# Making UV light visible by exciting polarization-gate phototransistor to achieve energy transfer into GaN-based blue emission

## TL;DR

This paper presents a device that makes UV light visible by converting it into blue light using a specialized phototransistor and LED.

## Contribution

The novel integration of a polarization-gated phototransistor with a blue mini-LED to convert UV light into visible blue emission.

## Key findings

- The device achieves a 49.8 times power ratio between UV excitation and blue LED emission.
- The integrated device can detect weak UV light and convert it into visible blue light.
- The polarization gate enables a normally-off state with minimal current leakage.

## Abstract

In this work, we have made ultraviolet (UV) light visible by proposing and fabricating an integrated optoelectronic device. The demonstrated device consists of a GaN-based blue mini-light-emitting diode (mini-LED) and a phototransistor. The phototransistor is specially designed with an Al0.20Ga0.80N polarization gate. The background electrons can be depleted by the polarization gate to enable the normally-off state for the integrated optoelectronic device when there is no UV illumination. Our measured results show that when the polarization-gated phototransistor is switched off, the current for the integrated optoelectronic device is as low as 1.4 × 10−4 mA even when the device is biased to 10 V. Upon the 12.7 mW UV excitation, the current for the integrated device can be increased to 44.4 mA at the bias of 10.0 V. This enables the GaN-based visible mini-LED to generate the optical power of 81.1 mW. The largest power ratio between the UV excitation light and the mini-LED light of 49.8 times can be achieved, indicating the advantage of monitoring weak UV light by using the proposed design.

We integrate polarization-gated UV phototransistor and blue InGaN/GaN mini-LED. The photon-generated electrons in the UV phototransistor make the mini-LED generate blue emission. This makes UV light “visible” to naked eyes.