- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2018
- differential low noise amplifier
- GaAs pHEMT
- Square Kilometre Array (SKA)
- fully- integrated
- balun
- broadband
- S-band
- Electronic Science and Technology
- National Taiwan University
- Academia Sinica
-
Surface passivation of GaAs (0?0?1) by Hg2Cl2 nanoplates combined with hexadecanethiol
摘要： Surface states in III–V semiconductor materials have detrimental effects on their optical and electronic properties, and the passivation of GaAs surface has become of longstanding interest. Here, we demonstrated a two-step process to greatly reduce surface states of GaAs (0 0 1) by a combination of Hg2Cl2 and alkanethiol. Firstly, uniformly distributed Hg2Cl2 nanoplates with a size around 200 nm were deposited on GaAs surface by the incubation of the etched wafer into the mercury (II) chloride solution, without the need of a reducing agent. Secondly, hexadecanethiol (HDT) molecules were assembled on the Hg2Cl2-GaAs hybrid surface, which decreases the density of surface states through electron transfer processes. Noticeably, after such two steps, a significant enhancement of photoluminescence (PL) signal was noted. It may be due to the fact that components of As2O3 and As0 which are identified as major sources of the surface states are reduced considerably, or even disappear. Chemical state changes of mercury species are expected to play a key role in achieving the surface passivation. Obtained hybrid GaAs materials with considerably improved photonic signals open a new avenue for the fabrication of electronic and optoelectronic devices.
关键词： Surface states,GaAs (0 0 1),Hg2Cl2 nanoplate,PL enhancement,Electrical passivation
更新于2025-09-23 15:22:29
-
Optimized chemical cleaning procedure for enhancing photoemission from GaAs photocathode
摘要： To obtain cleaner GaAs photocathode surface, various wet chemical cleaning methods to remove the oxides and carbon contaminations from the surface of GaAs photocathode are investigated, and an improved chemical etching method is presented to further enhance the cathode photoemission performance. By means of X-ray photoelectron spectroscopy analysis, characteristics of these methods are summarized. HF solution can effectively reduce surface oxides, but it does not effectively act on the absorbed carbon contaminations. The mixed solution of HCl and isopropanol scores well in removing carbon contaminations, but the ability of removing oxides is relatively weaker. The mixed solution of HCl and deionized water right after the mixed solution of H2SO4, H2O2 and deionized water is unfavorable to reduce Ga oxides. The improved chemical etching method, which uses HF solution followed by the mixture of HCl and isopropanol has more advantages in removing oxides and carbon contaminations at the same time. Moreover, a hydrophobic surface is obtained by using the improved method, which also plays a role in the contaminations removal. The quantum efficiencies of GaAs photocathode undergoing various wet chemical cleaning procedures are compared after subsequent heat treatment and activation. The results show that the chemical treatment of HF solution followed by the mixture of HCl and isopropanol can help GaAs photocathode obtain higher activated photocurrent and quantum efficiency.
关键词： Chemical cleaning,GaAs photocathode,Quantum efficiency,X-ray photoelectron spectroscopy
更新于2025-09-23 15:22:29
-
High-frequency breakdown of the integer quantum Hall effect in GaAs/AlGaAs heterojunctions
摘要： The integer quantum Hall effect is a well-studied phenomenon at frequencies below about 100 Hz. The plateaus in high-frequency Hall conductivity were experimentally proven to retain up to 33 GHz, but the behavior at higher frequencies has remained largely unexplored. Using continuous-wave terahertz spectroscopy, the complex Hall conductivity of GaAs/AlGaAs heterojunctions was studied in the range of 69–1100 GHz. Above 100 GHz, the quantum plateaus are strongly smeared out and replaced by weak quantum oscillations in the real part of the conductivity. The amplitude of the oscillations decreases with increasing frequency. Near 1 THz, the Hall conductivity does not reveal any features related to the filling of Landau levels. Similar oscillations are observed in the imaginary part as well; this effect has no analogy at zero frequency. This experimental picture is in disagreement with existing theoretical considerations of the high-frequency quantum Hall effect.
关键词： integer quantum Hall effect,GaAs/AlGaAs heterojunctions,terahertz spectroscopy,high-frequency Hall conductivity,quantum oscillations
更新于2025-09-23 15:22:29
-
[IEEE 2018 Dynamics of Systems, Mechanisms and Machines (Dynamics) - Omsk, Russia (2018.11.13-2018.11.15)] 2018 Dynamics of Systems, Mechanisms and Machines (Dynamics) - Automatic Nonlinear Modeling Technique for Gaas HEMT
摘要： A new technique for nonlinear transistor modeling is suggested. The technique includes an analytical extraction and a multistage optimization, providing fully automated modeling. An extraction algorithm for the parameters of an internal voltage-controlled current source Ids is shown. A fully automated workflow of small-signal model extraction is presented. An approach for obtaining parameters of nonlinear capacitances is described. A 0.15um GaAs pHEMT nonlinear model was built and verified with measured IV-curve, multi-bias S-parameters and power characteristics.
关键词： compact nonlinear model,microwave transistor,large-signal model,GaAs HEMT
更新于2025-09-23 15:22:29
-
Optical Properties of Energy-Dependent Effective Mass GaAs/GaxIn1?xAs and GaAs/AlxGa1?xAs Quantum Well Systems: A Shooting Method Study
摘要： In this paper, we study the effect of energy-dependent effective mass on optical properties of GaAs/GaxIn1?xAs and GaAs/AlxGa1?xAs quantum well systems through the compact density matrix approach. We solved the resulting non-linear Schro¨dinger equation by a simple shooting method and present the algorithm. We show that the energy-dependent effective mass effect is more important for systems with narrower quantum well systems. By an energy-dependent effective mass assumption, absorption coef?cient peak height increases with increasing the total system length L while in the constant effective mass limit, absorption coef?cient peak heights have not been in?uenced by changing L. In the GaAs/AlxGa1?xAs system, by increasing the number of wells, the linear absorption coef?cient amplitude at ?rst increases and then decreases in the ?xed effective mass approximation and monotonically decreases in the energy-dependent effective mass case. By increasing the number of wells, the linear absorption coef?cient peak position at ?rst shows a blue shift and then shows a redshift. In the GaAs/GaxIn1?xAs system, the situation is more complicated and it is described in more detail in the text. However, GaAs/GaxIn1?xAs quantum well systems have larger values of absorption coef?cient peak heights than GaAs/AlxGa1?xAs ones.
关键词： shooting method,GaAs/GaxIn1?xAs and GaAs/AlxGa1?xAs Quantum wells,refractive index changes,energy-dependent effective mass,absorption coef?cient
更新于2025-09-23 15:21:21
-
[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - High-frequency photocathode based on CNT-yarn emitter and GaAs photoswitch
摘要： A high frequency photocathode based on a carbon nanotube (CNT)-yarn in series to a semi-insulating (s.i.) GaAs was fabricated and used for field electron emission in a diode configuration. This hybrid two-chip technology allows the separate optimization of the yarn emitter and the photoswitch. This concept can overcome the capacitance limitations of miniaturized high-frequency vacuum tubes. The used CNT yarn emitter with 20 μm diameter had a threshold electric fields of ~1.8 V/μm (defined at 1mA/cm2) with a stable field emitter current up to 400 μA. The high-voltage photomodulation was up to 100 MHz.
关键词： carbon nanotube,CNT yarn,photocathode,semi-insulating GaAs
更新于2025-09-23 15:21:21
-
Novel design strategy for GaAsa??based solar cell by application of singlea??walled carbon nanotubes topmost layer
摘要： Attempts to improve solar cells efficiency touch all its constituents and are directly related to their fabrication protocols. While the most promising material platform for high efficiency photovoltaic devices is still III-V semiconductors, introduction of novel materials like single-walled carbon nanotubes (SWCNTs), which are characterized by unique combination of conductivity and transparency, might greatly yield the device performance. Here, for the first time, we present the results of the fabrication and characterization of a thin-film GaAs solar cell with a SWCNT top contact. We examine the contact between the SWCNT film and the semiconductor structure by means of the optical and electron beam-induced current techniques. The fabricated device demonstrates better performance, that is, increased power conversion efficiency from 10.6% to 11.5% when compared to the cell with the traditional metal contact grid, stemming from the enhanced photocurrent collection efficiency and low parasitic light absorption in the emitter layer. We envision future prospects to exploit the multifunctionality of the SWCNTs in fabrication of highly efficient photovoltaic devices including flexible solar cells.
关键词： EBIC,EQE,solar cell,GaAs,SWCNT,OBIC
更新于2025-09-23 15:21:01
-
Light-induced transition between the strong and weak coupling regimes in planar waveguide with GaAs/AlGaAs quantum well
摘要： Exciton-polaritons in planar waveguides are of great interest for application in polariton circuits due to the large polariton group velocity in the plane of the waveguide. We demonstrate the ability to control the exciton-polariton coupling by light in an AlGaAs-based planar waveguide with GaAs/AlGaAs quantum well. The transition between strong and weak coupling regimes observed with increasing light intensity is explained by the increase in exciton mode losses due to the quantum well charging. This assumption is confirmed by the reflection spectroscopy with resonant illumination.
关键词： AlGaAs,GaAs,planar waveguides,strong coupling,quantum well,exciton-polaritons,weak coupling
更新于2025-09-23 15:21:01
-
[Institution of Engineering and Technology 20th Italian National Conference on Photonic Technologies (Fotonica 2018) - Lecce, Italy (23-25 May 2018)] 20th Italian National Conference on Photonic Technologies (Fotonica 2018) - Second Harmonic Generation Circul Dichroism in Au Coated Gaas-based Nanowires
摘要： Nanostructures with broken symmetry can interact with circularly polarized light to mimic chiroptical (chiral-optical) effects, usually observable in chiral media. This phenomenon is known as extrinsic chirality. Second harmonic generation (SHG) is extremely sensitive to symmetry breaking, down to a single atomic monolayer and it has been extensively used as a probe of extrinsic chirality. Here we present SHG measurements of GaAs nanowires partially covered with Au, fabricated by a self-catalysed technique. The Au coated GaAs nanowires give rise to a dramatic circular dichroism in the generated second harmonic signal, compared to nanowires without coating.
关键词： plasmonic coating,extrinsic chirality,second harmonic generation,GaAs nanowires
更新于2025-09-23 15:21:01
-
Observation and implications of the Franza??Keldysh effect in ultrathin GaAs solar cells
摘要： Voltage-dependencies were observed in the external quantum efficiency (EQE) spectra of ultrathin GaAs solar cells. The subbandgap tail was shown to increase going from forward to reverse bias, while at energies above the bandgap, voltage-dependent oscillations in the EQE were measured. Using optical simulations, it is irrefutably shown that the voltage-dependencies are caused by the Franz-Keldysh effect, that is, an electric field-dependent absorption coefficient near the bandgap. The dependency on voltage of the subbandgap tail is demonstrated to be strongest in thin-film cells with a textured rear mirror, since the absorptivity below the bandgap is enhanced by light trapping. The voltage-dependent subbandgap tail has important implications for the use of the reciprocity relation between photovoltaic quantum efficiency and electroluminescence. It is shown that the radiative limit for the open-circuit voltage of thin-film cells integrated with light management schemes can be underestimated by more than 25 mV. Consequently, these cells may be assumed to be closer to the radiative limit than they really are.
关键词： Urbach tail,Franz-Keldysh effect,reciprocity,textured solar cells,ultrathin gaas
更新于2025-09-23 15:21:01