[institut] Seminar, Jacek Zakrzewski, Thursday, 24 October 2019, 11:00, “Zvonko Marić" hall

[Dr. Dragan D. Markushev]

Dear colleagues,

You are cordially invited to the seminar of the Photonics Center, 
Laboratory for photoacoustics, which will be held on Thursday, 24 
October 2019 at 11:00 in the “Zvonko Marić" hall, Institute of Physics 
Belgrade. The talk entitled

Photothermal Spectroscopy of Bulk Crystals and Heterostructures

will be given by Prof. Jacek Zakrzewski, Institute of Physics, Nicolaus 
Copernicus University in Torun, Poland. Abstract of the talk:

The presentation shows the latest results obtained in the Applied 
Physics  Group in Torun (Poland) by piezoelectric photothermal 
spectroscopy.  Thermal and optical parameters of CdZnSe mixed crystals 
and  AlGaAs/GaAs heterostructures were characterized by this method.

The investigated bulk crystals were grown by the high-pressure Bridgman 
method under argon overpressure. The crystals were cut into  1-1.2 mm 
thick plates and mechanically grounded, polished and chemically etched. 
The influence of zinc content and preparation method on the amplitude 
and phase spectra is observed.
Mechanical, chemical and thermal treatment of the surface can create the 
damaged subsurface layer which introduces additional defects states in 
the material. The increase of the zinc content can also be associated 
with the creation of volume defects in the material.   Several features 
of the crystals were revealed from the spectra, with the increase of 
zinc content: a shift of the energy gap, broadening of the absorption 
band, increase of the surface absorption.
For semiconductors, there are three main sources of photothermal signal: 
thermal, plasma waves (associated with diffusion and recombination of 
carriers). In the photoacoustic investigation of transport in 
semiconductors one can also take into account immediate thermalization 
of carriers and nonradiative surface recombination.   Their influence on 
the character of amplitude and phase spectra is showed and discussed.

Piezoelectric photothermal spectroscopy was also used to characterize  
AlGaAs/GaAs heterostructures. The two-layer model proposed by Fernelius 
and the interference model of Malinski were chosen to analyze the phase 
and amplitude of PPS spectra. For each type of experimental setup 
configuration, the theoretical models were fitted to experimental data 
in order to obtain the thermal and optical parameters of the 
investigated material.


Best regards,

-- 
Dr. Dragan D. MARKUSHEV
Principal Research Fellow
Photonics Center
Head of Laboratory for Photoacoustics
Institute of Physics Belgrade
Pregrevica 118,
11080 Belgrade, SERBIA
cell: +381603169816
phone: +381113713158
fax: +381113162190
http://photonics.ipb.ac.rs/
http://www.ipb.ac.rs/