Modeling and Engineering Impact Ionization in Avalanche Photodiodes for Near and Mid Infrared Applications

Avalanche photodiodes (APDs) are the preferred photodetector in many applications in which low light levels need to be detected. The reason why APDs are important in such applications is due to their internal gain, which improves the APD's sensitivity. Compared to receivers based on PIN photodiodes, which do not present internal gain, APD-based receivers achieve 5--10 dB improved sensitivity. The origin of the APD's internal gain is the impact ionization process. However, due to the stochastic nature of the impact ionization process the multiplication gain comes at the expense of extra noise. This multiplication noise is called the excess noise, and it is a measure of the gain uncertainty. In addition, as the multiplication gain increases the buildup time, which is the time required for all the impact ionizations to complete, also increases. Thus, for a given multiplication gain the buildup time limits the bandwidth of the APD.;The main challenge for state-of-the-art APDs, operating in linear and Geiger modes, is to achieve higher operating speeds. For application in which the APD is operated in linear mode the limited speed of APD-based receivers have limited their use in systems that operate at 2.5 and 10 Gbps. However, to meet the demand of the exponential growth in data transfer, the telecommunication industry has been moving toward 40-Gbps and 100-Gbps protocols for their core fiber-optic backbone networks alongside the existing 10-Gbps infrastructure operating at the low-loss wavelength of 1.55 microns. Moreover, the fast progress on quantum communications requires Geiger-mode APDs to operate at higher repetition rates. Currently, Geiger-mode APDs are limited to operate at detection rates of about 20 MHz. In addition, there has been relatively little work on infrared APDs, although there are many applications in remote sensing, medical imaging, and environmental monitoring. In particular, there is no GaAs-based APD operating in Geiger mode beyond 2 microns.;This dissertation provides theoretical analysis and experimental exploration of APDs working in linear and Geiger modes in the near infrared (NIR) and mid-infrared (MIR) ranges of wavelength. This research effort is geared to address the aforementioned current challenges of the state-of-the-art APD technology. In the theoretical part of this work the focus is on the development of new theoretical methods that allow us to model, understand, and characterize avalanche photodiodes working in linear and Geiger modes. The objective is that the developed methods help the design and optimization of high performance, high speed APDs. The experimental part of this research effort consists of the design, fabrication and characterization of a novel mid-infrared sensor, based on GaAs technology, called the quantum-dot avalanche photodiode (QDAP). The main motivation for the QDAP is to exploit its potential of working in Geiger mode regime, which can be utilized for single-photon detection. In addition, the QDAP represents the first GaAs-based APD operating in the mid infrared range of wavelength.