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15 Aug 2011

Volume 110, Issue 4, Articles (04xxxx)

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back to top Lasers, Optics, and Optoelectronics

Analytical modeling and numerical simulation of P+-Hg0.69 Cd0.31Te/n-Hg0.78Cd0.22Te/CdZnTe heterojunction photodetector for a long-wavelength infrared free space optical communication system

A. D. D. Dwivedi

J. Appl. Phys. 110, 043101 (2011); http://dx.doi.org/10.1063/1.3615967 (10 pages)

Online Publication Date: 16 August 2011

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In this paper an analytical modeling and 2D numerical simulation of P+-Hg0.69Cd0.31Te/ n-Hg0.78Cd0.22Te/CdZnTe single heterojunction photodetector using the commercially available atlasTM package from SILVACO® International for long-wavelength free space optical communication has been reported. The photodetector has been studied with respect to energy band diagram, electric field profile, doping profile, dark current, resistance area product, quantum efficiency, spectral response, responsivity, and detectivity by an analytical method using closed form equations. The results obtained on the basis of the analytical model have been compared and contrasted with the simulated results using atlasTM. The photodetector exhibits high values of quantum efficiency ∼80%, responsivity ∼6.75 A/W, specific detectivity ∼2.25 × 1011 mHz1/2W−1 at wavelength10.6 μm, and dark current of the order of 10−11 A. The estimated noise equivalent power (NEP) is of the order of 1 × 10−17 W.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Reflection of femtosecond laser light in multipulse ablation of metals

A. Y. Vorobyev and Chunlei Guo

J. Appl. Phys. 110, 043102 (2011); http://dx.doi.org/10.1063/1.3620898 (9 pages)

Online Publication Date: 16 August 2011

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The shot-to-shot reflectance of high-intensity laser light is studied as a function of both the number of laser shots and laser fluence in multipulse ablation of a metal when the irradiated surface undergoes structural changes from an initially smooth surface to a deep crater. Our study shows that the reflectance of the irradiated surface significantly decreases due to the high intensity of laser pulses and the laser-induced surface structures in ablation regimes typically used for femtosecond laser processing of materials. The high-intensity effect dominates in the reflection reduction at low numbers of laser shots when laser-induced surface structures do not cause the reflectance to decrease noticeably. With increasing the number of laser shots, the structural effect comes into play, and both high-intensity and structural effects quickly reduce the reflectance of the sample to a low value.
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81.05.Bx Metals, semimetals, and alloys
68.35.bd Metals and alloys
78.47.jg Time resolved reflection spectroscopy
79.20.Eb Laser ablation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Optical avalanche in Ho:Yb:Gd2O3 nanocrystals

Y. Dwivedi, A. Bahadur, and S. B. Rai

J. Appl. Phys. 110, 043103 (2011); http://dx.doi.org/10.1063/1.3622624 (8 pages) | Cited 1 time

Online Publication Date: 16 August 2011

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Intense green upconversion emission in Ho:Yb:Gd2O3 spherical nanoparticles is reported through hetrolooping enhanced energy transfer process. Different techniques used for structural characterization divulge the formation of spherical Ho:Yb:Gd2O3 crystals of diameter ∼100 nm. Efficient energy transfer from Yb3+ → Ho3+ ions set spherical nanocrystal to emit in the range of UV-NIR via three NIR photons absorption process. Power dependence and the temporal evolution of upconversion emission intensity suggest the occurrence of a photon avalanche process. The enhancement in emission intensity in nanophosphor sample has been explained and the photophysics involved is correlated with the unique structural properties of the crystallites formed and the time resolved spectroscopy.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.47.D- Time resolved spectroscopy (>1 psec)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
63.20.-e Phonons in crystal lattices
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics

Efficiency limit and example of a photonic solar cell

Marius Peters, Jan Christoph Goldschmidt, and Benedikt Bläsi

J. Appl. Phys. 110, 043104 (2011); http://dx.doi.org/10.1063/1.3622669 (5 pages) | Cited 3 times

Online Publication Date: 16 August 2011

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Restricting the angular emission characteristics of a solar cell results in a reduction of entropy generation and allows for higher solar cell efficiencies. In this paper, we present the concept of a photonic solar cell which exhibits the combination of a solar cell and a photonic crystal. The basic idea is to structure a solar cell in such a way that the applied structure is a photonic crystal consisting of the solar cell material. The aim of having a solar cell in the form of a photonic crystal is to restrict the emission of the solar cell into certain angles This reduction reduces the radiative losses and results in a higher VOC and, consequently, a higher efficiency of the cell. To calculate the efficiency of a photonic solar cell we introduce an adaptation of the detailed balance approach. This adaptation takes into account the reduced radiative losses due to the presence of a photonic band structure. In the second part of the paper we use this approach to calculate the efficiency for an exemplary system. The exemplary system is an idealized edge filter, similar to a Bragg stack. The idealization concerns the reflection characteristic of this filter and its dependence on the polarization. For this idealized system we calculate an efficiency that exceeds that of a conventional solar cell by up to 2.5% absolute.
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88.40.H- Solar cells (photovoltaics)
42.70.Qs Photonic bandgap materials
42.79.Dj Gratings
42.81.-i Fiber optics
88.40.J- Types of solar cells

A branched luminescent multinuclear platinum(II) complex

Hui Yang, S. J. Xu, Chi-Hang Tao, Vivian Wing-Wah Yam, and Jie Zhang

J. Appl. Phys. 110, 043105 (2011); http://dx.doi.org/10.1063/1.3622587 (4 pages) | Cited 1 time

Online Publication Date: 18 August 2011

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Nonlinear optical properties of luminescent multinuclear platinum(II) complex of branched alkynyls in benzene solution are investigated at room temperature by using two-photon fluorescence (TPF) technique. It is found that the material shows unusual nonlinear optical characteristics under the excitation of near infrared femtosecond laser pulses. The self-focusing of laser beam energy during propagation of the laser pulses in the sample with large nonlinear coefficient for the refractive index is observed. Based on this phenomenon, a new method for measuring the nonlinear coefficient and two-photon absorption cross section of materials is proposed.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Er Solid metals and alloys
78.30.cb Organic liquids

Photonic crystal cavity with one-way rotating state and its coupling with photonic crystal waveguide

Zhuoyuan Wang, Linfang Shen, Xianmin Zhang, Yigang Wang, Zaihe Yu, and Xiaodong Zheng

J. Appl. Phys. 110, 043106 (2011); http://dx.doi.org/10.1063/1.3622676 (4 pages)

Online Publication Date: 18 August 2011

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A photonic crystal (PhC) cavity formed by a closed interface between a dielectric PhC and a magnetooptical (MO) material PhC is proposed and analyzed theoretically. It is shown that such a cavity can support one-way rotating modes and thus the modal fields at different frequencies have a similar pattern. The loss effect of MO material is taken into consideration for the solution of quality-factors for the cavity. The coupling between a cavity with one-way state and a PhC waveguide is also studied through numerical simulations. Simulation results show that cavity mode only interacts with the waveguide mode propagating in a particular direction. This work paves the way to control waveguide-cavity interaction.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Predicted photonic band gaps in diamond-lattice crystals built from silicon truncated tetrahedrons

Léon A. Woldering, Leon Abelmann, and Miko C. Elwenspoek

J. Appl. Phys. 110, 043107 (2011); http://dx.doi.org/10.1063/1.3624604 (8 pages)

Online Publication Date: 19 August 2011

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Recently, a silicon micromachining method to produce tetrahedral silicon particles was discovered. In this report we determine, using band structure calculations, the optical properties of diamond-lattice photonic crystals when assembled from such particles. We show that crystal structures built from silicon tetrahedra are expected to display small stop gaps. Wide photonic band gaps appear when truncated tetrahedral particles are used to build the photonic crystals. With truncated tetrahedral particles, a bandgap with a width of 23.6% can be achieved, which is more than twice as wide compared to band gaps in self-assembled diamond-lattices of hard-spheres. The width of the bandgap is insensitive to small deviations from the optimal amount of truncation. This work paves the way to a novel class of silicon diamond-lattice bandgap crystals that can be obtained through self-assembly. Such a self-assembly approach would allow for easy integration of these highly photonic crystals in existing silicon microfluidic and -electronic systems.
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42.70.Qs Photonic bandgap materials
81.05.ug Diamond
71.20.Tx Fullerenes and related materials; intercalation compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effect of deposition parameters and semi-empirical relations between non-linear refractive index with linear refractive index and third order susceptibility for a-Ge20Se70-xIn10Bix thin films

Ishu Sharma, S. K. Tripathi, and P. B. Barman

J. Appl. Phys. 110, 043108 (2011); http://dx.doi.org/10.1063/1.3626043 (7 pages) | Cited 1 time

Online Publication Date: 24 August 2011

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Present work reports the influence of deposition parameters, i.e., the effect of the type of substrate on the optical properties of a-Ge20Se70-xIn10Bix (x = 0, 2, 4, 6, 8, and 10) thin films. Optical constants were accurately determined by envelope method using transmission spectra in the wavelength region of 400–1800 nm. The order obtained for the refractive index is nmica > nmicroscope glass > nquartz for different substrates used in the deposition of thin films. The bandgap of the film deposited on mica substrate is smallest as compared to the bandgap of the films deposited on microscopic glass and quartz. To open the possibility of the use of chalcogenide glasses for non-linear switching, these vitreous systems were studied with respect to their non-linear susceptibility and refractive index. Third-order optical susceptibility (χ(3)) is evaluated from changes of index of refraction using Wang approximations. We examined the dependence of susceptibility on the absorption edge, thereby showing that the susceptibility rapidly increases with the redshift in absorption edge. Different formulations were used to predict the non-linear behavior of the Ge-Se-In-Bi system. The linear refractive index and Wemple-DiDomenico parameters were used for the determination of nonlinear refractive index in the wavelength region of 400 to 1800 nm. The addition of Bi drastically increases the non-linear refractive index. In amorphous materials, maximum optical non-linearity has been predicted at a telecommunication wavelength (∼1550 nm). Comparison of our results shows a good agreement with values available in the literature at 0.8 eV or 1550 nm. Non-linear refractive indices, three orders higher than silica glass, were obtained in the system under investigation. The obtained results may lead to yield more sensitive optical limiting devices, and these glasses may be used as an optical material for a high speed communication fiber.
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81.05.Gc Amorphous semiconductors
42.70.Ce Glasses, quartz
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses

Crystal-field analysis and Zeeman splittings of energy levels of Nd3+ (4f3) in GaN

John B. Gruber, Gary W. Burdick, Nathaniel T. Woodward, Volkmar Dierolf, Sreerenjini Chandra, and Dhiraj K. Sardar

J. Appl. Phys. 110, 043109 (2011); http://dx.doi.org/10.1063/1.3625259 (6 pages)

Online Publication Date: 25 August 2011

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The crystal-field splitting and Zeeman splitting of energy levels of Nd3+ (4f3) doped into semi-conducting GaN (3.2 eV) grown in the hexagonal (huntite) phase by plasma-assisted molecular beam epitaxy have been modeled using a parameterized Hamiltonian defined to operate within the complete 4f3 electronic configuration of Nd3+ substituted for Ga3+ in the lattice. Zeeman splittings were obtained by applying magnetic fields up to 6.6 T with the fields parallel and perpendicular to the crystallographic c-axis. The experimental energy (Stark) levels were obtained from a recent spectroscopic study on the same samples, where the combined excitation emission spectroscopy (CEES) identified the majority of Nd3+ ions as replacing Ga3+ in sites of C3v symmetry. The manifolds of Nd3+ (4f3)2S+1LJ modeled for the crystal-field splitting include the ground state, 4I9/2, and excited states 4I11/2, 4I13/2, 4F3/2, 4F5/2, 2H9/2, 4F7/2, 4S3/2, 4G5/2, and 4G7/2. The energies of 41 experimental Stark levels from these manifolds were modeled through the use of a Monte Carlo method in which independent crystal-field parameters (CFP) were given random starting values and optimized using standard least-squares fitting between calculated and experimental Stark levels. Irreducible representations (irreps) and crystal field quantum numbers (μ) were assigned to the energy level states of the 4I9/2 and 4F3/2 multiplet manifolds based on an analysis of the Zeeman data. This allows determination of which of the competing local minima should be considered to be the physically significant minimum. Using standard least-squares fitting between calculated and experimental Stark levels for Nd3+ in C3v symmetry, we obtain a final standard deviation of 7.01 cm−1 (rms = 5.48 cm−1).
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71.70.Ch Crystal and ligand fields
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
81.05.Ea III-V semiconductors
52.77.-j Plasma applications
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.10.Hf Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems

Infrared plasmons on heavily-doped silicon

James C. Ginn, Robert L. Jarecki, Jr., Eric A. Shaner, and Paul S. Davids

J. Appl. Phys. 110, 043110 (2011); http://dx.doi.org/10.1063/1.3626050 (6 pages) | Cited 4 times

Online Publication Date: 25 August 2011

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We examine the long-wave infrared (LWIR) optical characteristics of heavily-doped silicon and explore engineering of surface plasmons polaritons (SPP) in this spectral region. Both phosphorus (n-type Si) and boron (p-type Si) implants are evaluated and various cap layers and thermal annealing steps are examined. The optical properties are measured using ellipsometry and fit to a Drude model for the infrared (IR) permittivity. The predicted metallic behavior for Si in the thermal IR and its impact on the spatial confinement and dispersion for surface plasmons is studied. We find that the transverse spatial confinement for a surface plasmon on highly doped Si is strongly sub-wavelength near the plasma edge, and the confinement to the surface is enhanced to greater than 10× that of the metal confined SPP over the entire LWIR spectrum.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.-j Infrared and Raman spectra
61.72.uf Ge and Si
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Size induced structural modifications in copper oxide nanoparticles synthesized via laser ablation in liquids

A. Nath and A. Khare

J. Appl. Phys. 110, 043111 (2011); http://dx.doi.org/10.1063/1.3626463 (6 pages) | Cited 1 time

Online Publication Date: 26 August 2011

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Laser induced breakdown at copper-water interface is employed to synthesize copper oxide nanoparticles. Copper forms two stable oxides: monoclinic CuO and cubic Cu2O. The characteristic traits of laser induced plasma at copper-water interface are altered to analyze the size induced structural modifications in these oxides. The properties of laser produced plasma were varied by changing the focusing conditions of the source laser. Tightly focused condition led to formation of CuO of size ≤ 200 nm whereas laser defocusing condition produces nanocolloids of Cu2O of size less than 10 nm. These findings were attributed to high pressure (60 GPa) accompanied by high temperature at tightly focused condition which results in growth of covalent CuO whereas lower pressure (1.3 GPa) and low temperature at defocused condition probably forms symmetric Cu2O.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Design of resonant-cavity-enhanced multi-band photodetectors

Yan-Feng Lao, Gamini Ariyawansa, and A. G. Unil Perera

J. Appl. Phys. 110, 043112 (2011); http://dx.doi.org/10.1063/1.3626812 (7 pages)

Online Publication Date: 26 August 2011

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A theoretical analysis to improve the quantum efficiency of detectors sensing in multiple spectral bands is presented. The effective coupling between the incoming light and multiple absorbing regions for simultaneously improving the multi-band absorption efficiency is obtained by using resonant-cavity structures. An optimized cavity with only a Au bottom reflector gives rise to an enhancement factor of 11 in absorption compared to the conventional detector without the cavity. Further improvement, by a factor of 26, can be attained with the aid of a dual-band Bragg reflector placed at the top. The resulting multi-band resonant-cavity detector increases the response in three out of four detection bands contributing to the spectral range from visible to long-wave infrared (IR). The optimized detector is capable of serving multiple purposes, such as regular IR detection for atmospheric windows, gas sensing, and for optical communications.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Reflectance spectrum of plasmon waveguide interband cascade lasers and observation of the Berreman effect

Robert T. Hinkey, Zhaobing Tian, Rui Q. Yang, Tetsuya D. Mishima, and Michael B. Santos

J. Appl. Phys. 110, 043113 (2011); http://dx.doi.org/10.1063/1.3627172 (8 pages) | Cited 4 times

Online Publication Date: 30 August 2011

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Noninvasive infrared reflectance measurements have been explored as a method for studying the optical properties of Si-doped cladding layers of plasmon waveguide interband cascade lasers. Measurements and theoretical simulations of the reflectance spectra were carried out on both the laser structures themselves, as well as highly doped InAs films grown on GaAs substrates. We have found that there is a sharp drop in the signal of the reflectance spectrum for p-polarized light oscillating near the plasma frequency. This is a manifestation of the so-called Berreman effect, which occurs at frequencies where the dielectric function approaches zero. This is distinct from the plasma edge feature seen in the reflectance spectrum of thick samples. The plasma frequencies of the highly doped layers were obtained by identifying the Berreman feature in the measured spectrum and fitting the spectrum to a modeled curve. Using a model for the effective mass, we were able to obtain measurements of the conduction electron concentration (in a range from 1018 to 1019 cm−3) in the waveguide cladding layers with values that were in good agreement with those found using Hall effect and SIMS measurements. The reflectance data was effectively used to achieve better calibration of the Si-doping during the growth of the n++-type InAs layers in the plasmon waveguide laser structures.
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07.60.-j Optical instruments and equipment
42.55.Px Semiconductor lasers; laser diodes
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Fishnet metastructure for efficiency enhancement of a thin film solar cell

Liming Ji and Vasundara V. Varadan

J. Appl. Phys. 110, 043114 (2011); http://dx.doi.org/10.1063/1.3626827 (8 pages)

Online Publication Date: 31 August 2011

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We propose embedment of a fishnet metastructure in the back passivation layer for enhancing the efficiency of hydrogenated amorphous silicon (a-Si:H) thin film solar cells. Incident light excites a plasmon resonance that results in frequency dependent effective impedance for the embedding layer so that the input impedance satisfies impedance matching condition. Reflection is very low under this condition. A planar 20 nm-thick fishnet structure is embedded in the back passivation layer of the solar cell to enhance light absorption near the bandgap of a-Si:H. This enhancement remains over a wide range of incident angles. Detailed electromagnetic modeling of the absorption in different layers of the solar cell is performed. Only absorption in the a-Si:H is included in computing the photocurrent generation. 64% of the total absorbed energy at resonance is in the silicon layer and this absorption is uniformly distributed inside the silicon. Based on the enhancement of photocurrent density near the bandgap of a-Si:H, we obtained 14.8% enhancement in total short circuit current at normal incidence and the estimated PV efficiency of the solar cell with the fishnet is 7.43% at normal incidence compared to 6.36% without fishnet. The fishnet can be tuned to provide absorption enhancement at any desired frequency where the intrinsic absorption of the semiconductor is low.
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88.40.H- Solar cells (photovoltaics)
82.45.Bb Corrosion and passivation
81.65.Rv Passivation
72.40.+w Photoconduction and photovoltaic effects

Impact of nonpolar AlGaN quantum wells on deep ultraviolet laser diodes

K. Kojima, A. A. Yamaguchi, M. Funato, Y. Kawakami, and S. Noda

J. Appl. Phys. 110, 043115 (2011); http://dx.doi.org/10.1063/1.3627180 (7 pages) | Cited 1 time

Online Publication Date: 31 August 2011

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The radiation properties of nonpolar AlGaN quantum wells (QWs) were theoretically investigated by comparing them to those of c-plane AlGaN QWs with heavy holes as the top valence band (VB). First, the conditions to minimize the threshold carrier density of c-plane QW laser diodes were explored. A thin well width (∼1 nm) and reduction of the Al content in the well layer were important to reduce threshold carrier density because narrow wells suppressed the quantum confined Stark effect and AlGaN with a lower Al content had a lower density of states. Moreover, the emission wavelength was widely controlled by tuning the Al contents of both the well and barrier layers under the proposed conditions. Then the properties of nonpolar AlGaN QWs were investigated. Nonpolar AlGaN had several superior characteristics compared to c-plane QWs, including large overlap integrals, optical polarization suitable for both edge and surface emissions, an almost linearly polarized optical dipole between the conduction band and top VB due to the isolated VBs, and a reduced VB density of state. Finally, the threshold carrier densities of both nonpolar and optimized c-plane QWs were compared as functions of the transition wavelength. At a given wavelength, the threshold of nonpolar QWs was lower than that of c-plane ones. Particularly below 260 nm, nonpolar QWs had a low threshold, whereas that of c-plane QWs drastically increased due to the large VB mass of AlN and carrier population in the crystal-field splitting band.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
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