High-sensitivity Ge/Si avalanche photodiodes (APDs) have recently gained attention for their application in sensing and optical communication due to their low cost and CMOS compatible process. However, compared to commercial III–V compound APDs, Ge/Si APDs usually suffer from the issue of relatively low primary responsivity. In this paper, we report Ge-on-Si separate absorption, charge, and multiplication avalanche photodiodes (SACM-APDs) with photon-trapping nanostructures to enhance light absorption. Besides, by optimizing the depth of the holes, the photon trapping structure could reduce the dark current without compromising the avalanche effect as confirmed by both simulations and experimental results. As a result, the responsivity of the photon trapping APDs increases by 20-50 % from that of control APDs at the 1,550 nm wavelength band. Furthermore, a quantum efficiency higher than 80% could be achieved at 1550 nm when the photon trapping Ge-on-Si APD is on Si-on-insulator (SOI) platforms as predicted by simulations. Our results demonstrate that the photon trapping Ge/Si APDs exhibit superior dark current, light absorption and gain than those of the control devices, which have the potential applications in sensing and optical quantum communications.

Plasma dynamics are essential in high-power electron beam diodes, as they influence the current density and can even cause gap closure because of fast expansion velocity during operation. In this study, the formation and expansion of the cathode plasma in a high-power planar diode has been investigated by particle-in-cell simulations. The results indicate that the expansion velocity of the cathode plasma in the planar diode is ∼2.5 cm/μs operating with a 340 kV peak voltage and 1.5 kA current, which possesses a maximum pressure of 1 Torr pressure and a gas desorption rate of 38 molecules per electron. Moreover, the enhanced emission on the edge causes a faster growth rate of the gas pressure and formation of plasma, which possesses a higher plasma density than other regions. A higher gas desorption rate and total amount of outgoing gas can cause a larger velocity of plasma expansion, and the expansion velocity is proportional to the logarithm of the rising speed of the diode voltage, while the amplitude of diode voltage did not show a clear correlation with plasma velocity. Finally, a combined dependence of the plasma velocity on the gas desorption rate, total gas volume, rising speed of the diode voltage, and diode voltage is concluded. This work provides new insights into the dynamics of cathode plasma in high-power diodes and may be helpful for engineering design.

We have investigated the recrystallization behavior of the argon (Ar) bubble-rich amorphous germanium (a-Ge) by utilizing the excimer laser annealing (ELA) in comparison with the conventional furnace annealing (FA). We demonstrate that the ELA can efficiently suppress the Ar bubbles to have good recrystallization of a-Ge in sharp contrast to the conventional FA treatment where the bubble-rich a-Ge can only be getting partial recrystallization with many dislocations and stacking faults. Transmission electron microscopy results exhibit that ELA can transform the Ar implantation-induced damaged layer into a fully crystalline matrix containing no visible defects except isolated bubbles in a low density. We reveal the critical role of the Ar bubbles played in the recrystallization behavior of the a-Ge by comparing the two types of annealing methods. This finding provides a new routine to suppress the implantation-induced noble-gas bubbles in semiconductors to solve the issue of the high-quality regrowth of the noble–gas implanted layer.

This work aims to investigate the influence of thickness of multilayered porous silicon (MPS) on its cold emission properties. The MPS layer with different thicknesses was prepared by adjusting the charge quantity Q ( $\text{mA}\cdot \text{min}$ ) in the pulsed electrochemical etching process and oxidized through rapid thermal oxidation (RTO). The microstructure of the oxidized MPS was characterized by the scanning electron microscope (SEM) and the cold emission performance of the MPS-based emitters were also measured in vacuum. The studies show that, to fully utilize the advantages of a multilayered structure, it is essential to use the appropriate thickness and achieve sufficient oxidation for the MPS in this electron emitter fabrication. The optimal electron emission performance, with a stable efficiency of nearly 1%, a high current density of about 300 $\mu$ A/cm $^{\text{2}}$ , and an emission current fluctuation of only 9.8% can be achieved with a 5.5- $\mu$ m thickness in the present MPS configuration and RTO condition at the operating voltage of 20 V. This work helps explore the intrinsic relationship between multilayered structures and the cold emission property of PS-based cathodes, facilitating their application in vacuum microelectronic devices.

This paper proposes an electrochemical-induced hydrogen passivation (CHP) method to improve the field emission performance of the multilayered porous silicon (MPS)-based electron source. We show that CHP treatment enhances the surface morphology of MPS and compensates for inefficient oxidation in the top half of the MPS layer caused by electrochemical oxidation (ECO), achieving complete and uniform oxidation properties for continuous electron acceleration. The measurement results demonstrate that this simple and convenient method significantly enhances the emission current and efficiency, while also improving the repeatability and stability of the MPS-based electron source. Therefore, CHP is a valuable method to enhance the cold emission properties of MPS-based electron sources, making it a promising on-chip electron emitter in vacuum electronic devices.

Most of the existing cement evaluation technologies suffer from tool eccentralization due to gravity in highly deviated wells and horizontal wells. This paper proposes a correction method to lessen the effects of tool eccentralization on evaluation results of cement bond using segmented bond tool, which has an omnidirectional sonic transmitter and eight segmented receivers evenly arranged around the tool 2 ft from the transmitter. Using 3-D finite difference parallel numerical simulation method, we investigate the logging responses of centred and eccentred segmented bond tool in a variety of bond conditions. From the numerical results, we find that the tool eccentricity and channel azimuth can be estimated from measured sector amplitude. The average of the sector amplitude when the tool is eccentred can be corrected to the one when the tool is centred. Then the corrected amplitude will be used to calculate the channel size. The proposed method is applied to both synthetic and field data. For synthetic data, it turns out that this method can estimate the tool eccentricity with small error and the bond map is improved after correction. For field data, the tool eccentricity has a good agreement with the measured well deviation angle. Though this method still suffers from the low accuracy of calculating channel azimuth, the credibility of corrected bond map is improved especially in horizontal wells. It gives us a choice to evaluate the bond condition for horizontal wells using existing logging tool. The numerical results in this paper can provide aids for understanding measurements of segmented tool in both vertical and horizontal wells.