The tunneling effect and interface state in the p-Ge/GeO2p-Si structure of a wafer-bonding Ge/Si avalanche photodiode (APD) are investigated. It is found that the thin interfacial GeO2 layer (1-2 nm) formed by the hydrophilic reaction at the wafer-bonding interface significantly affects the performance of the Ge/Si APD. With the increase of the GeO2 thickness, the dark current of the Ge/Si APD decreases enormously due to the blocking effect of this GeO2 layer. Owing to the carrier accumulation in Ge layer under illumination condition, the voltage sharing effect of the GeO2 layer (thicker) becomes serious, leading to the absence of the electric field in Ge layer. The photon-generated electrons at Ge/GeO2 interface can be captured and released by the interface states at certain reverse bias. This can adjust the avalanche current of the Ge/Si APD. The stronger interface recombination induced by the larger interface state density (ISD) results in the decrease of the electric field in Ge layer. This increases the transit time of carriers, which in turn decreases the 3dB-bandwidth. Due to the drastic increase of the dark current (larger ISD), the gain of the Ge/Si APD decreases.

Voltage sharing effect and interface state calculation of a wafer-bonding Ge/Si avalanche photodiode with an interfacial GeO2 insulator layer.

Microcrystal-Induced Crystallization Effect for High-Quality Germanium/Silicon Heteroepitaxial Nanofilms

This paper studies a set of globally coupled bistable oscillators, all subjected to the same weak periodic signal and identical coupling. The effect of mean field density (MFD) on global dynamics is analyzed. The oscillators switch from intra- to interwell motion as MFD increases, clearly demonstrating MFD-enhanced signal amplification. A maximum amplification also occurs at a moderate level of MFD, indicating that the response exhibits a nonmonotonic sensitivity to MFD. The MFD-enhanced response depends mainly on the signal intensity but not on the signal frequency or the network topology. The analytical investigation provides a simplified model to study the mechanism underlying this resonancelike behavior. It is shown that by modifying the bistability nature of the potential energy, the mean field density can promote well-to-well oscillations and larger amplitude motions. Finally, the robustness of this phenomenon to various signal waveforms is examined. It can therefore be used alternatively to efficiently amplify weak signals in practical situations with large network sizes.

Enhanced signal response in globally coupled networks of bistable oscillators: Effects of mean field density and signal shape.

The effects of surface defects at the sidewall of absorption and multiplication layers on the sidewall leakage current in separate-absorption-charge-multiplication Ge/Si avalanche photodiodes with a mesa structure are investigated. It is found that high-density surface defects and a strong electric field at the sidewall are the reasons for the large sidewall leakage current. In addition, the influence of the width of the guard ring on the sidewall leakage current is also studied. It is found that increasing the width of the guard ring is beneficial to the reduction of the sidewall leakage current by reducing the sidewall electric field and the reduction is not significant when the guard-ring width is greater than 2 µm.

Research on the leakage current at sidewall of mesa Ge/Si avalanche photodiode

Waveguide-coupled Ge/Si separate absorption, charge and multiplication avalanche photodiodes (SACM APDs) have shown significant potential as high-sensitivity, low-noise, and high-speed photo-detection for optical communications. Here we present a nanoscale single-mode waveguide-integrated vertical Ge absorption, lateral Si charge and single multiplication configuration for a waveguide Ge/Si SACM APD. This device can achieve 90% absorption at 1550 nm wavelengths with a 10 μm-long Ge layer. The device exhibits a seven times reduction in device length compared to conventional waveguide structures and a 29% increase compared to multi-mode interference coupling. Meanwhile, a 3-dB bandwidth can achieve 47 GHz, which is five times higher than the conventional vertical Ge absorption, lateral Si charge and multiplication devices.

Enhancement of responsivity and speed in waveguide Ge/Si avalanche photodiode with separate vertical Ge absorption, lateral Si charge and multiplication configuration

Exhibiting extremely high electric polarization, N-polar Group III-nitrides heterostructure has been widely used on high-electron-mobility transistors (HEMTs) and terahertz photodetectors in recent years In this paper, we numerically investigated an N-polar GaN/AlGaN/GaN HEMT device in which the two-dimension electron gas is induced at the top GaN/AlGaN interface Characteristics of the device were determined by using experimental data to calibrate the few adjustable parameters of our simulations Effects of interface charges on the device were researched by changing the component of Al In addition, the dependency of scaling the device dimensions on direct current (DC) output characteristics, such as the gate length and the barrier height was also analyzed in details Our simulations showed that increases of Al mole fraction and AlGaN barrier height and a decrease of the gate length can improve the DC performance of HEMT device to some extent That could be a significant guidance for designing or optimizing the structure of N-polar GaN-based devices

Analysis of direct current performance on N-polar GaN-based high-electron-mobility transistors for next-generation optoelectronic devices

A moderate degree of diversity, in form of quenched noise or intrinsic heterogeneity, can significantly strengthen the collective response of coupled extended systems. As yet, related discoveries on diversity-induced resonance are mainly concentrated on symmetrically distributed heterogeneity, e.g., the Gaussian or uniform distributions with zero-mean. The necessary conditions that guarantee the arise of resonance phenomenon in heterogeneous oscillators remain largely unknown. In this work, we show that the standard deviation and the ratio of negative entities of a given distribution jointly modulate diversity-induced resonance and the concomitance of negative and positive entities is the prerequisite for this resonant behavior emerging in diverse symmetrical and asymmetrical distributions. Particularly, for a proper degree of diversity of a given distribution, the collective signal response behaves like a bell-shaped curve as the ratio of negative oscillator increases, which can be termed negative-oscillator-ratio induced resonance. Furthermore, we analytically reveal that the ratio of negative oscillators plays a gating role in the resonance phenomenon on the basis of a reduced equation. Finally, we examine the robustness of these results in globally coupled bistable elements with asymmetrical potential functions. Our results suggest that the phenomenon of diversity-induced resonance can arise in arbitrarily distributed heterogeneous bistable oscillators by regulating the ratio of negative entities appropriately.

Diversity-induced resonance in a globally coupled bistable system with diversely distributed heterogeneity.

Results show that the astrocytes can not only listen to the talk of large assemble of neurons but also give advice to the conversations and are significant sources of heterogeneous couplings as well. In the present work, we focus on such regulation character of astrocytes and explore the role of heterogeneous couplings among interacted neuron-astrocyte components in a signal response. We consider reduced dynamics in which the listening and advising processes of astrocytes are mapped into the form of group coupling, where the couplings are normally distributed. In both globally coupled overdamped bistable oscillators and an excitable FitzHugh-Nagumo (FHN) neuron model, we numerically and analytically demonstrate that two types of bell-shaped collective response curves can be obtained as the ensemble coupling strength or the heterogeneity of group coupling rise, respectively, which can be seen as a new type of double resonance. Furthermore, through the bifurcation analysis, we verify that these resonant signal responses stem from the competition between dispersion and aggregation induced by heterogeneous group and positive pairwise couplings, respectively. Our results contribute to a better understanding of the signal propagation in coupled systems with quenched disorder.

Double resonance induced by group coupling with quenched disorder.

Resonance Induced by Heterogeneous Higher-Order Interaction in Linearly Coupled Systems

A balance in nature is maintained by the coexistence of multiple species through interspecific competition. The evolutionary dynamics of cyclic interactions contain interactions that represent different biological behaviors. Biological behavior is influenced by the external environment, which may affect the stability of ecosystems. We investigated the evolutionary dynamics of interspecific competition after a periodic change in the external environment affects species. We consider that when the periodic external environments affect mortality, interspecific cyclical competition may be more pronounced, and thus increase the probability of extinction of species. By performing Monte Carlo simulations, we observed that the evolutionary dynamics of interspecific cyclic competition have different responsivity when subjected to external periodic changes at different frequencies, and stochastic resonance phenomena occurred. We show that the influence of the periodic external environment and its frequency is one of the factors that determine whether ecosystems coexist stably.

Periodic environmental effect: stochastic resonance in evolutionary games of rock-paper-scissors

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