doped GaN buffer obtained the high breakdown voltage at short drift length. The proposed O₂ annealing is suitable for next-generation GaN power switches due to the simple process and the low the leakage current.

Effects of metal spikes on leakage current of high-voltage GaN Schottky barrier diode

We have investigated effects of metal spikes on the leakage current of high-voltage GaN Schottky barrier diodes (SBDs) on Si substrate. The metal spikes are formed underneath Ohmic contacts during a thermal annealing. The diffusion of Ti/Al/Mo/Au into GaN is analyzed by measuring Auger electron spectroscopy (AES). Ti/Al/Mo/Au on GaN is stripped by a wet etchant and its surface is observed to verify metal spikes by scanning electron microscope (SEM) and atomic force microscopy (AFM). The annealing temperature of the Ohmic contact is proportional to the diffusion depth of the metal spikes and the leakage current. The reverse current of GaN SBD with an Ohmic alloy at 700°C is 0.37A/cm2 at −100V while that of GaN SBD with the Ohmic alloy at 800°C is 13.45A/cm2 at −100V. The metal spikes in GaN power devices should be suppressed for the low power loss and the high breakdown voltage. The reverse current of GaN SBD is further decreased by a recessed Schottky contact because the Schottky contact is closer to unintentionally-doped (UID) GaN buffer and the depletion is increased. The reverse current of GaN SBD with the recessed Schottky contact is finally decreased to 0.05A/cm2 at −100V. When an anode–cathode distance (DAC) is 5μm, the measured on-resistance, breakdown voltage and figure-of-merit (BV2/Ron,sp) are 3.15mΩcm2, 320V, and 32.5MW/cm2, respectively. When DAC is increased to 20μm, fabricated devices show the breakdown voltage of 450V and good device-to-device uniformity.

Copper Oxide Edge-Termination for GaN Schottky Barrier Diodes with Low Turn-on Voltage

ABSTRACTIn this study, we propose copper oxide (CuOx) edge-termination for GaN-based Schottky barrier diodes (SBDs) with low turn-on voltage. CuOx fabricated by thermal oxidization of sputtered Cu film at 275°C consisted mainly of Cu2O which is known as a p-type semiconductor. We applied CuOx edge-termination to GaN SBDs with tantalum (Ta) Schottky electrode which has low work function of 4.25 eV. The experimental results of current-voltage characteristics insisted that CuOx edge-termination structure was effective to increase breakdown voltage of GaN SBDs with keeping low turn-on voltage of 0.29 V at 10 A/cm2.