# Gallium Oxide-Based Photodetectors for Water Quality Monitoring

## TL;DR

This paper introduces gallium oxide photodetectors for monitoring water quality by detecting absorption from nitrates, dissolved organic carbon, and suspended solids.

## Contribution

The use of gallium oxide semiconductors enables simultaneous, accurate water quality monitoring across a broad UV-visible spectrum.

## Key findings

- Gallium oxide's photocurrent response spans 200–465 nm, covering key absorption regions for water quality parameters.
- Three distinct wavelength regions correlate with nitrates, dissolved organic carbon, and suspended solids.
- Optimal excitation wavelengths at 225, 260, and 465 nm improve sensitivity for each monitored parameter.

## Abstract

We present an approach to water quality monitoring using
gallium
oxide (Ga2O3) ultrawide-band-gap semiconductors.
Nitrates, dissolved organic carbon, and suspended solid concentrations
are three commonly measured water quality parameters that display
optical absorption ranging from the deep ultraviolet to the visible
region. This broad spectral region poses a challenge for accurate
and efficient (simultaneous) measurement of absorption/extinction
arising from varying concentrations of these parameters because silicon
(Si), the classical detector material, has poor performance across
this optical region. To overcome these limitations, we propose the
use of ultrawide-band-gap semiconductors to trace changes in optical
absorption from varying water compositions by measuring the photocurrent
response at different wavelengths. Here, we use α-phase Ga2O3 as a suitable material to measure a broad photocurrent
response ranging from 200 to 465 nm. The photocurrent response consisted
of three well-defined regions inherently linked to the rich electronic
landscape of the material. Region (i) (200–250 nm) corresponds
to band-to-band excitation of charge carriers, aligning well with
the absorption characteristics of nitrates. Region (ii) (250–350
nm) corresponds to band tail-related transitions, allowing a photocurrent
response to dissolved organic carbon concentrations. Finally, we utilize
defect-mediated transitions in Region (iii) (350–465 nm) to
monitor suspended solid concentrations. It was observed here that
the sensitivity of the photocurrent response to the changing water
composition strongly depends on the excitation wavelength, where 225,
260, and 465 nm excitation yielded (for our setup) the best results
for the monitoring of nitrates, dissolved organic carbon, and suspended
solid concentrations, respectively.