TWI459670B - Vertical cavity surface emitting laser and manufacturing method thereof - Google Patents

Description

Vertical cavity surface type laser and manufacturing method thereof

The present invention relates to a laser element, and more particularly to a vertical cavity surface-emitting laser and a method of fabricating the same.

The main feature of a vertical cavity surface-emitting laser (VCSEL) is that it can emit light substantially perpendicular to the upper surface of its wafer. VCSELs are typically formed by deposition methods such as chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) to form epitaxial stacks having a multilayer structure and fabricated through common semiconductor processes.

The epitaxial stack includes an active region that is a primary illuminating region, and two Bragg mirror (DBR) stacked layers that are respectively located above and below the active region. A laser cavity is formed between the stacked layers of the two Bragg mirrors, and the active region can generate light of a specific wavelength to be reflected back and forth therein to generate gain amplification. In order to obtain better optoelectronic characteristics, a current confinement aperture is formed in the upper Bragg mirror stack layer to limit the current flow path, thereby reducing the critical current and improving the photoelectric conversion efficiency.

Traditional methods for making current-limited vias include ion implantation and selective oxidation, and both have their own advantages and disadvantages. As shown in the first figure, a known VCSEL, which is selected to use both methods, is in the epitaxial stack 10 of the VCSEL. It not only has an ion implantation limitation zone 11, but also has an oxidation localization zone 12 below the ion implantation limitation zone 11. The ion implantation local area 11 and the oxidation locality area 12 respectively have a confined through hole 110, 120, and the two confined through holes 110, 120 have to be aligned in the vertical direction in order to obtain better current confinement characteristics and have better Good spectral characteristics.

However, although the above design can lower the high-order mode, it also produces high-impedance and modal instability, which is detrimental to the operation of high-speed components.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a vertical cavity surface-emitting laser and a method of fabricating the same that provide a stable low-mode laser beam and a low-impedance vertical cavity surface-emitting laser.

To achieve the above object, the vertical cavity surface-emitting laser of the present invention comprises a substrate and an epitaxial stack. An epitaxial layer is formed on the substrate and includes a ring-shaped zinc diffusion region, a ring-shaped ion implantation region under the zinc diffusion region, an annular oxidation region under the ion implantation region, and a An active region below the annular oxidation region, wherein the zinc diffusion region has a zinc diffusion via, the ion implantation region has an ion implantation via, and the oxidation region has an oxide via, and the zinc diffusion The through hole, the ion implantation through hole and the oxidation through hole are in communication with each other.

Moreover, the method for fabricating the vertical cavity surface-emitting laser of the present invention comprises the steps of: first providing a substrate; forming an epitaxial layer on the substrate; forming a first mask on the epitaxial layer. The first mask has an annular aperture; the epitaxial layer is ion implanted through the annular aperture to form a ring-shaped ion implantation region; and the epitaxial layer is formed through the annular aperture Zinc diffusion to form a ring of zinc diffusion Forming a second mask on the first mask to shield the annular aperture of the first mask; and etching the epitaxial layer through the first mask and the second mask, To form an island-like platform.

In addition, another method for fabricating a vertical cavity surface-emitting laser according to the present invention comprises the steps of: providing a substrate; forming an epitaxial layer on the substrate, and the epitaxial layer comprises a layer of high aluminum content Forming a first mask on the epitaxial layer, the first mask having an annular aperture; diffusing the epitaxial layer through the annular aperture to form a circular zinc diffusion region; Forming a second mask on the first mask to shield the annular aperture of the first mask; etching the epitaxial layer through the first mask and the second mask to form a An island-like platform; and oxidizing the high aluminum content layer to form an annular oxidation zone.

21‧‧‧Substrate

22‧‧‧Elevation stack

221‧‧‧First Bragg mirror

222‧‧‧ first partition

223‧‧‧ active layer

224‧‧‧Second separation layer

225‧‧‧second Bragg reflector

23‧‧‧First mask

231‧‧‧Circular

232‧‧‧Round Department

233‧‧‧ annular pores

24‧‧‧Circular ion implantation area

241‧‧‧Ion implanted through holes

25‧‧‧ second mask

26‧‧‧ island platform

261‧‧‧ side

27‧‧‧Oxidation zone

271‧‧‧Oxidation through hole

28‧‧‧First electrode

29‧‧‧second electrode

30‧‧‧Zinc oxide film

31‧‧‧ Coverage

32‧‧‧Zinc diffusion zone

321‧‧‧Zinc diffusion through hole

The first figure is a conventional vertical cavity surface-emitting laser; the second figure A is a side view of the vertical cavity surface-emitting laser of the present invention; and the second figure B is a vertical cavity surface-emitting laser of the present invention. FIG. 3 is a side view showing the steps of the method for fabricating a vertical cavity surface-emitting laser according to the present invention.

The technical content, detailed description, and efficacy of the present invention are described below with reference to the following drawings: As shown in FIG. 2A, a vertical cavity surface-emitting laser of the present invention mainly includes a substrate 21 and is formed on One of the epitaxial layers 22 on the substrate 21. The epitaxial layer 22 can be based on a compound semiconductor of an AlGaAs/GaAs system, but not limited thereto. In actual implementation, it may be a material system such as AlN/GaN/InGaN, and may be determined according to the wavelength of the desired laser. The wavelength is not limited and may be infrared light, visible light or ultraviolet light. The structure of the epitaxial layer 22 includes a first Bragg mirror 221, a first spacer layer 222, an active layer 223, and a second spacer layer formed on the substrate 21 from bottom to top. 224, and a second Bragg reflector 225. The first Bragg reflector 221 and the second Bragg mirror 225 each have a plurality of stacked film layers for reflecting light. The active layer 223 can also have multiple layers of stacked layers. Also, the stacked film layer of the second Bragg reflector 225 has a high aluminum content layer (not shown).

In addition, the epitaxial layer 22 further includes an annular zinc diffusion region 32, a ring-shaped ion implantation region 24 under the zinc diffusion region 32, and a ring-shaped oxidation under the ion implantation region 24. District 27. It is to be noted that the zinc diffusion region 32 has a zinc diffusion via 321 having an ion implantation via 241, and the oxidation region 27 has an oxidized via 271, and the zinc diffusion is The hole 321 and the ion implantation through hole 241 and the oxidation through hole 271 communicate with each other.

The modal control of the vertical cavity surface-emitting laser of the present invention is performed by the zinc diffusion through hole 321 communicating with the ion implantation through hole 241 and the oxidation through hole 271, so that the laser light can be emitted. The state is stable and reduces the existence of higher order modes. In addition, the zinc diffusion region 32 can further exhibit a Gaussian distribution or a ring-like distribution of the laser light field distribution, and helps to reduce the impedance of the vertical cavity surface-emitting laser itself. Preferably, when the axis of the zinc diffusion via 321 and the axis of the ion implantation via 241 are aligned with the axis of the oxidation via 271, the modal control and the impedance reduction effect can be maximized. good. In addition, as another embodiment shown in FIG. 24B, the structure is substantially the same as that of the second FIG. A, except that the second electrode is instead disposed on the substrate. On the lower surface of 21, the second electrode 33 shown in the second drawing B is formed.

In the method for fabricating a vertical cavity surface-emitting laser of the present invention, first, as shown in the third figure, a substrate 21 is provided, and an epitaxial layer 22 is formed on the substrate 21.

Next, a first mask 23 is formed on the epitaxial layer 22 by a semiconductor process. The first mask 23 is made of a tantalum nitride film through a lithography and etching process. In actual implementation, the material is not limited thereto. As shown in the fourth figure, the first mask 23 includes a circular portion 231 formed on the epitaxial layer 22, and a circular portion surrounding the circular portion 231 and concentric with the circular portion 231. 232, and an annular aperture 233 is defined between the circular portion 231 and the annular portion 232.

Then, as shown in FIG. 5, the epitaxial layer 22 is ion-implanted through the annular aperture 233 of the first mask 23 to form a ring-shaped ion implant in the second Bragg mirror 225. District 24. The annular ion implantation region 24 has an ion implantation through hole 241 whose center is aligned with the center of the first mask 23.

Then, the epitaxial layer 22 is further subjected to zinc diffusion through the annular aperture 233. As shown in FIG. 6, first, a zinc oxide covering the first mask 23 and the upper surface of the ion implantation region 24 is formed. The film 30 is then further formed with a cover layer 31 on the zinc oxide film 30 as shown in the seventh figure. Next, as shown in FIG. 8, the zinc oxide thin film 30 is heat-treated to diffuse the zinc component of the zinc oxide thin film 30 downward into the ion implantation region 24 to form a ring-shaped zinc diffusion region 32. Further, as shown in the ninth figure, the zinc oxide thin film 30 and the overcoat layer 31 above the zinc diffusion region 32 are removed.

Next, as shown in FIG. 10, a second mask 25 is formed on the first mask 23 by a semiconductor process to shield the annular aperture 233 of the first mask 23. The second mask 25 is made of a tantalum nitride film through a lithography and etching process. In actual implementation, The material is not limited by this. As shown in FIG. 11 , the second mask 25 is circular, and can cooperate with the annular aperture 233 of the first mask 23 to protect a partial area of the second Bragg mirror 225, that is, the second cover. The area covered by the cover 25. In actual production, it should be noted that the edge of the second mask 25 completely falls on the annular portion 232 of the first mask 23 to at least completely cover the circular portion 231 and the annular aperture 233. And must not exceed the annular portion 232.

The width W of the annular portion 232 takes into account the minimum stacking error that can be achieved with the semiconductor process equipment used. As shown in the twelfth figure, when the stacking error of the semiconductor processing apparatus causes the center of the second mask 25 to be out of alignment with the center of the first mask 23, the edge of the second mask 25 can still completely fall. On the annular portion 232 of the first mask 23, that is, by controlling the width W of the annular portion 232, the stacking error of the semiconductor process equipment is absorbed. Therefore, if the minimum stacking error of the semiconductor processing device actually used is large, it is conceivable to widen the width W of the annular portion 232 so that the edge of the second mask 25 falls on the first mask 23 On the ring portion 232.

Then, as shown in FIG. 13, the epitaxial layer 22 is etched through the first mask 23 and the second mask 25, and etched down to the first Bragg mirror 221 to form an island. Form platform 26. Since the edge of the second mask 25 completely falls on the annular portion 232 of the first mask 23, the edge of the etched island-like platform 26 is actually controlled by the edge of the annular portion 232, that is, It is said that the edge of the island platform 26 is aligned with the edge of the first mask 23, and the center of the island platform 26 is actually aligned with the center of the first mask 23, and is also aligned with the ion implanted through hole. Center of 241.

Next, as shown in FIG. 14, the high aluminum content layer of the second Bragg reflector 225 is oxidized to form a bit between the ion implantation region 24 and the active region 223. The annular oxidized region 27 has an oxidized via 271. Since the oxidation is performed uniformly inwardly from the side 261 of the island-like platform 26, the center of the formed oxidized through-hole 271 is aligned with the center of the island-like platform 26 and also aligned with the center of the ion-implanted through-hole 241. Thereby, the element guiding effect of the oxidation zone 27 can be reduced, and the current can be concentrated to increase the gain guiding effect to improve the spectral characteristics.

Finally, the first mask 23 and the second mask 25 are removed. Further, as shown in FIG. A, a first electrode 28 is formed on the second Bragg mirror 225, and a second electrode 29 is formed on the first Bragg mirror 221 by a metal thin film deposition process. Alternatively, as shown in FIG. 24B, the second electrode 33 may be formed on the lower surface of the substrate 21. Thus, the fabrication of the vertical cavity surface-emitting laser of the present invention is completed.

It should be noted that, in the above method for fabricating the vertical cavity surface-emitting laser of the present invention, the ion implantation region 24, the zinc diffusion region 32, and the oxidation region 27 are formed. However, in actual implementation, only Both the ion implantation zone 24, the zinc diffusion zone 32, or both the zinc diffusion zone 32 and the oxidation zone 27 are performed.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Equivalent changes and modifications made by the scope of the present invention remain within the scope of the present invention.

21‧‧‧Substrate

22‧‧‧Elevation stack

221‧‧‧First Bragg mirror

222‧‧‧ first partition

223‧‧‧ active layer

224‧‧‧Second separation layer

225‧‧‧second Bragg reflector

24‧‧‧Circular ion implantation area

241‧‧‧Ion implanted through holes

26‧‧‧ island platform

261‧‧‧ side

27‧‧‧Oxidation zone

271‧‧‧Oxidation through hole

28‧‧‧First electrode

29‧‧‧second electrode

32‧‧‧Zinc diffusion zone

321‧‧‧Zinc diffusion through hole

Claims (9)

A vertical cavity surface-emitting laser comprising: a substrate; and an epitaxial layer formed on the substrate, the epitaxial layer comprising a ring-shaped zinc diffusion region and a ring under the zinc diffusion region An ion implantation site, an annular oxidation zone located below the ion implantation zone, and an active zone below the annular oxidation zone; wherein the zinc diffusion zone has a zinc diffusion via, the ion implantation zone An ion implantation through hole, and the oxidation region has an oxidation through hole, and the zinc diffusion through hole and the ion implantation through hole communicate with the oxidation through hole; wherein the axis of the zinc diffusion through hole, The axis of the ion implantation through hole is aligned with the axis of the oxidation via; wherein a first mask is formed on the epitaxial layer when the vertical cavity surface type laser is fabricated. a mask includes a circular portion formed on the epitaxial layer and an annular portion surrounding the circular portion and concentric with the circular portion, and a defined portion between the circular portion and the annular portion An annular aperture; subsequently forming a second mask on the first mask, through the first The cover and mask etching the second epitaxial stack, and that the second mask to cover at least one complete addition of the circular portion and the annular aperture, and not exceed the annular portion. The vertical cavity surface-emitting type laser according to claim 1, wherein the epitaxial layer stack includes a first Bragg mirror on one side of the active region, and one bit on the other side of the active region. The second Bragg mirror. A method for fabricating a vertical cavity surface-emitting laser includes the following steps: (A) providing a substrate; (B) forming an epitaxial layer on the substrate; (C) forming a first mask on the epitaxial layer, the first mask being included in the epitaxial layer Forming a circular portion and a circular portion surrounding the circular portion and concentric with the circular portion, and an annular aperture is defined between the circular portion and the annular portion; (D) through the ring The epitaxial layer is ion implanted to form a ring-shaped ion implantation region; (E) the epitaxial layer is zinc diffused through the annular hole to form a ring-shaped zinc diffusion region; (F) forming a second mask on the first mask, thereby shielding the circular portion and the annular aperture of the first mask from being beyond the annular portion; and (G) transmitting the first A mask and the second mask etch the epitaxial stack to form an island-like platform. The method for fabricating a vertical cavity surface-emitting laser according to claim 3, wherein the forming the epitaxial layer comprises forming a first Bragg mirror, a second Bragg mirror, and a bit An active region between the first Bragg mirror and the second Bragg mirror. The method for fabricating a vertical cavity surface-emitting laser according to claim 3, wherein the epitaxial layer comprises a high aluminum content layer, and further comprising the high aluminum after the island platform is formed. The content layer is oxidized to form an annular oxidation zone. The method of fabricating a vertical cavity surface-emitting laser according to claim 5, wherein the high aluminum content layer belongs to the second Bragg mirror. A method for fabricating a vertical cavity surface-emitting laser includes the steps of: (A) providing a substrate; (B) forming an epitaxial layer on the substrate, and the epitaxial layer comprises a high aluminum content Forming a first mask on the epitaxial layer, the first mask comprising forming a circular portion on the epitaxial layer and surrounding the circular portion and the circle a concentric annular portion, and an annular aperture is defined between the circular portion and the annular portion; (D) the epitaxial laminate is zinc diffused through the annular aperture to form a ring-shaped zinc a diffusion region; (E) forming a second mask on the first mask, thereby shielding the circular portion and the annular aperture of the first mask, and not beyond the annular portion; (F) The first mask and the second mask etch the epitaxial stack to form an island-like platform; and (G) oxidize the high aluminum content layer to form an annular oxidized region. The method for fabricating a vertical cavity surface-emitting laser according to claim 7, wherein the forming the epitaxial layer comprises forming a first Bragg mirror, a second Bragg mirror, and a bit An active region between the first Bragg mirror and the second Bragg mirror. The method of fabricating a vertical cavity surface-emitting laser according to claim 8, wherein the high aluminum content layer belongs to the second Bragg mirror.