JPH1012920A - Super luminescent diode and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a nonreflective structure at the end face of a waveguide through a simple fabrication process. SOLUTION: An n-InP butter layer 12a, an InGaAsP waveguide layer 13, a p-InP clad layer 14a, and the like are formed on an n-InP substrate 11 to prepare an original wafer 22 and then a mesa stripe 15 is formed by etching. Subsequently, the mesa stripe 15 is embedded by a p-InP block layer 12b and an n-InP block layer 16 and a p-InP clad layer 14b and the like are grown on the upper surface thereof. When it is immersed into a hydrochloric acid based etching liquid after forming respective electrodes 19, 20, the InGaAsP is not etched and only the InP is etched. Consequently, the end face of the InGaAsP waveguide layer 13 projects from theend face of an element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superluminescent diode which is one of light emitting devices used as a substitute for a light emitting diode or a laser diode, for example, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a light emitting diode (Light Emitter) has been used as a light source of an optical communication system using an optical fiber as a transmission line.
An itting diode, a semiconductor laser (Laser Diode) and the like are used. On the other hand, in recent years, a super luminescence diode (Su) which has a higher output than a light emitting diode and has a flat wavelength band different from that of a semiconductor laser has been developed.
per Luminescence Diode) is attracting attention. The superluminescent diode has an advantage that it can be coupled to a single mode fiber and has a wide modulation band of 100 MHz.

[0003] A super luminescence diode is a light emitting device located between a light emitting diode and a semiconductor laser. In other words, a superluminescent diode has a waveguide structure unlike a light emitting diode,
Unlike a semiconductor laser, it does not have a resonator structure. For this reason, the output light of the superluminescence diode is spontaneous emission light that has gained by stimulated emission in only one direction. That is, it can be said that the superluminescent diode is an incoherent and relatively high-output light source. Further, since it has a waveguide structure, it can be coupled with a single mode fiber at high output. I
The -L characteristic is a linear characteristic having no threshold value.
It is reported that the maximum CW output is about 10 mW in the 3 μm band. The wavelength characteristics are flat because there is no FP (Fabry-Perot) resonance mode.
A 3 μm band having a 3 dB bandwidth of about 40 nm has been reported. For the modulation band, stimulated emission accounts for most of the light output, so it is wider than light emitting diodes.
It is about 00MHz.

The structure of a superluminescent diode is almost the same as the structure of a semiconductor laser, and has a gain waveguide structure. However, in order to suppress the FP resonance mode, antireflection measures are taken on the end face of the waveguide.
FIG. 5 shows a typical example of a superluminescent diode in which an end face of a waveguide is subjected to a non-reflection treatment.

FIG. 5A shows an example of an oblique waveguide structure. In this structure, by forming the waveguide 1a obliquely with respect to the end face 2a, light reflected on the end face 2a is
To prevent binding to FIG. 5 (b)
Is an example of an end window structure. This structure eliminates the waveguide 1b near the end face 2b, thereby preventing the guided light from spreading at this window portion and coupling the light reflected by the end face 2b into the waveguide 1b. FIG. 5C shows an example of a bent waveguide structure. In this structure, by making a strong bend in the waveguide 1c, light reflected at this portion is emitted to the outside of the waveguide 1c. FIG.
(D) is an example of a non-reflective coating structure. This structure
By forming a non-reflective film 3d using a dielectric multilayer film or a refractive index control SiO _x film on the end face, the reflected light itself is suppressed.

[0006]

As described above, a superluminescent diode requires an antireflection treatment of an end face of a waveguide. However, in the case of conventional superluminescent diodes, any antireflection structure requires a process that is different from a general semiconductor laser manufacturing process mainly in the process before crystal growth, which complicates the manufacturing process. Had the problem that Specifically, for example, in the case of the end face window structure shown in FIG. 5B, an unusual crystal plane is formed due to the absence of the waveguide near the end face, and the crystal is normally formed in that part during the buried growth. Because the conditions for growing are significantly different from other parts,
Buried growth cannot be performed easily. Also,
If the burying growth is not successful, the current confinement structure may not function.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides a superluminescence diode and a method for manufacturing the same, which can realize a non-reflection structure of a waveguide end face by a simple manufacturing process. The purpose is to:

[0008]

In order to achieve the above object, a superluminescent diode according to the present invention is provided.
The following measures are taken. That is, a semiconductor substrate of a first conductivity type, a waveguide layer including an active layer provided on the semiconductor substrate, and a second conductivity type opposite to the first conductivity type provided on the waveguide layer. In a superluminescent diode having a cladding layer and an electrode layer provided below and above the semiconductor substrate, respectively, the end face of the waveguide layer is formed such that the end faces of the cladding layer and the semiconductor substrate are aligned in the light guiding direction. It is characterized by projecting from the end face. Another feature is that the end face of the waveguide layer is depressed from the end faces of the cladding layer and the semiconductor substrate in the light waveguide direction. In this case, InGaAsP can be used as a material of the waveguide layer, and InP can be used as a material of the cladding layer and the semiconductor substrate. Further, an anti-reflection coating layer may be provided on at least one of the end faces of the waveguide layer.

Further, a method for manufacturing a superluminescent diode according to the present invention employs the following means.
That is, a semiconductor substrate of a first conductivity type, a waveguide layer including an active layer provided on the semiconductor substrate, and a second conductivity type opposite to the first conductivity type provided on the waveguide layer. In a method for manufacturing a superluminescent diode having a clad layer and electrode layers provided below and above a semiconductor substrate, a waveguide layer made of InGaAsP is formed above a semiconductor substrate made of InP. Performing a step of forming a cladding layer made of InP above the waveguide layer; and forming an electrode layer below the semiconductor substrate and above the cladding layer, respectively.
A step of immersing the entire substrate manufactured in the preceding steps in a hydrochloric acid-based etching solution.
As another means, a step of immersing the entire substrate in a sulfuric acid-based etching solution is provided instead of the step of immersing the substrate in the hydrochloric acid-based etching solution.

[0010] The present invention particularly relates to a method for forming a waveguide layer using InG.
aP, InP for cladding layer and semiconductor substrate material
In an InP-based super luminescent diode using Pd, I
By using selective wet etching of nGaAsP and InP, the end face of the waveguide layer is made to protrude or be depressed from the end faces of the cladding layer and the semiconductor substrate. By doing so, the end face of the waveguide layer can have a non-reflection structure.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a super luminescent diode 10 of the present embodiment. In this super luminescent diode 10, InGaAsP is used for a material of a waveguide layer and InP is used for materials of other layers and a semiconductor substrate. It is an InP-based super luminescent diode of a mesa stripe type.

As shown in FIGS. 1A to 1C, nI
On the nP substrate 11 (semiconductor substrate of the first conductivity type), n-I
nP buffer layer 12a, InGaAsP waveguide layer 13,
A p-InP cladding layer 14a (second conductivity type cladding layer) is formed, and these layers 12, 13, and 14a constitute a mesa stripe 15. The sides of the mesa stripe 15 are sequentially arranged from the bottom in the p-InP block layer 12.
b, the n-InP block layer 16 is embedded, and the p-InP block layer 12b and the n-InP block layer 16 constitute a current confinement structure.

Further, a p-InP cladding layer 14b and ap ⁺ -InGaAs ohmic contact layer 18 are laminated thereon. An n-type lower electrode layer 19 is provided on the lower surface of the n-InP substrate 11, and a p-type upper electrode layer 2 is provided on the upper surface of the p ⁺ -InGaAs ohmic contact layer 18.
0 is provided respectively. Note that p ⁺ -InGaAs
The s-ohmic contact layer 18 is for obtaining a good ohmic contact with the electrode layer by forming a high-concentration p-type layer.

The InGaAsP waveguide layer 13 has an IW having a multi quantum well (hereinafter referred to as MQW) structure in which well layers and barrier layers are alternately stacked.
It comprises an active layer (not shown) made of nGaAsP, and a light confinement layer (not shown) made of i-InGaAsP sandwiching the upper and lower sides of the active layer. Then, FIG. 1 (a),
As shown in (b), the end face of the whole InGaAsP waveguide layer 13 protrudes from the end face of the element in the light guiding direction, and has a smoothly curved shape.

Next, a method of manufacturing the super luminescent diode 10 having the above configuration will be described with reference to FIG. First, as shown in FIG. 2A, Metal Organic Vapor Phase Epitaxy (hereinafter, referred to as M)
Using an OVPE method, an n-InP buffer layer 12a, an InGaAsP waveguide layer 13 including an active layer and an optical confinement layer, a p-InP cladding layer 14a, and a p-InGaAsP cap layer 21 Are sequentially stacked to produce an original wafer 22. Next, as shown in FIG. 2B, after removing the p-InGaAsP cap layer 21, a silicon oxide film 23 is formed on the entire surface. This silicon oxide film 23 serves as an etching mask when performing etching for forming the mesa stripe later.

After a photoresist 24 is formed on the upper surface of the silicon oxide film 23 as shown in FIG. 2C, the photoresist 24 is formed as shown in FIG.
Is used as a mask to etch the silicon oxide film 23 using BOE (Buffered Oxide Etchant), that is, a buffer solution of HF and NH ₄ F. Next, after removing the photoresist 24, as shown in FIG.
3 as a mask, p-InP cladding layer 14a, InG
The mesa stripe 15 is formed by etching the aAsP waveguide layer 13 and the n-InP buffer layer 12a using a solution of Br ₂ dissolved in methanol.

Next, as shown in FIG.
Using the E method, p-InP
The mesa stripe 15 is buried by sequentially growing the block layer 12b and the n-InP block layer 16.
Then, after removing the silicon oxide film 23, as shown in FIG.
The p-InP cladding layer 1 is formed on the upper surface of the InP block layer 16.
4b, p ⁺ -InGaAs ohmic contact layer 18
Grow.

Thereafter, as shown in FIG. 2 (h), an n-type lower electrode layer 19 is formed on the lower surface of the n-InP substrate 11 and a top surface of the p ⁺ -InGaAs ohmic contact layer 18 is formed by sputtering or vapor deposition. Then, a p-type upper electrode layer 20 is formed. The material of the p-type upper electrode layer 20 is, for example, a laminated structure of Au-Zn alloy and Au, and the material of the n-type lower electrode layer 19 is Au-Ge-Ni alloy and Au.
And the like.

Next, after the wafer on which the plurality of elements are formed is cut into chips, the chips are etched with a hydrochloric acid-based etchant, for example, 3HCl + H ₃ PO ₄ or 4HCl + H.
Immerse in ₂ O. Here, the hydrochloric acid-based etchant is
Since it has the selectivity of etching only the InP crystal without etching the InGaAsP crystal,
After the etching, the waveguide layer formed of InGaAsP has a shape that protrudes relatively to the cladding layer, the block layer, and the like formed of InP. In practice, the protruding corners of the waveguide layer are also slightly etched, so that the end faces of the waveguide layer are smoothly curved surfaces. Thus, the superluminescent diode 10 of the present embodiment as shown in FIG. 2 (i) is completed. Note that the p ⁺ -InGaAs ohmic contact layer 18 is not actually etched.

According to the superluminescent diode 10 of the present embodiment, the end face of the InGaAsP waveguide layer 13 protrudes from the end face of the element and has a smoothly curved surface. The reflected light is reflected at the end face and coupled to the waveguide layer 13 again, thereby preventing the occurrence of the FP resonance mode. Also, FIG.
FIG. 4 is a diagram illustrating a light emission angle-light intensity characteristic curve of the superluminescent diode. As shown in this figure, the intensity of light emitted at an angle parallel to the direction of the waveguide is highest. Therefore, when the superluminescent diode 10 is used, the coupling efficiency with another optical element such as an optical fiber is improved.

In the manufacturing method, the waveguide layer 13 is formed only by performing selective wet etching using a hydrochloric acid-based etchant after fabricating the device by a conventional method.
Since the non-reflection treatment of the end face can be performed, the manufacturing process is not so complicated, and no trouble is caused by adding this process. Therefore, according to the present method, a superluminescent diode having the above excellent characteristics can be manufactured by a simple manufacturing process.

Hereinafter, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a super luminescent diode 25 of the present embodiment. This super luminescent diode 25 uses InGaAsP for the material of the waveguide layer and InP for the materials of the other layers and the semiconductor substrate. The first point is that it is an InP-based super luminescent diode and the other is that it is a mesa stripe type.
This embodiment is the same as the first embodiment, and differs from the first embodiment only in the shape of the end face of the waveguide layer. Therefore, in FIG. 4, the same reference numerals are given to the same components as those in FIG.
Detailed description is omitted.

As shown in FIGS. 4A to 4C, nI
On the nP substrate 11 (semiconductor substrate of the first conductivity type), n-I
nP buffer layer 12a, InGaAsP waveguide layer 26,
A p-InP cladding layer 14a (cladding layer of the second conductivity type) is formed, and these layers 12a, 26, and 14a constitute a mesa stripe 15. Then, the sides of the mesa stripe 15 are p-InP block layers 1 in order from the bottom.
2b, embedded in the n-InP block layer 16.
Furthermore, a p-InP cladding layer 14b is provided above the
A p ⁺ -InGaAs ohmic contact layer 18 is stacked. An n-type lower electrode layer 19 is formed on the lower surface of the n-InP substrate 11, and a p-type upper electrode layer 20 is formed on the upper surface of the p ⁺ -InGaAs ohmic contact layer 18, respectively.

Further, the InGaAsP waveguide layer 26 comprises:
Active layer made of InGaAsP with MQW structure (not shown)
And a light confinement layer (not shown) made of i-InGaAsP sandwiching the upper and lower sides of the active layer. And FIG.
As shown in (a) and (b), the end face of the whole InGaAsP waveguide layer 26 is smoothly curved, and has a shape depressed from the end face of the element in the light waveguide direction.

The method of manufacturing the superluminescent diode 25 of the present embodiment is completely the same as the manufacturing method of the first embodiment from the step of forming the original wafer to the step of forming the chip. Then, in the case of this embodiment, after the device is formed into chips, a sulfuric acid-based etching solution, for example, 3H ₂ S
O ₄ + H ₂ O ₂ + H ₂ O or H ₂ SO ₄ + H ₂ O ₂ +10
Immerse in H ₂ O. Here, unlike the hydrochloric acid-based etchant used in the first embodiment, the sulfuric-acid-based etchant does not etch the InP crystal, but is formed of InGaAsP.
Has a selectivity of etching only the crystal of InGaAsP, the waveguide layer made of InGaAsP
It has a shape depressed with respect to the cladding layer, the block layer, and the like formed of nP. Thus, superluminescent diode 25 of the present embodiment is manufactured.

According to the super luminescent diode 25 of the present embodiment, since a smoothly curved dent is provided on the end face of the InGaAsP waveguide layer 26, similar to the first embodiment, light emission during emission is achieved. The occurrence of the FP resonance mode can be prevented. Regarding the manufacturing method, the antireflection treatment of the end face of the waveguide layer 26 can be performed only by performing selective etching using a sulfuric acid-based etchant after fabricating the element by a conventional general method. The process is not so complicated, and no inconvenience is caused by this process. Therefore, also in the present embodiment, a superluminescent diode having excellent characteristics can be realized by a simple manufacturing process.

The technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention. For example, in addition to the configurations of the first and second embodiments, an anti-reflection coating layer may be provided to cover the end surfaces of the elements including the end surfaces of the waveguide layers 13 and 26. As the anti-reflection coating layer, a conventional general dielectric multilayer film or a refractive index control SiO _x
A film or the like can be used. By providing this anti-reflection coating layer, the anti-reflection structure at the end face of the waveguide layer can be made more reliable. The anti-reflection coating layer does not necessarily need to be provided on both end faces of the element. For example, one side may be configured as a high-reflection coating layer to emit light to the anti-reflection coating layer side.
Further, the conductivity types of the semiconductor substrate side and the cladding layer side may be reversed from those of the above-described embodiment, or an inverted mesa stripe structure may be used instead of the mesa stripe structure of the above-described embodiment.

[0028]

As described above in detail, the superluminescent diode of the present invention has a shape in which the end face of the waveguide layer protrudes from the end face of the element or is depressed. It is possible to prevent the light propagated through the layer from being reflected at the end face and being coupled to the waveguide layer again, thereby preventing the occurrence of the FP resonance mode. Then, in the manufacturing method, after an element is manufactured by a conventional general method, the non-reflection treatment of the end face of the waveguide layer is performed only by performing selective wet etching using a hydrochloric acid-based etching solution or a sulfuric acid-based etching solution. It can be carried out. Therefore, the manufacturing process does not become so complicated, and no trouble occurs due to the addition of this process. Therefore, according to the present invention, a superluminescent diode having excellent characteristics can be manufactured by a simple manufacturing process.

[Brief description of the drawings]

FIG. 1A is a plan view showing a superluminescent diode according to a first embodiment of the present invention, and FIG.
FIG. 4A is a longitudinal sectional view taken along line AA, and FIG.
It is a longitudinal section along the B line.

FIG. 2 is a process flow chart showing the manufacturing steps of the superluminescent diode in order.

FIG. 3 is a diagram showing an emission angle-intensity characteristic curve of light of the superluminescent diode.

FIG. 4A is a plan view showing a superluminescent diode according to a second embodiment of the present invention, and FIG.
FIG. 4A is a longitudinal sectional view taken along the line CC, FIG.
It is a longitudinal section along the D line.

FIG. 5 is a view showing five modes of a non-reflection structure of an end face in a conventional superluminescent diode.

[Explanation of symbols]

 10, 25 ... super luminescent diode, 11
... n-InP substrate (semiconductor substrate of the first conductivity type), 12a
... n-InP buffer layer, 12b ... p-InP block
Layers, 13, 26... InGaAsP waveguide layers, 14a, 1
4b: p-InP cladding layer, 15: mesa stripe,
16 ... n-InP block layer, 18 ... p ⁺-InGaAs
s ohmic contact layer, 19... n-type lower electrode layer, 2
0 ... p-type upper electrode layer, 21 ... n-InGaAsP cap
Layer, 22: original wafer, 23: silicon oxide film, 24:
Photoresist.

Claims (6)

[Claims] 1. A semiconductor substrate of a first conductivity type, a waveguide layer including an active layer provided on the semiconductor substrate, and a conductivity type opposite to the first conductivity type provided on the waveguide layer. A certain second
In a superluminescent diode having a conductive cladding layer and electrode layers provided below the semiconductor substrate and above the cladding layer, respectively, the end face of the waveguide layer is arranged in a light-guiding direction. A superluminescent diode protruding from end surfaces of the cladding layer and the semiconductor substrate. 2. A semiconductor substrate of a first conductivity type, a waveguide layer including an active layer provided on the semiconductor substrate, and a conductivity type opposite to the first conductivity type provided on the waveguide layer. A certain second
In a superluminescent diode having a conductive cladding layer and electrode layers provided below the semiconductor substrate and above the cladding layer, respectively, the end face of the waveguide layer is arranged in a light-guiding direction. A superluminescent diode, wherein the superluminescent diode is depressed from end faces of the cladding layer and the semiconductor substrate. 3. The super luminescent diode according to claim 1, wherein a material of said waveguide layer is InGaAsP, and a material of said cladding layer and said semiconductor substrate are InP. Luminescent diode. 4. The superluminescent diode according to claim 1, wherein at least one of the end faces of the waveguide layer has:
A super luminescent diode, wherein a non-reflective coating layer is provided. 5. A semiconductor substrate of a first conductivity type, a waveguide layer including an active layer provided on the semiconductor substrate, and a conductivity type opposite to the first conductivity type provided on the waveguide layer. A certain second
In a method for manufacturing a superluminescent diode having a conductive type cladding layer and electrode layers provided below and above the semiconductor substrate, respectively, the method comprises: forming InGaAsP above a semiconductor substrate comprising InP. Forming a waveguide layer; forming a cladding layer of InP above the waveguide layer; forming electrode layers below the semiconductor substrate and above the cladding layer, respectively. Immersing the entire substrate manufactured up to the step in a hydrochloric acid-based etchant. 6. A semiconductor substrate of a first conductivity type, a waveguide layer including an active layer provided on the semiconductor substrate, and a conductivity type opposite to the first conductivity type provided on the waveguide layer. A certain second
In a method for manufacturing a superluminescent diode having a conductive type cladding layer and electrode layers provided below and above the semiconductor substrate, respectively, the method comprises: forming InGaAsP above a semiconductor substrate comprising InP. Forming a waveguide layer; forming a cladding layer of InP above the waveguide layer; forming electrode layers below the semiconductor substrate and above the cladding layer, respectively. Immersing the entire substrate manufactured up to the step in a sulfuric acid-based etchant.