The frame rate of the digital high-speed video camera was 2000 frames per second (fps) in 1989, and has been exponentially increasing. A simulation study showed that a silicon image sensor made with a 130 nm process technology can achieve about 10¹⁰ fps. The frame rate seems to approach the upper bound. Rayleigh proposed an expression on the theoretical spatial resolution limit when the resolution of lenses approached the limit. In this paper, the temporal resolution limit of silicon image sensors was theoretically analyzed. It is revealed that the limit is mainly governed by mixing of charges with different travel times caused by the distribution of penetration depth of light. The derived expression of the limit is extremely simple, yet accurate. For example, the limit for green light of 550 nm incident to silicon image sensors at 300 K is 11.1 picoseconds. Therefore, the theoretical highest frame rate is 90.1 Gfps (about 10¹¹ fps)

We investigated the characteristics of a type-II InAs/GaSb superlattice (SL) with various composition periods based on the k · p band calculation. Considering the application to the infrared photodetectors, the essential material parameters are calculated and evaluated from the electronic band structure as a function of the width of InAs and GaSb layers. Under dark conditions, the smaller effective mass in a short period SL (especially with small GaSb layer width) could result in the reduction of the Shockley–Read–Hall (SRH) leakage current which is proportional to the intrinsic carrier density. However, this merit is also concerned with the increase of the dark current due to the enhanced band-to-band tunneling in high electric field conditions. Moreover, in terms of the photo-absorption property, the smaller effective mass results in the smaller joint density of states, which compensates the contribution of the large optical matrix element to the absorption coefficient in short period SL.

The dark current characteristics in InAs/GaSb type-II superlattice (SL) barrier infrared photodetectors are theoretically investigated. The barrier photodetector is composed of a contact layer, a barrier layer, and an active region (n type), for which two different engineered structures, i.e., called pBn and nBn, are evaluated using the drift-diffusion-based device simulator. It is shown that both structures can effectively reduce the dark current compared to the p-i-n photodiode without barrier, and the dependence on the barrier doping density are discussed in detail. There exists an optimum doping density to minimize the dark current in both structures, but the different mechanisms contribute to the dark current.