JPH0951142A - Semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the semiconductor laser, which is operated with the power supply line having the same polarity by laminating a laser part having an active layer and a modulator part having an absorbing layer on a substrate, and providing the inverted type for respective upper and lower clad laysers of the active layer and the absorbing layer. SOLUTION: On the same substrate 1, a laser part having an active layer 3 and a modulator part having an absorbing layer 7 are laminated in the direction of an optical resonator. A clad layer 2 at the lower side of the active layer 3 has the same conducting type as the substrate 1. A clad layer 4 at the upper side has the reverse conducting type from the substrate 1. A clad layer 6 below the absorbing layer 7 has the reverse conducting type from the substrate 1. A clad layer 8 above has the same conducting type as the substrate 1. Therefore, the voltage in the foward direction required for the operation of the laser part and the voltage in the reverse direction required for the operation of the modulator part can be applied by imparting the voltage having the same polarity to the surface electrode. That is to say, the semiconductor laser can be operated with the power supply line having the same porality.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a semiconductor light emitting device,
In particular, it relates to a semiconductor laser integrated with an optical modulator.

A semiconductor laser integrated with an optical modulator has been used as a light source for optical communication. In recent years, as optical fiber information transmission spreads over a wide range from a trunk system to an optical LAN and a subscriber system, the Module simplification is required.

[0003]

2. Description of the Related Art FIG. 6 shows a conventional example of a semiconductor laser integrated with an optical modulator. In the figure, 1 is an n-type semiconductor substrate, 3 is an active layer, 4 is a p-type cladding layer, 7 is an absorption layer, 11 is a p-side electrode of the laser section, 12 is a p-side electrode of the modulator section, and 13 is a substrate side. The n-side electrode is a common electrode.

A laser section having an active layer 3 for amplifying light by current injection and a modulator section having an absorption layer 7 whose absorption coefficient is changed by applying a voltage are formed on the same substrate 1 in the optical resonator direction.
It is a device monolithically integrated on top.

In this device, a direct current equal to or higher than the oscillation threshold current of the laser is passed through the laser section for continuous oscillation, and a voltage is applied to the modulator section to apply an electric field to the absorption layer to change its absorption coefficient. As a result, the intensity of the laser light emitted to the outside is modulated and the signal is transmitted.

[0006]

However, in the semiconductor laser in which the conventional optical modulator is integrated, the polarity of the voltage applied to the surface electrode is positive with respect to the substrate, whereas it is negative in the modulator section. Therefore, two power supply lines with different polarities are required, which complicates the drive circuit.

An object of the present invention is to obtain a semiconductor laser integrated with an optical modulator that operates on a power supply line of a single polarity.

[0008]

[Means for Solving the Problems] The above problems can be solved by: 1) Modulation having a laser section having an active layer for amplifying light by current injection, and an absorption layer having an absorption coefficient changed by voltage application, on the same substrate. And an upper part of the active layer have the same conductivity type as that of the substrate, and an upper layer of the active layer has a conductivity type opposite to that of the substrate. Is a semiconductor light-emitting element whose conductivity type is opposite to that of the substrate, and the upper layer of the absorption layer is the same conductivity type as the substrate, or 2) when the conductivity type of the modulator section is an n-type substrate Is p / n / p / n from the upper layer, and is n / p / n / p from the upper layer when a p-type substrate is used, and the conductivity type of the device surface is the same in both the laser section and modulator section. This is achieved by the semiconductor light emitting device described in 1 above.

[0009]

FIG. 1 is a diagram for explaining the principle of the present invention. As shown in the figure, the conductivity type of the cladding layers 2 and 4 above and below the active layer 3 in the laser section and the conductivity type of the cladding layers 6 and 7 above and below the absorption layer in the modulator section are reversed to obtain a laser When a voltage having a forward polarity is applied to the modulator section, a reverse voltage is applied to the modulator section. At this time, in the modulator part, the pn junction formed by the substrate and the lower clad layer is connected in series in the opposite direction to the pn junction formed by the clad layers above and below the absorption layer. When the pn junction in the opposite direction is connected in series, the voltage is mainly applied to the pn junction biased in the reverse direction, so that a sufficient electric field for modulation can be applied to the absorption layer.

Therefore, in the present invention, a forward voltage necessary for the operation of the laser section and a reverse voltage necessary for the operation of the modulator section are applied by applying the same polarity voltage to the substrate to the surface electrode. can do. That is, this device can operate with a single-polarity power supply line.

[0011]

EXAMPLE 1 FIG. 2 is an explanatory diagram of Example 1 of the present invention. In the figure, the diffraction grating 1A is formed in the laser section on the n-InP substrate 1, and the active layer 3, p-InP clad layer 4, and p-In are formed on it.
GaAsP (wavelength for composition display λg = 1.3 μm) Contact layer 5
The p-InP clad layer 6, absorption layer 7, n-InP clad layer 8, n-InGaAsP (λ
g = 1.3 μm) The contact layer 9 is laminated.

With the above structure, the pn junction between the n-InP substrate 1 and the p-InP cladding layer 4 becomes forward by applying a positive voltage to the substrate in the laser portion, and the p- InP clad layer 6, absorption layer 7, n-InP clad layer
Since the pn junction composed of 8 is in the opposite direction, most of the applied voltage can be applied to the pn junction including the absorption layer and an electric field can be applied to the absorption layer, changing the absorption coefficient of the absorption layer. it can. Therefore, this device can operate only on the positive power supply line.

Next, an outline of a method of manufacturing this element will be described. First, only the laser section on the n-InP substrate 1 has a diffraction grating 1A.
And then by metalorganic vapor phase epitaxy (MOCVD)
A laser active layer 3, a 2 μm thick p-InP cladding layer 4, and a 0.2 μm thick p-InGaAsP (λg = 1.3 μm) contact layer 5 are grown on the substrate.

Next, a silicon oxide (SiO ₂ ) film is formed on the surface of the laser portion by photolithography, and the growth layer of the modulator portion is removed by etching until it reaches the substrate by using this as a mask.

Next, with the SiO ₂ mask remaining, the p-InP clad layer 6, the absorption layer 7, and the thickness of the p-InP clad layer 6, the thickness of which is 0.3 μm, are formed only on the modulator portion removed by etching by the MOCVD method again.
2 μm n-InP clad layer 8, 0.2 μm thick n-InGaAs
A P (λg = 1.3 μm) contact layer 9 is grown.

Next, in order to control the transverse mode, a mesa having a width of about 1.2 μm is formed by etching in the cavity direction, and then an iron (Fe) -doped InP layer is grown and embedded by MOCVD on both sides of the mesa.

Finally, the contact layer at the boundary between the laser section and the modulator section is removed, a SiO ₂ layer 10 is deposited on the surface of the substrate as an insulating film, and a window for electrode formation is opened in this film to form the laser section. The Ti / Pt / Au electrode 11 stacked in order from the bottom is formed on the surface of the substrate, and the AuGe stacked in order from the bottom on the modulator surface and the substrate side.
/ Au electrodes 12 and 13 are formed to form a device.

The layer structure of the active layer of the laser section and the absorption layer of the modulator section is not particularly related to the effect of the present invention, but is exemplified as follows. In a device with a wavelength of 1.55 μm, the active layer of the laser section has a thickness of 0.1 μm InGaAsP (λg =
1.1 μm) Guide layer and 0.1 μm thick InGaAsP (λg = 1.5
5 μm) The light emitting layer is formed, and the absorption layer of the modulator is 0.2 μm thick.
m InGaAsP (λg = 1.46 μm).

The above example is a bulk active layer. As an example using a quantum well, an InGaAsP (λg = 1.15 μm) guide layer having a thickness of 0.1 μm and an active layer of a laser portion having a thickness of 10 nm are used. InGaAsP (λg = 1.15μm) barrier layer and thickness of 5nm
10% multiple quantum well (MQW) layer consisting of 0.8% compressive strain InGaAsP well layer, 0.1 μm thick InGaAsP (λg = 1.15 μm)
m) It is composed of a guide layer. The absorption layer of the modulator is composed of a 0.1 μm thick InGaAsP (λg = 1.15 μm) guide layer and a 5 nm thick InGaAsP (λg = 1.15 μm) barrier layer.
It is composed of a 10-period multiple quantum well layer consisting of a 5 nm In _0.53 Ga _0.47 As well layer and a 0.1 μm thick InGaAsP (λg = 1.15 μm) guide layer.

Even if an active layer _or absorption layer having a composition _, number _of layers _{, and} layer thicknesses other than the layer structure exemplified above is used, or the wavelength is 1.3 μm.
The effect of the present invention does not change even if a layered structure for a band element is used. FIG. 3 is an explanatory diagram of the second embodiment of the present invention.

Although the distributed feedback laser having the diffraction grating in the laser section has been described in the first embodiment, there is a structure in which the laser section does not have the diffraction grating. This figure shows a Fabry-Perot laser without a diffraction grating, and 2 is an n-InP cladding layer.

In this laser, a direct current is passed through the laser section, and a voltage is applied to the modulator section to change the absorption coefficient of this section to change the internal loss in the laser resonator, thereby oscillating the laser. Switch non-oscillation.

Although the diffraction grating is not provided in the following embodiments, it goes without saying that the diffraction grating may be provided with the same structure as these. FIG. 4 is an explanatory diagram of the third embodiment of the present invention.

In this example, the p-InP upper clad layer 2 a is laminated on the n-InP upper clad layer 8 adjacent to the absorption layer 7. In this case, the layer structure of the modulator section is a pnpn structure. When the same positive voltage as that of the laser section is applied to the p-side electrode, the absorption layer 2 is provided in the pn junction in the opposite direction. The applied voltage is mainly applied here, and the electric field of the absorption layer can be changed.

With this structure, both the laser section and the modulator section are p-type on the substrate surface, and only electrode separation is performed.
Since the electrodes can be formed with the same material, the device manufacturing process is simplified.

FIG. 5 is an explanatory diagram of the fourth embodiment of the present invention.
Although the conductivity type of the substrate is all n-type in the above-described embodiments, it can be formed on the p-type substrate 1 '. In this case, the conductivity types of the clad layer and the contact layer are reversed from those of the previous embodiments. This figure shows Example 4
This is an example manufactured on a mold substrate. For other embodiments,
Similarly, it can be formed on a p-type substrate.

In this case, since a negative voltage is applied to the substrate in both the laser section and the modulator section, only a negative power supply line is needed. Since the polarity of the power supply line is determined by the drive circuit used, it is possible to deal with the power supply line of any polarity by selecting the conductivity type of the substrate according to it.

Next, the electrical separation of the laser section and the modulator section will be described. Also in the conventional laser integrated with the modulator shown in FIG. 6, the upper p-type cladding layer is common to the laser part and the modulator part, and the forward voltage is applied to the laser part and the modulator part is applied to the modulator part. Reverse voltage is applied. However, since the width of the active layer is as narrow as about 1 μm and both sides are high resistance layers, the resistance between the electrodes becomes MΩ or more when a certain distance (several tens of μm) is taken, and electrical isolation is sufficient. The same applies to the structure of each embodiment.

The applied voltage depends on the method of use, but is, for example, 2 V in the laser section, 1 V when the modulator section is on and 3 V when the modulator section is off in Example 1 of FIG.

[0030]

According to the present invention, it is possible to obtain a semiconductor laser integrated with an optical modulator that operates on a power supply line of a single polarity.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of Embodiment 1 of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of Embodiment 4 of the present invention.

FIG. 6 is an explanatory diagram of a conventional example.

[Explanation of symbols]

1 n-InP substrate 1'p-InP substrate 1A Diffraction grating 2 n-InP cladding layer 3 Active layer 4 p-InP cladding layer 5 p-InGaAsP (λg = 1.3 μm) Contact layer 6 p-InP cladding layer 7 Absorption layer 8 n-InP clad layer 9 n-InGaAsP (λg = 1.3 μm) contact layer 10 Insulating film SiO ₂ film 11 to 13 electrodes

Claims (2)

[Claims] 1. A laser section having an active layer for amplifying light by current injection and a modulator section having an absorption layer whose absorption coefficient changes by voltage application are integrated on the same substrate in the optical resonator direction. A lower layer of the active layer has the same conductivity type as the substrate, an upper layer of the active layer has a conductivity type opposite to the substrate, and a lower layer of the absorption layer has a conductivity type opposite to the substrate,
A semiconductor light emitting device, wherein an upper layer of the absorption layer has the same conductivity type as the substrate. 2. The conductivity type of the modulator portion is p / n / p / n from the upper layer when an n-type substrate is used, and n / p / from the upper layer when a p-type substrate is used. 2. The semiconductor light emitting device according to claim 1, wherein the semiconductor type is n / p, and the conductivity type of the device surface is the same in both the laser section and the modulator section.