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We demonstrate room-temperature pulsed current-injected operation
of InGaAlN heterostructure laser diodes with mirrors fabricated by
chemically assisted ion beam etching. The multiple-quantum-well devices
were grown by organometallic vapor phase epitaxy on c-face sapphire
substrates. The emission wavelengths of the gain-guided laser diodes
were in...
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... probed and operated while lying on a quartz wafer, so that the emission through the substrate could be detected and analyzed. The pulsed power output (spontaneous emission) of a working InGaN-AlGaN 10-QW laser diode heterostructure, measured for this geometry where only the light emitted through the bottom of the wafer is detected, is shown in Fig. 4 as a function of the injection current. The bottom-emitted power exceeds 70 mW at 500 mA, with a differential quantum efficiency of 5%. This value indicates that the internal quantum efficiency of the InGaN MQW's is reasonably ...
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Copyright: 2009. Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. In this paper researchers pr...
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Citations
... Prior to this work, the only semiconductor lasers emitting at blue wavelengths were based on II-VI materials and suffered from severe reliability issues, so that their potential for commercialization was limited. On the other hand, in a short time span after their initial demonstration, InGaN MQW lasers emitting in the 400-nm wavelength range have reached sufficient levels of performance and reliability to become attractive for practical applications [40,[213][214][215][216][217][218][219]. In fact, an operating lifetime of over 10 000 h was reported as early as in 1997 [214]. ...
This paper reviews the device physics and technology of optoelectronic devices based on semiconductors of the GaN family, operating in the spectral regions from deep UV to Terahertz. Such devices include LEDs, lasers, detectors, electroabsorption modulators and devices based on intersubband transitions in AlGaN quantum wells (QWs). After a brief history of the development of the field, we describe how the unique crystal structure, chemical bonding, and resulting spontaneous and piezoelectric polarizations in heterostructures affect the design, fabrication and performance of devices based on these materials. The heteroepitaxial growth and the formation and role of extended defects are addressed. The role of the chemical bonding in the formation of metallic contacts to this class of materials is also addressed. A detailed discussion is then presented on potential origins of the high performance of blue LEDs and poorer performance of green LEDs (green gap), as well as of the efficiency reduction of both blue and green LEDs at high injection current (efficiency droop). The relatively poor performance of deep-UV LEDs based on AlGaN alloys and methods to address the materials issues responsible are similarly addressed. Other devices whose state-of-the-art performance and materials-related issues are reviewed include violet-blue lasers, "visible blind" and "solar blind" detectors based on photoconductive and photovoltaic designs, and electroabsorption modulators based on bulk GaN or GaN/AlGaN QWs. Finally, we describe the basic physics of intersubband transitions in AlGaN QWs, and their applications to near-infrared and terahertz devices.
... However, this spectral region requires indium-rich InGaN QWs. Though light emission devices have been developed with high indium composition ratios (>0.2), fluctuations in indium concentration can occur in these QWs; even a slight InGaN segregation may provide a hindrance to the mechanism of optical gain in nitrides and therefore laser diodes [47]- [49]. Here, we consider an InGaN QW structure, which has been used for a laser diode [50], and we modify the QW thickness such that the gain peak is close to 480 nm wavelength. ...
The interaction between surface plasmons and optical emitters is fundamentally important for engineering applications, especially surface plasmon amplification and controlled spontaneous emission. We investigate these phenomena in an active planar metal-film system comprising InGaN/GaN quantum wells and a silver film. First, we present a detailed study of the propagation and amplification of surface plasmon polaritons (SPPs) at visible frequencies. In doing so, we propose a multiple quantum well structure and present quantum well gain coefficient calculations accounting for SPP polarization, line broadening due to exciton damping, and particularly, the effects of finite temperature. Second, we show that the emission of an optical emitter into various channels (surface plasmons, lossy surface waves, and free radiation) can be precisely controlled by strategically positioning the emitters. Together, these could provide a range of photonic devices (for example, surface plasmon amplifiers, nanolasers, nanoemitters, plasmonic cavities) and a foundation for the study of cavity quantum electrodynamics associated with surface plasmons.
Nitride-based semiconductor products emerged onto the scene in the last decade, and have become a major player in the opto-electronics market with their wide wavelength tunability from the ultraviolet (UV) to the visible spectral region illustrated in Fig. 1. Revenues from the use of blue and green light emitting diodes (LEDs) in home and commercial lightening business alone are predicted to reach almost three billion dollars by 2009. Furthermore, the rapid development of high-brightness LEDs has opened applications in traffic signals consuming less than a tenths of the power of the standard filtered incandescent solution. The energy saving results in a short (< 1 year) payback time on the initial investment of the LED solution. Automotive applications of LEDs include center-high-mount-stop-lamps (CHMLs), rear combination lamps (RCLs) and turn lights. The main driving force for LED application in automotive at present is styling, where the small size of LEDs allows flexible layout. Other applications of LEDs include backlights for liquid crystal displays (LCD) displays and full color displays.
The rigorous optical model of diode lasers has been used to investigate an impact of various construction details of multi-quantum-well nitride lasers, as the number of quantum wells placed in active region, as well as designs of their waveguides and buffer layers located between the substrate and the laser structure, on room-temperature laser operation. The model is used to discuss some possible structure modifications to reduce losing thresholds. Recommended design parameters have been found for each structure.
A detailed threshold analysis of room-temperature pulsed operation of GaN/AlGaN/AlN verticalcavity surface-emitting lasers (VCSELs) is carried out. The model takes advantage of the latest results concerning gain in active regions, material absorption in the cladding layers, as well as cavity diffraction and scattering losses. The simulation showed that although VCSELs with single (S) or multiple (M) quantum-well (QW) active regions exhibit lower threshold currents, they are much more sensitive to any increase in optical losses than their bulk counterparts. In particular, decreasing the active region radius of gain-guided QW VCSELs below 5 μm (which increases diffraction losses) or increasing dislocation densities (which, in turn, raises scattering losses) gives an enormous rise to their threshold currents. Therefore small-size GaN VCSELs should have an index-guided structure. In the case of MQW VCSELs, the optimal number of quantum wells strongly depends on the reflectivities of resonator mirrors. According to our study, MQW GaN lasers usually require noticeably lower threshold currents compared to SQW lasers. The optimal number of QW active layers is lower in laser structures exhibiting lower optical losses. Although the best result occurred for an active region thickness of 4 nm, threshold currents for the various sizes differ insignificantly.
Photoluminescence and time-resolved spectroscopy of gallium nitride (GaN)- and indium gallium nitride (InGaN)-based materials and devices are discussed in this chapter. The chapter discusses the results obtained in various studies of the photoluminescence properties of GaN and related materials. The experimental techniques covered in the chapter include optical absorption, photoreflection (PR), modulation spectroscopy, spectroscopic ellipsometry, photoluminescence (PL), time-resolved PL, micro-PL, cathodoluminescence, pump-probe spectroscopy, femtosecond spectrally resolved and time-resolved degenerate four-wave mixing, second harmonic generation, laser-induced gratings, and quantum beats. The development of large area single-crystal growth of GaN may provide the ultimate solution to the problem of lattice mismatch. GaN and other III–V nitrides have been realized as potential candidates in photonics. Light emitting diode (LEDs) and semiconductor lasers that emit in a variety of wavelengths from blue to yellow are now commercially available. They are being used in full-color displays and traffic lights. LEDs that emit various colors are also substitutes for traditional fluorescent lamps and can be used in homes and shops. The market for LEDs is huge. Blue LEDs also find applications in laser printers and underwater optical communications for the Navy. In the near future, it is possible to develop digital video disks in which InGaN and GaN lasers are used.
GaN and related materials have received a lot of attention because of their applications in a number of semiconductor devices such as LEDs, laser diodes, field effect transistors, photodetectors etc. An introduction to optical phenomena in semiconductors, light emission in p-n junctions, evolution of LED technology, bandgaps of various semiconductors that are suitable for the development of LEDs are discussed first. The detailed discussion on photoluminescence of GaN nanostructures is made, since this is crucial to develop optical devices. Fabrication technology of many nanostructures of GaN such as nanowires, nanorods, nanodots, nanoparticles, nanofilms and their luminescence properties are given. Then the optical processes including ultrafast phenomena, radiative, non-radiative recombination, quantum efficiency, lifetimes of excitons in InGaN quantum well are described. The LED structures based on InGaN that give various important colors of red, blue, green, and their design considerations to optimize the output were highlighted. The recent efforts in GaN technology are updated. Finally the present challenges and future directions in this field are also pointed out.
The effect of Si doping on the strain and microstructure in GaN films grown on sapphire by metalorganic chemical vapor deposition was investigated. Strain was measured quantitatively by x-ray diffraction, Raman spectroscopy, and wafer curvature techniques. It was found that for a Si concentration of 2×1019 cm−3, the threshold for crack formation during film growth was 2.0 μm. Transmission electron microscopy and micro-Raman observations showed that cracking proceeds without plastic deformation (i.e., dislocation motion), and occurs catastrophically along the low energy {100} cleavage plane of GaN. First-principles calculations were used to show that the substitution of Si for Ga in the lattice causes only negligible changes in the lattice constant. The cracking is attributed to tensile stress in the film present at the growth temperature. The increase in tensile stress caused by Si doping is discussed in terms of a crystallite coalescence model.
The amount of strain was measured in GaN films using X-ray diffraction, Raman, and curvature techniques as a function of film thickness and the Si doping concentration. It was found that for a doping concentration of 2×1019, the threshold thickness for crack formation was about 2.5μm. Transmission electron microscopy observations showed that cracking proceeds without plastic deformation (i.e., no dislocation motion), and occurs catastrophically along the low-energy {11̄00} cleavage plane of GaN.
