Showing papers on "Gallium nitride published in 2009"

High-detectivity polymer photodetectors with spectral response from 300 nm to 1450 nm.

Abstract: Sensing from the ultraviolet-visible to the infrared is critical for a variety of industrial and scientific applications. Today, gallium nitride-, silicon-, and indium gallium arsenide--based detectors are used for different sub-bands within the ultraviolet to near-infrared wavelength range. We demonstrate polymer photodetectors with broad spectral response (300 to 1450 nanometers) fabricated by using a small-band-gap semiconducting polymer blended with a fullerene derivative. Operating at room temperature, the polymer photodetectors exhibit detectivities greater than 10(12) cm Hz(1/2)/W and a linear dynamic range over 100 decibels. The self-assembled nanomorphology and device architecture result in high photodetectivity over this wide spectral range and reduce the dark current (and noise) to values well below dark currents obtained in narrow-band photodetectors made with inorganic semiconductors.

Coaxial Group III−Nitride Nanowire Photovoltaics

Abstract: Coaxial core/shell nanowires represent an important class of nanoscale building blocks with substantial potential for exploring new concepts and materials for solar energy conversion. Here, we report the first experimental realization of coaxial group III−nitride nanowire photovoltaic (PV) devices, n-GaN/i-InxGa1−xN/p-GaN, where variation of indium mole fraction is used to control the active layer band gap and hence light absorption. Current−voltage data reveal clear diode characteristics with ideality factors from 3.9 to 5.6. Electroluminescence measurements demonstrate tunable emission from 556 to 371 nm and thus confirm band gap variations in the InxGa1−xN active layer from 2.25 to 3.34 eV as In composition is varied. Simulated one-sun AM 1.5G illumination yielded open-circuit voltages (Voc) from 1.0 to 2.0 V and short-circuit current densities (Jsc) from 0.39 to 0.059 mA/cm2 as In composition is decreased from 0.27 to 0 and a maximum efficiency of ∼0.19%. The n-GaN/i-InxGa1−xN/p-GaN nanowire devices a...

Breakdown Enhancement of AlGaN/GaN HEMTs on 4-in Silicon by Improving the GaN Quality on Thick Buffer Layers

Abstract: We have achieved a 9 ?m-thick AlGaN/GaN high-electron mobility transistor (HEMT) epilayer on silicon using thick buffer layers with reduced dislocation density (DD). The crack-free 9 ?m-thick epilayer included 2 ?m i-GaN and 7 ?m buffer. The HEMTs fabricated on these devices showed a maximum drain-current density of 625 mA/mm, transconductance of 190 mS/mm, and a high three-terminal OFF breakdown of 403 V for device dimensions of LgWgLgd=1.5/15/3 ?m . Without using a gate field plate, this is the highest BV reported on an AlGaN/GaN HEMT on silicon for a short Lgd of 3 ?m. A very high BV of 1813 V across 10 ?m ohmic gap was achieved for i-GaN grown on thick buffers. As the thickness of buffer layers increased, the decreased DD of GaN and increased resistance between surface electrode and substrate yielded a high breakdown.

Room-Temperature Red Emission from a p-Type/Europium-Doped/n-Type Gallium Nitride Light-Emitting Diode under Current Injection

Abstract: We have succeeded in the growth of europium (Eu)-doped GaN layer grown by organometallic vapor-phase epitaxy (OMVPE) and demonstrated the first low-voltage operation of current-injected red emission from a p-type/Eu-doped/n-type GaN light-emitting diode (LED) at room temperature. The bright red emission was obtained with an applied voltage as low as 3 V under normal lighting conditions. At a dc current of 20 mA, the output power, integrated over the 5D0–7F2 transition in Eu3+ ions (around 621 nm), was 1.3 µW. This result suggests a novel way to realize GaN-based red LEDs and monolithic devices comprising red, green and blue GaN-based LEDs.

Metalorganic Vapor Phase Epitaxy of III-Nitride Light-Emitting Diodes on Nanopatterned AGOG Sapphire Substrate by Abbreviated Growth Mode

Abstract: Metalorganic vapor phase epitaxial (MOVPE) growth of GaN on nanopatterned AGOG sapphire substrates was performed, and characteristics of the light-emitting diode (LED) devices grown on patterned sapphire and planar substrates were compared. The nanopatterned sapphire substrates were fabricated by a novel process (AGOG) whereby aluminum nanomesas were epitaxially converted into crystalline Al2O3 via a two-stage annealing process. The GaN template grown on the nanopatterned sapphire substrate was done via an abbreviated growth mode, where a 15-nm thick, low-temperature GaN buffer layer was used, without the use of an etch-back and recovery process during the epitaxy. InGaN quantum wells (QWs) LEDs were grown on the GaN template on the nanopatterned sapphire, employing the abbreviated growth mode. The optimized InGaN QW LEDs grown on the patterned AGOG sapphire substrate exhibited a 24% improvement in output power as compared to LEDs on GaN templates grown using the conventional method. The increase in output power of the LEDs is attributed to improved internal quantum efficiency of the LEDs.

Single-Chip Boost Converter Using Monolithically Integrated AlGaN/GaN Lateral Field-Effect Rectifier and Normally Off HEMT

Abstract: We demonstrate a single-chip switch-mode boost converter that features a monolithically integrated lateral field-effect rectifier (L-FER) and a normally off transistor switch. The circuit was fabricated on a standard AlGaN/GaN HEMT epitaxial wafer grown with GaN-on-Si technology. The fabricated rectifier with a drift length of 15 mum exhibits a breakdown voltage of 470 V, a turn-on voltage of 0.58 V, and a specific on-resistance of 2.04 mOmegaldrcm2. The L-FER exhibits no reverse recovery current associated with the turn-off transient because of its unipolar nature. A prototype of GaN-based boost converter that includes monolithically integrated rectifiers and transistors is demonstrated using conventional GaN-on-Si wafers for the first time to prove the feasibility of the GaN-based power IC technology.

Measurement of Channel Temperature in GaN High-Electron Mobility Transistors

Abstract: In this paper, a simple and reliable method to estimate the channel temperature of GaN high-electron mobility transistors (HEMTs) is proposed. The technique is based on electrical measurements of performance-related figures of merit (I Dmax and R ON) with a synchronized pulsed I -V setup. As our technique involves only electrical measurement, no special design in device geometry is required, and packaged devices can be measured. We apply this technique to different device structures and validate its sensitivity and robustness.

Study of the Excitation Power Dependent Internal Quantum Efficiency in InGaN/GaN LEDs Grown on Patterned Sapphire Substrate

Abstract: The mechanisms of the excitation power dependent internal quantum efficiency in InGaN/GaN multiple quantum wells (MQWs) LEDs grown on the planar and the patterned sapphire substrates (PSS) at temperature of 15 and 300 K were investigated. From observation the tendency of emission peak energy and carrier lifetime variation in MQWs with different excitation power for both LED samples, we conclude the internal quantum efficiency would increase as coulomb screening effect dominates at lower carrier injection stage and decrease due to the band-filling effect at higher density stage. At room temperature, the majority of the initial injected carriers would be first consumed by the thermal activated nonradiative centers that hinder the further achievement of high-efficiency LED devices. Experimentally, the internal quantum efficiency of the LED grown on the PSS is ~70% and that of the LED grown on the planar sapphire substrate is ~62%. For the LED grown on the PSS, the observed higher internal quantum efficiency is due to the larger activation energy Therefore, the reduction of dislocation defects and the prevention of injected carriers escaping from extended states would be a promising prospective for InGaN/GaN MQWs LEDs to achieve high internal quantum efficiency.

Light-emitting device

Abstract: A light-emitting device in which a gallium nitride upper and lower electrode type light-emitting diode is provided on a ceramic substrate on which at least a pair of insulated metal substrates or at least two package electrodes are formed In the light-emitting device, a gallium nitride upper and lower electrode type light-emitting diode (11) is mounted on substrates (12, 14) The power of the gallium nitride upper and lower electrode type light-emitting diode (11) is connected on the substrates (12, 14), and is surrounded by a reflector (16) The reflector (16) is adhered to the substrates (12, 14) with an adhesive Further, the reflector (16) is provided in such a manner that a fluorescent layer covers an aperture plane

Seamless On-Wafer Integration of Si(100) MOSFETs and GaN HEMTs

Abstract: The first on-wafer integration of Si(100) MOSFETs and AlGaN/GaN high electron mobility transistors (HEMTs) is demonstrated. To enable a fully Si-compatible process, we fabricated a novel Si(100)-GaN-Si(100) virtual substrate through a wafer bonding and etch-back technique. The high thermal stability of nitride semiconductors allowed the fabrication of Si MOSFETs on this substrate without degrading the performance of the GaN epilayers. After the Si devices were fabricated, the nitride epilayer is exposed, and the nitride transistors are processed. By using this technology, GaN and Si devices separated by less than 5 mum from each other have been fabricated, which is suitable for building future heterogeneous integrated circuits.

Recent development of nitride LEDs and LDs

Abstract: We fabricated the high efficiency white LEDs. The white LEDs, the yellow YAG-phosphors-coated small-size (290µm × 500µm) blue LED, designed for minimizing forward voltage. At a forward current of 20mA, the luminous flux, the forward voltage (Vf), the correlated color temperature (Tcp), the luminous efficiency, and the wall-plug efficiency (WPE) are 9.5lm, 2.8V, 5193K, 169Lm/W, and 50.8%, respectively. The high-power white LEDs were fabricated from the larger-size (1mm × 1mm) blue LED chips with the output power of 651mW at 350mA. Flux, Vf, Tcp, luminous efficiency, and WPE of the high-power white LED are 145Lm, 3.09V, 4988K, 134Lm/W, and 39.5%, respectively, at 350mA. This power white LEDs showed total flux of 361Lm at 1A. Moreover, we succeeded in developing high-power and high-efficiency blue laser diodes (LDs) with an emission wavelength at 445nm range by using GaN-based materials. This achievement leads to the full-color laser display applications. We fabricated multi-transverse mode LDs by a single emitter, and adopting φ9mm packages for the reduction of the thermal resistance. The typical optical-output power, voltage and wall-plug efficiency of the LDs at forward current of 1.0A at a temperature of 25oC was 1.17W, 4.81V and 24.3%, respectively. The catastrophic optical damage at the facets of these LDs did not appear up to 3W in the optical output power. The estimated lifetime of the LDs at a temperature of 25oC under continuous-wave operation 1.0A in automatic current control condition was over 30,000 hours.

Method of fabricating nitride semiconductor laser

Abstract: A method of fabricating a nitride semiconductor laser comprises preparing a substrate having a plurality of marker structures and a crystalline mass made of a hexagonal gallium nitride semiconductor. The primary and back surfaces of the substrate intersect with a predetermined axis extending in the direction of a c-axis of the hexagonal gallium nitride semiconductor. Each marker structure extends along a reference plane defined by the c-axis and an m-axis of the hexagonal gallium nitride semiconductor. The method comprises cutting the substrate along a cutting plane to form a wafer of hexagonal gallium nitride semiconductor, and the cutting plane intersects with the plurality of the marker structures. The wafer has a plurality of first markers, each of which extends from the primary surface to the back surface of the wafer, and each of the first markers comprises part of each of the marker structures. The primary surface of the wafer is semipolar or nonpolar. The method comprises growing a number of gallium nitride based semiconductor layers for a semiconductor laser. The method comprises cleaving the substrate product at a cleavage plane of the hexagonal gallium nitride semiconductor, after forming a substrate product in an electrode forming step.

A normally-off GaN FET with high threshold voltage uniformity using a novel piezo neutralization technique

Abstract: In this paper, we successfully demonstrate a recessed gate normally-off GaN FET on a silicon substrate with high threshold voltage (V th ) uniformity and low on-resistance. In order to realize high V th uniformity, a novel V th control technique is proposed, which we call “piezo neutralization technique”. This technique includes a piezo neutralization (PNT) layer formed at the bottom of the gate recess. Since the PNT layer neutralizes the polarization charges under the gate, the V th comes to be independent of the gate-to-channel span. The fabricated normally-off GaN FET with PNT structure exhibits an excellent V th uniformity (σ(V th )=18 mV) and a state-of-the-art combination of the specific on-resistance (R on A=500 mΩmm2) and the breakdown voltage (V B ≫1000 V). The normally-off GaN FETs wtih PNT structure show great promise as power devices.

Gate-First AlGaN/GaN HEMT Technology for High-Frequency Applications

Abstract: This letter describes a gate-first AlGaN/GaN high-electron mobility transistor (HEMT) with a W/high-k dielectric gate stack. In this new fabrication technology, the gate stack is deposited before the ohmic contacts, and it is optimized to stand the 870degC ohmic contact annealing. The deposition of the W/high-k dielectric protects the intrinsic transistor early in the fabrication process. Three different gate stacks were studied: W/ HfO2, W/Al2O3, and W/HfO2/Ga2O3. DC characterization showed transconductances of up to 215 mS/mm, maximum drain current densities of up to 960 mA/mm, and more than five orders of magnitude lower gate leakage current than in the conventional gate-last Ni/Au/Ni gate HEMTs. Capacitance-voltage measurements and pulsed-IV characterization show no hysteresis for the W/HfO2/ Ga2O3 capacitors and low interface traps. These W/high-k dielectric gates are an enabling technology for self-aligned AlGaN/GaN HEMTs, where the gate contact acts as a hard mask to the ohmic deposition.

Negative capacitance in light-emitting devices

Abstract: The negative capacitance behavior in light-emitting diodes and laser diodes has been observed and characterized by using ac admittance–voltage method. Experimental results proved that the strong negative capacitance behavior is always accompanied by remarkable light emission. We confirmed that the negative capacitance is an effect of the junction instead of other behavior or measurement error. We presented a numerical calculation by solving one dimension continuity equation based on a simple diode model. The results show that the negative capacitance behavior in light-emitting diodes has great relation to injected carriers recombination in the active region of luminescence.

Recent advances in GaN transistors for future emerging applications

Abstract: In this paper, recent advances in GaN-based transistors for power switching and millimeter wave communications are reviewed. These two applications are emerging in addition to the widely developed power amplifiers at microwave frequencies mainly for cellular base stations. Reduction of the fabrication cost is strongly required for power switching GaN transistors, which is enabled by our epitaxial growth technology on large area Si substrates. Another requisite for the application is to achieve normally-off operation and our novel device structure called Gate Injection Transistors (GIT) enables it with low enough specific on-resistance (R on · A) and high drain current. Here, we also present the world highest breakdown voltage of 10400 V in AlGaN/GaN HFETs, extracting full advantage of the high breakdown strength of GaN. The used poly AlN passivation works as a surface heat spreader with its high thermal conductivity, which effectively relieves the channel temperature resulting in lower thermal resistances. The GaN device for future millimeter wave communication consists of MIS-type gate using so-called "in-situ" deposited SiN as a gate insulator, which exhibits high f max of 203 GHz and low noise figure of 1.4 dB at 28 GHz. The presented GaN transistors are promising for the two future emerging applications demonstrating high enough potential of the material systems.

Analysis of DC–RF Dispersion in AlGaN/GaN HFETs Using RF Waveform Engineering

Abstract: This paper describes how dc-radio-frequency (RF) dispersion manifests itself in AlGaN/GaN heterojunction field-effect transistors when the devices are driven into different RF load impedances. The localized nature of the dispersion in the I-V plane, which is confined to the ldquokneerdquo region, is observed in both RF waveform and pulsed I-V measurements. The effect is fully reproduced using 2-D physical modeling. The difference in dispersive behaviors has been attributed to the geometry of a trap-induced virtual-gate region and the resulting carrier velocity saturation being overcome by punchthrough effects under high electric fields.

Group-III nitride light-emitting device

Abstract: A group-III nitride light-emitting device is provided. An active layer having a quantum well structure is grown on a basal plane of a gallium nitride based semiconductor region. The quantum well structure is formed in such a way as to have an emission peak wavelength of 410 nm or more. The thickness of a well layer is 4 nm or more, and 10 nm or less. The well layer is composed of In X Ga 1-X N (0.15≦X<1, where X is a strained composition). The basal plane of the gallium nitride based semiconductor region is inclined at an inclination angle within the range of 15 degrees or more, and 85 degrees or less with reference to a {0001} plane or a {000-1} plane of a hexagonal system group III nitride. The basal plane in this range is a semipolar plane.

GaN monolithic inverter IC using normally-off gate injection transistors with planar isolation on Si substrate

Abstract: We present a GaN monolithic inverter IC on Si substrate and successful motor-drive by it for the first time. Taking advantages of the bi-directional operation free from the forward voltage off-set [1], the inverter can be operated just by the integrated six GaN-based normally-off gate injection transistors (GITs) without any external fast recovery diodes (FRDs) to flow the fly-wheel current. The IC enables the efficiency as high as 93% at low power operation where so far that of conventional Si-based inverters has remained lower value owing to the forward voltage off-set. The key processing technology is the newly introduced planar isolation using Fe ion implantation which fully isolates the GaN-based lateral devices each other.

Robust AlGaN/GaN Low Noise Amplifier MMICs for C-, Ku- and Ka-Band Space Applications

Abstract: The high power capabilities in combination with the low noise performance of Gallium Nitride (GaN) makes this technology an excellent choice for robust receivers. This paper presents the design and measured results of three different LNAs, which operate in C-, Ku-, and Ka-band. The designs are realized in 0.25 μm and 0.15 μm AlGaN/GaN microstrip technology. The measured noise figure is 1.2, 1.9 and 4.0 dB for the C-, Ku-, and Ka-frequency band respectively. The robustness of the LNAs have been tested by applying CW source power levels of 42 dBm, 42 dBm and 28 dBm for the C-band, Ku-band and Ka-band LNA respectively. No degradation in performance has been observed.

Reducing Thermal Resistance of AlGaN/GaN Electronic Devices Using Novel Nucleation Layers

Abstract: Currently, up to 50% of the channel temperature in AlGaN/GaN electronic devices is due to the thermal-boundary resistance (TBR) associated with the nucleation layer (NL) needed between GaN and SiC substrates for high-quality heteroepitaxy. Using 3-D time-resolved Raman thermography, it is shown that modifying the NL used for GaN on SiC epitaxy from the metal-organic chemical vapor deposition (MOCVD)-grown standard AlN-NL to a hot-wall MOCVD-grown AlN-NL reduces NL TBR by 25%, resulting in ~10% reduction of the operating temperature of AlGaN/GaN HEMTs. Considering the exponential relationship between device lifetime and temperature, lower TBR NLs open new opportunities for improving the reliability of AlGaN/GaN devices.

A Reliability Study on Green InGaN–GaN Light-Emitting Diodes

Abstract: In this letter, the reliability of green InGaN-GaN light-emitting diodes (LEDs) has been analyzed by correlating the defect density of wafers with various device parameters, including leakage current, 1/f noise, and degradation rate. It was found that as the wavelength of green LEDs increases from 520 to 550 nm by increasing the indium content in the quantum wells, the defect density also increases, thus leading to larger leakage current, enhanced noise magnitude, and shortened device lifetime.

Gate-Recessed InAlN/GaN HEMTs on SiC Substrate With $ \hbox{Al}_{2}\hbox{O}_{3}$ Passivation

Abstract: We studied submicrometer (LG = 0.15-0.25 ?m) gate-recessed InAlN/AlN/GaN high-electron mobility transistors (HEMTs) on SiC substrates with 25-nm Al2O3 passivation. The combination of a low-damage gate-recess technology and the low sheet resistance of the InAlN/AlN/GaN structure resulted in HEMTs with a maximum dc output current density of IDS,max = 1.5 A/mm and a record peak extrinsic transconductance of gm,ext = 675 mS/mm. The thin Al2O3 passivation improved the sheet resistance and the transconductance of these devices by 15% and 25%, respectively, at the same time that it effectively suppressed current collapse.

N-Face GaN/AlGaN HEMTs Fabricated Through Layer Transfer Technology

Abstract: We present a new method to fabricate N-face GaN/AlGaN high electron mobility transistors (HEMTs). These devices are extremely promising for ultrahigh frequency applications where low contact resistances and excellent carrier confinement are needed. In this letter, the N-face of a Ga-face AlGaN/GaN epilayer grown on Si (111) is exposed by removing the Si substrate. To provide mechanical support, prior to the substrate removal, the Ga-face of the wafer is bonded to a Si (100) carrier wafer. The resultant N-face GaN/AlGaN heterostructures exhibited record transport properties (mue = 1670 cm2/Vmiddots, ns = 1.6 times 1013/ cm2, and Rsh = 240 Omega/sq). These excellent transport properties rendered N-face HEMTs with 30% higher maximum drain current than Ga-face HEMTs and good RF characteristics (fT = 10.7 GHz middotmum and fmax = 21.5 GHzmiddotmum), comparable to state-of-the-art Ga-face devices.

An Efficient High-Frequency Drive Circuit for GaN Power HFETs

Abstract: The requirements for driving gallium nitride (GaN) heterostructure field-effect transistors (HFETs) and the design of a resonant drive circuit for GaN power HFET switches are discussed in this paper. The use of wideband III-nitride (such as GaN) devices today is limited to telecom and low-power applications. The current lack of high-frequency high-power drivers prevents their application in power converters. The proposed circuit is based upon resonant switching transition techniques, by means of an LC tag, to recover part of the power back into the voltage source in order to reduce the power loss. This circuit also uses level shifters to generate the zero and negative gate-source voltages required to turn the GaN HFET on and off, and it is highly tolerant to input-signal timing variances. The circuit reduces the overall power consumed in the driver and thus reduces the power loss. This is particularly important for high-frequency driver operation to take full advantage, in terms of efficiency, of the superior switching speed of GaN devices. In this paper, the topology of the low-power-loss high-speed drive circuit is introduced. Some simulation results and preliminary experimental measurements are discussed.