Abstract
Ultraviolet (UV) light plays an important role in air/water/surface sterilization now. Maintaining a certain light intensity is often required to attain the targeted effect. In this paper, on-chip power monitoring of a UV-A light-emitting diode (LED) via sapphire substrate is reported. A p–i–n photodiode loop that surrounds the UV-A LED was designed and fabricated to monitor the output power by detecting the scattered light of the LED propagating through the sapphire substrate. No particular waveguide structure or processing parameter control was needed. The monitoring responsivities per unit of surface-emitting power obtained were approximately 21 and 25 mA/W at photodiode biases of 0 and 3 V, respectively. When combined with a transimpedance amplifier, a monitoring responsivity of 1.87 V/mW at zero bias was measured, and a different monitoring responsivity could be customized by adjusting the gain of the transimpedance amplifier. The operation principle of this device might be applicable to UV-B or UV-C LEDs.
Highlights
Ultraviolet (UV) light-emitting diodes (LEDs) are used in various fields, such as for epoxy curing, air/water sterilization, and surface disinfection
Because the effectiveness of these applications depends on a minimum UV light intensity, the appropriate monitoring of in situ optical power is essential, because AlGaN-based UV LEDs have a shorter lifetime than InGaN-based visible LEDs have
The UV LED was surrounded by a p–i–n photodiode loop with a center-to-center distance of 575 μm and an monitoring photodiode (MPD)-to-LED
Summary
Ultraviolet (UV) light-emitting diodes (LEDs) are used in various fields, such as for epoxy curing, air/water sterilization, and surface disinfection. Because the effectiveness of these applications depends on a minimum UV light intensity, the appropriate monitoring of in situ optical power is essential, because AlGaN-based UV LEDs have a shorter lifetime than InGaN-based visible LEDs have. An external Si or InGaAs photodiode is often placed near the rear facet of a laser diode (LD) in commercial edge-emitting infrared LDs to monitor the output power level. On-chip power monitoring can be achieved by using the same active layer for both emission and detection under forward and reverse biases, respectively. Its responsivity is fairly low because the emission wavelength of the LED is near the cutoff wavelength of the photodiode.
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