Institute of High Pressure Physics

Despite seven decades of research on the unusual dielectric properties of relaxor ceramics in the wide surrounding of the paraelectric-ferroelectric transition, a fundamental model explaining and coherently describing this phenomenon remained a challenge. There are: specific 'diffused' changes in the 'dielectric constant' near the 'para-ferro' transition, extraordinary sensitivity to the external electric field ('tunability') and the so-called 'glassy' dynamics.

These subjects are addressed in a recent publication by the X-PressMatter/NL10 team [S.J. Rzoska et al. Critical insight into pretransitional behavior and dielectric tunability of relaxor ceramics. Materials 16 (2023) 7634 that is fully Open Access]. Authors propose a qualitatively new model for these systems. The work also includes an experimental test using the 'distortions-sensitive analysis'.

Fig. ‘Dielectric constant’ in  Ba_0.65Sr_0.35TiO₃ relaxor ceramic and the ‘classic’ Curie-Weiss (CW) equation focused analysis, with the Burns temperature T_B.

Nitride based materials still suffer from the lack of the understanding of the mechanisms of defects formation and their impact on the material properties. Dr Piotr Kruszewski with his collaborators from NL12 laboratory recently used deep-level transient spectroscopy (DLTS) to study Al_xGa_1-xN (x<0.05) grown by MOVPE.

It was shown that the electron emission signal related to the Fe_Ga (0/-) acceptor level splits into individual components due to aluminum fluctuations in the second-nearest neighbor (2NN) shell around the Fe_Ga impurity atoms. The calculations of the probability of finding a given number of aluminum atoms in the 2NN shell of the Fe_Ga defect agreed well with the experimental concentrations determined from Laplace DLTS peak intensities. This finding shows that in dilute Al_xGa_1-xN layers grown by MOVPE, aluminum and iron atoms are randomly distributed in the material. Finally, it was demonstrated that the energy level of the Fe_Ga acceptor with no Al atoms in the 2NN shell in the Al_xGa_1-xN samples shifts linearly with the aluminum content.

The publication "Alloy splitting of the Fe_Ga acceptor level in dilute Al_xGa_1−xN" (P. Kruszewski et al., Appl. Phys. Lett. 123, 222105 (2023)) is the result of the collaboration with colleagues from the Photon Science Institute and Department of Electrical and Electronic Engineering, the University of Manchester cooperating in NCN-OPUS project lead by Dr. Piotr Kruszewski.

Fig.1. Three-dimensional diagram of the Al_xGa_1-xN alloy showing two shells of atoms surrounding the Fe_Ga impurity (top image) and Laplace DLTS spectra for the Fe_Ga acceptor state in Al_xGa_1-xN (x ≤ 0.05) samples with energy-level-difference values at X axis (bottom image).

Narodowe Centrum Nauki (NCN) opublikowało wczoraj listy rankingowe projektów zakwalifikowanych do finansowania w konkursach OPUS 25 i PRELUDIUM 22. Są tam dwa projekty z naszego Instytutu:

• OPUS prof. Michała Boćkowskiego pt. „Badanie zjawiska dyfuzji krzemu w różnych kierunkach krystalograficznych azotku galu” oraz
• PRELUDIUM Mikołaja Żaka „Dwukierunkowe diody elektroluminescencyjne do pracy z prądem przemiennym”.

Gratulujemy!

Warto zauważyć, że w tym roku rekordowo mało projektów mogło uzyskać dofinansowanie. Wskaźniki sukcesu wynosiły zaledwie 8% i 10.7% dla OPUS i PRELUDIUM, więc były dwa razy niższe niż przed dwoma laty. Prof. Krzysztof Jóźwiak, Dyrektor NCN, podkreśla, że absolutnie konieczne jest zwiększenie budżetu NCN na finansowanie badań podstawowych w kolejnych latach.

Lista rankingowa OPUS 25

Lista rankingowa PRELUDIUM 22

This year the largest conference on nitride semiconductors – ICNS-14 was held in Japan, in Fukuoka  on November 12-17, 2023. There were 53 participants from Poland (51 presentations), with over 25 participants from Unipress (Institute of High Pressure Physics PAS) who contributed with 35 scientific presentations on the research carried out in our Institute. More than half of the Polish contributions at ICNS-14 came from our Institute.

We take pride in showcasing Poland's expertise in nitride semiconductors! Our young talents demonstrated exceptional performance. Three of our doctoral students honored for delivering the best presentations: Muhammed Aktas, Piotr Jaroszynski, and Kacper Sierakowski received Best Student Awards for their oral presentations.

Presentation statistics at ICNS-14 (credit: ICNS-14 program)