L. V. Belyakov

Electroluminescence from AlGaAs/GaAs quantum-cascade structures in the terahertz range

Electroluminescence from a quantum-cascade structure comprising 40 periods of GaAs/Al0.15Ga0.85As tunnel-coupled quantum wells (QW) was studied. A terahertz emission band in the range 1.0–1.8 THz is observed under bias exceeding 1.5–2.0 V. The emission band peak shifts linearly to higher frequency with the increasing bias. The effect is accounted for by spatially indirect electron transitions between states in the neighboring QWs.

On the mechanism of porous silicon formation

A new qualitative mechanism of pore nucleation and initial stages of porous silicon (por-Si) growth was proposed. The emphasis was on the charge exchange between Si2+ ions generated by electrolytic or chemical oxidation of initial silicon (disproportionation reaction). The mechanism eliminates, to a large extent, the contradictions typical of earlier proposed schemes of por-Si growth; in particular, it explains the morphological features of por-Si produced under various experimental conditions. The impact of light in these processes was also considered.

Electrolytic Fabrication of Porous Silicon with the Use of Internal Current Source

A new method of porous silicon fabrication is suggested which uses as a current source the potential difference arising between the silicon wafer and the platinum counter electrode immersed in an electrolyte solution. Addition of hydrogen peroxide to HF/ethanol electrolyte enables control over the current density in the process and fabrication of photoluminescent layers without an external current source.

Photoresponse and electroluminescence of silicon-〈porous silicon〉-〈chemically deposited metal〉 structures

Photoelectric and electroluminescent properties of silicon-〈porous silicon〉 structures with chemically deposited metal contacts were investigated. The large specific surface area of the contact and selective metal deposition only on the macrocrystalline elements of the structure provide better photoelectric performance of the photodiodes compared to the structures with evaporated contacts, especially in the short-wavelength spectral range. The obtained electroluminescence spectra are explained by metal-silicon barrier properties under forward bias and by double carrier injection into nanocrystallites under reverse bias.

Study of PbTe photodiodes on a buffer sublayer of porous silicon

The formation of epitaxial lead-telluride films on a silicon substrate with a porous-silicon sublayer is investigated. In these structures vertical-type infrared photodiodes were produced using ion doping. Despite a great mismatch in the lattice constants and the temperature expansion coefficients between silicon and lead telluride, the photodiode parameters are similar to those of photodiodes in the orienting substrates.

Composition and porosity of multicomponent structures: porous silicon as a three-component system

It is shown for the system porous silicon (por-Si)-silicon (Si) that effective nondestructive investigation of the interfacial morphology of layered semiconductor systems and of the composition of multicomponent layers by ellipsometry and Rutherford backscattering is possible. Both methods were used to determine the percentage composition of the main components of por-Si: crystal silicon, silicon oxide, and voids (porosity). It is shown that por-Si obtained by pulse-anodization contains a substantial quantity of silicon oxide. It is also shown that spectral ellipsometry can be used to determine the specific ratio of individual layers or components of multilayer and multicomponent systems (provided that the spectral dispersion of the optical constants of these components is known).

Role of singlet oxygen in formation of nanoporous silicon

The effect of singlet oxygen on the formation of nanoporous silicon in the case of photoelectrochemical etching of p-Si is studied. Pulsed electrolysis was used to discriminate between chemical and electrochemical processes. The pulsed etching of silicon was accompanied by pulsed illumination coinciding either with current pulses or with zero-current periods. An analysis of the results obtained demonstrated that, as the number of silicon nanocrystals increases under illumination, singlet oxygen starts to be generated from molecular oxygen dissolved in the electrolyte. This process leads to oxidation of the surface of silicon nanocrystallites and to a change in its passivation.

Free-standing luminescent layers of porous silicon

Free-standing layers of porous silicon with a thickness ranging from 50 to 200 μm have been fabricated using an electrolyte composed of HF and acetic acid. Chemical aspects of the etching process associated with the evolution of gases that favor detachment of layers from substrates are considered. The layers exhibit stable photoluminescence in the visible spectral region observed from both of their sides.

Effect of a fullerene coating on the photoluminescence of porous silicon

The interaction of a matrix of silicon nanocrystallites (porous silicon layer) with embedded fullerene molecules C60 was studied. The degradation of fullerene-containing layers as a result of irradiation with a strongly absorbed laser light was explored. It is shown that the layers with highest stability are obtained after high-temperature annealing in hydrogen. In this case, the photoluminescence spectra remain virtually unchanged when the layers are kept in air and irradiated with a high-intensity laser irradiation. Possible mechanisms of the phenomena studied are discussed.

Optical properties of iron-passivated nanoporous silicon

The intensity of photoluminescence from nanoporous silicon layers produced by electrochemical etching in an aqueous-alcoholic HF solution in the presence of iron ions increases and properties of these layers are stabilized. The optimal FeCl3 concentration in the etching solution has been found. The interaction of iron ions with the silicon surface and the nature and possible products of reactions involving oxygen and hydrogen have been studied.