Currently, in the information age, the realization of low light level digital night vision technology that can satisfy the remote transmission requirements of image information is urgently needed. The electron bombardment-type low light level imaging devices, namely, electron bombarded charge-coupled devices (EBCCDs) and electron bombarded complementary metal-oxide semiconductors (EBCMOSs), are used to package the back thinned charge-coupled devices (CCDs) and complementary metal-oxide semiconductor (CMOS) devices into an electric vacuum device. Accordingly, the chip replaces the microchannel plate and fluorescent screen to form a close proximity focusing system with the photocathode. Photoelectrons generated by the photocathode are accelerated by a high-voltage electric field and bombarded on the surface of the imaging device for direct imaging, which has many advantages, such as small size, high sensitivity, and ultra-low illumination. The processing steps in such imaging devices can be described as core making, back support, thinning, back processing, and tube sealing. Compared with EBCCDs, EBCMOSs, which are low light level imaging devices based on electron bombarded active pixel sensors (EBAPSs), have smaller size, faster imaging speed, low power consumption, and strong radiation resistance. Therefore, EBCMOS-based low light level night vision technology has become a popular research topic in the industry. Obtaining a high-gain EBCMOS electron multiplier layer is one of the key challenges in the development of EBCMOS low-light-level imaging devices. However, few relevant theoretical studies have been conducted to date. Therefore, this study focuses on the factors affecting the charge collection efficiency of electron multipliers in EBAPS imaging devices and builds a theoretical and technical foundation for constructing a high-gain EBCMOS electron multiplier.

Based on the carrier transport theory and Monte Carlo simulation algorithm, a calculation model of the electron transport process in the passivation and electron multiplication layers of EBAPSs is established; moreover, the influence of structural parameters on the distribution and collection of secondary electrons is analyzed. First, the influences of SiO₂ and Al₂O₃ passivation layers on the distribution and collection of secondary electrons are compared. Second, when the passivation layer material is SiO₂, the influence of changing passivation layer thickness, incident electron energy, and P-type base thickness on the distribution and collection of secondary electrons is analyzed. Finally, the influence of changing doping concentration of the P-type base on the distribution and collection of secondary electrons is discussed. The simulation results provide a theoretical basis for device fabrication.

When the passivity layer material is SiO₂, the charge collection efficiency is 42.5%, and the maximum incident depth and scattering radius of the incident electrons in the electron multiplication layer are 450 nm and 380 nm, respectively. With an increase in the incident depth, the distribution probability of the secondary electrons first increases and then decreases (Figs. 1 and 2). As the dead-layer thickness increases from 25 nm to 100 nm, the charge collection efficiency decreases. With an increase in the incident depth, the distribution probability of the secondary electrons first increases and then decreases. The probability trend of the secondary electron distribution with incident depth remains the same (Figs. 3 and 4). An increase in the incident photoelectron energy can improve the charge collection efficiency to some extent. With an increase in the incident depth, the probability of the secondary electron distribution first increases and then decreases. The greater the energy level, the greater the incident depth (Figs. 5 and 6). When the thickness of the P-type base increases from 5 μm to 20 μm, the charge collection efficiency decreases from 42.5% to 27.8% and collection efficiency of the center pixel decreases. In other words, the diffusion radius of the multiplier electron in the collection area increases, which is not conducive to constructing high-resolution imaging devices. With an increase in the incident depth, the distribution probability of the secondary electrons first increases and then decreases. The probability trend of the secondary electron distribution with depth remains the same (Figs. 7 and 8). The charge collection efficiency at different doping concentrations, ranging from 10¹⁵ cm^-3 to 10¹⁹ cm^-3, is simulated. It can be observed that the charge collection efficiency decreases as the doping concentration increases (Fig. 9).

In this study, the factors affecting the charge collection efficiency of the electron multiplier in EBAPS imaging devices are studied. When silicon dioxide with a low passivation layer density is used as the passivation layer, the incident depth of the incident photoelectrons improves; subsequently, the charge collection efficiency improves. Reducing the passivation layer thickness and increasing the energy of the incident electrons are beneficial for reducing the recombination of the secondary electrons in the dead layer, which improves the charge collection efficiency. Reducing the thickness and doping concentration of the P-type base is conducive to reducing the recombination of carriers while multiplying electron diffusion, thus improving the charge collection efficiency. The charge collection efficiency of the device after simulation optimization can reach 42.5%, which can provide theoretical support for the development of domestic EBCMOS devices.