POLARIZATION OF HOT PHOTOLUMINESCENCE IN QUANTUM-WELLS AND HEAVY-LIGHT HOLE MIXING

Hot electrons excited from the valence band by linearly polarized laser light are characterized by certain angular distributions in momenta. Owing to such angular distributions in momenta, the photoluminescence from the hot electrons shows a certain degree of polarization. A theoretical treatment of this effect observed in the photoluminescence in quantum wells is given, showing that the effect depends strongly on heavy and light hole mixing. The very large disparity between the experimentally observed and theoretically expected values of the degree of polarization in the hot-electron photoluminescence suggests the presence of random quasielastic scattering. The effects of such additional scattering and the presence of a perpendicular magnetic field are incorporated into the theory. it is shown that the measurements of the degree of polarization observed in the hot electron photoluminescence, with and without an applied perpendicular magnetic field can serve to determine the time constants for both LO-phonon inelastic and random quasielastic scattering. As an example, these time constants are determined for the experiments reported in the literature.

808 nm high-power laser grown by MBE through the control of Be diffusion and use of superlattice

808 nm high-power laser diodes are gown by MBE. In the laser structure, the combination of Si-doped GRIN (graded-index) region adjacent to n-AlGaAs cladding layer with reduced Be doping concentration near the active region has been used to diminish Be diffusion and oxygen incorporation. As compared with the laser structure which has undoped GRIN region and uniform doping concentration for Si and Be, respectively, in the cladding layers, the slope efficiency has increased by about 8%. Typical threshold current density of 300 A/cm(2) and the minimum threshold current density of 220 A/cm(2) for lasers with 500 mu m cavity length are obtained. A high slope efficiency of 1.3 W/A for coated lasers with 1000 mu m cavity length is also demonstrated, Recorded CW output power at room temperature has reached 2.3 W.

Deep centers in AlGaAs/GaAs GRIN-SCH SQW laser structures grown by MBE and MOCVD

The deep centers in AlGaAs/GaAs graded index-separate confinement heterostructure single quantum well (GRIN-SCHSQW) laser structures grown by MBE and MOCVD have been investigated using deep level transient spectroscopy (DLTS) technique, The majority and minority carrier DLTS spectra show that the deep (hole and electron) traps (Hi and E3), having large capture cross sections and concentrations, are observed in the graded n-AlxGa1-xAs layer of laser structures in addition to the well-known DX centers. For laser structures grown by MBE, the deep hole trap H1 and the deep electron trap E3 may be spatially localized in the interface regions of discontinuous variation Al mole fraction of the n-AlxGa1-xAs layer with x = 0.20-0.43. For laser structures grown by MOCVD, the deep electron trap E3 may be spatially localized in the n-AlxGa1-xAs layer with x = 0.18-0.30, and the DX center may be spatially localized in the interface regions of discontinuous variation Al mole fraction of the AlxGa1-xAs layer with x = 0.22-0.30.

Shubnikov de Haas oscillations of a two-dimensional electron gas in a modulation-doped Zn0.80Cd0.20Se/ZnS0.06Se0.94 single quantum well

The magnetotransport properties of the two-dimensional (2D) electron gas confined in a modulation-doped Zn0.80Cd0.20Se/ZnS0.06Se0.94 single quantum well structure were studied at temperatures down to 0.35 K in magnetic fields up to 7.5 T. Well resolved 2D Shubnikovde Haas (SdH) oscillations were observed, although the conductivity of the sample in the as grown state was dominated by a bulk parallel conduction layer. After removing most of the parallel conduction layer by wet chemical etching the amplitude and number of SdH oscillations increased. From the temperature dependence of the amplitude the effective mass of the electrons was estimated as 0.17 m(0). Copyright (C) 1996 Published by Elsevier Science Ltd

Valence hole subbands and optical gain spectra of GaN/Ga1-xAlxN strained quantum wells

The valence hole subbands, TE and TM mode optical gains, transparency carrier density, and radiative current density of the zinc-blende GaN/Ga0.85Al0.15N strained quantum well (100 Angstrom well width) have been investigated using a 6 X 6 Hamiltonian model including the heavy hole, Light hole, and spin-orbit split-off bands. At the k = 0 point, it is found that the light hole strongly couples with the spin-orbit split-off hole, resulting in the so+lh hybrid states. The heavy hole does not couple with the light hole and the spin-orbit split-off hole. Optical transitions between the valence subbands and the conduction subbands obey the Delta n=0 selection rule. At the k not equal 0 points, there is strong band mixing among the heavy hole, light hole, and spin-orbit split-off hole. The optical transitions do not obey the Delta n=0 selection rule. The compressive strain in the GaN well region increases the energy separation between the so1+lh1 energy level and the hh1 energy level. Consequently, the compressive strain enhances the TE mode optical gain, and strongly depresses the TM mode optical gain. Even when the carrier density is as large as 10(19) cm(-3), there is no positive TM mode optical gain. The TE mode optical gain spectrum has a peak at around 3.26 eV. The transparency carrier density is 6.5 X 10(18) cm(-3), which is larger than that of GaAs quantum well. The compressive strain overall reduces the transparency carrier density. The J(rad) is 0.53 kA/cm(2) for the zero optical gain. The results obtained in this work will be useful in designing quantum well GaN laser diodes and detectors. (C) 1996 American Institute of Physics.

TAILORED DFB LASER PROPERTIES BY INDIVIDUALLY CHIRPED GRATINGS USING BENT WAVE-GUIDES

DFB lasers with continuously and arbitrarily chirped gratings of ultrahigh spatial precision are implemented by a method we proposed recently, using bent waveguides on homogeneous grating fields. Choosing individual bending functions we generate special chirping functions and obtain additional degrees of freedom to tailor and improve specific device performances, We present two applications for lasers showing several improved device properties and the effectiveness of our method, First, we implement continuously distributed phase-shifted lasers, revealing a considerably reduced photon pile-up, higher single-longitudinal mode stability, higher output power, lower linewidth, and higher yield than conventional abruptly phase-shifted lasers, Second, a novel tuning principle is applied in chirped multiple-section DFB lasers, showing 5.5-nm wavelength tuning, without any gaps, maintaining high side-mode suppression.

A RESONANT RAMAN-STUDY ON PHONONS IN GAINAS/ALINAS MULTIPLE-QUANTUM WELLS

The LO phonon modes in the barrier layers of a GaInAs/AlInAs multiple quantum well structure are investigated by resonance Raman scattering (RRS), the excitation laser photon energy tuned to resonate with the above barrier interband transition energy. The resonance enhancement of LO phonon peaks are shown to be caused by Frohlich electron-phonon interaction. The pressure-dependent profiles for both AlAs-like (LO(2) mode) and InAs-like (LO(1) mode) Raman peak intensities are well fitted by the Gaussian lineshape. The shift between these two profiles can be explained by the outgoing RRS mechanism, providing information on the pressure-induced shift of the excitonic transition energy. The amplitude ratios of the two profiles are close to 1, showing a well defined two-mode behavior and the nearly equal polarizability for Al-As and In-As bonds in AlInAs alloy.

An asymmetric broad waveguide structure for a 0.98-μm high-conversion-efficiency diode laser

A novel asymmetric broad waveguide diode laser structure was designed for high power conversion efficiency (PCE). The internal quantum efficiency, the series resistance, and the thermal resistance were theoretically optimized. The series resistance and the thermal resistance were greatly decreased by optimizing the thickness of the P-waveguide and the P-cladding layers. The internal quantum efficiency was increased by introducing a novel strain-compensated GaAs_0.9P_0.1/InGaAs quantum well. Experimentally, a single 1-cm bar with 20% fill factor and 900 μm cavity length was mounted P-side down on a microchannel-cooled heatsink, and a peak PCE of 60% is obtained at 26.3-W continuous wave output power.The results prove that this novel asymmetric waveguide structure design is an efficient approach to improve the PCE.

1.3-μm uncooled 10 Gb/s directly modulated MQW AlGaInAs/InP laser diodes

In this paper, we report a novel 1.3-μm uncooled AlGaInAs/InP multiple quantum well (MQW) ridge waveguide laser diodes. By optimizing the design of MQW structure and facet coatings, together with the application of reversed-mesa ridge waveguide (RM-RWG) structure, polyimide planarization, and lift-off processes technology, an uncooled 1.3-μm, 10-Gb/s directly modulated MQW ridge waveguide laser diode was successfully fabricated. The threshold current and the slope efficiency were 7 mA and 0.48 mW/mA, respectively. The directly modulated bandwidths of 11 and 9.2 GHz were achieved at room temperature and 80 Celsius degrees, respectively.

Offset quantum-well method for tunable distributed Bragg reflector lasers and electro-absorption modulated distributed feedback lasers

A two-section offset quantum-well structure tunable laser with a tuning range of 7 nm was fabricated using offset quantum-well inethod. The distributed Bragg reflector （DBR） was realized just by selectively wet etching the multiquantum-well （MQW） layer above the quaternary lower waveguide. A threshold current of 32 mA and an output power of 9 mW at 100 mA were achieved. Furthermore, with this offset structure method, a distributed feedback （DFB） laser was integrated with an electro-absorption modulator （EAM）, which was capable of producing 20 dB of optical extinction.

Widely Tunable Sampled-Grating DBR Laser

The 3-section SG-DBR tunable laser is fabricated using an ion implantation quantum-well intermixing process. The over 30nm discontinuous tuning range is achieved with the SMRS greater than 30dB.

A 1.3μm Low-Threshold Edge-Emitting Laser with AlInAs-Oxide Confinement Layers

A 1.3μm low-threshold edge-emitting AlGaInAs multiple-quantum-well(MQW) laser with AlInAs-oxide confinement layers is fabricated.The Al-contained waveguide layers upper and low the active layers are oxidized as current-confined layers using wet-oxidation technique.This structure provides excellent current and optical confinement,resulting in 12.9mA of a low continuous wave threshold current and 0.47W/A of a high slope efficiency of per facet at room temperature for a 5-μm-wide current aperture.Compared with the ridge waveguide laser with the same-width ridge,the threshold current of the AlInAs-oxide confinement laser has decreased by 31.7% and the slope efficiency has increased a little.Both low threshold and high slope efficiency indicate that lateral current confinement can be realized by oxidizing AlInAs waveguide layers.The full width of half maximum angles of the Al-InAs-oxide confinement laser are 21.6° for the horizontal and 36.1° for the vertical,which demonstrate the ability of the AlInAs oxide in preventing the optical field from spreading laterally.

Quantum Well Intermixing of InGaAsP QWs by Impurity Free Vacancy Diffusion Using SiO_2 Encapsulation

Experiment on quantum well intermixing (QWI) of InGaAsP QWs by impurity free vacancy diffusion (IFVD) using SiO_2 encapsulation is reported. A maximum band gap wavelength blue-shift as large as 200nm is realized. Furthermore, an FP laser blue-shifted 21nm by QWI is fabricated with characteristics comparable with the asgrown one.