O. A. Golikova

Amorphous hydrogenated silicon films exhibiting enhanced photosensitivity

Amorphous hydrogenated silicon (a-Si:H) films with photoconductivities as high as 106, i.e., exceeding the photoconductivity of “standard” a-Si:H by two orders of magnitude, are investigated. The dark conductivity (σd) of the films has an activation energy ΔE=0.85–1.1 eV. The photoconductivity σph is measured at a photocarrier generation rate of 1019 cm−3 · s−1 and photon energy ɛ=2 eV. Several distinctive characteristics are ascertained in the behavior of σph and σd as functions of ΔE and also in the spectral curve and decay kinetics of σph during prolonged illumination. It is concluded that the investigated material holds major promise for photovoltaic device applications.

Medium-range order and optoelectronic properties of a tetrahedrally coordinated hydrogenated amorphous semiconductor

Correlations were determined between the medium-range-order characteristic in an a-Si:H structure and the density of defects, their charge state, the optical band gap, and its spatial fluctuations. It was shown that the modification of the structure at the medium-range-order level, owing to the formation of nanoinclusions, can lead to a radical increase in photoconductivity and to ordering of the structure of the amorphous matrix.

Crystallization of amorphous hydrogenated silicon films deposited under various conditions

The possibility of using the magnetron-assisted silane decomposition technique for the deposition of a-Si:H films as the basic materials for the production of polysilicon is analyzed. It is shown how specific features of the film structure affect the crystallization process.

Effect of Nanocrystalline Inclusions on the Photosensitivity of Amorphous Hydrogenated Silicon Films

Photosensitivity of amorphous hydrogenated silicon films containing inclusions of Si nanocrystals, along with spectral characteristics of photoconductivity, were studied. A correlation between photosensitivity and features of the Raman spectra was established. The highest photosensitivity is observed in films with medium-range order formed to the maximum extent.

Amorphous boron films with enhanced electrical conductivity

The results of studying the electrical properties of nanostructured films of amorphous boron a-B are compared with the results obtained for bulk samples of the same material and also for the crystals of certain quasi-amorphous borides with complex icosahedral structure. Models accounting for the enhanced electrical conductivity of amorphous boron films are suggested.

Changes in Short- and Medium-Range Order in a-Si:H Induced by Light-Soaking, Pseudodoping and Doping With Boron

A study of a-Si:H structure on the scales of short- and medium- range order has been carried out by the Raman spectroscopy method. Undoped a-Si:H films were deposited by the conventional rf- PECVD with some special variations in the process conditions ( pseudodoping technique); doping with boron was performed from a gas phase as well as by ion implantation. Changes in short- and medium- range order induced by light-soaking, pseudodoping and doping with boron were determined and compared.

Defects in intrinsic and pseudodoped amorphous hydrated silicon

The data on the dark conductivity and photoconductivity of a-Si:H films obtained by various methods in the soft-deposition regime are presented. It is shown that, regardless of the substrate temperature, the material obtained in this regime is intrinsic. Deviation from the soft-deposition regime results in the growth of pseudodoped a-Si:H, with an increased density of defects (dangling Si-Si bonds) and with inhomogeneous structure. The defects in intrinsic and pseudodoped a-Si:H are found, respectively, in D0 and D+ states.

Photoconductivity of nanostructured hydrogenated silicon films

The photoconductivity of nanostructured hydrogenated silicon films prepared by different techniques was studied in relation to the Fermi level position, the density of defects, and the type of Si-H bonding. The influence of Si+ ion implantation on the photoconductivity and other parameters of a-Si:H films was determined.

Special features of photoelectric properties of nanostructured films of hydrogenated silicon

Nanostructured Si films differing in hydrogen content, in the forms of Si-H bonds, and in certain characteristics of Si inclusions in an amorphous matrix (volume fraction, size, and structure) were studied. The behavior common to all the studied films, i.e., an increase in the defect density and nonmonotonic enhancement of photoconductivity at the “red wing” of the spectral characteristic compared to a-Si:H, was assessed. At the same time, there are films with either enhanced or reduced photoconductivity compared to a-Si:H.

Defects and short-and medium-range order in the structural network of hydrogenated amorphous silicon

The effect of defects (dangling Si-Si bonds) produced during the deposition of a-Si:H films by the glow-discharge method and upon boron doping, as well as photoinduced defects, on changes in the short-and medium-range order in the structural network is investigated. It is shown for a constant defect density ND=const that charged defects influence the a-Si:H structure much more strongly than do neutral defects.