Annual Report 2012 - Latvijas Universitātes Cietvielu fizikas institūts

Main Results
SUBWAVELENGTH STRUCTURES IN AMORPHOUS CHALCOGENIDE
THIN FILMS
Mara Reinfelde and Janis Teteris
Thin films of amorphous chalcogenide semiconductor As 2 S 3 , As-Se and As-S-Se
systems were used for recording of refractive index and surface-relief modulated
gratings. Amorphous chalcogenide semiconductors are high index materials with
refractive index in the range 2.2 – 3.5, depending on the film composition and light
wavelength. The photoinduced changes of refractive index down to Δn≈0.15 – 0.5 are
observed in these systems.
The photo- and electron-beam stimulated changes of wet etching rate in
amorphous As-S, As-Se and As-S-Se films have been studied. Amorphous chalcogenide
semiconductor (AChS) resists obtained by thermal deposition in vacuum are
characterized by very high resolution capability and they possess a number of
peculiarities that make them attractive for application in many photo- and electron-beam
lithographic (EBL) processes.
The recording of the subwavelength gratings with a period of 0.15 μm – 1 μm
was performed by holographic method. The fringe period for two intersecting light
beams in a media with high refractive index n can be expressed as Λ=λ 0 /2 n sinθ, where
λ 0 is the wavelength of laser light in vacuum, n is refractive index of the resist and θ is
the half-angle between the laser beams inside the resist. The right angle prisms with n=
1.8 – 2.6 were used to increase the value of θ. The grating period and profile after
chemical etching was measured by AFM. The transmission, reflection and polarization
properties of the obtained gratings were studied.
OPTICAL RECORDING IN AMORPHOUS CHALCOGENIDE THIN FILMS
Janis Teteris
During the past 10 years, research in the field of optical materials based on
amorphous chalcogenide semiconductors has made significant advances. Much of this
research is driven by applied interest and this field of research is extremely broad and
active. The use of amorphous chalcogenide thin films in holography and lithography has
probably only just begun, but already produced some promising results.
The main functional principles and practical application of amorphous
chalcogenide photoresists for production of the embossed rainbow holograms and
holographic optical elements are discused. The laser interference lithography is used as a
low-cost method for the exposure of large surfaces with regular patterns like
subwavelength-gratings and microsieves. The regular features with the sizes of about 50
nm and less can be fabricated by this method. The Bragg reflection gratings were
recorded and studied in amorphous As 2 S 3 and As-S-Se films. Amorphous chalcogenide
thin films are thought to be one of the potential materials for all-optical integrated
circuits for the optical communication systems due to their excellent infrared
transparency, large nonlinear refractive index, and low phonon energies. The possibility
to use the amorphous chalcogenide films as a media for holographic recording,
processing and storage of information with high density is discussed.
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