KR100413785B1 - Vertical cavity surface emitting laser diode and fabricating method thereof - Google Patents

Abstract

PURPOSE: A vertical cavity surface emitting laser diode and a fabricating method thereof are provided to inject smoothly carriers and form a mirror of high reflectivity by separating a carrier injection path from a top mirror layer and a bottom mirror layer. CONSTITUTION: A vertical cavity surface emitting laser diode includes a substrate(11), a bottom mirror layer(13), a first contact layer(14), an active layer(15), a first metal layer(19), a current confinement layer(16), a second contact layer(17), a top mirror layer(18), and a second metal layer(20). The bottom mirror layer(13) is laminated on the substrate(11). The first contact layer(14) is formed on the bottom mirror layer. The active layer(15) is formed on a center part of the first contact layer. The first metal layer(19) is formed on a peripheral part of the first contact layer. The current confinement layer(16) is formed on the active layer. A current passing region is formed on a center part of the current confinement layer. A current blocking region is formed on both sides of the current passing region. The second contact layer(17) is formed on the current confinement layer. The top mirror layer(18) is formed on a center part of the second contact layer. The second metal layer(20) is formed on a peripheral part of the second contact layer.

Description

Vertical Resonant Surface Emitting Laser Diode and Manufacturing Method Thereof

The present invention relates to a vertical cavity surface emitting laser diode (VCSEL) and a method of manufacturing the same, and more particularly, to a vertical cavity surface emitting laser diode using a GaN group III-V hybrid crystal system and a method of manufacturing the same. It is about.

While the edge-emitting laser diode has a resonant structure parallel to the stacking surface of the device, the laser beam oscillates in a direction parallel to the stacking surface, while the vertical resonant surface-emitting laser diode has a resonant structure perpendicular to the stacking surface of the device. While oscillating the laser beam in the vertical direction of the stacked surface of the device. The vertical resonance surface emitting laser diode (VCSEL) has a lower driving current and a smaller beam divergence than an edge emitting laser diode, so that optical communication, optical information recording, and holographic memory (holographic memory) memory). In addition, the vertical resonance surface emitting laser diode (VCSEL) exhibits a single longitudinal mode characteristic due to wide longitudinal mode spacing, low oscillation start current, and symmetry of the exit beam, resulting in coupling efficiency ( Due to the advantages of good coupling efficiency, the application range is gradually expanded.

1 is a vertical cross section of a conventional vertical resonance surface emitting laser diode.

In the conventional vertical resonator surface emitting laser diode shown in the drawing, an upper mirror layer 5 and a lower mirror layer 3 are formed above and below the active layer 4, and carrier injection into the active layer 4 is performed by the first metal layer 1. And through the upper mirror layer 5 and the lower mirror layer 3 from the second metal layer 7. In order to limit the current injection into the active layer 4 to a predetermined region, H ⁺ is selectively implanted from both sides of the upper mirror layer 5 to a part of the lower mirror layer 3 to a predetermined depth. H ⁺ injection zone 8 is provided to restrict the carrier passage to the central portion by the injected zone. In FIG. 1, reference numeral 2 denotes a substrate, and 6 denotes an ohmic buffer layer.

This stacking structure is called an H ⁺ injection planarization structure, and the planarization structure requires the upper and lower mirror layers 5 and 3 to act as resonators because carrier injection must pass through the upper and lower mirror layers 5 and 3. In addition to the mirror role, a carrier conduction path must also be provided. Therefore, the upper and lower mirror layers 5, 3 are preferably composed of a suitable composition to serve as a mirror that can exert maximum efficiency in the resonance of light generated in the active layer 4, but is repeated to obtain high reflectance. The greater the refractive index difference between the two materials to be laminated, the higher the electrical resistance, which hinders the carrier injection. Therefore, there is a constraint that the composition should be selected in consideration of the resistance characteristics for carrier injection. As a result, due to a problem that the composition of the upper and lower mirror layers 5, 3 is in conflict with the desired carrier injection and the improvement of the resonance efficiency, the thermal problem due to the increase in resistance cannot be avoided at the composition ratio corresponding to the high power factor. This thermal problem prevents stable oscillation. On the contrary, there is a problem that the light output efficiency is reduced in the composition ratio in which carrier injection is desired.

The present invention improves the above problems and uses a GaN-based mixed crystal compound to provide a light source of a high-density optical recording / reproducing apparatus. And its manufacturing method.

1 is a vertical cross-sectional view of a conventional vertical resonance surface emitting laser diode,

2 is a vertical cross-sectional view of a vertical resonance surface emitting laser diode according to the present invention.

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

1, 19: first metal layer 2, 11: substrate

3, 13: lower mirror layer 4, 15: active layer

5, 18: upper mirror layer 6: ohmic buffer layer

7, 20: second metal layer 8: H + injection region

12: buffer layer 13a: AlN layer

13b, 18b: GaN layer 14: first contact layer

16: Current limiting layer 16a: Current passing area

16b: current blocking region 17: second contact layer

18a: AlN oxide layer

In order to achieve the above object, a vertical resonance surface emitting laser diode according to the present invention includes a substrate and a lower mirror layer formed by a plurality of stacked on the substrate, and a first contact layer formed on the lower mirror layer and the first contact. An active layer formed on the central portion of the layer and a first metal layer formed on the peripheral portion of the first contact layer and the active layer formed on the active portion, and a current passing region is provided at the central portion thereof, and current blocking is provided at both sides thereof. On the current limiting layer provided with an area, the second contact layer formed on the current limiting layer, and the upper mirror layer formed by multiple laminations having a predetermined width in a central portion of the second contact layer, and on the peripheral portion of the second contact layer. It characterized in that it comprises a second metal layer formed in the.

Here, preferably, the upper mirror layer is a plurality of alternating layers of AlN oxide and GaN layer oxidized AlN alternately, the lower mirror layer is a plurality of alternating layers of AlN and GaN layers alternately, the active layer is InGaN, the first and second contact layers are formed of GaN, the current limiting layer is formed of AlGaN, and the current blocking region is formed by oxidizing AlGaN.

In order to achieve the above object, a method of manufacturing a vertical resonance surface emitting laser diode according to the present invention includes: repeatedly forming a plurality of AlN layers and GaN layers alternately on a substrate to form a lower mirror layer; Sequentially forming a first contact layer, an active layer, a current limiting layer, and a second contact layer on the lower mirror layer; Forming an upper mirror layer by repeatedly stacking an AlN layer and a GaN layer on the second contact layer in alternating manner; A portion of the upper surface of the second contact layer is exposed by etching from the upper mirror layer to a portion of the second contact layer, and a portion of the upper surface of the first contact layer is etched from the second contact layer to the upper surface of the first contact layer. Etching to expose a portion; The current blocking region is formed by oxidizing both regions except for the current passing region so that only the central portion of the current limiting layer is limited to the current passing region, and oxidizes the AlN layer constituting the upper mirror layer to form an AlN oxide layer. Forming an oxidation step; An electrode forming step of forming a first metal layer and a second metal layer used as electrodes in predetermined regions of the exposed portion of the upper surface of the first contact layer and the exposed portion of the upper surface of the second contact layer, respectively. Here, the order of the oxidation step and the electrode forming step after the etching step may be reversed.

Hereinafter, exemplary embodiments of a vertical resonator surface emitting laser diode and a method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a vertical cross-sectional view of a vertical resonator surface emitting laser diode according to the present invention.

As shown, the surface-emitting laser diode is sequentially disposed on the substrate 11, the buffer layer 12, the lower mirror layer 13, the first contact layer 14, the active layer 15, the current limiting layer 16, The second contact layer 17 and the upper mirror layer 18 are sequentially stacked, and the upper surfaces of the first metal layer 19 and the second contact layer 17 formed on the exposed portions of the upper surface of the first contact layer 14. The second metal layer 20 formed on the exposed portion is provided.

In each layer composition for realizing the desired blue-green wavelength, first, the buffer layer 12 on the substrate is composed of GaN or AlN, and the first and second contact layers 14 and 17 are ohmic with a metal. The GaN layer is composed of GaN having excellent properties, the active layer 15 is formed of InGaN, and the upper mirror layer 18 alternately repeats the AlN oxide layer 18a and the GaN layer 18b to become a distributed Bragg reflector (DBR). The lower mirror layer 13 is formed to alternately form the AlN layer 13a and the GaN layer 13b so as to be a distributed Bragg reflector (DBR), and the current limiting layer 16 is a central conduction path. Preferably, the portion of the current passing region 16a is formed of AlGaN, and the current blocking region 16b on both sides of the current passing region 16a is formed of oxidized AlGaN. Here, the upper mirror layer 18 is formed by alternately stacking the AlN oxide layer 18a and the GaN layer 18b formed by oxidizing AlN, so that the number of laminated layers repeatedly stacked to obtain a desired reflectance alternates between the AlN layer and the GaN layer. Since it is reduced than when making easier to manufacture, there is an effect that the defect rate is relatively reduced. When the surface-emitting laser diode thus constructed is manufactured in a cylindrical shape having a substantially stepped monolayer, the outer diameter b of the upper mirror layer 18 is related to the light efficiency, so that the current passing region 16a of the current limiting layer 16 is formed. It is determined to be larger than the outer diameter (a) of. In addition, for single transverse mode oscillation, it is preferable that the outer diameter c of the active layer 15, the current limiting layer 16, and the second contact layer 17 stacked side by side at the same radius are maintained at about 5 μm. Further, in the numerical determination of the outer diameter b of the upper mirror layer 18, the outer diameter c of the current limiting layer 16 and the outer diameter a of the current passing region 16a of the current limiting layer 16, respectively, The outer diameter (a) of the current passing region of the current limiting layer 16 is determined in relation to the selected optical output characteristic, and then the depth of penetration into the current blocking region by oxidation with respect to the oxidation rate is determined by the upper mirror layer 18. The outer diameter b of the upper mirror layer 18 is determined so as to completely oxidize the AlN layer. As described above, when the outer diameter of each layer is determined in association with the oxidation process, the device may be easily manufactured by one oxidation operation during fabrication.

According to the feature of the vertical resonance surface emitting laser diode of the present invention having the structure as described above, the passage through which the carrier is injected into the active layer 15 is the first metal layer 19 provided in the exposed portion of the upper surface of the first contact layer 14. A second metal layer provided on the upper surface of the first contact layer 14, the active layer 15, the current limiting layer 16 of the current passing region 16a, the second contact layer 17 and the second contact layer 17 Leads to 20. Therefore, the carrier current is smoothed by the first contact layer 14 and the second contact layer 17 made of GaN having low resistance, thereby lowering the threshold current, and lowering the lower mirror layer 13 and the upper mirror layer. 18 is separated from the carrier injection path so as to contribute only to the pure mirror role, thereby forming a mirror having a high reflectivity of 90% or more. As a result, each layer can be formed so as to be suitable for emitting light corresponding to a desired wavelength band, that is, a wavelength band to be used from the ultraviolet region to the cyan region, and in this regard, the upper and lower mirror layers 18 (13) ), The light output efficiency is improved by providing a high reflectance of 90% or more.

Looking at the manufacturing process of the vertical resonance surface emitting laser diode having such characteristics, first, the buffer layer 12, the lower mirror layer 13, the first contact layer 14, the active layer (1) on the substrate 11 by the crystal growth 15), the current blocking layer 16, the second contact layer 17 and the upper mirror layer 18 are sequentially grown side by side. Here, the current blocking layer and the upper mirror layer are laminated only with the composition before the oxidation process.

Looking at the composition of each layer in the crystal growth step, the buffer layer 12 is composed of GaN or AlN, the lower mirror layer 13 is a GaN layer (13b) and AlN layer (13a) of the λ / 4 of the oscillation wavelength (λ) Laminate alternately to optical thickness. In addition, the active layer 15 is laminated with AlGaN to a thickness corresponding to an integer multiple of the oscillation wavelength?, And the first and second contact layers 14 and 17 are made of GaN. The upper mirror layer 18 alternately repeats the AlN layer 18a and the GaN layer 18b, but the GaN layer 18b is laminated with an optical thickness of λ / 4 of the oscillation wavelength λ from the refractive index value. , The AlN layer 18a should be laminated with an optical thickness of λ / 4 corresponding to the refractive index value that has been oxidized after the oxidation step, which is a post-process.

Next, in the etching step, two etching processes are performed to secure a space for forming an n-type ohmic metal, which is the first metal layer 19, and a p-type ohmic metal, which is the second electrode layer 20. In the first step, the upper surface of the second contact layer 16 is etched vertically with the width of the outer diameter b of the upper mirror layer 18, and then the width of the outer diameter c of the second contact layer 17. In order to etch vertically to a depth of the first contact layer 14. Here, from the upper mirror layer 18 to the first contact layer 14 is first etched vertically at a width corresponding to the outer diameter c of the active layer, and again the width corresponding to the outer diameter b of the upper mirror layer 18. As a result, the second mirror layer 16 may be etched from the upper mirror layer to the second contact layer 16 vertically.

After the etching step, the AlN layer 18a of the upper mirror layer 18 and the current limiting layer 16 composed of AlGaN are oxidized, wherein the AlN layer 18a is evenly distributed over the entire region. On the other hand, the current limiting layer 16 performs a selective oxidation process so that the selected current passing region 16a is not oxidized and only the remaining portion of the current blocking region 16b is oxidized.

Thereafter, the first metal layer (n-type ohmic metal) 19 and the first metal layer, which are used as electrodes, are exposed to the exposed portion of the upper surface of the first contact layer 14 and the exposed portion of the upper surface of the second contact layer 17 formed through the etching step. A metal layer forming step of forming a second metal layer (p-type ohmic metal) 20 is performed.

The lateral wave guide of the device manufactured as described above determines the number of modes oscillated by the outer diameter of the light exit surface.

Conventionally, p-type and n-type dopants are injected into the upper and lower mirror layers 18 and 13 for the purpose of lowering the resistance in order to improve carrier injection characteristics. And the second contact layers 14 and 17 provide a carrier injection path, so that the upper and lower mirror layers 18 and 13 do not need to be separately doped, which is a non-oxidation region of the current limiting layer 16. The current limitation is appropriately set by the width of the current passing-through region 16a, so that the operating current is lowered, and at the same time, the single lateral mode characteristic is improved by the optical guide role. In addition, by providing a bluish green oscillation wavelength, it can function as a light source of a high density optical recording device such as a digital video disk (DVD) system.

As described above, in the vertical resonator surface emitting laser diode according to the present invention, the carrier injection path is separated from the upper and lower mirror layers, thereby achieving a smooth carrier injection and a high reflectivity mirror surface at the same time. When the characteristic is stable, the light output efficiency is increased.

Claims (7)

A substrate; A lower mirror layer formed by a plurality of laminations on the substrate; A first contact layer formed on the lower mirror layer; An active layer formed on a central portion of the first contact layer at a predetermined width; A first metal layer formed on a peripheral portion of the first contact layer; A current limiting layer formed on the active layer and provided with a current passing region at a central portion thereof and provided with current blocking regions at both sides thereof; A second contact layer formed on the current limiting layer; An upper mirror layer formed by multiple laminations having a predetermined width in a central portion of the second contact layer; And a second metal layer formed on a peripheral portion of the second contact layer. The method of claim 1, The upper mirror layer includes an AlN oxide layer and a GaN layer, which are alternately stacked a plurality of times, The lower mirror layer includes a plurality of alternatingly stacked AlN layers and GaN layers, the active layer is composed of InGaN, And the first and second contact layers are made of GaN. The vertical resonance surface emitting laser diode according to claim 2 or 3, wherein the current limiting layer is formed by AlGaN and the current blocking region is oxidized by AlGaN. The vertical resonance surface emitting laser diode according to claim 1, wherein the outer mirror layer has an outer diameter of about 5 μm. The vertical resonance surface emitting laser diode of claim 1, further comprising a buffer layer formed of GaN or AlN to facilitate crystal growth between the substrate and the lower mirror layer. Forming a lower mirror layer by alternately stacking a plurality of AlN layers and GaN layers on a substrate; Sequentially forming a first contact layer, an active layer, a current limiting layer, and a second contact layer on the lower mirror layer; Forming an upper mirror layer by repeatedly stacking an AlN layer and a GaN layer on the second contact layer in alternating manner; A portion of the upper surface of the second contact layer is exposed by etching from the upper mirror layer to a portion of the second contact layer, and a portion of the upper surface of the first contact layer is etched from the second contact layer to the upper surface of the first contact layer. Etching to expose a portion; The current blocking region is formed by oxidizing both regions except for the current passing region so that only the central portion of the current limiting layer is limited to the current passing region, and oxidizes the AlN layer constituting the upper mirror layer to form an AlN oxide layer. Forming an oxidation step; An electrode forming step of forming a first metal layer and a second metal layer to be used as electrodes in predetermined regions of the exposed portion of the upper surface of the first contact layer and the exposed portion of the upper surface of the second contact layer; Surface-emitting laser diode manufacturing method. The method of claim 5, The active layer is composed of InGaN, And the first contact layer and the second contact layer are made of GaN.

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