This PDF file contains the front matter associated with SPIE Proceedings Volume 11280, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Large size and low dislocation density bulk gallium nitride (GaN) crystals were successfully grown by original acidic ammonothermal method SCAAT™ (Super Critical Acidic Ammonia Technology). It enabled us to obtain extremely high crystallinity true bulk GaN. In this article, 2-inch size non-polar m-plane GaN and nearly 4-inch size polar c-plane GaN were demonstrated. The dislocation and stacking fault density of m-plane GaN were in the range of 10² to 10³ cm^-2 and 0 to 5 cm^-1, respectively. The full width at half maximum (FWHM) of X-ray rocking curve (XRC) on (10-12) plane was 6.4 arcsec. The dislocation density of c-plane GaN was in the range of 10³ to 10⁴ cm^-2. The off-angle distribution of nearly 4-inch size c-plane GaN was ±0.006° in the span of 80 mm. The types of dislocations in the c-plane GaN were identified by transmission electron microscope (TEM) observation. Hydride vapor phase epitaxy (HVPE) growth on the SCAA™ c-plane seed was carried out and obtained 2-inch wafer. The crystallinity was comparable to SCAAT™ seed; FWHM of XRC was less than 10 arcsec and off-angle distribution was ±0.017°.

Recent progress in bulk GaN growth technology will be presented. New results of basic ammonothermal GaN crystallization and halide vapor phase epitaxy (HVPE) of GaN will be shown and analyzed. The advantages, disadvantages and challenges of both methods will be discussed. An influence of lateral growth on critical thicknesses and structural quality of crystallized GaN layers by both methods will be demonstrated. Reduction of lateral crystallization and growth only in one crystallographic direction will be shown.

Experimental measurements of optical and crystallinity properties of MOCVD-grown quaternary AlGaInN lattice-matched to GaN are presented. The bandgaps, carrier life times, optical constants (n vs. k), doping profiles, effective masses, and structural and surface information from XRD and AFM are presented. This study reports important material parameters for the alloy, which will be key in the design and application of these alloys for UV and visible spectral regime optoelectronic devices.

InGaN-based devices have attracted a lot of attention, thanks to versatile optoelectronic applications. We show that the growth of these layers in an AIXTRON Close Coupled Showerhead is complicated due to the presence of gallium pollution in the chamber after the growth of GaN buffer layers. This pollution reacts with the TMIn precursor in the growth chamber to give thicker InGaN layers with reduced indium incorporation. We overcame this problem by limiting the presence of the metallic gallium in the growth chamber, resulting in more stable and predictable growth of InGaN layers.

The diffraction based scanning electron microscopy (SEM) technique of electron channeling contrast imaging (ECCI) provides rapid and non-destructive information on defects on length scales from tens of nanometres to tens of micrometres. ECCI may be complemented by electron backscatter diffraction (EBSD) and hyperspectral cathodoluminescence imaging (CL). EBSD provides orientation, phase, polarity and strain information, whilst CL reveals the influence of phase, composition, strain and defects on luminescence. I will discuss our recent investigations of phase, composition and polarity, the type, density and distribution of defects and the distribution of strain in a range of nitride semiconductor structures.

The dependence of growth temperature for the epitaxial films grown by tri-halide vapor phase epitaxy (THVPE) on the crystal characteristics, such as the surface morphology, the full width at half maximum (FWHM), the threading dislocation density (TDD), the impurity concentration, and the photoluminescence (PL) was investigated. The epitaxial films grown at relatively high growth temperature of 1300-1350 °C showed that the crystal quality, such as FWHM and TDD retained that for the used substrate. The near-band-edge emission for PL for 1300-1350 °C growth showed lager intensities due to low nonradiative recombination center (NRC). Moreover, the epitaxial growth on the supercritical acidic ammonia technology (SCAAT™) substrate was demonstrated. The TDD was as low as 2 × 10⁴ cm^-2, which indicated that the epilayer grown by THVPE retained the superior crystal quality of SCAAT™.

With respect to (Al,In,Ga)N epilayers and quantum wells, threading dislocations (TDs) have long been believed to as the principal limiting factor for the internal quantum efficiency of the near-band-edge emission. However, the realization of low TD density GaN and AlN substrates and (Al,In,Ga)N layers enabled investigating the roles of point defects and impurities without interferences by TDs, and vacancy-complexes have been revealed to act as origins of major Shockley- Read-Hall (SRH)-type nonradiative recombination centers (NRCs) in GaN. Accordingly, the concentration of NRCs (N_NRC) must be decreased in both optical devices and power-switching electronic devices. Here we show the results of positron annihilation and time-resolved luminescence measurements on n- and p-type GaN, AlN, and Al_0.6Ga_0.4N alloys to reveal the origins of major intrinsic SRH-NRCs and to obtain their capture coefficients for minority carriers. For unintentionally doped and doped n-type GaN, divacancies comprising of a Ga-vacancy (V_Ga) and a N-vacancy (V_N), namely V_GaV_N, are assigned as major SRH-NRCs with a hole capture-coefficient (C_p) of 6×10^-7 cm³s^-1. For Mg-doped ptype GaN epilayers grown by metalorganic vapor phase epitaxy (MOVPE), V_Ga(V_N)₂ are assigned as major NRCs with electron capture-coefficient (C_n) of 8×10^-6 cm³s^-1. For Mg-implanted GaN, V_GaV_N are the dominant NRCs right after implantation, and they agglomerate into (V_GaV_N)₃ clusters with C_n of 5×10^-6 cm³s^-1 after high-temperature annealing. Since AlN films grown by MOVPE usually contain vacancy-clusters comprising of an Al-vacancy (V_Al) such as V_Al(V_N)_2-3, complexes of a cation-vacancy and a few V_Ns may be the major NRCs in AlN and Al_0.6Ga_0.4N alloys.

Vacancy-type defects in Mg-implanted GaN were probed using monoenergetic positron beams. Mg⁺ ions were implanted to provide box profiles with Mg concentrations [Mg] of 10¹⁷-10¹⁹ cm-³. For as-implanted samples, the major defect species was determined to be Ga-vacancy (V_Ga) related defects such as divacancy (V_GaV_N) and/or their complexes with impurities. For Mg-implanted samples, an agglomeration of vacancies started at 800-1000°C annealing, leading to the formation of vacancy clusters such as (V_GaV_N)₃. For the sample with [Mg]=10¹⁹ cm^-3, the trapping rate of positrons to the vacancies decreased with increasing annealing temperature (≥1100°C), which was attributed to the change in the charge state of vacancy-type defects from neutral to positive (or negative to neutral) due to the activation of Mg. For Mg- and H-implanted samples, the hydrogenation of vacancy-type defects started after 800°C annealing. Comparing with the annealing behavior of defects for the samples without H-implantation, the clustering of vacancy-type defects was suppressed, which can be attributed to the interaction between Mg, H, and vacancies.

We present an investigation on the stability of high periodicity (30 pairs) multiple quantum well InGaN-GaN devices for photodetection and light harvesting in the UV and visible spectral range. The devices under test were characterized during optical stress by I-V measurements in dark condition and illuminated with a monochromatic LD emitting at 405 nm with intensities ranging from 1 mW/cm² to 50 W/cm². We submitted the devices to several step-stress experiments: a first one in short-circuit condition at 100 °C baseplate temperature with monochromatic excitation from 361 W/cm² to 1164 W/cm²; a second one at fixed optical power of 589 W/cm² and baseplate temperature increasing from 35°C to 175 °C. We also evaluated the carrier flow induced degradation by means of a current stress, ranging from 1 A/cm² to 14 A/cm² , without optical excitation. We then performed a 50 hours stress at 175 °C baseplate temperature and 589.3 W/cm² excitation. During this stress the open-circuit voltage and the optical-to-electrical conversion efficiency significantly decreased, especially at low characterization intensities, whereas short-circuit current and external quantum efficiency showed almost no variation.

BAlN films were performed by either the flow-modulated epitaxy method or continuous growth method. All BxAl1-xN films are single-phase confirmed by high-resolution 2θ–ω (002) X-ray diffraction. The Boron (B) content of each sample was determined by Secondary Neutral Mass Spectrometry with various values have been achieved from 22 to 34% and reconfirmed by Rutherford backscattering spectrometry. All BAlN samples clearly showed the columnar crystalline on the surface which was observed by AFM measurement. The high B contents can expand the applications of BAlN for deep ultraviolet and power electronic device applications.

In this work, we implement a technique of selective area sublimation to shape GaN or GaN/(Ga,In)N layers. The sublimation has a perfect selectivity with the mask material (either SixNy or SiOx) and vertical sidewalls over a depth up to 7 µm are obtained. The mask thickness can be as thin as 1 mono-layer. We apply this technique for the top-down fabrication of several structures: nanoporous GaN and GaN/(Ga,In)N quantum wells, deep nanoholes in GaN and arrays of GaN nanolasers.

A loss analysis of blue semipolar (20-2-1) vertical-cavity surface-emitting lasers with ion implanted apertures (IIA) reveals the presence of loss due to absorption in the implant and other absorbing regions. Devices using a buried tunnel junction (BTJ) scheme to confine the current are then analyzed to find the absence of any excess losses. The effect of changing the number of DBR periods on both device types is simulated to give a 70% and a 95% increase in output power for the IIA and BTJ devices, respectively, with the removal of one period from the top DBR at 10 kA/cm². The mode structure of two different BTJ devices with different index confinements is compared to show that the 0.034 increase in refractive index difference significantly increased the prevalence of higher order modes.

GaN-based vertical-cavity surface-emitting lasers (VCSELs) have drawn interest in recent years for their potential applications in data storage, laser printing, solid-state lighting, optical communications, sensing, and displays. Several research groups have demonstrated electrically injected GaN-based VCSELs utilizing different growth and fabrication techniques to address the many challenges associated with III-nitride materials. One such challenge is fabrication of highquality conductive epitaxial distributed Bragg reflectors (DBRs). A relatively new approach that yields high-index-contrast lattice-matched epitaxial DBRs is to introduce subwavelength air-voids (nanopores) in alternating layers of doped/undoped GaN. These nanoporous layers can be achieved by the controlled anodic electrochemical etching of highly doped n-type GaN in acids. The selective formation of the nanopores in the doped layers effectively lowers the refractive index compared to the adjacent undoped GaN layers, resulting in a refractive index difference of ~0.83, allowing high reflectance (>99%) with only ~16 pairs. Here, we will present electrically injected nonpolar m-plane GaN-based VCSELs with lattice-matched nanoporous GaN bottom DBRs and top dielectric DBRs. Lasing under pulsed operation at room temperature was observed at 409 nm with a linewidth of ~0.6 nm and a maximum output power of ~1.5 mW. The nonpolar m-plane orientation offers low transparency, high material gain, and anisotropic gain characteristics. The VCSELs were linearly polarized with a polarization ratio of ~0.94 and polarization-pinned emission along the a-direction. The mode profiles, thermal properties, and lasing yield of the VCSELs are also discussed.

We demonstrate the first electrically injected GaN-based VCSEL with a TiO₂ high-contrast grating (HCG) as the top mirror. The TiO₂-HCG rested directly on the n-GaN without an airgap for mechanical stability. A VCSEL with an aperture diameter of 10 μm had a threshold current of 25 mA under pulsed operation at room temperature. Multiple longitudinal modes coexist around 400 nm, each TM-polarized with a linewidth of 0.5 nm (spectral resolution limited). This first demonstration of a TiO₂-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as post-growth setting of resonance wavelength.

Light extraction of internally generated light in LEDs into air has always been a major issue from the early days. The reabsorption of emitted light, long a stumbling block, is now almost always solved by the use of heterostructures. The majority of the internal light undergoes total internal reflection at the materials/air interface due to the large index mismatch. This is mitigated by redirecting light rays by light diffusing/scattering structures situated at interfaces. Powerful simulation techniques exist taking into account the various physical mechanisms into play. The frontier is reaching 95%+ extraction efficiencies which would allow 100%+ LED wall-plug efficiencies

In this work, the effect of introducing a photonic crystal network of silicon nitride (SiN) micro-domes on the backside of silver coated gallium nitride (GaN) based light emitting diodes (LEDs) was studied. First, sapphire side of the top emitting LEDs, which is the bottom surface of the LEDs, is coated with silver (Ag). Light emitted towards the sapphire substrate is reflected upwards to the top surface and the amount of light extracted from the LED is expected to increase. In an alternative approach, SiN micro-domes forming a two dimensional photonic crystal, 2 μm in diameter and 80 nm in height in average, are deposited on the light emitting surface of the device with a period of 2 μm. Coating the backside with Ag has increased the efficiency of a top emitting LED by 11%. By introducing the SiN photonic crystal onto the Ag backside coated sample, total internal reflection is reduced via scattering and the amount of light emitted has been increased by 30% at 5·10⁴ mA/cm². Integration of SiN micro-domes with Ag coating has significantly impacted light extraction which has been shown to increase the efficiency of GaN based LEDs. Fabrication process and the results are discussed in detail.

We present a combined photoluminescence (PL) and photomodulated reflectivity (PMR) study of three GaN/InGaN multiquantum well samples. We reported previously that the change in carrier concentration (n) induced by the pump beam can be measured by lock-in techniques using a simple Drude model to calculate n from the change in reflectivity. Here we extend the work by simultansously measuring a thermal signal from the sample, we can thus measure the internal quantum efficiency ηi of samples as a function of carrier concentration. This yields an ηi vs n curve that is strikingly different to those reported previously by PL and electroluminescent techniques (EL), with a very rapid (in n) drop off due to the droop process.

Our goal is to fabricate a laser diode 2D array which combines the properties of both VCSEL and edge emitting laser. Proposed light emitter will have a horizontal cavity with 450 deflectors. The role of these deflectors would be to deflect light perpendicular to the cavity, achieving vertical out-coupling. The most challenging part of this project is the fabrication of the micro-mirrors which act as both as beam deviating mirrors and cavity forming mirrors. Owing to the excellent thermal conductivity of GaN substrates the properties of such a 2D array should be better than of conventional nitride laser diode arrays, not even mentioning nitride-based stacked bars systems. In this paper I will describe our new device design and processing, giving insight to its possible applications and advantages over simple light emitting laser diode.

This paper reports the latest device performance of high-power blue and green Laser Diodes (LDs). The epitaxial structures of LDs including n-type, active and p-type layers were grown by metal organic chemical vapor deposition (MOCVD) on C-plane free-standing GaN substrates. And a ridge type structure and Electrodes of the n-type and p-type were formed. Front and rear mirror facets were obtained by cleavage at the m-plane surface. We optimized the epitaxial and the device structures for high efficiency, high optical output power and reliability. Every LD chip was mounted on a heat sink using a junction down method in a TO-Φ9 mm package for suppressing thermal resistance. A New developed 455 nm blue LD showed the optical output power and the voltage of 5.67 W and 3.93 V at the forward current of 3 A under Continuous Wave (CW) operation. The wall plug efficiency of the 455 nm blue LD was 48.1% at 3A. The wall plug efficiency of the high-power blue LD we developed is the highest reported so far. A new developed green LD at 525 nm showed the optical output power of 1.75 W and the wall plug efficiency of 21.2 % at the forward current of 1.9A. The optical output power, the voltage and the wall plug efficiency of a new 532 nm LD showed 1.53 W and 4.35 V, 18.5 % at the forward current of 1.9 A under CW operation. The peak wall plug efficiency of the 532 nm LD was 20 % at the optical output power of 1W.

We investigate the angularly, temporally, and spectrally resolved far-field dynamics of a single lateral mode green (Al,In)GaN laser diodes. For applications as directly modulated light source in laser projection, for AR/VR/MR, etc., a stable beam pointing angle and width of the far-field is required. Combing an angle- resolved measurement with a spectrometer and streak camera, we characterize optical intensity as function of far-field angle, wavelength, and time. Beam pointing angle and width are then calculated from the moments of the angular intensity distributions. We observe a stable far-field behavior for the narrow ridge. This is in contrast to strong variations in beam pointing direction and far-field profile during short pulses for earlier (Al,In)GaN laser diodes, where the dynamics could be tracked to heating of the waveguide. Therefore we attribute the observed stable dynamics of state-of-the-art narrow ridge laser diodes to their low internal losses, low forward voltage, and consequently low heating.

Quantum based devices offer distinct advantages over conventional technology, such as improved sensitivity for sensing applications or enhanced accuracy for metrology. To utilize this potential, a number of technical requirements must be met, such as the cooling and trapping of neutral atoms for their use as quantum systems. We present our work on InGaN-based semiconductor cooling lasers for a variety of atomic species such as strontium, magnesium and ytterbium whos target wavelength was met by quantum-well composition engineering. Results on growth-epitaxy, facet coating as well as different configurations such as ECDL and MOPAs are presented, depending on the requirement of the application.

Green laser diodes are being used for many applications, especially for laser projection. An important parameter for laser diodes are the internal losses. The internal losses of blue and green (Al,In)GaN laser diodes have been decreased to values significantly below α_int = 10 cm^-1, such enabling laser diodes with low threshold, high efficiency, and high output power. However, it is difficult to measure such low internal losses. From the slope efficiency and from Hakki-Paoli gain spectra, we derive an upper and lower limit for the internal losses of 5.4 cm^-1 and 3.7 cm^-1, respectively, for a specific green laser diode. Furthermore, we perform transfer matrix method simulations of the waveguide modes to simulate the dispersion of the internal losses in the wavelength range where the quantum wells are transparent. Comparing simulated and measured dependency of the internal losses on wavelength, we argue that the leakage of the waveguide mode to the p-contact and into the substrate are the main contributions to the dispersion of the internal losses.

We report on the degradation of high-power blue semiconductor lasers, with nominal wavelength of 450 nm and output power of 1.6 W, used for lighting, projection and metrology applications. Our analysis consists in constant current stress, aimed at investigating the changes in electrical and optical characteristics of the lasers. For the first time, we describe the degradation of the spectral characteristics during high current stress.
The study showed three main effects: (i) the decrease in the sub-threshold optical power, which shows two different slopes, that we ascribe to the regions where A, Shockley-Read-Hall (SRH) recombination coefficient, and B, radiative coefficient, dominate. (ii) a logarithmic decrease during the stress time of the characteristic temperature T₀. (iii) the presence of a parasitic peak, with energy close to the main emission peak. This peak is ascribed to recombination in a second quantum well with slightly different energy, due to the different internal field. The intensity of this excited emission decreases during stress time, possibly due to a change in the injection efficiency.
We have also found an initial increase in the optical power at very low current levels, followed by a decrease with increasing stress time. This behavior is ascribed to an initial annealing, that favors the activation of magnesium, followed by an increment of the density of defects in the material caused by the stress.

New approach towards efficient light emission with bottom-tunnel junctions is developed. The bottom-tunnel junction design aligns the polarization fields in a desired direction in the vicinity of quantum well, while simultaneously eliminating the need for p-type contacts, and allowing efficient current spreading. By preventing electron overshoot past quantum wells, it disables carrier recombination in undesired regions of the heterostructures, increasing injection efficiency and opening new possibilities in heterostructure design. InGaN-based buried-tunnel junction is used to construct first monolithically grown p-type-down laser diode on n-type, Ga-polar bulk GaN substrate. Unique advantages of such construction that enables to separate design of carrier injection and optical mode confinement for such laser diode structures is discussed.

There has been a lack of research for proper understanding of defects relaxing the strained lattice of InGaN/(Al)GaN quantum wells. This motivates us to find the relation among the defects, the piezoelectric field (FPZ), and the bandgap shrinkage under high injection. In this work, five similar-structure near-ultraviolet (NUV) light-emitting diodes (LEDs) are used to find systematically that the increase of point defects in the sample decreases both the peak wavelength and FPZ. This effect clearly indicates that the strain relaxation is induced by defects. We propose a model that consistently explain the observed changes in macroscopic characterizations of NUV LEDs.

AlGaN-based UltraViolet Light Emitting Diodes (UV LEDs) are promising devices for replacing the conventional UV lamps, which contain toxic substances like mercury, in order to have smaller devices, lower operating voltage and the possibility of tuning the emission wavelength by changing the Al and Ga content in the alloy. However, UV-LEDs may suffer from a relatively fast degradation of electrical and optical characteristics, that can be due to the generation of defects that increase the Shockley-Read-Hall (SRH) recombination components. The aim of this paper is to study the behavior of UV-B LEDs submitted to a constant current stress, through electrical, optical and spectral characterization, and capacitance deep-level transient spectroscopy (C-DLTS). The results of this analysis demonstrate that UV-B LEDs show a decrease in the driving voltage, probably correlated with the increased activation of the Mg dopant, and an increase in subthreshold forward current, ascribed to the generation of mid-gap defects caused by the stress. We also found a strong optical degradation at low current levels, that indicates the increase in SRH recombination, probably due to the increased density of mid-gap defects. To investigate on the origin of the defects, we carried out C-DLTS measurements; the results indicate the presence of Mg-related defects and/or intrinsic defects related to the GaN growth. Moreover, after stress we notice the appearance of a peak that is strictly related to the increase of mid-gap defects generated during the stress.

Ultraviolet (UV) light-emitting diodes (LEDs) are useful in applications such as water/air purification, sterilization, and biosensing. However, due to the low external quantum efficiencies (η_EQE) of III-Nitride semiconductor UV LEDs, the technology has struggled to achieve penetration into many of these potential applications. While the active regions of UV LEDs have been well optimized, allowing for internal quantum efficiencies of greater than 60%, light extraction efficiency (η_EXT) remains a significant obstacle, and is limited to less than 10% in conventional UV LEDs, limiting their η_EQEs to around 1% for wavelengths below 300 nm. Surface texturing of the p-GaN or p-AlGaN layer in top-emitting UV LEDs has allowed for improvements in η_EQE at the expense of hole injection efficiency. Etching of the sapphire or AlN substrates to form lenses avoids this tradeoff in bottom-emitting LEDs, but is exceptionally time and resource intensive. Here, we investigated a novel method of enhancing η_EXT of AlGaN multiple quantum well UV LEDs at 280 nm using self-aligned monolayers of SiO₂ microspheres and microlenses. Finite-difference time-domain simulations were utilized to investigate the effects of these nanostructure monolayers on the η_EXT of DUV LEDs emitting at 280 nm, and predicted up to 2.31x times enhancement of η_EXT. Electroluminescence (EL) measurements were performed in tandem with our simulations of UV LEDs. At normal incidence, up to 6.1% and 12.7% EL intensity enhancements were observed using 700 nm SiO₂ microspheres and microlenses, respectively. These promising enhancements in output power may allow for high η_EQE in UV LEDs.

A deep understanding of semiconductors-dielectrics interface properties will provide guidelines to optimize efficient passivation solutions for InGaN/GaN based μLED. To this end, the quantum wells (QW) semiconductor is of tremendous interest since a lot of surface recombinations are likely to occur at LED active regions edges and are probably responsible for the low μLED efficiencies. Thus we discuss in this paper about X-ray photoemission (XPS) and wavelength dispersive X-ray fluorescence (WDXRF) characterizations of In_0.1Ga_0.9N surfaces after acid, basic or sulfur based chemical treatments followed or not by atomic layer deposition (ALD) of Al₂O₃ thin films with TMA/H₂O or TMA/O₂ plasma (plasma enhanced ALD) at 250°C. Depending on chemical treatments, variations of indium related XPS peaks were observed, which did not seem to be significantly affected by deposition of Al₂O₃ whatever the oxidizing precursor. The extreme surface concentration of indium was probably reduced, suggesting that some chemical pre-treatments for cleaning or passivation steps would have a direct impact on InGaN QW properties at LED edges. After sulfur based chemical treatments, even if sulfur was hardly detected by XPS, complementary measurements by WDXRF and subsequent calibration of the sulfur signal supported evaluation of a low surface concentration of sulfur. Changes of Al₂O₃ related XPS peaks suggested that the various studied pre-treatments induced different nucleations of first ALD cycles. Then, a clear variation of InGaN surfaces hydrolysis depending on surface treatments was finally highlighted by WDXRF based counting measurements, opening the way to a better understanding of first Al₂O₃ layers nucleation on InGaN.

Micro-LEDs based on gallium nitride semiconductors are the basis of new formats of high-brightness, fast response and high resolution display technology, but are also very promising for applications in optical wireless communications across a broad spectral range. Indeed, micro-LED technology offers exciting prospects for convergence between these two hitherto largely separate areas of application. Here, we report on recent developments in micro-LEDs for high-bandwidth optical wireless communications, including new formats of device such as series-driven multi-pixel structures, and new wavelength devices such as those operating in the deep ultraviolet. Highlights include 10Gbps data rates over distances beyond 5m and data rates of over 1Gb/s at 20m using blue series-driven devices, underwater optical communications link demonstrations, few-photon per bit (single photon counting) operation over 10's km distances for space-based applications, and 1Gb/s operation at a wavelength of 262nm

We report loading quantum dots (QDs) inside nanoporous (NP) GaN and using NP-GaN as a color converter to fabricate micro-LEDs. A strong light scattering can be induced by NP-GaN and blue pumping light can be significantly absorbed by red and green QDs. More than 90% of light conversion efficiency has been achieved for both red and green QDs inside NP-GaN. Monolithic red, green, and blue color micro-LEDs have been achieved with loading red and green QDs into NPGaN.

In this study, we review our progress in micro/mini LED arrays and their numerical simulation in optical fields. The variation in substrate thickness will be included in the calculation and the results can provide detailed insight for the optimization of the micro/mini LED structures.

In 2013 Raytheon began to integrate submicron (≤0.25 µm gate) 200mm GaN on Si HEMT processes within a commercial CMOS Si Foundry environment. When fully realized, these processes will demonstrate multi GHz GaN on Si MMICs by leveraging a fully subtractively processed transistor coupled with multi-level copper based back end of line (Cu BEOL) processes. This work provides a status update on the progress towards that goal.

GaN high electron mobility transistors (HEMTs) on SiC substrates are produced for both commercial and defense applications that require high voltage, high power, and high efficiency operation. Although leading GaN HEMT manufacturers have reported excellent RF power characteristics and encouraging reliability, long-term reliability in the space environment remains a major concern due to unknown degradation mechanisms. For the present study, we investigated stressed/degraded RF GaN HEMTs using micro-analytical techniques. Our RF AlGaN-GaN devices grown on SiC substrate had a Ni-Pd-Au Schottky gate length of 0.25 μm, a total gate width of 6 × 150 μm periphery, and a field plate. First, we performed DC bias-temperature stress tests on GaN HEMTs and some GaN HEMTs were thermally stressed as monitor samples. Second, we employed focused ion beam (FIB) to prepare TEM cross sections from degraded and monitor devices for defect analysis using a high resolution TEM. Defects containing highly Pd-enriched features were found at the edge of the drain side of the gate. We present our detailed analysis results including our understanding on the out-diffusion of Pd as a potential degradation mechanism in our RF devices.