JPH06132564A - Porous silicon and light-emitting device - Google Patents

Abstract

PURPOSE:To provide a porous silicon capable of emitting light of a short wavelength and an emitting device using the porous silicon. CONSTITUTION:As shown in FIG. 3, a porous silicon 12a of the present embodiment substitutes a heavy hydrogen for a part or all of a hydrogen adhering to the wall surface in a plurality of holes 120 of the porous silicon 12a. By substituting the heavy hydrogen for the hydrogen adhering to the wall surface in a plurality of the holes 120, a molecular weight of side chain is weighted. Accordingly, a light emitting of green or blue from conventional red can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to porous silicon which is a light emitting material using silicon and a light emitting device using the porous silicon.

[0002]

2. Description of the Related Art Since a silicon semiconductor is an indirect transition semiconductor, it is considered impossible to fabricate a light emitting device. Therefore, a conventional light emitting device using a pn junction is III-
Group V compound semiconductor, II-VI group compound semiconductor, or IV-VI
It was made of a genus compound semiconductor. However, compared with compound semiconductors, silicon semiconductors have more resources, have a high single-crystal manufacturing technology, and can supply large-area ones at low cost. In addition, silicon semiconductors have high device design / fabrication technology, and it is difficult to realize with the current compound semiconductors. It is possible to build highly integrated and highly reliable logic, operation, drive, light receiving elements, etc. Have advantages. Therefore, it has been desired to realize a light emitting element using silicon, and finally, a charge injection type light emitting element using a pn junction which can be finally applied to a laser.

In 1990, LTCanham showed that porous silicon obtained by anodizing single crystal silicon in a hydrofluoric acid solution exhibits strong photoluminescence at room temperature (Appl.
iedPhysics Letters 57,1990, p.1046). This is
It has shown that there is a possibility that a light emitting device can also be realized with silicon, and thereafter, active research has been conducted on the mechanism of this photoluminescence generation.

[0004]

By the way, the light emission color of the conventional light emitting device using porous silicon is almost red, and even the one with a short wavelength is orange / red. If the emission color is only red as described above, the use of the light emitting element is limited. Therefore, development of a light emitting element using silicon capable of emitting light of a shorter wavelength is desired.

The present invention has been made under the above circumstances, and an object of the present invention is to provide a porous silicon which can emit light of a short wavelength and a light emitting device using the porous silicon.

[0006]

In order to solve the above problems, the porous silicon according to claim 1 is characterized in that a part or all of hydrogen attached to the wall surfaces of a large number of pores is replaced with deuterium. It is what

A light emitting device according to a second aspect is a light emitting device having a pn junction structure using the porous silicon according to the first aspect.

[0008]

The function of the above-mentioned porous silicon will be described below. Si produced by photoexcitation of porous silicon
The σ-bond excitons on the −Si bond can freely move around in the one-dimensional potential created by hydrogen H, as shown in FIG. 2. At this time, this motion leads to the vibration of Si—H, Gradually transfer energy (Si-H vibr
The kinetic energy of σ-bonded excitons is attenuated while transferring the energy to the Si-H vibratinal mode. Written in Hamiltonian, Htot = Hfree + Hvib (1) According to the equation (1), if the σ-bonded excitons formed on the bond between Sis do not transfer energy to the vibratinal mode of Si-H, the confinement becomes strong and excitons. The binding energy of is increased, and the light emission is shifted to the high energy side. One-dimensional po
As a method of freezing the vibration of the side chain (bond between Si and H) for forming the tential, there are methods such as lowering the temperature to low and increasing the molecular weight of the side chain. Considering this, it is effective to increase the molecular weight of the side chain to freeze the vibration. Therefore, in the present invention, hydrogen attached to the wall surfaces of many holes is replaced with deuterium to increase the molecular weight of the side chain. As a result, it becomes possible to emit light from conventional red to green or blue.
Therefore, the light emitting element of the pn junction structure using this porous silicon can emit light of a shorter wavelength than the conventional light emitting element.

The reason why the molecular weight m is preferably large is as follows. A general equation of motion is m · dx / dt
= -Kx Therefore, the vibration angular frequency ω is
ω = (k / m) ^1/2 , and the vibration angular frequency increases in proportion to m ^−1/2 . Therefore, if the mass is doubled, the energy of the vibration angular frequency ω will be 1 / (2) ^1/2 times.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A porous silicon according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic enlarged sectional view showing a part of the porous silicon according to the first embodiment of the present invention. FIG. 2 is a diagram showing the state of bonding of silicon and hydrogen in the pores of porous silicon, and FIG. 3 is the state of bonding of silicon and deuterium in the pores of porous silicon according to the first embodiment of the present invention. FIG. As shown in FIG. 3, the porous silicon of this embodiment is porous silicon 1
A part or all of the hydrogen adhering to the wall surface in the many holes 120 of 2a is replaced with deuterium.

Next, the method of manufacturing the porous silicon of the first embodiment and the light emitting device using the porous silicon will be described. As shown in FIG. 4, a p-type single crystal silicon substrate ((100) or (111) plane, resistivity 0.1 to 20Ω)
(cm) is vapor-deposited on the back surface to form ohmic contact. Next, the portion to be made porous is masked with a wax and immersed in a solution of ethyl alcohol: hydrofluoric acid: water: heavy water = 2: 1: 1: 1 as shown in FIG. A constant current power source E is used, a platinum electrode is attached to the cathode side, and a single crystal silicon substrate is attached to the anode side. In this way, anodization is performed while applying a constant current of 10 to 50 mA / cm ² . The formation time differs depending on the thickness of the p-type single crystal silicon substrate 11, and is usually about 5 minutes in the case of 5 μm. When a p-type single crystal silicon substrate is used, the anodization may be performed in the dark or the light. After that, the impurity layer on the surface of the porous silicon is removed by photochemical etching or immersion in a KOH solution for several seconds. Next, the wax on the surface is thawed with an organic solvent, washed with pure water, and then placed in an electron cyclotron resonance plasma CVD apparatus to form an amorphous silicon carbon film containing n-type microcrystals in a thickness of 150.
Å Accumulated. Deposition conditions are gas pressure 0.001 to 0.008
Torr, input power 200 to 300 W, SiH4: CH
4: PH3: H2 = 1: 1-3: 0.005-0.0
3: 100-200, substrate temperature 150-300 degreeC. Next, an indium tin oxide (ITO) which is a transparent electrode is used for 400 to 700 by using an electron beam vapor deposition apparatus.
Å Accumulated.

By the way, when the porous silicon 12a is formed by anodization, if a conventional aqueous solution of hydrofluoric acid: ethanol: water = 1: 2: 1 is used, as shown in FIG. The dangling bonds on the wall are immediately terminated by hydrogen. On the other hand, by performing anodization with an aqueous solution of hydrofluoric acid: ethanol: water: heavy water = 1: 2: 1: 1 as in the present embodiment, as shown in FIG.
By replacing part or all of the side chain terminated with hydrogen with deuterium, the molecular weight of the side chain can be easily increased. Thus, by increasing the molecular weight of the side chain, the molecular vibration of the side chain can be more frozen, the σ-bonded excitons can be confined without loss, and light with a shorter wavelength can be emitted. You can FIG. 6 is a diagram showing the measurement results, and is a spectrum diagram of photoluminescence. As is clear from FIG. 6, according to the porous silicon of the present embodiment, a light emission phenomenon of a short wavelength occurs as compared with the conventional one. Therefore, the light emitting device using the porous silicon of the present embodiment can emit light of a shorter wavelength than the conventional light emitting device. It should be noted that in the above anodization, the proportion of heavy water should be 1 or more. Further, in the above anodization, DF is not commercially available, so heavy water was used. Alternatively, DF or TF may be used to perform anodization.

Next, a porous silicon and a light emitting device using the porous silicon according to a second embodiment of the present invention will be described. Since the porous silicon of this example is substantially the same as that of the first example shown in FIGS. 1 and 3, FIGS. 1 and 3 will be used also in the description of the porous silicon of this example. As shown in FIG. 3, the porous silicon of this embodiment is obtained by replacing a part or all of the hydrogen attached to the wall surfaces of the multiple holes 160 of the porous silicon 16a with deuterium. The light emitting device of the second embodiment uses an n-type single crystal silicon substrate.

As shown in FIG. 7, an n-type single crystal silicon substrate ((100) or (111) plane, resistivity 0.1 to 20).
Ωcm) is vapor-deposited on the back surface to form ohmic contact. Next, the portion to be made porous is removed by masking with a wax, and as shown in FIG. 5B, it is immersed in a solution of ethyl alcohol: hydrofluoric acid: water: heavy water = 2: 1: 1: 1. A constant current power source E is used, a platinum electrode is attached to the cathode side, and a single crystal silicon substrate is attached to the anode side. In this way, anodization is performed while applying a constant current of 10 to 50 mA / cm ² . The formation time depends on the thickness of the n-type single crystal silicon substrate 15, and is usually about 5 minutes in the case of 5 μm. When an n-type single crystal silicon substrate is used, it is necessary to irradiate light from a tungsten lamp or the like to perform anodization. After that, the impurity layer on the surface of the porous silicon is removed by photochemical etching or immersion in a KOH solution for several seconds. Next, the wax on the surface was thawed with an organic solvent, washed with pure water, and then placed in an electron cyclotron resonance plasma CVD apparatus to deposit 150 Å of an amorphous silicon carbon film containing p-type microcrystals. The deposition conditions are a gas pressure of 0.001 to 0.008 Torr and an input power of 200 to 3
00W, SiH4: CH4: B2 H6: H2 = 1: 1 to 1
3: 0.005-0.03: 100-200, substrate temperature 150-300 degreeC. Next, using an electron beam vapor deposition apparatus, indium tin oxide (IT
O) was deposited in the range of 400 to 700Å.

In this embodiment, an n-type single crystal silicon substrate 1 is used.
By using No. 5, the porous silicon of the present example is
As compared with the above-described first embodiment using the p-type single crystal silicon substrate 11, a light emission phenomenon of a shorter wavelength occurs. Therefore, the light emitting device using the porous silicon of the present embodiment can emit light having a shorter wavelength than the light emitting device of the first embodiment.

Since the light emitting device of the above embodiment can be manufactured by a low temperature process of 300 ° C. or lower, after the logic, operation, driving, light receiving device, etc. are manufactured, the device portion is covered with wax etc. If you make a light emitting element, logic, operation,
Since it is possible to monolithically integrate the light emitting element and the logic, operation, drive, light receiving element, etc. without destroying the driving, light receiving element, etc., it is particularly suitable as a light source for optical communication, self-luminous display, optical integrated circuit, etc. is there.

[0017]

As described above, according to the present invention, a part of or all of the hydrogen adhering to the wall surfaces of a large number of holes is replaced with deuterium. It is possible to provide porous silicon capable of emitting light and a light emitting device using the porous silicon.

[Brief description of drawings]

FIG. 1 is a schematic enlarged sectional view showing a part of porous silicon which is an embodiment of the present invention.

FIG. 2 is a diagram showing a state of bonding between silicon and hydrogen in the pores of porous silicon.

FIG. 3 is a diagram showing a state of bonding between silicon and deuterium in the pores of porous silicon that is an example of the present invention.

FIG. 4 is a schematic structural diagram of Example 1 of a light emitting device that is an example of the present invention.

FIG. 5 is a diagram for explaining a method for manufacturing a light emitting device that is an embodiment of the present invention.

FIG. 6 is a spectrum diagram of photoluminescence of the porous silicon according to the first embodiment.

FIG. 7 is a schematic structural diagram of Example 2 of a light emitting device that is an example of the present invention.

[Explanation of symbols]

1, 2 Light-Emitting Element 11 p-type Single Crystal Silicon Substrate 12 Amorphous Silicon Carbon Layer Containing n-type Microcrystals 12a, 16a Porous Silicon 14 ITO 15 n-type Single-crystal Silicon Substrate 16 p-type Microcrystal Amorphous silicon carbon layer containing silver 120,160 holes

Claims (2)

[Claims] 1. Porous silicon characterized in that a part or all of hydrogen attached to the wall surfaces of a large number of pores is replaced with deuterium. 2. A light emitting device having a pn junction structure using the porous silicon according to claim 1.