Microchannel avalanche photodiode with wide linearity range

Design and physical operation principles of new microchannel avalanche photodiode (MC APD) with gain up to 10^5 and linearity range improved an order of magnitude compared to known similar devices. A distinctive feature of the new device is a directly biased p-n junction under each pixel which plays role of an individual quenching resistor. This allows increasing pixel density up to 40000 per mm^2 and making entire device area sensitive.Comment: Submitted to Journal of Technical Physic

Some Aspects of Phosphorus Diffusion in Germanium in In0,01Ga0,99As / In0,56Ga0,44P / Ge Heterostructures

The results of experimental and theoretical researches of phosphorus distribution in the first cascade of a multi cascade solar cell based on nanoscale structures AIIIBV / Ge are presented. Secondary ion mass spectroscopy has been applied to obtain profiles of phosphorus and gallium in In0.01Ga0.99As / In0.56Ga0.44P / Ge heterostructure. In the germanium surface there is a thin layer of about 26 nm, in which the gallium concentration exceeds the concentration of phosphorus. Therefore a nanoscale p-n junction forms that does not have a significant impact on the solar cells performance at room temperature. Phosphorus diffusion is much slower in this area than in area with electronic conductivity. The main p-n junction is formed at a distance of 130-150 nm from the surface of the germanium. Diffusivity of gallium (DGa = 1,4×10 – 15 cm2/s) is markedly higher than described in a literature. Diffusivity of P increase from DP = 3×10-15 cm2/s on the boundary of the heterostructure In0, 49Ga0, 51P to DP = 5,2×10 – 14 cm2/s in n-type Ge. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3364

On the Applicability of HF and μ-PCD Methods for Determination of Carrier Recombination Lifetime in the Non-passivated Single-crystal Silicon Samples

Comparison of the results of measuring the carrier recombination lifetime in silicon single crystals by contactless HF and microwave μ-PCD methods was carried out. It has been shown that HF method gives a large error compared with a μ-PCD method. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3613

Phosphorus and Gallium Diffusion in Ge Sublayer of In0.01Ga0.99As/In0.56Ga0.44P/Ge Heterostructures

This chapter gives a short review on dopant diffusion in germanium and specifies the underlying mechanisms of diffusion that involve the point defects. Box-shaped diffusion profiles are discussed that may be described as the phosphorus diffusion controlled by doubly ionized vacancies. In this mechanism, the diffusion coefficient depends on the electron concentration. The particulars of P and Ga diffusion profiles in the Ga-doped substrate of In0.01Ga0.99As/In0.56Ga0.44P/Ge heterostructures for multilayer solar cells are discussed. To calculate the diffusion coefficient, two methods were used: the Boltzmann-Matano (version of Sauer-Freise) and the coordinate-dependent diffusion analysis. It is established that coordinate-dependent diffusion analysis, which involves drift components together with diffusion components for diffusion profile description, is more suitable for description of the experimental profiles in such structures near p-n junction. A strong influence of intrinsic electric field on the dopant diffusivity was detected

DNA methylation, transcription and chromatin assembly in vitro

Histone HI is implicated in the establishment of stable and tissue-specific gene repression. It is presumed to repress transcription by binding to the internucleosomal, linker DNA leading to chromatin compaction and the formation of the 30 nm chromatin fibre. Histone H1 is abundant in heterochromatin and is associated with nucleosomes containing 5-methylcytosine. Conversely, it is absent from CpG island chromatin which is characteristic of active autosomal housekeeping genes and it is depleted in chromatin that contains active genes. DNA methylation correlates with the inactivity of many genes in vertebrates. It has been proposed that methylation may direct the formation of an inactive chromatin structure that is inaccessible to transcription factors, in a process requiring the participation of proteins that bind preferentially to methylated DNA. This study is an attempt to understand the molecular mechanisms that underlie the repression of gene activity by a combination of DNA methylation and chromatin. In vitro systems for transcription and the formation of chromatin are used as simplified models. The extent of in vitro transcription from unmethylated or methylated template is assayed in the presence of varied levels of total histone HI. Two templates are used: plasmid pArg/Leu contains two tRNA genes, which are transcribed by RNA polymerase III (pol III), and plasmid pVHCk contains the SV40 promoter linked to a reporter gene, which is transcribed by RNA polymerase III (pol III). A nuclear extract of HeLa cells is used for in vitro transcription assays of both types of template. Histone H1 forms characterised complexes on DNA, under the conditions used for these studies. Histone H1-DNA complexes are presumed to be a valid model of inactive chromatin. Transcriptional inactivation by histone HI is effective at lower levels with methylated templates, in comparison with unmethylated templates. Complete inactivation of all types of template is obtained with a further increase in histone HI levels. Different somatic variants of histone HI show differing degrees of preferential inhibition. Furthermore, histone H1 is a contaminant of the nuclear extract. The extract can be depleted of endogenous histone H1 either by the addition of competitor DNA or by fractionation of the extract with ammonium sulphate. Both treatments increase the level transcription from the methylated pol III template to that of the unmethylated template. The effect is reversed by the addition of exogenous histone H1 to the pol III template. The preferential inhibition of transcription from methylated templates by histone HI does not appear to be due to a greater binding affinity of the protein to methylated DNA, in comparison to unmethylated DNA. Instead, the conformation of the complex between histone HI and methylated DNA is changed, which prevents the formation of initiation and elongation transcription complexes on the methylated pol III template. Endogenous histone HI in the nuclear extract therefore prevents fully methylated pol III and pol II templates from being transcribed as efficiently as the unmethylated templates. This effect is most obvious when only the promoter region of the pol II template is methylated. Fully methylated DNA is intrinsically resistant to limited digestion with the restriction enzyme Msp I, in comparison to unmethylated DNA. This differential effect of DNA methylation is also observed when these templates are reconstituted as chromatin using Xenopus SI50 egg extract. Chromatin reconstituted on fully methylated or regionally-methylated DNA shows a greater resistance to digestion with Mspl than chromatin reconstituted on unmethylated DNA. The preferential resistance to Mspl, which is enhanced by the addition of histone HI during the chromatin reconstitution, occurs even on regions of unmethylated DNA if another region of that DNA is patch- methylated prior to chromatin reconstitution. This is consistent with DNA methylation acting as a focus for the formation of inactive chromatin. The transcriptional activity of unmethylated, patch-methylated and fully methylated pol II templates supports these observations

Lanthanum-Gallium Tantalate Crystals and their Electrophysical Characterization

Lanthanum-gallium tantalate single crystal (La3Ta0.5Ga5.5O14, langatate, LGT) is a perspective piezoe-lectric material as an active component of pressure sensors. An investigation of the growth conditions in-fluence (the growth atmosphere) on the electrophysical сharacterization of LGT, obtained in different at-mospheres (Ar, Ar + O2) was carried out. The frequency dependences of the relative dielectric constant (ε11/ε0) and of the admittance depend on the growth atmosphere. The langatate electrophysical сharacteri-zation in alternating electric fields were analyzed by means of the impedance spectr oscopy method. The behavior of short circuit currents in specimens of polar cuts of LGT single crystals with the same material electrodes without preliminary polarization is described. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3628