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Avalanche photodiodes (APDs) are a promising detector technology for light detection and ranging (LIDAR) systems needed for a variety of DoD and commercial applications. However, a new material that is sensitive to 1.55 μm and has low “excess noise” is needed to achieve the required signal-to-noise. The main issue for improving APD signal-to-noise is to reduce excess noise. Excess noise is inevitable in APDs because impact ionization must occur to obtain a high multiplication gain. One solution to reduce the excess noise is to develop a new material system with favorable impact ionization coefficients. The ratio of electron (α) and hole (β) impact ionization coefficients, defined as k value, is intrinsically defined by the material and is a dominant factor for the APD’s excess noise. In this work, we investigate InAs/AlSb type-II superlattice (T2SL) APD. The superlattices provide us with additional degrees of freedom to engineer the electronic band structure. Our work is building on previous, promising results with the quaternary system AlInAsSb. We have theoretically modeled an InAs/AlSb type II superlattice (T2SL) system that can provide flexibility to engineer the electronic band structure to achieve single carrier impact ionization and reduce the excess noise. The simulation of this T2SL predicts that InAs/AlSb has higher absorption and would work as an electron- APD with low k. We will discuss design, growth, fabrication and IV characterization of this photodiodes. |
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