Enhanced light extraction in III-nitride ultraviolet photonic crystal light-emitting diodes (original) (raw)
Related papers
III-nitride blue and ultraviolet photonic crystal light emitting diodes
Applied Physics Letters, 2004
We present results on enhancement of 460 nm blue and 340 nm UV optical power output in III-nitride light emitting diodes ͑LEDs͒ using photonic crystals ͑PCs͒ under current injection. Triangular arrays of the PCs with diameter/periodicity of 300/700 nm were patterned using electron-beam lithography and inductively coupled plasma dry etching. The total power at 20 mA of 300ϫ300 m 2 unpackaged LED chips revealed an increase by 63% and 95% for the blue and UV LEDs, respectively, as a result of the PC formation. Possible ways for further improving enhancement of light extraction using PCs are discussed.
Applied Physics Letters, 2004
Transient responses of III-nitride photonic-crystal (PC) ultraviolet (UV) light-emitting diodes (LEDs) were measured by picosecond time-resolved electroluminescence (EL) spectroscopy. Triangular arrays of PCs with different diameters/periodicities were fabricated on 333 nm UV LEDs for enhancing light extraction efficiency using electron-beam lithography and inductively coupled-plasma dry etching. With the incorporation of PCs on LEDs, the EL decay time constant decreases systematically with the increase of the etched sidewall area indicating the strong effect of the surface recombination. The surface recombination velocities on the p-type epitaxial surface and on the sidewall of etched holes on LEDs were determined to be 1.73ϫ 10 4 cm/ s and 1.48 ϫ 10 5 cm/ s, respectively. The angular distribution of light emission from LEDs with PCs shows slight narrowing in far-field pattern. Because of the increased transient response along with enhanced light extraction, the incorporation of PCs in UV LEDs provide an effective method to control the modulation speed of UV LEDs, which could be very useful for many applications.
III-nitride blue and UV photonic-crystal light-emitting diodes
Fourth International Conference on Solid State Lighting, 2004
We report on the successful nano-fabrication and characterization of III-nitride blue and ultraviolet (UV) photonic crystal light emitting diodes (PC-LEDs) using electron beam lithography and inductively coupled plasma dry etching. Triangular arrays of holes with different diameters/periodicities were etched on the LEDs. Optical measurements on the photonic crystals (PCs) performed using near-field scanning optical microscopy (NSOM) showed a 60 o periodic variation with the angle between the propagation direction of emission light and the PCs lattice. Under optical pumping, an unprecedented enhancement factor of 20 in emission light intensity of wavelength 475 nm was achieved at room temperature with emission light parallel to the Γ-K direction of the PCs lattice. Guided by the optical pumping results, new design geometry of LEDs with PCs has been employed to optimize the light extraction. Enhancement in optical power of current injected blue and UV PC-LEDs over conventional LEDs is discussed. It was observed that the optical enhancement factor depends strongly on the PC lattice constant and hole size. The achievement of nitride photonic crystal emitters with enhanced light extraction efficiency is expected to benefit many new applications of III-nitrides including solid-state lighting for general illumination and photonic integrated circuits operating in the visible and UV spectral regions.
III-Nitride LEDs with photonic crystal structures
Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 2005
Electrical operation of III-Nitride light emitting diodes (LEDs) with photonic crystal structures is demonstrated. Employing photonic crystal structures in III-Nitride LEDs is a method to increase light extraction efficiency and directionality. The photonic crystal is a triangular lattice formed by dry etching into the III-Nitride LED. A range of lattice constants is considered (a ~ 270-340nm). The III-Nitride LED layers include a tunnel junction providing good lateral current spreading without a semi-absorbing metal current spreader as is typically done in conventional III-Nitride LEDs. These photonic crystal III-Nitride LED structures are unique because they allow for carrier recombination and light generation proximal to the photonic crystal (light extraction area) yet displaced from the absorbing metal contact. The photonic crystal Bragg scatters what would have otherwise been guided modes out of the LED, increasing the extraction efficiency. The far-field light radiation patterns are heavily modified compared to the typical III-Nitride LED's Lambertian output. The photonic crystal affects the light propagation out of the LED surface, and the radiation pattern changes with lattice size. LEDs with photonic crystals are compared to similar III-Nitride LEDs without the photonic crystal in terms of extraction, directionality, and emission spectra.
Analysis of transverse magnetic (TM) mode light extraction efficiency enhancement for AlGaN quantum wells (QWs) based deep ultraviolet (UV) light-emitting diodes (LEDs) with III-nitride microhemisphere and micro-dome structures on the p-type layer are studied and compared to that of the conventional deep-UV LEDs with flat surface. The transverse electric (TE) and TM components of the spontaneous emission of AlGaN QWs with AlN barriers were calculated by using a self-consistent 6band k·p method, which shows the TM component overtakes the TE component and becomes the dominant contribution of the spontaneous emission when the Al-content of the AlGaN QWs is larger than 0.66. The TM mode light extraction efficiency of the deep-UV LEDs emitting at 250 nm with AlGaN micro-domes as compared to the conventional LEDs with flat surface is calculated based on three dimensional finite difference time domain (3D-FDTD) method. The effects of the III-nitride micro-dome diameter and height as well as the p-type layer thickness on the light extraction efficiency were comprehensively studied. The results indicate optimized light extraction efficiency enhancement (>7.3 times) of the dominant TM polarized spontaneous emission for deep-UV LEDs with IIInitride micro-domes.
Advances in group III-nitride-based deep UV light-emitting diode technology
Semiconductor Science and Technology, 2011
The field of AlGaInN ultraviolet UV light-emitting diodes (LEDs) is reviewed, with a summary of the state-of-the-art in device performance and enumeration of applications. Performance-limiting factors for high-efficiency UV LEDs are identified and recent advances in the development of deep UV emitters are presented.
Ultraviolet light-emitting diodes based on group three nitrides
Nature Photonics, 2008
Research and development on III-nitride semiconductors gained momentum much later than other conventional semiconductors such as silicon and gallium arsenide. This was due to the difficulty in fabricating high-quality bulk III-nitride crystals and their epitaxial layers. Although initial synthesis of AlN, InN and GaN was reported in the early twentieth century, adequate quality for device fabrication has only been achieved in the past two decades. Despite the fact that the III-nitride materials have a direct bandgap, suitable for highefficiency generation of green, blue and violet light to complete the visible colour spectrum, research was limited owing to the lack of a suitably lattice-matched substrate and the difficulty of incorporating nitrogen into the semiconductor lattice 1 . After decades of research on GaN and its ternary alloys InGaN and AlGaN, experimental procedures were developed that enabled the growth of high-quality single-crystal materials by using a low-temperature nucleation layer 2,3 . Shortly afterwards, p-type GaN was realized using low-energy electron-beam treatment of the magnesium-doped material, followed by thermal annealing 4,5 . These two advancements began a period of tremendous growth and rapid progress in the development of IIInitride violet/blue/green/white LEDs and violet laser diodes. With AlInGaP-based red and yellow LEDs already available, this completed the colour spectrum that could be achieved using semiconductor sources. 'Visible' light-emission device technology is reaching its maturity, and many groups have shifted their research focus towards the shorter-wavelength UV devices. This interest is fuelled by the potential applications for these UV LEDs in air-and waterpurification, germicidal and biomedical instrumentation systems 6 . These combined markets are worth in excess of several billion dollars, which provides a strong impetus for research. Here, the progress of III-nitride-based UV and deep-UV LEDs is reviewed. Challenges associated with the growth and fabrication of AlInGaN-based
III-Nitride nanostructures for UV emitters
2015
This work reports on the design, epitaxial growth, and the structural, and optical characterization of two types of nanostructures, namely AlGaN/AlN Stranski-Krastanov quantum dots (SK-QD) and AlGaN/AlN nanodisks (NDs) on GaN nanowires (NWs). These nanostructures were grown using plasma-assisted molecular beam epitaxy (PA-MBE) and were conceived to be the active media of electron-pumped ultraviolet (EPUV) emitters for water purification, operating in mid-ultraviolet range. The peak emission wavelength of three-dimensional SK-QD can be tuned in mid-ultraviolet range while keeping high internal quantum efficiency (IQE > 35%) by modifying the Al composition and the QD geometry. The efficient carrier confinement was confirmed by the stability of the photoluminescence intensity and decay time with temperature. The optimal deposited amount of AlGaN in AlGaN/AlN QDs which grants maximum luminescence at room temperature was determined by finding a compromise between the designs providing...
High-Efficiency Nitride-Base Photonic Crystal Light Sources
2010
SEM image of a surface PhC embedded PhC SEM image of an Nanoimprint mask Example of highly directional emission in MC PhC LEDs Enhancement of the vertically outcoupled light in Embedded PhC LEDs Measurement of the extraction length of different guided modes. High resolution angular-resolved electroluminescence. Peak IQE-7.9 % Extraction efficiency-94% External quantum efficiency of embedded PhC LEDs U.S. Department of Energy Building Technologies Program Peer Reviews 7. Achievements Milestones Achievements Task 1 Achieve uniform, reproducible sub-micron mask patterning and etching over areas of at least 1x1 cm 2 • This milestone is achieved by optimizing a nanoimprint lithography technique. Optimize dry etching methods to achieve PhC depths of at least 300 nm.