Results of the project – Prin USE GAO

(as per August 2025)

The joint efforts of UNIPR, UNIMORE and IMEM led to fabrication of innovative photodiodes based on n-type epitaxial Ga₂O₃ and overgrown inorganic or organic p-type layers.

Different examples of photodiodes are provided in the figures below:

**Fig. 1: Ga₂O₃-based planar PN junction diode and I-V characteristics in dark**

**Fig. 2: Ga₂O₃-based vertical PN junction diode and I-V characteristics**

Performance of the self-powered photodiodes

The following figures reports typical responsivity and response time of a κ-Ga₂O₃ /NiO vertical photodiode illuminated from the rear across the transparent sapphire substrate. This configuration may be used as a broadband detector, in which the UV-C spectrum can excite the GaO layer while the photons of lower energy will excite the NiO film. This device can operate at 0 bias (self-powered).

**Fig. 3: Structure and performance of planar κ-Ga₂O₃ / NiO photodiode**

Simulation of device operation and properties

Modelling and simulation are important activities in USEGAO. The following figure provides an example of simulation applied to a photoresistor based on κ-Ga₂O₃.

Fig. 4: 2D contour plot of the optical generation rate within the simulated Ga₂O₃ photoresistor. Ohm1 and Ohm2 are the two ohmic contacts. A-A’ is the cutline along which the distributions of photocarriers were calculated (see Fig. 5)

Fig. 5: 1D plot along the A-A’ line of the following quantities: (yellow line) hole trapped charge density, N_DON⁺, (green line) hole density, p, (red line) electron density, n, and (blue line) net space-charge density, ρ=N_DON⁺-n+p. Deep donor density is assumed to be N_DON=10¹⁶ cm^-3 and 0 in (a) and (b), respectively

This type of simulation was useful in order to better understand and quantify the photogain phenomena in GaO-based photoresistors.