JPH10206808A - Semiconductor optical modulator and semiconductor laser device integrated therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor optical modulator which is capable of high speed modulation and has an Fe dope InP-buried layer buried into a mesa side face and a semiconductor laser device integrated therewith. SOLUTION: The semiconductor optical modulator, which has the Fe dope high resistance-buried layer 5 buried into the mesa side face, is constituted of an andope InGaAsP light absorbing layer 2 formed on an n-type InP substrate 1, a p-type InP-buried layer 3 in contact with this light absorbing layer 2 and having a low impurity concentration of p<=1×10<17> cm<-3> , a p-type InP clad layer 8 in contact with this buried layer 3 and having a high impurity concentration of >=4×10<17> cm<-3> and the lower side of an electrode pad, which are of a structure buried with a polyimide film 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical modulator, and more particularly to a III-V compound semiconductor optical modulator having an Fe-doped high resistance (rate) buried layer and a semiconductor laser device having the same. .

[0002]

2. Description of the Related Art With the development of optical communication technology, there is a demand for a high-speed and large-capacity optical communication system. Therefore, a semiconductor optical modulator capable of high-speed modulation is demanded. In order to meet such demands, it is desired to reduce the associated capacitance and improve the extinction efficiency. Conventionally, techniques in such a field include, for example, Japanese Patent Application No. 7-1 by the present inventors.
No. 90032 has been proposed.

According to this, as shown in FIG. 7, in a semiconductor optical modulator in which a side surface of a mesa having a light absorbing layer is embedded with an Fe-doped high-resistance buried layer, the Fe-doped In
1 × 10 ¹⁸ cm formed on P high resistance buried layer 44
N-type InP buried layer 4 having a high impurity concentration of ^-3 or more
5 and 1 formed on the n-type InP buried layer 45.
P-type InP with low impurity concentration of × 10 ¹⁷ cm ^-3 or less
The buried layer 46 and the p-type InP clad layer 43 having a high impurity concentration of 4 × 10 ¹⁷ cm ⁻³ or more formed on the light absorption layer 42 and the p-type InP buried layer 46 are provided.

Incidentally, 41 is an n-type InP substrate, 47 is a p-type InGaAsP contact layer, 48 is a p-side electrode, 49 is an n-side electrode, and 50 is an AR coat.

[0005]

In general, the amount of Fe in a conventional Fe-doped InP high resistance buried layer is, for example, about 6 × 10 ¹⁶ cm at a growth temperature of 600 ° C.
Even if Fe is saturated at around ^-3 and Fe is introduced to a value higher than the saturation value, the region is not electrically activated, and a region having a sufficiently high resistance cannot always be obtained.

Therefore, the semiconductor optical modulator having the structure disclosed in the above-mentioned document provides Fe-doped In
It is possible to prevent a wetting current via the P high resistance buried layer 44 and obtain good extinction characteristics. However, since the device capacity also depends on the resistivity and the thickness of the Fe-doped InP high-resistance buried layer, the device capacity is not reduced unless a sufficiently high resistivity is obtained, and high-speed modulation cannot be performed. .

An object of the present invention is to provide a semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high-resistance buried layer capable of high-speed modulation and a semiconductor laser device in which the same is integrated. Aim.

[0008]

According to the present invention, there is provided a semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high-resistance buried layer on an n-type compound semiconductor substrate. Light absorbing layer, and 1 × 1 in contact with the light absorbing layer.
A p-type buried layer having a low impurity concentration of 0 ¹⁷ cm ⁻³ or less is provided.

[2] In a semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high resistance buried layer, a light absorbing layer formed on an n-type compound semiconductor substrate and 1 × 10 ^{17 in} contact with the light absorbing layer low impurity concentration p less than cm ^-3
Buried layer and 4 × 10
A p-type clad layer having a high impurity concentration of ¹⁷ cm ^-3 or more is provided.

[3] In a semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high resistance buried layer, a light absorbing layer formed on an n-type compound semiconductor substrate and 1 × 10 ^{17 in} contact with the light absorbing layer. low impurity concentration p less than cm ^-3
Buried layer and 4 × 10
A p-type clad layer having a high impurity concentration of ¹⁷ cm ^-3 or more and an insulating film are buried under the electrode pad on the side surface of the mesa.

[4] In a semiconductor laser device having a semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high resistance buried layer, a light absorbing layer formed on an n-type compound semiconductor substrate and a light absorbing layer in contact with the light absorbing layer are formed. A semiconductor optical modulator having a p-type buried layer having a low impurity concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a semiconductor laser having an active layer connected to a light absorption layer of the semiconductor optical modulator. It is intended to be accumulated in the.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a semiconductor optical modulator according to a first embodiment of the present invention, FIG. 2 is a plan view of the semiconductor optical modulator, and FIG. 3 is a side view of the semiconductor optical modulator. As shown in these figures, this semiconductor optical modulator is for modulating incident light having a wavelength of 1.5 μm, for example. A bandgap wavelength of 1.45 on an n-type InP substrate 1
An undoped InGaAsP light absorbing layer 2 having a thickness of about 0.2 μm and a thickness of about 0.2 μm is formed, and an impurity concentration p = 1 × 10
A p-type InP buried layer 3 of ¹⁷ cm ^-3 and a thickness of about 0.1 μm
Are formed epitaxially.

These laminations are mesa-etched to the substrate, and the mesa side surfaces are buried with an Fe-doped high-resistance InP layer 5 followed by n-type InP having an impurity concentration of n = 5 × 10 ¹⁸ cm ^-3 and a thickness of about 0.3 μm. Layer 6 and impurity concentration p = 1 × 10 ¹⁷
A p-type InP buried layer 7 having a thickness of about 0.1 μm and a cm ⁻³ is formed epitaxially. Next, a p-type I having an impurity concentration p = 5 × 10 ¹⁷ cm ⁻³ and a thickness of about 1.5 μm
An nP cladding layer 8 is formed. Furthermore, a band gap wavelength of 1.3 μm, an impurity concentration p = 5 × 10 ¹⁸ cm ⁻³ ,
P-type InGaAsP contact layer 9 having a thickness of about 0.2 μm
Is formed.

Next, these laminations are etched into mesas having a width of 10 to 15 μm and a height of 2 to 3 μm including an absorption region, and both sides thereof are buried with an insulating film such as SiO ₂ , particularly a polyimide film 10. On the p-side surface, a p-side electrode 11 is formed on the polyimide film 10 at the bonding electrode pad portion. Further, an n-side electrode 12 is formed on the back surface of the substrate, and Al
An AR coat 13 made of a ₂ O ₃ film (refractive index: 1.75) or the like is applied to form a semiconductor optical modulator.

Hereinafter, the operation of the semiconductor optical modulator will be described. When a reverse bias voltage is applied between the p-side electrode 11 and the n-side electrode 12, undoped I
The absorption coefficient of the nGaAsP light absorbing layer 2 increases. This phenomenon of increasing the absorption coefficient is based on what is called the Franz-Keldysh effect. When the MQW structure is used for the undoped InGaAsP light absorbing layer 2, a similar increase in the absorption coefficient is observed due to the quantum confined Stark effect.

At this time, since the impurity concentration of the p-type InP buried layer 3 in contact with the undoped InGaAsP light absorbing layer 2 is low, the width of the depletion layer is widened and the element capacitance can be reduced. Here, lowering the impurity concentration of the p-type InP buried layer 3 contributes to an increase in the series resistance value of the element, so it is not appropriate to lower the impurity concentration of the p-type InP cladding layer 8. In an integrated light source of a semiconductor optical modulator and a semiconductor laser device, a p-type InP
Since the clad layer 8 is shared, it is necessary to increase the impurity concentration of the p-type InP clad layer 8 in order to obtain good laser characteristics. In that case, the structure of the present invention is considered to be suitable. .

FIG. 4 shows the calculation results of the element capacitance and the thickness of the buried layer when the shape of the p-side electrode of the semiconductor optical modulator according to the first embodiment of the present invention is changed. In this figure, the element length is 200 μm, the curve a is the entire surface electrode, and the curve b is 10 μm.
An m-width mesa shape and a curve c indicate the case of a 10 μm-width mesa shape + electrode pad, the horizontal axis indicates the thickness d (μm) of the Fe—InP layer, and the vertical axis indicates the element capacitance C (pF). I have. The calculation formula can be shown as follows.

Element capacitance C = (εA ₁ + ρτA ₂ ) / d where A ₁ : area of pad A ₂ : mesa width × element length ρ: resistivity of Fe-doped high resistance layer τ: carrier lifetime ３3 × 10 ^-7 d: Thickness of Fe-doped high resistance layer ε: Dielectric constant of Fe-doped high resistance layer Reference: Cheng et al. , App
l. Phys. Lett. 51 (22), 30 198
7 can be referred to.

As can be seen from FIG. 4, the element capacitance can be suppressed to 1 pF or less by adopting the mesa shape and the pad electrode structure. As described above, according to the first embodiment, a low-impurity-concentration p-type InP buried layer is formed in contact with the light absorption layer in the buried structure of the optical modulator in which the mesa side surface is buried with the Fe-doped high-resistance InP buried layer. And also
By filling the insulating film, particularly the polyimide film 10, under the pad electrode portion in the mesa structure, the device capacity can be reduced and high-speed modulation characteristics can be obtained.

Next, a second embodiment of the present invention will be described. FIG. 5 is a sectional view of a semiconductor optical modulator portion of a semiconductor optical modulator integrated DFB laser showing a second embodiment of the present invention, and FIG. 6 is an overall sectional view of the semiconductor optical modulator integrated DFB laser. As shown in these figures, a band gap wavelength of 1.45 μm and a thickness of about 0.2 μm are formed on an n-type InP substrate 21.
Undoped InGaAsP light absorbing layer 22 and p-type InP having an impurity concentration p = 1 × 10 ¹⁷ cm ⁻³ and a thickness of about 0.1 μm
Buried layer 23, undoped InGaAsP active layer 24 having a band gap wavelength of 1.55 μm and a thickness of about 0.2 μm
And an impurity concentration p = 5 × 10 ¹⁷ cm ⁻³ and a thickness of about 0.1 μm
An m-type p-type InP buried layer 25 is formed.

The undoped InGaAsP active layer 2
A grating 26 is formed on 4. These laminations are mesa-etched to the substrate 21 and the side surfaces of the mesa are Fe-doped high-resistance InP layers 27, followed by an n-type I layer having an impurity concentration of n = 5 × 10 ¹⁸ cm ⁻³ and a thickness of about 0.3 μm.
nP buried layer 28 and impurity concentration p = 1 × 10 ¹⁷ cm
^-3 , a p-type InP buried layer 29 having a thickness of about 0.5 μm is formed epitaxially.

Next, the entire impurity concentration p = 5 × 10 ¹⁷ c
A p-type InP clad layer 30 having a thickness of m ⁻³ and a thickness of 1.5 μm is formed. Further, a p-type semiconductor having a band gap wavelength of 1.3 μm, an impurity concentration p = 5 × 10 ¹⁸ cm ⁻³ , and a thickness of about 0.2 μm
A type InGaAsP contact layer 31 is formed.
After the mesa shape including the undoped InGaAsP active layer 24 and the light absorbing layer 22 is formed, a modulator region p-side electrode 33 having an electrode pad shape and a laser region p-side electrode 3
4, an n-side electrode 35 is formed on the back surface of the substrate 21, and an Al ₂ O film having a thickness of about 2000 °
An AR coat (not shown) formed of _three films (refractive index: 1.75) or the like is applied to form a semiconductor optical modulator integrated DFB laser.

The difference from the first embodiment is that a laser element is integrated in the modulator.
Hereinafter, the operation of such a semiconductor optical modulator integrated DFB laser will be described. First, the laser region p-side electrode 34
When a forward voltage is applied between the n-side electrode 35 and the n-side electrode 35, holes and electrons are injected into the undoped InGaAsP active layer 24, and laser oscillation occurs.

At this time, the wavelength is selected by the grating 26, and the DFB laser oscillates. The operation of the optical modulator area is the same as that described in the first embodiment. The present invention can further have the following usage modes. In the above, a mesa stripe is formed on an n-type InP substrate, and the side surface of the stripe is formed of Fe-doped InP.
Although the case of embedding with P has been described as an example, it is considered that the same effect can be obtained by the same structure in AlInAs and GaInP having the same crystal structure in which a high resistance region can be formed by doping Fe. Can be

Although the present invention has been described with reference to the embodiments, the present invention is not limited to these embodiments. For example, as long as the mesa side surface is buried with a high resistance buried layer, the configuration of the modulator, the band gap wavelength of the light absorbing layer, and the like are arbitrary. It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0026]

As described above in detail, according to the present invention, it is possible to obtain a semiconductor optical modulator capable of obtaining a high-speed modulation characteristic by reducing the element capacitance and a semiconductor laser device having the same integrated. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor optical modulator according to a first embodiment of the present invention.

FIG. 2 is a plan view of the semiconductor optical modulator according to the first embodiment of the present invention.

FIG. 3 is a side view of the semiconductor optical modulator according to the first embodiment of the present invention.

FIG. 4 is a graph showing the p value of a semiconductor optical modulator according to a first embodiment of the present invention.
FIG. 9 is a diagram showing calculation results of the element capacitance and the thickness of the buried layer when the shape of the side electrode is changed.

FIG. 5 is a sectional view of a semiconductor optical modulator portion of a semiconductor optical modulator integrated DFB laser according to a second embodiment of the present invention.

FIG. 6 is an overall sectional view of a semiconductor optical modulator integrated DFB laser showing a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a preceding semiconductor light modulation device.

[Explanation of symbols]

 1,21 n-type InP substrate 2,22 undoped InGaAsP light absorption layer 3,7,23,25,29 p-type InP buried layer 5,27 Fe-doped high-resistance InP layer 6,28 n-type InP buried layer 8,30 p InP clad layer 9, 31 p-type InGaAsP contact layer 10, 32 insulating film, especially polyimide film 11 p-side electrode 12, 35 n-side electrode 13 AR coat 24 undoped InGaAsP active layer 26 grating 33 modulator region p-side electrode 34 laser Area p-side electrode

Claims (4)

[Claims] 1. A semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high resistance buried layer, wherein (a) a light absorbing layer formed on an n-type compound semiconductor substrate; A semiconductor optical modulator comprising a p-type buried layer having a low impurity concentration of 1 × 10 ¹⁷ cm ⁻³ or less. 2. A semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high-resistance buried layer, wherein (a) a light absorbing layer formed on an n-type compound semiconductor substrate and (b) a light absorbing layer in contact with the light absorbing layer. Te 1 × 10 ¹⁷ cm ^-3 or lower concentration and p-type buried layer impurity concentration, (c) said a p-type buried layer in contact 4 × 10 ¹⁷ cm ^-3 or more of the high-concentration p-type impurity concentration of A semiconductor optical modulator having a cladding layer. 3. A semiconductor optical modulator in which a mesa side face is buried with an Fe-doped high resistance buried layer, wherein (a) a light absorbing layer formed on an n-type compound semiconductor substrate and (b) a light absorbing layer in contact with the light absorbing layer. A p-type buried layer having a low impurity concentration of 1 × 10 ¹⁷ cm ⁻³ or less, and (c) a p-type buried layer having a high impurity concentration of 4 × 10 ¹⁷ cm ⁻³ or more in contact with the p-type buried layer. A semiconductor optical modulator having a structure in which an insulating film is buried under a cladding layer and (d) an electrode pad on a side surface of a mesa. 4. A semiconductor laser device having a semiconductor optical modulator in which a side surface of a mesa is buried with an Fe-doped high-resistance buried layer, wherein (a) a light absorption layer formed on an n-type compound semiconductor substrate; A semiconductor optical modulator having a p-type buried layer having a low impurity concentration of 1 × 10 ¹⁷ cm ⁻³ or less in contact with the semiconductor optical modulator; and (b) a semiconductor having an active layer connected to a light absorbing layer of the semiconductor optical modulator. A semiconductor laser device wherein a laser is integrated integrally.