High Quality Multiple Quantum Wells Research Articles

Integrated fabrication of a high strain InGaAs/GaAs quantum well structure under variable temperature and improvement of properties using MOCVD technology

An InGaAs/GaAs quantum well (QW) structure was prepared by metal-organic chemical vapor deposition (MOCVD) via a new growth method, where the InGaAs well layer and the GaAs barrier layer were grown under a variable temperature. A GaAs protection layer was employed to avoid indium atom evaporation on the InGaAs surface during the temperature change. Room and low-temperature photoluminescence (RT/LT-PL), atomic force microscopy (AFM), and high-resolution X-ray diffraction (HRXRD) were carried out to investigate the effect of the variable temperature growth method. The theoretical and experimental results indicated that it could erase the 2D islands and rebuild the surface morphology to a step-flow mode surface. The quality of the InGaAs crystal layer was also improved because of the annealing-like treatment. In addition, the study found that when the thickness of the GaAs protection layer was 2 nm and the growth temperature of the InGaAs layer was 560°C, the maximal properties of the InGaAs/GaAs QW were achieved. Moreover, high-quality multiple QWs with five periods were grown with the tailored structure. The growth method will improve the properties of strained InGaAs/GaAs QW materials and provide technical support for a semiconductor laser's performance optimization.

UV electroluminescence emissions from high-quality ZnO/ZnMgO multiple quantum well active layer light-emitting diodes.

5-period ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) were employed as active layers to fabricate the p-GaN/MQWs/n-ZnO diode by molecular beam epitaxy. It exhibited an efficient UV emission around 370 nm at room temperature. Calculated band structures and carrier distributions showed that electrons were restricted to overflow to the p-type layer, and carriers were confined in the high-quality MQWs well layer.

Metamorphic growth of 1.55 μm InGaAs/InGaAsP multiple quantum wells laser structures on GaAs substrates

We fabricate a GaAs-based InGaAs/InGaAsP multiple quantum wells (MQWs) laser at 1.55 μm. Using two-step growth method and thermal cyclic annealing, a thin low-temperature InP layer and a thick InP buffer layer are grown on GaAs substrates by low-pressure metal organic chemical vapor deposition technology. Then, high-quality MQWs laser structures are grown on the InP buffer layer. Under quasi-continuous wave (QCW) condition, a threshold current of 476 mA and slope efficiency of 0.15 mW/mA are achieved for a broad area device with 50 μm wide strip and 500 μm long cavity at room-temperature. The peak wavelength of emission spectrum is 1549.5 nm at 700 mA. The device is operating for more than 2000 h at room-temperature and 600 mA.

Enhancing the Emission Efficiency of In0.2Ga0.8N ∕ GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates

In this paper, we report the fabrication of an multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0–1° by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the MQW structure fabricated on 0.2° off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be . It is therefore manifested that an MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of and a lowest fluctuation of in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2° off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality MQW blue light, emitting diode (LED) has been fabricated on 0.2° off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of and with the full width at half maximum of only . The same device also showed an output power of and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of MQW blue LED fabricated thereon.

High-quality multiple quantum wells selectively grown on taper-patterned substrates by ultra-low-pressure MOCVD

High quality InGaAsP/InGaAsP multiple quantum wells (MQWs) have been selectively grown by ultra-low-pressure (22 mbar) metal-organic chemical vapor deposition. A large bandgap energy shift of 46 nm and photoluminescence with FWHM less than 30 meV were obtained with a rather small mask width variation (15—30 μm). In order to study the uniformity of the MQWs grown in the selective area, novel tapered masks were employed, and the transition effect of the tapered region was also studied. The energy detuning of the tapered region was observed to be saturated at larger ratios of the mask width to the tapered region length.

High-quality multiple quantum wells selectively grown with tapered masks by ultra-low-pressure MOCVD

An InGaAsP/InGaAsP multiple quantum wells (MQWs) selectively grown by ultra-low-pressure (22 mbar) metal-organic chemical vapor deposition was investigated in this article. A 46 nm photoluminescence peak wavelength shift was obtained with a small mask width variation (15–30 μm). High-quality crystal layers with a photoluminescence (PL) full-width-at-half-maximum (FWHM) of less than 30 meV were achieved. Using novel tapered masks, the transition-effect of the tapered region was also studied. The energy detuning of the tapered region was observed to be saturated with the larger ratio of the mask width divided to the tapered region length.

Narrow-stripe selective growth of high-quality MQWs by atmospheric-pressure MOVPE

We report the first atmospheric-pressure narrow-stripe (<2 μm) selective MOVPE. The extremely large bandgap wavelength shift of 370 nm for a selectively grown InGaAsP/InGaAsP multiple quantum well (MQW) was obtained with a small mask width variation (0–30 μm). This shift was four times that obtained under growth at 75 Torr. High-quality MQWs with flat interfaces and a photoluminescence full-width-at-half-maximum of less than 40 meV (0.5 kW/cm 2) were obtained by optimizing growth conditions. We deduced that the essential flattening mechanism under these conditions is the formation of a (1 0 0) facet under step-flow growth mode. We fabricated 1.55 μm MQW Fabry-Perot laser diodes with a room temperature threshold current as low as 5 mA.

1.3-μm spot-size-converter integrated laser diodes fabricated by narrow-stripe selective MOVPE

High-performance 1.3-/spl mu/m spot-size-converter integrated laser diodes (SSC-LDs) have been developed by using narrow-stripe (<2.0 /spl mu/m) selective MOVPE. In order to decrease leak current at high temperature, a p-n-p-n current blocking structure was added using a self-alignment process. These LD's no longer require a semiconductor etching process. Superior lasing characteristics, such as a low driving current of 56 mA for output power of 10 mW, and high-slope efficiency at 85/spl deg/C, were achieved by using a high-quality multiple-quantum well (MQW) active layer of narrow-stripe selective MOVPE and a p-n-p-n current blocking structure. A narrow radiation angle of 12/spl deg/ was obtained by optimizing the tapered-waveguide profile. A high-coupling efficiency of -2.8 dB was achieved between a LD chip and a single-mode fiber (SMF). This SSC-LD is very appropriate as a light source for access network systems, which require a low-cost LD module. It has excellent coupling efficiency, using a SMF, and a simple fabrication process, using selective MOVPE.

Migration-controlled narrow-stripe selective MOVPE for high-quality [formula omitted] MQWs

Narrow-stripe (< 2.0 μm) selective MOVPE was investigated to grow high-quality InGaAsPInGaAsP multiple quantum well (MQW) layers. Focusing on metalorganic species surface migration, which is an important transport process in narrow-stripe selective MOVPE, growth conditions were optimized by using the VIII ratio and the growth temperature as parameters. A lower VIII ratio and an optimum growth temperature were essential to achieve high-quality MQW layers. Consequently, high-quality MQW layers comparable to those grown on an unmasked substrate were obtained by migration-controlled narrow-stripe selective MOVPE.

Stable cw operation at room temperature of a 1.5-μm wavelength multiple quantum well laser on a Si substrate

Room-temperature cw operation of an InGaAs/InGaAsP multiple quantum well (MQW) laser diode on a Si substrate is reported. The MQW laser emits at a 1.54 μm wavelength and exhibits no degradation after over 2000 h of operation. Employing a hybrid organometallic vapor phase epitaxy/vapor mixing epitaxy method and a layer structure for improving crystalline quality, high-quality MQW layers are obtained. A stable longitudinal mode spectrum demonstrates the effectiveness of the MQW active layer.

1.5 µm-Long-Wavelength Multiple Quantum Well Laser on a Si Substrate

Room-temperature cw operation of an InGaAs/InGaAsP multiple quantum well (MQW) laser diode on a Si substrate is reported. The MQW laser emits at 1.54-µm wavelength and exhibits no degradation after over 1,000 hours of operation. Employing a hybrid organometallic vapor-phase epitaxy/vapor mixing epitaxy method and a layer structure for improving crystalline quality, high-quality MQW were obtained. The stable longitudinal mode spectrum demonstrates the effectiveness of the MQW active layer and results in low-intensity noise. Annealing phenomena under cw operation are also discussed.

Gas-source molecular beam epitaxy growth of highly strained device quality InAsP/InP multiple quantum well structures

InAsxP1−x/InP strained multiple quantum wells with strain as high as 2.5% were grown by gas-source molecular beam epitaxy. Successful control of the arsenic composition over a wide range was achieved by two different growth techniques. Structural and optical studies, such as high-resolution x-ray rocking curve, cross-sectional transmission electron microscopy, photoluminescence, and absorption measurement, indicate that we have obtained high quality multiple quantum wells that are suitable for optoelectronic applications.

Mbe Growth of Strained-Layer InSb/InAlSb Structures

ABSTRACTThe MBE growth and related materials characterisation of InSb/InAlSb strained-layer structures is described. Band-gap considerations and critical thickness calculations are presented and indicate that this material system should offer considerable device potential. Detailed structural studies, performed using both transmission electron microscopy and X-ray diffraction, confirm the growth of high quality multiple quantum-wells, and 2K photoluminescence has shown corresponding energy upshifted transitions.

Optical transitions and acceptor binding energies in GaAs/AlxGa1−xAs single quantum well heterostructures grown by molecular beam epitaxy

Single quantum wells of varying well size (150–300 Å) exhibiting sharp photoluminescence lines were grown by molecular beam epitaxy. Photoluminescence structure and intensity were comparable to high quality multiple quantum wells in that linewidths as low as 0.5 meV and transitions associated with free heavy-hole excitons as well as bound excitons and acceptor impurities were observed. Also reported for the first time in optical transmission measurements on single wells are excitonic absorption lines. These are as narrow as 0.38 meV full width at half-maximum. In contrast to earlier findings, the binding energy of the acceptor in single quantum wells displays the same functional dependence on the well thickness as in multiple quantum wells as a consequence of an improved bottom (inverted) interface.