The monolithic integration of an ultraviolet (UV) sensor and warning lamp would reduce the cost, volume, and footprint, in comparison to a hybrid combination of discrete components. We constructed a module comprising a monolithic sensor indicator device based on basic p–i–n (PIN) photodiodes and a transimpedance amplifier. GaN-based light-emitting diodes (LEDs) with an indium-tin oxide (ITO) current-spreading layer and PIN photodiodes without ITO deposition on the light-receiving area, were simultaneously fabricated. The resultant incident photon-to-electron conversion efficiencies of the PIN photodiodes at UV wavelengths were significantly higher than those of the reverse-biased LEDs. The photocurrent signals of the PIN photodiode were then converted to voltage signals to drive an integrated visible LED, which functioned as an indicator. The more the ambient UV-light intensity exceeded a specified level, the brighter the glow of the LED. The responsivities of 0.20 and 0.16 A/W were obtained at 381 and 350 nm, respectively, under a bias voltage of 5 V. We also addressed the epitaxial structural details that can affect the collection efficiency of the photocurrent generated by UV light absorption. The crosstalk between the PIN photodiode and LEDs (of various center-to-center distances) was measured.

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