JP3524745B2 - Method for manufacturing embedded semiconductor optical modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for optical communication.
Embedded semiconductor light modulationVesselRelated to the manufacturing method
is there. [0002] 2. Description of the Related Art Semiconductor optical modulators can be embedded and structured.
Is essential to ensure a high degree of reliability.
In addition, to perform high-speed modulation, reduce the capacitance of the element.
Buried layer is semi-insulating
Fe-doped InP is generally used. However
While it is a commonly used p-type dopant
Zn and Fe interdiffuse (Reference Jounal of Appl
ied Physics 69, 1862-1865 19
As a result, the diffusion of Zn toward the core layer
Problems such as deterioration of device characteristics
I have. This problem is particularly serious when the core layer is an MQW layer.
MQW is mixed crystal due to Zn diffusion in MQW
As a result, the device characteristics are greatly deteriorated. Conventional semiconductor Fe-doped embedded modulator
Is shown in FIG. 01 is the active layer, 02 is the guy
The layer portion 03 is an electrode. Next, the line a-a 'in FIG.
A plan view is shown in FIG. 04 is a p-type electrode, 05 is Zn-doped
P-InGaAs contact layer, 06 is Zn-doped p
-InGaAsP contact layer, 07 is Zn-doped p-
InP clad layer 08 is non-doped InGaAsP
(1.3 μm composition) layer, 09 is a non-doped InP layer,
10 is a non-doped InGaAs / InAlAs MQW core
Layer, 011 is a Si-doped n-InP substrate, 012 is n
Side electrode, 013 is Fe-doped InP buried layer, 014
Is an n-InP buffer layer. FIG. 12 is a model diagram of the interdiffusion of Fe and Zn.
Is shown. 015 is a Zn-doped p-InP cladding layer;
16 is an Fe-doped InP buried layer, and 017 is a non-doped layer.
InGaAs / InAlAs MQW core layer. Ma
And interdiffusion between Zn and Fe as seen in Reference 1.
Is Zn-doped p-InP cladding layer 015 and Fe-doped
This occurs between the InP buried layer 016 and the InP buried layer 016. As a result, Z
Many holes are generated in the n-doped p-InP cladding layer 015
And Zn is likely to move. As a result, Zn
Is considered to diffuse downward and enter the MQW layer. FIG. 13 shows the light absorption of the optical modulator shown in FIG.
The measurement results of the yield spectrum are shown. Around 1.5μm wavelength
There is an exciton absorption peak. Applying an electric field
Then, the absorption peak falls off toward the longer wavelength side.
The skirting phenomenon that is often seen in such bulk crystals is M
It is considered that the QW layer was mixed and deteriorated due to the diffusion of Zn.
available. For this reason, the 1.55 μm wave we use
In the long range, even at 0 V, the bottom of the absorption edge
However, there is a problem that the optical loss of the element becomes large. Sa
Furthermore, with the deterioration of MQW, the quantum confined Stark effect
(QCSE) efficiency is also reduced, and the
This is a factor that degrades all the performance. [0006] As described above, F
By embedding with an e-doped layer,
If the diffusion of Zn diffuses into the MQW layer and causes deterioration of device characteristics,
There is a problem. [0007] It is an object of the present invention to embed in an Fe-doped layer.
The diffusion of Zn from the cladding layer caused by the
This prevents the problem that the device characteristics are degraded due to diffusion into the QW layer.
And high performance and highly reliable semiconductor embedding
Type light modulationVesselIt is to provide a manufacturing method. [0008] Means for Solving the Problems To solve the above-mentioned problems
A semiconductor embedded optical modulator according to claim 1The manufacturing method of
In a method of manufacturing a semiconductor optical modulator, a semiconductor device having a first conductivity type is provided.
A first cladding having a first conductivity type on a substrate to be
Layer, first core layer, Zn doped with second conductivity type
A second cladding layer, and a core having a second conductivity type.
A step of growing an active layer comprising a contact layer and a mask
And forming a part of the active layer in a first stripe shape.
Leaving and etching to the first core layer; [0009]The band gap is higher than that of the first core layer.
Guide consisting of a large second core layer and a third cladding layer
A layer wherein the second core layer connects to the first core layer
Selective filling in contact with both side surfaces of the first stripe
And growing the first stripe on the substrate.
Perpendicular to the mask, form a second striped mask
And etching the layer structure to the substrate.
Thus, the guide layer portion was connected to both ends of the active layer portion.
Forming a mesa stripe structure; [0010]Fe-doped semiconducting semiconductor
Select body layer in contact with both sides of the mesa stripe structure
Burying and growing, forming a mask, and forming the active layer
Of the mesa stripe structure with the guide layer part connected to both ends of the part
Of these, only the side surfaces of the active layer are etched to the substrate.
The active layer in the form of a mesa stripe.
Half exposed to Fe and exposing both sides of
A step of preventing contact with the semiconductor layer having an insulating property;
It is characterized by having. A semiconductor embedded optical modulator according to the present invention comprises:
Side surface of the first core layer in the active layer portion and the semi-insulating half
Since there is no contact with the conductor crystal, Zn in the cladding layer
Interdiffusion with In of the InP buried layer does not occur, and the semiconductor
The characteristics of the embedded optical modulator are as follows.
Degradation does not occur due to cracking. Further, the first core layer in the active layer portion
Because the side and the semi-insulating semiconductor crystal are not in contact
The guide layer is in contact with the input / output
As a result, a heat dissipation path is secured,
It does not cause. [0013] BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The embodiment will be described in detail. FIG. 1 shows the present invention.Manufacturing by manufacturing methodsemiconductor
FIG. 2 is a top view of the optical modulator. Shown in FIG.
As described above, the semiconductor-embedded optical modulation according to the present embodiment
The device has a first conductivity type on a substrate having the first conductivity type.
Having a first cladding layer, a first core layer, a second conductivity type
And a second cladding layer having a second conductivity type
Active with mesa stripe structure consisting of contact layer
The band gap of the layer portion 11 is larger than that of the first core layer.
Mesas comprising a large second core layer and a third cladding layer
And a guide layer portion 12 having a tripe structure.
A core layer is connected to the first core layer at both ends in the optical axis direction
In the semiconductor optical modulator described above, the active layer portion 11
And a mesa stripe structure composed of
Of these, only the side portions of the guide layer portion 12 have semi-insulating properties.
SemiconductorIn layersIt is more embedded. This
Here, the active layer 11 is formed by applying an electric field.
This is a part that performs light modulation. The length of the active layer portion 11 is
In the present embodiment, the stripe width is 100 μm and the stripe width is 2.0 μm.
μm. The guide layer section 12 is provided with the active layer section 11.
Efficiently linking light input and output to and optical fiber
Play a role. In the present embodiment, the guide layer
The length of the part 12 is 250 μm, and the stripe width is 2 μm.
This taper structure changes up to 4 μm.
The length of the pad is 200 μm. In this embodiment
Thus, the total element length is 600 μm. Note that reference numeral 13 is
Preparation electrode, 14 shows the polyimide embedding part respectively
You. [0015] Semiconductor embedded optical modulation according to the present embodiment
The side wall of the first core layer in the active layer portion 11 and the half
Since there is no contact with the insulating semiconductor crystal, the cladding layer
Diffusion between Zn and Fe in the InP buried layer occurs
The characteristics of the semiconductor embedded optical modulator are
There is no deterioration due to the provision of the embedded layer. Ma
Further, the side surface of the first core layer in the active layer portion 11 and
This is a problem due to lack of contact with the edge semiconductor crystal.
As for heat, the guide layer 12 is connected to the input / output side of the active layer 11
The heat dissipation path is secured, causing the element to deteriorate.
And even if high optical power is input, reliability is lost.
It will not be done. Next, an embodiment of the present invention will be described with reference to FIGS.
A method for manufacturing the embedded semiconductor optical modulator will be described.
Metalorganic vapor phase epitaxy (MOVP) on the InP substrate 101
E), the n-InP buffer layer 102 and the non-doped
Of InGaAs / InAlAs MQW core layer (thickness: 0.
19 μm) 103, non-doped InP layer 104, non-doped
InGaAsP (1.3 μm composition) layer 105, p-type
InP cladding layer (p-type impurity concentration 5 × 10¹⁷cm^-3,
Thickness 1.5 μm) 106, Zn-doped p-InGaAs
P contact layer (p type impurity concentration 1 × 10¹⁸cm^-3, Thickness
0.1 μm) 107 and P⁺InGaAs contactor
Layer (p-type impurity concentration 2 × 10¹⁸cm^-3, Thickness 0.2μ
m) 108 is sequentially grown (see FIG. 2). Where MQ
The structure of the W layer is such that the InGaAs well layer has a thickness of 12 nm.
0.5% elongation strain, InAlAs barrier layer with thickness of 7 nm
A compression strain of 0.4% was introduced. repetition
Period is 10, peak wavelength of exciton is 1.50 μm
is there. Next, on the growth surface, SiO_Two109
Photolithography and CF_FourWhen
H_TwoDry etching method using mixed gas of
A mask for a butt joint is formed. Striped
The length is 100 μm. Next, CH_FourAnd H_TwoMixing moth
Dry etching method with wet etching and wet etching
By using a combination of the
Remove as shown in FIG. Next, SiO_TwoSelect a mask and a mask for growth
Then, the non-doped InGaAsP (1.
3 μm composition) layer 110, non-doped InP clad layer 1
11 grows butt joint by MOVPE method
(See FIG. 4). Next, an SiO for forming a stripe is formed._Twomask
After forming 112, CH_FourAnd H _TwoDepending on the gas mixture
Form a mesa stripe by reactive dry etching
To achieve. The stripe width at this time is 20 μm. this
Afterwards, semi-insulating, all doped with iron by MOVPE method
It is embedded with the InP crystal 113 (see FIG. 5). Next, the SiO 2_TwoPut the mask 114
After the thinning, a stripe with a width of 2 μm (active layer part)
It is formed by dry etching (see FIG. 6). Next, both sides of the stripe of the active layer portion are made of poly.
Embed with imide 115. Next, P ⁺InGaAs type
A p-side electrode 116 is provided on the contact layer, and an n-side
The pole 117 is attached by a lift-off method and a vapor deposition method, respectively.
And perform alloying at 420 ° C for about 20 seconds (see Fig. 7).
See). Then, A is used as a metal electrode for wire bonding.
Attach u. Next, the operation of the semiconductor optical modulator of the embodiment will be described.
I will talk about it. FIG. 8 is a light absorption spectrum. In FIG.
As shown in the figure, the exciton absorption peak near the wavelength of 1.5 μm.
There is a peak, but no tail of the absorption peak is seen. we
In the 1.55 μm wavelength range used by
There is no hem at the bottom end, and the absorption
There is no problem that the light loss of the element becomes large. electric field
The peak of absorption shifts to longer wavelengths as
However, the shape of the peak is well maintained compared to the conventional example.
And suggests that a strong QCSE is working. FIG. 9 shows the extinction characteristic of the semiconductor optical modulator.
The semiconductor optical modulator has an extinction characteristic of 27 dB at an applied voltage of 2.4 V.
I got sex. This value is the
The characteristics are equivalent to those of a semiconductor optical modulator having a
This shows the superiority of the semiconductor embedded optical modulator. Also,
Optical modulator with a high mesa structure with an insertion loss of 5.0 dB
Approximately 2 dB improvement was obtained as compared with. This is
By adopting a superstructure, the field distribution of light spreads,
This is because the coupling with the fiber has been improved. Note that here, InGaAs / InAlA
An s-based MQW semiconductor optical modulator is taken as an example, but the material and structure are
It is not limited to this, but InGaAlAs / In
AlAs, GaAs / AlGaAs, InGaAs
P / InP and InGaAs / InGaAsP materials
The material and the core layer may have a bulk structure other than the MQW structure. [0025] As described above, the present inventionManufacturing method
Manufactured inA semiconductor embedded optical modulator is mounted on the active layer.
Contact between the side surface of the first core layer and the semi-insulating semiconductor crystal.
Since it does not touch, burying of Zn and InP in the cladding layer
No interdiffusion with Fe of layer occurs, and semiconductor embedded light modulation
The characteristics of the device are improved by providing an Fe-doped buried layer.
It does not deteriorate. The first core layer in the active layer portion
Because the side and the semi-insulating semiconductor crystal are not in contact
The guide layer is in contact with the input / output
As a result, a heat dissipation path is secured,
No problem, even if high optical power is input
No problem.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a semiconductor embedded optical modulator whose structure is described in an embodiment of the present invention. FIG. 2 is a diagram illustrating a manufacturing method according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a manufacturing method according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a manufacturing method according to an embodiment of the present invention. FIG. 5 is a diagram illustrating a manufacturing method according to the embodiment of the present invention. FIG. 6 is a diagram illustrating a manufacturing method according to the embodiment of the present invention. FIG. 7 is a diagram illustrating a manufacturing method according to the embodiment of the present invention. FIG. 8 is a light absorption spectrum diagram of a semiconductor embedded optical modulator according to the embodiment of the present invention. FIG. 9 is an extinction characteristic diagram of the semiconductor embedded optical modulator according to the embodiment of the present invention. FIG. 10 is a top view of a semiconductor embedded optical modulator illustrating a conventional example. FIG. 11 is a cross-sectional view of a semiconductor embedded optical modulator illustrating a conventional example. FIG. 12 shows Z in a conventional example of a semiconductor embedded optical modulator.
FIG. 9 is a model diagram illustrating diffusion of n. FIG. 13 is a light absorption spectrum diagram of a conventional semiconductor embedded optical modulator. DESCRIPTION OF SYMBOLS 11 Active layer portion 12 Guide layer portion 13 Electrode 14 Polyimide buried portion 101 Si-doped n-InP substrate 102 n-InP buffer layer 103 Non-doped InGaAs / InAlAs MQW
Core layer 104 Non-doped InP layer 105 Non-doped InGaAsP (1.3 μm composition)
Layer 106 Zn-doped p-InP clad layer 107 Zn-doped p-InGaAsP contact layer 108 Zn-doped p-InGaAs contact layer 109 SiO ₂ film 110 Non-doped InGaAsP (1.3 μm composition)
Layer 111 non-doped InP cladding layer 112 SiO ₂ film 113 Fe-doped InP buried layer 114 SiO ₂ film 115 polyimide buried layer 116 p-side electrode 117 n-side electrode 01 active layer section 02 guide layer section 03 electrode 04 p-side electrode 05 Zn-doped p -InGaAs contact layer 06 Zn-doped p-InGaAsP contact layer 07 Zn-doped p-InP cladding layer 08 Non-doped InGaAsP (1.3 μm composition) layer 09 Non-doped InP layer 010 Non-doped InGaAs / InAlAs MQW
Core layer 011 Si-doped n-InP substrate 012 n-side electrode 013 Fe-doped InP buried layer 014 n-InP buffer layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/00-1/125

Claims (1)

(57) [Claim 1] In a method for manufacturing a semiconductor optical modulator, a first method is provided.
A substrate having a first conductivity type on a substrate having a first conductivity type.
Having a cladding layer, a first core layer, and a second conductivity type
a step of growing an active layer comprising a second cladding layer doped with n and a contact layer having a second conductivity type, forming a mask, and forming a part of the active layer into a first stripe. Etching to the first core layer while leaving a second core layer having a larger band gap than the first core layer, and a guide layer including a third cladding layer; Selectively growing the first stripe in contact with both side surfaces of the first stripe so as to be connected to the first core layer; and forming a second stripe on the substrate in a direction perpendicular to the first stripe. Forming a mask, etching the layer structure to the substrate to form a mesa stripe structure in which the guide layer portion is connected to both ends of the active layer portion, and has a semi-insulating property doped with Fe. A step of selectively embedding and growing a conductor layer in contact with both side surfaces of the mesa stripe structure; and forming a mask, and forming a mask and connecting the guide layer portion to both ends of the active layer portion. A step of exposing only the both side portions to the substrate to expose both side surfaces of only the mesa stripe-shaped active layer portion so as not to contact the Fe-doped semi-insulating semiconductor layer. A method for manufacturing a semiconductor-embedded optical modulator, comprising: