Improvements of the internal quantum efficiency by reduction threading dislocation density and light extraction using UV transparent p-type cladding contact layers, reflecting ohmic contact, chip encapsulation with optimized shape refractive index allowed us to obtain external 10.4% at 20 mA CW current output power up 9.3 mW 278 nm for AlGaN-based deep-ultraviolet light-emitting diodes grown on sapphire substrates.

We report on a study of Al and Ti/Al contacts to n-type GaN. n-GaN (7×1017 cm−3) annealed in forming gas at 600 °C reached minimum contact resistivity 8×10−6 Ω cm2 had much better thermal stability than reported by previous researchers. (35/115 nm) (5×1017 resistivities 7×10−6 5×10−6 after annealing Ar 400 for 5 min 15 s, respectively. Depth profiles showed that low resistance was only achieved diffused the GaN interface. propose mechanism Ohmic formation 400–600 range includes Ti reducing...

We report on a metal–insulator–semiconductor heterostructure field-effect transistor (MISHFET) using Si3N4 film simultaneously for channel passivation and as gate insulator. This design results in increased radio-frequency (rf) powers by reduction of the current collapse it reduces leakage currents four orders magnitude. A MISHFET room temperature about 90 pA/mm increases to only 1000 at ambient high 300 °C. Pulsed measurements show that unlike metal–oxide–semiconductor HFETs regular HFETs,...

High performance AlGaN/GaN high electron mobility transistors (HEMTs) with 0.12 /spl mu/m gate-length have been fabricated on an insulating SiC substrate. The devices exhibited extrinsic transconductance of 217 mS/mm and current drive capability as 1.19 A/mm. threshold voltage the was -5.5 V. For HEMTs same gate-length, a record unity gain cut-off frequency (f/sub T/) 101 GHz maximum oscillation max/) 155 were measured at V/sub ds/=16.5 V gs/=5.0 microwave noise performances characterized...

The performance results AlGaN-GaN Heterostructure Field Effect Transistors (HFETs) grown on SiC substrates are reported. maximum transconductance of these devices was 142 mS/mm and the source-drain current as high 0.95 A/mm. dissipated DC power at room temperature 0.6 MW/cm/sup 2/, which is more than three times higher that in similar sapphire. This thermal breakdown threshold achieved primarily due to effective heat sink through substrate. These demonstrated stable elevated temperatures up...

We report blue-purple pn-junction light-emitting diodes (LEDs) with a-plane GaN–InGaN multiple quantum well active region. The LEDs were grown over r-plane sapphire substrates. Our study has shown the low pump intensity photoluminencence and electroluminescence to be dominated by emission from band-tail states which then saturates rapidly giving rise band-edge emission.

We report on an AlN/AlGaN superlattice approach to grow high-Al-content thick n+-AlGaN layers over c-plane sapphire substrates. Insertion of a set superlattices is shown significantly reduce the biaxial tensile strain, thereby resulting in 3-μm-thick, crack-free Al0.2Ga0.8N layers. These high-quality, low-sheet-resistive are key importance avoid current crowding quaternary AlInGaN multiple-quantum-well deep-ultraviolet light-emitting diodes

We report on an approach of using AlN/AlGaN superlattices (SLs) for threading-dislocation-density reduction to grow high quality thick AlGaN sapphire. Using x-ray diffraction (XRD) measurements and etch pits counting by atomic force microscopy, we show that the insertion SLs suppresses material mosaicity decreases threading dislocation density two orders magnitude, then eliminates cracking. Dislocation densities deduced from XRD results those chemical etching are in a good agreement.

The breakdown voltages in unpassivated nonfield-plated AlGaN/GaN HFETs on sapphire substrates were studied. These studies reveal that the is limited by surface flashover rather than channel. After elimination of air, voltage scaled linearly with gate-drain spacing reaching 1.6 kV at 20 mum. corresponding static ON-resistance was as low 3.4 mOmegamiddotcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This translates to a power device...

We present the analysis of external quantum efficiency in AlGaN deep ultraviolet (DUV) light-emitting diodes (LEDs) on sapphire substrates and discuss factors affecting output power DUV LEDs. Performance LED is related to optimization device structure design improvements epitaxial material quality.

Inspired by unparalleled adhesion of mussels, bioinspired poly(dopamine) (PDA) has been used to functionalize the surface aluminum oxide (Al2O3) nanoparticles aiming at improving thermal conductivity silicone rubber (SR). The successful and effective preparation PDA modified Al2O3 (Al2O3–PDA) was confirmed XPS, HR-TEM, XRD. coating on improved its interfacial interaction between polymeric matrix facilitated uniform-dispersion filler, leading 30 vol % Al2O3–PDA/SR composite that exhibited a...

We report on the microwave operation of 1 μm gate AlGaN/GaN doped channel heterostructure field effect transistors (DC-HFET's) with cutoff frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> 18.3 GHz. These devices exhibit frequency-gate length product in excess 18 GHz/spl middot/μm, comparable to that state-of-the-art GaAs MESFET's. explain these improvements device performance by increased sheet carrier density and a reduction...

a-plane GaN templates and coalesced epitaxial lateral overgrown (ELOG) films on r-plane sapphire substrates were investigated by x-ray diffraction (XRD). The found to have [0001]-oriented stripe-features, which is related anisotropic mosaicity. For the mosaic blocks, mosaicity reached largest smallest values along [11̄00] [0001] directions. ELOG procedure with SiO2 mask stripes perpendicular direction limits preferable growth this direction, thereby enhances growth. This leads large-area,...

We present the results of a comparative photoluminescence (PL) study GaN and InGaN-based epilayers, InGaN/GaN multiple quantum wells (MQWs). Room-temperature PL spectra were measured for very broad range optical excitation from 10 mW/cm2 up to 1 MW/cm2. In contrast all In-containing samples exhibited an excitation-induced blueshift peak emission. addition, emission in InGaN epilayers with same composition as well was significantly smaller. The comparison “bulk” MQWs allowed us separate two...

We report on 245–247 nm AlGaN-based deep ultraviolet (DUV) light-emitting diodes with continuous wave output power up to 2 mW. DUV peak emission wavelength of 245 and 247 exhibit turn-on voltage less than 10 V. At room temperature cw operation the maximum external quantum efficiency was close 0.18%, which is highest value published date for devices shorter 250 nm. A large droop observed at current densities above 100 A/cm2 attributed self-heating, carrier spillover from QWs into barrier...

The fabrication and characterization of high performance AlGaN/GaN heterostructure field effect transistors (HFETs) grown on p-type SiC substrates are reported for the first time. HFETs were fabricated with gate lengths 0.25, 0.5, 1 μm. These devices exhibited simultaneously drain currents, extrinsic transconductances, excellent frequency response. 0.25-μm gate-length produced a peak current 1.43 A/mm, transconductance 229 mS/mm, unity current-gain cutoff 53 GHz, maximum oscillation 58 GHz....

We report novel GaN detectors grown by molecular beam epitaxy on Si(111) substrates. Wurtzite structure epitaxial exhibits room-temperature photoluminescence with a band-edge-related emission width as narrow 7 nm and intensities comparable to high quality layers sapphire metalorganic chemical vapor deposition. Spectral response of lateral geometry Schottky shows sharp cutoff at 365 peak responsivities ∼0.05 A/W 0 V, ∼0.1 −4 V bias. The dark current is ∼60 nA −2 noise equivalent power...

Gated transmission line model pattern measurements of the transient current–voltage characteristics AlGaN/GaN heterostructure field-effect transistors (HFETs) and metal–oxide–semiconductor HFETs were made to develop a phenomenological for current collapse. Our show that, under pulsed gate bias, collapse results from increased source–gate gate–drain resistances but not channel resistance gate. We propose linking this increase in series (and, therefore, collapse) decrease piezoelectric charge...

Novel, current collapse free, double heterostructure AlGaN/InGaN/GaN field effect transistors (DHFETs) are fabricated on the insulating SiC substrates. The simulations show that a combined of bandgap offsets and polarization charges provides an excellent 2D carrier confinement. These devices demonstrate output RF powers as high 4.3 W/mm in CW mode 6.3 pulsed mode, with gain compression low 4 dB.

The characteristics of a novel nitride based field-effect transistor combining SiO/sub 2/ gate isolation and an AlGaN/InGaN/GaN double heterostructure design (MOSDHFET) are reported. with InGaN channel layer significantly improves confinement the two-dimensional (2-D) electron gas compensates strain modulation in AlGaN barrier resulting from voltage modulations. These decrease total trapped charge hence current collapse. combination improved carrier confinement/strain management results...

We report on the fabrication and characterization of Al0.15Ga0.85N/GaN heterostructure field-effect transistors (HFETs) with transconductance as high 120 mS/mm saturated current density 0.35 A/mm for a device gate length width 1 100 μm. This represents one best results such device. A comparison maximum devices wafers different channel conductance is presented to analyze factors limiting performance. Our data indicates series resistance between source drain be factor dc transconductance.

High crystalline quality epitaxial GaN films with thicknesses 0.5–1.5 μm have been successfully grown directly on Al2O3(0001) substrate by pulsed laser deposition (PLD). For at 950 °C, we obtained an x-ray diffraction rocking curve linewidth of 7 arc min. The ion channeling minimum yield in the near-surface region (∼2000 Å) for a 0.5 thick film was ∼3%–4% indicating high degree crystallinity. optical absorption edge measured UV-visible spectroscopy sharp, and band gap found to be 3.4 eV....

Polarization effects have been studied in GaN/AlGaN multiple quantum wells (MQWs) with different c-axis orientation by means of excitation-dependent photoluminescence (PL) analysis. Quantum structures were grown on [0001]-oriented sapphire substrates (C plane) and single-crystalline [11̄00]-oriented freestanding GaN (M using the metalorganic chemical vapor deposition technique. Strong PL spectrum line blueshifts (up to 140 meV) which are correlated excitation intensity obtained for C-plane...

The energies of photo- and electroluminescence transitions in InxGa1−xN quantum wells exhibit a characteristic “blueshift” with increasing pumping power. This effect has been attributed either to band-tail filling, or screening piezoelectric fields. We have studied the pressure temperature behavior radiative recombination InxGa1−xN/GaN x=0.06, 0.10, 0.15. find that, although primarily band-to-band character, excitation-power induced blueshift can be uniquely screening. Calculations field...