Showing papers on "Gallium nitride published in 2015"

Vertical GaN p-n Junction Diodes With High Breakdown Voltages Over 4 kV

Abstract: Vertical structured GaN power devices have recently been attracting a great interest because of their potential on extremely high-power conversion efficiency. This letter describes increased breakdown voltages in the vertical GaN p-n diodes fabricated on the free-standing GaN substrates. By applying multiple lightly Si doped n-GaN drift layers to the p-n diode, the record breakdown voltages ( $V_{B}$ ) of 4.7 kV combined with low specific differential ON-resistance ( $R_{\mathrm{\scriptscriptstyle ON}}$ ) of 1.7 $\text{m}\Omega $ cm2 were achieved. With reducing the Si-doping concentration of the top n-GaN drift layer adjacent to the p-n junction using well-controlled metal-organic vapor phase epitaxy systems, the peak electric field at the p-n junction could be suppressed under high negatively biased conditions. The second drift layer with a moderate doping concentration contributed to the low $R_{\mathrm{\scriptscriptstyle ON}}$ . A Baliga’s figure of merit ( $V_{B}^{2}/R_{\mathrm{\scriptscriptstyle ON}}$ ) was 13 GW/cm2. These are the best values ever reported among those achieved by GaN p-n junction diodes on the free-standing GaN substrates.

Ultrahigh-Speed GaN High-Electron-Mobility Transistors With $f_{T}/f_{\mathrm {max}}$ of 454/444 GHz

Abstract: This letter reports record RF performance of deeply scaled depletion-mode GaN-high-electron-mobility transistors (GaN-HEMTs). Based on double heterojunction AlN/GaN/AlGaN epitaxial structure, fully passivated devices were fabricated by self-aligned-gate technology featuring recessed $n^{+}$ -GaN ohmic contact regrown by molecular beam epitaxy. Record-high $f_{T}$ of 454 GHz and simultaneous $f_{{\rm {max}}}$ of 444 GHz were achieved on a 20-nm gate HEMT with 50-nm-wide gate-source and gate-drain separation. With an OFF-state breakdown voltage of 10 V, the Johnson figure of merit of this device reaches 4.5 THz-V, representing the state-of-the-art performance of GaN transistor technology to-date. Compared with previous E-mode GaN-HEMTs of similar device structure, significantly reduced extrinsic gate capacitance and enhanced average electron velocity are the key reasons for improved frequency characteristic.

Wafer-Level Artificial Photosynthesis for CO2 Reduction into CH4 and CO Using GaN Nanowires

Abstract: We report on the first demonstration of high-conversion-rate photochemical reduction of carbon dioxide (CO2) on gallium nitride (GaN) nanowire arrays into methane (CH4) and carbon monoxide (CO). It was observed that the reduction of CO2 to CO dominates on as-grown GaN nanowires under ultraviolet light irradiation. However, the production of CH4 is significantly increased by using the Rh/Cr2O3 core/shell cocatalyst, with an average rate of ∼3.5 μmol gcat–1 h–1 in 24 h. In this process, the rate of CO2 to CO conversion is suppressed by nearly an order of magnitude. The rate of photoreduction of CO2 to CH4 can be further enhanced and can reach ∼14.8 μmol gcat–1 h–1 by promoting Pt nanoparticles on the lateral m-plane surfaces of GaN nanowires, which is nearly an order of magnitude higher than that measured on as-grown GaN nanowire arrays. This work establishes the potential use of metal-nitride nanowire arrays as a highly efficient photocatalyst for the direct photoreduction of CO2 into chemical fuels. It al...

Origin and Control of OFF-State Leakage Current in GaN-on-Si Vertical Diodes

Abstract: Conventional GaN vertical devices, though promising for high-power applications, need expensive GaN substrates. Recently, low-cost GaN-on-Si vertical diodes have been demonstrated for the first time. This paper presents a systematic study to understand and control the OFF-state leakage current in the GaN-on-Si vertical diodes. Various leakage sources were investigated and separated, including leakage through the bulk drift region, passivation layer, etch sidewall, and transition layers. To suppress the leakage along the etch sidewall, an advanced edge termination technology has been developed by combining plasma treatment, tetramethylammonium hydroxide wet etching, and ion implantation. With this advanced edge termination technology, an OFF-state leakage current similar to Si, SiC, and GaN lateral devices has been achieved in the GaN-on-Si vertical diodes with over 300 V breakdown voltage and 2.9-MV/cm peak electric field. The origin of the remaining OFF-state leakage current can be explained by a combination of electron tunneling at the p-GaN/drift-layer interface and carrier hopping between dislocation traps. The low leakage current achieved in these devices demonstrates the great potential of the GaN-on-Si vertical device as a new low-cost candidate for high-performance power electronics.

Mesoporous GaN for Photonic Engineering-Highly Reflective GaN Mirrors as an Example

Abstract: A porous medium is a special type of material where voids are created in a solid medium. The introduction of pores into a bulk solid can profoundly affect its physical properties and enable interesting mechanisms. In this paper, we report the use of mesoporous GaN to address a long-standing challenge in GaN devices: tuning the optical index in epitaxial structures without compromising the structural and electrical properties. By controlling the doping and electrochemical etching bias, we are able to control the pore morphology from macro- to meso- and microporous. The meso- and microporous GaN can be considered a new form of GaN with unprecedented optical index tunability. We examine the scattering loss in a porous medium quantitatively using numerical, semiempirical, and experimental methods. It is established that the optical loss due to scattering is well within the acceptable range. While being perfectly lattice-matched to GaN, the porous GaN layers are found to be electrically highly conductive. As a...

Active-Matrix GaN Micro Light-Emitting Diode Display With Unprecedented Brightness

Abstract: Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of $10^{6}$ cd/ $\text{m}^{2}$ .

Evaluation of Gallium Nitride Transistors in High Frequency Resonant and Soft-Switching DC–DC Converters

Abstract: The emergence of gallium nitride (GaN)-based power devices offers the potential to achieve higher efficiencies and higher switching frequencies than possible with mature silicon (Si) power MOSFETs. In this paper, we will evaluate the ability of gallium nitride transistors to improve efficiency and output power density in high frequency resonant and soft-switching applications. To experimentally verify the benefits of replacing Si MOSFETs with enhancement mode GaN transistors (eGaNFETs) in a high frequency resonant converter, 48–12 V unregulated isolated bus converter prototypes operating at a switching frequency of 1.2 MHz and an output power of up to 400 W are compared using Si and GaN power devices.

Wide-Bandgap-Based Power Devices: Reshaping the power electronics landscape

Abstract: For the last few years, the virtues of power devices based on gallium nitride (GaN) and silicon carbide (SiC) technologies have been well promoted. Now, with the availability of qualified devices from multiple suppliers and falling prices due to the rise in production and the use of larger substrates, more designers are adopting widebandgap (WBG)-based power devices in their new designs to get to the next level of performance, while others are looking to replace the maturing silicon (Si) with more robust emerging technologies.

Modeling of Wide-Bandgap Power Semiconductor Devices—Part II

Abstract: Wide bandgap power devices have emerged as an often superior alternative power switch technology for many power electronic applications. These devices theoretically have excellent material properties enabling power device operation at higher switching frequencies and higher temperatures compared with conventional silicon devices. However, material defects can dominate device behavior, particularly over time, and this should be strongly considered when trying to model actual characteristics of currently available devices. Compact models of wide bandgap power devices are necessary to analyze and evaluate their impact on circuit and system performance. Available compact models, i.e., models compatible with circuit-level simulators, are reviewed. In particular, this paper presents a review of compact models for silicon carbide power diodes and MOSFETs.

Low-Loss and High-Voltage III-Nitride Transistors for Power Switching Applications

Abstract: This paper describes recent technological advances on III-nitride-based transistors for power switching applications. Focuses are placed on the progress toward enhancing the breakdown voltage, lowering the ON-resistance, suppressing current collapse, and reducing the leakage current in AlGaN/GaN high-electron mobility transistors (HEMTs). Recent publications revealed that the tradeoff relation between ON-resistance and breakdown voltage in AlGaN/GaN HEMTs exceeded the SiC limit and was getting close to the GaN limit; however, the breakdown voltage achieved was still lower than the theoretical impact ionization limit. A novel process featuring strain-controlled annealing with a metal stack, including Al gave rise to significant reduction in the sheet resistance in AlGaN/GaN heterostructures, suggesting the possibility of dramatic reduction in ON-resistance of GaN-based power devices. Some of the interesting approaches to suppress current collapse indicated that surface trapping effects must be controlled by the optimization of surface processing as well as by the reduction of bulk traps in the epitaxial layers. Close correlation between the local gate leakage current and point defects exposed on the free-standing GaN substrate demonstrated that further reduction of defects on bulk GaN substrates is truly required as future challenges.

Characterization of an enhancement-mode 650-V GaN HFET

Abstract: GaN heterojunction field-effect transistors (HFETs) in the 600-V class are relatively new in commercial power electronics. The GaN Systems GS66508 is the first commercially available 650-V enhancement-mode device. Static and dynamic testing has been performed across the full current, voltage, and temperature range to enable GaN-based converter design using this new device. A curve tracer was used to measure R ds-on across the full operating temperature range, as well as the self-commutated reverse conduction (i.e. diode-like) behavior. Other static parameters such as transconductance and gate current were also measured. A double pulse test setup was constructed and used to measure switching loss and time at the fastest achievable switching speed, and the subsequent over-voltages due to the fast switching were characterized. Based on these results and analysis, an accurate loss model has been developed for the GS66508 to allow for GaN-based converter design and comparison with other commercially available devices in the 600-V class.

Characterization and Enhancement of High-Voltage Cascode GaN Devices

Abstract: Gallium nitride (GaN) devices are gathering momentum, with a number of recent market introductions for a wide range of applications such as point-of-load converters, OFF-line switching power supplies, battery chargers, and motor drives. This paper studies the basic characteristics of a 600 V cascode GaN switch, such as voltage distribution during the turn-ON and turn-OFF transition. The switching loss mechanism of the cascode GaN switch is analyzed in detail, including the impact of the package parasitic inductance in both hard- and soft-switching modes. A soft-switching 5 MHz boost converter is developed and shows the advantages and the potential of the cascode GaN.

GaN-Based Metal-Insulator-Semiconductor High-Electron-Mobility Transistors Using Low-Pressure Chemical Vapor Deposition SiN x as Gate Dielectric

Abstract: In this letter, silicon nitride (SiN x ) film deposited at 780 °C by low-pressure chemical vapor deposition (LPCVD) was employed as gate dielectric for GaN-based metal–insulator–semiconductor high-electron-mobility transistors. The LPCVD-SiN x exhibit improved gate dielectric performance than the plasma enhanced chemical vapor deposition-SiN x , including smaller forward and reverse gate leakage, and higher forward gate breakdown voltage.

Channel Temperature Analysis of GaN HEMTs With Nonlinear Thermal Conductivity

Abstract: This paper presents an enhanced, closed-form expression for the thermal resistance, and thus, the channel temperature of AlGaN/gallium nitride (GaN) HEMTs, including the effect of the temperature-dependent thermal conductivity of GaN and SiC or Si substrates. In addition, the expression accounts for temperature increase across the die-attach. The model’s validity is verified by comparing it with experimental observations. The model results also compare favorably with those from finite-element numerical simulations across the various device geometric and material parameters. The model provides a more accurate channel temperature than that from a constant thermal conductivity assumption; this is particularly significant for GaN/Si HEMTs where the temperature rise is higher than in GaN/SiC. The model is especially useful for device and monolithic microwave integrated circuit designers in the thermal assessment of their device design iterations against required performance for their specific applications.

4-kV and 2.8- $\text{m}\Omega $ -cm 2 Vertical GaN p-n Diodes With Low Leakage Currents

Abstract: There is great interest in bulk GaN-based power electronics devices for applications requiring breakdown voltages greater than 3.3 kV. In this letter, the vertical GaN p-n diodes fabricated on improved bulk GaN substrates demonstrating low leakage currents ( $10^{4}$ cm $^{-2}$ ) bulk GaN substrates with improved quality and specifications that are uniquely suitable for power electronic device applications. The measured devices show breakdown voltages larger than 4 kV with an area differential specific ON-resistance ( $R_{\textrm {sp}}$ ) of less than 3 $\text{m}\Omega $ -cm2. Applications that would require such breakdown voltages, include ship propulsion, rail, wind, uninterruptable power supplies, and the power grid.

Design space and origin of off-state leakage in GaN vertical power diodes

Abstract: Variable-range-hopping through dislocations was identified as the main off-state leakage mechanism for GaN vertical diodes on different substrates. The behavior of leakage current for vertical devices as a function of dislocation density and electric field was derived by TCAD simulations, after careful calibration with experiments and literature data. Designed GaN vertical diodes demonstrate 2–4 orders of magnitude lower leakage current while supporting 3–5 times higher electric field, compared to GaN lateral, Si and SiC devices.

A Simplified Method of Making Flexible Blue LEDs on a Plastic Substrate

Abstract: A much-simplified method of making flexible GaN blue light-emitting diode (LED) array on a plastic substrate was demonstrated. A sticky elastomeric stamp was first brought into contact with prefabricated GaN LED array on a sapphire substrate. Laser liftoff was applied by shining laser light through the sapphire substrate. The released LED array sitting on the stamp was transferred to a polyethylene terephthalate substrate that was coated with an adhesive layer to finish the fabrication process. Careful investigation of the built-in stress in the GaN LED layer using Raman spectroscopy revealed that the maximum stress that allows for intact GaN LED layer release and transfer was 0.7 GPa. The method drastically simplifies the cumbersome conventional GaN layer transferring method while preserving the original layout of the GaN LED array. Due to its simple and practical characteristics, the method is expected to greatly facilitate the development of versatile transferrable GaN LED applications on various substrates at a much-reduced cost.

Review of using gallium nitride for ionizing radiation detection

Abstract: With the largest band gap energy of all commercial semiconductors, GaN has found wide application in the making of optoelectronic devices. It has also been used for photodetection such as solar blind imaging as well as ultraviolet and even X-ray detection. Unsurprisingly, the appreciable advantages of GaN over Si, amorphous silicon (a-Si:H), SiC, amorphous SiC (a-SiC), and GaAs, particularly for its radiation hardness, have drawn prompt attention from the physics, astronomy, and nuclear science and engineering communities alike, where semiconductors have traditionally been used for nuclear particle detection. Several investigations have established the usefulness of GaN for alpha detection, suggesting that when properly doped or coated with neutron sensitive materials, GaN could be turned into a neutron detection device. Work in this area is still early in its development, but GaN-based devices have already been shown to detect alpha particles, ultraviolet light, X-rays, electrons, and neutrons. Furthermo...

Neural approach for temperature-dependent modeling of GaN HEMTs

Abstract: Gallium nitride high electron-mobility transistors have gained much interest for high-power and high-temperature applications at high frequencies Therefore, there is a need to have the dependence on the temperature included in their models To meet this challenge, the present study presents a neural approach for extracting a multi-bias model of a gallium nitride high electron-mobility transistors including the dependence on the ambient temperature Accuracy of the developed model is verified by comparing modeling results with measurements Copyright © 2014 John Wiley & Sons, Ltd

Robust SiN x /AlGaN Interface in GaN HEMTs Passivated by Thick LPCVD-Grown SiN x Layer

Abstract: Low-pressure chemical vapor deposition (LPCVD) technique is utilized for SiN x passivation of AlGaN/GaN high-electron-mobility transistors (HEMTs). A robust SiN x / AlGaN interface featuring high thermal stability and well-ordered crystalline structure is achieved by a processing strategy of “passivation-prior-to-ohmic” in HEMTs fabrication. Effective suppression of surface-trap-induced current collapse and lateral interface leakage current are demonstrated in the LPCVD-SiN x passivated HEMTs, as compared with conventional plasma-enhanced chemical vapor deposition-SiN x passivated ones. Energy dispersive X-ray spectroscopy mapping analysis of SiN x /AlGaN interfaces suggests the interface traps are likely to stem from amorphous oxide/oxynitride interfacial layer.

Systems and methods for preparing gan and related materials for micro assembly

Abstract: The disclosed technology relates generally to a method and system for micro assembling GaN materials and devices to form displays and lighting components that use arrays of small LEDs and high-power, high-voltage, and or high frequency transistors and diodes. GaN materials and devices can be formed from epitaxy on sapphire, silicon carbide, gallium nitride, aluminum nitride, or silicon substrates. The disclosed technology provides systems and methods for preparing GaN materials and devices at least partially formed on several of those native substrates for micro assembly.

Improving the quality of GaN crystals by using graphene or hexagonal boron nitride nanosheets substrate.

Abstract: The progress in nitrides technology is widely believed to be limited and hampered by the lack of high-quality gallium nitride wafers. Though various epitaxial techniques like epitaxial lateral overgrowth and its derivatives have been used to reduce defect density, there is still plenty of room for the improvement of gallium nitride crystal. Here, we report graphene or hexagonal boron nitride nanosheets can be used to improve the quality of GaN crystal using hydride vapor phase epitaxy methods. These nanosheets were directly deposited on the substrate that is used for the epitaxial growth of GaN crystal. Systematic characterizations of the as-obtained crystal show that quality of GaN crystal is greatly improved. The fabricated light-emitting diodes using the as-obtained GaN crystals emit strong electroluminescence under room illumination. This simple yet effective technique is believed to be applicable in metal–organic chemical vapor deposition systems and will find wide applications on other crystal growth.

Near-junction thermal management: thermal conduction in gallium nitride composite substrates

Abstract: The thermal management challenge posed by gallium nitride (GaN) high-electron-mobility transistor (HEMT) technology has received much attention in the past decade. The peak amplification power density of these devices is limited by heat transfer at the device, substrate, package, and system levels. Thermal resistances within micrometers of the transistor junction can limit efficient heat spreading from active device regions into the substrate and can dominate the overall temperature rise. Gallium nitride composite substrates, which consist of AlGaN/GaN heterostructures with thickness of a few microns on a thicker non-GaN substrate, govern the thermal resistance associated with the “near-junction” region. Silicon and silicon carbide have been widely used as a substrate material, but the performance of GaN devices grown on these substrates is still severely limited by thermal constraints and associated reliability issues. The importance of effective junction-level heat conduction has motivated the development of composite substrates containing high-thermal-conductivity diamond, but these composites require careful attention to thermal resistances between the GaN and the diamond. This chapter reviews thermal conduction phenomena in GaN composite substrates containing Si, SiC, and diamond. The review discusses the governing conduction physics and overviews the relevant measurement techniques. The best available experimental data for GaN composite substrates as well as the relevant thermal modeling are presented. The review concludes with an assessment of the potential benefits of the use of diamond on the device thermal performance.

13.56 MHz 1.3 kW resonant converter with GaN FET for wireless power transfer

Abstract: This paper presents a 1.3 kW resonant power amplifier using a Gallium Nitride (GaN) device at 13.56 MHz for wireless power transfer (WPT). The power amplifier driving the power transmitting coils is based on a Class Φ 2 inverter, a single switch topology with low switch voltage stress and fast transient response. This implementation utilizes a recently available GaN device in a low inductance package that is compatible with operation in the 10's of MHz switching frequency. These power GaN switching devices have low gate resistance RG and low capacitance C GS which greatly reduces the power requirements of the gate drive circuitry. This paper shows experimental measurements of the inverter in a WPT application and characterization of the system performance over various distances and operating conditions.

GaN HEMT: Dominant Force in High-Frequency Solid-State Power Amplifiers

Abstract: The gallium nitride (GaN) high-electron-mobility transistor (HEMT) has emerged as the dominant force in high-frequency solid-state power amplifiers (PAs)?not that it does not have competition. Silicon (Si) bipolar junction transistors (BJTs) and Si laterally diffused metal?oxide?semiconductor (LDMOS) field-effect transistors (FETs) are still commercially available. They are viable alternatives to GaN HEMTs in aerospace/defense applications such as L-band transponders/interrogators for the identification friend or foe; Link 16 data links; electronic warfare; and surveillance radar; and, in the case of Si LDMOSs, commercial cellular base stations. These older technologies can be favored due to their mature heritage, good performance, and low cost. The pseudomorphic HEMT (PHEMT) is ubiquitous in microwave and millimeter-wave power applications. Vacuum electron devices (VEDs) still reign in the regime of brute power. The GaN HEMT has been displacing these technologies as it has matured and costs have come down.

Low-Temperature Bonded GaN-on-Diamond HEMTs With 11 W/mm Output Power at 10 GHz

Abstract: We report recent progress on GaN-on-diamond high electron mobility transistors (HEMTs) fabricated using a low-temperature device-transfer process. The devices were first fabricated on a GaN-on-SiC epitaxial wafer and were subsequently separated from the SiC and bonded onto a high-thermal-conductivity diamond substrate at low temperature. The resulting $12 \times 50~\mu \text{m}$ GaN-on-diamond HEMTs demonstrated the state-of-the-art electrical characteristics, including a maximum drain current density of 1.2 A/mm and a peak transconductance of 390 mS/mm. CW load-pull measurements at 10 GHz yielded an RF output power density of 11 W/mm with 51% associated power-added efficiency. Device measurements show that the GaN-on-diamond devices maintained slightly lower channel temperatures than their GaN-on-SiC counterparts while delivering 3.6 times higher RF power within the same active area. These results demonstrate that the GaN device-transfer process is capable of preserving intrinsic GaN-on-SiC transistor electrical performance while taking advantage of the excellent thermal properties of diamond substrates.

Semiconductor light -emitting device

Abstract: Semiconductor light -emitting device is including substrate, the crystallizing layer on the substrate, gallium nitride buffer layer, N type gallium nitride layer, transition layer, multi -quantum well layer and P type gallium nitride layer, still include low temperature nitrogenize gallium layer, low temperature nitrogenize gallium layer and forms a plurality of pits on it on N type gallium nitride layer, release of stress layer, the thickness on release of stress layer are lighter than 100nm and by 1 constituting to K layer inx (k) ga1 -x (k) N on low temperature nitrogenize gallium layer in proper order, wherein, k layer inx (k) ga1 -x (k) N's thickness dk is lighter than k -1 layer inx (k -1) ga1 -x (k -1) N's thickness dk -1, and x (k) > x (k -1), k=1,. K, K <= 5, P type gallium nitride layer covers the pit. The utility model discloses an according to inGaN's in the component adjustment release of stress layer of the indium of quantum well the number of piles and gross thickness, make the component of each layer inGaN's indium scale up to the surface from the bottom, thickness steadilys decrease, reaches the purpose of progressively releasing stress.

Monolithic integration of four-colour InGaN-based nanocolumn LEDs

Abstract: The monolithic integration of four-colour indium gallium nitride (InGaN)-based nanocolumn light-emitting diodes (LEDs) is demonstrated. In the integrated nanocolumn LED unit, blue-, sky-blue-, green- and yellow-emitting micro-LEDs (LEDs 1–4) with a 65 μm diameter circular indium tin oxide emission window were arrayed in a 2 × 2 square lattice with a lattice constant of 190 μm. LEDs 1–4 consisted of nanocolumn arrays arranged in a triangular lattice with a lattice constant of 300 nm and their nanocolumn diameters at the position of the InGaN/gallium nitride (GaN) multiple quantum wells (MQWs) were 119, 145, 188 and 231 nm, respectively. The increase in nanocolumn diameter from LED 1 to LED 4 resulted in increasing emission peak wavelengths, which were 465, 489, 510 and 570 nm for LEDs 1–4, respectively. On the same substrate, a red-emitting micro-LED was prepared, in which the nanocolumn diameter was increased to 260 nm by using a 350 nm-lattice-constant nanocolumn array. A combination of different lattice constants in an integrated LED unit is expected to contribute to the achievement of red–green–blue–yellow (RGBY)-colour-integrated nanocolumn LEDs.