Tuning Electrical Properties of Amorphous Ga₂O₃ Thin Films for Deep UV Phototransistors

In recent years
$\beta $
-Ga
₂
O
₃
thin films and crystals have gained attention as excellent candidates for transparent and high-power applications due to its wide band gap (4.6 – 4.9 eV) and large breakdown field (~8 mV/cm). However,
$\beta $
-Ga
₂
O
₃
single crystals and highly crystalline
$\beta $
-Ga
₂
O
₃
thin films require high temperature, long processing times and, often, expensive tools that limit integration with other technologies. Amorphous Ga
₂
O
₃
has not been studied as intensely as
$\beta $
-Ga
₂
O
₃
and mostly metal-semiconductor-metal (MSM) structures and diodes using this material have been reported. In this paper, we discuss a simple and economical method to fabricate thin film transistors (TFTs) based on un-doped amorphous Ga
₂
O
₃
thin films deposited at room temperature by magnetron sputtering. Control of the Ga
₂
O
₃
thin films resistivity over a wide range is demonstrated by controlling the deposition power and pressure. The TFTs show a threshold voltage (
$\text{V}_{{\mathrm {T}}}$
) of 0.92 V, saturation mobility (
$\mu _{{\mathrm {sat}}}$
) of 0.511 cm
²
/
$\text{V}\cdot \text{s}$
and subthreshold slope (SS) of 83.62 mV/dec. More importantly, these devices have been evaluated as phototransistors, which has not been intensely studied yet. The phototransistors tested under DUV radiation exhibited a rejection ratio UV-Visible of 10
³
and responsivity of
$10^{2}\text{A}$
/W (
$\text{V}_{{\mathrm {G}}} =0$
V) and 10
⁴
A/W (
$\text{V}_{{\mathrm {G}}} =6$
V), gain of 10
³
, specific detectivity of 10
¹⁵
Jones and a photosensitivity of 10
⁷
.