Strained Single Quantum Well Research Articles

Measurement of junction temperature and thermal resistance in InGaAlAs/AlGaAs quantum-well superluminescent diodes (SLDs)

This paper reports on the experimental method of the determination of junction temperature and thermal resistance in 840 nm InGaAlAs/AlGaAs compressive strained single quantum well (SQW) superluminescent diodes (SLDs). The linear relation between forward voltage and junction temperature clearly occurs by utilizing the forward voltage–temperature ([Formula: see text]–[Formula: see text]) method. The temperature coefficient [Formula: see text] has been determined. Under 100 mA continuous-wave (CW) operation condition, the thermal resistance is measured to be 81.6[Formula: see text]C/W, which is not significantly different with the theoretical calculation result.

Nonlocal optical properties in InGaN/GaN strained quantum wells with a strong built-in electric field

Based on the microscopic nonlocal optical response theory, the linear and nonlinear intersubband optical absorption properties in InyGa1−yN/GaN strained single quantum wells (SQWs) with a strong built-in electric field are investigated. The numerical results show that the optical absorption spectrum has an obvious blueshift originating from the nonlocal optical responses. The dependence of the blueshift on the SQW width and the mixing fraction y is clarified. In addition, the influence of the SQW structural parameters, the incident light intensity, and the incident angle on the optical absorption properties is demonstrated. These properties are desirable for controlling the nonlocal effect and optical absorption loss in optical device application.

Quantum beats of type-I and type-II excitons in an InxGa1−xAs/GaAs strained single quantum well

We have investigated the quantum beat of the type-I heavy-hole (HH) and the type-II light-hole (LH) excitons in an In0.15Ga0.85As/GaAs strained single quantum well (SQW) using a reflection-type pump-probe technique. The type-II LH exciton consists of the electron and LH located in the In0.15Ga0.85As and GaAs layers, respectively. The energies of the type-I and the type-II excitons were evaluated with photoreflectance spectroscopy. The exciton states were calculated based on a variational method. The time-domain signals clearly show the oscillatory structure with the period corresponding to the splitting energy of the HH and the LH excitons. From the pump-energy dependence of the Fourier transform spectrum and intensity, it is concluded that the oscillation originates from the quantum beat of the type-I HH and the type-II LH excitons.

Temperature dependence of photoluminescence from as-grown and plasma-etched InAs0.45P0.55/In0.68Ga0.32As0.45P0.55 strained single quantum well

The temperature and laser pumping power dependent photoluminescence (PL) has been investigated on strained single quantum wells (SSQWs) using inductively coupled-plasma (ICP) etching method. Significant improvement of PL performances was observed in the plasma-etched SSQW in comparison with the as-grown samples. The enhancement factor increases with the increasing of temperature, but decreases with the increasing of pump power. At lower temperatures, the larger full width at half maximum (FWHM) and the blue-shift of PL peak positions for the plasma-etched SSQW may be attributed to the damage and reduced composition fluctuation within the quantum well structure aroused during plasma etching.

Effect of dry etching on light emission of InAsP/InP SMQWs

The cap layers of InAsP/InP SMQWs and InAsP/InGaAsP strained single quantum wells (SSQW) are etched to different depths using ICP. The PL intensity of the quantum wells is enhanced by different degrees after dry etching. The quantum well surface becomes rough and the microstructure inside the quantum well is changed during dry etching. The influence of surface roughness to the photoluminescence of quantum well is eliminated by selectively wet etching the InP cap layer of the SSQW. It is attained that after the cap layer is dry etched off about 20 nm the PL intensity of SSQW is enhanced about 1.8 and 1.2 times due to the change in microstructure and the roughening of surface, respectively.

ALE growth and optical characterization of ZnSe/ZnS strained quantum well structures on Si substrate

The ZnSe/ZnS strained single quantum well (SSQW) and strained multiple quantum well (SMQW) structures were grown on (1 0 0)-oriented Si substrates at 150°C in a horizontal cold-wall quartz reactor by low-pressure metalorganic atomic layer epitaxy (ALE) at a pressure of 30 Torr. Dimethylzinc (DMZn), hydrogen sulfide (H 2S) and hydrogen selenide (H 2Se) were used as the reactants. X-ray diffraction (XRD), secondary ion mass spectromery (SIMS) and photoluminescence (PL) were used to characterize the strained quantum wells. The high-quality crystalline ZnS(1000 Å)/ZnSe(7l Å)/ZnS(1000 Å)/Si sub. SSQW structure exhibits a 32 meV full-width at half-maximum (FWHM) for the 7 K PL spectra. The PL peak emission energy dependence on the well thickness for the ZnSe/ZnS SSQW structure is in good agreement with predictions based on a parabolic well-strain mode. In addition, the well-thickness dependence of the PL peak energy and FWHM of SSQW structures are described in detail. The temperature dependence of the PL peak energy and FWHM of SMQW structures are also measured from 7 to 156 K using a He–Cd laser operated at a wavelength of 325 nm as an excitation source. Better understanding of the temperature-dependent behavior would be helpful in the optoelectronic device development.

Deep-level transient spectroscopy and cathodoluminescence of Cd xZn 1− xTe/ZnTe QW structures grown on GaAs(1 0 0) by MBE

MBE-grown ZnTe/CdZnTe/ZnTe strained single quantum well (SQW) and multiple quantum well (MQW) structures with non-doping layers were investigated by cathodoluminescence (CL) and deep-level transient spectroscopy (DLTS). The DLTS method with electrical current relaxation was used because the as-grown structures were compensated. The activation energies of 0.21 and 0.58 eV for deep levels in ZnTe buffer layers grown on GaAs were determined by the DLTS spectra. Besides, an additional DLTS peak ( E t =34 –133 meV) that depends on the quantum well parameters and correlates with the QW emission line position in the CL spectra was observed. This peak is interpreted as an emission of electrons from a ground level of dimensional quantization in a conduction band. Obtained DLTS and CL results were used for an estimation of a conduction-band offset parameter Q C .

Effects of rapid thermal annealing on InAsP/InP strained multiquantum well laser diodes grown by metal organic chemical vapour deposition

The authors report on the effect of rapid thermal annealing (RTA) on the performance of InAsP/InP strained multiquantum well (SMQW) laser diodes (LDs) grown by metal organic chemical vapour deposition. From the photoluminescence (PL) measurements, the optimal RTA temperature for the InAsP/InP strained single quantum well (SSQW) stack was found to be 700°C. The 700°C annealed SSQW stack was found to have a stronger PL peak intensity, no halfwidth broadening and small peak shift, indicating that the degree of interdiffusion of group-V elements can be much reduced. The threshold current and slope efficiency of the 700°C RTA SMQW LDs can be reduced significantly as compared to those of as-grown LDs.

Effects of rapid thermal annealing on the optical properties of GaNxAs1−x/GaAs single quantum well structure grown by molecular beam epitaxy

The effect of rapid thermal annealing (RTA) on the optical properties of GaNxAs1−x/GaAs strained single quantum well (SQW) was studied by low-temperature photoluminescence (PL). The GaNxAs1−x/GaAs SQW structures were prepared by dc active nitrogen plasma assisted molecular beam epitaxy. PL measurements on a series of samples with different well widths and nitrogen compositions were used to evaluate the effects of RTA. The annealing temperature and time were varied from 650 to 850 °C and 30 s to 15 min, respectively. Remarkable improvements of the optical properties of the samples were observed after RTA under optimum conditions. The interdiffusion constants have been calculated by taking into account error function diffusion and solving the Schrodinger equation. The estimated interdiffusion constants D are 10−17–10−16 cm2/s for the earlier annealing conditions. Activation energies of 6–7 eV are obtained by fitting the temperature dependence of the interdiffusion constants.

Temperature dependence of photoluminescence from InAsP/InP strained quantum well structures grown by metalorganic chemical vapor deposition

In this article, we report the growth and characterization of InAsP/InP strained single quantum well (SSQW), strained single quantum well (SSQW) stack, and strained multiple quantum well (SMQW) structures on (1 0 0)-oriented InP substrates grown by metalorganic chemical vapor deposition. Double-crystal X-ray diffraction, photoluminescence (PL) and transmission electron microscope (TEM) are used to characterize the strained quantum wells. The high-quality crystalline InAs y P 1 −y (72Å)/InP SSQW structure with y⩽0.36 exhibits a 9.9 meV full-width at half-maximum (FWHM) of 10 K PL spectra. The peaks in the PL spectra for SSQW stack structure with a well thickness of 8, 14, and 35 Å vanish above 100, 150, and 296 K, respectively, presumably due to the decrease of photons yielded by electron–hole recombination in thinner quantum well regions on increasing the temperature. The PL peak emission energy dependence of well thickness in the InAsP/InP SSQW stack structure is in good agreement with the calculated results. In addition, the variations of the PL peak energy and FWHM in all the InAsP/InP SSQW, SSQW stack, and SMQW structures are described in detail.

MOCVD growth of strained multiple quantum well structure for 1.3 μm InAsP/InP laser diodes

In this article, we describe the growth and characterization for 1.3 μm InAsP/InP strained multiple quantum well (SMQW) laser diodes (LDs) with separate confinement heterostructure grown at 580°C by metalorganic chemical vapor deposition. The grown strained single quantum well (SSQW) stack and strained multiple quantum well (SMQW) structures are characterized using double-crystal X-ray diffraction and photoluminescence (PL) to confirm the structural and optical qualities for practical device applications. The InAsP/InP SSQW stack grown at 580°C appears to be extremely abrupt, uniform, free of misfit dislocations and narrow PL half width. Although the InAsP/InP SMQWs grown at 580°C maintain its structural integrity throughout the deposition sequence, the slightly broader PL half width for InAsP/InP SMQW structure is attributed to the dislocations resulted from a large net strain. Laser emission can be achieved by using the InAsP/InP SMQWs and the lasing wavelength is in a good agreement with our designed structure. The experimental data of broad-area and ridge waveguide LDs are described in detail.

Influence of growth temperature of InAsP/InP strained multiple quantum wells grown by metalorganic chemical vapor deposition

In this article, we report the influence of growth temperature on the luminescent and structural properties of InAsyP1−y/InP strained multiple quantum wells (SMQWs) and strained single quantum wells (SSQWs) grown by metalorganic chemical vapor deposition (MOCVD). The strained quantum wells are characterized by high-resolution transmission electron microscope (TEM), photoluminescence (PL), and double-crystal x-ray diffraction (DC-XRD). An AsH3/(AsH3+PH3) gas flow ratio of 0.50% and 1.48% at 580 and 650 °C growth temperatures, respectively, will result in an InAsP layer with y=0.3 solid composition. The experimental PL emission energies at 10 K at different well thicknesses for the InAsyP1−y/InP SSQWs grown at 580 and 650 °C are in well agreement with the trend of the calculated curves. The TEM lattice image of an InAsP/InP SSQW grown at 580 °C on the order of two monolayers has been demonstrated. The InAsP/InP SSQW structure grown at 580 °C appears to be extremely abrupt, uniform, free of misfit dislocations, and narrow PL linewidth. Besides, the growth of InAsP/InP SMQWs at 580 °C maintains its structural integrity throughout the deposition sequence with smooth interface and well-defined periodicity. However, the InAsP/InP SSQWs or SMQWs exhibit an adverse property at 650 °C growth temperature. From the above results, the lower growth temperature is necessary for the InAsP/InP SMQW growth by MOCVD.

Optical investigation of the relaxation process in InGaAs/GaAs single strained quantum wells grown on (001) and (111)B GaAs substrates

Molecular Beam Epitaxy (MBE) growth of a series of Single Strained Quantum Wells (SSQWs) of InGaAs/GaAs with indium content ranging from 10% to 35% and 100Å well thickness was performed on (001) and (111)B GaAs substrates under optimized growth conditions for simultaneous growth. The Critical Layer Thickness (CLT) of the heterostructures grown on both substrates was comparatively studied by low temperature Photoluminescence (PL). Relaxation is readily observed in the structures grown on (001) GaAs for 24% In-content. This value is in close agreement with both a calculation of the excess strain associated with the two Matthews and Blakeslee strain relieving dislocation mechanisms and the onset of three-dimensional growth. By contrast, heterostructures grown on (111)B GaAs remain pseudomorphic for In-contents above 25%. A maximum PL peak wavelength of 1.1microns at room temperature has been reached under the growth conditions used. This would correspond to an In-content around 31%. The study shows that (111)B is a preferable choice of substrate orientation for the growth of InGaAs/GaAs heterostructures for optoelectronic applications at wavelengths beyond 1μm.

Influence of substrate misorientation on the optical and structural properties of InGaAs/GaAs single strained quantum wells grown on (111)B GaAs by molecular beam epitaxy

A series of InGaAs/GaAs Single Strained Quantum Wells (SSQWs) with indium content ranging from 25% to 35% and 100Å well thickness were grown on two different (111)B GaAs off-axis substrates under optimized growth conditions for simultaneous growth. Optoelectronic properties were studied in terms of low temperature photoluminescence (PL). Results indicate a PL emission dependence with the substrate used, this dependence being stronger for highly strained systems. In order to determine the source of this dependence, samples were studied by Planar View Transmission Electron Microscopy (PVTEM). Relaxation mechanisms seem to act in a different way regarding the misoriented substrate used. Although previous theoretical results have already reported this dependence, this is the first direct evidence of this phenomenon for SSQWs. The results of these two different techniques will be compared and discussed.

Cathodoluminescence spectra of tensile strained ZnSe/ MBE single quantum wells

This paper discusses the hydrostatic and shear deformation potentials of ZnSe by investigating cathodoluminescence (CL) spectra of biaxial tensile strained single quantum wells (SQW). The dependence of the shift of light- and heavy-hole exciton lines on the built-in strain of these MBE-grown strained layer heterostructures is discussed. We found a hydrostatic deformation potential of eV and a shear (tetragonal) deformation potential of eV. From the temperature dependence of the ground state exciton energy, an exciton gap meV at T = 297 K was deduced for unstrained bulk ZnSe.

Temperature-dependent exciton behavior in quaternary GaInAsSb/AlGaAsSb strained single quantum wells

We report the temperature-dependent exciton behavior in a quaternary Ga0.67In0.33As0.01Sb0.99/Al0.25Ga0.75As 0.2Sb0.98 strained single-quantum-well (SQW) structure by photoluminescence spectroscopy. Strong exciton resonances are observed and have been attributed to localized excitons below 80 K and to free excitons at high temperatures. Nevertheless, we show that the experimental results of stronger exciton–phonon coupling in the quaternary SQW structure would lead to partial ionization of free excitons at temperatures above 125 K, in good agreement with the line-shape analysis of the luminescence spectra which clearly shows the presence of band-to-band recombination.

Novel [formula omitted] compound system grown on InP substrates by MBE and theoretical investigation of 550–640 nm range [formula omitted] lasers

Novel MgZnCdSe layers with various Mg composition and a high optical property ZnCdSeMgZnCdSe quantum well (QW) structure were grown on (100) InP substrates by molecular beam epitaxy. For Cl-doped Mg0.25(Zn0.5Cd0.5)0.75Se layers, the electron density of 4 × 1017cm−3 was obtained. In addition, refractive indices of the MgZnCdSe layers were evaluated. Using the refractive indices, ZnCdSeMgZnCdSe strained single quantum well (SSQW) lasers are theoretically investigated for the first time. As a result, it is predicted that the lasing wavelength is controlled from 550 to 640 nm by changing the strain amount of the ZnCdSe SSQW active layer from − 1.5% (tensile) to 1.5% (compressive), and that threshold current density values are from 0.2 to 0.4 kA/cm2.

Low threshold 1.3 µm-GaInAsP/InP tensile strained single quantum well lasers grown by low-pressure MOCVD

1.3 µm Ga0.49In0.51As0.7P0.3 –1.15% tensile strained single quantum well (SQW) lasers are successfully fabricated. The lowest threshold current for a 200 µm-long, 20 µm-wide ridge waveguide laser with high reflectivity coating is as low as 6 mA, corresponding to a very low threshold current density of 150 A/cm2.

Fabrication of In/sub 0.25/Ga/sub 0.75/As/InGaAsP strained SQW lasers on In/sub 0.05/Ga/sub 0.95/As ternary substrate

A uniform In/sub 0.05/Ga/sub 0.95/As ternary substrate was grown by using liquid encapsulated Czochralski (LEC) technique with a method of supplying GaAs source material at a constant temperature, and InGaAs/InGaAsP strained single quantum well (SQW) lasers were fabricated on the substrate for the first time. The lasers lased at 1.03 /spl mu/m and exhibited low threshold current density of 222 A/cm/sup 2/ and excellent characteristic temperature of 221 K, showing that the ternary substrate has a sufficient quality for laser fabrication. >

Stable singlemode operation of 0.98 µm GaInAs/GaInAsP/GaInP buried ridge stripe laser with AlGaInP current blocking layer

By using a AlGaInP current blocking layer lattice-matched to GaAs, a GaInAs/GaInAsP/GaInP strained single quantum well (SSQW) buried ridge stripe laser emitting at 0.98 µm wavelength region was fabricated and successful operation was achieved for the first time. Single-longitudinal-mode operation with single-lobed far-field patterns was obtained at up to an output power of 50 mW for the uncoated laser (4 × 1000 µm2) under continuous-wave (CW) operation at room temperature. In addition, CW operation beyond 50 mW output was obtained at up to 100°C for the same device.