Ni Haiqiao

GaAs-based long-wavelength InAs quantum dots on multi-step-graded InGaAs metamorphic buffer grown by molecular beam epitaxy

Molecular beam epitaxy growth of GaAs-based long-wavelength metamorphic InAs/InGaAs quantum dots (QDs) is investigated. With optimized multi-step-graded InGaAs metamorphic buffer layers and growth conditions, room temperature 1.46 µm emission from InAs/In0.15Ga0.85As QDs is realized, and broad-area laser diodes are fabricated with a very low etch pit defect density of less than 5.0 × 103 cm−2. The lasers operate under pulsed operation mode at room temperature with a low threshold current density of 146.7 A cm−2.

Extremely low density InAs quantum dots with no wetting layer

Extremely low density InAs quantum dots (QDs) are grown by molecular beam droplet epitaxy, The gallium deposition amount is optimized to saturate exactly the excess arsenic atoms present on the GaAs substrate surface during growth, and low density InAs/GaAs QDs (4x10(6) cm(-2)) are formed by depositing 0.65 monolayers (ML) of indium. This is much less than the critical deposition thickness (1.7 ML), which is necessary to form InAs/GaAs QDs with the conventional Stranski-Krastanov growth mode. The narrow photoluminescence line-width of about 24 meV is insensitive to cryostat temperatures from 10 K to 250 K. All measurements indicate that there is no wetting layer connecting the QDs.

Influence of window layer thickness on double layer antireflection coating for triple junction solar cells

The optimization of a SiO2/TiO2, SiO2/ZnS double layer antireflection coating (ARC) on Ga0.5In0.5P/In0.02Ga0.98As/Ge solar cells for terrestrial application is discussed. The Al0.5In0.5P window layer thickness is also taken into consideration. It is shown that the optimal parameters of double layer ARC vary with the thickness of the window layer.

Optimization of InAs/GaAs quantum-dot structures and application to 1.3-μm mode-locked laser diodes

The self-assembled growth of InAs/GaAs quantum dots by molecular beam epitaxy is conducted by optimizing several growth parameters, using a one-step interruption method after island formation. The dependence of photoluminescence on areal quantum-dot density is systematically investigated as a function of InAs deposition, growth temperature and arsenic pressure. The results of this investigation along with time-resolved photoluminescence measurements show that the combination of a growth temperature of 490 °C, with a deposition rate of 0.02 ML/s, under an arsenic pressure of 1 × 10−6 Torr (1 Torr = 1.33322 × 102 Pa), provides the best compromise between high density and the photoluminescence of quantum dot structure, with a radiative lifetime of 780 ps. The applicability of this 5-layer quantum dot structure to high-repetition-rate pulsed lasers is demonstrated with the fabrication and characterization of a monolithic InAs/GaAs quantum-dot passively mode-locked laser operating at nearly 1300 nm. Picosecond pulse generation is achieved from a two-section laser, with a ~ 19.7-GHz repetition rate.

High quality above 3-μm mid-infrared InGaAsSb/AlGaInAsSb multiple-quantum well grown by molecular beam epitaxy

The GaSb-based laser shows its superiority in the 3–4 μm wavelength range. However, for a quantum well (QW) laser structure of InGaAsSb/AlGaInAsSb multiple-quantum well (MQW) grown on GaSb, uniform content and high compressive strain in InGaAsSb/AlGaInAsSb are not easy to control. In this paper, the influences of the growth temperature and compressive strain on the photoluminescence (PL) property of a 3.0-μm InGaAsSb/AlGaInAsSb MQW sample are analyzed to optimize the growth parameters. Comparisons among the PL spectra of the samples indicate that the In0.485GaAs0.184Sb/Al0.3Ga0.45In0.25As0.22Sb0.78 MQW with 1.72% compressive strain grown at 460 °C posseses the optimum optical property. Moreover, the wavelength range of the MQW structure is extended to 3.83 μm by optimizing the parameters.

GaAs-based long-wavelength InAs bilayer quantum dots grown by molecular beam epitaxy

Molecular beam epitaxy growth of a bilayer stacked InAs/GaAs quantum dot structure on a pure GaAs matrix has been systemically investigated. The influence of growth temperature and the InAs deposition of both layers on the optical properties and morphologies of the bilayer quantum dot (BQD) structures is discussed. By optimizing the growth parameters, InAs BQD emission at 1.436 μm at room temperature with a narrower FWHM of 27 meV was demonstrated. The density of QDs in the second layer is around 9 × 109 to 1.4 × 1010 cm−2. The BQD structure provides a useful way to extend the emission wavelength of GaAs-based material for quantum functional devices.

Tunable Metamorphic Resonant Cavity Enhanced InGaAs Photodetectors Grown on GaAs Substrates

Tunable metamorphic InGaAs partially depleted absorber photodiodes with resonant cavity enhanced structure are fabricated on GaAs substrate. Dark-current densities of 7.2 × 10−7 A/cm2 at 0 V and 3.6 × 10−4 A/cm2 at −5 V, a high quantum efficiency of 74.4% at 1546 nm, and a 3-dB bandwidth up to 12 GHz are achieved. The full width at half maximum of the detector is about 16 nm. Furthermore, through thermal tuning, the peak wavelength red shifts from 1527 nm to 1544 nm, and a tuning range of 17 nm is realized without fabricating extra tuning electrodes.

Metal electrode influence on the wet selective etching of GaAs/AlGaAs

Metal electrodes were found to influence the wet selective etching of GaAs in a citric acid/hydrogen peroxide solution. The authors found that metal films such as a Cr/Au or Ti/Au alloy deposited on a semiconductor surface can mostly prevent the etching of GaAs. The GaAs sacrificial material that was exposed to the selective etchant near the metal electrode was not removed at all. Contrast experiments show that it can be removed selectively if no metal is present on the surface or if the GaAs is located far enough from the metal. Electrochemical analyses were undertaken to determine the passivation mechanism.

High-density and narrow size-distribution InAs quantum dots formed by a modified two-step growth

We develop a modified two-step method of growing high-density and narrow size-distribution InAs/GaAs quantum dots (QDs) by molecular beam epitaxy. In the first step, high-density small InAs QDs are formed by optimizing the continuous deposition amount. In the second step, deposition is carried out with a long growth interruption for every 0.1 InAs monolayer. Atomic force microscope images show that the high-density (similar to 5.9x 10(10) CM-2) good size-uniformity InAs QDs are achieved. The strong intensity and narrow linewidth (27.7 meV) of the photoluminescence spectrum show that the QDs grown in this two-step method have a good optical quality.

Temperature Dependence of Photoluminescence from Single and Ensemble InAs/GaAs Quantum Dots

We investigate the temperature dependence of photoluminescence from single and ensemble InAs/GaAs quantum dots systematically. As temperature increases, the exciton emission peak for single quantum dot shows broadening and redshift. For ensemble quantum dots, however, the exciton emission peak shows narrowing and fast redshift. We use a simple steady-state rate equation model to simulate the experimental data of photoluminescence spectra. It is confirmed that carrier-phonon scattering gives the broadening of the exciton emission peak in single quantum dots while the effects of carrier thermal escape and retrapping play an important role in the narrowing and fast redshift of the exciton emission peak in ensemble quantum dots.