JPH06224471A - Microcavity structure containing porous silicon as light source for caf2:nd laser and arrangement of the light source - Google Patents

Abstract

PURPOSE: To provide method and device for a generating laser light from a thin film, doped with a rare earth by using porous Si as a light source for optical pumping. CONSTITUTION: A method and device 242 cause intense spectral emission by relating a porous Si layer 230 to a CaF2 film 234 which is doped with a rare earth, so that the CaF2 film 234 doped with the rare earth absorbs light from the porous Si layer 230. Circuits 228 and 244 related to the device 242 cause light emission by activating the porous Si layer 230. The porous Si layer 230 is formed electrically by a chemical vapor-depositing method or by forming crystalline silicon into an anode.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to lasers, and in particular, using porous Si as a light source for optical pumping, C
The present invention relates to a method and apparatus for generating light from an aF ₂ : Nd thin film.

[0002]

The availability of all-silicon based optoelectronic integrated circuit (OEIC) technology promises a revolution in the optoelectronic industry and its widespread implications for both military and commercial applications. One area of such impact is the interconnection of multichip modules. Silicon-based OEI
C not only solves the resistivity and high capacitance problem by replacing electron transport with photons, but it also provides new functionality such as circuit level imaging. Silicon-based OEICs also cost-invade the commercial market because the silicon bulk process has economic advantages that are incomparable to other electronic or optoelectronic material technologies. In addition, silicon-based OEI
C also provides new functionality such as circuit level image processing.

In order to realize an OEIC based on silicon, the following four device technologies are required. (1) Detector, (2) Waveguide, (3) Modulator, (4) Light emitter. Although considerable progress has been made in the first three areas, the lack of suitable silicon-based light emitting devices, especially silicon-based lasers, has largely hindered the development of the technology of fully integrated silicon-based OEICs.

Here, the Nd transistor that functions as a gain medium is used.
CaF₂A thin film is described, which is also
Scope of Claims of US Patent Application (TI-16928)
The details are shown in the box. These results are silicon
As a stepping stone to realize OEIC based on
is important. However, Ca by electrical pumping
F ₂: Light emission from Nd has not been realized so far.
CaF for laser light emission ₂: Light for pumping Nd
Sources are needed. Like CaAs or ZnSe
III-V or IV-VI compounds are electroluminescent
And emits light of an appropriate wavelength to emit Ca
F₂: Nd can be pumped. However,
Recon or CaF₂III-V or even grown up
Or, IV-VI compounds usually have too many defects in practical use. Sorry
This reduces the efficiency of electroluminescence while
Let In addition, III-V and IV-VI compounds are
It is a complicated and expensive source of troll luminescence. It
Hope to use silicon as a light emitting material to replace
Good However, silicon has a non-linear bandgap
Have characteristics. This reduces the firing efficiency of silicon.

[0005]

As a result, CaF ₂ :
A light source that pumps Nd for laser light emission is needed. There is also a need for compounds that are less defective and more efficient than the III-V and IV-VI compounds used for electroluminescence. Furthermore, CaF
There is a need for simple and cost-effective methods and devices that use silicon as a light source for optically pumping ₂ : Nd thin films.

There is also a need for Si-based compounds that can be used as emissive materials and that can overcome the nonlinear bandgap problem of silicon and the associated low emission efficiency properties. Accordingly, the present invention uses porous Si as an emission source to produce a strong spectral emission from a CaF ₂ : Nd thin film, overcoming the constraints associated with conventional optical pumping methods and devices for microcavity lasers and A method and apparatus for reducing are provided.

[0007]

SUMMARY OF THE INVENTION One feature of the present invention is to provide a method for producing a strong spectral emission, in which a rare earth-doped CaF ₂ thin film is removed from a porous Si layer. Porous Si so as to absorb the luminescence of
Associating the layer with a rare earth-doped CaF ₂ thin film. The method further includes activating the porous Si layer to produce light emission. Activation can be done by optically pumping or electrically pumping the porous Si layer. In the present invention, the emission of porous Si is from 5200Å to 900
It has a wavelength range up to 0Å. Porous Si can be formed electrically by chemical vapor deposition or by anodizing crystalline silicon. Porous Si can also be formed by physical vapor deposition methods such as sputtering or molecular beam epitaxy.

The technical advantage of the present invention is that porous Si is C
Since the aF ₂ : Nd thin film can be electrically or optically pumped so that the aF ₂ : Nd thin film is optically pumped to emit light of an appropriate wavelength, a structure in which porous Si is integrated with the CaF ₂ : Nd thin film is manufactured. The solid-state laser based on Si is to be formed.

Another technical advantage of the present invention is that porous Si can be formed in various ways. These methods include electrochemical fabrication, crystalline silicon anodization, and conventional chemical vapor deposition and molecular beam epitaxy growth techniques. Therefore, the established silicon manufacturing technology can be fully utilized in the manufacture of porous Si as a light emitting source.

Yet another technical advantage of the present invention is:
It is possible that a structure using porous Si can be attractive for surface emitting lasers because a porous Si layer can be formed outside the output path of the laser. This increases the power efficiency of laser devices that use porous Si. This is because in the manufacture of a structure using porous Si as an optical pumping medium for a CaF ₂ : Nd thin film,
It can have important advantages. A more complete understanding of the present invention, and its advantages, will be obtained from the following description taken in conjunction with the accompanying drawings.

[0011]

EXAMPLE I. Introduction The development of microcavity lasers began with the study of interactions between atoms / molecules and the electromagnetic radiation field. In 1946, Purcell predicted that the spontaneous emission rate of an excited atom would change if the atom were placed in a cavity with dimensions comparable to the emission wavelength of the atom. . In 1974, Drexhage
ge) demonstrated this phenomenon experimentally with fluorescent dyes. In 1981, this issue was addressed by Kleppna.
re-introduced by
Increasingly, numerous experimental and theoretical results have been reported. Recently, increased interest in surface emitting laser devices, which consist essentially of high quality cavities and radiation wavelengths that are often of similar size, has significantly enhanced the study of microcavity effects. .

II. Micro-cavity effect A. Factors controlling the microcavity effect . In a conventional laser, the efficiency of coupling the emitted radiation into a mode is on the order of 10 ^-4 to 10 ^-5 . The coupling efficiency can be close to unity when the optical modes are reduced to a single mode by the formation of microcavities. Other unique features of microcavity lasers include thresholdless laser light emission, elimination of relaxation oscillations, increased dynamic response speed, and altered firing life. The degree of the microcavity effect is defined by the emission line width of the gain medium, the reflectivity of the mirror, the difference in the refractive index between the gain medium material and the mirror material, the position and thickness of the gain medium, and the three-dimensional dimension of the cavity. , Depends on.

It has been calculated that the microcavity effect increases as the firing linewidth decreases. FIG. 1 shows the gain enhancement of microcavities with some launch linewidths in the range of 30 nm to 100 nm typical of III-V semiconductors.
In particular, graph 50 of FIG. 1 shows reflectivity plotted along abscissa 54 versus gain enhancement along ordinate 52.
Line 56 for a line width of 30 nm, which is an example line width
However, for the line width of 62.5 nm, the line 58 is 100
Line 60 is shown for a line width of nm. 100n
Gain enhancement in launches with a linewidth of m has a reflectance of 1
Saturates at 2.4 when close to. In contrast, when the launch linewidth is 30 nm, the gain enhancement is 7.6.

The microcavity effect also strongly depends on the quality of the cavity mirror. FIG. 1 also shows that high reflectivity mirrors provide high gain enhancement, especially when the launch linewidth is small. When the mirror is made from a quarter-wave multilayer dielectric film (ie, distributed Bragg reflector (DBR)), the quantum efficiency increases as the index difference between different films increases. In addition to the difference in refractive index, other factors such as film stoichiometry, interface sharpness, and film stress also affect the performance of the mirror.

The large difference in refractive index between CaF ₂ and other semiconductors has facilitated efforts to use CaF ₂ as a high quality Bragg reflector. For example, CaF ₂ and Zn
With a Bragg reflector made from Se and Si /
Microcavity III-V semiconductor lasers can be formed that exhibit superior laser performance in terms of threshold current and laser light emission compared to lasers using SiO ₂ mirrors.

Enhancement or inhibition of spontaneous emission in the microcavity is achieved by controlling the length of the microcavity and the position of the active gain medium within the cavity. Enhanced emission occurs when the cavity length is tuned to the emission wavelength and the active gain medium is placed in the antinode position. In this arrangement, the field interacts with the gain medium. Reduced emission is observed when the gain medium is placed in the nodal position.

A three-dimensional structure is defined by the DBR in the direction perpendicular to the surface and in the lateral direction by the cleavage plane.
Theoretical analysis of a quadrangular microcavity shows that when the emission line width is 1.5 nm, the coupling efficiency (spontaneous emission factor) of the total radiant energy into the resonance mode is large, and the lateral dimension is the radiant wavelength. If it is reduced from 15 times to 2 times,
It is suggested to increase more than. Similar increases in coupling efficiency have been suggested for cylindrical microcavity structures.

B. CaF ₂ for microcavity effect . In an example, the Al and CaF ₂ films consist of an ultra high vacuum device (VG Semicon V8) consisting of a molecular beam epitaxy (MBE) chamber, a metallization chamber and a chemical vapor deposition chamber.
In (0), a silicon wafer having a diameter of 10.16 cm (4 inches) was grown. Wafers can be transferred between these three chambers via an ultra high vacuum transfer device fitted with two load locks. The base pressures of the MBE chamber and the metallization chamber were lower than 1 × 10 ⁻¹⁰ mbar and 1 × 10 ⁻⁹ mbar, respectively. The chamber pressure during CaF ₂ growth is 5 × 10 5.
^-10 mbar, processing pressure during Al growth is 2 × 10
^-9 mbar. CaF ₂ and NdF ₃ are thermally evaporated from the effusion cell. The deposition rate of these fluorides is determined by controlling the temperature of the cell and monitoring the pressure of the flux. The deposition rate increases proportionally with increasing flux pressure. The composition of the membrane is determined by X-ray fluorescence. The film thickness is determined by step profile measurements. The CaF ₂ : Nd film has Si (111) and Al (1) at a substrate temperature of 100 ° C. to 700 ° C.
11) / Si (111) substrate. The results from the photoluminescence (PL) spectra show that the optimal growth temperature for CaF ₂ : Nd growth is 500 ° C. on silicon and 10 on Al.
0-300 ° C.

C. Photoluminescence from CaF ₂ : Nd thin film
Sense . Characterization of the optical properties of the film by photoluminescence (PL) is 0.9 including the 1.046 μm laser emission line observed in bulk CaF ₂ : Nd.
Strong PL at μm, 1.3 μm, and 1.1 μm
Shows firing. As the film thickness decreases from 1 μm to 0.2 μm, the intensity decreases proportionally, and the emission wavelength and relative band intensity of the PL spectrum from CaF ₂ : Nd grown on Al / Si are: It remains unchanged. This result suggests that the luminescence properties of the film are not distorted even though the 0.2 μm film is closer to the CaF ₂ / Al interface where defects are more likely to exist.

It is important to note that for the purposes of the present invention, transition elements may be used as dopants instead of rare earth elements. Moreover, the PL intensity of the CaF ₂ : Nd film does not depend on the crystal quality of the film. This is very different from semiconductor light emitting materials, where PL intensity strongly depends on the crystal quality of the material. Therefore, they are more susceptible to defects in the material.

2 and 3 show Al (111) / Si.
Thickness of 1.0 μm grown on (111) substrate
3 shows a PL spectrum of the CaF ₂ : Nd (0.48 wt%) film of FIG. In FIG. 2, chart 6
4 has a possible intensity measuring range of 0.000 to 0.140 in arbitrary units along the ordinate 66 and a wavelength measuring range of 1040 nm to 1100 nm along the abscissa 68. The L-center emission, shown by luminescence spike 68, has a linewidth of 0.12 nm. Other luminescence peaks include peaks 70, 72, and 74. The transition shown in FIG. 2 is ⁴ F _3/2
→ ⁴ It is between 2 states of 1 _11/2 .

The chart 76 of FIG. 3 shows 0.0 in arbitrary units along the ordinate 78 plotted against the wavelength range of 8500Å to 9300Å along the abscissa 80.
Includes a range of possible intensity measurements from 00 to 0.020. The luminescence peaks include peaks 82 and 84 of approximately equal intensity and a smaller luminescence peak 86.
And 88 and even less intense peaks 90 and 92 are included. The peaks in Figure 3 are ⁴ F
_3/2 → ⁴ I arise from the transition of _9/2 . Bulk CaF ₂ : N
The emission wavelength observed from the L center of d is indicated by the arrow. Thickness on CaF ₂ substrate 10 μm, 0.3 wt
The spectra from the% CaF ₂ film show similar wavelengths and relative intensities as those in FIG.

The similarity of the PL spectra in CaF ₂ : Nd grown on different substrates by different methods suggests that the emission from L centers dominates at low Nd concentrations. In contrast, a more pronounced difference in PL spectra is observed with increasing Nd concentration.

FIG. 4 shows the concentration dependence of the luminescence from a 1 μm thick CaF ₂ : Nd film grown on Al / Si (111). The chart 100 of FIG.
10400Å or 10600Å along the abscissa 104
2 shows the intensities in the range 0.000 to 0.600 in arbitrary units along the ordinate 102 plotted against wavelengths in Angstrom units within In particular, plot 106 shows the MBE of Al / Si (111).
Thickness 1 containing 0.48% Nd formed on the growth layer
Luminescence intensity in a μm CaF ₂ : Nd film is recorded. Plot 108 shows Al / Si (1
11) Ca of the same thickness containing 0.96% Nd above
It is a plot of the luminescence intensity in the F ₂ : Nd film. Plot 110 shows Al / Si (111)
Figure ₃ shows the luminescence in the same thickness CaF2: Nd film with 1.9% Nd above. Plot 112 is Al
7 shows the luminescence intensity in a CaF ₂ : Nd film of the same thickness with 3.8% Nd on / Si (111). The 10457Å line normally used for laser operation is
When the Nd concentration exceeds 3.8 wt%, it completely disappears in the bulk material.

Current membranes and previously reported bulk Ca
The most important difference between F ₂ : Nd and CaF ₂ : Nd / CaF ₂ is the emission line from the M and N defect centers of the current film, even when the Nd concentration is as high as 3.8 wt%. Is that the intensity of is decreasing. 3.8 wt
For bulk CaF ₂ : Nd with% Nd, the launch intensity from the M and N centers is about the same as that from the L center. CaF containing at least 3.7 wt% Nd
_{In the case of 2} : Nd / CaF ₂ , the intensity of luminescence at the N center is 80% of the intensity at the L center. In contrast, FIG. 4 shows that for any CaF ₂ : Nd on Al / Si sample, the N center wavelength (1044
It indicates that the launch at 8Å) is not observed. As the Nd concentration increases, a small peak corresponding to the M center (10467Å) appears, but the intensity is still 3.8 wt% N
There is only 50% of the intensity of the L center at the d concentration.

These comparisons show that in the current CaF ₂ : Nd grown by MBE at low temperature,
It shows that the orthorhombic N and M centers formed by aggregated Nd ³⁺ -F ⁻ can be reduced. Ca
The low substrate temperature used to grow F ₂ : Nd / Al / Si results in low M and N defects CaF ₂ : N.
to allow d to be created. The low growth temperature prevents the loss of fluorine and therefore bulk CaF
₂ : Avoid charge compensation mechanism in Nd. Furthermore, N
The distribution of dF and its aggregation can be altered by low temperature steps. The reason is that the kinetic energy of an atom is 6
It is too small for atomic diffusion and equilibrium to occur as occurs at temperatures above 00 ° C.

FIG. 5 shows growth on Al / Si (111).
CaF with various thicknesses ₂: Nd (1.9w
t%) film and a 0.1% film grown on Si (111).
2 μm CaF₂: Nd (1.9 wt%) film and
10 shows the relative intensity of the 10457 line. Plot 1 in Figure 5
34 is 0.0 in arbitrary units along the ordinate 136
The expected strength within the range of 1.2 is 0.0 μm
CaF in the range of 1.2 μm₂: Nd film thickness
It is recorded together with the measured value. That is, 0.2μ
CaF on Al / Si (111) for m thickness₂:
The relative intensity in the Nd film was recorded as point 140
There is. In the case of Si (111) substrate, the thickness of 0.2 μm
CaF₂: Relative intensity in Nd film recorded at point 142
Has been done. Two types of CaF₂: Other in Nd film
The film thickness and relative strength are 0.5 at point 144.
μm film thickness and 1.0 μm thickness at point 146
And are included.

The PL intensity decreases proportionally as the film thickness decreases from 1.0 μm to 0.2 μm. Moreover, the emission wavelength and relative PL intensity of the film will be the same regardless of the film thickness. These results show that even if the film thickness is only 0.2 μm,
Suggests that the luminescence properties are not distorted, even though the film of (1) is closer to the CaF ₂ / Al interface and is more susceptible to interface defects. For substrates of the same thickness but different, the PL intensity of CaF ₂ : Nd on Al is greater than that of CaF ₂ : Nd on Si. Al
The PL intensity from CaF ₂ : Nd on / Si (111) is larger than 90% or more of 514.5 nm incident light is reflected from the Al layer into the CaF ₂ : Nd film. , Most of the light is S of CaF ₂ : Nd / Si (111)
This is because it is absorbed in the i-substrate.

Each of FIGS. 6 and 7 has a thickness of 0.2 μm.
3 shows PL spectra at room temperature of a CaF ₂ : Nd (1%) film of m and a GaAs film of 4.0 μm in thickness. In particular, the plot 120 of FIG. 6 shows, along the ordinate 122,
Relative intensities in the range 0.00 to 0.45 in arbitrary units are shown for the wave number range along the abscissa 124 from 6,000 cm ^-1 to 13,000 cm ^-1 . PL intensity peaks exist in regions 126, 128, and 130. Regions 126, 128, and 13
Within 0, the specific local frequencies associated with the identified intensity peaks are indicated by the associated wave numbers in plot 120 of FIG.

In FIG. 7, plot 150 shows a range of relative intensities of 0.000 to 0.450 along ordinate 152 from 6,000 cm ⁻¹ along abscissa 154 to above 13,000 cm ^−1. Is shown with the wave number in the unit of cm ⁻¹ . Within this range, peak 156 exhibits a relative intensity of about 0.40 at the L center of 11,423 cm ^-1 . The CaF ₂ film is Al (11
1) / Si (111) substrate is grown. Ga
The As film is grown on a Si (100) substrate.
It is clearly shown that the line width of the CaF ₂ : Nd laser emission line (9560 cm ⁻¹ ) is narrower than the line width of the GaAs peak at 11423 cm ⁻¹ .

The intensity of the CaF ₂ : Nd emission line in FIG. 6 is such that the CaF ₂ thickness is 1/2 the GaAs thickness.
Even if it is only 0, it is about the same as the intensity of the GaAs peak in FIG. This indicates that CaF ₂ : Nd film can be a good gain medium for laser emission. The crystal quality of the film was characterized by X-ray diffraction and GaA
The full width at half maximum of 130 arc seconds from the s film is shown. P
In contrast to GaAs, whose L intensity strongly depends on the crystalline quality of the material, the PL intensity of CaF ₂ : Nd shows no detectable dependence on the crystalline quality of the film. Similar room temperature PL spectra were observed from polycrystalline and single crystal CaF ₂ : Nd films with the same thickness and Nd concentration.

These CaF ₂ : Nd samples and Si
High quality GaAs film grown on (111) (half width of X-ray rocking curve of GaAs film = 130a
rcsec) is 0.2 μm CaF ₂ : Nd
The PL intensity from (3.8 wt%) / Al / Si thin film is
4 μm thick GaAs / S with the same incident light intensity
It is shown to have a size similar to that of the i sample.
The line width from the CaF ₂ : Nd film has a spectrum of 4.2K.
And 1.2 Å each when taken at 300K
And 15Å. By comparison, the PL linewidths from the GaAs / Si sample are 40Å and 220Å at 4.26K and 300K, respectively. Ca
The narrow emission linewidth of the F ₂ : Nd film and the small index of refraction of CaF ₂ are attractive properties of a microcavity laser using the principles of the present invention. Good optical gain is realized due to the narrow line width. Also, by taking advantage of the large difference in refractive index between CaF ₂ and the semiconductor, high reflectance mirrors can be manufactured.

In summary, the Al / Si (11
1) CaF epitaxially grown on top₂: N
The thin film of d reduces the thickness of the film down to 0.2 μm.
Even when raped, it exhibits strong photoluminescent emissions. Low
CaF grown at high temperature ₂: M obtained from Nd film
And the luminescence from the N center is suppressed
Can be. Bulk CaF₂: Laser operation from Nd
The 10457Å line of fire that was used to
Shows a narrow line width until the Nd concentration exceeds 3.8 wt%
Not suppressed. These features are the CaF₂: Nd thin
Microcavity laser with film fabricated on Si-based substrate
As an attractive gain medium for.

III. CaF ₂ microcavity device A. Structure of CaF ₂ microcavity device . Another of the examples
One feature lies in the formation of CaF ₂ : Nd microcavity devices. High-strength PL obtained from polycrystalline CaF ₂ : Nd
Is a polycrystalline CaF ₂ : Nd sandwiched by two DBRs (distributed Bragg reflectors) showing the principle of the embodiment of the present invention.
It forms the basis of a microcavity structure composed of a membrane. The DBR for these arrangements has 10 pairs of Ta ₂ O ₅ / SiO ₂
Made from multiple layers. As a substrate, 10.16 cm
A (4 inch) silicon wafer was used.

FIG. 8 shows C grown on the DBR.
Room temperature PL spectra taken from aF ₂ : Nd films are shown. In FIG. 8, plot 190 shows intensities in the range 0 to 4 in arbitrary units along ordinate 191 and 8000 Å to about 150 along abscissa 192.
The wavelength is recorded in units of Å within the range of 00Å. The peak areas of interest are peak areas 1
94 and small peak areas 196 and 198. No mirror was manufactured on top of the CaF ₂ : Nd film. The spectra are Si (111) and A
It showed emission wavelengths and relative intensities very similar to those observed from CaF ₂ : Nd films on 1 (111) / Si (111).

FIG. 9 shows CaF₂: Nd and Ta₂O_Five
/ SiO₂Room temperature PL of micro cavity structure made from multiple layers
The spectrum is shown. The plot 200 of FIG. 9 shows the ordinate 2
Intensity in the range 0 to 4 in arbitrary units, along 02
8000Å to about 1500 along the abscissa 204
Record for wavelength in units of Å within 0Å
There is. In plot 200, peak 206 is
3 shows a room temperature PL spectrum in which a small cavity structure is generated. This structure
Structure is 1 wavelength of CaF₂: Nd // (Ta₂O _Five/ S
i)₂The top DBR mirror is used to form the cavity
Used in Figure 14, except added to the structure
It is the same as the sample.

Comparing FIG. 8 and FIG. 9, strong firing lines are detected at 10453Å and 10472Å in FIG. 9, but other lines near 10500Å disappear completely. Furthermore, it is observed that the intensities of the firing lines near 9000Å and 13000Å become significantly smaller for the 10460Å transition. These results are 10453Å
And emissivity at 10472Å are enhanced by the microcavity and the transitions around 9000Å and 13000Å are suppressed. Strength increase and line width decrease
It is also observed in the PL measurement at 77K.

In FIG. 10, one wavelength CaF ₂ : Nd //
Calculated reflectance spectra for (Ta ₂ O ₅ / SiO ₂ ) microcavity structures are shown. This structure is
It is designed to form a resonant mode at 10460Å. FIG. 10 shows 1050 nm ( ⁴ F _3/2 → ⁴ I
The emission line near the transition of _11/2 ) is the "stop band" of the mirror structure
Within, but 900 nm ( ⁴ F _3/2 → ⁴ I _9/2 transition)
_And the transition near 1300 nm (transition of ⁴ F _3/2 → ⁴ I _13/2 ) is in the “pass band”. Therefore, the launch lines near 9000Å and 13000Å are not directly affected by the reflector and their intensity is 1050
It can be used as a reference when compared to those near 0Å.

IV. CaF doped with rare earth (RE)
₂ Microcavity Device Embodiments also take advantage of the optical properties of other RE-doped CaF ₂ to use the effects of different emission wavelengths in the microcavity. Rare earth ions that luminesce in the visible region are a particularly important feature of the embodiment.
It is difficult to predict whether stimulated emission may be obtained at a given dopant transition, but rare earth-doped bulk CaF ₂ and other when the crystal is in a similar environmental field. Bulk crystal studies indicate that a wide range of other laser-centered dopants that are compatible with the principles of the present invention are possible. CaF ₂ doped with Eu
Electroluminescence and photoluminescence from thin films have an emission wavelength centered on blue 420 nm,
This shows that CaF ₂ doped with Eu can be a good gain medium. Strong electroluminescence in the ultraviolet region, which has a short wavelength of 306 nm, causes GdF
It was observed in doped ZnF ₂ film _2. CaF ₂ doped with Nd on silicon and Al / Si
Besides thin films, bulk crystals doped with Dy can be used in the examples. The Dy-doped material exhibits photoluminescent emission characteristics in the blue-green (near 486 nm), yellow (575 nm), red (665 nm), and near-infrared region (7540Å and 8390Å) of the spectrum. Ho and Dy are good dopant candidates for green and yellow emitters.

V. Instead of porous Si single crystal silicon as a light source for RE-doped CaF ₂ microcavity devices, the emission from “porous Si” has been realized by both electrical and optical pumping. The integration of porous silicon with Nd-doped CaF ₂ is a silicon-based material with a wide emission bandwidth as a light source (“porous Si”),
A silicon-based gain medium (CaF ₂ : Nd) with a narrow emission bandwidth for laser light emission. The emission wavelength of porous silicon lies between 5200Å and 9000Å. These wavelengths are ideal for pumping CaF ₂ : Nd thin films.

Up until now, porous silicon has been formed electrochemically, but analytical studies of porous silicon have revealed that this material is amorphous silicon, crystalline silicon, silicon oxide, and hydrogenated silicon. It was found to be a mixture of For example, Applied Phy
P. sics Letters, 1991. St
and evens. Esters, W.F. Duncan,
J. Villalobos, J .; Perez, R.M. Gl
Osser, and P. McNeill, Infrared and Raman Radiation Studies of Microcrystals (Infrared
and RamanStudies of Micro
and “amorphous phase of porous silicon (Amorphous Phases)”.
of Porous Silicon) ". These documents are specifically referred to herein, the contents of which are incorporated herein. The term "porous Si" refers to
In this way, it is the name of a silicon material that can emit visible light. These launches are feasible not only by anodization of crystalline silicon, but also by conventional growth techniques such as chemical vapor deposition (CVD) and molecular beam epoxy (MBE).

FIG. 11 shows a typical photoluminescence spectrum of porous silicon. Plot 2 of FIG.
16 records intensities in the range 0 to 200,000 in arbitrary units along the ordinate 218 and wavelengths in the range 5,200 Å to 9000 Å along the abscissa 220. There is. Curve 222 shows the luminescence region in porous silicon with a peak 224 between about 7,250 and 7,400 Å. The luminescence of the example has a maximum intensity around 7000Å and a maximum intensity of 5200
It is in the range of Å to 9000Å. The absorption spectra of CaF ₂ : Nd are 7250-7450Å, 7800-
Photons emitted from porous silicon show strong peaks at 8000Å and 8500-8700Å.
Effectively absorbed by CaF ₂ : Nd. As a result, high intensity photoluminescence from CaF ₂ : Nd can be obtained.

12 and 13 show two structures that integrate porous silicon with CaF ₂ : Nd. The structure 226 of FIG. 12 includes a transparent electrode 228 attached to a porous silicon layer 230 formed on a first Bragg reflector set 232. The CaF ₂ : Nd layer 234 is then sandwiched between the Bragg reflector set 232 and the Bragg reflector set 236. The set of Bragg reflectors 236 is the substrate 2
It is attached to a metal electrode 238 having 40 as a base. In these arrangements, the porous silicon is C
It can be used as a light source for pumping aF ₂ : Nd. Only five layers of dielectric are shown for each Bragg reflector, but to achieve high reflectivity,
For vertical surface emitting laser devices, the number of layers can be more than 10 pairs. In edge emitting laser devices, the requirement for high reflectivity is not as strong as in vertical surface emitting lasers. A metal layer or a few pairs of Bragg reflectors are sufficient.

FIG. 13 shows another example of porous Si as a light emission source starting from the transparent electrode 228 on the porous Si layer 230.
The structure of the porous Si layer 230 is
It covers one transparent electrode 244. Attached to transparent electrode 244 is a first set of Bragg reflectors 232, which is attached to CaF ₂ : Nd layer 234. The bottom surface of the CaF ₂ : Nd layer 234 is attached to the Bragg reflector set 236. In the arrangement of FIG. 13, Bragg reflector set 236 is attached directly to substrate 240. In FIG. 12, porous silicon and CaF ₂ : Nd are sandwiched between two electrodes. This structure allows the CaF ₂ : Nd layer to emit electroluminescent in some cases. Ca
The F ₂ : Nd layer is also optically pumped by electroluminescence from porous Si. The disadvantage of the arrangement of FIG. 13 is that the electric field gradient in the porous Si is
That is not so strong in i. In FIG. 13, the CaF ₂ : Nd layer is optically pumped by electroluminescence from porous Si. In this arrangement, no electric field change occurs in CaF ₂ : Nd.

In FIGS. 14 and 15, the porous Si is Ca.
F₂: Must be grown between Nd and Si substrate
Two other structures similar to FIGS. 12 and 13 except for and
Shows the structure. In FIG. 14, porous Si is CaF.₂: Nd profit
Another embodiment 244 between the medium and the substrate is
Shows. Particularly, the transparent electrode 228 is made of CaF.₂: Nd
Mounted on first Bragg reflector set 232 over layer 234
It has been burned. CaF ₂: Nd234 is Bragg reflection
Attached to the set of vessels 236. In the embodiment of FIG.
In addition, the porous Si layer 230 is the second Bragg reflector.
Between the pair 236 and the metal electrode 238.
The metal electrode 238 includes a porous Si layer 230, a substrate 240, and
Installed between.

FIG. 15 also shows that the porous Si layer 230 is C
An example is shown disposed between a CaF ₂ : Nd gain medium having an aF ₂ : Nd layer 234 and a substrate 240. In particular,
The set 232 of Bragg reflectors is the set 23 of Bragg reflectors.
6 is formed on the CaF ₂ : Nd layer 234 that covers a part of No. 6. Below the Bragg reflector set 236 is a porous Si
There is a metal electrode 238 attached to layer 230. The second metal electrode 248 separates the porous Si layer 230 from the substrate 240. Compared to the structures of FIGS. 12 and 13, the structures of FIGS. 14 and 15 make it difficult to grow single crystal material on top of porous Si. But,
These structures are more attractive for surface emitting lasers because the porous Si is not located in the laser output path. This increases the power efficiency of the laser device. It is not necessary to obtain a monocrystalline layer on top of the porous Si for laser light emission, as the intensity of the photoluminescence from the monocrystalline CaF ₂ : Nd is comparable to that from the polycrystalline one.

VI. RE by electroluminescence
In order to increase the efficiency of light-emitting electroluminescence from CaF ₂ thin films doped with
Several methods can be used: (1) Semi-insulating CaF ₂
The film can be grown by sputtering. (2) Ca
Superlattice structures and other semiconductor layers made from F ₂ : Nd have the effect of accelerating the carriers within the semiconductor layers to produce Ca
F _2: to obtain enough energy to induce excitation of Nd in the Nd layer, it can be used. (3) Nd,
C together with another dopant such as Eu
It can be added to aF ₂ . Since CaF ₂ : Eu can emit light of 420 nm by electroluminescence, Nd
Are either pumped by photons emitted by the electroluminescence of Eu, or even excited by direct energy transfer from adjacent Eu atoms.

The following sections discuss example methods for improving the efficiency of electroluminescence.
It should also be noted that these methods can also be used in electroluminescent pumped lasers. The superlattice structure is similar to that of a microcavity laser. When the length of the laser cavity is comparable to the emitted wavelength, the characteristics of the laser can be changed significantly. Analysis and experiments suggest that in the microcavity region, especially when the reflectance of the mirror is high, the optical gain increases remarkably as the emission line width decreases. Sub-micron thick CaF ₂ as described above:
The extremely narrow line width from Nd and the high reflectance mirror are Ca
Given the fact that it was proved to be made from F ₂ / ZnSe, and the microcavity CaF pumped by electroluminescence by improving the efficiency of electroluminescence by the following method:
₂ : Nd laser can be realized.

The first of the above methods for improving the efficiency of electroluminescence is sputtered C.
Due to the use of aF ₂ . Ca grown by vapor deposition
The resistivity of the F ₂ film is about 10 ¹⁶ Ω-cm, but 3 × 10
CaF ₂ film having a low resistivity of about ³ Omega-cm can be obtained by sputtering. Reduced resistivity is usually undesirable. This is because CaF ₂ has often been used as a good insulator that can be epitaxially grown on silicon or GaAs. However, good conductivity is required if the film is to be used for electroluminescence applications. Since more carriers can be driven through the semi-conductive film than the insulating film, the carrier and Ca
The collision cross section between the luminescence centers in F ₂ : Nd is larger in the semiconductive sputtered film. This increases the luminescence intensity. In order to cause CaF ₂ : Nd to emit laser light by electroluminescence, CdF ₂ : M in vapor of Cd
A similar strategy was taken by annealing n. One possible drawback of sputtered CaF ₂ is that the suppression of the emission is enhanced by the deterioration of crystal quality. But this is not a serious problem. This is because the photoluminescence intensity of the polycrystalline CaF ₂ : Nd film is the same as that of the single crystal CaF ₂ : Nd, as shown for the CaF ₂ : Nd grown by MBE. . This indicates that crystal quality is not important.

A second above-mentioned method for increasing the efficiency of electroluminescence is the formation of CaF ₂ : Nd semiconductor superlattices. Superlattices made from CaF ₂ : Nd and other semiconductor layers provide carriers with sufficient energy to effectively accelerate the carriers in the semiconductor layer and thus induce Nd excitation in the CaF ₂ : Nd layer. Can be used to obtain. This significantly improves the firing efficiency of the Y ₂ O ₃ : Eu thin film electroluminescent device. further,
If the thickness of each superlattice is less than the emission wavelength,
When the thicknesses are properly tuned, constructive interference can be created to enhance luminescence.

FIG. 16 shows a superlattice structure that can be used to obtain effective electroluminescence from a CaF ₂ : Nd / ZnS multilayer structure. CaF ₂ : Nd in FIG.
The semiconductor superlattice structure 250 includes a transparent electrode 252 on a CaF ₂ : Nd / semiconductor superlattice 254. CaF ₂ : Nd
/ A semiconductor superlattice 254 is a CaF ₂ : N layer, such as layer 256, interspersed with semiconductor layers, eg, using ZnS, to achieve the desired degree of electroluminescence.
Includes d layer. CaF ₂ : Nd / semiconductor superlattice 254 is
It is formed on the metal electrode 238 formed on the substrate 240.

The transparent conductor is indium tin oxide (IT
O) or aluminum doped conductive oxides such as zinc oxide or strongly doped semiconductors such as ZnSe or ZnS. These materials have good conductivity and optical clarity at the emission wavelength. The transparent conductor also acts as a mirror for optical feedback, so that the index of refraction of CaF ₂ : Nd (or other RE-doped CaF ₂ ) is such that a strong microcavity effect can be achieved. It should differ from the refractive index as much as possible. The refractive index of ITO is in the range 1.75 to 2.3. The refractive index of zinc oxide, ZnS, and ZnSe is about 1.86 at a wavelength of 1 μm, respectively.
2.37, and 2.89. Since the refractive index of RE-doped CaF ₂ is about 1.43, these materials are of high quality in distributed feedback lasers where RE-doped CaF ₂ enhances the cavity effect. Should be able to form a DBR, or a periodic gain structure.

Another method for improving the efficiency of electroluminescence is co-dope.
This is due to the formation of CaF ₂ that has been formed. Nd and Eu
Or another dopant such as Er can be added together in CaF ₂ . CaF ₂ : Eu has been shown to emit light with a wavelength of 420 nm by electroluminescence. Eu and Er together with Nd are Ca
When co-doped in F ₂ , absorptions at 398 nm and 449 nm for Eu and Er respectively were observed. These results show that by growing CaF ₂ : Nd / Eu or CaF ₂ : Nd / Er films,
We show that Nd is pumped by photons emitted from Eu or Er electroluminescence, or even excited by direct energy transfer from adjacent Eu atoms, resulting in enhanced luminescence.

17, FIG. 18, FIG. 19 and FIG.
Based on knowledge of the materials and features of the laser cavity,
Easy realization of laser light emission by ctoluminescence
Other laser structures are shown. Vertical direction in FIG.
The arrangement 260 creates a transparent conductor 262 and a laser 268.
The voltage applied from an independent voltage source 266 for driving
A metal conductor 264 having a position. Laser 268
Are the quarter-wave semiconductor layers 270, which are alternately arranged,
Quarter-wave CaF acting as a gain medium₂: Nd layer 272
And, including. Similarly, the horizontal arrangement 27 of FIG.
4 is a number of transparent conductors such as transparent conductors 276 and 278.
Body and CaF scattered between them ₂: RE profit
A gain medium 280.

19 and 20 show two arrangements using ZnS as the electroluminescent emission source, arrangements 290 and 291. Arrangement 290 of FIG.
Includes a transparent electrode 292 formed on the ZnS layer 294. The ZnS layer 294 is a Bragg reflector set 232, C.
It serves as an electroluminescent light source for the aF ₂ : RE layer 296 and the second Bragg reflector set 236. The second set of Bragg reflectors 236 is formed on a metal electrode 238 attached to the substrate 240.

The arrangement 291 of FIG. 20 includes a transparent electrode 292 formed on the ZnS layer 294. ZnS layer 294
Are formed on a second transparent electrode 298 connected to the Bragg reflector set 232. Bragg reflector set 23
2 between the Bragg reflector set 236 and Ca
There is an F ₂ : RE layer 296. The second set of Bragg reflectors 236 is directly attached to the substrate 240 in the arrangement of FIG.

VII. Examples of applications within the scope of the present invention Extensive research has recently been done to realize emission from Group IV materials. Emissions from porous Si, isoelectronically doped silicon, and strained GeSi alloys have been reported. Considering that these materials are compatible with silicon-based technologies and that extremely low laser emission thresholds can be achieved with RE-doped CaF ₂ microcavity lasers, the proposed microcavity is proposed. Laser embodiments can utilize these materials within the scope of the present invention.

Silicon-based OEICs and Photon Integrated Circuits (PICs) have a wide range of military and commercial applications. Silicon based OEIC or PIC 1
One application is in the field of interconnection of multichip modules. With the increasing complexity of multi-chip modules, the interconnect resistivity and parasitic capacitance created by high density metal lines are major obstacles to device performance. Optical interconnections have long been considered the solution to these interconnection problems. Silicon-based OE
ICs and PICs have particular application, for example to optically coupled phased array radar devices. Although there have been significant advances in the field of monolithic microwave integrated circuits (MMIC) based on GaAs and other III-V materials for radar devices, research on digital logic and memory circuits based on III-V materials Didn't do much. Therefore, light sources and modulators monolithically integrated into silicon digital circuits provide a mechanism for optically coupling state-of-the-art silicon digital and logic circuits to GaAs MMIC devices.

Current research in the field of optical computing is III
It is limited strongly apparatus -V and LiNbO ₃ material. With the exception of silicon-based laser sources, all other functions required for optical calculations (modulators, detectors, and waveguides) have already been commercialized. In fact, large scale integrated (LSI) silicon detectors (eg CCD) are commercially available and medium scale integrated (MSI) modulators (eg DMD) on silicon are being commercialized and commercial production has begun. DMD is a free space modulator, but BaTi
O ₃ and (Pb, La) (Zr, Ti) material, such as (these have excellent electro-optical properties) O _3, in its application to the post ULSI silicon memory used various arrangements of the embodiments Used for high capacity dielectric capacitors. The SiO ₂ waveguide on silicon has already been advertised in kind.

Silicon-based OEICs and PICs formed according to the principles of the embodiments are particularly useful because conventional silicon bulk processes have economic advantages that are incomparable to other electronic or optoelectronic material technologies. It has charm. Silicon-based O formed by the present invention
Possible applications of EICs include silicon-based light emitters for displays, fibers to home and other cable networks, computer communication devices for automotive electronics, and medical and in vivo uses. It is a low cost disposable OEIC for. Finally,
The silicon-based OEICs of the present invention provide new capabilities such as circuit level image processing devices or high performance pixels.

VIII. Summary In summary, as a basic concept within the scope of the present invention,
(1) Preparation of a thin film of CaF ₂ : RE, (2) Fabrication of optically pumped silicon-based CaF ₂ : Nd microcavity laser, including growth of CaF ₂ with other RE dopants, (3) CaF ₂ : Growth and manufacture of an electroluminescent source suitable for pumping RE microcavities, and (4) realization of laser action by either electroluminescence or direct electrical pumping,
Is included.

While the invention and its advantages have been described in detail above, various changes, substitutions and changes can be made therein without departing from the spirit and scope of the invention as defined by the claims. You should understand that.

With respect to the above description, the following items will be further disclosed. (1) In a microcavity structure for producing strong spectrum emission, a semiconductor substrate and Ca containing a rare earth dopant
A F ₂ thin, empty for reflecting the CaF ₂ film said CaF ₂ thin film containing該稀earth dopants to produce the strong spectral firing in response to being optically pumped, the strong spectral firing comprising a reflective cavity forming medium to form a cylinder, a porous Si layer for optically pumping the CaF ₂ film, and the activation circuit for optically pumping the CaF ₂ film, a strong spectrum A micro-cavity structure for producing firing.

(2) The device according to item 1, wherein the rare earth dopant contains Nd. (3) The apparatus of claim 1, wherein the reflective cavity forming medium comprises a plurality of Bragg reflectors. (4) The number of Bragg reflectors is about 10 pairs for high reflectivity to make a vertical surface emitting laser device,
The apparatus according to item 3.

(5) The porous Si layer and the CaF
The device of claim 3 wherein _two thin film layers are disposed between a plurality of electrodes associated with the activation circuit for electroluminescent emission. (6) The device of claim 3, wherein the porous Si layer is associated with the activation circuit to be optically pumped.

(7) In order to form a surface emitting laser such that the porous Si layer is located outside the path of the strong spectral emission, the porous Si is added to the CaF ₂
A first thin film disposed between the thin film and the semiconductor substrate;
The device according to the item.

(8) In a method of providing a light source for a rare earth-doped CaF ₂ thin film, the rare earth-doped CaF ₂ thin film is used to absorb light emitted from a porous Si layer. A light source for a rare earth-doped CaF ₂ thin film, comprising: associating the porous Si layer with a doped CaF ₂ thin film; and activating the porous Si layer to produce the emission. How to deploy.

(9) The method according to claim 8, further comprising the step of activating the porous Si layer by optically pumping the porous Si layer. 10. The method of claim 8, further comprising the step of activating the porous Si layer by electrically pumping the porous Si layer.

(11) The activation step comprises about 520
9. The method according to claim 8, further comprising activating the porous Si layer to emit light having a wavelength in the range of 0Å to 9000Å. (12) The method according to claim 8, further comprising a step of electrochemically forming the porous Si layer.

(13) The method according to claim 8, further comprising the step of forming the porous Si layer by anodizing crystalline silicon. 14. The method of claim 13, further comprising: (14) forming the porous Si layer from a mixture consisting essentially of amorphous silicon, crystalline silicon, silicon oxide, and silicon hydride.

(15) The method according to claim 8, further comprising the step of forming the porous Si layer by a chemical vapor deposition method. (16) The method according to claim 8, further comprising the step of forming the porous Si layer by a sputtering technique. (17) The method according to Item 16, further comprising the step of sputtering the porous Si layer by molecular beam epitaxial.

(18) Porous Si layer and CaF ₂ : Nd
CaF ₂ : Nd laser cavity on a substrate material comprising a film layer, a first electrode, a second electrode, a first plurality of reflector layers, a second plurality of reflector layers and a substrate material. In which the porous Si layer is associated with the first electrode and the first plurality of reflector layers for generating light that photoluminescently pumps the CaF ₂ : Nd film layer. To produce a strong spectral emission in response to the CaF ₂ : Nd film layer being photoluminescently pumped by the light from the porous Si layer.
Associated with the first plurality of reflector layers and the second plurality of reflector layers, wherein the first electrode and the second electrode are the first plurality of reflector layers; A CaF ₂ : Nd laser cavity on a substrate material adapted to electrically activate a second plurality of reflector layers, the CaF ₂ : Nd film layer and the porous Si layer.

(19) The rare earth-doped CaF ₂ film 234 absorbs light emitted from the porous Si layer 230 so that the rare earth-doped CaF ₂ film 234 absorbs light emitted from the porous Si layer 230.
₂ Method and apparatus 242 for producing a strong spectral emission by associating with the membrane 234. Circuitry 228, 244 associated with device 242 causes light emission by activating porous Si layer 230. Porous Si
Layer 230 can be formed electrically, by chemical vapor deposition, or by anodizing crystalline silicon.

The present application is a co-pending application, "Si-based microlasers with doped thin films (Si
licon-Based Microlaser by
Doped Thin Films ”19
It is a partial continuation application of US Patent No. 945,991 (TI-17364) filed on September 15, 1992.

[Brief description of drawings]

1 is a typical 10 nm for III-V semiconductor materials.
FIG. 6 shows gain enhancement for microcavities with several launch linewidths in the range from 1 to 100 nm.

FIG. 2 is a diagram showing a photoluminescence spectrum at a helium temperature of a 1.0 μm-thick CaF ₂ : Nd film grown on an Al (111) / Si (111) substrate.

FIG. 3 shows a photoluminescence spectrum at a helium temperature of a 1.0 μm-thick CaF ₂ : Nd film grown on an Al (111) / Si (111) substrate.

FIG. 4 shows the concentration dependence of luminescence from a 1.0 μm thick CaF ₂ : Nd film grown on Al / Si (111).

FIG. 5 10457Å in CaF ₂ : Nd films grown on Al / Si (111) with different thickness.
The figure which shows the relative intensity of a line.

FIG. 6 is a diagram showing a photoluminescence spectrum at room temperature of a 0.2 μm-thick CaF ₂ : Nd film (1%) film.

FIG. 7 shows a photoluminescence spectrum at room temperature of a GaAs film having a thickness of 4.0 μm.

FIG. 8 shows a photoluminescence spectrum from CaF ₂ : Nd on a Ta ₂ O ₅ / SiO ₂ distributed Bragg reflector.

FIG. 9: Half-wavelength CaF ₂ : Nd // (Ta
₂ O ₅ / SiO ₂ ) Photoluminescence from minute cavities
The figure which shows a spectrum.

FIG. 10: Half-wavelength C calculated using a one-dimensional model
_{aF 2: Nd // (Ta 2} O 5 / SiO 2) shows the reflectance spectrum from the microcavity.

FIG. 11 shows a typical photoluminescence spectrum of porous silicon.

FIG. 12 illustrates an embodiment of the invention in which porous silicon is integrated with CaF ₂ : Nd such that the porous silicon can be used to pump CaF ₂ : Nd gain media.

FIG. 13 illustrates an embodiment of the invention in which porous silicon is integrated with CaF ₂ : Nd such that the porous silicon can be used to pump CaF ₂ : Nd gain media.

FIG. 14 is a diagram similar to the embodiment of FIGS. 12 and 13, showing another embodiment of the present invention.

FIG. 15 shows another embodiment of the present invention, similar to the embodiment of FIGS. 12 and 13.

FIG. 16 shows a superlattice structure that can be used to obtain effective electroluminescence from a CaF ₂ : ZnS multilayer structure.

FIG. 17 is a conceptual illustration of an electrically pumped quarter-wavelength shift DFB laser embodiment using RE-doped CaF ₂ as a gain medium.

FIG. 18 is a diagram conceptually illustrating an example of an electrically pumped quarter-wavelength shift DFB laser using RE-doped CaF ₂ as a gain medium.

FIG. 19 is a diagram showing a structure in which electroluminescence ZnS is used as a light emitting source and CaF ₂ : RE is used as a gain medium.

FIG. 20 is a diagram showing a structure in which electroluminescence ZnS is used as a light emitting source and CaF ₂ : RE is used as a gain medium.

[Explanation of symbols]

228 Transparent electrode 230 Porous silicon layer 232 Bragg reflector set 234 CaF ₂ : Nd layer 236 Bragg reflector set 238 Metal electrode 240 Substrate 244 Transparent electrode 248 Metal electrode

Claims (2)

[Claims] 1. A microcavity structure for producing strong spectral emission, comprising a semiconductor substrate and a CaF ₂ thin film containing a rare earth dopant, the CaF ₂ thin film comprising:
A CaF ₂ thin film containing the rare earth dopant that produces the strong spectral emission in response to the F ₂ thin film being optically pumped, and a reflective cavity forming a cavity for reflecting the strong spectral emission. Forming medium and porous Si for optically pumping the CaF ₂ thin film
A microcavity structure for producing a strong spectral emission, comprising a layer and an activation circuit for optically pumping the CaF ₂ thin film. 2. A method of deploying a light source for CaF ₂ film doped with rare earth, in該稀earth as CaF ₂ film doped with該稀earth absorbs emission from porous Si layer doped Ca
Providing a light source for the rare earth-doped CaF ₂ thin film, comprising: associating the porous Si layer with an F ₂ thin film; activating the porous Si layer to produce the light emission. Method.