KR100918400B1 - Long wavelength vertical cavity surface emitting laser device and method for fabricating the same - Google Patents

Abstract

According to the surface emitting laser device of the present invention, a lower mirror layer for surface emitting long wavelength light, an active layer providing optical gain, a tunnel junction layer and an upper mirror layer for reducing free carrier absorption loss are formed on the compound semiconductor substrate. A slit is formed on the side of at least one of the active layer, the tunnel junction layer, and the upper mirror layer by sequentially etching, and a heat dissipation layer having a greater thermal conductivity than the layer on which the caliber is formed is formed. It is characterized by being filled in wealth.

Description

Long wavelength vertical cavity surface emitting laser device and method for fabricating the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting laser device and a method for manufacturing the same, and more particularly, to a long wavelength surface emitting laser device having a band of 1.3 μm to 1.6 μm for optical communication and a method of manufacturing the same. [Management Number: 2005-S-051-02, Project Name: Optical Integrated Module for Optical Access]

Surface-emitting lasers are lasers that emit light in a direction perpendicular to the substrate, unlike a side-emitting laser whose output light is asymmetrical in cylindrical shape and inferior to the optical fiber. Vertical-Cavity Surface-Emitting Laser (VCSEL), which produces output light by vertical resonance, has a lower threshold current and circular shape compared to conventional edge emitting laser diodes. It has a high optical fiber coupling efficiency according to the beam shape (circular beam shape). And because it can be driven with a small current of several mA, it can be driven directly through a general CMOS IC, reducing the cost. Such a surface emitting laser can be easily manufactured in the form of a two-dimensional array device, and, unlike an edge emitting laser, it can be mass-produced and tested in units of wafers, and thus has sufficient mass productivity. It is being developed as a device that can replace a laser diode).

However, surface emitting lasers having wavelengths in the 850 nm to 980 nm band have limitations in distance and speed traveled through optical fibers, and thus are used for near field communication and are difficult to use for long distance optical communication. Therefore, a long wavelength surface emitting laser of 1.3 μm to 1.6 μm with a communication distance of several Km has been developed as a light source that overcomes the limitation of the surface emitting laser of the existing 850 nm band. As part of this, various studies such as lowering the threshold current and series resistance value, effective heat dissipation method, and proper light induction method are conducted to ensure continuous oscillation, high operating speed, and high output from room temperature to high temperature (85 ° C). It is becoming.

Long wavelength surface emitting laser devices in the band 1.3 μm to 1.6 μm require a mirror layer with high reflectivity and a gain medium with high optical gain, and a combination of materials constituting an InP substrate-based device and a GaAs substrate It is largely classified into a base element.

A device implemented on a GaAs substrate is a material pair having a large refractive index difference, and is capable of growing a reflector made of a pair of GaAs / Al (Ga) As, and has a high current and photon confinement structure using a wet oxidized layer of AlAs. An optical / carrier confinement structure can be realized, and since the active layer providing the gain of output light has a large energy gap, heat generation has little effect on performance degradation. As a representative example of a GaAs-based device, a device having an InGaAsN / GaAsN quantum well structure as a gain medium may be mentioned.

However, as nitrogen increases or the wavelength of the oscillating light becomes longer, the gain and stability of the gain medium may be lowered, and gain characteristics in the long wavelength band of 1.3 μm or more are difficult to see.

Therefore, recently, surface-emitting lasers are fabricated mainly using InGaAsP or InAlGaAs materials on InP substrates. When based on an InP substrate, it is difficult to obtain a material pair having a large difference in refractive index as a reflector, and thus there is an optical problem of growing many layers to obtain high reflectance. In this example, InAlGaAs / InAlAs and InAlGaAs / InP material pairs have been tried.

In addition, as the material forming the active layer or the reflector, the quarternary materials such as InGaAsP and InAlGaAs have a low thermal conductivity that is 1/10 of that of the binary materials such as GaAs. There is a problem of deterioration. The long wavelength VCSELs are characterized by a small band gap inherent in the material, which leads to a drastic decrease in device performance with increasing temperature, so efficient heat dissipation is an important issue.

On the other hand, the manufacturing method of the surface-emitting laser is classified into a monolithic method and a hybrid method. One example of a hybrid method is an active layer that provides optical gain, and a method of growing the mirror layers separately and then bonding them. In this case, by growing the individual structures in a separate process (e.g. by using a quarternary material for the long-wave gain material and using a binary material such as GaAs / AlAs with large refractive index differences). ), The advantages of the GaAs substrate type and the InP substrate type can be compromised and excellent thermal and optical properties can be obtained.

However, in order to bond two epitaxially grown wafers in a separate process, a wafer bonding process must be performed, resulting in problems such as poor wafer bonding, lower reliability and mass production, and higher prices. In other words, in the case of wafer bonding or metamorphic growth of dissimilar material wafers such as GaAs and InAlGaAs, the joints play a very sensitive role in the laser emission structure, and thus the reliability and mass production There is a problem of deterioration and consequent rise in chip price.

Meanwhile, the monolithic method is a method in which structures such as a mirror layer and an active layer are grown at a time by using a semiconductor epitaxial growth method. This is an advantage of the process simplification, but there is a problem of deterioration of heat dissipation characteristics due to the difficulty of thick mirror layer growth and the application of a quarternary material.

The technical problem to be achieved by the present invention is to improve the above-mentioned problems, the surface-emitting laser device that can effectively release the heat generated from the device while still using the advantages of the productivity improvement of the long-wavelength vertical resonance surface emission laser (VCSEL) And a method for producing the same.

In order to achieve the above object, the surface-emitting laser device of the present invention,

A lower mirror layer which surface-emits long wavelength light, an active layer providing optical gain, a tunnel junction layer and an upper mirror layer for reducing free carrier absorption loss are sequentially stacked on the compound semiconductor substrate, and the active layer, tunnel A aperture is formed on the side of at least one of the bonding layer and the upper mirror layer by etching, and the heat dissipation layer having a greater thermal conductivity than the layer on which the aperture is formed is filled with the aperture.

In one embodiment, the heat dissipation layer includes an insulating layer deposited on the aperture and a metal layer stacked on the insulating layer.

In one embodiment, the insulating layer is deposited to be smaller than the thickness of the aperture by atomic layer deposition (ALD) or plasma enhanced atomic layer deposition (PEALD).

In one embodiment, the insulating layer is at least one selected from Al ₂ O ₃ SiO ₂ , SnO ₂ , TiO ₂ , ZrO ₂ , In2O ₃ , HfO _{2 ,} AlN as an oxide film or a nitride film, the metal layer is Cu, Al, At least one of Pd, Ru, Ti, Ta, W, TiN, TaN is selected.

In one embodiment, the surface emitting laser device is to inject a current, the first electrode layer between the lower mirror layer and the active layer, the second electrode layer, the tunnel junction layer and the upper mirror between the active layer and the tunnel junction layer. A third electrode layer is further stacked between the layers.

In some embodiments, the aperture may be formed by selectively wet etching side surfaces of the active layer, the second electrode layer, the tunnel junction layer, the third electrode layer, and the upper mirror layer exposed by dry etching to form the active layer, the tunnel junction layer, and the upper mirror layer. It is formed on at least one side of the.

In one embodiment, the diameter of the tunnel junction layer is smaller than the diameter of the active layer and the upper mirror layer as the aperture is formed.

In one embodiment, the substrate is made of InP, and the lower mirror layer, the active layer, the tunnel junction layer, and the upper mirror layer include the same material as the substrate.

In an embodiment, the lower mirror layer includes an InAlGaAs / InAlAs pair, the active layer includes a multi-quantum well structure, InAlGaAs, and the upper mirror layer includes an InP / InAlAs pair.

In an embodiment, when the first electrode layer, the second electrode layer, and the third electrode layer for injecting the current are further stacked, the first electrode layer, the second electrode layer, and the third electrode layer are n-InP, p- in the stacking order. InP and n-InP.

On the other hand, the manufacturing method of the surface-emitting laser according to the present invention,

A lower mirror layer for surface emitting long wavelength light, a first electrode layer for injecting current, an active layer for providing optical gain, a second electrode layer, a tunnel junction layer for reducing free carrier absorption loss, a third electrode layer and an upper mirror Sequentially depositing layers on the compound semiconductor substrate;

Dry etching the active layer, the second electrode layer, the tunnel junction layer, the third electrode layer and the upper mirror layer to expose each side surface;

Selectively wet etching sides of at least one of the active layer, the tunnel junction layer, and the upper mirror layer to form a aperture;

Filling the aperture with a heat release layer having a greater thermal conductivity than the layer where the aperture is formed; Characterized in that it comprises a.

In one embodiment, the heat release layer is formed by depositing an insulating layer on the aperture and then laminating a metal layer on the insulating layer.

In one embodiment, the insulating layer is deposited to be smaller than the thickness of the aperture by atomic layer deposition (ALD) or plasma enhanced atomic layer deposition (PEALD).

In one embodiment, the diameter of the tunnel junction layer is smaller than the diameter of the active layer and the upper mirror layer as the aperture is formed.

In one embodiment, the substrate is made of InP, and the lower mirror layer, the active layer, the tunnel junction layer, and the upper mirror layer include the same material as the substrate.

In an embodiment, the lower mirror layer includes an InAlGaAs / InAlAs pair, the active layer includes a multi-quantum well structure, InAlGaAs, and the upper mirror layer includes an InP / InAlAs pair.

In an embodiment, the first electrode layer is disposed between the lower mirror layer and the active layer, the second electrode layer is disposed between the active layer and the tunnel junction layer, and the third electrode layer is disposed between the tunnel junction layer and the upper mirror layer by injecting a current. In the case of lamination, the first electrode layer, the second electrode layer, and the third electrode layer include n-InP, p-InP, and n-InP in the stacking order.

According to the present invention, a technical complexity that arises from a surface-emitting laser based on the prior art, for example, a method of growing the mirror layer material and the active layer material differently and then bonding the wafers together during the device fabrication process, or metamorphic It is possible to overcome the problem of reliability deterioration due to crystal defects or plastic deformation that occurs in the method of joining the dielectric mirror layers after (metamorphic) growth.

The present invention can realize the surface emission laser of a long wavelength band with a highly reliable lattice matched crystal growth structure and at the same time improve the properties of low thermal conductivity.

In the present invention, the device is manufactured using a stable homogeneous material system rather than a bonding of dissimilar material systems to improve thermal properties, and by forming an air layer aperture in the heat generating portion and depositing an insulating layer and a metal material having high thermal conductivity in the aperture. It can facilitate heat dissipation and improve operating characteristics and reliability.

As described above, according to the surface-emitting laser device of the present invention and a fabrication method thereof, a structure in which the same material is epitaxially grown at a time compared to the conventional method of bonding the wafers of different materials to each other, thereby preventing defects due to wafer bonding. Can improve the economics and productivity, and all layers are grown in a lattice match to improve the performance and reliability of the device, and the device is composed of InP series suitable for the long wavelength band, but the heat dissipation layer is selectively wet-etched. And by forming by using the atomic layer deposition method can solve the degradation of the thermal properties of the quaternary material, and the heat emission is improved compared to the conventional long wavelength band surface emitting laser can be obtained stable laser operating characteristics at room temperature and high temperature.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention. Embodiments of the invention are not limited to what is shown in the accompanying drawings, it is to be understood that various modifications can be made within the scope of the same invention.

1 to 5 are cross-sectional views sequentially showing the surface-emitting laser device of the present invention and a fabrication method thereof.

Referring to FIG. 1, the lower mirror layer 20, the active layer 40, the tunnel junction layer 60, and the upper mirror layer 80 are formed on the compound semiconductor substrate 10 using epitaxial growth. Growing sequentially. In this case, between the lower mirror layer 20 and the active layer 40, the second electrode layer 50, the tunnel junction layer 60, and the upper portion between the first electrode layer 30, the active layer 40, and the tunnel junction layer 60 are formed. It is preferable to further provide a third electrode layer 70 between the mirror layers 80. The first electrode layer 30, the second electrode layer 50, and the third electrode layer 70 serve as electrodes for current injection, and are preferably made of a material having better heat dissipation characteristics than the surrounding layer. In the surface emitting laser device, the composition of the tunnel junction layer 60, the active layer 40, and the mirror layers 20 and 80 is mainly of interest.

The tunnel junction layer 60 is a region for reducing free carrier absorption loss and may have a p-n junction structure.

The active layer 40 is a gain medium that provides a gain in the operation of the laser. A multi-quantum well structure made of InAlGaAs is preferable.

The substrate 10 is made of InP having a high thermal conductivity as a binary material. Unlike the method of wafer bonding the InP substrate and the GaAs-based mirror layer to each other, the lower mirror layer 20, the active layer 40, the tunnel junction layer 60, the upper mirror layer 80, and the first electrode layer of the present invention. The 30, the second electrode layer 50, and the third electrode layer 70 are epitaxially grown on the InP substrate 10 at the same time with the same material as the substrate 10 and the InP substrate 10. Therefore, all the layers constituting the surface emitting laser device of the present invention are grown on the InP substrate 10 in a lattice match form.

The lower mirror layer 20 may be obtained by stacking InAlGaAs / InAlAs pairs and the upper mirror layer 80 by InP / InAlAs pairs. The light reflectance is lower in the lower mirror layer 20 than in the upper mirror layer 80. Thus, a laser is emitted at the surface of the lower mirror layer 20. The lower mirror layer 20 epitaxially grows several layers ranging from 21 to 25 in order to secure a high refractive index. As the material of the lower mirror layer 20, it is preferable to use InAlGaAs and InAlAs as a material pair having a large refractive index difference. Two layers having different refractive indices may be alternately stacked to obtain desired light reflection characteristics. For example, if reference numerals 21 and 25 are InAlGaAs layers having a high refractive index, reference numerals 22 and 24 are InAlAs layers having a low refractive index.

Similarly to the lower mirror layer 20, the upper mirror layer 80 epitaxially grows several layers from 81 to 85. As the material of the upper mirror layer 80, a material having a large difference in refractive index should be used, and InAlAs and InP are alternately stacked to have a selectivity difference for selective wet etching to form a aperture (89 in FIG. 4). It is desirable to.

The first to third electrode layers 30, 50, and 70 preferably include n-doped InP (n-InP) and n-doped InP (p-InP) in the stacking order. For example, it may be stacked in the order n-InP, p-InP, n-InP.

2 to 3, the side surfaces of the active layer 40, the second electrode layer 50, the tunnel junction layer 60, the third electrode layer 70, and the upper mirror layer 80 are exposed by dry etching. . That is, when the epi structure for the surface emitting laser is completed as shown in FIG. Use After masking using SiN or the like, CH ₄ or H ₂ series ions may be used as etching ions.

When these side surfaces are exposed, as shown in FIG. 4, some of the side surfaces of the active layer 40, the tunnel junction layer 60, and the upper mirror layer 80 are removed to form apertures 49, 69, and 89. Selective wet etching is used. In this case, the diameter d3 of the active layer 40 and the diameter d1 of the upper mirror layer 80 should be larger than the diameter d2 of the tunnel junction layer 60 so as not to interfere with the light induction of the laser. In view of this, the relative depths of the apertures 69 formed in the tunnel junction layer 60, the apertures 89 formed in the upper mirror layer 80, and the apertures 49 formed in the active layer 40 are determined. Adjust.

FIG. 5 shows that the thermally conductive insulating layer 91 and the metal layer 92 are sequentially deposited in the regions 49, 69, and 89 formed by selective wet etching. The heat dissipation layer 90 of the present invention includes the insulating layer 91 and the metal layer 92. In view of the narrow space of the apertures 49, 69 and 89, an oxide film or a nitride film having good thermal conductivity can be viewed by atomic layer deposition (ALD) or plasma enhanced atomic layer deposition (PEALD). It is formed smaller than the thickness of the portions (49, 69, 89), and then the metal layer 92 having good thermal conductivity is deposited to fill the apertures (49, 69, 89).

As the insulating layer 91, an oxide film Al ₂ O ₃ SiO ₂ , SnO ₂ , TiO ₂ , ZrO ₂ , In ₂ O ₃ , HfO ₂ , AlN, or the like may be used. The metal layer 92 is most preferably Cu having good thermal conductivity, and may be a material such as Al, Pd, Ru, Ti, Ta, W, TiN, TaN, or the like. An electrode 100 for ohmic contact may be provided by applying current to the first electrode layer 30 and the third electrode layer 70.

6 is a cross-sectional view showing the overall structure of the surface-emitting laser device completed as an embodiment of the present invention. By growing the structure of FIG. 1 on a wafer of a general size and performing the process of FIGS. 2 to 5, dicing the wafer may yield several devices of FIG. 6. On the other hand, the output light of the surface-emitting laser produced by the above method is emitted downward through the lower mirror layer (20). Although the substrate 10 is shown, some or all of the substrate 10 may be removed to facilitate laser emission through the surface of the lower mirror layer 20. Since the heat emission layer 90 is provided, the heat generated from the laser continuously oscillating from room temperature to high temperature can be effectively released, and the performance of the device can be prevented from being degraded by heat generation.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and those skilled in the art to which the art belongs can make various modifications and other equivalent embodiments therefrom. Will understand. Therefore, the true technical protection scope of the present invention will be defined by the claims below.

1 to 5 are cross-sectional views sequentially showing the structure of the surface-emitting laser device of the present invention and a method of manufacturing the same.

6 is a cross-sectional view showing the completed structure of the surface emitting laser device of the present invention.

<Description of the symbols for the main parts of the drawings>

10 ... substrate 20 ... bottom mirror layer

30.First electrode layer 40.Active layer

49,69,89 ... Aperture 50 ... Secondary electrode layer

60 ... tunnel junction layer 70 ... third electrode layer

80 ... upper mirror layer 90 ... heat dissipation layer

91 Insulation layer 92 Metal layer

100 ... electrode

Claims (20)

A lower mirror layer which surface emits a laser, an active layer providing optical gain, a tunnel junction layer and an upper mirror layer to reduce free carrier absorption loss are sequentially deposited on the compound semiconductor substrate, An aperture is formed on the side of at least one of the active layer, the tunnel junction layer, and the upper mirror layer by etching. A heat dissipation layer having a greater thermal conductivity than the layer in which the aperture is formed is filled in the aperture, The first electrode layer between the lower mirror layer and the active layer, the second electrode layer between the active layer and the tunnel junction layer, and the third electrode layer between the tunnel junction layer and the upper mirror layer for injecting current, A surface emitting laser device characterized by the above-mentioned. The method of claim 1, The heat release layer, And an insulating layer deposited on the aperture and a metal layer laminated on the insulating layer. The method of claim 2, The insulating layer, A surface emitting laser device characterized in that the deposition is smaller than the thickness of the aperture by the atomic layer deposition (ALD) or plasma enhanced atomic layer deposition (PEALD). The method of claim 2, The insulating layer, And at least one selected from Al ₂ O ₃ SiO ₂ , SnO ₂ , TiO ₂ , ZrO ₂ , In ₂ O ₃ , HfO _{2 , and} AlN as an oxide film or a nitride film. The method of claim 2, The metal layer, Surface-emitting laser device, characterized in that at least one selected from Cu, Al, Pd, Ru, Ti, Ta, W, TiN, TaN. delete The method of claim 1, The caliber is, By selectively wet etching the side surfaces of the active layer, the second electrode layer, the tunnel junction layer, the third electrode layer, the upper mirror layer exposed by dry etching is formed on at least one side of the active layer, tunnel junction layer and the upper mirror layer. Surface-emitting laser device, characterized in that. The method of claim 1, The diameter of the tunnel junction layer is smaller than the diameter of the active layer and the upper mirror layer according to the formation of the aperture portion. The method according to any one of claims 1 to 5, 7 and 8, The substrate is made of InP, And the lower mirror layer, the active layer, the tunnel junction layer, and the upper mirror layer comprise a material of the same type as the substrate. The method of claim 9, And the lower mirror layer is an InAlGaAs / InAlAs pair, the active layer is a multi-quantum well structure, InAlGaAs, and the upper mirror layer is an InP / InAlAs pair. According to claim 1, And the first electrode layer, the second electrode layer, and the third electrode layer include n-InP, p-InP, and n-InP in the stacking order. A lower mirror layer for surface emitting a laser, a first electrode layer for injecting current, an active layer for providing optical gain, a second electrode layer, a tunnel junction layer for reducing free carrier absorption loss, a third electrode layer and an upper mirror layer Sequentially depositing a compound on a compound semiconductor substrate; Dry etching the active layer, the second electrode layer, the tunnel junction layer, the third electrode layer and the upper mirror layer to expose each side surface; Selectively wet etching sides of at least one of the active layer, the tunnel junction layer, and the upper mirror layer to form a aperture; Filling the aperture with a heat release layer having a greater thermal conductivity than the layer where the aperture is formed; Method for producing a surface-emitting laser device comprising a. The method of claim 12, The heat release layer, And depositing an insulating layer on the aperture and then laminating a metal layer on the insulating layer. The method of claim 13, The insulating layer, A method of manufacturing a surface-emitting laser device, characterized in that the deposition is smaller than the thickness of the aperture by atomic layer deposition (ALD) or plasma enhanced atomic layer deposition (PEALD). The method of claim 12, The diameter of the tunnel junction layer becomes smaller than the diameter of the active layer and the upper mirror layer as the aperture is formed. The method according to any one of claims 12 to 15, The substrate is made of InP, And the lower mirror layer, the active layer, the tunnel junction layer and the upper mirror layer comprise a material of the same kind as the substrate. The method of claim 16, The lower mirror layer is an InAlGaAs / InAlAs pair, The active layer is a multi-quantum well structure, InAlGaAs, And the upper mirror layer comprises InP / InAlAs pairs. The method of claim 12, And the first electrode layer, the second electrode layer and the third electrode layer comprise n-InP, p-InP and n-InP in the order of their lamination. According to claim 1, The laser is a surface-emitting laser device, characterized in that the long wavelength laser of 1.3 ~ 1.6 ㎛ band. The method of claim 12, The laser is a method of manufacturing a surface-emitting laser device, characterized in that the long wavelength laser of 1.3 ~ 1.6 ㎛ band.

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