Development of wide-band-gap AlxGa1-xAs (x>0.7) photodiodes

Abstract

The development of high-performance scintillation materials that emit light below 400 nm has prompted the development of improved solid-state UV photodetectors. While silicon provides a mature context for UV photodetectors, the high dark current due to its low band-gap (1.1 eV) limits the signal-to-noise performance when scaling the detector to large areas. Photodetectors fabricated in materials with a larger band-gap have the potential to surmount the performance limitations experienced by silicon. Al x Ga 1-x As, is a material that provides a band gap from 1.55 eV to 2.13 eV, depending on the Al concentration. Using high Al concentration (0.7 x Ga 1-x As to engineer a wider bandgap > 2eV is very desirable in terms of reducing dark noise. Due to its strong absorption of UV-light at the material surface, however, surface effects limit the quantum efficiency below 400 nm. Introducing surface layers that have a longer penetration depth for UV photons promises to boost the quantum efficiency in the UV while maintaining low dark current. This work describes the development of a photodiode fabricated in Al x Ga 1-x As, x > 0.7, compared to an Al x Ga 1-x As, x > 0.7 photodiode with an AlAs surface (x = 1). It presents the design of the photodiodes, simulations of their performance, the fabrication process, along with characterization data of fabricated photodiodes. We report on the surface effects of high aluminum concentration Al x Ga 1-x As, x > 0.7, to provide a high quantum efficiency for photons below 400 nm, by examining the charge collection.