Contatto di riferimento: Beatrice Fraboni
Partecipanti: Prof. Roberto Fornari: Dip. di Fisica e Scienze della Terra, Università di Parma
The possibility of growing high-quality gallium oxide (Ga2O3) single crystals and films has triggered a great interest on this materials, as very promising candidate for applications in new areas such as high power transistors and UV detectors.
Although the homo-epitaxy is possible, most research on Ga2O3 thin films is still carried out on hetero substrate such as sapphire. Despite the relatively quick advancements of the last few years, there are still many open questions regarding the deposition of Ga2O3 on foreign substrates, for instance related to the appearance of different crystallographic phases: beta (monoclinic), alfa (hexagonal), gamma (cubic), delta (cubic) and epsilon (hexagonal/orthorhombic).
This talk will focus on the recent advancements in epitaxial growth -Ga2O3 [1] and the extensive characterization by X-ray, TEM, photo-conductivity and absorption spectroscopy. The interest in phase arises from the possibility of coupling its high energy gap, similar to that of the more popular -Ga2O3, with less critical growth conditions, for example a much lower deposition temperature. Moreover, -Ga2O3 films provide a more advantageous crystallographic symmetry than monoclinic -Ga2O3 and can be easily
deposited on c-oriented sapphire and gallium nitride, which is good in view of developing a novel oxide nitride technology. The growth of -Ga2O3 was seen to proceed via generation of small oriented nuclei that later expand to produce large hexagonal islands (size of 200-400 nm), which ultimately merge producing a flat and homogeneous film. Under appropriate growth conditions, epilayers of the same -Ga2O3 phase were also successfully deposited on alternative hetero-substrates such as (0001)-GaN and (111)-SiC with good results. The major disadvantage of the epsilon phase comes from its intrinsic instability: it tends to convert to monoclinic beta when annealed above 700 °C. Nevertheless, this is a relatively high value, which in principle enables the use of hexagonal Ga2O3 for device fabrication.
[1] F. Boschi, M. Bosi, T. Berzina, E. Buffagni, C. Ferrari, R. Fornari, J. Cryst. Growth 443 (2016) 25