Laboratory of Semiconductor Optoelectronics

Members of the group:

Research interests

• Nonlinear optical properties of semiconductors and semiconductor nanostructures.
• Strong optical nonlinearities in semiconductor quantum wires and dots.
• Gain and laser emission of semiconductor quantum wires and dots.
• Optical bistability in semiconductors and semiconductor nanostructures.
• Optical and nonlinear optical properties of porous silicon.
• Ultrafast transient processes and mechanisms of relaxation in semiconductors with reduced dimensionality.

Recent results

• The method of picosecond laser saturation spectroscopy has been applied to investigate the energy spectra of semiconductor quantum dots and wires with essential size dispersion that smears out all peculiarities of the linear absorption spectra that should arise due to the quantum confinement. The application of picosecond laser has allowed to excite basically nanostructures which absorb its radiation resonantly. The saturation of discrete optical transitions can be resolved.
• Discrete optical transitions between the energy levels of size quantization in quantum dots and wires have been observed in the samples with great dispersion of the size of nanostructures using picosecond laser saturation spectroscopy method.
• The gain at the frequency of the lower optical transitions between the energy levels of size quantization has been observed for the first time in semiconductor quantum dots.
• The first observation of stimulated emission at the frequency of the quantum dot lower optical transition and lasing in Fabry-Perot resonator made of glass containing CdSe quantum dots.
• Discrete optical transitions that arise due to quantum confinement and strong optical nonlinearities have been registered in quantum wires and dots of porous silicon.
• Nonlinear optical absorption at discrete frequencies (bleaching bands) has been observed for GaAs quantum wires in crysotile asbestos nanotubes with average diameter 6 nm. The induced decrease of absorption has been explained by filling of the size-quantized energy levels of quantum wires with nonequilibrium carriers (saturation effect).
• A considerable slowing down of energy relaxation in quantum dots of CdSe and in quantum wires and dots of porous Si compared with intraband relaxation in the bulk has been observed.
• Preliminary measurements of the first samples of CdS nanostructures crystallized in molecular filters with different lateral dimensions of the channels have shown that the peculiarities in optical spectra arise due to quantum confinement in nanostructures of the designed size.

Experimental possibilities

The picosecond laser spectroscopy methods utilizing different types of powerful picosecond lasers, optical multichannel analyzers, modern streak cameras, photon counting technique, cryogenic technique, etc. are used in the laboratory.

Recent publications

• V.S. Dneprovskii, V.I. Klimov, D.K. Okorokov and Yu.V. Vandyshev. Strong optical nonlinearities and laser emission of semiconductor microcrystals. Solid State Commun. 81, 227 (1992).

• Yu.V. Vandyshev, V.S. Dneprovskii, V.I. Klimov and D.K. Okorokov. Lasing on a transition between quantum-well levels in a quantum dot. Pis'ma v Zh.Eksp.Teor.Fiz. 54, 441 (1991).

• V. Dneprovskii, N. Gushina, D. Okorokov, V. Karavanskii and E. Dovidenko. Saturation of optical transitions in quantum dots and wires of porous silicon. Superlattices and Microstructures 17, 41 (1995).

• V.I. Klimov, V.S. Dneprovskii and V.A. Karavanskii. Nonlinear-transmission spectra of porous silicon: Manifestation of size quantization. Appl.Phys.Lett. 64 (20), 2691 (1994).

• V. Dneprovskii, A. Ejov, N. Gushina, D. Okorokov, V. Panov, V. Karavanskii, A. Maslov, V. Sokolov and E. Dovidenko. Strong Optical Nonlinearities in Quantum Wires and Dots of Porous Silicon. Phys.Stat.Sol. (b) 188, 297 (1995).

• V. Dneprovskii, N. Gushina, O. Pavlov, V. Poborchii, I. Salamatina and E. Zhukov. Nonlinear optical absorption of GaAs quantum wires. Phys.Lett.A 204, 59 (1995).