Niu Zhichuan

Effect of Annealing on Structural and Magnetic Properties of a Thick (Ga,Mn)As Layer

We investigate effects of annealing on magnetic properties of a thick (Ga,Mn)As layer, and find a dramatic increase of the Curie temperature from 65 to 115 K by postgrowth annealing for a 500-nm (Ga,Mn)As layer. Auger electron spectroscopy measurements suggest that the increase of the Curie temperature is mainly due to diffusion of Mn interstitial to the free surface. The double-crystal x-ray diffraction patterns show that the lattice constant of (Ga,Mn)As decreases with increasing annealing temperature. As a result, the annealing induced reduction of the lattice constant is mainly attributed to removal of Mn interstitial.

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.

GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy

InAs/GaSb superlattice (SL) short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs(001) semi-insulating substrates. An interfacial misfit mode AlSb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2ML/8ML InAs/GaSb SL active layer are fabricated with a pixel area of 800 x 800 mu m(2) without using passivation or antireflection coatings. Corresponding to the 50% cutoff wavelengths of 2.05 mu m at 77K and 2.25 mu m at 300 K, the peak detectivities of the detectors are 4 x 10(9) cm.Hz(1/2)/W at 77K and 2 x 10(8) cm.Hz(1/2)/W at 300 K, respectively.

Growth and Characterization of GaSb-Based Type-II InAs/GaSb Superlattice Photodiodes for Mid-Infrared Detection

InAs/GaSb superlattice (SL) midwave infrared photovoltaic detectors are grown by molecular beam epitaxy on GaSb(001) residual p-type substrates. A thick GaSb layer is grown under the optimized growth condition as a buffer layer. The detectors containing a 320-period 8ML/8ML InAs/GaSb SL active layer are fabricated with a series pixel area using anode sulfide passivation. Corresponding to 50% cutoff wavelengths of 5.0 mu m at 77 K, the peak directivity of the detectors is 1.6 x 10(10) cm.Hz(1/2) W-1 at 77 K.

Molecular Beam Epitaxy of GaSb on GaAs Substrates with AlSb Buffer Layers

We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using AlSb buffer layers. Optimization of AlSb growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of AlSb layers are found to be 450 degrees C and 2.1 nm, respectively. A rms surface roughness of 0.67 nm over 10 x 10 mu m(2) is achieved as a 0.5 mu m GaSb film is grown under optimized conditions.

Investigation of interfaces in AlSb/InAs/Ga0.71In0.29Sb quantum wells by photoluminescence

We have investigated excitation power and temperature dependent PL spectra to systematically study the influences of the interfaces in the both InAs/Ga0.71In0.29Sb and InAs/AlSb on the optical properties of AlSb/Ga0.71In0.29Sb/InAs quantum wells (QWs). The localized states as well as the activation energy were analyzed to discuss the possible thermal quenching and non-radiative recombination mechanisms. We found two non-radiative recombination processes were involved in the thermal quenching of radiative emission for the QW structures. The GaAs-like interface in InAs/Ga0.71In0.29Sb with higher activation energy (62.7 meV) in high temperature region (70 K–300 K) supplies a deeper hole confinement and less roughness than the InSb-like one, which suppress non-radiative recombination process and promote the optical qualities of the quantum wells. The peak energy of the InSb-like sample exhibited “step-curve” behavior with increase temperature. Neither InSb-like nor AlAs-like interface in InAs/AlSb favored the...

Growth and fabrication of a mid-wavelength infrared focal plane array based on type-II InAs/GaSbsuperlattices

We present the fabrication of a mid-wavelength infrared focal plane array (FPA) based on type-II InAs/GaSb strain layer superlattices (SLs). The detectors contain a 400-period 8 ML InAs/8 ML GaSb SL active layer, which is grown by solid source molecular beam epitaxy on GaSb (100) N type substrates. Lattice mismatch between the superlattices and GaSb substrate achieves 148.9 ppm. The full width at half maximum of the first order satellite peak from X-ray diffraction was 28 arcsec. Single element detectors and FPA with a 128 × 128 pixels were fabricated using citric acid based solution wet chemical etching. Chemical and physical passivation effectively reduces the surface leakage and this process was characterized by I—V measurement. The devices showed a 50% cut-off wavelength of 4.73 μm at 77 K. The photodiode exhibited an R0A of 103 Ω cm2. The FPA was characterized with an integration time of 0.5 ms and F/2.0 optics at 77 K and the average blackbody detectivity of the detectors is 2.01 × 109 cm Hz1/2/W.

Metamorphic InGaAs Quantum Well Laser Diodes at 1.5μm on GaAs Grown by Molecular Beam Epitaxy

National Natural Science Foundation of China 60607016 60625405National Basic Research Programme of China National High Technology Research and Development Programme of China Supported partly by the National Natural Science Foundation of China under Grand Nos 60607016 and 60625405, the National Basic Research Programme of China and the National High Technology Research and Development Programme of China.

Tuning Photoluminescence Energy and Fine Structure Splitting in Single Quantum Dots by Uniaxial Stress

We report a photoluminescence (PL) energy red-shift of single quantum dots (QDs) by applying an in-plane compressive uniaxial stress along the [110] direction at a liquid nitrogen temperature. Uniaxial stress has an effect not only on the confinement potential in the growth direction which results in the PL shift, but also on the cylindrical symmetry of QDs which can be reflected by the change of the full width at half maximum of PL peak. This implies that uniaxial stress has an important role in tuning PL energy and fine structure splitting of QDs.

Optical spectra and exciton state in vertically stacked self-assembled quantum discs

We study the oscillator strengths of the optical transitions of the vertically stacked self-assembled InAs quantum discs. The oscillator strengths change evidently when the two quantum discs are far apart from each other. A vertically applied electric held affects the oscillator strengths severely, while the oscillator strengths change slowly as the radius of one disc increases. We also studied the excitonic energy of the system, including the Coulomb interaction. The excitonic energy increases with the increasing radius of one disc, but decreases as a vertically applied electric field increases.