摘要 : The emergence of vertical GaN devices solves the problem of insufficient voltage withstand capacity of horizontal GaN devices. However, the current output capability of vertical GaN devices is not comparable to that of lateral GaN devices. So we propose a Al0.3Ga0.7N/GaN current-aperture vertical electron transistor with a SiO2-In0.05Ga0.95N hybrid current-blocking layer (CBL). Through simulation and in-depth study of the proposed device, the results show that the GaN/InGaN secondary channel enhances the saturation output current of the device, achieving a saturated output current (I (DSS)) of 985 mA mm(-1) and a transconductance (G (m)) of 256 mS mm(-1), which are 30% and 25% higher than that of the single-channel SiO2 CBL device, respectively. The breakdown voltage is 230 V and the on-resistance (R (on)) is only 0.58 m omega cm(2).

摘要 : Ferroelectric (FE) HfZrO/Al2O3 gate stack AlGaN/GaN metal-FE-semiconductor heterostructure field-effect transistors (MFSHEMTs) with varying Al x Ga1-x N barrier thickness and Al composition are investigated and compared by TCAD simulation with non-FE HfO2/Al2O3 gate stack metal-insulator-semiconductor heterostructure field-effect transistors (MISHEMTs). Results show that the decrease of the two-dimensional electron gas (2DEG) density with decreasing AlGaN barrier thickness is more effectively suppressed in MFSHEMTs than that in MISHEMTs due to the enhanced FE polarization switching efficiency. The electrical characteristics of MFSHEMTs, including transconductance, subthreshold swing, and on-state current, effectively improve with decreasing AlGaN thickness in MFSHEMTs. High Al composition in AlGaN barrier layers that are under 3-nm thickness plays a great role in enhancing the 2DEG density and FE polarization in MFSHEMTs, improving the transconductance and the on-state current. The subthreshold swing and threshold voltage can be reduced by decreasing the AlGaN thickness and Al composition in MFSHEMTs, affording favorable conditions for further enhancing the device.

摘要 : Surface-acoustic-wave (SAW) devices have been widely investigated over many years as demand has grown for information sensing above 1000°C. At such high temperatures, metal electrode creep occurs, thereby causing the transformation of an electrode from a continuous uniform film to a discontinuous film with hollows or isolated grains. In this study, 100 nm thick ITO conductive oxide film is deposited on 100 nm thick Pt film to form an ITO/Pt bilayer-film composite electrode for high-temperature SAW devices. According to this way, the conductive stability of the Pt film electrode at high temperature can be greatly improved. Compared with the initial value, the electrical conductivity of single-layer 100 nm thick Pt film decreases to 65.4% with the area fraction of Pt at 64.1%. Meanwhile, the electrical conductivity of ITO/Pt bilayer-film decreases to only 95% with the area fraction of Pt at 63.1%. Then, the enhancement of high-temperature conductive stability can be attributed to the added ITO conduction channels. These findings demonstrate a potential route to design multilayer electrodes that can operate above 1000°C with promising applications in SAW devices needing to operate at high temperatures.

摘要 : CuO/beta-Ga2O3 hybrid structures with beta-Ga2O3 nanorods coated with CuO nanoparticle layers were successfully synthesized by a multi-cycle dipping and annealing process method. Compared with bare beta-Ga2O3 nanorods, the CuO/beta-Ga2O3 hybrid structures had greatly enhanced and dramatically broadened responses to light in the range from the near-ultraviolet to visible light. This novel synthetic pathway will provide new possibilities to prepare nanomaterials that integrate oxide heteroj unctions for photodetection applications.

摘要 : A double-recessed offset gate process technology for InP-based high electron mobility transistors (HEMTs) has been developed in this paper. Single-recessed and double-recessed HEMTs with different gate offsets have been fabricated and characterized. Compared with single-recessed devices, the maximum drain-source current (I (D,max)) and maximum extrinsic transconductance (g (m,max)) of double-recessed devices decreased due to the increase in series resistances. However, in terms of RF performance, double-recessed HEMTs achieved higher maximum oscillation frequency (f (MAX)) by reducing drain output conductance (g (ds)) and drain to gate capacitance (C (gd)). In addition, further improvement of f (MAX) was observed by adjusting the gate offset of double-recessed devices. This can be explained by suppressing the ratio of C (gd) to source to gate capacitance (C (gs)) by extending drain-side recess length (L (rd)). Compared with the single-recessed HEMTs, the f (MAX) of double-recessed offset gate HEMTs was increased by about 20%.

摘要 : The intriguing properties of the toroidal mode (TM) resonance can potentially promote a low-loss light-matter interaction. This study proposes an electromagnetically induced transparency (EIT) resonance with a high quality factor, which can reach 7798, and low mode volume can reach 0.009 mu m(3), high contrast ratio can reach nearly 100%, in the near-infrared region, which is generated by the magnetic TM in a reverse-symmetric coupling spiral metasurface. A two-oscillator model can only explain the influence of near-field coupling at the EIT point for weak coupling. Moreover, a multipole decomposition method shows that the excitation mechanism of EIT resonances originates from the destructive interference between the subradiant modes (magnetic toroidal dipole-electric quadrupole) and magnetic dipole resonance. Consequently, a new general extinction spectrum interference model is applied to fit all coupling conditions for both weak and strong coupling results that perfectly correspond to the multipole decomposition method. The results of this study could be useful in the analysis and understanding of the electromagnetic coupling characteristics of nanoparticles and provide a design approach for novel metasurfaces for low-loss optical applications.

摘要 : We proposed a sandwich structure to realize broadband asymmetric transmission (AT) for both linearly and circularly polarized waves in the near infrared spectral region. The structure composes of a silica substrate and two sand-clock-like gold layers on the opposite sides of the substrate. Due to the surface plasmons of gold, the structure shows that the AT parameters of linearly and circularly polarized waves can reach 0.436 and 0.403, respectively. Meanwhile, a broadband property is presented for the AT parameter is over 0.3 between 320 THz and 340 THz. The structure realizes a diode-like AT for linearly wave in forward and circularly wave in backward, respectively. The magnetic dipoles excited by current in the two gold layers contribute to the broadband AT. The current density in top and bottom metallic layers illustrates the mechanism of the polarization conversion for broadband AT in detail.

摘要 : Theoretical studies of ultra-thin silicon solar cells with cylindrical, conical and parabolic surface nanostructures inherited from natural self-assembled anodic alumina oxide (NSA-AAO) were performed by finite-difference time-domain (FDTD) method. All nanostructured solar cells obtained an optimized efficiency enhancement as high as more than 33% comparing with that of the anti-reflective (AR) one. Numerical results reveal that the range of efficient structural parameters for the nanostructured (e.g., cylindrical) solar cell can be effectively enlarged as the period of the nanostructure changes from 0.1 μm to 0.5 μm. Moreover, the improvements of absorption photocurrent density (Jph) in conical and parabolic nanostructured solar cells are comparable with the cylindrical nanostructured one but less sensitive to the fill factor and structural height in the whole simulation region of 0.1–0.9 and 0–0.25 μm, respectively. Equivalent refractive index models were used to analysis the antireflection performance of surface nanostructures from the point of view of sidewall profiles. Resonance modes induced through nanostructures have greatly improved the absorptance of solar cells in broadening wavelength bands which consequently raised the Jph. This study serves as a way for the practical design and application of AAO nanostructure based high-efficiency ultra-thin solar cells.

摘要 : A stacked lateral double-diffused metal–oxide–semiconductor field-effect transistor (LDMOS) with enhanced deple-tion effect by surface substrate is proposed (ST-LDMOS), which is compatible with the traditional CMOS processes. The new stacked structure is characterized by double substrates and surface dielectric trenches (SDT). The drift region is sepa-rated by the P-buried layer to form two vertically parallel devices. The doping concentration of the drift region is increased benefiting from the enhanced auxiliary depletion effect of the double substrates, leading to a lower specific on-resistance (Ron, sp). Multiple electric field peaks appear at the corners of the SDT, which improves the lateral electric field distribution and the breakdown voltage (BV). Compared to a conventional LDMOS (C-LDMOS), the BV in the ST-LDMOS increases from 259 V to 459 V, an improvement of 77.22%. The Ron, spdecreases from 39.62 m?·cm2to 23.24 m?·cm2and the Baliga's figure of merit (FOM) of is 9.07 MW/cm2.

摘要 : The optical properties and band structure evolution from amorphous to crystalline Ga 2 O 3 films was investigated in this work. Amorphous and crystalline Ga 2 O 3 films were obtained by changing the growth substrate temperatures of pulsed laser depo- sition and the crystallinity increase with the rising of substrate temperature. The bandgap value and ultraviolet emission intensity of the films increase with the rising of crystallinity as observed by means of spectrophotometer and cathodoluminescence spectroscopy. Abrupt bandgap value and CL emission variations were observed when amorphous to crystalline transition took place. X-ray photoelectron spectroscopy core level spectra reveal that more oxygen vacancies and disorders exist in amorphous Ga 2 O 3 film grown at lower substrate temperature. The valence band spectra of hard X-ray photoelectron spectroscopy present the main contribution from Ga 4sp for crys- talline film deposited at substrate temperature of 500 o C, while extra subgap states has been observed in amorphous film deposited at 300 o C. The oxygen vacancy and the extra subgap density of states are suggested to be the parts of origin of bandgap and CL spectra variations. The experimental data above yields a realistic picture of optical properties and band structure variation for the amorphous to crystalline transition of Ga2O3 films.