Vitalijus Bikbajevas

Temperature dependence of the absorption coefficient in 4H- and 6H-silicon carbide at 355 nm laser pumping wavelength

We report on the absorption coefficient at 355 nm laser wavelength for 4H- and 6H-SiC over a wide temperature range. The measurements were carried out using a depth- and time-resolved free-carrier- ...

Spatially and time-resolved infrared absorption for optical and electrical characterization of indirect band gap semiconductors

The current status of the spatially and time-resolved free-carrier absorption (FCA) method is provided. The FCA technique allows monitoring carrier dynamics in a time scale from nanoseconds to miliseconds by employing either collinear or orthogonal geometry between pump and probe beams. A high spatial resolution is achieved allowing in-depth carrier profiles to be extracted. The method is particularly suited for investigation of injection-dependent optical and recombination phenomena: band gap optical absorption, Shockley-Read-Hall (SRH) lifetime, Auger recombination coefficient, and the injection-dependent surface (interface) recombination velocity. We summarize important aspects of the technique demonstrating numerous measurements that have been implemented in studies of bulk Si, epilaxial 4H-SiC and porous silicon.

Strong photoacoustic pulses generated in TlGaSe2 layered crystals

Periodic deflections of infrared probe beam in TlGaSe2 crystal after its lateral excitation by laser pulse with photon energy near the band gap are observed. Such deflections arise from travelling of the acoustic pulse within sample which, in turn, is produced by optical pump pulse through photoacoustic effect. The photoacoustic pulse is generated within thin region near the crystal excited face, much shorter then the light penetration depth. In the case of volume excitation photoacoustic pulse is also generated in the region near back face as well. Tentative explanation of the generation mechanism is discussed.

Two-photon indirect absorption in GaSe

Two-photon absorption (TPA) in GaSe is detected in the narrow (about kT) spectral range above the indirect exciton energy for E⊥c light polarization. The appearance of TPA enhancement within narrow spectral region links to the resonant Raman scattering and anti-Stockes photoluminescence previously identified in GaSe. Extracted TPA coefficient is of the order of 10 cm/W and 5–10 times exceeds ones obtained previously for lower quanta energies.