High Quality InGaN/AlGaN Multiple Quantum Wells for Semipolar InGaN Green Laser Diodes (original) (raw)
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AlGaN-Cladding Free Green Semipolar GaN Based Laser Diode with a Lasing Wavelength of 506.4 nm
We demonstrate electrically driven InGaN based laser diodes (LDs), with a simple AlGaN-cladding-free epitaxial structure, grown on semipolar ð20 " 21Þ GaN substrates. The devices employed In 0:06 Ga 0:94 N waveguiding layers to provide transverse optical mode confinement. A maximum lasing wavelength of 506.4 nm was observed under pulsed operation, which is the longest reported for AlGaN-cladding-free III-nitride LDs. The threshold current density (J th ) for index-guided LDs with uncoated etched facets was 23 kA/cm 2 , and 19 kA/cm 2 after application of highreflectivity (HR) coatings. A characteristic temperature (T 0 ) value of 130Kandwavelengthred−shiftof130 K and wavelength red-shift of 130Kandwavelengthred−shiftof0:05 nm/K were confirmed.
400-nm InGaN-GaN and InGaN-AlGaN multiquantum well light-emitting diodes
IEEE Journal of Selected Topics in Quantum Electronics, 2002
Rcenctly, tremendous progress has been achieved in GaN-based blue and green lightemitting diodes (LEDs). These blue/green LEDs have already been extensively used in fullcolor displays and high-efficient light sources for traffic light lamps. Although these blue/ green LEDs are already commercially available, it is still difficult to achieve LEDs emitting at even shorter wavelength regions, such as ultraviolet (UV) region. Short wavelength emitters are of interest for various fluorescence-based chemical sensing applications, high efficiency lighting, flame detection, and possibly optical storage applications. Conventional nitridebased multiquantum well (MQW) LEDs use InGaN as the material for well layers and GaN as the material for barrier layers. To achieve a short wavelength emitter, one needs to reduce the indium composition in the well layers so as to increase its bandgap energy. However, a reduction in indium composition in the well layers will result in a small bandgap discontinuity at the well/barrier interfaces. Thus, the quantum well depth in the MQW active region will become smaller and the carrier confinement effect will be reduced. As a result, severe carrier leakage problem might occur in the short wavelength InGaN-GaN MQW LEDs. One possible way to solve this problem is to use AlGaN or AlGaInN as the barrier layers instead of GaN. The quaternary AlGaInN permits an extra degree of freedom by allowing independent control of the bandgap and lattice constant. Thus, the use of quaternary AlGaInN for barrier layers could potentially offer better carrier confinement while minimizing lattice mismatch issues. However, it is much more difficult to grow high-quality AlGaInN than AlGaN. Since the bandgap energy of AlGaN is also larger than that of GaN, InGaN-AlGaN MQW should still be able to provide a better carrier confinement, as compared to InGaN-GaN MQW. Also, since the lattice constant of AlGaN is smaller while the lattice constant of InGaN is larger than that of GaN base layer, it is possible to achieve a strain compensated InGaN-AlGaN MQW on GaN with proper composition ratios in InGaN and AlGaN layers. As a result, we could increase the effective MQW critical thickness, and thus reduce the probability of relaxation occurred within the MQW active region. In this study, InGaN-GaN LED and InGaN-AlGaN LED will both be fabricated. The optical and electrical properties of these LEDs will be reported.
Optics and Photonics Society of Iran, 2014
In this paper a new structure for InGaN/GaN multi quantum well (MQW) light emitting diodes (LEDs) with emission wavelengths of 400-450 nm and peak wavelength at 435 nm is reported. In this configuration a tri-step quantum wells have been considered that high quantum efficiency up to 80% was obtained. Since carriers would experience more cross-section of the localized states at outer well, both short wavelength emission and stable quantum efficiency have been observed.
Indium-tin-oxide clad blue and true green semipolar InGaN/GaN laser diodes
Applied Physics Letters, 2013
Replacing a portion of the upper III-nitride cladding with indium-tin-oxide (ITO) has several potential advantages for GaN-based laser diodes (LDs). For green LDs, use of ITO in the waveguide structure reduces the epitaxial p-cladding thickness and growth time, which in turn may reduce thermal damage to the active region. We design ITO-clad blue and green semipolar ð20 21Þ LDs using asymmetric InGaN waveguiding layers to center the mode on the active region. Lasing is demonstrated at 471 nm with threshold current density of 6.2 kA/cm 2 for a device with 200 nm p-GaN and at 518 nm for a device with only 300 nm of p-GaN. V C 2013 AIP Publishing LLC.
Optically-pumped lasing of semi-polar InGaN/GaN(1122) heterostructures
physica status solidi (c), 2010
Results for long-wavelength emitters are presented for semi-polar InGaN/AlGaN/GaN heterostructures grown on GaN(1122)/m-sapphire templates by metalorganic chemical vapor deposition. The semi-polar GaN layers were 10 to 25 µm thick and grown by HVPE on sapphire substrates. X-ray diffraction measurements indicate high crystallographic quality that approaches that of GaN(0001) layers on sapphire. Growth studies on the semi-polar GaN templates established the high efficiency of indium incorporation into InGaN layers, with a wide growth-temperature window up to 800°C for green light emitting structures. Basic LEDs were fabricated with peak emission up to 527 nm wavelength. Further growth studies established conditions for growing reasonably smooth, undoped InGaN/GaN laser heterostructures suitable for optical pumping. Optically-pumped lasing was achieved at wavelengths from 400 nm up to 500 nm. The results demonstrate the viability of semi-polar GaN(1122) on sapphire templates for long-wavelength nitride laser diodes.
Role of substrate quality on the performance of semipolar (112¯2) InGaN light-emitting diodes
Journal of Applied Physics, 2016
We compare the optical properties and device performance of unpackaged InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) emitting at ∼430 nm grown simultaneously on a high-cost small-size bulk semipolar (112¯2) GaN substrate (Bulk-GaN) and a low-cost large-size (112¯2) GaN template created on patterned (101¯2) r-plane sapphire substrate (PSS-GaN). The Bulk-GaN substrate has the threading dislocation density (TDD) of ∼105 cm−2–106 cm−2 and basal-plane stacking fault (BSF) density of 0 cm−1, while the PSS-GaN substrate has the TDD of ∼2 × 108 cm−2 and BSF density of ∼1 × 103 cm−1. Despite an enhanced light extraction efficiency, the LED grown on PSS-GaN has two-times lower internal quantum efficiency than the LED grown on Bulk-GaN as determined by photoluminescence measurements. The LED grown on PSS-GaN substrate also has about two-times lower output power compared to the LED grown on Bulk-GaN substrate. This lower output power was attributed to the higher TDD and BSF density.
A detailed study on optical properties of InGaN/GaN/Al2O3 multi quantum wells
Journal of Materials Science: Materials in Electronics, 2019
In this study optical properties of InGaN/GaN/Al 2 O 3 multi-quantum well (MQW) structures are investigated in detail. Three samples containing InGaN/GaN/Al 2 O 3 MQWs are grown by using metal organic chemical vapor deposition technique. Sapphire (6H-Al 2 O 3) is used as the substrate. Forbidden energy band gaps (E g) of these three samples are determined from photoluminescence and absorption spectra. Results gained from these two spectra are compared with each other. It is found that E g values are between 2 and 3 eV. For determining refraction index, absorption coefficients, extinction coefficients and thickness of the films a rare method called Swanepoel envelope method is used. It is seen that results gained from this method are consistent with those in literature.
Journal of Applied Physics, 2016
In this paper, we report on a detailed spectroscopic study of the optical properties of InGaN/GaN multiple quantum well structures, both with and without a Si-doped InGaN prelayer. In photoluminescence and photoluminescence excitation spectroscopy, a 2nd emission band, occurring at a higher energy, was identified in the spectrum of the multiple quantum well structure containing the InGaN prelayer, originating from the first quantum well in the stack. Band structure calculations revealed that a reduction in the resultant electric field occurred in the quantum well immediately adjacent to the InGaN prelayer, therefore leading to a reduction in the strength of the quantum confined Stark effect in this quantum well. The partial suppression of the quantum confined Stark effect in this quantum well led to a modified (higher) emission energy and increased radiative recombination rate. Therefore, we ascribed the origin of the high energy emission band to recombination from the 1st quantum well in the structure. Study of the temperature dependent recombination dynamics of both samples showed that the decay time measured across the spectrum was strongly influenced by the 1st quantum well in the stack (in the sample containing the prelayer) leading to a shorter average room temperature lifetime in this sample. The room temperature internal quantum efficiency of the prelayer containing sample was found to be higher than the reference sample (36% compared to 25%) which was thus attributed to the faster radiative recombination rate of the 1st quantum well providing a recombination pathway that is more competitive with nonradiative recombination processes. V
High efficiency InGaN/GaN light emitting diodes with asymmetric triangular multiple quantum wells
Applied Physics Letters, 2014
In this study, we demonstrated high efficiency InGaN/GaN light emitting diodes (LEDs) with asymmetric triangular multiple quantum wells (MQWs). Asymmetric triangular MQWs not only contribute to uniform carrier distribution in InGaN/GaN MQWs but also yield a low Auger recombination rate. In addition, asymmetric triangular MQWs with gallium face-oriented inclination band profiles can be immune from the polarization charge originating from typical c-plane InGaN/GaN quantum well structures. In the experiment, LEDs incorporated with asymmetric triangular MQWs with gallium face-oriented inclination band profiles exhibited a 60.0% external quantum efficiency at 20 mA and a 27.0% efficiency droop at 100 mA (corresponding to a current density of 69 A/cm 2 ), which accounted for an 11.7% efficiency improvement and a 31.1% droop reduction compared with symmetric square quantum well structure LEDs. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4867023\]
Journal of Crystal Growth, 2011
InGaN/GaN quantum wells (QWs) with symmetrical ultra thin (about 0.5nm) low temperature GaN (LT-GaN) layers bounding each InGaN layer were grown by metal-organic vapor phase epitaxy (MOVPE). From the high resolution X-ray diffraction (HR-XRD) measurement, it showed improved well-barrier interface abruptness compared to the reference MQWs without the LT-GaN layers. In addition, the V-defect density and surface roughness were reduced, especially with the depth of V-defect as low as 0.7nm. Based on the temperature dependence photoluminescence (TDPL) experiments, the internal quantum efficiency (IQE) was increased from 21.2% to 30.1% by inserting the LT-GaN layers. The carrier lifetime obtained from room temperature time resolved photoluminescence (TRPL) measurement was 7.95ns, which was longer than 5.34ns for reference MQWs. These results indicated that these additional symmetrical thin LT-GaN layers enhanced the mobility of indium and gallium atoms as well as suppressed the indium desorption for growth high quality InGaN layers and in turn improved its structural and luminescence properties.