JP2005050990A - Surface emitting laser, wavelength filter and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface emitting laser, a wavelength filter by which the yield of manufacturing the surface emitting laser and the wavelength filter can be improved, by relaxing a limit of run-to-run variance and variance in a wafer face when epitaxially growing the layer thickness of layers constituting a surface emitting laser provided with a DBR (distributed Bragg reflector) mirror consisting of an air gap and a semiconductor and a wavelength filter, and a method of manufacturing them. <P>SOLUTION: The surface emitting laser is provided with reflection mirrors 2 and 4 wherein air gaps 2A<SB>1</SB>, 2C<SB>1</SB>and 4A<SB>1</SB>and semiconductors 2B and 4B. In addition, it is provided with semiconductor layers 3B<SB>2</SB>and 3C<SB>2</SB>for adjusting resonance wavelength on the side of at least one air gap of the semiconductor layers forming a cavity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface emitting laser for wavelength division multiplexing transmission, a wavelength filter, and a method for manufacturing the same.

  An optical pump type 1.55 μm surface emitting laser having a distributed Bragg reflector (DBR) mirror composed of an air gap and InP pair above and below the active layer has been reported by N. Chitica et al. (Non-Patent Document 1). Cross sections of this laser are shown in FIGS. 9 is an enlarged view of a broken line portion N in FIG. The epitaxial growth layer is formed on the InP substrate 101 by a single growth. The DBR mirror 102 on the substrate 101 side is composed of an InGaAs layer 102A and four pairs of InP / InGaAs from the substrate 101 side. One pair is composed of an InP layer 102B and an InGaAs layer 102C.

The InGaAs layers 102A and 102C under the laser oscillation part are partly removed by wet etching when the air gaps 102A ₁ and 102C ₁ are formed. The thicknesses of the InGaAs layer 102A and the pair of InGaAs layers 102C are ¼ of the oscillation wavelength (λ ₀ ) in air. The thickness of each pair of InP layers 102B is 3/4 of the oscillation wavelength (λ) in InP.

  The cavity 103, which is a laser active layer, has a configuration in which three active layers 103A of 1.55 μm wavelength multiple quantum wells (thickness: λ / 2) are stacked, and spacer layers 103B and 103C are arranged above and below them. . These spacer layers 103B and 103C are made of InP and have a layer thickness of λ / 4.

On the cavity portion 103, a DBR mirror portion 104 on the front side is disposed. The DBR mirror unit 104 is composed of four pairs of InGaAs / InP, and the layer thickness is the same as that of the DBR mirror unit 102 on the substrate 101 side. One pair consists of the InGaAs layer 104A and the InP layer 104B, the InGaAs layer 104A, the air gap 104A ₁ are formed. All the epitaxial growth layers are non-doped.

In order to oscillate a surface emitting laser having such a configuration, the resonance wavelength of the DBR mirror must be within the width of the gain spectrum of the laser active layer. The width of the gain spectrum is as narrow as about 15 nm when an active layer of multiple quantum wells is used. For this reason, in order for the resonance wavelength of the DBR mirror to fall within this range, the air gap constituting the DBR mirror and the layer thickness of InP must be controlled within a variation accuracy within about ± 0.5% (non- Patent Document 2).
Appl. Phys. Lett. Vol.78, No.25, 18 June 2001, pp.3935-3937 (Title: Room-temperature operation of photopumped monolithic InP vertical-cavity laser with two air-gap Bragg reflector) CJ Chang-Hasnain, “Tunable VCSEL”, IEEE j. Select, Topics Quantum Electron., Vol.6, pp.978-987, 2000.

  The surface emitting laser described above has the following problems. In order for this surface emitting laser to oscillate, it is necessary to control the air gap constituting the DBR mirror and the layer thickness of InP within a variation accuracy of about ± 0.5%. For this reason, there has been a problem that surface-emitting lasers that oscillate lasers cannot be manufactured with high yield due to severe restrictions on run-to-run variations in layer thickness and in-plane variations in the wafer during epitaxial growth.

  In order to realize a filter having a specific wavelength, it is necessary to adjust the resonance wavelength of the DBR mirror to the specific wavelength, and there is a problem similar to that of the surface emitting laser.

  The present invention solves the above-described problems, and includes a surface-emitting laser having a DBR mirror composed of a pair of an air gap and a semiconductor, and run-to-run variation in epitaxial growth of layer thicknesses of layers constituting a wavelength filter, a wafer It is an object of the present invention to provide a surface emitting laser, a wavelength filter, and a method for manufacturing the surface emitting laser, which can alleviate restrictions on the in-plane variation and improve the production yield of the surface emitting laser and the wavelength filter.

In order to solve the above-mentioned problem, the invention according to claim 1 is a surface emitting laser having a reflecting mirror in which an air gap and a semiconductor are alternately laminated, and is resonant with at least one air gap side of a semiconductor layer constituting a cavity. A surface-emitting laser comprising a semiconductor layer for wavelength adjustment.
According to a second aspect of the present invention, in the surface emitting laser according to the first aspect, the semiconductor material for adjusting the resonance wavelength is made of a material having selective etching property with respect to the semiconductor material constituting the reflector and the spacer layer. It is characterized by that.
According to a third aspect of the present invention, there is provided a surface emitting laser having a reflecting mirror in which an air gap and a semiconductor are alternately laminated, and a semiconductor layer for adjusting a resonant wavelength on at least one air gap side of a semiconductor layer constituting a cavity. In this manufacturing method, after the air gap processing, the resonant wavelength is changed by changing the layer thickness of the semiconductor layer for adjusting the resonant wavelength by etching.
According to a fourth aspect of the present invention, in the wavelength filter having a reflecting mirror in which air gaps and semiconductors are alternately stacked, a semiconductor layer for adjusting a resonance wavelength is provided on at least one air gap side of the semiconductor layer constituting the cavity. Is a wavelength filter characterized by
According to a fifth aspect of the present invention, in the wavelength filter according to the fourth aspect of the present invention, the semiconductor material for adjusting the resonance wavelength is configured to have a selective etching property with respect to the semiconductor material constituting the reflector and the spacer layer. It is characterized by that.
A sixth aspect of the invention is a wavelength filter having a reflecting mirror in which an air gap and a semiconductor are alternately stacked, and a semiconductor layer for adjusting a resonance wavelength on at least one air gap side of a semiconductor layer constituting a cavity. A method for manufacturing a wavelength filter according to a manufacturing method, wherein after the air gap is processed, the resonance wavelength is changed by changing the thickness of the semiconductor layer for adjusting the resonance wavelength by etching.

  According to the present invention, after adjusting the thickness of the semiconductor layer for adjusting the resonance wavelength, which is the adjustment layer, by etching after the air gap processing, the resonance wavelength is changed. Therefore, the DBR configured by a pair of the air gap and the semiconductor layer. The restriction on the control of the epitaxial layer thickness of the mirror can be relaxed, and the surface emitting laser and the wavelength filter can be manufactured with good yield.

  According to the present invention, the following effects can be achieved. That is, in the past, the run-to-run variation of the epitaxial layer thickness was required to be within ± 0.5%, but according to the present invention, the run-to-run variation was reduced to within ± 2%. There is an advantage of improving the yield of manufacturing the surface emitting laser and the wavelength filter.

Next, an embodiment of the present invention will be described.
[Embodiment 1]
An optical pump type surface emitting laser according to this embodiment is shown in FIGS. 1 is a cross-sectional view showing a surface emitting laser, and FIG. 2 is a cross-sectional view showing a II cross section of FIG. FIG. 3 is an enlarged view in which a broken line portion A in FIG. 1 is enlarged. An epitaxial growth layer is formed on the n-InP substrate 1 by a single growth. The DBR mirror section 2 on the substrate 1 side is composed of an InGaAs layer 2A and three pairs of InP / InGaAs from the substrate 2 side. One pair is composed of an InP layer 2B and an InGaAs layer 2C.

The InGaAs layers 2A and 2C are sacrificial layers when the air gaps 2A ₁ and 2C ₁ are formed. That is, the InGaAs layers 2A and 2C are layers from which a part is removed in order to form the air gaps 2A ₁ and 2C ₁ . InGaAs layer 2A, 2C thickness of a thickness that is 1/4 odd multiple of the oscillation wavelength (lambda ₀₎ in the air, here, and a thickness of λ _0/4. The thickness of the InP layer 2B is a thickness that is an odd multiple of ¼ of the oscillation wavelength (λ) in InP, and here it is 3λ / 4. A cavity portion 3 is formed on the InGaAs layer 2C.

The cavity portion 3 has a configuration in which three active layers 3A of 1.55 μm wavelength multiple quantum wells (thickness: λ / 2) are stacked, and spacer layers 3B and 3C are arranged above and below. These spacer layers 3B and 3C are composed of InP layers 3B ₁ and 3C ₁ and InGaAsP layers 3B ₂ and 3C ₂ having a composition very similar to InP. The total thickness of these two layers was λ / 4. The InGaAsP layers 3B ₂ and 3C ₂ have a thickness of several tens of nm or less. InGaAsP layers 3B ₂ and 3C ₂ are hardly etched when etching the InGaAs layers 2A and 2C, which are sacrificial layers. These InGaAsAs layers 3B ₂ and 3C ₂ are resonance wavelength adjustment layers for adjusting the resonance wavelength.

On the cavity part 3, a DBR mirror part 4 on the surface side is arranged. The DBR mirror unit 4 is composed of three pairs of InGaAs / InP. One pair is composed of an InGaAs layer 4A and an InP layer 4B. Further, in the InGaAs layer 4A, the air gap 4A ₁ is formed. The layer thickness of the InGaAs layer 4A and the InP layer 4B is the same as that of the DBR mirror section 2 on the substrate side. Furthermore, all of the epitaxial growth layers are non-doped. The above-described layer thickness does not use the InGaAsP resonance wavelength adjustment layer, and the range of the layer thickness variation for causing laser oscillation needs to be within ± 0.5%.

In the surface emitting laser having the above structure, the resonance wavelength is adjusted as follows. InGaAs layer 2A, 2C, the 4A, after forming the air gap _{2A 1, 2C 1, 4A 1} , by the InGaAsP layer _3B 2, 3C ₂ is the resonant wavelength adjustment layer of InGaAsP is etched, the resonant wavelength of the DBR mirror Consider the case of changing.

It is assumed that the thickness of the resonance wavelength adjusting layer of InGaAsP is 20 nm and the thickness of each epitaxial layer is increased by 4%. According to the calculation, the resonance wavelength is 1.612 μm. FIG. 4 shows changes in the resonance wavelength when the InGaAsP layers 3B ₂ and 3C ₂ for adjusting the resonance wavelength are etched. When the InGaAsP layers 3B ₂ and 3C ₂ having a thickness of 20 nm are completely removed, the resonance wavelength becomes 1.554 μm, and the gain spectrum of the 1.55 μm active layer 3A overlaps, thereby enabling laser oscillation. In consideration of these, when the growth thickness of the epitaxial layer is set to 2% larger than the thickness when the above-described resonance wavelength adjustment layer is not used, and when adjusting the resonance wavelength by etching of InGaAsP, each layer The thickness variation is allowed up to ± 2%. That is, the layer thickness deviation is relaxed four times or more. Thus, by using the resonance wavelength adjustment layer of InGaAsP, it is possible to increase the range of allowable variation in layer thickness.

As a laser manufacturing process after epitaxial layer growth, first, a mesa having a width of several tens of μm and a length of about 100 μm is formed by etching. Thereafter, air gap processing is performed using the SiN film formed by plasma CVD as a mask. FIG. 2 is a sectional view after processing. InGaAs in the sacrificial layer was removed using a mixture of FeCl ₃ and water to form air gaps 2A ₁ , 2C ₁ , 4A ₁ . At this stage, the resonance wavelength of the DBR mirror is measured, the deviation from the active layer wavelength is grasped, and the etching thickness of the resonance wavelength adjusting layer of InGaAsP is determined by calculation.

  Next, the InP layer constituting the DBR mirror and the spacer layer is hardly etched, but the InGaAsP layer for adjusting the resonance wavelength is etched to a desired thickness by using an etching solution that can be removed in about 1 to 2 minutes. The gain wavelength of the active layer and the resonance wavelength of the DBR mirror were overlapped. By doing so, it becomes possible to oscillate the surface emitting laser while allowing a deviation of the thickness of the epitaxial layer to ± 2%.

  As described above, the first embodiment of the present invention has been described in detail, but the specific configuration is not limited to the present embodiment, and even if there is a design change or the like without departing from the gist of the present invention, include. For example, in this embodiment, an optical pump type surface emitting laser has been described. However, the present invention is also applicable to a current injection type having an air gap. In this embodiment, InGaAs is used as the sacrificial layer and InGaAsP layer is used as the resonance wavelength adjustment layer. However, an InAlAs layer can also be used as the sacrificial layer. It is also possible to use a resonant wavelength adjusting layer that is lattice-matched to an InP layer such as an InAlGaAs layer or an InAlGaAsP layer close to the InP composition.

Furthermore, providing the resonance wavelength adjustment layer only on one side of the spacer layer can narrow the adjustment range of the resonance wavelength.
[Embodiment 2]

  The wavelength filter according to the present embodiment will be described. In the first embodiment, when an InP layer without gain is used instead of the active layer 3A of FIGS. 1 and 2, a wavelength filter is obtained. FIG. 5 and FIG. 6 show the layer configuration of the wavelength filter according to the present embodiment and the cross-sectional view after the air gap processing, respectively. Moreover, the enlarged view of the broken-line part B of FIG. 5 is shown in FIG.

In this embodiment, a DBR mirror unit 12 is formed on the substrate 11, a filter unit 13 is formed on the DBR mirror unit 12, and a DBR mirror unit 14 is formed on the filter unit 13. The DBR mirror unit 12 is composed of an InGaAs layer 12A and three pairs of InP / InGaAs. One pair is composed of an InP layer 12B and an InGaAs layer 12C. Air gaps 12A ₁ and 12C ₁ are formed in the InGaAs layer 12A and the InGaAs layer 12C.

  The filter unit 13 is formed of an InP layer 13A and InGaAsP layers 13B and 13C formed above and below the InP layer 13A. In this embodiment, the InGaAsP layers 13B and 13C are resonance wavelength adjustment layers for adjusting the resonance wavelength.

A DBR mirror unit 14 is formed on the filter unit 13. The DBR mirror unit 14 is composed of three pairs of InGaAs / InP. One pair is composed of an InGaAs layer 14A and an InP layer 14B. The InGaAs layer 14A, the air gap 14A ₁ is formed.

The laser active layer 3A and spacer layers 3B and 3C InP layers 3B ₁ and 3C _{1 in the first} embodiment are formed of a single InP layer 13A in this embodiment. Further, in this embodiment, InGaAsP layers 13B and 13C are formed above and below the InP layer 13A. That is, if the gain spectrum wavelength of the surface emitting laser in the first embodiment is replaced with a wavelength for filtering, the present invention can be applied in the same manner as the surface emitting laser in the first embodiment.

  The present invention can be applied to a device having a reflecting mirror composed of an air gap and a semiconductor.

It is sectional drawing which shows Embodiment 1 of this invention. It is sectional drawing which shows the II cross section of FIG. It is the enlarged view to which the broken-line part of FIG. 1 was expanded. It is a figure which shows the change of the resonant wavelength at the time of etching an InGaAsP layer. It is sectional drawing which shows Embodiment 2 of this invention. It is sectional drawing which shows the II-II cross section of FIG. It is the enlarged view to which the broken-line part of FIG. 5 was expanded. It is sectional drawing which shows the conventional laser. It is the enlarged view to which the broken-line part of FIG. 8 was expanded.

Explanation of symbols

1 substrate 2, 4 DBR mirror unit 2A, 2C, 4A InGaAs layer _{2A 1,} 2C 1, 4A ₁ air gap 2B, 4B InP layer 3 cavity 3A active layer 3B, 3C spacer layer _3B 1, _3C 1 InP layer 3B ₂ 3C ₂ InGaAsP layer 11 Substrate 12, 14 DBR mirror part 12A, 12C, 14A InGaAs layer 12B, 14B, 13A InP layer 13 Filter part 13B, 13C InGaAsP layer

Claims (6)

In a surface emitting laser having a reflector (2, 4) in which air gaps (2A ₁ , 2C ₁ , 4A ₁ ) and semiconductors (2B, 4B) are alternately stacked,
A surface emitting laser comprising a semiconductor layer (3B ₂ , 3C ₂ ) for adjusting a resonance wavelength on at least one air gap side of a semiconductor layer constituting a cavity.   The semiconductor material for adjusting the resonance wavelength is composed of a material having a selective etching property with respect to the semiconductor material constituting the reflecting mirror (2, 4) and the spacer layer (3B, 3C). 2. The surface emitting laser according to 1. It has a reflecting mirror in which air gaps (2A ₁ , 2C ₁ , 4A ₁ ) and semiconductors (2B, 4B) are alternately stacked, and is used for adjusting the resonance wavelength on at least one air gap side of the semiconductor layer constituting the cavity. In a method for manufacturing a surface emitting laser including a semiconductor layer (3B ₂ , 3C ₂ ),
A method of manufacturing a surface emitting laser, wherein after the air gap processing, the resonant wavelength is changed by changing the thickness of the semiconductor layer (3B ₂ , 3C ₂ ) for adjusting the resonant wavelength by etching. In a wavelength filter having reflectors (12, 14) in which air gaps (12A ₁ , 12C ₁ , 14A ₁ ) and semiconductors (12B, 14B) are alternately laminated,
A wavelength filter comprising a semiconductor layer (13B, 13C) for adjusting a resonance wavelength on at least one air gap side of a semiconductor layer constituting a cavity.   5. The wavelength according to claim 4, wherein the semiconductor material for adjusting the resonance wavelength is made of a material having a selective etching property with respect to the semiconductor material constituting the reflecting mirror (12, 14) and the spacer layer. filter. It has a reflector (12, 14) in which air gaps (12A ₁ , 12C ₁ , 14A ₁ ) and semiconductors (12B, 14B) are alternately stacked, and at least one air gap side of the semiconductor layer constituting the cavity, In the manufacturing method of the wavelength filter including the semiconductor layer for resonance wavelength adjustment,
A method of manufacturing a wavelength filter, wherein after the air gap is processed, the resonance wavelength is changed by changing a layer thickness of the semiconductor layers (13B, 13C) for adjusting the resonance wavelength by etching.

Images