RU2362243C1 - Method of forming solid-state silicon nanostructure for optical-pumping laser and optical amplifier based thereon - Google Patents

Abstract

FIELD: nanotechnologies.

SUBSTANCE: invention relates to quantum electronics. Solid-state silicon nanostructures intended for lasers and optical amplifiers are formed by consecutive application of silicon oxides layers on silicon body. Resulted structure is subjected to annealing in nitrogen atmosphere. This allows the silicon monoxide layers transform into the silicon nanocrystal layers separated by those of silicon dioxide. Erbium ions are implanted into the formed structure silicon dioxide layer for the structure to be subjected again to annealing. Above described silicon nanostructure can be used for laser and optical amplifier optical pumping out.

EFFECT: laser and optical amplification in solid-state and silicon nanostructures.

5 cl, 3 dwg

Description

The invention relates to the field of quantum electronics, in particular to methods for generating coherent electromagnetic radiation, technology and construction of quantum-optical generators and optical amplifiers based on semiconductor structures.

Technical solutions for the formation of an active medium based on semiconductors and heterostructures for the generation and amplification of coherent radiation, lasers and optical amplifiers based on them are well known in the art.

So, from the prior art is known "Active element of a solid-state laser", which contains activator ions and sensitizer ions. Pumping is carried out through the lateral surface of the active element into the absorption bands of the activator and sensitizer by radiation in the near infrared, visible or near ultraviolet wavelength ranges. The active element has a thickness L in the direction of pumping z, 0≤z≤L, a cross section S (z) and a distribution of ion concentrations of the activator and sensitizer inhomogeneous in the volume of the active medium. The concentrations of activator n _a and sensitizer n _c averaged over the cross sections S (z) are functions of the z coordinate, which makes it possible to control the profile of energy absorbed in the active medium. When the active medium is pumped simultaneously into the absorption bands of both the activator and the sensitizer, it is possible to obtain a profile aligned with the thickness of the active element, which makes it possible to increase the energy stored in the active medium and reduce the thermo-optical distortions of the medium, which improves the spatial and angular characteristics of the laser beam formed in the medium. To create a medium with a variable concentration of activator and sensitizer, laser ceramics is used, consisting of crystal microgranules containing only activator ions, and microgranules containing activator ions together with sensitizer ions. See the description of patent No. 2226732, H01S 3/06, H01S 3/16, 2002.

Also known from the prior art is “Solid-state longitudinal pumped laser”, which includes a series-connected optical pump module and a laser cavity with an output mirror and an active element glued by a heat-conducting compound into a calibrated lodgement, disclosed in the description of the patent of the Russian Federation No. 2172544, H01S 3/02 , 2000.

In addition, the “Solid-state dye laser” disclosed in the description of the RF patent No. 2105401, H01S 3/16, 1996 is known. The feature of the laser is that in the solid-state active element of the laser, made in the form of a plane-parallel polymer plate, the surface the layer of the plate along the propagation of pump radiation with a thickness of not less than the diameter of the pump radiation beam is made transparent.

In addition, the “Transverse-pumped Optical Amplifier” is known, which comprises a device substrate, a waveguide integrated in the device substrate, and a plurality of lasers. Many lasers are distributed over a common substrate. Many lasers are connected to the substrate surface of the device and the waveguide is located under the lasers. A method for amplifying an optical signal comprises a direction of the optical signal along a waveguide embedded in the device’s substrate, light beams from lasers on the substrate are provided transversely to the first propagation direction, and a plurality of light beams are reflected back into the waveguide after passing through the waveguide. See the description of the patent of the Russian Federation No. 2302067, H01S 5/50, 2002.

Also known from the prior art is an injection laser based on heterostructures disclosed in the description of the patent of the Russian Federation No. 2176841, H01S 5/00, H01S 5/32 "Method for manufacturing an injection laser." The method includes growing a first confining layer containing a doped sublayer of the first type of electrical conductivity and a composition providing the greatest optical radiation limitation, an active layer, a second confining layer containing a doped sublayer of the second type of electrical conductivity, and a composition providing the greatest optical radiation limitation. In this case, the restrictive doped sublayers of the greatest optical limitation, closest to the active layer, are doped so as to ensure the ratio of the hole concentration P in the sublayer of the highest optical limitation of the p-type electrical conductivity from the p-type side to the electron concentration N in the sublayer of the largest optical limitation of the n-type electrical conductivity from the n-type side (P / N more than one). Between the doped restrictive sublayers of the greatest optical restriction, including in the active layer, the level of background impurity is provided. In this case, the boundaries of the space charge p – i – n of the heterojunction are located in the bounding doped sublayers of the greatest optical limitation. As a result of this embodiment, a laser is obtained with an increased output radiation power in single-mode and single-frequency modes. The stabilization of these modes is provided with increasing temperature stability, the reliability of the laser is increased.

A known method of producing a laser effect and creating a nanolaser, which is disclosed in the description of the patent of the Russian Federation No. 2219278, H01L 31/00, H01S 5/00 "Method for generating coherent electromagnetic radiation and dipole nanolaser based on it." This invention can significantly reduce the geometric dimensions of lasers for generating coherent electromagnetic radiation and the width of its spectral line for these lasers due to the fact that metallic or semiconductor nanoparticles are introduced into its system of ultrathin semiconductor layers and excite electric dipole vibrations involving electrons of these nanoparticles by pumping.

In addition, prior art technologies and methods for obtaining a laser effect in semiconductor materials and heterostructures are disclosed in the descriptions of foreign security documents, for example, US 3843551, US 5661738, US 5781573, GB 111223.

The disadvantage of these analogues is the impossibility of their integration with other optoelectronic devices on a single, for example, silicon substrate widely used in microelectronic technology.

The problem to which the invention is directed, is to obtain the generation of coherent optical radiation and amplification of optical coherent radiation in semiconductor silicon nanostructures.

This problem is solved by using a semiconductor silicon nanostructure in which the necessary and sufficient conditions for the appearance of the laser effect and optical amplification are satisfied - the population of the electronic levels of the optical centers of the active medium is inverted, as well as the necessary level of amplification of this active medium.

When implementing this invention, several technical results are achieved. Firstly, to create lasers with optical pumping and optical amplifiers with optical pumping, it becomes possible to use a material widely used in microelectronic technology - silicon, and secondly, the integration of these coherent-optical devices with other optoelectronic devices on a single silicon substrate is simplified. while reducing their size and increasing speed.

In semiconductor lasers, mainly binary compounds of the A ³ B ⁵ , A ² B ⁶ , A ⁴ B ^{6 type} and their mixtures, solid solutions, are used.

All of them are direct-gap semiconductors in which interband radiative recombination can occur without the participation of phonons or other electrons, and therefore has the greatest probability among recombination processes. In addition to these substances, there are a number of promising materials, including silicon.

Information about various silicon emitters has repeatedly appeared in print. However, the high efficiency of their luminescence is achieved either at low temperature or at room temperature, but in the reverse bias mode under extreme, almost prebreakdown, operating conditions [1].

There are also reports on the implementation of the necessary conditions for the generation of coherent optical radiation in structures standard for modern microelectronics - silicon / germanium epitaxial layers Si / SiGe: Er / Si (Ge content up to 28%) grown on silicon substrates. In these structures cooled to helium temperatures, a transition to the state of inverse population of optically active centers, erbium ions Er ³⁺ , was reliably detected [2].

However, the laser effect in such structures is absent due to the absence or insufficient level of amplification.

To overcome these difficulties, including reducing losses and creating conditions for the generation of coherent optical radiation at room temperatures, the most promising structures are those based on an ion-doped rare-earth elements dielectric matrix containing layers of silicon nanocrystals (nc-Si) [2].

Among rare-earth ions, erbium ion Er ^{3+ is} of the greatest interest, the radiative transition ⁴ I 13/2 _→ ⁴ I _15/2 in the inner 4f shell of which leads to the emission of light with a wavelength of 1.54 μm, which corresponds to the minimum loss in quartz fiber-optic communication lines [2].

Foreign sources also have reports on work being carried out in this direction.

So, in [3] provides information on the manufacture of effective radiation sources based on silicon. These devices demonstrate strong electroluminescence near 1.54 μm at room temperature (300K) with a quantum efficiency of 10%, comparable to the electroluminescence of standard LEDs based on III-V group semiconductors.

The following is a description of graphic materials illustrating the structure in which coherent optical radiation is generated and coherent optical radiation is amplified, and the population level energy levels are inverted by optical pumping, which in no way limit all possible options for its implementation.

On figa, b, c presents the stages of formation of a semiconductor silicon nanostructure, and figure 2 and figure 3 is a schematic illustration of a laser with optical pumping and an optical amplifier based on it. The following are the numbers of the components of a semiconductor silicon nanostructure, the main elements of a laser and an optical amplifier based on it, their name and designation:

1 - silicon substrate (c-Si)

2 - layers of silicon oxide (SiO),

3 - layers of silicon dioxide (SiO ₂ ),

4 - silicon nanocrystals (nc-Si),

5 - implanted erbium ions (Er ³⁺ ),

6 - active waveguide layer with silicon nanocrystals in the matrix of silicon dioxide doped with erbium (ABC),

7 - optical pumping (OH),

8 - laser radiation (LI),

9 - incoming radiation (VI),

10 - amplified radiation (UI).

The following is an example of a method for forming a semiconductor silicon nanostructure, in no way limiting all possible options for its implementation.

Stage 1. Semiconductor silicon nanostructures are formed by sequential deposition of layers of SiO (2) and SiO ₂ (3) on a c-Si (1) substrate, for example, by reactive thermal sputtering.

The thicknesses of the SiO (2) and SiO ₂ (3) layers are from 2 to 6 nm, due to which the size and density of nanocrystals, which determine the optical characteristics of the semiconductor silicon structure, are varied.

The structures consist of 30-40 pairs of layers with a total active layer thickness of 200-300 nm. The structure in step 1 is presented in figa.

Stage 2. The resulting structure undergoes thermal annealing at a temperature of 1100 ° C in a nitrogen atmosphere for 1 hour.

As a result of the thermochemical decomposition of silicon monoxide, SiO (2) layers are transformed into layers of densely arranged Si (4) nanocrystals, which are separated by SiO ₂ layers (3).

The average sizes of Si (4) nanocrystals are from 1.5 to 5 nm, depending on the thickness of the initial SiO layers. The structure in step 2 is presented in figb.

Stage 3. Er ³⁺ ions (5) with an energy of 300 kV and a dose of 10 ¹⁵ cm ^{-2 are} implanted into the formed structure. The structure of step 3 is presented in figb.

After implantation of Er ³ ions (5), the structure is again subjected to thermal annealing for 5 min at a temperature of 950 ° С. In the resulting structure, the concentration of Er ³ (5) ions is about 10 ¹⁹ cm ^–3 .

The method of creating an inversion of the level population by optical pumping of the active medium has the following advantages. Firstly, it is applicable for the excitation of media with a high concentration of particles distributed on the surface of a silicon substrate in the required geometry. Secondly, a distinctive feature of the active medium formed in accordance with the proposed method is the possibility of using a wide range of frequencies for optical pumping of emitters.

In the laser circuit (FIG. 2), OH radiation (7) is directed perpendicular to the ABC layers (6). In this case, ABC (6) is excited to the state of inverse population of its optically active centers - Er ³⁺ ions. The subsequent spontaneous radiative transitions, for example, ⁴ I _{13.2 →} ⁴ I _15/2 in the inner 4f shell of Er ³⁺ , lead to the emission of light and its amplification in ABC (6) with a wavelength of 1.54 μm characteristic of this example. Inside the active medium, LI (8) propagates between the surfaces of the extreme layers of a semiconductor silicon nanostructure, forming a trajectory in the active medium in the form of a broken line, as shown in Fig. 2.

Experimental studies have shown that a similar structure is capable of amplifying coherent optical radiation, in particular, at a wavelength of 1.54 μm.

In the optical amplifier circuit (Fig. 3), OH radiation (7) is also directed perpendicular to ABC spruces (6). Optical pumping (7) excites a semiconductor silicon nanostructure to a state of inverse population of optically active centers - Er ³⁺ ions. The incoming radiation, for example, with a wavelength of 1.54 μm, induces the radiative transition ⁴ I 13/2 _→ ⁴ I _15/2 in the inner 4f shell of Er ³⁺ , which leads to the amplification of the VI (9) in the ABC (6). The input of the VI (9) and the output of the VU (10) is through the opposite side sections of the ABC (6) in the direction of the optical axis of the amplifier. Inside the active medium, VI (9) and SI (10) propagate between the surfaces of the extreme layers of a semiconductor silicon nanostructure, forming a trajectory in the active medium in the form of a broken line, as shown in Fig. 3.

The semiconductor silicon nanostructures thus formed after optical excitation are capable of generating coherent optical radiation and amplifying coherent optical radiation, in particular, at a wavelength of 1.54 μm, which is characterized by minimal losses in quartz fiber-optic information transmission lines.

This circumstance makes it possible to create lasers with optical pumping and optical amplifiers with optical pumping, which differ from known quantum devices in the possibility of their integration with other optoelectronic devices on a single silicon substrate due to the use of semiconductor silicon nanostructures as an active medium.

Information sources

1. A.M. Emelyanov, N. A. Sobolev and others. Effective silicon LED with temperature-stable spectral characteristics. Physics and Technology of Semiconductors, 2003, Volume 37, Issue 6.

2. MV Stepikhova, DM Zhigunov, VG Shengunov and others. Inverse population of energy levels of erbium ions during excitation transfer from a semiconductor matrix in silicon / germanium based structures. Letters to the ZhTF, Volume 81, Issue 10, pp. 614-617.

3. M.E. Castagna, S. Coffa, M. Monaco, L. Caristia, A. Messina, R. Mangano, C. Bongiomo // Physica E 16 (2003), p. 547-553.

Claims (5)

1. A method of forming an active medium for an optical pumped laser and an optical amplifier based on it, characterized in that the active medium is formed on a silicon substrate by sequentially depositing layers of silicon dioxide and silicon oxide, the latter being transformed into dense layers after thermal annealing in a nitrogen atmosphere silicon nanocrystals, and erbium ions are implanted into the silicon dioxide layers, after which thermal annealing of the formed semiconductor silicon nanostructure is again performed. 2. An optical pumped laser, characterized in that an active medium formed in accordance with claim 1 is used as an active medium for generating coherent optical radiation. 3. The laser with optical pumping according to claim 2, characterized in that the laser with optical pumping is designed so that it can be integrated on a single silicon substrate with other microelectronic devices. 4. An optical amplifier with optical pumping, characterized in that the active medium formed in accordance with claim 1 is used as an active medium for amplifying coherent optical radiation. 5. An optical amplifier with optical pumping according to claim 4, characterized in that the optical amplifier with optical pumping can be integrated on a single silicon substrate with other microelectronic devices.

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