GaN Schottky Diodes Research Articles

Study of GaN Radiation Sensor After In-core Neutron Irradiation

GaN Schottky diode radiation detectors were fabricated on a 450-μm freestanding GaN wafer with a guard ring structure. The detectors were irradiated with neutron fluences up to 1016 n/cm2. The current-voltage relation, capacitance-voltage relation, charge collection efficiency, and alpha particle spectrum before and after irradiation were measured to characterize the radiation resistance of GaN devices. The detectors' performance showed insignificant changes after in-core neutron irradiation at 1015 n/cm2.

(Invited) Hydrogen Sensing Characteristics of Gallium Nitrides with Various Crystal Planes

We investigated hydrogen sensing characteristics of semipolar (11-22) GaN Schottky diode, and compared to various crystal planes of GaN including conventional gallium polar c-plane (0001), nitrogen polar c-plane (000-1), and a-plane (11-20). The semipolar GaN diode showed remarkable current change to 4% hydrogen in nitrogen and the device exhibited full recovery into original current level under nitrogen ambient. Each plane has its own surface configuration and shows different hydrogen responsivity. In case of (11-22) plane GaN, its current response to hydrogen is very large even though its surface is terminated with gallium atoms, since active nitrogens position beneath the gallium atoms.

Hydrogen sensing characteristics of semipolar (112¯2) GaN Schottky diodes

The hydrogen detection characteristics of semipolar (112¯2) plane GaN Schottky diodes were investigated and compared to c-plane Ga- and N-polar and nonpolar a-plane (112¯0) GaN diodes. The semipolar GaN diodes showed large current response to 4% hydrogen in nitrogen gas with an accompanying Schottky barrier reduction of 0.53 eV at 25 °C, and the devices exhibited full recovery to the initial current level upon switching to a nitrogen ambient. The current-voltage characteristics of the semipolar devices remained rectifying after hydrogen exposure, in sharp contrast to the case of c-plane N-polar GaN. These results show that the surface atom configuration and polarity play a strong role in hydrogen sensing with GaN.

Electronic parameters and carrier transport mechanism of high-barrier Se Schottky contacts to n-type GaN

The electrical properties and current conduction mechanism of high-barrier Se/n-GaN Schottky diode have been investigated for the first time by current–voltage (I–V) and capacitance–voltage (C–V) measurements. High resolution transmission electron microscopy (HRTEM) results confirmed that no reaction occurs between Se film and the GaN substrate during Se deposition. Investigations reveal that the contact exhibited an excellent rectification behavior. The estimated barrier height of Se/n-GaN Schottky contact is 0.92eV (I–V) and 1.27eV (C–V) with the ideality factor of 1.10. The barrier height and series resistance are extracted by Cheung's functions. It is observed that the series resistance values obtained from Cheung's functions is in good agreement with each other. Further, capacitance–voltage measurements of the Se/n-GaN Schottky diode are carried out at different frequencies. The discrepancy between Schottky barrier heights obtained from I–V and C–V measurements is also explained. The AFM results showed that the surface morphology of the Se Schottky contacts on n-GaN is fairly smooth. The forward bias current transport mechanism of the Se/n-type GaN Schottky diode is determined by the log–log plot of I–V characteristics. Investigations reveal that the Schottky emission mechanism is found to be dominant in the reverse bias region of Se/n-GaN Schottky diode.

Scaling of GaN HEMTs and Schottky Diodes for Submillimeter-Wave MMIC Applications

In this paper, we report state-of-the-art high frequency performance of GaN-based high electron mobility transistors (HEMTs) and Schottky diodes achieved through innovative device scaling technologies such as vertically scaled enhancement and depletion mode (E/D mode) AlN/GaN/AlGaN double-heterojunction HEMT epitaxial structures, a low-resistance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$n^{+}$</tex></formula> -GaN/2DEG ohmic contact regrown by MBE, a manufacturable 20-nm symmetric and asymmetric self-aligned-gate process, and a lateral metal/2DEG Schottky contact. As a result of proportional scaling of intrinsic and parasitic delays, an ultrahigh <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{T}$</tex></formula> exceeding 450 GHz (with a simultaneous <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{\rm max}$</tex></formula> of 440 GHz) and a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{\rm max}$</tex></formula> close to 600 GHz (with a simultaneous <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{T}$</tex></formula> of 310 GHz) are obtained in deeply scaled GaN HEMTs while maintaining superior Johnson figure of merit. Because of their extremely low on-resistance and high gain at low drain voltages, the devices exhibited excellent noise performance at low power. 501-stage direct-coupled field-effect transistor logic ring oscillator circuits are successfully fabricated with high yield and high uniformity, demonstrating the feasibility of GaN-based E/D-mode integrated circuits with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&gt;}{1000}$</tex> </formula> transistors. Furthermore, self-aligned GaN Schottky diodes with a lateral metal/2DEG Schottky contact and a 2DEG/ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n^{+}$</tex></formula> -GaN ohmic contact exhibited <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$RC$</tex></formula> -limited cutoff frequencies of up to 2.0 THz.

Effects of high-energy proton and electron irradiation on GaN Schottky diode

We performed high-energy proton and electron irradiation on a GaN Schottky diode and investigated the effects on its electrical properties. No significant changes in the dark current or breakdown voltage of the diode were observed for fluences up to ∼1014protons/cm2. The currents increased by a factor of ∼103 at a fluence of ∼1015protons/cm2. The currents also fluctuated unstably at these fluences but this unstable behavior was not observed after a few months. Intrinsic defects may have been induced by particle irradiation and some of them annealed through a relaxation process. Under electron irradiation, the dark currents did not show a notable increase even with the fluence of ∼1016electrons/cm2.

&gt;1200 V GaN‐on‐silicon Schottky diode

AbstractM/A‐COM Technology Solutions has continuing joint development efforts sponsored by the Department of Energy with MIT main campus and MIT Lincoln Laboratory to develop GaN on silicon two and three terminal high voltage/high current switching devices. The initial developmental goals were for a Schottky diode that has a reverse breakdown blocking voltage of &gt;600 V and is capable of handling 10 A of forward current. A comparison of the M/A‐COM Technology Solutions lateral GaN Schottky diode on‐resistance as a function of reverse breakdown voltage for a number of both lateral and vertical GaN Schottky diode geometries taken from the literature is presented. The substrates employed for all of these data points are either sapphire, SiC, silicon, and even one study which utilized single crystal GaN. Also included in this plot are theoretical limits for the basic materials typically used in GaN Schottky diode construction. It can be seen that the reverse breakdown results of approximately 1500 V for M/A‐COM Technology Solutions lateral anode connected field GaN Schottky diodes on silicon substrates compare extremely favorably with the reported performance of the state‐of‐the‐art devices, regardless of substrate material or design geometry. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Achieving Low Doped (

Point defects in the GaN cause premature breakdown in GaN Schottky diodes at least to the same extent as dislocations do. The most likely cause is impact ionization of deep acceptors. A primary deep acceptor in MOCVD-grown GaN is C. Another is a Ga vacancy, which is likely to be the primary deep acceptor in HVPE-grown material. Lower net carrier concentrations, and therefore larger breakdown voltages, can be achieved in the HVPE material.

Molecular beam epitaxial growth of (1 1 ‐2 2) GaN on m‐plane sapphire

AbstractThe structural and optical properties of semipolar (1 1 ‐2 2) GaN grown on m‐plane (1 0 ‐1 0) sapphire substrates by molecular beam epitaxy were investigated. An inplane orientation relationship was found to be [1 ‐1 0 0] GaN || [1 2‐1 0] sapphire and [‐1 ‐1 2 3] GaN || [0 0 0 1] sapphire for semipolar GaN on m‐plane sapphire substrates. The near band emission (NBE) was found at 3.432 eV, which is slightly blue shifted compared to the bulk GaN. The Raman E2 (high) peak position observed at 569.1 cm–1, which indicates that film is compressively strained. Schottky barrier height (φb) and the ideality factor (η) for the Au/ semipolar GaN Schottky diode found to be 0.55 eV and 2.11, respectively obtained from the TE model. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

DC and RF characteristics of bilayer Schottky metal contact on n-GaN Schottky diode

In device technology, the multilayer contacts provide improved performance. The comparative study of different high work function bilayer Schottky metal (Pt/Pd, Pt/Ni and Pt/Ti) contact has been taken to study the DC and RF performance of n -GaN Schottky diode. The fabricated Schottky metal contact Pt/Pd, Pt/Ni and Pt/Ti annealed from room temperature to 800 °C studied shows that Pt/Pd Schottky metal contact on n -GaN shows high thermal stability and maximum barrier height 1.10 eV, ideality factor 1.001, lower series resistance and lower insertion loss (S 21 dB) at high frequency compared to Pt/Ni and Pt/Ti bilayer Schottky metal contact.

Interface state effects in GaN Schottky diodes

Current voltage (I-V) and capacitance voltage (C-V) measurements have been performed versus temperature on GaN Schottky diodes. The results show an increase of the Schottky barrier height ϕb and a decrease of the ideality factor n both with the increase of the temperature. We show that this behavior originates in the existence of an interface state density distribution, which is determined via the analysis of the temperature dependence of the I-V measurements, and allows the tunneling of the carriers from the semiconductor to the metal. Those interface states are shown to be responsible for interface inhomogeneities which result in two Gaussian voltage dependent Schottky barrier distributions. We show also that, in the presence of this interface state distribution, C-V measurements, without the correction of the built in voltage by taking into account the effect of both the high values of the ideality factor and series resistance, lead to erroneous values of the Schottky barrier height ϕb.

The influence of the Franz-Keldysh effect on the electron diffusion length in p-type GaN determined using the spectral photocurrent technique

The zero-bias spectral response of a p-type GaN Schottky diode with an acceptor doping density of 1019 cm−3 was measured, and the electron diffusion length was calculated using the standard theoretical equation that relates this parameter to the measured photocurrent. Here it is shown that the minor but perceptible spectral variation of the diffusion length calculated can be explained by taking into account the Franz-Keldysh effect. Consideration of this effect, through the use of an equation that describes the electric field and spectral dependence of the absorption coefficient, leads to a constant diffusion length value of 14 nm. By also taking into account the inherent inaccuracy of the theoretical equation, a final value of 10 nm was estimated for the electron diffusion length.

High sensitivity hydrogen sensors based on GaN

AbstractHigh quality graphite based Schottky diodes are presented. Schottky barriers were prepared by mechanical deposition of colloidal graphite on GaN substrates uncoverd and partly covered with Pt nanoparticles deposited by electrophoretic techniques. The electron transport for both diodes can be well described by thermionic emission. Hydrogen sensing characteristics of graphite‐Pt/GaN Schottky diodes were investigated. Temperature dependence of the sensitivity, the barrier height variation, the ideality factor and the barrier height itself were studied. The proposed hydrogen sensor responds well to various hydrogen containing gases. The room‐temperature sensitivity response of 2x107 was obtained in 1000 ppm H2/N2ambient. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Schottky barriers on InP and GaN made by deposition of colloidal graphite and Pd, Pt or bimetal Pd/Pt nanoparticles for H2-gas detection

The paper reports on InP and GaN Schottky diode hydrogen sensors prepared by printing colloidal graphite on InP and GaN with catalytic metal Pd, Pt or bimetal Pd/Pt nanoparticles (NPs), electrophoretic depositions of metal NPs on surfaces of semiconductor wafers were performed from isooctane colloid solutions prepared by reverse micelles technique with dioctyl sodium sulfosuccinate (AOT) surfactant. Deposited metal NPs were characterized by SEM. Current voltage characteristics of the diodes showed high rectification ratio (about 107 at voltage 1V), low leakage currents and high Schottky barrier heights giving evidence of small Fermi level pinning. Currents changed by more than six orders of magnitude after diode exposures to 0.1% hydrogen in nitrogen, showing extremely high sensitivity of hydrogen detection. Time response of the current of forward voltage biased diodes to exposure of various concentrations of hydrogen in nitrogen was measured in the range from 1 to 1000ppm of hydrogen. The detection limit of hydrogen was estimated at 0.5ppm.

GaN Schottky Diode with TiW Electrodes on Silicon Substrate Based on AlN/AlGaN Buffer Layer

We report the fabrication of GaN Schottky photodiodes (PDs) on Si(111) substrates coated with an AlN/AlGaN buffer multilayer. It was found that their dark current was much smaller than that of identical devices prepared on sapphire substrates. With an incident wavelength of 359 nm, the maximum responsivity of the n−‐GaN Schottky photodetectors with TiW contact electrodes was 0.1544 A/W, corresponding to a quantum efficiency of 53.4%. For a given bandwidth of 1 kHz and bias of 5 V, the resultant noise equivalent power (NEP) of n−‐GaN Schottky photodetectors with TiW electrodes was 1.033 × 10−12 W, corresponding to a detectivity (D*) of 1.079 × 1012 cm‐Hz0.5 W−1.

고전압 응용분야를 위한 GaN 쇼트키 다이오드의 산화 공정

1 ㎸ high-voltage GaN Schottky diode is realized using GaN-on-Si template by oxidizing Ni-Schottky contact. The Auger electron spectroscopy (AES) analysis revealed the formation of NiOx at the top of Schottky contact. The Schottky contact was changed to from Ni/Au to Ni/Ni-Au alloy/Au/NiOx by oxidation. Ni diffusion into AlGaN improves the Schottky interface and the trap-assisted tunneling current. In addition, the reverse leakage current and the isolation-leakage current are efficiently suppressed by oxidation. The isolation-leakage current was reduced about 3 orders of magnitudes. The reverse leakage current was also decreased from 2.44 A/㎠ to 8.90 ㎃/㎠ under -100 V-biased condition. The formed group-III oxides (AlOx and GaOx) during the oxidation is thought to suppress the surface leakage current by passivating surface dangling bonds, N-vacancies and process damages.

The effect of carbon impurities on lightly doped MOCVD GaN Schottky diodes

Abstract

(Invited) High Voltage Normally-Off Transistors and Efficient Schottky Diodes based on GaN Technology

High voltage GaN based power switching transistors in normally-off technology and efficient GaN Schottky di-odes are indispensable for a steady improvement of effi-ciency in power converters and for cutting down volume and weight of these systems. To obtain ultimate device performance, novel concepts in epitaxial design and growth techniques as well as in processing and packaging technology are required. At FBH, normally-off GaN based power transistors and Schottky diodes have been and are being developed. These efforts cover the full val-ue added chain from epitaxial growth of GaN/AlGaN de-vice structures on 3" n-type SiC substrates, device proc-essing, characterization and interfacing to novel packag-ing techniques. The paper will summarize the most im-portant achievements towards high power GaN devices at FBH and will show up important dependencies towards further improved GaN power devices.

Analysis of leakage current mechanisms in Pt/Au Schottky contact on Ga-polarity GaN by Frenkel-Poole emission and deep level studies

We report the Frenkel-Poole emission in Pt/Au Schottky contact on Ga-polarity GaN grown by molecular beam epitaxy using current-voltage-temperature (I-V-T) characteristics in the temperature ranging from 200 K to 375 K. Using thermionic emission model, the estimated Schottky barrier height is 0.49 eV at 200 K and 0.83 eV at 375 K, respectively, and it is observed that the barrier height increases with increase in temperature. The extracted emission barrier height (ϕt) for Ga-polarity GaN Schottky diode by Frenkel-Poole theory is about 0.15 eV. Deep level transient spectroscopy study shows a deep level with activation energy of 0.44 eV, having capture cross-section 6.09 × 10−14 cm2, which is located between the metal and semiconductor interface, and trap nature is most probably associated with dislocations in Ga-polarity GaN. The analysis of I-V-T characteristics represents that the leakage current is due to effects of electrical field and temperature on the emission of electron from a trap state near the metal-semiconductor interface into continuum states associated with conductive dislocations in Ga-polarity GaN Schottky diode.

Study of edge termination structures for high power GaN Schottky diodes

AbstractDifferent structures of field plate termination were analysed by numerical simulation to enhance the breakdown voltage of quasi‐vertical GaN Schottky diodes. A bevel shaped field plate achieved a maximum breakdown voltage of 1990 V for 1.5 µm thick oxide layer with 18 µm bevel width. Maximum breakdown voltage was achieved when the bevel angle is 5°. A fabrication friendly 4 step field plate structure achieved a breakdown voltage of 1650 V and 1970 V respectively, with oxide and silicon nitride passivation. The width and thickness of the first step were the most influential factors in deciding the maximum breakdown voltage. A multi‐step field plate structure, which is an emulation of bevel structure, achieved a breakdown voltage of 1600 V and 1850 V with oxide and silicon nitride passivation layers, respectively. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)