Search

Owing to their wide direct bandgap tunability, III-nitride (III-N) compound semiconductors have been proven instrumental in the development of blue light-emitting diodes that led to the so-called solid-state lighting revolution and blue laser diodes that are used for optical data storage. Beyond such conventional optoelectronic devices, in this review, we explore the progress made in the past 15 years with this low refractive index material family for the realization of microdisks as well as 2D and 1D photonic crystal (PhC) membrane cavities. Critical aspects related to their design and fabrication are first highlighted. Then, the optical properties of passive PhC structures designed for near-infrared such as their quality factor and their mode volume are addressed. Additional challenges dealing with fabrication pertaining to structures designed for shorter wavelengths, namely the visible to ultraviolet spectral range, are also critically reviewed and analyzed. Various applications ranging from second and third harmonic generation to microlasers and nanolasers are then discussed. Finally, forthcoming challenges and novel fields of application of III-N photonic cavities are commented.

Crystallographic point defects (PDs) can dramatically decrease the efficiency of optoelectronic semiconductor devices, many of which are based on quantum well (QW) heterostructures. However, spatially resolving individual non-radiative PDs buried in such QWs has so far not been demonstrated. Here, using high-resolution cathodoluminescence (CL) and a specific sample design, we spatially resolve, image, and analyse non-radiative PDs in InGaN/GaN QWs. We identify two different types of PD by their contrasting behaviour with temperature, and measure their densities from $10^{14}$ cm$^{-3}$ to as high as $10^{16}$ cm$^{-3}$. Our CL images clearly illustrate the interplay between PDs and carrier dynamics in the well: increasing PD concentration severely limits carrier diffusion lengths, while a higher carrier density suppresses the non-radiative behaviour of PDs. The results in this study are readily interpreted directly from CL images, and represent a significant advancement in nanoscale PD analysis., Main text: 8 pages, 6 figures. Supplementary: 11 pages, 8 figures

Ultrafast nonlinear photonics enables a host of applications in advanced on-chip spectroscopy and information processing. These rely on a strong intensity dependent (nonlinear) refractive index capable of modulating optical pulses on sub-picosecond timescales and on length scales suitable for integrated photonics. Currently there is no platform that can provide this for the UV spectral range where broadband spectra generated by nonlinear modulation can pave the way to new on-chip ultrafast (bio-) chemical spectroscopy devices. We demonstrate the giant nonlinearity of UV hybrid light-matter states (exciton-polaritons) up to room temperature in an AlInGaN waveguide. We experimentally measure ultrafast nonlinear spectral broadening of UV pulses in a compact 100 μm long device and deduce a nonlinearity 1000 times that in common UV nonlinear materials and comparable to non-UV polariton devices. Our demonstration promises to underpin a new generation of integrated UV nonlinear light sources for advanced spectroscopy and measurement., Nonlinearity enhancement in different materials is relevant for many scientific applications. Here the authors demonstrate pulse modulation in the UV regime due to polariton-based nonlinearity in an AlInGaN waveguide structure, including at room temperature.

The success story of blue light-emitting diodes over the past decade is underpinned by the high internal quantum efficiency (IQE) of the InGaN/GaN quantum wells (QWs) within the active region. Yet this extraordinary IQE can only be achieved by adding an indium-containing layer before the QWs—the “underlayer” (UL). In this work, we evidence that any indium-containing III-nitride layer acts to incorporate surface defects; the UL hence acts as a getter for surface defects to avoid their incorporation into the QWs as IQE-reducing point defects (PDs). We directly observe the reduction in PD-density caused by increasing the UL thickness.

Exploring the limits of spontaneous emission coupling is not only one of the central goals in the development of nanolasers, it is also highly relevant regarding future large-scale photonic integration requiring energy-efficient coherent light sources with a small footprint. Recent studies in this field have triggered a vivid debate on how to prove and interpret lasing in the high-β regime. We investigate close-to-ideal spontaneous emission coupling in GaN nanobeam lasers grown on silicon. Such nanobeam cavities allow for efficient funneling of spontaneous emission from the quantum well gain material into the laser mode. By performing a comprehensive optical and quantum-optical characterization, supported by microscopic modeling of the nanolasers, we identify high-β lasing at room temperature and show a lasing transition in the absence of a threshold nonlinearity at 156 K. This peculiar characteristic is explained in terms of a temperature and excitation power-dependent interplay between zero-dimensional and two-dimensional gain contributions., Here the authors present temperature dependent studies of GaN nanobeam lasers grown on a silicon substrate and demonstrate high-βlasing at room temperature. Comprehensive optical and quantum-optical characterization, complemented by microscopic modeling, of the nanolasers allow identification of lasing behavior.

Since the early 1960s, alloys are commonly grouped into two classes that feature either bound states in the band gap (I) or additional, nondiscrete band states (II). Consequently, one can observe either excitons bound to isoelectronic impurities or the typical band edge emission of a semiconductor that shifts and broadens with rising isoelectronic doping concentration. Microscopic parameters for class I alloys can directly be extracted from photoluminescence (PL) spectra, whereas any conclusions drawn for class II alloys usually remain limited to macroscopic assertions. Nonetheless, we present a spectroscopic study on exciton localization in a mixed-crystal alloy (class II) that allows us to access microscopic alloy parameters. In order to illustrate our approach, we study bulk InxGa1-xN epilayers at the onset of alloying (0

The electrical properties and deep trap spectra were compared for near-UV GaN/InGaN quantum well (QW) structures grown on free-standing GaN substrates. The structures differed by the presence or absence of a thin (110 nm) InGaN layer inserted between the high temperature GaN buffer and the QW region. Capacitance-voltage profiling with monochromatic illumination showed that in the InGaN underlayer (UL), the density of deep traps with optical threshold near 1.5 eV was much higher than in the QW and higher than for structures without InGaN. Irradiation with 5 MeV electrons strongly increased the concentration of these 1.5 eV traps in the QWs, with the increase more pronounced for samples without InGaN ULs. The observations are interpreted using the earlier proposed model explaining the impact of In-containing underlayers by segregation of native defects formed during growth of GaN near the surface and trapping of these surface defects by In atoms of the InGaN UL, thus preventing them from infiltrating the InGaN QW region. Deep level transient spectroscopy (DLTS) also revealed major differences in deep trap spectra in the QWs and underlying layers of the samples with and without InGaN ULs. Specifically, the introduction of the InGaN UL stimulates changing the dominant type of deep traps. Irradiation increases the densities of these traps, with the increase being more pronounced for samples without the InGaN UL. It is argued that light emitting diodes (LEDs) with InGaN UL should demonstrate a higher radiation tolerance than LEDs without InGaN UL. (C) 2020 Elsevier B.V. All rights reserved.

Blue light-emitting diodes based on III-nitride semiconductors are nowadays widely used for solid-state lighting. They exhibit impressive figures of merit like an internal quantum efficiency close to 100%. This value is intriguing when considering the high dislocation density running throughout the InGaN/GaN quantum well (QW) active region. This striking feature is currently ascribed to carrier localization occurring in the InGaN alloy, which hinders their diffusion toward dislocations. However, it was recently reported that another source of defects, disconnected from dislocations, dramatically decreases the radiative efficiency of InGaN/GaN QWs. Those defects, present at the surface, are usually trapped in an InGaN underlayer (UL), which is grown before the QW active region. To get insight into the trapping mechanism, we varied the UL thickness, In content, and materials system (InGaN or InAlN) and studied the photoluminescence decay time at 300 K of a single InGaN/GaN QW. Our data demonstrate that defects are incorporated proportionally to the indium content in the UL. In addition, we show that those defects are created during the high-temperature growth of GaN and that they segregate at the surface even at low-temperature. Eventually, we propose an intrinsic origin for these surface defects. (C) 2018 Author(s).

We demonstrate optically-pumped waveguides grown on freestanding GaN substrate featuring AlInN claddings and GaN/Al0.1Ga0.9N multiple quantum wells exhibiting narrow bandwidth (3.8 nm) optical gain around 370 nm. Due to the high refractive index contrast between the cladding layers and the active region, the confinement factor is as high as 48% and net modal gain values in excess of 80 cm−1 are measured. The results agree well with self-consistent calculations accounting for built-in electric field effects and high carrier density related phenomena. These results open interesting perspectives for the realization of more efficient near-UV lasers and optical amplifiers.

III-nitride surface states are expected to impact high surface-to-volume ratio devices, such as nano- and micro-wire light-emitting diodes, transistors, and photonic integrated circuits. In this work, reversible photoinduced oxygen desorption from III-nitride microdisk resonator surfaces is shown to increase optical attenuation of whispering gallery modes by 100 cm−1 at λ = 450 nm. Comparison of photoinduced oxygen desorption in unintentionally and n+-doped microdisks suggests that the spectral changes originate from the unpinning of the surface Fermi level, likely taking place at etched nonpolar III-nitride sidewalls. An oxygen-rich surface prepared by thermal annealing results in a broadband Q improvement to state-of-the-art values exceeding 1 × 104 at 2.6 eV. Such findings emphasize the importance of optically active surface states and their passivation for future nanoscale III-nitride optoelectronic and photonic devices.

Thin-wall tubes composed of nitride semiconductors (III-N compounds) based on GaN/InAlN multiple quantum wells (MQWs) are fabricated by metalorganic vapor-phase epitaxy in a simple and full III-N approach. The synthesis of such MQW-tubes is based on the growth of N-polar c-axis vertical GaN wires surrounded by a coreshell MQW heterostructure followed by in situ selective etching using controlled H-2/NH3 annealing at 1010 degrees C to remove the inner GaN wire part. After this process, well-defined MQW-based tubes having nonpolar m-plane orientation exhibit UV light near 330 nm up to room temperature, consistent with the emission of GaN/InAlN MQWs. Partially etched tubes reveal a quantum-dotlike signature originating from nanosized GaN residuals present inside the tubes. The possibility to fabricate in a simple way thin-wall III-N tubes composed of an embedded MQW-based active region offering controllable optical emission properties constitutes an important step forward to develop new nitride devices such as emitters, detectors or sensors based on tubelike nanostructures.

The origin of efficiency droop in state-of-the-art quality In GaN/GaN and GaN/AlGaN quantum wells (QWs) grown on various crystal planes is studied by means of time-resolved photoluminescence spectroscopy associated with a precise determination of the QW carrier density. In a first set of experiments, it is shown that a polar InGaN/GaN QW under nonresonant high optical excitation shows clear signatures of Auger loss mechanism and thus behaves quite differently compared to its binary based GaN/AlGaN QW counterpart, where no Auger signature is observed. In order to get rid of the impact of the built-in polarization field and illustrate the dominant role of carrier localization, similar experiments have been conducted on two m-plane In GaN/GaN QWs with similar In composition but a different degree of disorder. We demonstrate that carrier localization strongly enhances the Auger recombination process in nonpolar In GaN/GaN QWs. We also show that this effect may be further amplified by the presence of polarization fields on polar QWs. The relaxation of the k-selection rule during the Auger recombination process, resulting from QW potential disorder, can account for the enhancement of the efficiency droop in In GaN/GaN QWs.

Contrary to the case of III-nitride based visible light-emitting diodes for which the inhomogeneous linewidth broadening characteristic of InGaN-based multiple quantum well (MQW) heterostructures does not appear as a detrimental parameter, such a broadening issue can prevent a microcavity (MC) system entering into the strong light-matter coupling regime (SCR). The impact of excitonic disorder in low indium content (x similar to 0.1) InxGa1-xN/GaN MQW active regions is therefore investigated for the subsequent realization of polariton laser diodes by considering both simulations and optical characterizations. It allows deriving the requirements for such MQWs in terms of absorption, emission linewidth, and Stokes shift. Systematic absorption-like and photoluminescence (PL) spectroscopy experiments are performed on single and multiple In0.1Ga0.9N/GaN quantum wells (QWs). Micro-PL mappings reveal a low temperature PL linewidth of similar to 30 meV, compatible with SCR requirements, for single QWs for which the microscopic origin responsible for this broadening is qualitatively discussed. When stacking several InGaN/GaN QWs, a departure from such a narrow linewidth value and an increase in the Stokes shift are observed. Various possible reasons for this degradation such as inhomogeneous built-in field distribution among the QWs are then identified. An alternative solution for the MC design to achieve the SCR with the InGaN alloy is briefly discussed. (C) 2014 AIP Publishing LLC.

Using cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope at liquid helium temperatures, the optical and structural properties of a 62 InGaN/GaN multiple quantum well embedded in an AlInN/GaN based microcavity are investigated at the nanometer scale. We are able to spatially resolve a spectral redshift between the individual quantum wells towards the surface. Cathodoluminescence spectral linescans allow directly visualizing the critical layer thickness in the quantum well stack resulting in the onset of plastic relaxation of the strained InGaN/GaN system. (C) 2014 AIP Publishing LLC.

Two types of near-UV light-emitting diodes (LEDs) with an InGaN/GaN single quantum well (QW) differing only in the presence or absence of an underlayer (UL) consisting of an InAlN/GaN superlattice (SL) were examined. The InAlN-based ULs were previously shown to dramatically improve internal quantum efficiency of near-UV LEDs, via a decrease in the density of deep traps responsible for nonradiative recombination in the QW region. The main differences between samples with and without UL were (a) a higher compensation of Mg acceptors in the p-GaN:Mg contact layer of the sample without UL, which correlates with the presence of traps with an activation energy of 0.06 eV in the QW region, (b) the presence of deep electron traps with levels 0.6 eV below the conduction band edge (E-c) (ET1) and at E-c 0.77 eV (ET2) in the n-GaN spacer underneath the QW, and the presence of hole traps (HT1) in the QW, 0.73 eV above the valence band edge in the sample without UL (no traps could be detected in the sample with UL), and (c) a high density of deep traps with optical ionization energy close to 1.5 eV for the LEDs without UL. Irradiation with 5 MeV electrons led to a strong decrease in the electroluminescence (EL) intensity in the LEDs without UL, while for the samples with UL, such irradiation had little effect on the EL signal at high driving current, although the level of driving currents necessary to have a measurable EL signal increased by about an order of magnitude. This is despite the 5 times higher starting EL signal of the sample with UL. Irradiation also led to the appearance in the LEDs with UL of the ET1 and HT1 deep traps, but with concentration much lower than without the UL, and to a considerable increase in the Mg compensation ratio.

We report on the epitaxial growth of high-quality core–shell nonpolar m-plane GaN/InAlN multiple quantum wells (MQWs) on the sidewall facets of c-oriented hexagonal GaN wires. Pseudomorphic growth without generation of threading dislocations has been established for planar GaN/InAlN (In = 15%) MQWs grown on m-GaN substrates, although m-plane InAlN epilayers cannot be grown perfectly lattice-matched to GaN along the two in-plane directions. Calculations based on elasticity theory indicate that the significant amount of strain oriented along the c-axis is the likely factor favoring the formation of cracks along this direction. For the core–shell wire geometry, such cracks are not observed, leading to high structural quality MQWs. A significant UV emission centered around 3.7 eV at room temperature with a strong polarization perpendicular to the wire axis is observed for those core–shell wires, which is consistent with k·p method calculations, proving the absence of quantum confined Stark effect on nonpolar ...

We report a numerical and experimental investigation of fabrication tolerances and outcoupling in optically pumped III-nitride nanolasers operating near lambda = 460 nm, in which feedback is provided by a one-dimensional photonic crystal nanobeam cavity and gain is supplied by a single InGaN/GaN quantum well. Using this platform, we [1] and others [2] previously demonstrated single-mu W lasing thresholds due to the high beta Q-product inherent to the nanobeam geometry (beta is spontaneous emission coupling fraction into desired mode). In this work, we improved the fraction of emission emitted into our microscope's light cone by combining a redesigned photonic crystal cavity (c.f. [3]) with a cross-grating coupler with period approximately twice the photonic crystal lattice constant [4]. The samples were fabricated in epitaxial III-nitride layers grown on (111) silicon substrates using metal organic vapor phase epitaxy. The photonic crystal and output couplers were patterned using a single electron beam lithography exposure and subsequently transferred to the underlying III-nitride layers using dry etching. The nanobeams were then suspended via vapor phase etching of silicon in XeF2 (Figure 1) [5]. Scanning electron microscopy cross-sections revealed high-aspect ratio (>5), sub-70 nanometer diameter holes with near-vertical sidewalls. Fabrication-induced geometry errors were characterized by processing scanning electron micrographs with custom critical dimension software (Figure 2). Using UV micro-photoluminescence spectroscopy at room temperature, we measured the nanobeams' emission intensity, far-field profile, and quality factor. By comparing more than ten nominally identical nanobeams for each geometry with finite-difference time-domain simulations taking into account the geometrical deviations measured during fabrication [8], we characterized the role of fabrication-induced imperfections. Finally, we explored the trade-off between the quality factor and collected signal via lithographic variations of the output coupler grating amplitude. Our results demonstrate the robustness of III-nitrides for short-wavelength photonic crystal applications, such as photonic integrated circuits, optoelectronics, and cavity quantum electrodynamics.

III-nitride based microcavities (MCs) appear as one of the most promising candidates for the realization of room temperature (RT) polariton laser diodes. The present work focuses on the properties of low In content InGaN/GaN multiple quantum wells (MQWs) in terms of inhomogeneous broadening, exciton localization energy, and plastic strain relaxation. For a small number of such QWs, an inhomogeneous line broadening of 41 meV is reported, which is compatible with strong coupling regime requirements. By contrast when considering an InGaN/GaN MQW set, a high density of defects is reported, which is ascribed to plastic strain relaxation. From the evolution of the inhomogeneous line broadening as a function of the number of QWs probed by microphotoluminescence measurements, it is concluded that for the realization of polariton light-emitting devices the QW number should not go beyond 30 for MC structures grown on FS-GaN substrate relying on InGaN/GaN QWs with an indium content similar to 12-15% and thicknesses of 1.5-2 nm/3 nm for the wells and the barriers, respectively. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We report on the current properties of Al1-x InxN (x approximate to 0.18) layers lattice- matched ( LM) to GaN and their specific use to realize nearly strain- free structures for photonic and electronic applications. Following a literature survey of the general properties of AlInN layers, structural and optical properties of thin state- of- the- art AlInN layers LM to GaN are described showing that despite improved structural properties these layers are still characterized by a typical background donor concentration of ( 1 - 5) x 10(18) cm(-3) and a large Stokes shift (similar to 800 meV) between luminescence and absorption edge. The use of these AlInN layers LM to GaN is then exemplified through the properties of GaN/ AlInN multiple quantum wells ( QWs) suitable for near- infrared intersubband applications. A built- in electric field of 3.64MVcm(-1) solely due to spontaneous polarization is deduced from photoluminescence measurements carried out on strain- free single QW heterostructures, a value in good agreement with that deduced from theoretical calculation. Other potentialities regarding optoelectronics are demonstrated through the successful realization of crack- free highly reflective AlInN/ GaN distributed Bragg reflectors ( R > 99%) and high quality factor microcavities ( Q > 2800) likely to be of high interest for short wavelength vertical light emitting devices and fundamental studies on the strong coupling regime between excitons and cavity photons. In this respect, room temperature ( RT) lasing of a LM AlInN/ GaN vertical cavity surface emitting laser under optical pumping is reported. A description of the selective lateral oxidation of AlInN layers for current confinement in nitride- based light emitting devices and the selective chemical etching of oxidized AlInN layers is also given. Finally, the characterization of LM AlInN/ GaN heterojunctions will reveal the potential of such a system for the fabrication of high electron mobility transistors through the report of a high two- dimensional electron gas sheet carrier density ( n(s) similar to 2.6 x 10(13) cm(-2)) combined with a RT mobility mu(e) similar to 1170 cm(2) V-1 s(-1) and a low sheet resistance, R similar to 210 Omega square.

IIIV photonics on silicon is an active and promising research area. Here, we demonstrate room-temperature (RT) lasing in short-wavelength III-nitride photonic crystal nanobeam cavities grown on silicon featuring a single InGaN quantum well (QW). In the low-absorption QW region, high quality factors in excess of 104 are measured, while RT blue lasing under continuous-wave optical pumping is reported in the high-absorption wavelength range, hence the high QW gain region. Lasing characteristics are well accounted for by the large spontaneous emission coupling factor (beta > 0.8) inherent to the nanobeam geometry and the large InGaN QW material gain. Our work illustrates the high potential of III-nitrides on silicon for the realization of low power nanophotonic devices with a reduced footprint that would be of prime interest for fundamental lightmatter interaction studies and a variety of lab-on-a-chip applications including biophotonics.

Lasing is demonstrated in III-nitride photonic crystal nanobeam cavities grown on silicon. Laser characteristics are well accounted for by the large spontaneous emission coupling factor inherent to nanobeams and the InGaN quantum well material gain.

We propose to use lattice-matched AlInN/GaN to replace the Al(Ga)N/GaN material system for III-nitride Bragg reflectors, despite the poor material quality of AlInN reported until very recently. We report an improvement of AlInN material that allowed for successful fabrication of a microcavity light emitting diode, a distributed Bragg reflector with 99.4% reflectivity and microcavities with a quality factor over 800. These results establish state-of-the-art values for III-nitrides, and announce the future importance of AlInN in GaN-based optoelectronics. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stimulated polariton scattering in semiconductor microcavities is reported. The phenomena arise from the bosonic character of the coupled exciton-photon modes of the system. The ability to manipulate and control the polariton dispersions in microcavities is shown to be a key factor underlying the new observations. The potential of such phenomena to form the basis of a new type of coherent light source ("polariton" lasers) and highly efficient optical parametric oscillators is discussed.

We report on a clear experimental demonstration of the presence of biexciton recombination in high quality GaN/AlGaN quantum wells, thus opening the way to relevant improvements of the performances of GaN based devices. The samples have been grown by metalorganic vapor phase epitaxy optimizing the deposition conditions to strongly reduce the Al fluctuations in the barriers. This leads to a photoluminescence broadening of only 5 meV at a temperature of 10 K for an Al content in the barriers of 5%. The biexciton binding energy if found to be of the order of 9 meV. The recombination kinetics show that the exciton and biexciton components are not thermalized at low temperature allowing to extract the intrinsic lifetimes of the two components. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thanks to its high refractive index contrast, band gap, and polarization mismatch compared to GaN, In0.17Al0.83N layers lattice-matched to GaN are an attractive solution for applications such as distributed Bragg reflectors, ultraviolet light-emitting diodes, or high electron mobility transistors. In order to study the structural degradation mechanism of InAlN layers with increasing thickness, we performed metalorganic vapor phase epitaxy of InAlN layers of thicknesses ranging from 2 to 500 nm, on free-standing (0001) GaN substrates with a low density of threading dislocations, for In compositions of 13.5% (layers under tensile strain), and 19.7% (layers under compressive strain). In both cases, a surface morphology with hillocks is initially observed, followed by the appearance of V-defects. We propose that those hillocks arise due to kinetic roughening, and that V-defects subsequently appear beyond a critical hillock size. It is seen that the critical thickness for the appearance of V-defects increases together with the surface diffusion length either by increasing the temperature or the In flux because of a surfactant effect. In thick InAlN layers, a better (worse) In incorporation occurring on the concave (convex) shape surfaces of the V-defects is observed leading to a top phase-separated InAlN layer lying on the initial homogeneous InAlN layer after V-defects coalescence. It is suggested that similar mechanisms could be responsible for the degradation of thick InGaN layers. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790424]

Al0.49Ga0.51N∕Al0.16Ga0.84N distributed Bragg reflectors (DBRs), designed for the ultraviolet spectral region, are reported. The crack-free structures are grown on sapphire substrates by metalorganic chemical vapor deposition. A peak reflectivity of 91% at 353nm with a stop-band width of 17nm was obtained at 300K using a 25pair DBR. Structures at 6nm shorter wavelength show asymmetric spectra, a narrower stop band, and slightly decreased peak reflectivity. By studying the spectra as a function of temperature, the degradation is shown to arise from internal absorption at short wavelengths. Simulations based on transfer matrix theory agree well with the experimental data.

We optimized the far-field emission pattern of one-dimensional photonic crystal nanobeams by modulating the nanobeam width, forming a sidewall Bragg cross-grating far-field coupler. By setting the period of the cross-grating to twice the photonic crystal period, we showed using three-dimensional finite-difference time-domain simulations that the intensity extracted to the far-field could be improved by more than three orders of magnitude compared to the unmodified ideal cavity geometry. We then experimentally studied the evolution of the quality factor and far-field intensity as a function of cross-grating coupler amplitude. High quality factor (>4000) blue (lambda = 455 nm) nanobeam photonic crystals were fabricated out of GaN thin films on silicon incorporating a single InGaN quantum well gain medium. Micro-photoluminescence spectroscopy of sets of twelve identical nanobeams revealed a nine-fold average increase in integrated far-field emission intensity and no change in average quality factor for the optimized structure compared to the unmodulated reference. These results are useful for research environments and future nanophotonic light-emitting applications where vertical in-and out-coupling of light to nanocavities is required. Published by AIP Publishing.

We report the fabrication of high-finesse strongly coupled microcavities composed of a polystyrene film doped with the dye tetraphenyl-porphyrin zinc positioned between two high reflectivity dielectric mirrors. The bottom mirror was deposited by plasma enhanced chemical vapor deposition, and was composed of 11 lambda/4 thick (silicon oxide/silicon nitride) pairs. The organic layer was deposited on to this by spin coating. Finally, the top mirror was deposited by thermal evaporation and consisted of 12 lambda/4 thick (tellurium oxide/lithium fluoride) pairs. Such cavities are characterized by Q factors of between 440 and 620. Strong coupling was evidenced via white light reflectivity measurements. Due to the high cavity Q factor, a Rabi splitting of 135 meV at resonance was very clearly resolved. (C) 2003 American Institute of Physics.

The authors report on room temperature (RT) lasing action in two different types of nitride-based microcavities (MCs): vertical cavity surface emitting lasers (VCSELs) and polariton lasers which operate in the weak and in the strong coupling regime, respectively. Following a brief description of these two operating regimes, an analysis of lasing action at RT is reported for a crack-free planar VCSEL structure based on a bottom lattice-matched AlInN/GaN distributed Bragg reflector (DBR) and a top dielectric DBR. The cavity region, formed by n- and p-type GaN layers surrounding only three InGaN/GaN quantum wells, corresponds to a typical active region suitable for an electrically driven VCSEL. Processing issues of such planar VCSEL structures and electroluminescence characteristics of processed devices are also reported. Then, an alternative approach relying on the realization of coherent GaN-MC light sources based on the spontaneous decay of a macroscopic polariton population, the so-called polariton laser, is described. It is shown that this kind of devices could work at RT with a potentially much lower threshold current density than VCSELs as it does not necessitate reaching population inversion conditions. As for VCSELs, we demonstrate laser-like properties above threshold, i.e. an intense polarized emission and a strong spectral narrowing. Differences of polariton lasers with conventional lasers are also highlighted.

In this presentation, the main drawbacks of GaN based microcavities (MCs) are first pointed out. Achieving high quality factor MCs is a tough task because of intrinsic material properties like the lattice mismatch existing between GaN and AlN. To circumvent this issue, a different strategy based on lattice-matched AlInN alloy is adopted. Although difficult to grow, AlInN epitaxial layers can be successfully implemented to make high reflectivity distributed Bragg reflectors, and subsequently, high quality factor MCs. AlInN based MCs exhibit photonic disorder but record quality factor in excess of 6000 has been measured. Combining these MCs to low linewidth GaN QWs demonstrate SCR at 300 K with a Rabi splitting of 56 meV, the largest value reported so far for inorganic MCs. Optical pumping experiments performed on GaN bulk MCs have already shown the potential of III-V nitride semiconductors for polariton lasing. Recent results obtained on QW-MC indicate very low threshold lasing and polariton condensation in the lower polariton branch well. This is accompanied by the appearance of spontaneous linear polarization. The threshold is dependent on the detuning of the cavity mode with respect to the exciton mode. Finally, preliminary results obtained on electrical injection in these MC structures are presented.

The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of InGaN/GaN quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found (Q>4000). Laser action at similar to 420 nm is achieved under pulsed excitation at room temperature for a peak power density of 400 kW/cm(2). The lasing emission linewidth is down to 0.033 nm.

Intersubband (lSB) optical absorption in different nitride-based heterostructures grown by metal-organic chemical vapour deposition (MOCVD) is reported. The role of indium in AlInN/GaN multi-quantum wells (MQWs) is investigated. At high concentration (15%) AlInN is quasi lattice-matched to GaN and no cracks appear in the structure. At very low indium concentration (similar to 2%) the material quality is improved without decreasing the ISB transition wavelength with respect to the case of indium-free structures. Different mechanisms of strain relaxation in pure and 2% indium-doped AlN/GaN MQW structures are also investigated. ISB transition wavelengths of 2 urn for AlN/GaN MQWs, and 3 mu n for AlInN/GaN MQWs with 15% of In are achieved. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report a full optical deep sub-wavelength imaging of the vectorial components of the electric local density of states for the confined modes of a modified GaN L3 photonic crystal nanocavity. The mode mapping is obtained with a scanning near-field optical microscope operating in a resonant forward scattering configuration, allowing the vectorial characterization of optical passive samples. The optical modes of the investigated cavity emerge as Fano resonances and can be probed without the need of embedded light emitters or evanescent light coupling into the nanocavity. The experimental maps, independently measured in the two in-plane polarizations, turn out to be in excellent agreement with numerical predictions.

We report strong exciton-photon coupling at room temperature in a hybrid high quality bulk 3 lambda/2 GaN cavity with a bottom lattice-matched AlInN/AlGaN distributed Bragg reflector through angle-resolved polarized photoluminescence (PL). Coupling of the optically active free excitons (X-A, X-B, and X-C) to the cavity mode is demonstrated, with their contribution to the PL spectra varying with polarization. Under TE polarization, exciton oscillator strengths for X-A and X-B are about one order of magnitude larger than in bulk GaAs. Photoluminescence exhibits a strong bottleneck effect despite its thermal lineshape.

The strong coupling of excitons and photons inside a semiconductor microcavity forms a trap in k-space for the coupled polaritons. This trap produces new behaviour from the strong parametric scattering of polaritons on the walls of the trap, from condensation of polaritons at the bottom of the trap and from the bottleneck in relaxation at the neck of the trap. We predict the operation of polariton lasers pumped non-resonantly. either electrically or optically, based on efficient scattering of polaritons into the trap. (C) 2002 Elsevier Science B.V. All rights reserved.

The ability to fabricate an array of GaN light emitters on an amorphous glass substrate could lead to significant improvements in the scalability and cost of blue and white LED technology.

P-type AlInN layers lattice-matched to GaN are achieved by Mg doping. The net acceptor concentration N-A-N-D is 5 x 10(18) cm(-3) at a Mg concentration [Mg] of similar to 2 x 10(19) cm(-3). Mg acceptors are partly compensated and one of the compensating defects is related to the occurrence of surface pits. At [Mg] < 2 x 10(19) cm(-3), the pit density is independent of [Mg] and N-A-N-D increases together with increasing [Mg]. At [Mg] > 2 x 10(19) cm(-3), as [Mg] increases, the pit density increases and the N-A-N-D decreases. By decreasing the pit density, a higher N-A-N-D value is obtained and light-emitting diodes with p-type AlInN layer show improved emission intensity. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4747524]

The pronounced optical in-plane anisotropy of a suitably designed nonpolar GaN-based microcavity, mainly inherited from the valence-band complexity of wurtzite semiconductors, allows the coexistence of two different light-matter coupling regimes along orthogonal polarization planes. When increasing the excitation power density, a transition to a nonlinear coherent emission is observed under nonresonant optical pumping for both polarization directions at carrier densities remaining well below the exciton-saturation level. Their differing nature is experimentally revealed by means of polarization-resolved Fourier space and near-field imaging. While one polarization direction exhibits all specificities of the strong light-matter coupling regime and features polariton lasing at high injection, the other one lacks a straightforward interpretation due to its complex coupling regime. Possible mechanisms are addressed and evaluated.

We report on the achievement of freestanding GaN photonic crystal L7 nanocavities with embedded InGaN/GaN quantum wells grown by metal organic vapor phase epitaxy on Si (111). GaN was patterned by e-beam lithography, using a SiO2 layer as a hard mask, and usual dry etching techniques. The membrane was released by underetching the Si (111) substrate. Micro-photoluminescence measurements performed at low temperature exhibit a quality factor as high as 5200 at similar to 420 nm, a value suitable to expand cavity quantum electrodynamics to the near UV and the visible range and to develop nanophotonic platforms for biofluorescence spectroscopy. (C) 2012 American Institute of Physics. [doi:10.1063/1.3684630]

The authors report room temperature polariton lasing at λ∼345nm in a hybrid AlInN∕AlGaN multiple quantum well microcavity (MQW-MC) containing a GaN∕AlGaN MQW active region, i.e., the achievement under nonresonant optical excitation of coherent light emission of a macroscopic population of polaritons occupying the lowest energy state of the lower polariton branch. This was made possible by taking advantage of the efficient relaxation of polaritons in a MQW-MC exhibiting a large vacuum Rabi splitting ΩVRS=56meV.

Nonpolar GaN based microcavity (MC) made of a bottom AlN∕GaN distributed Bragg reflector (DBR) and a top dielectric SiO2∕SiNx DBR has been fabricated on a-plane GaN template. The 13 pair AlN∕GaN DBR, centered around 372nm, exhibits a peak reflectivity of ∼95% together with a flat stopband of 30nm width. The cavity mode centered around 390nm is characterized by a full width at half maximum of 4nm. The optical properties of both the DBR and MC are well reproduced when accounting for linear birefringence effects.

A report is presented on InGaN/GaN multiple quantum well laser diodes, grown by metal organic vapour phase epitaxy on c-plane sapphire substrates, including an Al0.83In0.17N cladding layer lattice-matched to GaN. Lasing action is demonstrated for gain-guided devices at room temperature under pulsed current injection conditions. Direct comparison with structures including only a standard Al0.07Ga0.93N bottom cladding shows an improved optical confinement. This is exemplified by a decreased threshold current density.

The authors report on the achievement of narrow ultraviolet emission using GaN∕AlGaN quantum wells grown by metal organic vapor phase epitaxy. The origin of the inhomogeneous broadening of the emission is explained by means of micro-photoluminescence and atomic force microscopy measurements. The effect of the well/barrier interface roughness on the linewidth is found to be marginal, while the impact of Al composition fluctuations of the barriers is highly critical. Emission linewidths as small as 5meV at 10K are obtained by decreasing the aluminum concentration fluctuations in the AlGaN barrier.

Laser action with low threshold average pump power density (similar to 50 W. cm(-2)) at room temperature is reported for a crack-free planar vertical cavity surface emitting laser (VCSEL) structure based on a bottom lattice-matched AllnN/GaN distributed Bragg reflector (DBR) and a top dielectric DBR. The cavity region, formed by n- and p-type GaN layers surrounding only three InGaN/GaN quantum wells, corresponds to a typical active region suitable for an electrically driven VCSEL. In addition to low threshold, a spontaneous emission coupling factor beta 2 x 10(-3) is derived for this ready-to-be-processed laser structure.

The authors report on the micron scale characterization of a monolithic GaN microcavity (MC) with lattice matched AlInN/GaN distributed Bragg reflectors by means of a microtransmission setup. This technique allows extracting very high quality factors (Q up to 2800), in accordance with theoretical predictions, contrary to what was previously reported for nitride based MCs. Furthermore, two-dimensional mappings of the MC transmission spectrum allow probing the disorder in this MC. The direct relationship between an increased disorder and a reduction in the Q factor is clearly observed. (c) 2006 American Institute of Physics.

The authors report on the demonstration of strong light-matter coupling at room temperature using a crack-free UV microcavity containing GaN/AlGaN quantum wells (QWs). Lattice-matched AlInN/AlGaN distributed Bragg reflectors (DBRs) with a maximum peak reflectivity of 99.5% and SiO2/Si3N4 DBRs were used to form high finesse hybrid microcavities. State-of-the-art GaN/Al0.2Ga0.8N QWs emitting at 3.62 eV with a linewidth of 45 meV at 300 K were inserted in these structures. For a 3 lambda/2 microcavity containing six QWs, the interaction between cavity photons and QW excitons is sufficiently large to reach the strong coupling regime. A polariton luminescence is observed with a vacuum field Rabi splitting of 30 meV at 300 K. (c) 2006 American Institute of Physics.

We report a thorough study of the growth of self-assembled GaN∕AlN quantum dots (QDs). These QDs were grown on sapphire substrates using the Stranski-Krastanov (SK) growth mode by means of low-pressure metal organic vapor phase epitaxy. The influence of the V∕III ratio on the QD height, shape, and density is studied. Emissions above (3.8eV) and below (2.8eV) the band gap of GaN are observed for small dots (1.3nm) and large ones (4.4nm), respectively. Special emphasis was given to the SK growth mode transition and the parameters influencing the QD formation. The two-dimensional–three-dimensional transition is studied continuously by photoluminescence mapping showing its high sensitivity to the V∕III ratio.