JPH11212035A - Semiconductor optical function element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the deterioration of both end faces on and from which light is made incident and is emitted in the mesa stripe part of a semiconductor optical function element, such as a semiconductor optical modulator. SOLUTION: This element has the mesa stripe part 20 which is laminated with at least a lower clad layer 3, a light absorption layer 4 and an upper clad layer 5, a drive electrode 10 which is formed on the surface of the upper part of the mesa stripe part 20 and an embedment layer 8 which embeds the mesa stripe part 20. Both ends of the mesa stripe part 20 are perpendicular to the optical axis and the surface in the upper part of the mesa stripe part 20 is provided with a region where the drive electrode 10 is not formed on the side inner than both ends described above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor optical functional device, and more particularly, to a semiconductor optical modulator used for optical communication and various optical signal processing.

[0002]

2. Description of the Related Art Conventionally, there has been a semiconductor optical modulator provided with a light absorbing layer whose absorption edge shifts according to an applied voltage. FIG. 4 is a perspective view of such a semiconductor optical modulator.

The conventional semiconductor optical modulator shown in FIG.
A mesa stripe portion 20 including the light absorption layer 4 is formed on the semiconductor substrate 1, and a voltage is applied between the drive electrode 10 provided on the upper surface of the mesa stripe portion 20 and the electrode 9 on the back surface of the semiconductor substrate 1. The light that passed through the absorption layer 4 was modulated.

[0004]

However, if the above-described semiconductor optical modulator is driven for a long time or high-intensity incident light is modulated, both ends of the mesa stripe portion 20 where light enters and exits are significantly deteriorated. There was a disadvantage.

Accordingly, an object of the present invention is to reduce the deterioration of both end faces of the mesa stripe portion 20 of a semiconductor optical functional device such as a semiconductor optical modulator where light enters and exits.

[0006]

According to a first aspect of the present invention, there is provided a semiconductor optical function device comprising: a mesa stripe portion having at least a lower clad layer, a light absorption layer, and an upper clad layer laminated; A semiconductor optical functional device comprising: an electrode formed on the upper surface of the portion; and a buried layer for burying the mesa stripe portion, wherein both end faces of the mesa stripe portion are perpendicular to an optical axis, and Each region including each end surface of the upper surface of the stripe portion is a portion where the electrode is not formed.

[0007]

Embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 is a perspective view of an embedded semiconductor optical function device of the present invention.

[0008] The embedded semiconductor optical functional device of the present invention comprises:
The semiconductor device includes a semiconductor substrate 1, a mesa stripe portion 20 provided on the semiconductor substrate 1, and a buried layer 8 that embeds the mesa stripe portion 20 from right and left. Then, the insulating layer 11 is formed on the upper surface of the mesa stripe portion 20 and the buried layer 8.
Is provided, the insulating layer 11 is opened by photoetching to expose the upper surface of the mesa stripe portion 20, and the drive electrode 10 is formed on the upper surface of the mesa stripe portion 20. Further, the drive electrode 10 with the electrode pad 10 a is formed on the insulating layer 11. Also, this electrode pad 1
The lead wire 10b is wire-bonded on 0b.

On the back surface of the semiconductor substrate 1, a substrate electrode 9 paired with the drive electrode 10 is provided and grounded.
Therefore, each component of the semiconductor device of the present invention shown in FIG. 1 will be described.

The semiconductor substrate 1 is a support for the mesa stripe portion 20, and its material is determined according to the wavelength of light to which the semiconductor optical functional device of the present invention is applied. For example, when light has a wavelength of 1.1 μm to 1.6 μm as in optical communication, the material of the semiconductor substrate 1 is preferably InP.

The mesa stripe section 20 has an intermediate layer 2, a lower cladding layer 3, a light absorbing layer 4, an upper cladding layer 5, an intermediate layer 6, and a contact layer 7. Here, the intermediate layer 2 is a base layer of the lower cladding layer 3, and a material having good electrical and crystallographic compatibility between the semiconductor substrate 1 and the lower cladding layer 3 is selected.

The lower cladding layer 3 and the upper cladding layer 5 sandwich the light absorbing layer 4 and are provided to confine light in the light absorbing layer 4. Therefore, in general, the refractive indices of the lower cladding layer 3 and the upper cladding layer 5 are
It is made lower than the refractive index of the light absorbing layer 4.

The intermediate layer 6, like the intermediate layer 2, is a base layer for the contact layer 7, and has good electrical and crystallographic matching between the upper clad layer 5 and the contact layer 7. Material is selected.

The contact layer 7 is provided for making ohmic contact with the drive electrode 10. The selection of the material, the film thickness and the like of each layer of the mesa stripe portion 20 as described above is variously possible. For example, 1.1 μm to 1.m.
In a semiconductor laser for optical communication in the 6 μm band, a quaternary InGaAsP mixed crystal is used for the light absorption layer 4, and InP is used for the lower cladding layer 3 and the upper cladding layer 5. In this case, n-type InP doped with Si or Sn is used as the semiconductor substrate 1.
For example, when the intermediate layer 2 is n-type doped InP, the lower cladding layer 3 is InGaAsP, and the light absorbing layer 4 is non-doped InGaAsP / InGaAsP.
System multiple quantum well or undoped bulk InGaAs
sP, the upper cladding layer 5 may be InGaAsP, the intermediate layer 6 may be p-type InP, and the contact layer 7 may be p-type InGaAsP.

The layers of the mesa stripe portion are determined as described above. Next, the buried layer 8 is a layer for confining light entering and exiting the semiconductor optical functional device of the present invention in the light absorbing layer 4. Therefore, when the semiconductor substrate 1 is made of n-type InP doped with Si or Sn, and the light absorbing layer 4 is made of the above-described material such as a multiple quantum well made of non-doped InGaAsP or a non-doped bulk InGaAsP, Fe having a lower refractive index than the light absorbing layer 4
Doped InP is preferred.

Since this Fe-doped InP is a semi-insulating material, it is also suitable in that it does not become a parasitic capacitance during high-frequency modulation. In addition, since the light absorbing layer 4 has appropriate thermal conductivity and thermal diffusivity, it is also preferable in that heat generated by the light absorption layer 4 absorbing incident light energy can be efficiently radiated.

Next, the substrate electrode 9 is a counter electrode that forms a pair with the drive electrode 10. As a material of the substrate electrode 9, a material that makes good ohmic contact with the semiconductor substrate 1 is selected. That is, for example, if the material of the semiconductor substrate 1 is F
In the case of n-type doped InP doped with e or Si, AuGeNi or the like is preferable.

As a material of the drive electrode 10, a material that makes good ohmic contact with the contact layer 7 is selected. That is, for example, when the material of the contact layer 7 is p-type doped InGaAsP, AuZnN
i and the like are preferred.

The drive electrode 10 and the electrode pad 10a
Is formed by uniformly depositing a metal film such as AuZnNi on the insulating layer 11 and then performing photoetching. When the electrode material is AuZnNi, the lead wire 10b is preferably a gold wire.

The insulating layer 11 is a layer that electrically limits the width of the drive electrode 10 to the width of the mesa stripe portion 20. As a material of the insulating layer 11, there are various oxides and nitrides such as silicon oxide. Each component of the semiconductor optical functional device of the present invention is as described above.

To drive the semiconductor optical functional device of the present invention to modulate the light incident on the light absorbing layer 4, a driving voltage is applied to the driving electrode 10. The semiconductor optical function device of the present invention has a pin structure as described above. When a reverse voltage is applied to this pin junction, the absorption edge wavelength of the light absorption layer 4 that is the i-layer shifts to the longer wavelength side. Therefore, the incident light can be modulated by setting the absorption edge wavelength of the light absorbing layer 4 when no drive voltage is applied to be shorter than the wavelength of the incident light to be modulated. Note that this absorption edge shift is caused by the quantum confined Stark effect when the light absorption layer 4 is the multiple quantum well of the non-doped InGaAsP described above, and the non-doped bulk InGaAs is used.
In the case of sP, it is due to the Franz-Keldysh effect.

In the semiconductor optical function device having such an operation principle, according to the present invention, the end surfaces of both end surfaces of the mesa stripe portion 20 through which light enters and exits are provided on the surface of the contact layer 7 above the mesa stripe portion 20. Accordingly, each region including each end surface is a portion where the drive electrode 10 is not formed. That is, the length of the drive electrode 10 is shorter than the length of the mesa stripe portion 20, and the drive electrode 10 is not in contact with both end surfaces of the mesa stripe portion 20.

With this arrangement, the absorption edge is always shorter than the wavelength of the incident light to be modulated in a portion where the driving voltage is not applied, which is inside both end surfaces perpendicular to the optical axis of the mesa stripe portion 20 of the semiconductor optical function element. Because it is on the side, little incident light energy is absorbed. Therefore, even when the semiconductor optical function element of the present invention is driven, the heat generation of the light absorbing layer 4 is limited to the inside of both end faces of the mesa stripe portion 20 to which the driving voltage is applied effectively. As a result, the thermal stress on the both end faces, which is the most difficult to dissipate heat, is reduced.

By the way, in the conventional semiconductor optical function device in which the drive electrode 10 protrudes to both end faces, the largest thermal stress in the mesa stripe portion 20 is applied to the both end faces.

The results of measuring the characteristics of such a semiconductor optical functional device of the present invention with a measuring system shown in FIG. 3 are shown.
FIG. 3 is a schematic diagram of a measurement system for measuring the incident light limit intensity of the semiconductor optical function device of the present invention. This measurement system measures the minimum value of the incident light intensity at which the light input / output end face of the semiconductor optical function element is destroyed, that is, the incident light limit intensity.

In this measurement system, as shown in FIG. 3, a laser light having a wavelength of 1.55 μm from a variable wavelength light source is amplified by an erbium-doped fiber amplifier (EDFA) via an optical fiber, and further guided to another optical fiber. To the semiconductor optical function element. Further, the semiconductor optical function device is driven at a constant voltage of 10 V by a voltage source. Then, the current flowing through the semiconductor optical function device is measured by a current monitor, and the light emitted from the semiconductor optical function device is measured by an optical power meter, and the incident light limit intensity is obtained based on these measured values.

Table 1 shows the device of the present invention shown in FIG. 1 in which only the length of the drive electrode 10 was changed (the distance L between both end faces was 50 μm,
The width W of the drive electrode 10 is 50 μm, and the distance d from both end faces to the electrode is 5 μm. Therefore, the length of the drive electrode is 40
μm. ) And the conventional element of FIG. 4 (the distance L between both end faces is 5).
0 μm, and the width W of the drive electrode 10 is 50 μm. Therefore, the length of the drive electrode is 50 μm. ) Is a result of comparing each production lot.

Each element layer is common to both, the semiconductor substrate 1 is an n-type InP doped with Si, the intermediate layer 2 is an n-type InP, the lower cladding layer 3 is InGaAsP, and the light absorbing layer 4 is a non-doped InGaAsP. InGaAsP multiple quantum well, upper cladding layer 5 is InGaAsP, intermediate layer 6 is p-type InP, and contact layer 7 is p-type InGaAs.
P, buried layer 8 is Fe-doped InP, substrate electrode 9 is AuGeNi, drive electrode 10 and electrode pad 10a are AuZnNi, lead wire 10b is gold wire, and insulating layer 11 is silicon oxide.

[0029]

[Table 1]

According to Table 1, the limit intensity of incident light of the device of the present invention was higher by 5 to 8 dBm than that of the conventional device. As another embodiment of the present invention, first, the semiconductor substrate 1 is formed by p
The type InP may be selected, and the material or the like of another layer may be determined based on the selected type.

Second, the material of the light absorbing layer 4 is the same as that of the exemplified I.
InP and InGaAsP which are II-V compound semiconductors
It is not limited to. That is, according to the wavelength of the incident light, I
GaAs and InGaAs as II-V compound semiconductors
s, AlAs, AlGaAs, AlInGaAs, Al
GaInP or the like, or Zn which is a II-VI group compound semiconductor
Select S, ZnSe, CdSe, ZnSSe, or the like.

Third, as shown in FIG. 2, the drive electrode 10 may be tapered toward both end surfaces of the mesa stripe portion 20. By doing so, the mesa stripe portion 20
The closer to both end faces, the smaller the area where the electric field is effectively applied to the light absorbing layer 4, and thus the smaller the light absorbing area. As a result, a heat generation region based on light absorption is narrowed, and thermal stress on both end surfaces of the mesa stripe portion 20 is reduced. Therefore, deterioration and destruction of both end faces of the mesa stripe portion 20 can be prevented while suppressing a decrease in the modulation degree of the incident laser light.

[0033]

As described above, according to the present invention,
The deterioration with time of the light input / output end face of the semiconductor optical functional device such as the semiconductor optical modulator is reduced.

Further, according to the present invention, the light input / output end face of the semiconductor optical function element is hardly deteriorated even when a large output laser beam is modulated.

[Brief description of the drawings]

FIG. 1 is a perspective view of a semiconductor optical function device of the present invention.

FIG. 2 is a perspective view of a semiconductor optical functional device according to another embodiment of the present invention.

FIG. 3 is a schematic view of a measurement system for measuring the incident light limit intensity of the semiconductor optical function device.

FIG. 4 is a perspective view of a conventional semiconductor optical function device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Intermediate layer 3 Lower cladding layer 4 Light absorption layer 5 Upper cladding layer 6 Contact layer 7 Contact layer 8 Buried layer 9 Substrate electrode 10 Drive electrode 10a Electrode pad 10b Lead wire

Claims (1)

[Claims] At least a lower cladding layer, a light absorbing layer,
An embedded semiconductor optical functional device, comprising: a mesa stripe portion in which an upper clad layer is laminated; an electrode formed on an upper surface of the mesa stripe portion; and an embedded layer for embedding the mesa stripe portion. A semiconductor optical function, wherein both end surfaces of the mesa stripe portion are perpendicular to the optical axis, and each region including each end surface of the upper surface of the mesa stripe portion is a portion where the electrode is not formed. element.