T.Ya. Gorbach

Growth of III–V semiconductor layers on Si patterned substrates

Abstract Patterned unheated Si{100} substrates in the form of the regular tetragonal pyramids and a structure like hemispherical plates have been found to be effective for a pulse vacuum thermal deposition (pulse-VTD) of GaAs and GaP thin layers (50–500 nm). The effect of the pulse-VTD technological parameters (pulse duration, pulse period, pulse number, pulse current) and the features of the substrate patterns (terraces, steps, kinks, sponges) on the morphology, the composition and the crystallinity of GaAs and GaP layers have been characterized by scanning electron microscopy, electron X-ray analysis and electron diffraction.

Thin films of HgCdTe on silicon surfaces

Thin (about 300 nm and less) HgCdTe and CdTe films have been deposited on Si flat and anisotropically etched microrelief surfaces by YAG:Nd3+ pulsed laser at various substrate temperatures in the range from 323 K to 423 K with 100 laser shots. These films and HgCdTe/Si heterosystems were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and current–voltage characteristics (CVC) analyses. It has been shown that under above conditions laser layer deposition method forms polycrystal films of CdTe, CdHgTe both for microrelief and flat Si substrates in the low temperature range

Deposition of HgCdTe epitaxial layers on anisotropically etched silicon surfaces by laser evaporation

Abstract HgCdTe films have been deposited on Si anisotropically etched microrelief (AEMR) surfaces by YAG:Nd3+ pulsed laser without substrate heating. The formation and a comparative investigation of morphology and some electrophysical properties of HgCdTe films andHgCdTeSi heterosystems on flat and microrelief substrates have been made in dependence on the distance from target to substrate and series of laser pulses. The deposited films and heterosystems were characterized by different techniques: scanning electron microscopy (SEM), micro X-ray electron probe analysis and current-voltage characteristics method. Based on these data it has been shown that the film growth process on Si AEMR surface in the morphological stability conditions (films reproduce the substrate microrelief) is the result of layer by layer mechanism with step migration and without nucleation. The difference in current-voltage characteristics are discussed in term of injection phenomena and depends strongly on laser deposition conditions.

Anisotropically etched Si surface and the electrical properties of Si/HgCdTe heterostructures

Abstract We used (001)-oriented silicon wafers, chemically etched under special conditions, as substrates for laser epitaxy of HgCdTe. Three types of Si surface with different microrelief were obtained: flat, pyramid-like and plate-like. Thin films of HgCdTe were deposited using a YAG:Nd 3+ laser. The electrical properties of the structures under investigation were analysed on the basis of current–voltage characteristics. These characteristics are interpreted in relation to the structural properties of the Si substrate surface. The carrier transport mechanisms for different HgCdTe/Si interfaces are presented.

Effect of the Si wafer pretreatment on the patterned substrate morphology and growth of Hg1−xCdxTe PLD films

Silicon patterned substrates and Hg 1-x Cd x Te films prepared by pulse laser deposition (PLD) on these substrates were examined by scanning electron microscopy (SEM), electronography (EG) and low-field electroreflectane (ER) spectroscopy in dependence on a pretreatment of Si wafers and the microrelief type. Change in morphologies of the substrates and films is discussed. The crystallinity data and analysis of ER spectra parameters are presented.

PLD of HgCdTe on two kinds of Si substrate

Abstract Films of HgCdTe have been obtained by pulse laser deposition method in dynamic vacuum (pressure∼10 −6 Torr) at 293–543 K. Two different kinds of Si surface were used as substrate: (a) flat standard polished {100} surface and (b) anisotropically chemically etched patterned surface. The results of a scanning electron microscopy investigation, electron probe microanalysis and I – V characteristic measurements showed a strong influence of the substrate kind on the morphology, composition, growth mode, growth defects and transport of HgCdTe/Si heterostructure.

Probe microanalysis investigation and electroreflectance spectroscopy of Hg1−xCdxTe PLD films on silicon patterned substrates

Abstract Hg1−xCdxTe films were prepared on Si-patterned substrates by the pulse laser deposition technique from a Hg1−xCdxTe target (x≈0.2). The effects of different substrate temperatures, ranging from 293 to 543 K, different laser shots number in the range of 10–380, and the morphological type of the patterned substrate on the x-composition of films were studied by electron probe microanalysis (EPMA) and electroreflectance (ER) spectroscopy. The correlation between a film composition measured by EPMA and one determined from ER spectra data was observed.

Electrical behaviour of HgCdTe/Si heterostructures

HgCdTe/Si heterostructures (HSs) were obtained by pulsed laser deposition (PLD) on Si (p- or n-type) flat and patterned (pyramid-like and plate-like) substrate from p- or n-type HgCdTe target. The I–V characteristics of p–n and isotype HSs were investigated by the differential approach. This approach is based on monitoring of differential slope α of the I–V characteristics in log–log plot (α=d lgI/d lgV). Influence of the substrate kind (flat, pyramid-like or plate-like), type of conductivity, type of HS (p–n or isotype) and substrate resistivity were studied. In all cases, the main feature of the I–V characteristics behaviour was α=3/2. It means that the bimolecular recombination is the main recombination mechanism in all HSs types.

SEM observation, photoconductivity investigation and I–V study of Si structures with patterned morphology for solar irradiance detection

Abstract Different types of silicon modified patterned substrates with and without p–n-junction were applied as a way for improving solar cells performance in order to prevent the light losses: (i) pyramid like (textured) surfaces (PrS); (ii) hemispherical plate like surface forms (PIS); (iii) dendritic structures (DS); (iv) porous morphology (LEPSi); (v) combinations of a textured surface with a porous one, etc. To realize them the anisotropical chemical and electrochemical etching in various etched mixtures and regimes, epitaxy and ion implantation were performed. Using scanning electron microscopy, spectral photoresponse measurements and current–voltage data, the morphological design, the variations in the photosensitivity, the wavelength peak position and the recombination parameters induced by the patterned processing and their influence for achieving the successful Si solar irradiance detection have been studied and analysed.

Changes in properties of a 〈porous silicon〉/silicon system during gradual etching off of the porous silicon layer

Scanning electron microscopy has shown etching of a porous silicon layer in an HF solution to be irregular. The intensity of porous silicon photoluminescence significantly decreases during gradual etching off, and its peak initially shifts to shorter and then to longer wavelengths. Under red-light pulse excitation, photo-voltage measurements have shown that the boundary potential ϕs of the p-Si substrate is positive, and ϕs grows with the etching time and as the temperature decreases from 300 to 200 K. At T<230 K, the photomemory of ϕs caused by nonequilibrium electron capture by p-Si boundary traps is observed. The concentration of shallow traps and boundary electron states in p-Si increases as porous silicon is etched. At T<180 K, the system of boundary electron states is rearranged. Photovoltage measurements with white-light pulses have revealed electron capture at oxide traps of aged porous silicon.