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Laser-pulsed atom probe tomography (LAPT) is a materials characterization technique that has been widely applied in the study and characterization of III-nitride semiconductors. To date, most of th...

We demonstrate a superluminescent diode fabricated on a nonpolar ${m}$ -plane GaN substrate by employing a linearly tapered waveguide design. A high electrical −3dB modulation bandwidth ( $f_{\mathbf {3dB}}$ ) of 2.5 GHz at a current density of 30 kA/cm2 is achieved. The high modulation bandwidth is attributed to the shorter carrier recombination lifetime, the linear gain curve in the nonpolar ${m}$ -plane quantum wells, and the ability to operate at high current densities while effectively suppressing lasing. We derive a general expression for the −3dB bandwidth as a function of current density for SLDs using a similar approach to that for laser diodes. The −3dB bandwidth of a nonpolar superluminescent diode increases exponentially with current density. The experimental results are consistent with the derived expression for $f_{\mathbf {3dB}}$ vs . current density.

A fundamental understanding and advancement of nanopatterning and nanometrology are essential in the future development of nanotechnology, atomic scale manipulation, and quantum technology industries. Scanning probe-based patterning/imaging techniques have been attractive for many research groups to conduct their research in nanoscale device fabrication and nanotechnology mainly due to its cost-effective process; however, the current tip materials in these techniques suffer from poor durability, limited resolution, and relatively high fabrication costs. Here, we report on employing GaN nanowires as a robust semiconductor material in scanning probe lithography (SPL) and microscopy (SPM) with a relatively low-cost fabrication process and the capability to provide sub-10 nm lithography and atomic scale (

We present the first demonstration of RF characteristics of electrically injected GaN/InGaN core–shell nanowire-based micro light-emitting diodes (μLEDs) for μLED displays and visible-light communi...

The unique growth conditions of BluGlass’ low growth temperature technology Remote Plasma Chemical Vapour Deposition (RPCVD) are capable of producing Activate As-Grown (AAG) buried p-GaN layers. This ability renders RPCVD a highly attractive technique to produce GaN-based Tunnel Junctions (TJ) without the complexities associated with the post-growth lateral activation steps required by MOCVD. In this paper we discuss the use of hybrid RPCVD/MOCVD TJs for MOCVD-grown ridge guide laser diode (LD) applications. The impact of both the structure and placement of the TJ on the total optical loss of the LD are investigated. TJs conforming to the strict compositional requirements in order to yield a net reduction in optical loss are demonstrated, paving the way to improved conversion efficiencies through the replacement of the highly resistive p-AlGaN cladding layers and p-type Ohmic contacts with lower resistance n-AlGaN cladding layers and n-type Ohmic contacts.

We report on silicon delta doping of metalorganic vapor-phase epitaxy-grown \b{eta}-Ga2O3 thin films using silane precursor. Delta-doped \b{eta}-Ga2O3 epitaxial films are characterized using capacitance-voltage profiling and secondary-ion mass spectroscopy. Electron sheet charge density in the range of 2.9e12 cm-2 to 8e12 cm-2 with a half width at half maximum ranging from 6.2 nm to 3.5 nm is measured. We also demonstrate a high density (6.4e12 cm-2) degenerate two-dimensional electron gas using a delta-doped \b{eta}-(Al0.26Ga0.74)2O3/\b{eta}-Ga2O3 heterostructure.The total charge could also include a contribution from a parallel channel in the \b{eta}-(Al0.26Ga0.74)2O3 alloy barrier.

We demonstrate a high-speed nonpolar ${m}$ -plane InGaN/GaN micro-scale light-emitting diode (LED) with a record electrical −3 dB modulation bandwidth of 1.5 GHz at a current density of 1 kA/cm2. A differential carrier lifetime (DLT) of 200 ps at 1 kA/cm2 was extracted using a rate-equation model. The short DLT is attributed to the high electron–hole wave function overlap in polarization-free nonpolar InGaN/GaN quantum wells, which leads to a higher spontaneous emission rate at low current densities compared to polar $c$ -plane quantum wells. LEDs with improved high-speed performance at low current densities will help to reduce power dissipation and increase efficiency in Gb/s visible-light communication systems.

We utilize a rate equation approach and RF measurement technique to study carrier dynamics in InGaN/GaN LEDs. Study of carrier dynamics aids in understanding efficiency challenges and design of high-speed, efficient micro-LEDs for visible-light communication and micro-LED display applications.

III-nitride high-speed optoelectronics are emerging for a variety of applications, including visible-light communication (VLC) in light-fidelity (Li-Fi) networks, optical communication using photonic-integrated circuits, and micro-pixel LED displays. III-nitride materials offer efficient light emission and the potential to route, modulate, and detect light on a single chip. Previous research into III-nitride optoelectronics has mainly focused on developing emitters with high efficiencies and large optical output powers, which are needed for conventional lighting and data storage applications. Here, we present the more recent development of III-nitride high-speed emitters, including planar micro-LEDs, nanowire-based micro-LEDs, and superluminescent diodes. We demonstrate record-high modulation bandwidths by growing devices on nonpolar and semipolar orientations of GaN, which are free from the polarization-related effects that limit the modulation bandwidths of $c$ -plane III-nitride. We also combine a rate equation model with an RF measurement technique to extract the carrier dynamics in the devices [1].

Field emission scanning probe lithography (FE-SPL) is based on the exposure of a resist covered substrate with low energy electrons emitted from an ultra-sharp tip placed in close vicinity to a sample. GaN nanowires (NWs) present high mechanical stability, suitable geometry for FE-SPL, and controllable electrical properties achieved by adjusting dopant concentration. Here, the authors will present long time exposure results performed using GaN NWs tips, mounted on active scanning probes, working as field electron emitters. Using GaN NW tips, features down to the sub-10 nm were achieved in the FE-SPL process. A systematic study of the field emission current stability, exposure reproducibility, and results on exemplary high-resolution exposure and nanostructure imaging done with the same GaN tips will also be presented.

We report the fabrication and electro-optic characterization of nonpolar GaN-based superluminescent diodes with a tapered waveguide design. The devices were grown and fabricated on freestanding m-plane GaN. An electrical −3dB modulation bandwidth of 2.5 GHz is reported at the highest current density.

We demonstrate a high-speed nonpolar InGaN/GaN micro-LED with a record −3dB bandwidth of 1.5 GHz at a current density of 1 kA/cm2. The high-speed at low current density is attributed to the large electron-hole wavefunction overlap in nonpolar QWs leading to a shorter carrier lifetime.

We report on n-type degenerate doping in β-(Al0.26Ga0.74)2O3 epitaxial thin films grown by metalorganic vapor-phase epitaxy and modulation doping in β-(Al0.26Ga0.74)2O3/β-Ga2O3 heterostructures. Alloy composition is confirmed using high-resolution X-ray diffraction measurements. Carrier concentration in the thin films is proportional to the silane molar flow. Room-temperature Hall measurements showed a high carrier concentration of 6 × 1018 cm–3 to 7.3 × 1019 cm−3 with a corresponding electron mobility between 53–27 cm2 V–1 s–1 in uniformly doped β-(Al0.26Ga0.74)2O3 layers. Modulation doping is used to realize a total electron sheet charge of 2.3 × 1012 cm−2 in a β-(Al0.26Ga0.74)2O3/β-Ga2O3 heterostructure using a uniformly doped β-(Al0.26Ga0.74)2O3 barrier layer and a thin spacer layer.

We investigate the spectrally resolved internal quantum efficiency (IQE) and carrier dynamics in semipolar [Formula: see text] core-shell triangular nanostripe light-emitting diodes (TLEDs) using temperature-dependent photoluminescence (TDPL) and time-resolved photoluminescence (TRPL) at various excitation energy densities. Using electroluminescence, photoluminescence, and cathodoluminescence measurements, we verify the origins of the broad emission spectra from the nanostructures and confirm that localized regions of high-indium-content InGaN exist along the apex of the nanostructures. Spectrally resolved IQE measurements are then performed, with the spectra integrated from 400-450 nm and 450-500 nm to obtain the IQE of the QWs mainly near the sidewalls and apex of the TLEDs, respectively. TDPL and TRPL are used to decouple the radiative and non-radiative carrier lifetimes for different regions of the emission spectra. We observe that the IQE is higher for the spectral region between 450 nm and 500 nm compared to the IQE between 400 and 450 nm. This result is in contrast to the typical observation that the IQE of planar GaN-based LEDs is lower for longer wavelengths (i.e., higher indium contents). We also observe a longer non-radiative recombination lifetime for the longer wavelength portion of the spectrum. Several explanations are proposed for the improved IQE and longer non-radiative lifetime observed near the apex of the nanostructures. The results show that nanostructures may be leveraged to design more efficient green LEDs, potentially addressing a long-standing challenge in GaN-based materials.

We have developed an ion beam assisted deposition (IBAD) texturing process for biaxially aligned films as substrates for GaN epitaxy. The IBAD process enables low-cost, large-area flexible metal foil substrates to be used as potential alternatives to single-crystal sapphire and silicon for GaN electronic devices. Epitaxial GaN films are grown by the MOCVD process on these engineered flexible substrates. We have achieved epi GaN films of several microns on polycrystalline metal foils that have in-plane and out-of-plane alignment of less than 1° FWHM and typical threading dislocation densities of 4-8 x 10^8/cm^2. We use the epitaxial GaN films on IBAD/polycrystalline metal foil as a template to deposit epitaxial multi-quantum well light emitting diode (LED) InGaN structures. From these layered structures we have successfully fabricated LED devices. These are the first LED devices fabricated directly on metal foil. We observe photoluminescence intensities from the LED structures up to 70% of those fabricated on sapphire. We will present data on performance of such devices and how these LED devices could be printed using a roll-to-roll process. This work was supported by the Department of Energy ARPA-E agency.

The internal quantum efficiencies (IQE) and carrier lifetimes of semipolar (202¯1¯) InGaN/GaN LEDs with different active regions are measured using temperature-dependent, carrier-density-dependent, and time-resolved photoluminescence. Three active regions are investigated: one 12-nm-thick single quantum well (SQW), two 6-nm-thick QWs, and three 4-nm-thick QWs. The IQE is highest for the 12-nm-thick SQW and decreases as the well width decreases. The radiative lifetimes are similar for all structures, while the nonradiative lifetimes decrease as the well width decreases. The superior IQE and longer nonradiative lifetime of the SQW structure suggests using thick SQW active regions for high brightness semipolar (202¯1¯) LEDs.

In this work, we demonstrate high-performance electrically injected GaN/InGaN core-shell nanowire-based LEDs grown using selective-area epitaxy and characterize their electro-optical properties. To assess the quality of the quantum wells, we measure the internal quantum efficiency (IQE) using conventional low temperature/room temperature integrated photoluminescence. The quantum wells show a peak IQE of 62%, which is among the highest reported values for nanostructure-based LEDs. Time-resolved photoluminescence (TRPL) is also used to study the carrier dynamics and response times of the LEDs. TRPL measurements yield carrier lifetimes in the range of 1–2 ns at high excitation powers. To examine the electrical performance of the LEDs, current density–voltage (J-V) and light-current density-voltage (L-J-V) characteristics are measured. We also estimate the peak external quantum efficiency (EQE) to be 8.3% from a single side of the chip with no packaging. The LEDs have a turn-on voltage of 2.9 V and low series resistance. Based on FDTD simulations, the LEDs exhibit a relatively directional far-field emission pattern in the range of $$\pm $$ ± 15°. This work demonstrates that it is feasible for electrically injected nanowire-based LEDs to achieve the performance levels needed for a variety of optical device applications.

We demonstrate the growth of ordered arrays of nonpolar $$\{ 10\bar{1}0\} $$ core–shell nanowalls and semipolar $$ \{ 10\bar{1}1\}$$ core–shell pyramidal nanostripes on c-plane (0001) sapphire substrates using selective-area epitaxy and metal organic chemical vapor deposition. The nanostructure arrays are controllably patterned into LED mesa regions, demonstrating a technique to impart secondary lithography features into the arrays. We study the dependence of the nanostructure cores on the epitaxial growth conditions and show that the geometry and morphology are strongly influenced by growth temperature, V/III ratio, and pulse interruption time. We also demonstrate the growth of InGaN quantum well shells on the nanostructures and characterize the structures by using micro-photoluminescence and cross-section scanning tunneling electron microscopy.

Free-standing nonpolar GaN substrates provide an excellent platform for the fabrication of high-speed blue and green light-emitting diodes (LEDs), which are attractive for visible-light communication, plastic optical fiber communication, and short-range under water optical communication. Nonpolar LEDs on free-standing GaN exhibit a large electron-hole wave function overlap, low extended defect density, and favorable thermal properties. Here, we demonstrate high-speed nonpolar InGaN/GaN LEDs with a peak emission wavelength between 455 and 465 nm on free-standing nonpolar GaN substrates. A large frequency modulation bandwidth of 524 MHz is demonstrated at a current density of 10 kA/cm 2 .

Controlled bottom-up selective-area epitaxy (SAE) is used to tailor the morphology and photoluminescence properties of GaN/InGaN core-shell nanowire arrays. The nanowires are grown on c-plane sapphire substrates using pulsed-mode metal organic chemical vapor deposition. By varying the dielectric mask configuration and growth conditions, we achieve GaN nanowire cores with diameters ranging from 80 to 700 nm that exhibit various degrees of polar, semipolar, and nonpolar faceting. A single InGaN quantum well (QW) and GaN barrier shell is also grown on the GaN nanowire cores and micro-photoluminescence is obtained and analyzed for a variety of nanowire dimensions, array pitch spacings, and aperture diameters. By increasing the nanowire pitch spacing on the same growth wafer, the emission wavelength redshifts from 440 to 520 nm, while increasing the aperture diameter results in a ∼35 nm blueshift. The thickness of one QW/barrier period as a function of pitch and aperture diameter is inferred using scanning electron microscopy, with larger pitches showing significantly thicker QWs. Significant increases in indium composition were predicted for larger pitches and smaller aperture diameters. The results are interpreted in terms of local growth conditions and adatom capture radius around the nanowires. This work provides significant insight into the effects of mask configuration and growth conditions on the nanowire properties and is applicable to the engineering of monolithic multi-color nanowire LEDs on a single chip.

In this study we introduce Gallium Nitride (GaN) nanowire (NW) as high aspect ratio tip with excellent durability for nano-scale metrology. GaN NWs have superior mechanical property and young modulus compare to commercial Si and Carbon tips which results in having less bending issue during measurement. The GaN NWs are prepared via two different methods: i) Catalyst-free selected area growth, using Metal Organic Chemical Vapor Deposition (MOCVD), ii) top-down approach by employing Au nanoparticles as the mask material in dry-etch process. To achieve small diameter tips, the semipolar planes of the NWs grown by MOCVD are etched using AZ400k. The diameter of the NWs fabricated using the top down process is controlled by using different size of nanoparticles and by Inductively Coupled Plasma etching. NWs with various diameters were manipulated on Si cantilevers using Focus Ion Beam (FIB) to make tips for AFM measurement. A Si (110) substrate containing nano-scale grooves with vertical 900 walls were used as a sample for inspection. AFM measurements were carried out in tapping modes for both types of nanowires (top-down and bottom-up grown nanowires) and results are compared with conventional Si and carbon nanotube tips. It is shown our fabricated tips are robust and have improved edge resolution over conventional Si tips. GaN tips made with NW’s fabricated using our top down method are also shown to retain the gold nanoparticle at tip, which showed enhanced field effects in Raman spectroscopy.

The patterning process in field-emission scanning probe lithography (FE-SPL), a high-resolution and cost-effective method for nanofabrication, is based on the field emission of electrons from ultrasharp tips in close proximity to a sample (distances below 100 nm). Thereby, the emitted electrons expose directly an ultrathin resist film. The field enhancement at the tip apex is crucial for the field emission current, which follows the Fowler–Nordheim theory. Despite the success of FE-SPL in nanofabrication, systematic experimental studies of the field-emission process, including the determination of the tip radius and tip-to-sample distance during the measurement, for these small tip-to-sample distances and different tip materials are lacking. To resolve this issue, experimental measurements of the field-emission current for tip–sample proximity distances below 100 nm were performed. For this purpose, the developed AFM in SEM system was modified,1,2 which enables one to monitor the tip–sample distance with a high accuracy using SEM while simultaneously recording the field-emission current. The authors present experimental results of the dependence of the field-emission current on the tip shape, tip material, applied voltage, and tip–sample distance. Therefore, the emission characteristics of silicon, diamond, GaN, and tungsten tips are shown. The knowledge about the field-emission process for small tip-to-sample distances will help to understand and improve the current FE-SPL, regarding also the choice of tip material. Furthermore, these measurements enable the detailed comparison with current FE models beyond state-of-the-art since all necessary parameters (voltage, current, tip diameter, and tip-to-sample distance) could be measured and controlled during the FE experiment due to the unique experimental system.The patterning process in field-emission scanning probe lithography (FE-SPL), a high-resolution and cost-effective method for nanofabrication, is based on the field emission of electrons from ultrasharp tips in close proximity to a sample (distances below 100 nm). Thereby, the emitted electrons expose directly an ultrathin resist film. The field enhancement at the tip apex is crucial for the field emission current, which follows the Fowler–Nordheim theory. Despite the success of FE-SPL in nanofabrication, systematic experimental studies of the field-emission process, including the determination of the tip radius and tip-to-sample distance during the measurement, for these small tip-to-sample distances and different tip materials are lacking. To resolve this issue, experimental measurements of the field-emission current for tip–sample proximity distances below 100 nm were performed. For this purpose, the developed AFM in SEM system was modified,1,2 which enables one to monitor the tip–sample distance with ...

Field emission scanning probe lithography (FE-SPL), which offers sub-10 nm resolution under ambient conditions, strongly relies on the quality and shape of the applied scanning probe tip. The technological development of AFM systems is also strongly connected to the performance of the cantilever. Thereby, the probes evolved from a simple passive deflection element to a complex MEMS through integration of functional groups, such as piezoresistive detection sensors and bimaterial based actuators. Here, the authors show actual trends and developments of miniaturization efforts for fabrication of active cantilevers with mounted sharp GaN and diamond nanowires. Both materials exhibit a higher mechanical stability than the typically applied silicon, which is supposed to increase tip lifetime and reproducibility of the lithography process. Furthermore, diamond offers a high chemical stability, whereas electrical and optical properties of GaN are tunable. They present preliminary results on the applicability of GaN nanowires and diamond tips, mounted on active scanning probes, as field emitter for FE-SPL. Therefore, field emission measurements, stability of field emission current, and exemplary high resolution features generated with the tested tips are shown.Field emission scanning probe lithography (FE-SPL), which offers sub-10 nm resolution under ambient conditions, strongly relies on the quality and shape of the applied scanning probe tip. The technological development of AFM systems is also strongly connected to the performance of the cantilever. Thereby, the probes evolved from a simple passive deflection element to a complex MEMS through integration of functional groups, such as piezoresistive detection sensors and bimaterial based actuators. Here, the authors show actual trends and developments of miniaturization efforts for fabrication of active cantilevers with mounted sharp GaN and diamond nanowires. Both materials exhibit a higher mechanical stability than the typically applied silicon, which is supposed to increase tip lifetime and reproducibility of the lithography process. Furthermore, diamond offers a high chemical stability, whereas electrical and optical properties of GaN are tunable. They present preliminary results on the applicability of G...

This study describes the elimination of threading dislocations (TDs) in GaN nanostructures. Cross-sectional transmission electron microscopy (XTEM) analysis reveals that the nominal [0001] line direction of a TD changes when it enters a GaN nanostructure and the dislocation then terminates at a sidewall facet. It is suggested that the driving force for this process is the reduction of dislocation line energy, and for a pure-edge dislocation, this TD elimination process can be accomplished simply by dislocation climb. This mechanism is active whenever a threading defect is in close proximity to a surface. Preliminary XTEM analysis of defects in AlGaN and InGaN core–shell growth onto GaN nanostructures is also shown. Although more work is required to improve the quality of core–shell InGaN epitaxial growth, nanostructures appear to offer a route to defect-free, nonpolar GaN-based devices.

We investigate the spectrally resolved internal quantum efficiency (IQE) and carrier dynamics in semipolar [Formula: see text] core-shell triangular nanostripe light-emitting diodes (TLEDs) using temperature-dependent photoluminescence (TDPL) and time-resolved photoluminescence (TRPL) at various excitation energy densities. Using electroluminescence, photoluminescence, and cathodoluminescence measurements, we verify the origins of the broad emission spectra from the nanostructures and confirm that localized regions of high-indium-content InGaN exist along the apex of the nanostructures. Spectrally resolved IQE measurements are then performed, with the spectra integrated from 400-450 nm and 450-500 nm to obtain the IQE of the QWs mainly near the sidewalls and apex of the TLEDs, respectively. TDPL and TRPL are used to decouple the radiative and non-radiative carrier lifetimes for different regions of the emission spectra. We observe that the IQE is higher for the spectral region between 450 nm and 500 nm compared to the IQE between 400 and 450 nm. This result is in contrast to the typical observation that the IQE of planar GaN-based LEDs is lower for longer wavelengths (i.e., higher indium contents). We also observe a longer non-radiative recombination lifetime for the longer wavelength portion of the spectrum. Several explanations are proposed for the improved IQE and longer non-radiative lifetime observed near the apex of the nanostructures. The results show that nanostructures may be leveraged to design more efficient green LEDs, potentially addressing a long-standing challenge in GaN-based materials.

High-speed InGaN/GaN blue light-emitting diodes (LEDs) are needed for future gigabit-per-second visible-light communication systems. Large LED modulation bandwidths are typically achieved at high current densities, with reports close to 1 GHz bandwidth at current densities ranging from 5 to 10 kA/cm2. However, the internal quantum efficiency (IQE) of InGaN/GaN LEDs is quite low at high current densities due to the well-known efficiency droop phenomenon. Here, we show experimentally that nonpolar and semipolar orientations of GaN enable higher modulation bandwidths at low current densities where the IQE is expected to be higher and power dissipation is lower. We experimentally compare the modulation bandwidth vs. current density for LEDs on nonpolar (101¯0), semipolar (202¯1¯), and polar 0001 orientations. In agreement with wavefunction overlap considerations, the experimental results indicate a higher modulation bandwidth for the nonpolar and semipolar LEDs, especially at relatively low current densities....

We report the fabrication of m-plane nanoporous distributed Bragg reflectors (DBRs) on free-standing GaN substrates. The DBRs consist of 15 pairs of alternating undoped and highly doped n-type ([Si] = ∼3.7 × 1019 cm−3) GaN. Electrochemical (EC) etching was performed to convert the highly doped regions into a porous material, consequently reducing the effective refractive index of the layers. We demonstrate a DBR with peak reflectance greater than 98% at 450 nm with a stopband width of ∼72 nm. The polarization ratio of an incident polarized light source remains identical after reflection from the DBR, verifying that there is no drop in the polarization ratio due to the interfaces between the porous layers. We also quantify the porosity under various EC bias conditions for layers with different doping concentrations. The bias voltage controls the average pore diameter, while the pore density is primarily determined by the doping concentration. The results show that nanoporous DBRs on nonpolar free-standing GaN are promising candidates for high-reflectance, lattice-matched DBR mirrors for GaN-based resonant cavity devices.

The growth of ordered arrays of group III-nitride nanostructures on c-plane gallium nitride (GaN) on sapphire using selective-area metal organic chemical vapor deposition (MOCVD) is presented. The growth of these nanostructures promotes strain relaxation that allows the combination of high indium content active regions with very low dislocation densities and also gives access to nonpolar and semipolar crystallographic orientations of GaN. The influence of the starting template and the growth conditions on the growth rate and morphology is discussed. The growth of indium gallium nitride (InGaN) active region shells on these nanostructures is discussed and the stability of various crystallographic orientations under typical growth conditions is studied. Finally, the effect of the growth conditions on the morphology of pyramidal stripe LEDs is discussed and preliminary results on electrical injection of these LEDs are presented.

This work describes a small-signal microwave method for determining the differential carrier lifetime and transport effects in electrically injected InGaN/GaN light-emitting diodes (LEDs). By considering the carrier diffusion, capture, thermionic escape, and recombination, the rate equations are used to derive an equivalent small-signal electrical circuit for the LEDs, from which expressions for the input impedance and modulation response are obtained. The expressions are simultaneously fit to the experimental data for the input impedance and modulation response for nonpolar InGaN/GaN micro-LEDs on free-standing GaN substrates. The fittings are used to extract the transport related circuit parameters and differential carrier lifetimes. The dependence of the parameters on the device diameter and current density is reported. We also derive approximations for the modulation response under low and high injection levels and show that the transport of carriers affects the modulation response of the device, espe...

We demonstrate selective-area growth of patterned III-nitride core-shell nanowalls with nonpolar InGaN quantum well shells over large areas. Transmission electron microscopy and photoluminescence are utilized to examine the growth morphology and emission characteristics.

We report a simple method to improve the p-type doping efficiency and eliminate the diode leakage current in selective-area-grown GaN-based core–shell nanostructure LEDs by growing an n-type AlGaN layer underneath the InGaN/GaN active region. A significant reduction in reverse-leakage current density is correlated with longer AlGaN layer growth time and higher flow rate of the aluminum precursor. A comparison of the SIMS profiles with and without the underlayer indicates a high concentration of donor-type impurities (e.g., silicon and oxygen) in the p-GaN layer in the structure with no AlGaN underlayer. Conversely, LEDs with an AlGaN underlayer exhibit enhanced magnesium incorporation and much lower silicon and oxygen impurity concentrations within the p-GaN layer. The reverse current density was also reduced by the addition of a p-type AlGaN electron blocking layer above the active region.

The fabrication of electrically injected triangular-nanostripe core–shell semipolar III–nitride LEDs (TLEDs) is demonstrated using interferometric lithography and catalyst-free bottom-up selective-area metal–organic chemical vapor deposition (MOCVD). This alternative approach enables semipolar orientations on inexpensive, c-plane sapphire substrates, in comparison with planar growth on free-standing GaN substrates. Transmission electron microscopy and energy dispersive X-ray spectroscopy reveal nonuniform quantum well thickness and composition, respectively, as a function of location on the triangular stripes. The broad electroluminescence spectra, wavelength shift with increasing current density, and nonlinear light vs current characteristics are well correlated with the observed quantum-well nonuniformities.

This work highlights the development of three-dimensional (3D) GaN templates grown by metal organic vapor phase epitaxy (MOVPE). These templates are ideally suited for the subsequent growth of nonpolar (11¯00) m-plane InGaN-based coaxial wire/wall light-emitting diodes (LEDs) using molecular beam epitaxy (MBE). The use of MBE is expected to result in increased indium incorporation on the (11¯00) m-plane, compared with growth using MOVPE, which provides an attractive approach for the development of nonpolar green LEDs. While planar free-standing m-plane GaN substrates are prohibitively expensive (approximately ∼$500 per cm2), the coaxial LED approach offers an attractive lower-cost alternative. These nonpolar nanoscale LED templates are also free from threading dislocations and are expected to provide a number of benefits, including higher light extraction and a larger effective active region area. Previous work in our group has demonstrated the controlled growth of GaN nanowires using a catalyst-free sele...

GaN optoelectronic devices based on nanowires offer potential advantages that merit further investigation for applications in solid-state lighting and displays. Reported is the operation GaN nanowire, light-emitting diodes that are based on a uniform and scalable nanowire process. For light-emitting diodes consisting of approximately 300 nanowire pn homojunctions, operating in parallel, the electroluminescence intensity was found to grow superlinearly with current. For individual nanowire light-emitting diodes the forward and reverse leakage current was