Hybrid Heterojunctions Between Ga2O3 and Organic Semiconductors for Sustainable Optoelectronic Applications

Solar-blind photodetectors are devices which are sensible to UV-C radiation only, being able to promptly detect threats such as wildfires, rocket/turbojet-propelled military assets and corona discharges in power lines, other than being applicable in space exploration and monitoring of sanitization processes employing UV-C light sources. In the framework of sustainable development, their mass production and employment require the use of suitable materials and energy-efficient modalities of their operation. Heterojunctions between gallium oxide (Ga2O3), an ultra-wide bandgap semiconductor with a great absorption coefficient, and organic electronic materials, known for their availability and easy processing, are ideal in this regard, since they can function without any external energy supply (self-powered mode). In this work, solar-blind photodetectors based on a planar heterojunction between various Ga2O3 phases and highly conductive PEDOT:PSS are fabricated by depositing the polymer directly on the surface of Ga2O3 by aerosol-jet printing, an additive manufacturing technique, directly in a custom-made shape of the contact terminal. e device based on epitaxially grown β-Ga2O3 shows the best performance levels, in line with similar devices reported in literature. However, amorphous Ga2O3 deposited at room temperature by radio-frequency magnetron spuering (RFMS), introduced to further enhance the sustainability of this device, was proved to be a valid alternative. e exploration is then extended to similar heterojunctions made instead with small molecule hole-transport layers deposited by vacuum-assisted thermal evaporation in the same custom-made interdigitated shape of the planar contacts. e emerging of a photoresponse due to the absorption of light by the organic layer allowed to obtain a bias-switchable device, both operable as a UV-broadband photodetector in self-powered mode and as a solar-blind photodetector when a DC bias of just +1 V is applied. e influence of some parameters of the organic layer such as its total thickness, its doping level and the employed host molecule on the observed phenomenology has been studied. Impedance spectroscopy measurements were used to find an equivalent circuit of the fabricated devices when an AC current is applied to them. Two separate RC elements connected in series permit to account for the heterojunction itself and the additional resistance and capacitance introduced by the planar geometry of the device.