Solar-blind UV detectors based on wide band gap semiconductors

Solid-state photon detectors based on semiconductors other than silicon are not yet considered mature technology but their current development opens new possibilities, also for space observations. Such devices are especially attractive for ultraviolet radiation detection, as semiconductor materials with band gaps larger than that of silicon can be produced and used as “visible-blind” or “solar-blind” detectors that are not affected by daylight. Here we evaluate the advantages of such detectors compared to silicon-based devices and report on the semiconductor detectors that have been fabricated in recent years with materials having large band-gap energies. We describe the most common pixel designs and characterize their general properties. Wide band gap materials and solar blindness The present chapter addresses the prospects provided by sensors based on wide band gap materials (henceforth WBG materials or WBGM) as the “active” semiconducting volume. The latter corresponds usually to a solid-state layer where the photons create electron/hole pairs, subsequently collected to produce the signal. WBG materials have also been applied to photo-emissive detectors, e.g., as photocathode coatings on micro-channel plate detectors (Siegmund et al 2003), but in this chapter, we restrict ourselves to solid-state ultraviolet (UV) detection devices made of WBG semiconductors where charge creation and charge collection are taking place inside the material. One advantage of detectors made of WBG materials is that they can be made “solar-blind”. However, solar blindness is a relatively ill-defined concept because it would depend on typical outdoor lighting conditions varying with local time and the Earth’s atmosphere. “Visible-blind” UV detectors are required to have a higher responsivity in the UV range than in lower energy ranges. The cut-off of a visible-blind detector is thus at a wavelength shorter than 400 nm. Detectors MPS—Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany ROB—Royal Observatory of Belgium, Brussels; now at LATMOS—Laboratoire Atmosphères, Milieux, Observations Spatiales, Guyancourt, France