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We demonstrate that a low-temperature GaN insertion layer could significantly improve the surface morphology of non-polar a-plane GaN.The two key factors in improving the surface morphology of non-polar a-plane GaN are growth temperature and growth time of the GaN insertion layer. The root-mean-square roughness of a-plane GaN is reduced by 75% compared to the sample without the GaN insertion layer. Meanwhile, the GaN insertion layer is also beneficial for improving crystal quality. This work provides a simple and effective method to improve the surface morphology of non-polar a-plane GaN. [ABSTRACT FROM AUTHOR]

The performance of type-II superlattice (T2SL) long-wavelength infrared devices is limited by crystalline quality of T2SLs. We optimize the process of growing molecular beam epitaxy deposition T2SL epi-layers on GaSb (100) to improve the material properties. Samples with identical structure but diverse In/Ga beam-equivalent pressure (BEP) ratio are studied by various methods, including high-resolution x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy. We find that appropriately increasing the In/Ga BEP ratio contributes to improving the quality of T2SLs, but too large In BEP will much more easily cause a local strain, which can lead to more InSb islands in the InSb interfaces. The InSb islands melt in the InSb interfaces caused by the change of chemical potential of In atoms may result in the “nail” defects covering the whole T2SLs, especially the interfaces of GaSb-on-InAs. When the In/Ga BEP ratio is about 1, the T2SL material possesses a lower full width at half maximum of +1 first-order satellite peak, much smoother surface and excellently larger area uniformity. [ABSTRACT FROM AUTHOR]

Semiconductors grown by the solution-processed method have shown low-cost, facile fabrication process and comparable performance. However, there are many reasons why it is difficult to achieve high quality films. For example, lattice constant mismatch is one of the problems when photovoltaic devices made of organ metallic perovskites. In this work, MAPbBr3 () perovskites single crystals grown on the surface of MAPbBr2.5Cl0.5 perovskites single crystals via liquid epitaxial growth method is demonstrated. It is found that when the lattice constants of the two perovskite single crystals are matched, another crystal can be grown on the surface of one crystal by epitaxial growth. The whole epitaxy growth process does not require high heating temperature and long heating time. X-ray diffraction method is used to prove the lattice plane of the substrate and the epitaxial grown layer. A scanning electron microscope is used to measure the thickness of the epitaxial layer. Compared with perovskite-based photodetectors without epitaxial growth layer, perovskite-based photodetectors with epitaxial growth layer have lower dark current density and higher optical responsibility. [ABSTRACT FROM AUTHOR]

We choose nano-Pt in hydrogen environment to explore the size effect on the formation of metal hydrides. At 30 GPa, a phase transition in the metal lattice from the cubic to hexagonal phase is observed characterized by a drastically increased volume per metal atom, indicating the formation of PtH-P63/mmc. We find that nano-Pt could form PtH at a lower pressure than the bulk Pt due to its high specific surface and structure defects. The present work provides the possible route to new metal hydrides under mild conditions. [ABSTRACT FROM AUTHOR]

Heterojunction phototransistors (HPTs) with scaling emitters have a higher optical gain compared to HPTs with normal emitters. However, to quantitatively describe the relationship between the emitter-absorber area ratio (Ae/Aa) and the performance of HPTs, and to find the optimum value of Ae/Aafor the geometric structure design, we develop an analytical model for the optical gain of HPTs. Moreover, five devices with different Ae/Aaare fabricated to verify the numerical analysis result. As is expected, the measurement result is in good agreement with the analysis model, both of them confirmed that devices with a smaller Ae/Aaexhibit higher optical gain. The device with area ratio of 0.0625 has the highest optical gain, which is two orders of magnitude larger than that of the device with area ratio of 1 at 3 V. However, the dark current of the device with the area ratio of 0.0625 is forty times higher than that of the device with the area ratio of 1. By calculating the signal-to-noise ratios (SNRs) of the devices, the optimal value of Ae/Aacan be obtained to be 0.16. The device with the area ratio of 0.16 has the maximum SNR. This result can be used for future design principles for high performance HPTs. [ABSTRACT FROM AUTHOR]

The synergism effect of total ionizing dose (TID) on a single event transient (SET) in a bipolar comparator is investigated. Experimental results show that the shapes of the SET are considerably influenced by the TID accumulated in low dose rates. The variation tendency of SET shapes can be accurately simulated by temperature switching irradiation. The mechanism of this synergism effect is also analyzed in brief via the operating schematic of a comparator. After the accumulation of 100 krad(Si), the lower tendency of negative SET can be attributed to the degeneration of β. The change tendency of a positive SET, either lower or higher, is dependent on the load condition that limits the output range of the comparator. [ABSTRACT FROM AUTHOR]

The recently proposed method of our research group named as directional Lyapunov exponents (DLEs) is presented. Then, DLEs are used to analyze the eigenstructure of the output phase space around the equilibrium points. Finally, the impacts of the superlattice parameter changes on the characteristics of the output chaotic signal are analyzed. The experimental results show that parameter changes of the superlattice will affect the eigenstructure around the equilibrium points in the output phase space, and DLEs are sensitive to these changes. [ABSTRACT FROM AUTHOR]

We derive an N-fold Darboux transformation for the nonlinear Schrödinger equation coupled to a multiple self-induced transparency system, which is applicable to optical fiber communications in the erbium-doped medium. The N-soliton, N-breather and Nth-order rogue wave solutions in the compact determinant representations are derived using the Darboux transformation and limit technique. Dynamics of such solutions from the first- to second-order ones are shown. [ABSTRACT FROM AUTHOR]

The Dick effect is an important factor limiting the frequency stability of sequentially-operating atomic frequency standards. Here we study the impact of the Dick effect in the integrating sphere cold atom clock (ISCAC). To reduce the impact of the Dick effect, a 5 MHz local oscillator with ultra-low phase noise is selected and a new microwave synthesizer is built in-house. Consequently, the phase noise of microwave signal is optimized. The contribution of the Dick effect is reduced to(τ is the integrating time). The frequency stability ofis achieved. The development of this optimization can promote the space applications of the compact ISCAC. [ABSTRACT FROM AUTHOR]

A widely tunable microwave photonic (MWP) notch filter with high linearity based on a dual-parallel Mach—Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. The motivation of this work lies in the fact that the MWP notch filter previously reported has nonlinear distortions generally induced by the nonlinear property of electro-optic devices. In this scheme, even-order modulated sidebands at the DPMZM output are effectively suppressed by properly adjusting bias voltages of the DPMZM, which are the dominant factor to induce the nonlinear distortions into the MWP notch filter. The proposed scheme is theoretically analyzed and experimentally verified. [ABSTRACT FROM AUTHOR]

The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p—n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p—n junction escape from quantum wells and form photocurrent rather than relax to the ground state of the quantum wells. The photo absorption coefficient of multiple quantum wells is also enhanced by a p—n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure. [ABSTRACT FROM AUTHOR]

The radiation damage responses of fluorinated and non-fluorinated lateral PNP transistors are studied with specially designed gated-controlled lateral PNP transistors that allow for the extraction of the oxide trapped charge (Not) and interface trap (Nit) densities. All the samples are exposed in the Co-60γ ray with the dose rate of 0.5 Gy(Si)/s. After the irradiation, the buildup of Not and Nit of the samples with total dose is investigated by the gate sweep test technique. The results show that the radiation resistance of fluorinated lateral PNP transistors is significantly enhanced compared with the non-fluorinated ones. [ABSTRACT FROM AUTHOR]

Using in situ electric-field-modulated anisotropic magnetoresistance measurement, a large reversible and nonvolatile in-plane rotation of magnetic easy axis of ∼35° between the positive and negative electrical poling states is demonstrated in Co40Fe40B20/(001)-cut Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 (PMN-PT). The specific magnetoelectric coupling mechanism therein is experimentally verified to be related to the synchronous in-plane strain rotation induced by 109° ferroelastic domain switching in the (001)-cut PMN-PT substrate. [ABSTRACT FROM AUTHOR]

The similarity law of gas discharge is not always valid due to the occurrence of some elementary processes, such as the stepwise ionization process, which are defined as the forbidden processes. To research the influence of forbidden processes on the similarity law, physical parameters (i.e., the electric field, electron density, electron temperature) in similar gaps are investigated based on the fluid model of gas discharge. The products of gas pressure p and dimensions are kept to be constant in similar gaps and the discharge model is solved with and without the forbidden processes, respectively. Discharges in similar gaps are identified as glow discharges and the typical similarity relations all are investigated. The results show that the forbidden processes cause significant deviations of similarity relations from the theoretical ones and the deviations are enlarged as the scaled-down factor k increases. If the forbidden processes are excluded from the model, the similarity law will be valid in argon glow discharge at low pressure. [ABSTRACT FROM AUTHOR]