A. Vivas Hernandez

Raman-scattering and structure investigations on porous SiC layers

Raman scattering spectroscopy, scanning electron microscopy, and scanning acoustic microscopy were studied on porous SiC layers prepared by different technological routes and subjected to reactive ion treatment. The Raman spectra revealed a number of features specific for nanocrystallite materials, which can be used for characterization and diagnostics of porous SiC layers for technological applications.

Ballistic regime and photoluminescence excitation in Si wires and dots

Abstract This article presents the experimental results supporting the role of the ballistic effect in strong “red” photoluminescence (PL) of silicon low-dimensional structures: wires and dots. The peculiarities of the PL and PL excitation spectra in dependence on the morphology of porous silicon layers and the size of Si nano-crystallites have been investigated. The porous silicon layers with different morphology were created by the variation of preparation regimes. The size of Si nano-crystallites is estimated using the atomic force microscopy and Raman scattering methods. The mechanisms of PL and PL excitation in Si low-dimensional structures are discussed as well.

Some reasons of emission variation in InAs quantum dot-in-a-well structures

Photoluminescence (PL) and X ray diffraction have been studied in InAs quantum dots (QDs) embedded in symmetric In0.15Ga1-0.15As/GaAs quantum wells (dot-in-a-well, DWELL) with QDs grown at different temperatures. The density of QDs decreases from 1.1×1011 down to 1.3×1010 cm-2 with increasing the QD growth temperatures from 470 to 535°C. The QD density decreasing in DWELLs is accompanied by the non monotonous variation of QD parameters. The PL intensity increases and the PL peak shifts to low energy in structures with QDs grown at 490 and 510°C. On the contrary the structures with QDs grown at 525 and 535°C are characterized by lower PL intensities and PL peak positions shifted to higher energy. The method of X-ray diffraction has been applied with the aim to study the variation of elastic strain in DWELL structures with QDs grown at different temperatures. It was shown that the minimum of elastic strain corresponds to DWELL with QDs grown at 490-525 °C. For lower (470 °C) and higher (535 °C) QD growth temperatures the level of compressive strain increased in DWELLs. The reasons of strain variation are discussed as well.

Mechanism of photoluminescence investigation of Si nano-crystals embedded in SiOx

Nanoscaled Si (Ge) systems continue to be of interest for their potential application as Si (Ge) based light emiting materials and photonic structures. Optical properties of such systems are sensitive to nanocrystallite (NC) size fluctuations as well as to defects effects due to large surface to volume ratio in small NCs. Intensive research of Si (Ge) NCs is focused on the elucidation of the mechanism of radiative recombination with the aim to provide high efficient emission at room temperature in different spectral range. The bright visible photoluminescence (PL) of the Si (Ge)-SiOX system was investigated during last 15 years and several models were proposed. It was shown that blue (~2.64 eV) and green (~2.25 eV) PL are caused by various emitting centers in silicon oxide [1], while the nature of the more intensive red (1.70-2.00 eV) and infrared (0.80-1.60 eV) PL bands steel is no clear. These include PL model connected whit quantum confinement effects in Si (Ge) nanocrystallites [2-4], surface states on Si (Ge) nanocrystallites, as well as defects at the Si/SiOX (Ge/SiOX) interface and in the SiO2 layer [5-11]. It should be noted, that even investigation of PL on single Si quantum dots [12] cannot undoubtedly confirm the quantum confinement nature of red emission.

Photoluminescence and In/Ga Intermixture in InAs/InGaAs DWELL Structures

The photoluminescence (PL) and photoluminescence temperature dependences have been studied in InAs quantum dots (QDs) embedded in the In 0.15 Ga 1–0.15 As/GaAs quantum wells (QWs) with QDs grown at different temperatures (470–535 °C). Ground state (GS) related QD PL peaks shift into the red side with increasing QD growth temperature to 510 °C and the blue shift is observed when the temperature increased to 535 °C. The temperature dependences of GS PL peak positions were fitted on the base of Varshni relation and the fitting parameters were compared with the bulk InAs and the In 0.21 Ga 0.79 As allow. This comparison has revealed that for QDs grown at 490–510 °C the PL fitting parameters are the same as for the bulk InAs crystal. The DWELL structures with QDs grown at other temperatures have fitting parameters different from the bulk InAs. Last fact testifies that in these structures the Ga/In inter-diffusion between QDs and a QW has been realized. This Ga/In intermixture can be stimulated not only by the high temperature (535 °C), but by the essential elastic stress as well in the DWELL structure with lower QD densities.