JPH1117217A - Manufacture of material for light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light-emitting element and a photocoupler element having excellent durability by injecting a high concentration of a rare-earth metal oxide such as Er2 O3 to an Si substrate. SOLUTION: After forming may pores on the surface of an Si substrate by mesa etching using electrochemical etching or a mask pattern, a rare earth metal oxide such as Er2 O3 is stuck by spattering to a porous Si surface layer, then annealing is applied for turning a multiporous structure into polycrystalline structure. For Si substrate, single crystal Si, polycrystalline Si or amorphous Si or the like is used. Before annealing, the pore holes on the Si substrate surface are filled up with Si powder, or Si may have an epitaxial growth on the surface of Si substrate. Since the rare earth metal oxide is injected with a high concentration, excellent light-emitting characteristics can be obtained and brittleness can be eliminated by polycrystallization. Also, since the injection is performed in the form of an oxide, the oxidation process in the conventional ion implantation method can be omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a light emitting device material used for optical communication, self-luminous display, optical integrated circuit, light emitting source and the like.

[0002]

2. Description of the Related Art When a rare earth element is implanted into Si, light emission occurs due to the combination of oxygen atoms in the Si and ions of the rare earth element. Above all, Er exhibits a light emission of 1.54 μm corresponding to the wavelength at which the loss of the optical fiber is the smallest, and therefore, application to optical communication, an optical integrated circuit, and the like is expected. For example, Appl. Phys. Lett. 43,
In p943-945 (1983), it has been reported that ion implantation of Er into a Si substrate exhibits photoluminescence characteristics of 1.54 μm at a temperature of 6K.

[0003]

In order to obtain a sufficient luminous intensity with a light emitting element into which Er has been implanted, it is necessary to implant Er at a high concentration. However, in the conventional ion implantation method, since Er ions are heavy, it is difficult to stably obtain an Er ³⁺ beam. Er on a Si substrate at a depth of several μm.
^High acceleration voltage is required to drive ³⁺ . Moreover, when implanting Er ³⁺ ions into the front surface of the Si substrate, several m
It is necessary to scan the ion beam of m ² over the entire wafer for a long time. From such a thing,
The concentration of Er ions implanted into the entire Si substrate is 10 ¹⁹ / c
It stops to a low concentration of about m ^3. High concentration Er ³⁺ single crystal S
There is a limit in injecting into i, and it is difficult to increase the Er injection amount to a concentration required for a required emission intensity. Further, in the ion implantation method, Er ions are implanted into the Si substrate at a high speed, so that defects such as point defects, line defects, loop defects, and dislocations are easily generated. If such a defect exists, the luminous efficiency decreases, and a required light emitting element cannot be obtained. Attempts to use poly-Si, amorphous-Si, porous-Si, etc. in addition to single-crystal Si for the Er-implanted substrate are also being studied. In this case, a large amount of Er ions can be implanted as compared with the single crystal Si substrate, but defects such as point defects, line defects, and dislocations are likely to be generated by the large amount of implantation. As a result, an increase in the injection amount causes a reduction in luminous efficiency.

Some attempts have been made to electrochemically deposit Er on the surface of porous Si. For example,
Appl. Phys. Lett. 65, p983 (19
94), p-type (100) Si having a specific resistance of several Ω · cm
Using a substrate, 1 to 8 mA / cm ² in a hydrofluoric acid solution
To produce porous Si by anodizing treatment for supplying a current, and then immersing the porous Si as a cathode in an ethanol solution in which ErCl ₃ has been dissolved, and removing Er ³⁺ from the porous Si.
Has been reported to be electrodeposited on the surface of a steel sheet. However, porous Si has a brittle structure, and when a current injection type light emitting device is manufactured, the contact between the porous Si and the electrode is very small. Therefore, the porous Si light emitting device electrodeposited with Er is
A large electric field is applied to the contacts, and the life is extremely short. The present invention has been devised in order to solve such a problem, in which an oxide of a rare earth metal is attached to a porous Si surface layer by sputtering, and then the porous Si is polycrystallized by annealing. Accordingly, an object of the present invention is to produce a high-quality film having excellent light-emitting characteristics.

[0005]

According to the manufacturing method of the present invention, after a large number of pores are formed on the surface of a Si substrate by electrochemical etching or mesa etching using a mask pattern to achieve the object, A feature is that an oxide of a rare earth metal is attached to the porous Si surface by sputtering, and then annealing is performed to convert the porous structure to a polycrystalline structure. As the Si substrate, single crystal Si, polycrystal Si, amorphous Si, or the like is used. Rare earth metal oxides include Er ₂ O ₃ , Ce ₂ O ₃ , Eu ₂ O ₃ , D
_{y 2 O 3, Nd 2 O} 3, La 2 O 3, Pr 2 O 3, Pm 2
O ₃ , Sm ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Ho ₂ O
₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ or the like is used, and the injection concentration can be controlled by the sputtering time, plasma intensity, and the like. The porous Si to which the oxide of the rare earth metal is attached is heated at a temperature of 800 to 1400 ° C. to 10 to 6 ° C.
It is polycrystallized by annealing for 0 minutes and then slowly cooling. In the following description, a rare earth metal oxide is referred to as E
A description will be given using r ₂ O ₃ as a representative.

Depending on the degree of porosity, the surface of the Si substrate may not be sufficiently polycrystallized by annealing.
In such a case, prior to annealing, a method of filling pores on the surface of the sputtered Si substrate with Si powder, a method of epitaxially growing Si on the surface of the sputtered Si substrate, and the like are employed. In the following description, Er will be described as an example of the rare earth metal, but the present invention is not limited to this, and Yb (emission wavelength 1 μm), Nd (emission wavelength 1.06
Other rare earth elements such as μm) can be used as well.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a Si substrate, single crystal Si, polycrystal Si, amorphous Si, or the like is used. The surface of the Si substrate is made porous by electrochemical etching. For example, a p-type Si substrate is immersed in a solution obtained by adding 0.1 to 5 times ethyl alcohol to a 48% hydrofluoric acid aqueous solution, and a current density of 5%.
When anodizing at ~ 500 mA / cm ² for 1-60 minutes,
The substrate surface is made porous. At this time, if the amount of ethyl alcohol is less than 0.1 times the amount of the hydrofluoric acid aqueous solution, the formation of porosity is hindered by bubbles generated during the anodic treatment. Conversely, if the amount of ethyl alcohol exceeds 5 times, the porous structure becomes extremely brittle, so that stable handling of the sample becomes difficult. On the other hand, if the current density exceeds 500 mA / cm ² , electropolishing starts to occur instead of making the electrode porous, and conversely, 5 mA / c 2
If the current density is less than m ² , long-time processing is required.

When an n-type substrate is used, a similar process is performed.
In addition to the conditions, light irradiation of the Si substrate during anodization
Is necessary. Porous Si fabricated from n-type Si substrate
Is compared to porous Si produced from a p-type Si substrate,
Even if the chemical conversion treatment is performed at the same current density, the porosity is low.
The quality structure becomes stable. Use the mask pattern to
When V is etched, the V-groove is formed on the Si (100) substrate,
Vertical grooves are formed in the (110) substrate. Use V-groove
In this case, Er over the entire V-groove_Two O_Three Is uniformly
Because it is putter, it is thick and Er_Two O_ThreeSlow concentration gradient
A gentle light emitting layer is formed. On the other hand, in a vertical groove, the bottom of the groove
Er on the surface _Two O_Three Is sputtered.
Functionally and locally Er_Two O_Three Is injected at high concentration
A layer is formed.

An oxide of a rare earth metal is adhered to the porous Si substrate by plasma sputtering or the like. When using RF magnetron sputtering,
Ar gas pressure 10 ^-1 to 10 ^-3 Torr, RF output 0.1 to 5
When Er ₂ O ₃ is sputtered at W / cm ² , the S ₂ in which the Er ₂ O ₃ film of 50 to 100 ° per minute is made porous is formed.
deposited on the i-substrate. When sputtering is continued for about 10 minutes under these deposition conditions, Er ₂ O ₃ adheres to the surface of the pores of the porous Si at a high concentration of 10 ²⁰ to 10 ²² / cm ³ .
The amount of Er ₂ O ₃ adhered is determined by the sputtering time, plasma intensity, etc., but the Er adhered concentration is 10 ²⁰ particles / cm 2.
It is preferable to set conditions so as to be ³ or more. The oxide of the rare earth metal sputtered in this manner already has an effective function as a light emitter. It does not require an oxidation treatment step unlike the ion implantation method.

The porous Si sputtered with Er ₂ O ₃ has a brittle porous structure converted to polycrystalline Si by a process such as laser annealing or vacuum annealing.
At this time, since Er ₂ O ₃ is diffused into the polycrystalline Si, Er ₂ O ₃ is contained by annealing at a higher concentration of 10 ²⁰ / cm ³ or more as compared with the conventional ion implantation. A polycrystalline Si film is formed.
For the annealing, a non-oxidizing atmosphere such as an inert atmosphere or a vacuum atmosphere is used. For example, a condition of heating to 800 to 1400 ° C. for 10 to 60 minutes and then gradually cooling is employed.
If the heating temperature is lower than 800 ° C. or the heating time is shorter than 10 minutes, polycrystallization does not sufficiently proceed. Conversely, 1400 ° C
If the heating temperature exceeds 60 minutes or the heating time is longer than 60 minutes, Er ₂ O ₃ itself uniformly dispersed throughout the film causes re-aggregation, thereby deteriorating the light emission characteristics of the film.

[0011] Depending on the degree of porosity, polycrystallization may not proceed sufficiently by annealing. For example,
When an n-type Si substrate is used, a large porous structure having pores and Si columns of several μm in diameter is used.
At a temperature of 00 ° C., the film cannot be planarized by annealing. In such a case, the porous Si after the sputtering treatment is heated to a melting point of Si of 1400 ° C. or higher, or ultrafine powder Si of about 0.05 μm is sprayed on the porous Si to fill the pores or epitaxially grow the Si. Thereby, it is preferable to anneal under conditions in which the evaporation of Er ₂ O ₃ is suppressed. In this way, when the pores of the porous structure are filled, a structure similar to that of polycrystalline Si is obtained, and thus annealing can be performed at a temperature of 800 to 1400 ° C. similarly to polycrystalline Si.

Si in which Er is implanted at a high concentration is used for a light emitting element, a visible light emitting element and the like. For example, a light emitting element employs a laminated structure as shown in FIGS. The pn junction type light emitting device of FIG. 1 is manufactured as follows. p
B is ion-implanted on the back surface of the mold Si substrate 1 to form ap ⁺ layer, and an Al electrode (+ electrode) 2 that forms an ohmic junction with the p ⁺ layer is formed by a vapor deposition method. On the surface side of the p-type Si substrate 1, to form a light emitting layer 3 containing 10 ²⁰ / cm ³ or more Er ₂ O ₃ in the manner described above, Si epitaxial growth with activated by doping a large amount of P A film 4 is formed on the light emitting layer 3. A V-groove is formed in the multilayer film thus formed by mesa etching, and a surface facing the V-groove is oxidized to form an oxide film 5. Next, the surface oxide film is removed by etching, and the Al electrode 6 is formed on the n ⁺ epitaxial growth film 4.
(-Pole) is deposited. In this pn junction type light emitting element, light emission is extracted through the oxide film 5.

When an n-type Si substrate is used, a pn junction type light emitting device having a structure as shown in FIG. 2 is manufactured. In this case, P ions are implanted into the back surface of the n-type Si
^{A +} layer is formed, and an Al electrode (− pole) 8 that forms an ohmic junction with the n ⁺ layer is formed by a vapor deposition method. On the surface side of the n-type Si substrate 7, at least 10 ²⁰ / cm ³ of Er ₂
A light emitting layer 9 containing O ₃ is formed, and a p ⁺ layer 10 doped with B at a high concentration is formed on the light emitting layer 9. Then B
The doped layer 10 is oxidized to form an oxide film 11, and the oxide film 1
1 is removed by etching, and A
1 electrode 12 (+ electrode) is deposited. In this pn junction type light emitting element, light emission is extracted from the upper part.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS P-type (100) Si having a specific resistance of 3 to 5 .OMEGA.cm
A light emitting device was manufactured from the substrate by the following procedure. HF: C _{2
H 5 OH: H 2 O =} 1: 2: The Si substrate was immersed as an anode 1 of a solution, a current 10 mA / cm ² was supplied for 60 minutes,
The Si substrate was electrolytically etched. The surface of the Si substrate was made porous by electrolytic etching. The porous structure formed on the surface of the Si substrate was composed of pores of about 5 nm and Si columns. Si with porous surface
Ar gas pressure 10 ^-2 Torr, RF output 2 W /
Er ₂ O under the conditions of cm ² and a sputtering time of 10 minutes.
₃ was subjected to RF magnetron sputtering. When the surface after sputtering is observed by SEM, a large amount of E is present on the surface of the porous Si and the bottom of the pores 13 as schematically shown in FIG.
r ₂ O ₃ was attached, and Er ₂ O ₃ was attached thinly on the side surface of the Si column 14 facing the pores 13.

Next, annealing was carried out by heating to 1000 ° C. for 30 minutes in a vacuum and gradually cooling at a temperature lowering rate of 1 ° C./sec. The surface of the annealed Si substrate is 100 nm
Porous Si with a film thickness of about 5 μm consisting of crystal grains of
The porous Si has an E of 10 ²⁰ / cm ³ .
An r ₂ O ₃ phosphor was included. S having such a film
The pn junction type light emitting device shown in FIG. 1 was manufactured from the i substrate. When the light emission characteristics of the obtained pn junction type light emitting device were examined, the light emission efficiency (about 10 ^-2 ) was about 10 ⁴ times higher than the light emission efficiency (about 10 ⁻⁶ ) of the element by the conventional ion implantation. Indicated.

[0016]

As described above, in the present invention, Er ₂ O ₃ is sputtered on porous Si, followed by annealing to increase the Er concentration in the surface layer. Therefore, a much higher concentration of Er can be implanted into the Si surface layer as compared with the conventional ion implantation, and a material exhibiting excellent light emission characteristics can be obtained. Further, since the porous Si surface layer is polycrystallized, there is no brittleness due to the porosity, the contact point with the electrode can be made relatively large, and the life of the obtained light emitting element is prolonged.

[Brief description of the drawings]

FIG. 1 shows a light emitting device formed of a p-type Si substrate in which Er is implanted into a surface layer at a high concentration according to the present invention.

FIG. 2 shows a light emitting device formed of an n-type Si substrate in which Er is implanted into a surface layer at a high concentration according to the present invention.

Fig. 3 Porous S by RF magnetron sputtering
Schematic diagram showing Er ₂ O ₃ attached to i

[Explanation of symbols]

1: p-type Si substrate 2, 12: Al electrode (+)
3, 9: light emitting layer 4: epitaxial growth film 5, 11: oxide film
6, 8: Al electrode (-) 7: n-type Si substrate 10: B-doped layer 13: pore 14: Si column

Claims (4)

[Claims] After forming a large number of pores on the surface of a Si substrate by electrochemical etching or mesa etching using a mask pattern, an oxide of a rare earth metal is attached to the porous Si surface by sputtering. Then, annealing is performed to convert the porous structure to a polycrystalline structure. 2. A single crystal Si and a polycrystal Si as a Si substrate.
2. The method according to claim 1, wherein amorphous Si is used. 3. The method according to claim 1, wherein prior to the annealing, pores on the surface of the Si substrate to which the oxide of the rare earth metal is attached are filled with Si powder. 4. The method according to claim 1, wherein, prior to the annealing, Si is epitaxially grown on the surface of the Si substrate to which the rare earth metal oxide is attached.