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Multiple Quantum Wells (multiple + quantum_well)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Low thermal resistance, high-speed 980 nm asymmetric intracavity-contacted oxide-aperture VCSELs

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009
Y. M. Song
Abstract We demonstrated high-speed characteristics of an oxide-aperture vertical-cavity surface-emitting laser (VCSEL) with intracavity structures for both p- and n-contacts, based on InGaAs/GaAs multiple quantum wells operating at , , 980 nm, indicating a low thermal resistance (Rth). The asymmetric current injection scheme is employed for reducing current crowding around the rim of the oxide aperture. A high aluminium content undoped Al0.88Ga0.12As and GaAs distributed Bragg reflector (DBR) mirror is used for efficient heat dissipation. The VCSEL with a 7 ,m oxide aperture exhibited an output power of 2.5 mW and a threshold current of 0.8 mA with a slope efficiency of 0.39 mW/mA at 20 °C under continuous-wave operation and it still worked with 1.3 mW at 90 °C. The temperature tuning coefficient of 0.081 nm/°C and dissipated electrical power tuning coefficient of 0.104 nm/mW were observed, leading to a low Rth of 1.28 °C/mW. A high modulation bandwidth up to 13 GHz with a modulation current efficiency factor of 6.1 GHz/mA1/2 was achieved. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wells

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006
Hamid Haratizadeh
Abstract We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time-resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Development of CdSSe/CdS VCSELs for Application to Laser Cathode Ray Tubes

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2004
K. P. O'Donnell
Abstract This report summarises recent progress towards the realisation of Laser Cathode Ray Tube (LCRT) devices on the basis of II,VI semiconductors. Although such devices were demonstrated over 30 years ago, using bulk crystalline materials as the active media, practical lasers that operate at room temperature for extended periods of time are not yet readily available. We aim to overcome this roadblock by reducing the threshold power densities of working lasers. By embedding heterostructures, grown using metalorganic vapour phase epitaxy (MOVPE), within all-dielectric microcavities, the necessary threshold reductions can be made. The construction and testing of an exemplar device, based upon CdSSe/CdS (hex) multiple quantum wells, is described. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Strong ultraviolet emission from non-polar AlGaN/GaN quantum wells grown over r -plane sapphire substrates

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
W. H. Sun
Abstract GaN and GaN/Al0.25Ga0.75N multiple quantum wells (MQWs) over c - and r -plane sapphire substrates have been grown by metal-organic chemical vapor deposition. A comparative study of photoluminescence (PL) in GaN epitaxial layers and AlGaN/GaN MQWs on these two types of substrates is reported. At low excitation levels, the measured room temperature PL signal in GaN layers grown over r -plane sapphire was more than order of magnitude lower than in GaN on c -plane substrates. In contrast, the emission intensity from AlGaN/GaN MQWs grown over r -plane substrates was almost 30 times stronger than in the structures grown over c -plane sapphire. Furthermore, with excitation power density up to 1 MW/cm2, the PL peak position for the non-polar MQWs kept completely stable whereas the one for the c -plane structures exhibited a blue shift as large as 250 meV. We attribute this large difference in the ultraviolet emission intensity to the suppression of a strong quantum Stark effect in the AlGaN/GaN MQWs on the r -plane sapphire. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optically pumped lasing and gain formation properties in blue Inx Ga1,x N MQWs

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004
K. Kojima
Abstract Lasing and gain formation properties have been studied in an InxGaN1,x multiple quantum wells lasing at around 460 nm by employing the modified variable stripe length method (VSLM) and pump and probe spectroscopy (P&P). It was found that the spontaneous emission (Esp) appeared far below absorption edge (Ea) that is observed as a photo-bleaching negative-peak in P&P, indicating the formation of localized tail states. Lasing peaks appeared in between Esp and Ea with wide spectral distribution. This is consistent with the results where VSLM revealed the broad feature of optical gain spectra associated with rapid peak saturation of lasing even just above the threshold photo-pumping power density. Such mechanism observed in In-rich InxGa1,xN MQWs is contributed not only from the broad distribution of localized density-of-states but also from hot carrier distribution (determined by Maxwell,Boltzmann statistics), temperature of which is raised up due to long energy relaxation time to localized tail states. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Large excitation-power dependence of pressure coefficients of InxGa1,xN/InyGa1,yN quantum wells

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
Q. Li
Abstract Excitation-power dependence of hydrostatic pressure coefficients (dE/dP) of InxGa1,xN/InyGa1,yN multiple quantum wells is reported. When the excitation power increases from 1.0 to 33 mW, dE/dP increases from 26.9 to 33.8 meV/GPa, which is an increase by 25%. A saturation behavior of dE/dP with the excitation power is observed. The increment of dE/dP with increasing carrier density is explained by an reduction of the internal piezoelectric field due to an efficient screening effect of the free carriers on the field. [source]

Asymmetric barrier composition GaN/(Ga,In)N/(Al,Ga)N quantum wells for yellow emission

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
Benjamin Damilano
Abstract It is shown that by using asymmetric barrier composition GaN - (Ga,In)N (GaInN) - (Al, Ga)N (AlGaN) multiple quantum wells it is possible to redshift the room temperature photoluminescence wavelength from 503 nm (blue-green) to 577 nm (yellow) when the Al composition in the AlGaN barrier increases from 0 to 0.15. This is obtained without modifying the GaInN QW composition and thickness. This effect is attributed to an increase of the internal electric field inside the GaInN QW originating to additional polarization charges at the AlGaN - GaN and GaInN - AlGaN interfaces. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Mechanism of thermal degradation in GaInN/GaN quantum wells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
H. Bremers
Abstract In this contribution we focus on degradation processes of GaInN multiple quantum wells (MQWs) used in laser structures grown by metallorganic vapor pressure epitaxy (MOVPE). The influence of ramp-up time as well as the maximum temperature during growth of the barrier on the quantum well (QW) is investigated. Comparison of X-ray and photoluminescence (PL) measurements implies that a sufficient thickness of a cover layer grown at low temperature is required to prevent degradation of the QW. In a next step samples were grown using an optimal thermal budget during growth of the active region to investigate the influence of capping layers. To improve crystalline quality of these layers high temperatures are required. Our measurements show that these high temperatures lead to a decrease in average indium concentration of the QWs. This decrease is temperature as well as time dependent (, ,t) and can only explained by diffusion processes. The activation energies are in the range 0.7-0.9 eV (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Fabrication and optical properties of nano-structured semipolar InGaN/GaN quantum wells on c-plane GaN template

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
Hongbo Yu
Abstract High density self-assembled nanostructured semipolar (NSSP) GaN pyramids are fabricated based on c-plane GaN template by in situ silane treatment followed by high temperature treatment. Semipolar InGaN/GaN multiple quantum wells (MQWs) were subsequently grown on the NSSP GaN. Optical properties of the MQWs were studied by temperature- dependent and excitation density varied photoluminescence. It was found that the internal electric field in the NSSP MQWs were remarkably reduced in comparison with planar c-plane MQWs. The internal quantum efficiency of the NSSP MQWs was measured to be > 30% which showed potential applications in III-nitride light emitters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Defect density dependence of carrier dynamics in AlGaN multiple quantum wells grown on GaN substrates and templates

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
G. A. Garrett
Abstract Subpicosecond time-resolved photoluminescence (TRPL) has been used to compare the room temperature carrier dynamics in Al0.1Ga0.9N/Al0.3Ga0.7N multiple quantum well (MQW) structures simultaneously deposited on a high quality free standing HVPE GaN substrate (dislocation density ,1 × 107cm,2) and 1 µm MOCVD GaN template on sapphire. The PL lifetime of ,500 ps in the MQW on GaN substrate is about 5 times longer than that for the MQW on GaN template, with a concomitant increase in CW PL intensity. This behavior is attributed primarily to an increase in nonradiative lifetime associated with a 100 times reduction in dislocation density in the GaN substrate. The observation that the PL lifetime in the MQW falls short of the ,900 ps dominant decay time in the GaN substrate may be indicative of generation of additional defects and dislocations due to substrate surface preparation, strain relaxation, and nonoptimal growth temperature associated with the difference in heating of the thin GaN template on sapphire and the thick GaN substrate. An extended PL rise time of greater than 20 ps for the MQW emission when above barrier pumping is employed implies that both wells and barriers are of high quality. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]