JPH1090635A - Flush type semiconductor optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the performance and also the reliability of an optical element by inserting at least one layer of a diffusion control layer whose band gap is different from that of a core layer and a second clad layer in between the core layer and the second layer. SOLUTION: Diffusion control layers 25, 26 whose band gaps are different from those of a core layer 27 and a second clad layer 24 are inserted in between the core layer 27 and the second layer 24. Consequently, since the diffusing of Zn from the clad layer 24 suppresses a heteroboundary, the diffusing of Zn to the core layer 27 is remarkably reduced and the charactreristic of a flush type semiconductor optical modulator is never deteriorated by providing an Fe doped buried layer 30. As a result, the efficiency of quantum confining Schutalk effect is never reduced and also the performance such as light quenching ratio as an optical modulator is never deteriorated and, moreover, since a secular change due to moisture is negligibly small as compared with that of an element in which polyimide used conventionally heavily is buried, the reliability of this element is remarkably enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an embedded semiconductor optical device such as an embedded semiconductor optical modulator used for optical communication.

[0002]

2. Description of the Related Art An embedded semiconductor optical modulator is indispensable for securing high reliability. Moreover, in order to perform high-speed optical modulation, the capacity of the semiconductor optical modulator must be reduced. Therefore, semi-insulating Fe-doped InP is generally used for the buried layer.

FIG. 5 is a sectional view showing a conventional embedded semiconductor optical modulator. As shown in the figure, Si-doped n-
On a semiconductor substrate 16 made of InP, a Si-doped n-
InP clad layer 19, undoped InGa
As / InAlAs MQW (Multiple Quantum Well; Multiple
-Quantum-Well) core layer 15, Zn-doped p
-InP cladding layer 14, Zn-doped p-I
A contact layer 13 made of nGaAsP and a contact layer 12 made of Zn-doped p-InGaAs are formed in a mesa stripe structure, a p-side electrode 11 is formed on the upper surface of the contact layer 12, and an n-side electrode 17 is formed on the back surface of the semiconductor substrate 16. Is formed, and the side surface of the mesa stripe structure is buried by the burying layer 18 made of Fe-doped InP.

[0004]

However, Zn, which is a p-type dopant generally used for the cladding layer 14, and Fe, which is a dopant of the buried layer 18, diffuse into each other (see Journal of Applied Physics). of Applied Physics) 69, 186
2-1865, 1991). As a result, the diffusion of Zn toward the core layer 15 is promoted, and the characteristics of the buried semiconductor optical modulator deteriorate. This problem is particularly serious when the core layer 15 is made of MQW.
The MQW of No. 5 becomes a mixed crystal, which significantly deteriorates the characteristics of the embedded semiconductor optical modulator.

FIG. 6 is a sectional view showing the state of interdiffusion between Fe and Zn in the embedded semiconductor optical modulator shown in FIG. As shown, interdiffusion of Zn and Fe occurs between the cladding layer 14 and the buried layer 18. For this reason,
Since many holes are generated in the cladding layer 14 and Zn is easily moved, Zn diffuses downward and the core layer 1
5

FIG. 7 is a graph showing the results of analysis of the embedded semiconductor optical modulator shown in FIG. 5 by SIMS (secondary ion mass spectrometer). The horizontal axis represents the depth, and the vertical axis represents the analyzed element. It shows the carrier concentration. This graph shows that Zn is diffused from the cladding layer 14 into the core layer 15.

FIG. 8 is a graph showing the measurement results of the light absorption spectrum of the embedded semiconductor optical modulator shown in FIG. As is clear from this graph, there is an exciton absorption peak near a wavelength of 1.5 μm. Also, as the electric field is applied, the peak of absorption falls off toward the longer wavelength side. It is considered that the bottom drooping phenomenon often seen in such a bulk crystal is that the core layer 15 is deteriorated by the diffusion of Zn. Therefore, in the wavelength region of 1.55 μm, 0
Also at V, there is a problem that the bottom of the absorption edge is applied and the optical loss of the semiconductor optical modulator due to absorption increases. Further, as the MQW of the core layer 15 deteriorates, the efficiency of the quantum confined Stark effect (QCSE) also decreases, and the performance as an optical modulator such as the extinction ratio deteriorates, which becomes a factor of deteriorating the reliability.

As described above, by burying the side surfaces of the mesa stripe structure with the buried layer 18 of Fe-doped InP, Zn diffuses from the cladding layer 14 into the core layer 15 and the characteristics of the buried type semiconductor optical modulator. , Resulting in deterioration of reliability.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide a high-performance and highly reliable embedded semiconductor optical device.

[0010]

According to the present invention, a first cladding layer having a first conductivity type, a core layer having a first conductivity type, and a second cladding layer having a second conductivity type are provided on a semiconductor substrate. Wherein the cladding layer and the contact layer having the second conductivity type are formed in a mesa stripe structure, and a side surface of the mesa stripe structure is embedded with a semi-insulating semiconductor crystal. At least one diffusion suppressing layer having a band gap different from that of the second clad layer and the core layer is inserted between the second clad layer and the second clad layer.

In this case, at least a first diffusion suppression layer and a second diffusion suppression layer immediately below the first diffusion suppression layer are inserted as the diffusion suppression layer, and the band gap of the second diffusion suppression layer is reduced. Is made larger than the band gap of the first diffusion suppressing layer.

[0012]

FIG. 1 is a sectional view showing an embedded semiconductor optical modulator according to the present invention. As shown in FIG.
On a semiconductor substrate 28 made of i-doped n-InP, S
a first cladding layer 31 made of i-doped n-InP,
A core layer 27 made of non-doped InGaAs / InAlAs MQW, a diffusion suppression layer 26 made of non-doped InP, a diffusion suppression layer 25 made of non-doped InGaAsP (bandgap wavelength 1.3 μm composition), and a Zn-doped p-InP Second cladding layer 24, Zn
Contact layer 2 made of doped p-InGaAsP
3. A contact layer 22 made of Zn-doped P ⁺ -InGaAs is formed in a mesa stripe structure, a p-side electrode 21 made of AuZnNi is formed on the upper surface of the contact layer 22, and an n-side made of AuGeNi is formed on the back surface of the semiconductor substrate 16. An electrode 29 is formed, and the side surface of the mesa stripe structure is buried with a buried layer 30 made of InP doped with Fe.

Next, a method of manufacturing the embedded semiconductor optical modulator shown in FIG. 1 will be described. First, metal organic chemical vapor deposition (MOVPE) is performed on the semiconductor substrate 28.
Cladding layer 31, core layer 27 having a thickness of 0.19 μm, diffusion suppressing layer 26, diffusion suppressing layer 25, p-type impurity concentration 5 × 10
¹⁷ cm ⁻³ , 1.5 μm thick cladding layer 24, p-type impurity concentration 1 × 10 ¹⁸ cm ⁻³ , 0.1 μm thick contact layer 23 and p-type impurity concentration 2 × 10 ¹⁸ cm ⁻³ , thickness A contact layer 22 having a thickness of 0.2 μm is sequentially grown. In this case, the core layer 27 is formed to have a thickness of 12 nm and an I.sub.
It comprises an nGaAs well layer and an InAlAs barrier layer having a thickness of 7 nm and a compressive strain of 0.4%, and a repetition period of 10 nm.
And the peak wavelength of the exciton is 1.50 μm.

Next, the SiO 2 is grown on the growth surface._TwoSputter film
By photolithography and CF_FourAnd H_Two
By reactive dry etching with a mixed gas of
iO _TwoBy selectively etching the film, SiO 2_Two
A stripe-shaped mask made of a film is formed. This place
If the optical modulator has a single transverse mode,
The width of the mask is 2 μm. Next, CH_FourAnd H_TwoWhen
The reactive dry etching method using a mixed gas of
Etching to the middle of the conductor substrate 28,
A lip structure is formed. Next, SiO_TwoFilm made of film
MOV using a tripe-shaped mask as a selective growth mask
Embed all sides of mesa stripe structure by PE method
It is embedded by the only layer 30. Next, lift-off method and vapor deposition
The p-side electrode 21 is formed on the contact layer 22 by
Forming an n-side electrode 29 on the back surface of the semiconductor substrate 28;
Perform alloying at 420 ° C. for about 20 seconds. Then Wai
Au is attached as a metal electrode for back bonding. this
In this case, the size of the P-side electrode 21 is 300 μm in the stripe portion.
m × 2 μm, and 40 μm × 30 μm at the pad.

In the buried semiconductor optical modulator shown in FIG. 1, between the cladding layer 24 and the diffusion suppressing layer 25, between the diffusion suppressing layer 25 and the diffusion suppressing layer 26, and between the diffusion suppressing layer 26 and the core layer 27. Is formed, the diffusion of Zn from the cladding layer 24 is suppressed at the hetero interface, so that the diffusion of Zn into the core layer 27 is greatly reduced, and the embedded semiconductor optical modulator is formed. Is not deteriorated by providing the buried layer 30 doped with Fe. Thus, the efficiency of the quantum confined Stark effect does not decrease, and the performance as an optical modulator such as the extinction ratio does not deteriorate, and the reliability can be improved. Further, the band gap of InGaAsP of the diffusion suppressing layer 25 is 0.95 eV, the band gap of InP of the diffusion suppressing layer 26 is 1.35 eV, and the MQW equivalent band gap of the core layer 27 (the InGaAs well layer and the InAlA
The band gap obtained by weighting and averaging the band gap with the s barrier layer by the value of each film thickness is about 1.1 eV. Therefore, the band gap of the diffusion suppression layer 26 immediately below the diffusion suppression layer 25 immediately above the hetero interface between the diffusion suppression layer 25 and the diffusion suppression layer 26 is large. Even more effectively at the hetero interface between the diffusion suppressing layer 25 and the diffusion suppressing layer 26, Zn
Can be suppressed. Also, the buried layer 30
The embedding of the side surface of the mesa stripe structure makes it possible to greatly improve the coupling efficiency with the optical fiber. Performance can be greatly improved.

FIG. 2 is a graph showing the result of SIMS analysis of the embedded semiconductor optical modulator shown in FIG.
As is clear from this graph, the carrier concentration of the core layer 27 is n-type at a low concentration, and in the conventional buried semiconductor optical modulator, the core layer 15 becomes p-type by diffusion of Zn as shown in FIG. On the other hand, in the buried type semiconductor optical modulator shown in FIG. 1, the core layer 27 does not become p-type due to the diffusion of Zn.

FIG. 3 is a graph showing a light absorption spectrum of the embedded semiconductor optical modulator shown in FIG. As is clear from this graph, there is an exciton absorption peak near a wavelength of 1.5 μm. Then, no tail of the absorption peak due to the embedding is observed, and in the wavelength region of 1.55 μm,
At 0 V, the bottom of the absorption edge is not applied, and the conventional buried type semiconductor optical modulator has a problem that the optical loss of the element due to absorption is increased as shown in FIG. In the semiconductor light modulator, there is no problem that the optical loss of the element due to absorption is increased. Further, as the electric field is applied, the absorption peak shifts to the longer wavelength side, but the shape of the peak is maintained better than in the conventional case (FIG. 8), and the strong quantum confined Stark effect works. Suggest that.

FIG. 4 is a graph showing the extinction characteristics of the embedded semiconductor optical modulator shown in FIG. As is clear from this graph, an extinction ratio of 25 dB was obtained at an applied voltage of 2.4 V. This value is equivalent to that of the semiconductor optical modulator having the high mesa structure without the embedded structure, and indicates the significance of the embedded semiconductor optical modulator shown in FIG. Also, the insertion loss of the embedded semiconductor optical modulator was 4.0 dB, which was an improvement close to 3 dB as compared with the semiconductor optical modulator having a high mesa structure. This is because the adoption of the buried structure broadens the field distribution of light and improves the coupling with the optical fiber.

In the above embodiment, the case where the buried semiconductor optical device is a buried semiconductor optical modulator has been described. However, the buried semiconductor optical device may be a buried semiconductor laser, a buried semiconductor light receiving device, or the like. The present invention can be applied to such cases. In the above-described embodiment, heterostructures are provided at three places between the cladding layer 24 and the diffusion suppressing layer 25, between the diffusion suppressing layer 25 and the diffusion suppressing layer 26, and between the diffusion suppressing layer 26 and the core layer 27. Although the interface is formed, any number of hetero interfaces may be provided as long as the characteristics of the embedded semiconductor optical modulator are not affected. Further, in the above embodiment, the diffusion suppressing layer 26 made of non-doped InP as the diffusion suppressing layer, the non-doped InGaAsP (band gap wavelength 1.3 μm composition)
Although the diffusion suppressing layer 25 made of GaAs is used, a diffusion suppressing layer made of another semiconductor such as InGaAs may be used. Also,
In the above embodiment, InGaAs / InAlA
Although the buried semiconductor optical modulator having the core layer 27 made of s-based MQW has been described, the material and structure of the core layer are not limited thereto, and the material of the MQW may be InGaAlAs / InAlAs, GaAs / AlG
aAs-based, InGaAsP / InP-based, InGaAs /
InGaAsP-based or the like can be used.
A core layer having a bulk structure other than the above may be used. In the above embodiment, the semiconductor substrate 28 made of n-InP doped with Si is used as the semiconductor substrate, but a semiconductor substrate made of non-doped InP may be used.

[0020]

In the buried semiconductor optical device according to the present invention, the diffusion of the second conductivity type dopant in the cladding layer is suppressed at the hetero interface between the cladding layer and the diffusion suppressing layer. Since the diffusion of the second conductivity type dopant is greatly reduced, performance and reliability can be improved.

Further, at least a first diffusion suppression layer and a second diffusion suppression layer immediately below the first diffusion suppression layer are inserted as diffusion suppression layers, and the band gap of the second diffusion suppression layer is set to the first diffusion suppression layer. When the band gap is made larger than the band gap of the diffusion suppressing layer, the diffusion of the second conductivity type dopant in the cladding layer is more effectively suppressed at the hetero interface between the first diffusion suppressing layer and the second diffusion suppressing layer. can do.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embedded semiconductor optical modulator according to the present invention.

FIG. 2 shows the SI of the embedded semiconductor optical modulator shown in FIG.
4 is a graph showing the results of analysis by MS.

FIG. 3 is a graph showing a light absorption spectrum of the embedded semiconductor optical modulator shown in FIG.

FIG. 4 is a graph showing extinction characteristics of the embedded semiconductor optical modulator shown in FIG.

FIG. 5 is a cross-sectional view showing a conventional embedded semiconductor optical modulator.

FIG. 6 shows an example of the embedded semiconductor optical modulator shown in FIG.
FIG. 4 is a cross-sectional view showing a state of mutual diffusion between Zn and Zn.

FIG. 7 shows the SI of the embedded semiconductor optical modulator shown in FIG.
4 is a graph showing the results of analysis by MS.

8 is a graph showing a measurement result of a light absorption spectrum of the embedded semiconductor optical modulator shown in FIG.

[Explanation of symbols]

 Reference Signs List 22 contact layer 23 contact layer 24 second cladding layer 25 diffusion suppressing layer 26 diffusion suppressing layer 27 core layer 28 semiconductor substrate 30 buried layer 31 first cladding layer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Etsuo Noguchi 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] A first conductive type having a first conductivity type on a semiconductor substrate;
A cladding layer, a core layer, a second cladding layer having a second conductivity type, and a contact layer having a second conductivity type are formed in a mesa stripe structure, and the side surfaces of the mesa stripe structure are formed of semi-insulating semiconductor crystals. In the buried embedded semiconductor optical device, the core layer and the second
Wherein at least one diffusion suppressing layer having a bandgap different from that of the second cladding layer and the core layer is inserted between the second cladding layer and the core layer. 2. The method according to claim 2, wherein at least a first diffusion suppression layer and a second diffusion suppression layer immediately below the first diffusion suppression layer are inserted as the diffusion suppression layer, and the band gap of the second diffusion suppression layer is reduced. 2. The buried semiconductor optical device according to claim 1, wherein the band gap is larger than the band gap of the first diffusion suppressing layer.