Gallium nitride substrates are needed for advanced electronic and optoelectronic devices based on GaN-on-GaN technology. The wafers can be prepared from crystals grown by three main methods: crystallization from gas phase, basic or acidic ammonothermal process or growth from solution of gallium and sodium. In this paper a detailed investigation of the basic ammonothermal growth process is presented. By analyzing the crystallization process on a native seed of a lenticular shape we wanted to answer some basic questions: i/ which crystallographic planes play the most important role (which are formed and which disappear)?; ii/ what is the relation between the growth rates in different crystallographic directions?; iii/ what is the influence of the off-cut of the seed on the growth process?.

Co-doping with manganese and carbon was performed in gallium nitride (GaN) grown by halide vapor phase epitaxy (HVPE). The crystallized material was examined in terms of its structural, optical, and electrical properties. Basing on Raman and photoluminescence spectra of the samples it will be presented that in the GaN:Mn,C crystals Mn is in a different electrical state (Mn^(3+/4+)) in comparison to Mn in GaN:Mn (Mn^(2+/3+)). This change is due to the presence of carbon, which forces manganese to change the oxidation state. This phenomenon will be analyzed and confirmed by the examination of the electrical properties of obtained crystals.

III-Nitride laser diodes (LDs) emitting in the near ultraviolet spectral region can enable various important applications such as high-precision chip-scale atomic clocks. However, III-N LDs emitting near 369nm suffer from material and heterostructure design challenges including stress-induced layer cracking and p-type doping limitations. We will present a detailed study on the influence of the Al mole fraction and thickness on the occurrence of surface cracks of heterostructures using nonplanar growth by metalorganic chemical vapor deposition on macro-patterned GaN/sapphire templates and bulk GaN substrates. Data on the nonplanar growth of full III-N UV LD structures will be presented.

We demonstrate that MOCVD growth of AlGaN on GaN via facet controlled epitaxial lateral overgrowth (FACELO) allows for the growth of thick, relaxed, doped, c-oriented layers. The process includes patterning of the substrate, growth of GaN with pyramidal planes, and epitaxy of AlGaN. We show that AlGaN films with 30% Al-content and several microns of thickness can be grown. The fully coalesced films have a clean, crack free surface with an AFM RMS of 1 nm in a 10x10 μm2 area. Dislocation density is investigated via XRD and etch-pit-density and a dislocation density ranging 106 – 108 cm-2 is measured.

Silicon diffusion process was investigated in GaN layers crystallized by metal-organic vapor phase epitaxy (MOVPE) on native ammonothermal substrates of the highest structural quality. N-type (Si-doped) and p-type (Mg-doped) layers were implanted with Si and treated with ultra-high-pressure annealing. The morphology of the layers was examined at each step by optical microscopy and atomic force microscopy. The crystallographic structure was evaluated by X-ray diffraction measurements. The diffusion of Si was analyzed basing on depth profiles from secondary ion mass spectrometry. Temperature-dependent diffusion coefficients, pre-exponential factors, and activation energies for Si diffusion in n-type and p-type MOVPE-GaN were determined and compared.

III-nitride semiconductors, GaN, in particular, had played an important role in optoelectronic and electronic devices through the advancement of heteroepitaxy. These heteroepitaxy processes have been well established on single-crystalline substrates, such as Si, SiC, and sapphire. However, the mismatch between GaN and these substrates in lattice constant as well as thermal expansion coefficient imposes the limit on device performance and reliability. The search for a better substrate still continues. Here, we report the heteroepitaxy of III-nitride semiconductors on polycrystalline and amorphous substrates using a layered two-dimensional material as a buffer and seed layer. The two-dimensional material on a polycrystalline or amorphous substrate mitigates the lattice mismatch conditions, and shields the random oriented atomic registry of polycrystalline or amorphous substrates to promote single-crystalline hetroepitaxy of III-nitrides without any requisites from the substrate itself.

Current injection through tunnel junctions (TJs) can enhance the external quantum efficiency of nanowire (NW) and multi-quantum-shell-based optical devices, compared. However, control of the impurity concentration profile is difficult in such tiny structure. In this study, we show a simple evaluation method of impurities in TJs growing flatly on m-plane GaN substrates, which have the same crystalline orientation as the luminescent surface of MQS/NWs. It was found to decrease the differential resistance by increase the concentration of Mg in p^(++)-GaN in the TJ.

In this work, we study the optoelectrical properties of nitride LED structures employing polarization doping for the p-type layers. We compare standard Mg-doped, partially doped, and undoped AlGaN p-type layers. The electrical properties of these samples are similar, proving the successful use of polarization doping. The optical measurements suggest that doping of the electron blocking layer is required for preserving good light emission efficiency. We also studied our samples at lowered temperatures and observed no freeze-out region down to 77K. For top metal contact, sub contact doping is indispensable because the intrinsic top layer causes the Schottky barrier.

P-type doping in III-Nitrides has long presented a challenge in the development of wide bandgap optoelectronic devices. To date, magnesium is the only commercially viable acceptor in III-Nitrides. Beryllium has been considered a potential alternative to magnesium, and initial theoretical calculations as well as photoluminescence studies suggested that it is shallower than magnesium in GaN. However, to date, there have been no reliable or repeatable examples of p-type GaN:Be in literature. Here, we present a systematic study of MOCVD-grown GaN:Be with varied doping conditions. All samples show prominent UV and yellow luminescence, characteristic of beryllium acceptor in GaN.

V-defects play an important role in carrier recombination in polar InGaN quantum wells (QWs). Here we report a study of V-defects in QWs emitting from 410 to 570 nm performed by time-resolved near-field optical spectroscopy. In V-defect regions, the radiative carrier lifetime is longer and the nonradiative - shorted than in defect free regions, showing strong spatial variations of the internal quantum efficiency (IQE). The areas with the low IQE, however, are limited to regions just above the dislocations (~2% of the total sample area) showing that the nonradiative recombination at dislocations is not a major factor determining the IQE.

In recent years, there has been tremendous improvement in the performance of blue-emitting vertical-cavity surface-emitting lasers (VCSELs) and they are now on the cusp of commercialization. We will summarize state-of-the-art results and outline the main challenges in extending the emission wavelength into the ultraviolet (UV). Our method to simultaneously achieve high-reflectivity mirrors and good cavity length control by selective electrochemical etching has been essential to demonstrate the world’s first UV-B VCSEL. The use of dielectric mirrors, where one material has a negative thermo-optical coefficient, counteracts the inherent red-shift of the resonance wavelength, enabling a temperature-stable emission.

This presentation recorded at SPIE Photonics West 2022.

Single photon emitters in GaN have aroused great interest as they operate at room temperature, and can emit both in the telecom and near-IR (typically around 700 nm) ranges. We study the growth conditions that enable their presence in GaN, and address the fabrication of different GaN photonic circuits at the corresponding operating wavelengths. In particular, we discuss the fabrication of bullseye nano-antennas, as well as of a more complex system that includes a waveguide cavity surrounded by two asymmetric Distributed Bragg Reflectors, which enable the coupling to an auxiliary waveguide terminated by a grating out-coupler.

We will provide our results on low resistive GaN-based tunnel junctions and optoelectronic devices grown by MOVPE. In order to obtain low resistive GaN-based tunnel junctions grown by MOVPE, we have pointed out that high impurity concentrations were required. We also found that large overlap with Mg/Si and small Mg segregation were key factors. The lowest contact resistivity value in our GaN tunnel junctions is now less than 1e-4 Ωcm2 over 8 kA/cm2. We have used such low GaN-based tunnel junctions in edge-emitting laser diodes and VCSELs, showing comparable laser characteristics to standard p-contact lasers.

Nowadays, there is a growing need for light-sources meeting seemingly contradictory requirements such as very narrow emission spectrum and high optical power or high quality of the light beam combined with a broad emission spectrum. These specific requirements trigger the development of optoelectrical elements such as superluminescent diodes (SLD) and semiconductor optical amplifiers (SOA). In this presentation, we will review the basic work principles of SLDs and SOAs as well as discuss the important challenges such as: suppression of the feedback from the device facets, reduction of gain saturation, broadening of SLD emission spectra. We will also analyze the limits related to self-heating.

GaN based edge emitting laser diodes typically use AlGaN or InGaN for mode confinement in waveguide cladding layers. Defect formation, high voltage, and lifetime issues limit the possible thickness and composition. Nano-porous GaN is a lattice matched, high index contrast material under investigation to replace AlGaN or InGaN for optical confinement. This opens up new designs to improve power and efficiency in GaN laser diodes. Electrically injected lasers have been fabricated using nano-porous GaN cladding, leading to a reduction in threshold current density at a cost to efficiency. Methods to reduce excess loss and improve heat dissipation will be discussed.

Deep-ultraviolet laser diodes have achieved pulsed lasing at room temperature by improving the crystal quality and establishing a hole injection method using polarization doping techniques. In the initial demonstration, the threshold current density was very high at 25kA/cm2, which is a major barrier to continuous-wave lasing. The reason for this high threshold current density was found to be process-induced non-uniformity of emission. By suppressing this non-uniformity through LD device design, we were able to significantly reduce the threshold current density to about 12 kA/cm2.

Recently emerged “quantum technologies” motivate researchers and engineers to develop a specific class of light sources. The expected devices should emit spectrally narrow and tunable light with excellent beam properties. Semiconductor laser diodes are the light source of choice for these applications. InGaN laser diodes, emitting in the visible part of the spectrum, should play very important role in these applications. Within this presentation we will describe InGaN external cavity laser diodes, semiconductor optical amplifiers and distributed feedback lasers. We will discuss the progress in development of these devices as well as main physical and technological challenges.

We report on state-of-the-art performance in violet, multi-mode, edge-emitting laser diodes fabricated on semi-polar oriented GaN substrates. Using these novel crystal orientations, we demonstrate high-power and high-efficiency continuous-wave laser operation. We report on violet laser diodes achieving continuous-wave output powers with peak wall-plug-efficiencies above 40% and optical output powers above 5 W at wavelengths between ~405 and ~415 nm. To the best of the author's knowledge, these wall-plug-efficiencies represents the highest reported to date for a multi-mode GaN diode laser emitting in the range of 400-410 nm. These InGaN-based laser-diodes will offer dramatic improvements in performance, size, weight, and cost of conventional solid-state and gas-based violet laser sources for use in defense, medical, and materials processing applications.

Solar-blind (<280nm) deep-ultraviolet (DUV) avalanche photodetectors (APDs) are of importance in various applications such as quantum communication, biomedical, defense, and non-line-of-sight (NLOS) communication. This makes the detectors from AlxGa1-xN materials attractive for such applications owing to their wide direct-bandgap characteristics. In this work, top-illuminated DUV Al0.6Ga0.4N p-i-n APD structures were designed, grown by metalorganic chemical vapor deposition on bulk AlN substrates, and fabricated. The devices showed distinctive avalanche breakdown behavior, with breakdown voltages of -150V, and low-leakage current density of <10-8A/cm2. The peak spectral response is 141mA/W at the wavelength of 245nm under 0V.

Nowadays, power-independent, compact, and highly environment-sensitive self-powered photoelectrochemical-type photodetectors (PEC−PDs) have lately intrigued intensive interest to realize next-generation optoelectronic systems. Herein, we demonstrate p-AlGaN nanowire-based self-powered solar-blind PEC-PDs. After decorating nanowires with noble metal platinum (Pt), the constructed solar-blind PEC−PDs exhibited excellent responsivity of 45 mA/W, fast response/recovery time of 47/20 ms. Such high solar-blind photodetection originates from the unparalleled material quality, fast interfacial kinetics, as well as high carrier separation efficiency which suggests that using AlGaN nanowires with appropriate surface decoration offers an unprecedented opportunity for designing future energy-efficient and large-scale optoelectronic systems on a silicon platform.

In this work, we demonstrate a high-performance ultraviolet phototransistor (UVPT) based on the AlGaN/GaN high-electron-mobility transistor (HEMT) configuration. When the device is biased at off state, the peak photoresponsivity of 3.6×107 A/W under 265nm illumination and 1.0×106 A/W under 365nm illumination can be obtained. Those two responsivity values have achieved the highest among the reported UVPTs at the same detection wavelength under off-state conditions. Furthermore, we observed a distinct difference between the rise time and decay time of the device under 265 nm and 365 nm light illumination which can be attributed to the unique device operating principle of the constructed AlGaN/GaN-based UVPT structure with different absorption mechanisms in the device.

Photoluminescence, electroluminescence, and bias-dependent time-resolved photoluminescence spectroscopies are performed to study the current injection efficiency, internal quantum efficiency, and light external quantum efficiency of 265-nm AlGaN DUV LEDs grown on AlN substrates. The studies showed that the current injection and light extraction efficiencies, and not the internal quantum efficiency, limit the external quantum efficiency. To solve the issue, we revisited the effect of Si-doping in AlN. Our spectroscopic study deduced the significantly lower neutral Si donor bound exciton and Si donor binding energies than those reported, indicating the possibility to realize highly conductive and transparent n-type AlN:Si layers.

We will give an overview of different concepts to increase the light extraction efficiency (LEE) of ultraviolet (UV) light-emitting diodes (LEDs) with a focus on thin-film flip-chip (TFFC) devices. Optical simulations show that a TFFC design can greatly improve the LEE with a transparent p-side, reflective contacts, and optimized surface roughening. We will demonstrate UVB-emitting TFFC LEDs based on our fabrication platform for AlGaN thin films with high aluminum content. The fabrication is compatible with a standard LED process and uses substrate removal based on selective electrochemical etching as the key enabling technology.

Recently, there has been an increased interest in germicidal ultraviolet (GUV) lamps for disinfection. Despite extensive studies on GUV LEDs, their efficiency and cost per Watt is still far from that of mercury lamps due to electrical injection issues, among others. Also, the fact that 254 nm radiation is highly carcinogenic and cataractogenic, has motivated research on radiation with shorter penetration (200-230 nm) depth, for non-invasive disinfection. In this study, we propose electron pumped UV lamps as an alternative to LEDs (to tackle electrical issues) in the spectral range 230-330 targeting both wavelength ranges of disinfection and exhibiting IQE ranging from 20%-50%.

A deep ultraviolet LED structure with a double-side step n-AlGaN inserted layer was constructed to alleviate the electron leakage and improve confinement capability of holes, thus enhancing the optical power and the internal quantum efficiency.

Fabrication of InGaN-based RGB micro-LEDs is crucial to realize inexpensive micro-LED displays. We have grown InGaN-based red LED structures on c-plane patterned sapphire substrates (PSS) by our original metalorganic vapor-phase epitaxy (MOVPE). The structures are p-GaN/hybrid MQWs/(InGaN/GaN) SLs/n-AlGaN/thick-n-GaN/GaN/PSS. The hybrid MQWs consist of red DQWs and blue SQW, resulting in intense red EL emissions. The thick-n-GaN can release compressive strain from substrates and reduce defect density. The overall structure was pseudomorphic. The device performance of the standard-size red LEDs and 17 m x 17 m micro-LEDs will be shown in the presentation.

In this paper, we try to resolve problems related to decreasing the size of an LED, and find a solution that would let us preserve optoelectronics parameters. The main idea is to use tunnel junctions to define the current path and, therefore, define the size of µLED. This way, during fabrication, there is no need to etch the active region. That way, it does not introduce any degradation nor problems related to surface states or differences in electrical fields inside the device. We have fabricated such devices with sizes ranging from 100 µm-5 µm. In the characterization of these devices, it became apparent that, both electrical and optical parameters, are fully scalable with size. Most importantly, we do not observe an increase in the non-radiative recombination coefficient even for the smallest device. In addition, we observe excellent thermal stability of their light emission characteristics.

InGaN-based three dimensional structures fabricated on (-1-12-2) through a regrowth technique are promising for highly efficient polychromatic emitters because the structures do not involve (0001) polar-plane facets. We experimentally demonstrate (1) fast radiative recombination in all the facet quantum wells, (2) structure and eventually emission color tunability through the control of mask geometry for the regrowth, and (3) LED operation with pastel and white color emission. These findings suggest promising features of our polar-plane-free faceted InGaN quantum wells as the next generation visible emitters.

We demonstrated amber InGaN-based micro LEDs (47 × 47 µm2) with 606 nm peak emission at 20 A/cm2. The amber LEDs were obtained the output power density of 2.26 mW/mm2 at 20 A/cm2 by on-wafer EL measurement. Also, the peak on-wafer EQE was obtained as 0.56%. The peak wavelength of the micro-LEDs exhibited a large blue-shift from 624 to 591 nm at 5 to 100 A/cm2. We evaluated the temperature stability of the micro-LEDs. It found that the characteristic temperature was gradually increased with current density increase because SRH non-radiative recombination could be suppressed at high current densities.

The single-crystalline GaN nanowires play crucial roles in the pursuit of modern nanophotonic and nanoelectronic devices. Here, a photoelectrochemical-type ultraviolet photodetector consisting of GaN p-n junction nanowires as photoelectrodes is constructed. It is found that two competing charge transport processes co-determine the photoresponsive behavior of the device. Furthermore, the surface platinum (Pt) decoration has successfully tuned the charge transfer dynamics by enhancing the charge transport efficiency of the one process at the surface, resulting in a twenty-fold increase of the photocurrent. Theoretical calculations reveal that the high photoresponse benefits from the newly formed electronic states at the Pt/GaN interface and the optimized hydrogen adsorption energy.

In this work, we study the internal quantum efficiency and the lasing threshold of AlGaN/GaN heterostructures designed for UV laser emission. We discuss the effect of carrier diffusion and carrier localization in the optical properties at low and room temperature. The implementation of a graded-index separate confinement heterostructure results in enhanced carrier collection, reducing the lasing threshold. However, this improvement is not correlated with the internal quantum efficiency of the samples.

In this study, rA is investigated by different growth temperature between from 1200℃ to 1650℃ during AlN growth by high temperature metalorganic vapor phase epitaxy (MOVPE). The value of dislocation density calculated by X-ray rocking curve (XRC) fullwidth at half-maximum (FWHM) is decreasing with increasing AlN layer thickness. Moreover, it is found that there is threshold value in rA at the temperature of 1400℃. As a result, rA value is observed 20.2 nm in AlN with growth temperature of 1650℃, this represents close to rA value (27.5 nm) in GaN.

GaInN/GaN multi-quantum shells nanowires (NWs) are coaxially grown in non-polar m-plane or semi-polar r-plane surface, which is expected to improve the luminous efficiency. The emission wavelengths usually redshift from the sidewall to top c-plane region. However, the emission from c-plane has low luminous efficiency. In this research, the c-plane area of NWs in one sample was removed by dry etching prior to the fabrication process, while the other one without c-plane etching was prepared to investigate the effect of c-plane region on the luminescence intensity. The sample with etching shows 12 times higher output power than the sample without etching.

A nitride-based light-emitting structure composed of a GaN nanowire core and GaInN/GaN multi-quantum shells (MQSs) is promising for high performance optoelectronic devices. By growing high crystalline quality MQS on the nonpolar (m-plane) sidewall of the nanowires, an improvement of luminous efficiency is expected. For Mg activation in p-GaN under the tunnel junction is a big challenge, in this work, we carried out the sputtering growth of n-GaN capping layer on the tunnel junction/p-GaN/MQS/nanowire structures for the first time. Single crystalline n-GaN was successfully grown mainly on the tip of the nanostructures.

We investigated the performance of InGaN-based red and green micro LEDs ranging from 98 × 98 μm² to 17 × 17 μm². The 47 × 47 μm² red and green micro-LEDs were obtained an on-wafer EQE of 0.36% at the peak wavelength of 626 nm at 4 A/cm². The peak wavelength was close to the red primary color defined in the Rec. 2020 standard in CIE 1931. We also evaluated the temperature stability of the micro-LEDs. The characteristic temperature was obtained 50 and 411 K under 10 A/cm² operation for the red and green LEDs, respectively.

Normally-off AlGaN/GaN HEMTs with p-GaN-gate, which offer high drain current and low on-state resistance at high threshold voltage and breakdown voltage values above 600V, are particularly attractive for high-power electronics applications. In this work we present the results of development of high power normally-off p-GaN gate AlGaN/GaN high electron mobility transistors carried out at Łukasiewicz Research Network-Institute of Microelectronics and Photonics. We have developed key technological steps i.e. selective etching of p-GaN layers over AlGaN, deposition of proper passivation layer as well as thermally stable isolation of adjacent devices using selective Fe+ ion implantation, which were integrated in the process flow of manufacturing of high power transistors. Finally we have shown measurements of developed normally-off p-GaN gate AlGaN/GaN HEMT power transistors assembled using in-house developed process in TO-220 package.

We have fabricated InGaN/GaN multiple-quantum-well flip-chip blue ultrathin side-emitting (USE) light-emitting diode (LED) by top and bottom mirrors and investigated the sidewall light emission performances for backlight unit. Fabricated USE-LED has uniform light-output-power (LOP) and peak wavelength characteristics at each sidewall except poor light extraction efficiency (LEE) which is improved by fabricating ZnO nanorods on each sidewall. The optimized nanorods improve the LEE of USE-LED. Thus, the LOP increases >80% compared to the Reference-LED. Furthermore, the light-tools simulation results reveal that the LEE of nanorods-based USE-LED increases in lateral direction due to decrease in internal reflection of light.