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kent, ised f line 2 ith r ut-off e mu alan high responsivity (>600 A/W), high speed, high expensive filters. In order to avoid these disadvantages, high performance solid-state UV photodetectors with Photonics and Nanostructures – Fundamentals ansurface for wavelengths shorter than 280 nm. In this case, ultraviolet (UV) photodetectors with cut-off wavelengths around 280 nm, which are also called solar-blind detectors, can detect very weak UV signals under intense background radiation. These devices have important applications including missile plume detec-tion, chemical/biological agent sensing, flame alarms, covert space-to-space and submarine communications, semiconductor photodetectors, such as AlxGa1xN with x 0.4 are ideal candidates for this purpose. These devices are intrinsically solar-blind, in which no additional filters are needed, they have low noise [7], and fast response times [8]. The lack of high internal gain has been the major limitation for the usage of AlGaN photodetectors for applications that require high sensitivity detectors. There have been several theore-tical research work that examined the avalanche effect in GaN and AlGaN-based structures [9–11]. Experi-mental work on both GaN [12–18] and AlGaN-base