Optical characteristics of III-nitride quantum wells with different crystallographic orientations (original) (raw)
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A program for self-consistent modeling of electron-hole energy spectrum and space-charge distribution in III-nitride based quantum well (QW) structures has been developed. The program assumes arbitrary crystallographic orientation of the heterostructure template. The model takes into consideration full 6-band description of the valence band states, nonparabolicity of the electron spectrum, quantum confinement of electrons and holes, strain induced modifications of the band structure, spontaneous-and piezo-polarization fields, background layer doping, and variable level of charge carrier injection. Calculated optical characteristics include electron-hole optical susceptibility, spontaneous and stimulated emission rates, polarization coefficients for light emission and absorption, radiative recombination rates, and optical gain spectra in optically active nitride QWs.
Optimum quantum well width for III-nitride nonpolar and semipolar laser diodes
Applied Physics Letters, 2009
The advantage of using wider quantum wells in III-nitride lasers offered by nonpolar/semipolar technology is limited by narrower valence subband separation, thermal hole redistribution, and resulting optical gain degradation in wider wells. We show that corresponding increase in radiative carrier lifetime in wider quantum wells can lower the laser threshold, thus inferring the existence of an optimum quantum well width for laser design.
Japanese Journal of Applied Physics, 2021
In this paper we review the recent studies on wide InGaN quantum wells (QWs). InGaN QWs are known to suffer from an extremely high built-in piezoelectric polarization, which separates the electron and hole wavefunctions and causes the quantum-confined Stark effect. We show both by means of modeling and experimentally, that wide InGaN QWs can have quantum efficiency superior to commonly used thin QWs. The high efficiency is explained by initial screening of the piezoelectric field and subsequent emergence of optical transitions involving the excited states of electrons and holes, which have a high oscillator strength. A high pressure spectroscopy and photocurrent measurements are used to verify the mechanism of recombination through excited states. Furthermore, the influence of QW width on the properties of optoelectronic devices is studied. In particular, it is shown how the optical gain forms in laser diodes with wide InGaN QWs.
Journal of Applied Physics, 2010
Carrier confinement and injection characteristics of polar and nonpolar III-nitride quantum well ͑QW͒ light-emitting diode or laser diode structures are compared. We demonstrate that strongly inhomogeneous QW injection in multiple-QW ͑MQW͒ active region is one of the possible reasons holding back the advance of nonpolar laser structures. In polar structures, strong interface polarization charges induce the nonuniform carrier distribution among the active QWs so that the extreme p-side QW always dominates the optical emission. On the contrary, in nonpolar MQW structures, the inhomogeneity of QW populations is supported mainly by QW residual charges and the prevailing QW is the one closest to the n-side of the diode. For both polar and nonpolar structures, the QW injection inhomogeneity is strongly affected by the QW carrier confinement and becomes more pronounced in longer wavelength emitters with deeper active QWs. We show that in nonpolar structures indium incorporation into optical waveguide layers improves the uniformity of QW injection. On the contrary, QW injection in polar structures remains inhomogeneous even at high-indium waveguide layer compositions. We show, however, that polarization-matched design of the electron-blocking layer can noticeably improve the injection uniformity in polar MQW structure and enhance the structure internal quantum efficiency.
COMSOL-based Ostendo's Opto-electronic Device Modeling Software (ODMS) has been updated to include effects of non-equilibrium QW populations in semiconductor light-emitting and laser diodes. III-nitride light emitters with different levels of polarity have been compared as an illustrative example of ODMS performance. Modeling proved that high intra-QW recombination rates in III-nitride light emitters make the QW populations strongly non-equilibrium and vulnerable to inhomogeneous injection in multiple-QW devices. QW popu-lations are further affected by disparate electron and hole transport across the active region.
Optical properties of group-III nitride quantum wells and quantum boxes
Journal of Physics: Condensed Matter, 2001
We propose an overview of specific optical properties of quantum-size artificial structures made of group-III nitride semiconductors with natural wurtzite symmetry. We consider the cases of quantum wells and of quantum boxes obtained by the Stranski-Krastanov growth mode. We comment on results of continuous-wave and time-resolved optical spectroscopy, in comparison with our envelope-function calculations of excitonic energies and oscillator strengths. The influence on recombination dynamics of internal electric fields and carrier localization is discussed in detail.
Modeling of III-Nitride Multiple-Quantum-Well Light-Emitting Structures
IEEE Journal of Selected Topics in Quantum Electronics, 2000
Spatial inhomogeneity of carrier injection across the multiple quantum well (MQW) active region of a semiconductor light emitter can impose severe limitations on the device efficiency. In III-nitride based devices, the large disparity of electron and hole transport and the excessive depth of active QWs trigger the process of inhomogeneous QW injection which is further aggravated by strong dependence of QW radiative characteristics on the QW injection conditions due to (i) intra-QW screening of polarization fields in polar and semipolar materials, (ii) phase-space filling effect in lowest QW subbands at higher levels of carrier injection, and (iii) exceedingly nonequilibrium character of the electron and hole populations in deep QWs. All these tendencies become more pronounced in longer-wavelength emitters. The residual QW charges provide strong feedback to the QW injection conditions thus requiring a high level of self-consistency between the active region transport simulation and the QW emission modeling.
N-polar III-nitride quantum well light-emitting diodes with polarization-induced doping
Applied Physics Letters, 2011
Nitrogen-polar III-nitride heterostructures present unexplored advantages over Ga(metal)-polar crystals for optoelectronic devices. This work reports N-polar III-nitride quantum-well ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy that integrate polarization-induced p-type doping by compositional grading from GaN to AlGaN along N-face. The graded AlGaN layer simultaneously acts as an electron blocking layer while facilitating smooth injection of holes into the active region, while the built-in electric field in the barriers improves carrier injection into quantum wells. The enhanced doping, carrier injection, and light extraction indicate that N-polar structures have the potential to exceed the performance of metal-polar ultraviolet light-emitting diodes.
III-nitride nanostructures have recently emerged as promising materials for new intersubband (ISB) devices in a wide variety of applications. These ISB technologies rely on infrared optical transitions between quantum-confined electronic states in the conduction band of GaN/Al(Ga)N nanostructures, namely quantum wells or quantum dots. The large conduction band offset (about 1.8 eV for GaN/AlN) and sub-picosecond ISB relaxation of III-nitrides render them appealing materials for ultrafast photonic devices in near-infrared telecommunication networks. Furthermore, the large energy of GaN longitudinal-optical phonons (92 meV) opens prospects for high-temperature THz quantum cascade lasers and ISB devices covering the 5-10 THz band, inaccessible to As-based technologies due to phonon absorption. In this paper, we describe the basic features of ISB transitions in III-nitride quantum wells and quantum dots, in terms of theoretical calculations, material growth, spectroscopy, resonant transport phenomena, and device implementation. The latest results in the fabrication of control-by-design devices such as all-optical switches, electro-optical modulators, photodetectors, and lasers are also presented.