KR100340037B1 - A InAlGaAs vertical-cavity surface-emitting laser having improved current confinement scheme and fabrication method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor manufacturing technology, and more particularly, to a structure and method of fabricating an InAlGaAs-based vertical resonant surface light laser having an improved current confinement structure. The present invention has no problem of rapidly increasing resistance as the current injection diameter decreases, and can realize a low threshold current, and can be applied to a 1.3-1.55 μm long wavelength vertical resonant surface light laser composed of InAlGaAs, InAlAs, and InP. The purpose of the present invention is to provide an InAlGaAs-based vertical resonant surface light laser and a method of manufacturing the same, which can be applied to mass production of an actual device because the fabrication process is simple and stable. The present invention relates to an InAlGaAs-based vertical resonant surface light laser having a lower structure including a lower mirror layer and a laser pillar including a current confinement layer and an upper mirror layer provided thereon. An InP layer is disposed, and a second InP layer is disposed below the upper mirror layer of the laser pillar, and the diameter of the current confinement layer disposed between the first and second InP layers is smaller than the diameter of the laser pillar. It is characterized by being provided.

Description

Indium-Aluminum-Gallium-Acenic vertical resonant surface light laser with improved current confinement structure and its manufacturing method {A InAlGaAs vertical-cavity surface-emitting laser having improved current confinement scheme and fabrication method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor manufacturing technology, and more particularly, to a structure and method of fabricating an InAlGaAs-based vertical resonant surface light laser having an improved current confinement structure.

Vertical resonant surface light lasers are more suitable for mass production than edge emitting lasers because of their geometrical structure, and thus, the production cost is low. In particular, the vertical surface optical laser having a wavelength of 1.3 to 1.55 µm is attracting attention as a major element of the next generation optical communication network because its communication distance can be extended to several kilometers compared to hundreds of meters of the 850 nm laser. A structure in which InAlGaAs / InAlAs is grown on InP as one of the long-wavelength vertical resonant surface light lasers has been attempted, and recent reports of continuous room temperature oscillation have continued. Boucart, et al, 'Metamorphic DBR and Tunnel-Junction Injection: A CW RT Monolithic Long-Wavelength VCSEL', IEEE Journal of Selected Topics in Quantum Electronics, Vol. 5, No. 3, p520-529 (1999).

One of the important structures in the fabrication of vertical resonant surface-light lasers, the current confinement scheme, regulates the laser gain area by supplying charge carriers to a certain area of active medium. It is responsible for causing laser oscillation. Conventional vertical surface lasers use etched pillar, oxidation and air gap techniques for this purpose, but most of them are based on AlGaAs material, which is the same wavelength as InAlGaAs / InAlAs. It is difficult to apply to surface light lasers.

Since the laser pillar can be easily manufactured by dry ion etching, it is currently used for fabricating long wavelength vertical resonant surface light lasers [J. K. Kim, E. Hall, O. Sjolund, G. Almuneau and LA Coldren, 'Room-temperature, electrically-pumped multiple-active-region VCSELs with high differential efficeiency at 1.55 μm' Vol. 35, No. 13, p1084 -1085 (1999)]. However, as the diameter of the pillar decreases, the critical current decreases, but the resistance increases in proportion to the square of the diameter, which deteriorates overall device characteristics. In addition, etching through the active medium results in surface recombination at the surface, reducing laser efficiency with current loss.

In addition, the oxidation method is difficult to realize because the AlAs layer cannot be used in a very efficient current confinement structure or a long wavelength, and even though InAlAs is used, the oxidation rate is very slow and uneven compared to AlAs.

Finally, the air gap technique utilizes the selective chemical etching properties between the AlAs layer and GaAs, placing the AlAs layer directly above the active medium and removing it, except for small diameters, using HCl solution. This method also shows characteristics comparable to the oxidation method, but since AlAs is not grown on InP substrates, it cannot be used either. On the other hand, there is a similar method to include InP in the epi layer and selectively etch. In general, however, InAlGaAs / InAlAs contains Al, which oxidizes well and corrodes well with acid. Therefore, it is difficult to find a selective etching solution having a relatively small thickness and capable of etching a long distance in the horizontal direction.

On the other hand, the long-wavelength vertical resonant surface light laser has a characteristic that the device performance deteriorates rapidly with the increase of temperature due to the small band gap inherent in the material, and thus requires an efficient heat dissipation structure to solve this problem.

The present invention proposed to solve the problems of the prior art as described above, there is no problem that the resistance is rapidly increased as the current injection diameter is reduced, InAlGaAs-based vertical resonant surface light laser that can realize a low threshold current and its manufacture The purpose is to provide a method.

In addition, the present invention can be applied to a 1.3 ~ 1.55 ㎛ long wavelength vertical resonant surface light laser consisting of InAlGaAs, InAlAs, InP, the manufacturing process is simple and stable, InAlGaAs-based vertical resonant surface light that can be applied to the production of the actual device It is an object of the present invention to provide a laser and a method of manufacturing the same.

In addition, an object of the present invention is to provide an InAlGaAs-based vertical resonant surface light laser and a method of manufacturing the same that can increase heat emission efficiency.

1A is a cross-sectional view of an InAlGaAs-based vertical resonant surface light laser according to an embodiment of the present invention.

1B is a cross-sectional view of an InAlGaAs-based vertical resonant surface light laser according to another embodiment of the present invention.

Figures 2a to 2d is an exemplary process for manufacturing the InAlGaAs-based vertical resonant surface light laser of Figure 1a.

* Explanation of symbols for the main parts of the drawings

10: InAlGaAs / InAlAs bottom reflective mirror layer

11: active medium and cladding layer

12a: First InP Wet Etch Mask Layer

12b: second InP wet etching mask layer

13: InAlGaAs / InAlAs current confinement layer

14: InP Insulation Layer

15: InAlGaAs / InAlAs upper reflective mirror layer

16: electrode

In order to achieve the above technical problem, the present invention provides an InAlGaAs-based vertical resonant surface light laser including a lower structure including a lower mirror layer, and a laser pillar including a current confinement layer and an upper mirror layer provided thereon. The first InP layer may be disposed on an uppermost portion of the lower structure, and a second InP layer may be disposed below the upper mirror layer of the laser pillar, and the current confinement layer may be disposed between the first and second InP layers. It is characterized in that the diameter is provided smaller than the diameter of the laser pillar.

Preferably, the laser pillar includes an air gap between the first and second InP layers where the current confinement layer is not disposed.

Preferably, the laser pillar includes an InP insulating layer between the first and second InP layers on which the current confinement layer is not disposed.

Preferably, the substructure comprises a stacked structure of the lower mirror layer, the active medium and the cladding layer, and the first InP layer, and the current confinement layer is formed of InAlGaAs / InAlAs.

Preferably, the substructure has a laminated structure of the lower mirror layer and the first InP layer, and the current confinement layer includes an active medium therein.

In addition, the InAlGaAs-based vertical resonant surface light laser manufacturing method of the present invention includes a lower reflection mirror layer, an active medium and a cladding layer, a first InP wet etching mask layer, an InAlGaAs / InAlAs current confinement layer, and a second InP wet type on an InP substrate. A first step of sequentially forming an etching mask layer and an upper reflection mirror layer; Etching at least the upper reflective mirror layer and the second InP wet etch mask layer to form a laser pillar structure; Forming a etching mask layer covering at least sidewalls of the laser pillar structure; And performing a fourth wet etching of the InAlGaAs / InAlAs current confinement layer in a horizontal direction to form an air gap between the first and second InP wet etching mask layers.

In addition, the InAlGaAs-based vertical resonant surface light laser manufacturing method of the present invention includes an InAlGaAs / InAlAs current confinement layer including a lower reflection mirror layer, a first InP wet etching mask layer, and an active medium layer on an InP substrate. A first step of sequentially forming an etching mask layer and an upper reflection mirror layer; Etching at least the InAlGaAs / InAlAs upper reflective mirror layer and the second InP wet etch mask layer to form a laser pillar structure; Forming a etching mask layer covering at least sidewalls of the laser pillar structure; And a fourth step of forming an air gap between the first and second InP wet etching mask layers by partially wet etching the InAlGaAs / InAlAs current confinement layer including the active medium layer in a horizontal direction.

In another aspect, the present invention further comprises a fifth step of filling the InP insulating layer that is undoped or semi-conducting in the air gap.

Preferably, the wet etching is performed using an etching solution comprising H ₃ PO ₄ or H ₂ SO ₄ .

Hereinafter, preferred embodiments of the present invention will be introduced in order to enable those skilled in the art to more easily carry out the present invention.

1A is a cross-sectional view of an InAlGaAs-based vertical resonant surface light laser according to an embodiment of the present invention, which will be described with reference to the following.

According to this embodiment, an InAlGaAs / InAlAs bottom reflective mirror layer 10 and an active medium and cladding layer (eg, InAlGaAs) 11, a first InP wet etch mask layer on an InP substrate (not shown) (12a) is laminated, and the InAlGaAs / InAlAs current confinement layer 13 is disposed at the center portion thereof. The InP insulating layer 14 is disposed in a form surrounding the InAlGaAs / InAlAs current confinement layer 13 on the first InP wet etching mask layer 12a. In addition, the second InP wet etching mask layer 12b, the InAlGaAs / InAlAs upper reflective mirror layer 15, and the electrode 16 are stacked thereon. The upper and lower reflective mirror layers 15 and 10 are made of InAlGaAs / InAlAs as a distributed Bragg reflector.

Among them, the first and second InP wet etching mask layers 12a and 12b are layers used to form the InAlGaAs / InAlAs current confinement layer 13, and the InP insulation surrounding the InAlGaAs / InAlAs current confinement layer 13. The layer 14 serves to increase the heat dissipation effect at the same time as the undoped or semi-conductor to obtain an electrical insulation effect. If the heat dissipation effect is not largely considered, the InP insulating layer 14 can be replaced with an air gap. InP has a higher heat transfer coefficient than InAlGaAs or InAlAs to effectively release heat generated.

The InP insulating layer 14 or the air gap acts as an insulating layer so that the current injected through the electrode 16 reduces the current passing diameter in the InAlGaAs / InAlAs current confinement layer 13. This has the effect of current confinement in the vertically resonant surface light laser to supply charge carriers only below the reduced current injection diameter to control the optical gain area in the laser active medium and cladding layer 11. This current confinement structure provides a small amount of current to the active medium and the cladding layer 11 compared to the area of the electrode 16, and avoids a sudden increase in resistance that may occur when the diameter of the entire laser pillar itself is reduced. Current injection of diameters can be obtained. In addition, this reduction in current injection diameter leads to various performance improvements of vertical resonant surface light lasers, including critical current reduction [Eric R. Hegblom, Doctoral dissertation, 'Engineering Oxide Apertures in Vertical Cavity Lasers', University of California at Santa Barbara, 1999].

In addition, when the InAlGaAs / InAlAs current confinement layer 13 is disposed directly on the laser active medium, there is no surface coupling, thereby reducing the critical current without carrier loss.

1B is a cross-sectional view of an InAlGaAs-based vertical resonant surface light laser according to another embodiment of the present invention. In FIG. 1A, except for the active medium and the cladding layer 11, the InAlGaAs / InAlAs current confinement layer ( In place of 13), an InAlGaAs / InAlAs current confinement layer 17 including an active medium (eg, InGaAs) 18 is used to simultaneously perform the role of the current confinement layer 17 generating optical gain. Such a structure has a disadvantage in that there is a loss due to carrier bonding on the surface, compared to the structure shown in FIG. 1A, but there is an advantage in that the process is easier. On the other hand, in long wavelengths, it is known that surface loss due to carrier bonding is reduced.

Basically, the current confinement structure proposed by the present invention may be applied at any position of the laser epitaxial layer, but considering the current spreading, the closer to the laser active medium, the better.

2A to 2D illustrate a process for manufacturing the vertical resonant surface light laser of FIG. 1A, which will be described below with reference to the drawing.

According to the present embodiment, first, an InAlGaAs / InAlAs bottom reflective mirror layer 20, an active medium and a cladding layer (e.g., InAlGaAs) 21, first on an InP substrate (not shown) as shown in FIG. 2A InP wet etch mask layer 22a, InAlGaAs / InAlAs current confinement layer 23, second InP wet etch mask layer 22b, and InAlGaAs / InAlAs upper reflective mirror layer 24 are grown in turn, and dry or wet etching is performed. Through the laser pillar structure. At this time, the etching is stopped in the InAlGaAs / InAlAs current confinement layer 23 using a method such as laser monitoring or time control. InAlGaAs / InAlAs and InP constituting the current confinement structure can be grown on InP substrates under lattice matching conditions.

Next, as shown in FIG. 2B, a mask pattern 25 is formed to protect the side surface of the laser pillar structure from the etching solution. For example, a mask pattern 25 covering the laser pillar structure may be obtained by using photoresist and photolithography, or performing chemical vapor deposition (CVD) on SiN _x , SiO ₂ , or the like, followed by lithography and dry etching. The mask pattern 25 may be manufactured in various ways, such as a lift-off method, but it is important to protect the side surface of the laser pillar structure from the etching solution.

Subsequently, the InAlGaAs / InAlAs current confinement layer using a selective etching solution (InAlGaAs / InAlAs shows a very fast etching rate compared to InP in an acid solution such as H ₃ PO ₄ or H ₂ SO ₄₎ , as shown in FIG. 2C. By etching 23 in the horizontal direction, the current confinement structure is defined, and the air gap 26 is formed. Here, as the etching solution, a solution obtained by diluting H ₃ PO ₄ or H ₂ SO ₄ to H ₂ O ₂ , H ₂ O, or the like is used.

Subsequently, as shown in FIG. 2D, the InP insulating layer 27 is grown by using the crystal regrowth method or the mass transport method to fill the air gap 26. At this time, the InP insulating layer 27 is not grown on the InAlGaAs / InAlAs upper reflective mirror layer 24 by using SiN _x .

Thereafter, an electrode (not shown) is formed on the InAlGaAs / InAlAs upper reflective mirror layer 24.

Through the above process, it is possible to form a current confinement structure that enters inwardly than the outer diameter of the laser pillar, thereby obtaining a structure in which the current injection diameter is reduced while suppressing an increase in resistance. Meanwhile, the InP insulating layer 27 increases the heat dissipation effect due to the relatively high thermal conductivity of InP while maintaining the current confinement structure as described above.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

For example, in the above-described embodiment, the case where the active medium is formed of InGaAs or the like has been described as an example. However, the present invention can be applied to the case where other materials are used as the active medium.

The present invention described above can be expected to reduce the critical current of the vertical resonant surface light laser according to the current injection diameter decrease and thereby the heat generation. In addition, the present invention can significantly reduce the contact resistance of the electrode compared to the conventional etch column method, and especially when the current confinement structure is placed below or above the active medium, there is no surface bond also carrier loss used for laser oscillation Also no. This advantage leads to a more pronounced performance difference compared to the conventional etch pillar method, for example, with smaller current confinement diameters, for example within a few micrometers. In the long wavelength vertical resonant surface light laser, the degradation of performance is inevitable due to temperature increase due to auger coupling or intraband absorption. Therefore, it is important to suppress heat generation by reducing the operating current. Presents the solution. In particular, when the current confinement structure is surrounded by InP, it has an effect of further increasing the efficiency of transferring the generated heat to the heat sink.

Claims (9)

An InAlGaAs-based vertical resonant surface light laser having a lower structure including a lower mirror layer and a laser pillar including a current confinement layer and an upper mirror layer provided thereon, A first InP layer is disposed on an uppermost portion of the lower structure, and a second InP layer is disposed below the upper mirror layer of the laser pillar, and a diameter of the current confinement layer disposed between the first and second InP layers is InAlGaAs-based vertical resonant surface light laser, characterized in that provided smaller than the diameter of the laser column. The method of claim 1, And the laser pillar includes an air gap between the first and second InP layers on which the current confinement layer is not disposed. The method of claim 1, The laser pillar is an InAlGaAs-based vertical resonant surface light laser, characterized in that it comprises an InP insulating layer between the first and second InP layer is not disposed the current confinement layer. The method according to claim 2 or 3, The lower structure is made of a laminated structure of the lower mirror layer, the active medium and cladding layer, the first InP layer, the current confinement layer is InAlGaAs-based vertical resonant surface light laser, characterized in that made of. The method according to claim 2 or 3, The lower structure is formed of a laminated structure of the lower mirror layer and the first InP layer, wherein the current confinement layer includes an active medium therein, InAlGaAs-based vertical resonant surface light laser. A first step of sequentially forming a lower reflective mirror layer, an active medium and cladding layer, a first InP wet etch mask layer, an InAlGaAs / InAlAs current confinement layer, a second InP wet etch mask layer, and an upper reflective mirror layer over the InP substrate; Etching at least the upper reflective mirror layer and the second InP wet etch mask layer to form a laser pillar structure; Forming a etching mask layer covering at least sidewalls of the laser pillar structure; And A fourth step of forming an air gap between the first and second InP wet etching mask layers by partially wet etching the InAlGaAs / InAlAs current confinement layer in a horizontal direction InAlGaAs-based vertical resonant surface light laser manufacturing method comprising a. A first step of sequentially forming a lower reflective mirror layer, a first InP wet etch mask layer, an InAlGaAs / InAlAs current confinement layer including an active medium layer, a second InP wet etch mask layer, and an upper reflective mirror layer on an InP substrate; Etching at least the InAlGaAs / InAlAs upper reflective mirror layer and the second InP wet etch mask layer to form a laser pillar structure; Forming a etching mask layer covering at least sidewalls of the laser pillar structure; And A fourth step of forming an air gap between the first and second InP wet etching mask layers by partially wet etching the InAlGaAs / InAlAs current confinement layer including the active medium layer in a horizontal direction InAlGaAs-based vertical resonant surface light laser manufacturing method comprising a. The method according to claim 6 or 7, And a fifth step of filling the air gap between the doped or semi-conducting InP insulating layer. The method according to claim 6 or 7, The wet etching method of manufacturing an InAlGaAs-based vertical resonant surface light laser, characterized in that performed using an etching solution containing H ₃ PO ₄ or H ₂ SO ₄ .