Papers by Keyword: Molecular Beam Epitaxy

Abstract: The GaAs nanowires are grown on Si (111) substrates by Ga-assisted molecular beam epitaxy growth technique. The effect of SiO₂ thickness on the structural properties of GaAs nanowires is investigated by Scanning Electron Microscope (SEM). The nucleation of GaAs nanowires related to the presence of a SiO₂ layer previously coated on Si substrate. The results show that the density, length, and diameter of GaAs nanowires strongly depend on the oxidation time (or SiO₂ thickness).

Abstract: We study the GaSb/GaAs nanostructures (NSs) grown by droplet epitaxy technique with various Ga amounts. Ga amount deposited on the GaAs (001) substrate was varied between 3-5 ML to form the different size and density of liquid Ga droplets. The Sb flux was subsequently irradiated to crystallize the droplets. Morphology of GaSb NSs was investigated by atomic force microscopy (AFM). Quantum rings were obtained after crystallizing 3-ML Ga droplets, whereas some kind of quantum dots were formed after crystallizing 4-and 5-ML Ga droplets. The formation mechanisms leading to the different structure are discussed. The photoluminescence (PL) measurement was performed to examine the optical properties of GaSb/GaAs NSs.

Abstract: GaN-based InGaN/GaN self-organized quantum dots and InGaN quantum dots (disks) in GaN nanowires are important nanostructures with potential advantages over planar quantum wells, including luminescence at the longer visible wavelengths. We describe the epitaxy and characteristics of red-emitting InGaN/GaN quantum dot edge-emitting lasers and InGaN/GaN nanowire light emitting diodes, which can be used in a host of applications.

Abstract: Zinc oxide is a promising candidate for application in UV photodetectors due to the large direct band gap and the high absorption coefficient in the UV. The high quality p-n and p-i-n structures consist of single or dual acceptor doped ZnO:(As,Sb) films grown by MBE, thin HfO₂ layer grown by ALD method and n-type GaN templates. The As and Sb concentrations is 10²⁰ cm^-3.The maximum forward-to-reverse current ratio I_F/I_R in the obtained p-n diodes is of about 10⁵ at ±4 V and in the case of p-i-n diodes is of about 10⁶, which are very good results for this type of heterojunctions. The UV photodetectors are highly selective. The maximum of the detection wavelength was found at about 365 nm (FWHM of the photocurrent peak is ~17 nm). In the case of p-i-n detectors, the maximum of detection was found at 376, 360, and 341 nm. Additionally, it is possible to control the detection range by the applied reverse voltage. The dark to light current ratio in both cases is ~10⁴.

Abstract: Hexadecafluorophthalocyanine (F₁₆CuPc) and Cobalt phthalocyanone (CoPc) thin films of different thickness (20-200nm) have been grown by Molecular Beam Epitaxy (MBE) using different deposition rate (0.2 – 1.0 Å/s). For nanowire type growth lower deposition rate and for films of smooth surface higher deposition rate are found suitable. Charge transport (J~V) of CoPc and F₁₆CuPc films is governed by bulk-limited processes with a bias dependent crossover from Ohmic to trap-free space-charge-limited conduction. The mobility (μ) values at 300 K were found 4.5 and 5.5 cm2 V−1 s−1 for CoPc and F₁₆CuPc films respectively. Mechanism of reverse rectification behavior of an organic heterojunction comprising of CoPc and F₁₆CuPc is explained by Kelvin Probe measurement.

Abstract: We report the growth of Cu₂O thin films on glass and MgO(100) substrates by molecular beam epitaxy. Crystal orientation of Cu₂O thin films on glass substrate were changed from (100) to (111) with increasing the deposition rate. The Cu₂O thin films were epitaxially grown on MgO(100) substrate with an orientation relationship of Cu₂O(110) // MgO(100). The film quality and electrical properties of Cu₂O thin films were changed with deposition rate. The slow deposition rate resulted in high conductivity and mobility, as well as good crystallinity and orientation.

Abstract: 2.3 μm InGaAsSb/AlGaAsSb lasers with multiple quantum wells(MQWs) have been demonstrated.The growth temperature of quantum wells is 440°C,and the growth quality of InGaAsSb/AlGaAsSb MQWs is examined by X-ray diffraction and Photoluminescence(PL) at room temperature.The energy band structure of MQWs was calculated by one-dimensional finite-difference method(1D-FDM)

Abstract: Obtaining photocathodes with high quantum yield has been the focus during the process of photocathode development. With the limitation of basic industrial manufacturing level, the further performance improvement of the negative electron affinity photocathode is subject to the quality of grown material itself. For this reason, according to the band engineering science, we have proposed an exponential-doping structure applied to the active-layer of reflection-mode and transmission-mode AlGaAs/GaAs photocathodes via molecular beam epitaxy technique, to increase the photocathode emission efficiency. A series of theoretical and experimental researches including structure design, material growth, surface cleanness, Cs-O activation and performance evaluation have been carried out to confirm the actual effect of exponential-doping photocathodes. As a result of the built-in electric field, the cathode performance was enhanced for exponential-doping AlGaAs/GaAs photocathodes.

Abstract: In this paper, GaAs PHEMT samples are prepared by the method of molecular beam epitaxy (MBE), The optimal parameters are determined by studying the impact of the barrier layer thickness, spacer layer thickness, Al composition of the barrier layer and the spacer layer , the channel thickness and channel In composition on Ns and μn.

Abstract: To improve the techniques of molecular beam epitaxy, the electron bombardment evaporator for high temperature evaporation in ultra-high vacuum is designed, and then its performances, such as power-temperature relationship, stability of beam flux as well as molecular beam distribution, are tested by using Ag source. Through adjusting the electric current of tungsten filament can achieve the remarkable heating power in high-voltage, and the crucible temperature rises with increasing heating power, and it exceeds 1600°C at around 60W. The evaporator can reach thermal equilibrium state in a quite short time and produce a highly stable beam flux of Ag at low deposition rate. A 9mm diameter homogeneous flux platform area is obtained at the position 60mm away from the nozzle, and this area can provide high quality beam flux for molecular beam epitaxy. These results show, the electron bombardment evaporator can meet the demands for ultra-high vacuum molecular beam epitaxy growth completely.