Institute of High Pressure Physics

At the upcoming EMRS Fall Meeting 2025, in Symposium I - Frontiers of imaging and spectroscopy in transmission electron microscopy, dr hab. inż. Julita Smalc-Koziorowska will present an invited paper entitled. "Revealing defects in nitride semiconductor structures in TEM".

The 2025 Fall Meeting of the European Materials Research Society (E-MRS) will take place from September 15 to 18, 2025 at the main campus of the University of Technology in Warsaw (Poland) and will consist of 23 parallel symposia with invited speakers, oral and poster presentations assorted by one plenary session to provide an international forum for discussing recent advances in the field of materials science.

One of the most formidable barriers in development of nitride-based optoelectronic devices: laser diodes (LDs) and light emitting diodes (LEDs) is high resistance of the metal/p-type nitride contact. The present date solutions are mostly based on Ni/Au contact still they are far from satisfactory. The situation requires basic investigations of the contact nature and technical implementation of new designs. Researchers from IHPP PAS applied complex ab initio and drift-diffusion calculation to elucidate contact nature. The results obtained include:

• elucidation of basic nature of the contact,
• evidence that in any metal/p-type GaN contact there exist tunneling barrier,
• explanation of the role of oxygen-ambient annealing during formation of the Ni-Au contact,
• new design, based on multilayer arrangement of deep acceptors, to achieve low resistance contact.

These results were published in the paper in Electronics vol. 14, p. 3309 (2025): Fundamentals of Metal Contact to p-Type GaN—A New Multilayer Energy-Saving Design Konrad Sakowski, Cyprian Sobczak, Pawel Strak, Stanislaw Krukowski

This study opens a new possibility of application of the new design by implantation formation of the low resistance electric contacts in the near future.

Doping Gallium Nitride (GaN) with beryllium has attracted much attention due to its potential applications in electronics and optoelectronics. Early studies suggested Be acceptors to have a lower ionization energy than the commonly used magnesium (Mg). However, previous attempts mostly lead to fabrication of semi-insulating material, due to a self-compensation effect – the tendency of Be atoms to occupy interstitial positions in GaN lattice (instead of substitution ones), forming competing donor defects.

Recent studies indicate that Be may have a more complex dual nature: acting as a shallow acceptor or as a deeper polaronic acceptor. Research carried out by the Institute of High Pressure Physics PAS, in collaboration with Virginia Commonwealth University and the University at Albany (USA), published in the Journal of Applied Physics, confirmed this hypothesis.

Hall effect measurements on GaN:Be layers showed p-type conductivity without overcompensation by donors, with an acceptor activation energy of ~0.40 eV. These results suggest that effective p-type doping of GaN with Be is more challenging than previously expected.

The research was funded by the National Science Centre, Poland (grant no. 2020/37/B/ST5/03746).

More details can be found in the following publication: M. Zając et al., Journal of Applied Physics 138, 095705 (2025). https://doi.org/10.1063/5.0283055.

Experimental pT^-3/2 vs inverse temperature dependence of GaN:Be epitaxial layers of various Be content. Solid lines represent fits yielding deep Be acceptor level at T=0.

Josephson junctions are building blocks of qubits in quantum computers. Researchers from MBE laboratory from our Institute just published a study in Nature Communications Materials showing an important step for the technology of their fabrication. They presented a new approach for growing thin films of superconducting niobium nitride (NbN) on GaN substrates using plasma-assisted molecular beam epitaxy (PAMBE) with indium as a surfactant. The use of indium enabled the growth of NbN thin films with quality suitable for Josephson junction applications. The study demonstrated the world's first NbN/InAlN/NbN Josephson junction fabricated using the MBE method. The junctions achieved a critical current density of 1 kA/cm².

This work shows that MBE technology can be fully exploited for the integration of NbN with group III nitrides, opening the path toward a new class of devices.

The full article A. Lachowski et al. NbN-based Josephson junctions grown by plasma-assisted molecular beam epitaxy Commun Mater 6, 169 (2025) is available at: https://www.nature.com/articles/s43246-025-00891-3