[en] GaN films were grown in pairs on two opposite c faces of Al₂O₃ substrate by low-pressure metal-organic vapor phase epitaxy, and studied by scanning electron microscopy and converged beam electron diffraction. It is found that GaN film on the c-Al₂O₃ whose c face is forward to its crystal seed has [0001] polarity, and the other film on the c-Al₂O₃ whose c face is backward to its crystal seed has [000 bar 1] polarity. [copyright] 2001 American Institute of Physics

[en] We investigate theoretically the persistent charge current (PCC) and pure spin current (PSC) in a hybrid mesoscopic ring with Rashba spin–orbit interaction (RSOI). The PCC and PSC surviving in the ring would experience a periodic potential formed by the band offset of the constituent materials. Similarly, an effective tunnel barrier can be introduced by a region with different RSOI strength. This provides us a convenient way to manipulate the periodic potential by changing the RSOI strength through an electric field. With the increment of the RSOI strength, the PCC is suppressed, while the PSC presents an oscillatory pattern changing from negative to positive.

[en] The study of the photoluminescence (PL) of neutron irradiation induced defects in float zone silicon grown in hydrogen Si[H] is reported for the first time. It is found that the thermal stability of the well-known damage lines G (0.970 eV) and I1 (1.018 eV) is significantly increased in comparison with that of crystal grown in argon. The PL lines 0.987 (HB) and 0.975 eV (HC) and their phonon replicas are observed for the samples annealed at temperatures from 350 to 600⁰C. The temperature dependent measurements demonstrate a transition with energy 0.978 eV (HC^e) which is caused by thermalisation on the excited states of the HC transition. Both lines HB and HC are believed to arise from the iso-electronic defects associated with both hydrogen and radiation damage. (author)

[en] Electrodeposition is a promising and low cost method to synthesize CuIn_x Ga_1-x Se₂ (CIGS)thin films as an absorber layer for solar cells. The effect of bath temperature on the properties of CIGS thin films was investigated in this paper. CIGS films of 1 μm thickness were electrodeposited potentiostatically from aqueous solution, containing trisodium citrate as a complexing agent, on Mo/glass substrate under a voltage of -0.75 V, and bath temperatures were varied from 20 to 60⁰C. The effects of bath temperature on the properties of CIGS thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy. XRD revealed the presence of the CuIni_0.7Ga_0.3 Se₂ phase, the optimal phase for application in solar cells. The grain dimensions and crystallizability increase along with the increase of the bath temperature, and the films become stacked and homogeneous. There were few changes in surface morphology and the composition of the films. (semiconductor materials)

[en] In this work, we present the growth of InAs rings by droplet epitaxy. A complete process from the rings formation to their density saturation has been demonstrated. A morphological evolution with the varying of the indium deposition amount has been clearly observed. Our results indicate that there is a critical deposition amount (∝1.1 ML) for the indium to form InAs dots before droplets form; there is also a critical deposition amount (∝1.4 ML) to form InAs rings, but it is caused by the formation of droplets as the deposition amount increases. The density of the rings saturates when the deposition amount exceeds ∝3.3 ML, because the adsorbed indium atoms block sites for further adsorption and the following supplied In only contributes to the size increase of In droplets. Still, as the In deposition amount increases, we can find coupled quantum rings. Moreover, the wetting layer properties of these structures are studied by reflectance difference spectroscopy, which shows a complicated evolution with the In amount. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] A normal-incidence quantum cascade detector coupled by a nanopore array structure (NPS) is demonstrated. The NPS is fabricated on top of an In_0.53Ga_0.47As contact layer by inductively coupled plasma etching using anodic aluminum oxide as a mask. Because of the nonuniform volume fraction at different areas of the device mesa, the NPS acts as subwavelength random gratings. Normal-incidence light can be scattered into random oblique directions for inter-sub-band transition absorption. With normal incidence, the responsivities of the device reach 24 mA/W at 77 K and 15.7 mA/W at 300 K, which are enhanced 2.23 and 1.96 times, respectively, compared with that of the 45°-edge device. (author)

[en] The folded acoustic phonon and confined optical phonon modes in chirped InGaAs-InAlAs superlattices have been studied by micro-Raman spectroscopy. The folded and confined phonons were probed at the (1 anti 10) and (001) faces. Raman scattering measurements for the chirped superlattices and an InGaAs film were performed at different temperatures. The temperature dependence of the longitudinal optical phonon frequencies indicates that a compressive strain existed in the InGaAs layers of the chirped superlattices, which is significant for analyzing the device failure of quantum cascade lasers operating at higher active region temperatures. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Carbon films with an open-ended structure were obtained by mass-selected ion-beam deposition technique at 800 deg. C. Raman spectra show that these films are mainly sp²-bonded. In our case, threshold ion energy of 140 eV was found for the formation of such surface morphology. High deposition temperature and ion-beam current density are also responsible for the growth of this structure. Additionally, the growth mechanism of the carbon films is discussed in this article. It was found that the ions sputtered pits on the substrate in the initial stage play a key role in the tubular surface morphology

[en] Spin splitting of conduction subbands in Al_0.3Ga_0.7As/GaAs/Al_xGa_1-xAs/Al_0.3Ga_0.7 As step quantum wells induced by interface and electric field related Rashba effects is investigated theoretically by the method of finite difference. The dependence of the spin splitting on the electric field and the well structure, which is controlled by the well width and the step width, is investigated in detail. Without an external electric field, the spin splitting is induced by an interface related Rashba term due to the built-in structure inversion asymmetry. Applying the external electric field to the step QW, the Rashba effect can be enhanced or weakened, depending on the well structure as well as the direction and the magnitude of the electric field. The spin splitting is mainly controlled by the interface related Rashba term under a negative and a stronger positive electric field, and the contribution of the electric field related Rashba term dominates in a small range of a weaker positive electric field. A method to determine the interface parameter is proposed. The results show that the step QWs might be used as spin switches.

[en] Eu³⁺-doped zinc aluminate (ZnAl₂O₄) nanorods with a spinel structure were successfully synthesized via an annealing transformation of layered precursors obtained by a homogeneous coprecipitation method combined with surfactant assembly. These spinel nanorods, which consist of much finer nanofibres together with large quantities of irregular mesopores and which possess a large surface area of 93.2 m² g^-1 and a relatively narrow pore size distribution in the range of 6-20 nm, are an ideal optical host for Eu³⁺ luminescent centres. In this nanostructure, rather disordered surroundings induce the typical electric-dipole emission ⁵D₀ → ⁷F₂ of Eu³⁺ to predominate and broaden