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Practical Holography XV

Stephen A. Benton

3. ABSTRACT TITLE: Use of materials on a basis As2S3 - As2Se3 for manufacture of holographic optical elements.

AUTOR LISTING:

Ivan I. Burdiyan, Karla Libknekhta str. No 176, flat 1, Tiraspol, 3300, Moldova

Igor S. Feshchenko, Benderskogo vosstanja str. No 3, flat 22, Benderi 278100, Moldova, feshchenko@mail.ru;

Yury N. Vigovsky, Novoslobodskaja str. No 31/1, Moscow, 103055, Russia, vigovsky@dol.ru

Valery S. Feshchenko, Benderskogo vosstanja str. No 3, flat 22, Benderi 278100, Moldova, feshchenko@mail.ru;

5. PRESENTATION: Poster Presentation

6. ABSTRACT TEXT:

The chalcogenide glasslike materials on a basis As2S3 - As2Se3 are widely applied in various fields of a science and technology. It is connected with their such properties, as wide spectral sensitivity, high resistance and high photoconduction, ability to photostructural transmutations and also with simplicity of their production.

We was studing the photographic and holographic properties of photoresist on a basis As2S3 - As2Se3 which was doped by metals. The including into a system of metals IV of group has allowed to increase holographic sensitivity of a photoresist and has expanded a spectral range of a material. Nonequilibrium doping of a photoresist by tungsten has made process of photostructural transmutations more controllable, what permit to obtain on the same material, both phase images with high contrast, and halftone images.

The dependence of photographic and holographic propertyes of investigated materials for various parameters of process and types of used etchants are demonstrated also.

7. KEY WORDS: Chalcogenide glasslike semiconductors, photoresist, photostructural transmutations.

8. BRIFF BIOGRAPHY:

Ivan I. Burdiyan finished in 1952 the Kishinev State University and A.F. Ioffe Physics-Technical Institute post-graduate course in 1969. In 1969 he has received the DSc degree in this Institute. In 1973 he has received the professor degree in Lvov State University. He works as the professor of the Dniestr State University, 25 October str. 128, Tiraspol, Moldavia and carry out researches on a semiconductors technology.

Use of materials on a basis As2S3-As2Se3 for manufacture of holographic optical elements.

Ivan I. Burdiyan¹, Igor S. Feshchenko¹, Yury N. Vigovsky², Valery S. Feshchenko¹

¹Dniestr State University, 25 October str. 128, Tiraspol, Moldavia, feshchenko@mail.ru.

²MeDia Co, Novoslobodskaja str. No 31/1, Moscow, Russia, vigovsky@dol.ru.

Abstract

In this paper we was studing the photographic and holographic properties of photoresist on a basis As2S3 - As2Se3 which was doped by metals. The including into a system of metals IV of group has allowed to increase holographic sensitivity of a photoresist and has expanded a spectral range of a material. Nonequilibrium doping of a photoresist by tungsten has made process of photostructural transmutations more controllable, what permit to obtain on the same material, both phase images with high contrast, and halftone images.

1. Introduction

The chalcogenide glassy semiconductors (CGS) [1] already for a long time, call huge interest (more than 400 000 references in a Internet). They are widely employed for manufacturing of waveguides [2], of elements of integrated optics [2,7], of acoustooptical modulators [3], of superfast semiconducting switches [4,5], of meshes of memory [1,6], of holographic optical elements [1], of the holograms [1] and are used as photoresists for a nanolithography [1,8]. The virtues of CGS is the high velocity of switching, the high resolving power the wide spectral sensitivity range, the relative simplicity of deriving and the low cost.

But despite of a great many of articles on this theme until now up to an extremity the mechanisms of photostructural transformations happening in a CGS are not clear that does not allow to develop new gears and recording mediums.

Therefore the making of new semiconducting materials on the basis of CGS and study of mechanisms of photostructural transformations constitute topical task.

In work [1] was shown that an alloying of chalcogenide glassy semiconductors by tin reduces to magnification of photosensitivity at the expense of a normalization of a matrix of a glass. In work [1] was shown the important influence of metals of incidental subgroup of sixth group of periodic table on increase of photosensitivity in a CGS. In this connection we carried out experiments for showing up of influence of these metals at a combined alloying on holographic properties of a glassy semiconductor. For this purpose we used layers of a CGS of composition (As2S3)0.3× (As2Se3)0.7 which alloyed at a liquid melt by an dope of tin 0,015 at.% that according of our previous researches [9] raised the photosensitivity in comparison with a nonalloyed semiconductor. Also we investigated thin-film glassy semiconductors of composition As2S3-As2Se3, As2S3-As2Se3:Sn 0.015 at. % and As2Se3 which we nonequilibrium alloyed by a tungsten.

2. Experiments and discussion

We prepared the initial photosensitive mediums by a sequential thermal spraying of layers WO2 and As2Se3-As2S3, As2S3-As2Se3:Sn 0.015at.%, in vacuum ~ 3× 10^-3 Pa on glass substrates. For an oxide of a tungsten of a thickness of layers amount 0,1-0,3 microns and for As2Se3-As2S3 - 0,7-1 micron. If we used CGS of composition As2Se3 the nonequilibrum alloying was carried out with the help of thermal diffusion at room temperature. While CGS of compositions As2S3-As2Se3 and As2S3-As2Se3:Sn 0.015at.% were alloyed at temperature 80° С during 5, 10, 15 and 20 minutes because at room temperature the alloying was insignificant.

On these layers the diffraction gratings with spatial frequency 300 mm^-1 were recorded.. We measured of diffraction efficiency during an process of record of diffraction gratings. The outcomes are presented on fig. 1. From the graph (fig.1. a curve 1) it is visible the greatest sensitivity corresponds to composition (As2S3)0.3× (As2Se3)0.7 which was alloyed by tungsten by means of a thermal diffusion at 80˚C within 5 minutes. Medium of same composition (As2S3)0.3× (As2Se3)0.7 with a underlayer WO2 but without a preliminary annealing has smaller holographic sensitivity. A decrease of sensitivity for the given medium is connected that the energy is expended not only on photostructural transformations but also on a photodiffusion of a tungsten in a layer of a CGS (fig.1. a curve 2). The worst diffraction efficiency corresponded to structures containing tin (fig.1. a curves 4-6). Apparently, the atoms of tin compete with atoms of tungsten in the process of photostructural transformations. Therefore diffraction efficiency was decreased.

For explanation of above outcomes we obtained absorption spectrums of researched structures. A spectrum of an absorption of a system As2S3-As2Se3:Sn 0.015at.% alloyed by tungsten differs from the appropriate spectrum of a system As2S3-As2Se3 owing to of small concentration of tin therefore we have considered influence of a tungsten on an example of structure (As2S3)0.3× (As2Se3)0.7. From fig.2. (a curves 1-5) we see what the spectrum has appreciable change because of a thermal diffusion of ions of a tungsten. There are two singularities on lengths of waves 606nm and 656nm if to carry out the annealing of sample during 5 minutes (fig.2. a curve 4). Further at magnification of time of an annealing up to 10, 15 minutes of a singularity disappeared (fig.2. a curve 3). And only at an annealing during 20 minutes appear two singularities but already on length of waves 614nm and 670nm (fig.2. a curve 5). Such behavior of a curve of absorption is connected in our opinion with to origin of forming the ordered microareas of tungsten compounds in CGS The dope of a tungsten are included in a CGS by two ways: Its one part with concentration of an dope x1 is in microareas, another - with concentration x2 is uniformly distributed in a matrix of a glass, forming a homogeneous solid solution (ideal glass).

Fig.1. The graphs of an dependence of diffraction efficiency from an energy of exposure:

1 - (As2S3)0.3× (As2Se3)0.7 with a underlayer WO2 an annealing 5 minutes.

2 - (As2S3)0.3× (As2Se3)0.7 with a underlayer WO2 without an annealing;

3- (As2S3)0.3× (As2Se3)0.7 with a underlayer WO2 an annealing 20 minutes;

4 - (As2S3)0.3× (As2Se3)0.7:Sn 0.015at.% with a underlayer WO2 an annealing 5 minutes;

5 - (As2S3)0.3× (As2Se3)0.7: Sn 0.015at.% with a underlayer WO2 an annealing 20 minutes;

6- (As2S3)0.3× (As2Se3)0.7: Sn 0.015at.% with a underlayer WO2 without an annealing.

The modifications in an absorption spectrum are connected with microareas which are responsible for extrinsic conduction in glassy chalcogenide semiconductors. They become apparent as singularities on lengths of waves 606, 614, 656 and 670nm (fig.2. a curve 4, 5). The displacement of an edge of a fundamental absorption in long wave area of spectrum is connected to formation of a series of solid solutions of a CGS with a tungsten. The tungsten dope which was in microareas and are identified by peaks 656nm and 670nm does not take part in photostructural transformations when carry out exposure of a system As2S3-As2S3 by He-Ne laser (l =632,8nm) since after exposure these peaks do not disappear. The dope x1 which formed singularities on lengths of waves 606nm and 614nm take part in photostructural transformations at an exposure by light He-Ne of the laser. The dope x2 which has formed a homogeneous solution of a glass take part in photostructural transformations also. At an exposure of sample by integrated light both mode of tungsten dope take part in photostructural transformations. That become apparent because disappear singularities in an absorption spectrum and was moving an edge of a fundamental absorption into short-wave area of an absorption spectrum (fig.2. a curve 2.). I.e. the dope in microarea take part in photostructural transformations at the time of exposure by appropriate length of a wave. It permit to expand spectral sensitivity range of our materials into area of long wavelength of a spectrum.

The explanation of obtained spectra can be the following at an annealing during five minutes at 80° C of sample of structure As2S3-As2Se3 with a underlayer WO2 the singularity on length of a wave 606nm has place. It apparently is connected to microareas the base of which make up the compound of sulfur with a tungsten. The peak on length of a wave 656nm is connected to microareas formed by compound of sulfur, selenium and tungsten. At the further annealing during time 10 and 15 minutes of a singularity disappear but the edge of a fundamental absorption was displaced into long wavelength area of spectrum (fig.2. a curve 3). I.e. the homogeneous glass is formed. The new microareas which absorb on lengths of waves 614nm and 670nm are formed at an annealing within 20 minutes. They are connected in our opinion with compound of a selenium and tungsten, as these peaks earlier by us were observed at a thermal diffusion of tungsten on layers As2Se3. At an exposure by integrated light the full disappearing of singularities occurs and the edge of a fundamental absorption is displaced into short-wave area of a spectrum (fig.2. a curve 2).

Fig.2. Absorption spectrums of layers of composition As2S3 - As2Se3 with a underlayer WO2:

1 - not exposed layer;

2 - annealing of layers during 5 minutes with a postexposure by integrated light

3 - annealing of layers during 10-15 minutes;

4 - annealing of layers during 5 minutes;

5 - annealing of layers during 20 minutes.

For clarification a nature of processes happening in a CGS of alloyed by tungsten and for determination of fitness of this practically of new material for manufacture of the holographic optical elements we realized the etching in various chemical etchants. In an outcome of these experiences was found out that the solutions of alkali on base KOH, NaOH dissolve faster exposed areas of films. But the etchants on base of amine substances on the contrary dissolve faster not exposed areas of films. Besides at magnification of tungsten concentration in a system As2S3-As2Se3 the dissolution of the exposed area of films in an amine etchant was considerably worsened. And at tungsten concentration which correspond to thickness d=0.3 micron of a underlayer WO2 the dissolution practically was not observed. That has allowed to receive diffraction gratings of 1000 mm^-1 with diffraction efficiency about 21 %.

Because of these experiments on etching we suppose, that in an outcome of a thermal diffusion of a tungsten in a system As2S3-As2Se3 there are compounds of a type WS, WSe, WS2, WSSe, WSe2. Further during exposure the tungsten compound which include the three atoms chalcogen will formed i.e. compound of a type WSSe2.

3. Conclusions

In connection with above, it is possible to make the following conclusions

1. The new material on base of CGS with increased holographic sensitivity to light on length of a wave l = 632,8nm is obtained.

2. Is shown, that the holographic sensitivity on length of a wave 632,8nm has maximum for composition As2S3-As2Se3. It is connected with that what the optical breadth of a forbidden region coincides with an energy of photons of a recording radiation. And also with existence of microareas which is formed by compounds W-S.

3. The alloying by a tungsten has allowed to expand a spectral range of a photosensitivity of structures (As2S3)0.3× (As2Se3)0.7, (As2S3)0.3× (As2Se3)0.7:Sn 0.015at.% and also has shown a possibility them of use for recording of high contrasting and gray-scale picture.

Reference

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