GaN Schottky Barrier Research Articles

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.

Graphene GaN-Based Schottky Ultraviolet Detectors

Graphene GaN-based Schottky ultraviolet detectors are fabricated. The monolayer graphene is grown by chemical vapor deposition. The graphene is much more transparent than metals, as confirmed by the fact that our devices retain their high responsivity up to 360-nm wavelength (corresponding to the band edge absorption of GaN). Importantly, by virtue of the tunable work function of graphene, the graphene GaN Schottky barrier height can be greatly enlarged. The built-in field is enhanced, and the detector performance is improved. The current ratio with and without luminescence is up to $1.6\times 10^{4}$ . The characteristic time constants of the devices are in the order of a few milliseconds. The device open-circuit voltage and short-circuit current are also increased. At last, special type Schottky devices consisting of GaN nanorods or surface-etched GaN are prepared for complementary study. It is found although the dry etching induced surface defects lead to an increase in the dark current, and these carrier traps also greatly contribute to the photoconductivity under luminescence, resulting in extraordinarily large responsivity (up to 360 A/W at −6 V).

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.

Modeling the spectral responsivity of ultraviolet GaN Schottky barrier photodetectors under reverse bias

The responsivity of GaN Schottky barrier photodetector (SBPD) as a function of incident wavelength and reverse bias has been studied theoretically. It was found that Schottky barrier (SB) lowering can explain the significant increase in the spectral responsivity as the reverse bias increases. The image force and the occupation of surface defects at the metal/semiconductor interface of the SBPD are the main factors for the SB lowering. The occupation of the surface defects was assumed to depend on the photogenerated current under reverse bias. The SB lowering causes a large leakage current that dominates the spectral responsivity at high reverse applied bias. The good agreement between the calculated and experimentally measured spectral responsivities suggests that the model is valid.

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.

Neutron irradiation effects on metal-gallium nitride contacts

We have measured the effect of fast and thermal neutrons on GaN Schottky barriers and ohmic contacts using current–voltage and transmission line method electrical techniques, optical, atomic force and scanning electron microscopy morphological techniques, and X-ray photoemission spectroscopy chemical techniques. These studies reveal a 1015 n/cm2 neutron threshold for Schottky barrier ideality factor increases, a 1015 n/cm2 fast plus thermal neutron threshold for ohmic contact sheet and contact resistance increases, and 1016 n/cm2 neutron fluence threshold for major device degradation identified with thermally driven diffusion of Ga and N into the metal contacts and surface phase changes. These results demonstrate the need for protecting metal-GaN contacts in device applications subject to neutron radiation.

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.

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.

Low-Frequency Noise Characteristics of GaN Schottky Barrier Photodetectors Prepared With Nickel Annealing

In this paper, GaN Schottky barrier photodetectors (PDs) prepared with and without Ni treatment were fabricated. I-V and noise characteristics of these devices were then investigated. Comparing the GaN PDs with and without Ni treatment, it was found that GaN PDs prepared with Ni treatment can not only reduce dark current, but also enhance the UV-to-Vis rejection ratio. With an applied bias of -2 V, it was found that noise equivalent power (NEP) and detectivity (D*) for the PDs prepared without Ni treatment were 9.95 × 10-8 W and 1.59 × 107 cmHz0.5W-1, respectively. At the same applied bias, it was also found that NEP and D* for PDs prepared with Ni treatment were 1.74 × 10-11 W and 9.07 × 1010 cmHz0.5W-1, respectively.

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.

Carrier transport mechanism of AlGaN/GaN Schottky barrier diodes with various Al mole fractions

AbstractThe evolution of the dominant carrier transport mechanism of Alx Ga1‐xN/GaN Schottky barrier diodes with increasing Al mole fraction x (x = 0.2, 0.3, 0.4, and 0.5) is investigated. The Schottky barrier height (SBH) linearly increases with the work function of Schottky metal with the slope factor of ∼0.5 irrespective of x. The SBH, the ideality factor, and the reverse leakage current, however, show an increasing deviation from the predicted values given by the thermionic‐emission theory as x increases. The XPS analysis reveals enhanced predominant incorporation of oxygen donors and an increase in the energy band bending at the surface of AlGaN with increasing x, indicating that the carrier transport by tunnelling through the thin, heavily doped Schottky barrier becomes dominant. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

GaN Schottky Barrier Photodetectors With a Lattice-Matched ${\rm Al}_{0.82}{\rm In}_{0.18}{\rm N}$ Intermediate Layer

GaN Schottky barrier ultraviolet (UV) photodetectors (PDs) with a low-temperature Al0.82In0.18N intermediate layer were fabricated and characterized. With the intermediate layer, it was found that we could reduce the reverse leakage current by more than three orders of magnitude and achieve a 45 times larger UV-to-visible rejection ratio. Compared with the conventional GaN PDs, it was found that we could also reduce noise level and achieve a larger detectivity by inserting the lattice-matched AlInN intermediate layer.

Finite-Zone Argon Implant Edge Termination for High-Voltage GaN Schottky Rectifiers

In this letter, the results obtained with a finite termination by argon ion implantation at the periphery of GaN Schottky barrier diodes are reported. It is demonstrated that the implant region width required to obtain the ideal plane parallel breakdown voltage of 1700 V is 50 μm.

Body-bias Effect in a GaN Schottky Barrier MOSFET Fabricated on a Silicon (111) Substrate with an ITO Source/Drain

Body-bias Effect in a GaN Schottky Barrier MOSFET Fabricated on a Silicon (111) Substrate with an ITO Source/Drain