Abstract
A high figure‐of‐merit UV‐C solar‐blind photodetector (PD) fabricated from thin‐film beta‐gallium oxide (β‐Ga2O3) grown on n‐Si substrates by plasma‐assisted molecular beam epitaxy is demonstrated. Film growth sequences for nucleation of Ga2O3 on (100)‐ and (111)‐oriented Si substrates are developed, and the influence of crucial growth parameters is systematically investigated, namely, substrate temperature, oxygen flow rate, and plasma power on the functional properties of the PDs. The PDs show an ultra‐high responsivity of 837 A W−1 and a fast ON/OFF time below 4 ms at −5 V. In addition, they display strong rectifying properties and a sharp cutoff below 280 nm with the average responsivities between 10 and 80 A W−1, a detectivity on the order of 1010 Jones, and rise/fall times between 4 and 500 ms. High photoconductive gain is likely to be due to the mid‐bandgap donor/acceptor defect levels, including oxygen vacancies in the form of self‐trapped holes. It is demonstrated that these defect levels can be modified by controlling the growth conditions, thereby allowing for tailoring of the PD characteristics for specific applications. The methodology represents a cost‐effective solution over homoepitaxial approaches, with characteristics that meet or exceed those reported previously, offering new possibilities for on‐wafer integration with Si opto‐electronics.
Highlights
Prior to investigating the impact of various growth conditions on the Ga2O3/Si heterostructures, we investigated the role of Ga and oxygen on the nucleation of the Ga2O3 epilayers
Oxygen flow, and plasma power were found to have significant impact on the resultant epilayers and characteristics of vertical Schottky photodiodes fabricated from the Ga2O3/n-Si heterostructures
Growth under sufficient Ga flux but lower oxygen supply favors the formation of volatile Ga sub-oxides, which promote SiO2 formation, thereby suppressing the Ga2O3 film growth
Summary
Ga2O3 epilayers were grown by PAMBE on n-type (100) and (111) silicon substrates. Oxygen was supplied by an SVT Associates Inc. plasma source, and a standard Knudsen effusion cell was used to source the Ga. The substrate was thermally cleaned at high temperature (800 C) under vacuum (%1 Â 10À9 Torr) inside the MBE chamber for several hours to remove the SiO2 surface layer and ensure the high crystalline quality of the underlying Si substrate. Prior to opening the MBE oxygen plasma shutter, metallic Ga was pre-deposited for several minutes to form a thin layer of Ga at a substrate temperature of 500 C. After this low temperature nucleation of Ga2O3, the substrate temperature (Tsub) was ramped up to 660–730 C.
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