Magneto-photoluminescence study of type-II charge confinement in epitaxially grown GaInP2

We have studied the photoluminescence from GaInP₂ grown by molecular beam epitaxy as a function of laser power, magnetic field and temperature. We show that the single luminescence peak observed in such samples arises from weakly bound (type-II) excitons in which the electrons are localised and the holes are free, and that it is the same as the additional low-energy peak typically observed in strongly CuPt-ordered GaInP₂ grown by chemical vapour deposition techniques. We propose that the electron is confined in In-rich regions of the sample and the hole is delocalised by coupling between heavy- and light-hole bands.     

Ferromagnetic resonance study of interface anisotropies in exchange-biased Fe(0 0 1)/KNiF3 bilayers

Magnetic anisotropies at epitaxial Fe/KNiF₃ interfaces were probed by ferromagnetic resonance. Fe(0 0 1) films coupled to single crystal KNiF₃ exhibit four-fold in-plane anisotropy and a unidirectional bias upon field-cooling. In Fe(0 0 1) with polycrystalline KNiF₃, the bias direction deviates from the field-cooling direction. Lattice mismatch strain due to polycrystalline KNiF₃ also induces uniaxial anisotropy in Fe.     

Valuing of the critical layer thickness from the deading time constant of RHEED oscillation in the case of InxGa1−xAs/GaAs heterojunction

In this work, we have looked for the correlation between the observed decay of reflection high-energy electron diffraction intensity oscillation and the critical layer thickness in the case of strained In_xGa_1−xAs/GaAs heterojunctions. The value of deading time constant of oscillation depends on the mismatch and on growth parameters, too. The decay of oscillation was described by two deading time constants which are responsible for the influences of the parameters mentioned above. The critical layer thickness was valued from the deading time constant responsible for the influence of mismatch only. The critical layer thickness determined this way shows good agreement with the theoretical model.     

Initial stages of MnAs/GaAs(0 0 1) epitaxy studied by RHEED azimuthal scans

We study the nucleation phase of molecular beam epitaxy of (hexagonal) MnAs on (cubic) GaAs (0 0 1) using reflection high-energy electron diffraction (RHEED) azimuthal scans. The nucleation proceeds from a non-reconstructed initial stage through randomly oriented small nuclei and two orientation stages to the final single-phase epitaxial orientation. The fascinatingly complex nucleation process contains elements of both Volmer-Weber and Stranski-Krastanov growth. The measurement demonstrates the potential of high-resolution RHEED techniques to assess details of the surface structure during epitaxy.     

采用N2-RF等离子体氮化GaAs(001)

研究了在MBE系统中,GaAs(001)表面的氮化过程。GaAs(001)表面直接和间接地暴露在等离子体激发的N₂气流下。两种氮化过程显示了完全不同的表面氮化结果。在打开N₂发生器挡板的情况下,氮化导致GaAs(001)表面损伤,并且形成多晶结构。当增加N₂气压时,损伤变得更严重。但是,在关闭N₂发生器挡板的情况下,在500℃下,经过氮化将观察到(3×3)再构的RHEED花样,表面仍保持原子级的平整度。上述结果表明,不开N₂发生器挡板,低温(500℃下)氮化将在GaN外延生长之前形成平整的薄层c-GaN。     

Fabrication of aluminum nitride heterostructures on Si (1 1 1) substrate by plasma-assisted MBE

The aluminum nitride (AlN) heterostructures were successfully grown on silicon substrate by plasma-assisted molecular beam epitaxy. The surface morphology and structural and optical properties of the sample have been investigated by reflection high electron diffraction, scanning electron microscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray, high-resolution X-ray diffraction (HR-XRD), Raman spectroscopy, and photoluminescence, respectively. HR-XRD measurement showed that the sample has a typical diffraction pattern of hexagonal AlN/GaN/AlN heterostructures. The Schottky characteristic of Pt contact on AlN/GaN/AlN heterostructures was also investigated under different annealing temperatures in nitrogen ambient. The temperature dependence and structural evolution of the Schottky barrier height (SBH) of Pt contacts were studied using the current–voltage measurement and FESEM, respectively. Our findings presented that the SBH of the samples change with different annealing temperatures.     

Ni/Ag Schottky contacts on Al0.11Ga0.89N grown on Si (1 1 1) substrate by plasma-assisted MBE

Al_0.11Ga_0.89N/GaN samples are grown by plasma-assisted molecular beam epitaxy method on (1 1 1) silicon substrates. High purity gallium (7N) and aluminum (6N5) were used to grow Al_0.11Ga_0.89N, GaN, and AlN, respectively. The surface morphology, structural and optical properties of the sample has been investigated by scanning electron microscope (SEM), and high-resolution X-ray diffraction (HR-XRD), respectively. HR-XRD measurement showed that the sample has a typical diffraction pattern of hexagonal Al_0.11Ga_0.89N/GaN heterostructures. Ni/Ag bilayers are deposited on Al_0.11Ga_0.89N as the Schottky contacts. The effect of annealing in oxygen ambient on the electrical properties of Ni/Ag/Al_0.11Ga_0.89N is studied by current–voltage measurement. The annealing at a temperature of 700 °C for 10?min results in an increase in the ideality factor from 1.033 to 1.042 and an increase in the Schottky barrier height from 0.708 to 0.811 eV. Furthermore, the annealing in oxygen ambient also leads to an increase in the surface roughness of the contacts from 0.0098 to 0.1360 μm which is in agreement with the SEM results.     

Fabrication of BDD quantum node switches on embedded GaAs quantum wires grown by selective MBE

In view of applications to hexagonal binary decision diagram (BDD) LSIs, a first attempt is made to form quantum BDD node switches on selectively grown (SG) embedded quantum wires (QWRs) by molecular beam epitaxy (MBE). SG branch switches controlled by a Schottky wrap gate (WPG) were successfully fabricated by MBE growth and subsequent device processing. Gate control characteristics were studied by gate-dependent Shubnikov–de-Haas measurements, and the behavior was found to be similar to that of devices fabricated on wires by etching. The switch exhibited clear conductance quantization at low temperature, and temperature dependence of the voltage slope of conductance jump was clarified. A Y-branch BDD node device using two SG branch switches was successfully fabricated, and realized clear path switching characteristics.     

Reflectance difference spectroscopy during CdTe/ZnTe interface formation

We have investigated the first stages of epitaxial growth of CdTe on ZnTe and ZnTe on CdTe with reflectance difference (RD) spectroscopy. Spectroscopic RD data show strong optical anisotropy responses at the critical points of the bulk dielectric function at the E₀, E₁ and E₁+Δ₁ interband transitions of ZnTe and CdTe, respectively, which indicate that anisotropic in-plane strain occurs during epitaxial growth. Kinetic RD data taken at the E₁ transition of the respective material exhibit with an accuracy of 1 ML the onset of the formation of misfit dislocations for these material systems.     

Si(001)衬底上闪锌矿ZnO的制备与分析

采用分子束外延方法在室温下于Si(001)表面上生长ZnO材料。实验发现:样品为闪锌矿和六角结构的ZnO混合多晶薄膜,其表面分布着一系列具一定取向的近似长方形的纳米台柱结构。在不同参数的高温退火后,这些梯形台柱将变小,形成梯形纳米环,或分解为较小的纳米柱及其团簇结构等。分析表明:ZnO混合多晶薄膜的形成,以及表面纳米台柱的演变,与Si(001)衬底、较低温的生长温度及热效应等因素相关联。