RU2421551C1 - Procedure for growth of 3-d photon crystal on base of film of opal with silicon - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in sedimentation of opal film of 5.0-40.0 mcm thickness out of suspension of spherical particles of amorphous silicon dioxide in ethyl alcohol on dielectric substrate. Also, particles have average diameter 880 nm, dispersion of diameters less, than 1 % and concentration 0.5÷2 vol. %. Further, the procedure consists in drying, in settling a layer of amorphous silicon in vacuum on internal surface of opal film pores by thermal decomposition of mixture of mono-silane with argon at concentration of 5 vol. % and pressure of gas mixture 50÷70 kPa, voluminous gas mixture flow rate 0.02±0.01 cm³/min, temperature 520÷540°C, and duration 5÷7 h, in etching film in water solution of hydrofluoric acid for removal of spherical particles of amorphous silicon dioxide, in inversion, repeated drying and in settling a layer of amorphous silicon on internal surface of pores of opal film under the same conditions.

EFFECT: creation of film inverted composite of opal-silicon with increased width of total photon forbidden-zone in spectral region of 1.5 mcm.

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Description

The invention relates to the field of optical devices, specifically to the creation of three-dimensional photonic crystals with a full photonic band gap, which can be used in optical communication systems and information transfer.

Opal films filled with amorphous-nanocrystalline silicon are three-dimensional (3M) photonic crystals (PCs) that allow monitoring, control, and modification of light fluxes due to the large relative width of the total photonic band gap (Δω / ω), which opens the way for their possible applications in telecommunications and laser technology. Unlike bulk opals, opal films have a higher reflection coefficient characterizing the content of point and extended defects in the volume and on the surface of the structure, which affect the quality of the crystals, and can be integrated into optical and optoelectronic microdevices (optical chips). Single-crystal regions in the films reach sizes 5 * 5 μm (in bulk opals 30 ÷ 50 μm). Silicon is chosen because of its high refractive index, transparency in the near infrared region, the compatibility of the used technological methods with planar technology.

Known analogue / patent WO2004063432, METHOD OF SYNTHESIS OF 3D SILICON COLLOIDAL PHOTONIC CRYSTALS BY MICROMOLDING IN INVERSE SILICA OPAL (MISO), 2004-07-29, C30B 29/60; G02B 6/12 /, which proposes a method for the synthesis of three-dimensional silicon colloidal photonic crystals using microprocessing of inverted silica opals. It includes the preparation of an opal film from polymer (latex) spherical particles with an fcc (face-centered cubic) structure, the deposition of a layer of amorphous silicon dioxide of controlled thickness by the sol-gel method on the surface of polymer (latex) spherical particles (due to their low heat resistance), removal (dissolution or annealing) spherical polymer particles, depositing the silicon layer having a relative thickness of 0.3019 <R _si /L<0.3995 (where R _Si - radius of the sphere with the deposited amorphous silicon layer, L = 2 * R * √2 - fcc unit cell parameter p Keturah, R - the radius of the spherical particles) by using the thermal decomposition of disilane (pressure 700 torr ≈ 70 kPa, temperature of 200 ÷ 400 ° C) removing the layer of amorphous silicon dioxide by etching in 3% aqueous HF solution.

As a result, the authors obtained a three-dimensional (3M) photonic crystal with a total photonic band gap with a relative width Δω / ω = 0.12 (ω is the energy position of the center of the photonic band gap) at a wavelength of 1.5 μm, having the structure of an inverted opal. The reflection coefficient of the obtained structure in the region of the total photonic band gap (FZZ) is 82% for L = 1485 nm (the corresponding diameter of spherical particles is D = 1050 nm), the silicon layer thickness is 70 nm.

The disadvantages of the analogue are the low reflection coefficient, because With this technology, a layer of bulk silicon is formed on the surface of the opal film, which leads to the creation of uncontrolled photonic surface states, and an insufficiently high value of the relative width of the photonic band gap.

The prototype of the proposed method is a method of forming silicon photonic crystals on a chip (substrate) [On-chip natural assembly of silicon photonic bandgap crystals YAVlasov, X.-Z.Bo, JCSturm, DJNorris. Nature 414289 (2001)], coinciding in most essential respects. It produces the preparation of an opal film 5–30 μm thick with an fcc (face-centered cubic) structure on a vertically oriented silicon substrate by the controlled evaporation of a dispersion medium (alcohol) from 1% vol. alcohol suspension of spherical particles of silicon dioxide with a diameter of 760 nm at temperatures of ~ (65 ÷ 80) ° C, deposition (deposition) of a silicon layer with a relative thickness of 0.354 <R _Si /L<0.428 using the method of low-pressure chemical vapor deposition (chemical vapor deposition at low pressure) on the inner surface of the pores of the opal film at a temperature of (550 ÷ 580) ° C using monosilane as a starting reagent, reactive ion etching of the formed bulk silicon layer with a thickness of (0.2 ÷ 0.4) μm from the surface of the composite, removal of spherical amo particles fnogo silica using wet etching in HF.

As a result, we obtained a three-dimensional photonic crystal with a total band gap with a relative width Δω / ω = 0.08 at a wavelength of 1.3 μm, having the structure of an inverted opal. The reflection coefficient of the obtained inverted opal-silicon composite (the diameter of the balls in the initial film is D = 760 nm (L = 1070 nm)) in the region of the total photonic band gap is almost 100% in the [111] direction and more than 90% in the [100] direction.

The disadvantage of the prototype is the small relative width of the total forbidden zone, limiting the possibility of using such 3M photonic crystals in broadband telecommunication devices, and the formation of a layer of massive silicon on the surface of the opal film, leading to the appearance of uncontrolled photonic surface states (defects in the photonic band gap of the PC), which optical experiments were removed by reactive ion etching. In addition, the center of the PPZ of the obtained three-dimensional crystal is in the region of 1.3 μm. This spectral range is used in transmission and information systems, however, most modern telecommunication devices operate in the 1.5 μm region, which coincides with the maximum transmittance of optical silica fibers.

The proposed method solves the problem of creating a film inverted opal-silicon composite with an increased width of the total photonic band gap in the spectral region of 1.5 μm.

The problem is solved by a method for producing a three-dimensional photonic crystal based on an opal film with silicon, including the deposition of a face-centered cubic opal film (5.0–40.0) μm thick from a suspension of spherical particles of amorphous silicon dioxide in ethanol with an average diameter of 880 nm, a dispersion of particle diameters of less than 1% and concentration (0.5 ÷ 2)% vol. on a dielectric substrate, drying, vacuum deposition of a layer of amorphous silicon on the inner surface of the pores of the opal film by thermal decomposition of a mixture of monosilane with argon with a concentration of 5% vol. at a pressure of the gas mixture (50 ÷ 70) kPa, volumetric flow rate of the gas mixture (0.02 ± 0.01) cm ³ / min, temperature (520 ÷ 540) ° С, duration (5 ÷ 7) h, film etching in an aqueous solution of hydrofluoric acid for removal of spherical particles of amorphous silicon dioxide (inversion) and repeated drying and deposition of a layer of amorphous silicon on the inner pore surface of the opal film under the same conditions.

As the authors of the invention have revealed, in the implementation of this set of operations, it becomes possible to change the structural parameters (relative thickness of the silicon layer in the pores of the opal film within 0.29 <R _{Si /} L <0.43) and the associated optical properties (parameters of the photonic band gap), which leads to the creation of a three-dimensional photonic crystal based on film opal and silicon, which has, in particular, a complete forbidden zone with a center in the region of 1.5 μm wide Δω / ω = 0.14 ÷ 0.16 and the reflection coefficient in all directions is not its 95%.

The initial opal film consists of monodisperse spherical particles of amorphous silicon dioxide with an average diameter of 880 nm (in accordance with a preliminary calculation of the band structure of a photonic crystal centered at 1.5 μm), which form an fcc lattice. There are pores between the SiO ₂ spheres, the volume of which is ~ 26% of the total film volume. The film thickness (5 ÷ 40) μm provides the full FZZ in the region of 1.5 μm in an inverted opal-silicon composite according to the authors. An increase in the thickness leads to a decrease in the adhesion of the film to the substrate and to an increase in the concentration of point and extended defects, and a decrease in the absence of a photonic crystal structure of the film.

The deposition of a silicon layer is carried out by thermal decomposition of a mixture of monosilane with argon with a concentration of 5% vol. at a gas mixture pressure (50 ÷ 70) kPa, because such a mixture is not explosive, in contrast to pure monosilane and disilane, used, respectively, in the prototype and analogue.

With an increase in the decomposition temperature above 540 ° С, a layer of bulk silicon begins to precipitate on the surface of the opal film, leading to the appearance of defects in the photonic band gap of the photonic crystal. When the decomposition temperature decreases below 520 ° С, the decomposition rate decreases by 3–5 times and the time significantly increases.

It was found that when the vacuum deposition of a layer of amorphous silicon on the inner surface of the pores of the opal film is less than five hours, the pores are not completely filled, and at a time of more than seven hours, a layer of bulk silicon appears on the surface of the film.

The volumetric flow rate of the gas mixture (0.02 ± 0.01) cm ³ / min at the above temperature and pressure provides the condition for limiting the rate of filling the opal film with silicon by the rate of the chemical reaction of thermal decomposition of monosilane, rather than the rate of mass transfer of gas-phase reagents in the pores of opal, which necessary for uniform deposition of a layer of amorphous silicon on the inner surface of the pores of the opal film.

These modes are determined empirically.

Repeated thermal decomposition allows one to additionally increase the thickness of the silicon layer in the film composite, which determines the type (geometry) of the structural units that make up the FC, and, as a result, allows one to modify the translational symmetry of the PC and the photonic-crystalline properties (photonic band structure) of the composite providing a solution to the tasks.

The method is as follows.

An alcohol suspension of spherical particles of amorphous SiO _{2 with} an average diameter of 880 nm is prepared by the hydrolysis of tetraethoxysilane (TEOS) in an alcohol-ammonia medium (Stöber's method [Stöber W, Fink A and Bohn E 1968 J. Colloid Interface Sci. 26 62]) or use, for example, at Bangs Laboratories Inc. or Duke Scientific Corp. An opal film is then grown on a substrate of fused silica, glass, silicon or sapphire. After that, the resulting film is dried in air (at a temperature of 100 ÷ 150 ° C.) Next, thermal decomposition of a mixture of monosilane with argon in the pores of the opal film is carried out to deposit a uniform layer of amorphous silicon on the inner surface of the pores of the opal film. Then, selective etching of amorphous silicon dioxide from the resulting composite is carried out (inversion). Next, the drying and thermal decomposition operations of the monosilane mixture described above are repeated under the same conditions.

Example 1

To create a three-dimensional FC based on film opal and silicon, a suspension was prepared by the hydrolysis of tetraethoxysilane (TEOS) in an alcohol-ammonia medium. To prepare the suspension, a solution in ethanol containing 0.28 mol / L TEOS, 4 mol / L NH ₃ and 7 mol / L H ₂ O was placed on a magnetic stirrer for 1.5 h at room temperature. Received 1% vol. a suspension of spherical particles of amorphous SiO _{2 with} an average diameter of 880 nm with a size dispersion of less than 1%. Then, an opal film was grown on a fused silica substrate in the same way as described in [YAVlasov et al. Nature 414 289 (2001)]. For this, the substrate was vertically placed in a 50 ml beaker containing 30 ml of a 1% alcohol suspension of spherical particles of SiO ₂ . The glass was heated so that the temperature of the suspension near the bottom was ~ 80 ° C, and at the surface ~ 65 ° C. This temperature gradient is organized to create convective flows in the suspension, which prevent sedimentation of particles. Due to the evaporation of alcohol from the suspension, the liquid level in the glass decreases and on the surface of the substrate under the action of capillary forces within 3 hours an opal film is formed with a thickness of 15 μm and a length of 8 mm, the width of the film is equal to the width of the substrate. After that, the obtained film was dried in air at a temperature of 120 ° C. Next, thermal decomposition of the monosilane mixture in the pores of the opal film was carried out to deposit a uniform layer of amorphous silicon on the inner pore surface of the opal film. For this, an opal film was placed on a metal heating stage in a vacuum chamber, the chamber was evacuated to a pressure of 10 Pa, the temperature of the heating stage was set at 530 ° C, and the chamber was evacuated for 1 h. Using a gas flow regulator, a monosilane mixture was fed into the chamber (5% vol.) with argon with a flow rate of 0.02 cm ³ / min and a pressure of 60 kPa. The filling process lasted 6 hours, then the gas mixture was stopped flowing into the chamber, the stage heating was turned off, and the chamber was evacuated to a pressure of 10 Pa for 30 minutes. Next, selective etching of amorphous silicon dioxide from the resulting composite was carried out (inversion). For this, the sample was placed for 3 hours in 3% of the mass. HF solution. Then, the drying and thermal decomposition operations of the monosilane mixture described above were repeated under the same conditions. The obtained samples of the inverted opal-silicon composite (three-dimensional photonic crystal) were dark brown and had bright interference coloration (irization) from blue to red, depending on the angle of incidence of light. A comparison of the experimental reflection and transmission spectra of the obtained three-dimensional photonic crystal with theoretical calculations of the photonic band structure performed by the plane wave method showed that it has a total photonic band gap in the region of 1.5 μm with a width Δω / ω = 0.16. The experimentally measured using an Ocean Optics NIR256 IR spectrometer, the reflection coefficient in the [111], [100] and [110] directions was 99 ± 1%.

The values of the relative thickness of the silicon layer in the pores of the inverted composite, obtained from a comparison of the experimental and theoretical reflection spectra, were 0.29 <R _{Si /} L <0.43 (absolute layer thickness 170 nm). As shown by optical and scanning electron microscopy, there is no layer of bulk silicon on the surface of the sample, leading to defects in the photonic band gap of the photonic crystal.

Example 2

The same as in example 1, but the suspension was taken with a concentration of 0.5% vol. As a result, an opal film with a thickness of 5 μm was obtained, the remaining characteristics of a three-dimensional photonic crystal are the same as in example 1.

Example 3

The same as in example 1, but the suspension was taken with a concentration of 2.0% vol.

As a result, an opal film 40 μm thick was obtained, the remaining characteristics of a three-dimensional photonic crystal (including the width of the total photonic band gap) are the same as in example 1.

Example 4

Same as in example 1, but the pressure of the gas mixture is 50 kPa.

The result is similar to example 1, but the thickness of the silicon layer in the pores of the inverted composite is 0.30 <R _Si /L<0.42 (absolute layer thickness is 150 nm), the width of the total photonic band gap in the region of 1.5 μm is Δω / ω = 0.15.

Example 5

Same as in example 1, but the pressure of the gas mixture is 70 kPa.

The result is similar to Example 1, the obtained three-dimensional photonic crystal has a total photonic band gap in the region of 1.5 μm Δω / ω = 0.16, but the reflection coefficient in the [100] and [110] directions was 98 ± 1%.

Example 6

The same as in example 1, but the temperature is 520 ° C.

The result was an inverted opal-silicon composite (three-dimensional photonic crystal), but the thickness of the silicon layer in the pores of the inverted composite is 0.31 <R _{Si /} L<0.41 (absolute layer thickness 125 nm), the width of the total photonic band gap in the region of 1.5 μm Δω / ω = 0.14.

Example 7

The same as in example 1, but the temperature is 540 ° C.

The result was an inverted opal-silicon composite with the same characteristics as in Example 1 (the width of the total photonic band gap in the region of 1.5 μm is Δω / ω = 0.16), but the reflection coefficient in the [100] and [110] directions was 96 ± 1%, in the direction [111] - 98 ± 1%.

Example 8

The same as in example 1, but the duration of thermal decomposition of 5 hours

The result was a three-dimensional photonic crystal with the same characteristics as in example 4.

Example 9

The same as in example 1, but the duration of thermal decomposition is 7 hours. The result is an inverted opal-silicon composite with the same characteristics as in example 1 (the width of the total photonic band gap in the region of 1.5 μm is Δω / ω = 0.16), but the reflection coefficient in the [100] and [110] directions was 96 ± 1%, and in the [111] direction it was 96 ± 1%.

Thus, the performed experiments confirm the creation of three-dimensional photonic crystals based on film opal and silicon, having a complete forbidden zone centered in the region of 1.5 μm with a relative width of Δω / ω = 0.14 ÷ 0.16, with a reflection coefficient in all directions of at least 95%.

Claims (1)

A method for producing a three-dimensional photonic crystal based on an opal film with silicon, including the deposition of an opal film with a thickness of (5.0 ÷ 40.0) μm from a suspension of spherical particles of amorphous silicon dioxide in ethanol with an average diameter of 880 nm, a dispersion of particle diameters of less than 1% and concentration of 0.5 ÷ 2 vol.% on the dielectric substrate, drying, vacuum deposition of a layer of amorphous silicon on the inner pore surface of the opal film by thermal decomposition of a mixture of monosilane with argon with a concentration of 5 vol.% at a gas mixture pressure of 50 ÷ 70 kPa, about Removable flow rate of the gas mixture 0.02 ± 0.01 cm ³ / min, a temperature of 520 ÷ 540 ° C, duration of 5 ÷ 7 h, etching the film in an aqueous solution of hydrofluoric acid for removing the spherical particles of amorphous silica, invert and re-precipitation and drying a layer of amorphous silicon on the inner pore surface of the opal film under the same conditions.