JPH06150367A - Optical disk - Google Patents

Abstract

PURPOSE:To record information in a high density and to exactly reproduce the information recorded in the high density by having a quantum well structure and reducing the diameter of a light beam with which the optical disk is irradiated for the purpose of reading or writing. CONSTITUTION:Plural information pit parts 12 corresponding to the information on sounds, videos, et., are formed on the quantum well layer forming flanks 11a of a substrate 11 consisting of a single crystal GaAs. The plural information pit parts 12 are irradiated with the light of 780nm wavelength from the substrate surface 11a formed with these pit parts and the information is read out by the reflection from the substrate surface 11a side. A quantum confining effect is generated by the quantum structure at this time and a nonlinear optical effect is increased, as the result, the pits smaller than the size regulated by k.lambda (wavelength)/CN, A. (numerical aperture) are read out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk which is an optical recording medium for recording various information signals such as audio and video.
Particularly, the present invention relates to an optical disc capable of recording information at high density or reproducing information recorded at high density accurately.

[0002]

2. Description of the Related Art Generally, an optical disc has a center hole in the center thereof, and information is recorded on the outer periphery of the center hole as one track connected in a spiral shape. Conventionally, as shown in FIG. 7A, a recording disk of this type has an acrylic resin (Polymethylmethacrylate; PMMA).
An information pit portion 112 having an uneven shape corresponding to information is formed on a transparent disc substrate 111 such as a glass substrate, and an aluminum film 115 having a high reflectance is deposited on the disc substrate 111 on which the information pit portion 112 is formed. A protection layer 116 made of plastic or the like is formed on the aluminum film 115.

When reproducing information from a recording disk based on the above structure, a light beam 130 such as a laser beam is projected from the transparent disk substrate 111 side onto the information pit portion 112 of the track to be reproduced, and FIG. As shown in b), the reflected light 131 reflected by the mirror surface portion between the pits without the information pit portion 112 is detected as “bright”, and the reflected light 132 reflected by the information pit portion 112 is detected as “dark”. To be detected. In this way, the recording pits 112a, 112 of the information pit portion 112 are reflected by the "bright" and "dark" reflected light.
The information corresponding to b, 112c ... Is reproduced.

[0004]

Since the above-mentioned conventional optical disc and the reproducing method thereof are configured as described above, when the track pitch of adjacent tracks is narrowed to record information with high density. Has a problem that a light beam is projected over a plurality of tracks of the recording disc having the high density. That is, since the diameter of the beam spot is determined based on the wavelength of the light beam, there is generally a limit to reducing the spot diameter, and when information is recorded at a narrow track pitch that exceeds this limit, FIG. As shown in (c), a plurality of pieces of information "dark" (or bright 131) of the reflected light 132 are simultaneously detected from the information pits 112a, 112b, 112c of a plurality of tracks, and the information cannot be accurately reproduced. Was occurring.

On the other hand, there is also a demand for the development of an optical disc having a writable recording film, which can record information at a high density. The present invention has been made to solve such problems,
An object of the present invention is to provide an optical disc capable of recording information at a high density or an optical disc capable of accurately reproducing the recorded information.

[0006]

In order to solve the above-mentioned problems, an optical disk of the present invention is provided on a substrate which may form a part of a quantum well structure in which information is recorded in advance, or on an information recordable recording film. A quantum well structure including a quantum well layer for quantum confinement is provided, and the diameter of the light beam irradiated for reading or writing is narrowed.

[0007]

When the optical disk of the present invention is irradiated with light,
Due to the quantum confinement effect based on the quantum well structure, the reflectance is higher in a place where the light intensity is strong and is lower in the place where the light intensity is weak. As a result, for example, the same effect as that when the reading beam diameter is further narrowed can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical disc of the present invention will be described below with reference to FIGS. FIG. 1 and FIG. 2 show a first so-called phase pit for recording and reproducing by utilizing the phase difference.
An optical disc 1 as an example is shown.

The optical disk 1 includes a substrate 11 made of single crystal GaAs, a GaAlAs layer 13 as a quantum well layer formed on the substrate 11, and a single crystal formed on the quantum well layer 13. And a GaAs layer 16 of. In this embodiment, the substrate 11 and the GaAlAs layer 13 are
The GaAs layer 16 forms a so-called quantum well structure. GaAlAs is further formed on the GaAs layer 16.
The two layers of the layer / GaAs layer may be laminated once or several tens of times. This forms a layer whose reflectance depends on the light intensity.

A plurality of information pit portions 12 corresponding to information such as audio and video are formed on the side surface 11a of the quantum well layer formation of the substrate 11 made of single crystal GaAs. The other side 11
b is a flat surface. The information pit portion 12 is formed by a manufacturing process such as patterning to etching which is generally used in a so-called semiconductor process. At this time, the groove depth D1 of the information pit portion 12 (in FIG. 2, since the GaAlAs layer 13 and the GaAs layer 16 are formed to have a uniform film thickness at each portion, D1 is the groove depth of the information pit portion 12). Is set so as to satisfy the depth giving the optical phase difference, that is, D1 = λ / 4n. Note that λ represents the wavelength of the light used and n represents the refractive index of the optical path.

Ga formed on such a substrate 11
The thicknesses of the AlAs layer 13 and the GaAs layer 16 are
It is about 10-100 angstroms, and these are
MO-CVD (Metal Organic-Chemical Vapor Deposit)
ion) or MBE (Molecular Beam Epitaxy) method. Furthermore, a protective film transparent to the wavelength of the reading light may be provided on the outermost surface on the side where the information pit portion 12 is formed.

A method of reading information recorded on an optical disk having a quantum well structure having such a composition is performed as follows. That is, as shown in the drawing, light having a wavelength of 780 nm is emitted from the substrate surface 11a on which a plurality of information pit portions 12 are formed, and information is read by reflection from the substrate surface 11a side. At that time, a quantum confinement effect occurs due to the quantum structure, and the nonlinear optical effect becomes large. As a result, pits smaller than the size defined by K · λ (wavelength) / (NA (numerical aperture)) are read. I can put it out.

In this embodiment, the light irradiation direction is set to be from the side of the substrate surface 11a because GaAlAs is 620.
This is because light having a wavelength longer than nm, for example, light having a wavelength of 780 nm passes, while GaAs does not transmit light having a wavelength shorter than 867 nm, for example, light having a wavelength of 780 nm.

Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. The second embodiment is also an optical disk 2 having so-called phase pits, like the first embodiment.

The optical disk 2 has a substrate 21 made of single crystal ZnSe, a GaAs layer 23 as a quantum well layer formed on the substrate 21, and a quantum well layer 23.
And a single-crystal ZnSe layer 26 formed on the top surface of the. In this embodiment, the substrate 21, the GaAs layer 23 and the ZnS
A so-called quantum well structure is formed by the e layer 26. On the ZnSe layer 26, two layers of a GaAs layer / ZnSe layer may be laminated once to several tens of times in the same manner as the pattern of the first embodiment.

A plurality of information pit portions 22 corresponding to information such as audio and video are formed on the quantum well layer forming side surface 21a of the substrate 21 made of single crystal ZnSe. The other side 21
b is a flat surface. The information pit portion 22 is formed by the same manufacturing process as that of the first embodiment. At this time, the depth D2 of the groove of the information pit portion 22 (in FIG. 4, since the GaAs layer 23 and the ZnSe layer 26 are formed to have a uniform film thickness in each portion, D2 is the depth of the groove of the information pit portion 22). Is set so as to satisfy the depth giving the optical phase difference, that is, D1 = λ / 4n.

Ga formed on such a substrate 21
The thickness of each of the As layer 27 and the ZnSe layer 26 is 10
The thickness is set to about 100 angstroms, and these are also MO-CVD (Metal Or) as in the case of the first embodiment.
ganic-Chemical Vapor Deposition) and MBE (Molecu
lar beam epitaxy method. Further, a light reflection film 29 may be provided on the outermost surface on the side where the information pit portion 22 is formed. The light reflecting film 29 is made of Au, Ag,
It is made of a metal such as Cu or Al, and is formed by various vacuum film forming methods such as vacuum deposition, sputtering, and ion plating. The thickness of such a light reflecting film 29 is about 0.03 to 0.3 μm.

A method of reading information recorded on an optical disk having a quantum well structure having such a composition is performed as follows. That is, as shown in FIG. 3, light having a wavelength of 780 nm is irradiated from the substrate surface 11b on which the plurality of information pit portions 22 are not formed, and the substrate surface
Information is read by the reflection from the 1a side. At that time, a quantum confinement effect occurs due to the quantum structure, and the nonlinear optical effect becomes large. As a result, pits smaller than the size defined by K · λ (wavelength) / (NA (numerical aperture)) are read. I can put it out.

In this embodiment, the direction of light irradiation is set from the side of the substrate surface 21b because ZnSe is 477 nm.
This is because light having a longer wavelength, for example, light having a wavelength of 780 nm passes, while GaAs does not transmit light having a wavelength shorter than 867 nm, for example, light having a wavelength of 780 nm.

The operation of the quantum well layer will be described with reference to FIG. FIG. 6 is a schematic explanatory diagram for explaining that the diameter of the light beam can be further reduced by providing the quantum well layer of the present invention. That is, FIG. 6A shows the beam profile in the state where the quantum well layer is not provided.
(B) is a beam profile with the quantum well layer provided. As can be seen from the profiles shown in (a) and (b), the beam diameter can be remarkably narrowed by providing the quantum well layer, and one recording pit which could not be read conventionally (FIG. 6 (a)) is surely formed. Can be read out (FIG. 6 (b)).

The optical beam wavelength for reading or writing, which is the target of the optical disk of the present invention, is 48.
It is 0 to 830 nm. In the above, the quantum well layer is used as a film whose reflectance depends on the light intensity, but it can also be used as a film whose transmittance depends on the light intensity. As an example of this case, the optical disc 3 shown in FIG.
Is shown as a third embodiment.

The optical disk 3 comprises a quantum well layer for quantum confinement and a recording film 39. The optical disc 3 as the third embodiment is substantially similar to that of the second embodiment, but the recording pits are not formed on the surface of the substrate 31 as in the second embodiment, and instead, it will be described later. The recording film 39 is provided, and the recording pit portion is formed in the recording film 39. That is, the optical disc 3 includes, for example, a substrate 31 made of single crystal ZnSe, a GaAs layer 33 as a quantum well layer formed on the substrate 31, and a single crystal formed on the quantum well layer 33. ZnSe layer 36 of In this embodiment, the substrate 31 and the GaAs layer 3
7 and the ZnSe layer 36 form a so-called quantum well structure. Two layers of a GaAs layer / ZnSe layer may be further laminated on the ZnSe layer 36 once to several tens of times.

The recording film 39 is formed of a material that can obtain a difference in reflectance between the light-irradiated portion and the light-irradiated portion by recording with light irradiation. As an example of these materials, As-Te-Ge system, Sn-Te system, which carries out information by utilizing the phase change between amorphous and crystalline, is mentioned.
-Se system, TeOx (0 <X <2), Sb ₂ Se ₃ , B
There are phase change type recording film materials such as i ₂ Te ₃ . Further, a recording material by pit formation using an inorganic thin film of Te-based material or an organic dye thin film such as cyanine dye or phthalocyanine dye is an example of the recording film 18 material. Other,
TbFeCo, GdCo used for magneto-optical memory,
Materials such as PtCo may also be used.

In the present embodiment, the description has been centered on focusing on the beam diameter of the reading light, but it goes without saying that the beam diameter of the writing light can be focused and applied to high density recording.

[0025]

As described above, the optical disc of the present invention has a quantum confinement structure on a substrate which may form a part of a quantum well structure in which information is recorded in advance, or on a recording film capable of recording information. Since it has a quantum well structure including a quantum well layer for reducing the diameter of the light beam irradiated for reading or writing, information can be recorded at high density or information recorded at high density. Can be reproduced accurately.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining the structure of an example of an optical disc of the present invention.

FIG. 2 is a partially enlarged cross-sectional view around a phase pit portion in FIG.

FIG. 3 is a schematic cross-sectional view for explaining the structure of an example of another optical disc of the present invention.

FIG. 4 is a partially enlarged cross-sectional view around a phase pit portion in FIG.

FIG. 5 is a schematic cross-sectional view for explaining the structure of an example of another optical disc of the present invention.

FIG. 6 is a schematic explanatory view for explaining that the diameter of the light beam is further narrowed by providing the shutter layer of the present invention, and (a) is a beam profile in a state in which the quantum well layer is not provided. And (b) is a beam profile with the quantum well layer provided.

FIG. 7A is a partially cutaway sectional view of an optical disc for schematically showing a state in which information is recorded, and FIG.
FIG. 4 is a diagram for explaining the principle of reading, and FIG. 7C is a diagram for explaining the conventional inconvenience that occurs when reproducing information recorded at high density.

[Explanation of symbols]

 1, 2, 13 ... Optical disc 11, 21, 31 ... Substrate 13, 23, 33 ... Quantum well layer 39 ... Recording film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G11C 13/04 6741-5L

Claims (3)

[Claims] 1. A quantum well structure including a quantum well layer for quantum confinement is provided on a substrate which may form a part of a quantum well structure in which information is recorded in advance, or a recording film capable of recording information. An optical disc characterized in that the diameter of a light beam emitted for reading or writing is narrowed. 2. The quantum well structure comprises a GaAlAs layer as a quantum well layer formed of single-crystal GaAs from both plane sides thereof.
The optical disc according to claim 1, wherein the optical disc has a structure of being sandwiched between layers. 3. The optical disk according to claim 1, wherein the quantum well structure is a structure in which a GaAs layer serving as a quantum well layer is sandwiched by single-crystal ZnSe layers from both plane sides thereof.