JPH0964459A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor device in which the thermal diffusion of a dopant is suppressed and whose quality is high. SOLUTION: In a semiconductor device, an MQW layer 7 and current stop layers 2, 3, 4, which are formed on an InP substrate 1 and which constitute a current constriction means used to constrict a current are formed, an InP clad layer 11 which is formed on the current constriction means and which is doped with Be is provided, and an InGaAs contact layer 12 which is formed on the InP clad layer 11 and which is doped with Zn and Be is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a semiconductor laser used as a light source in an optical transmission system or the like.

[0002]

2. Description of the Related Art Development of an optical transmission system is in progress, and a semiconductor laser diode or the like is used as a light source thereof. Among them, an electro-absorption type (hereinafter referred to as EA) optical modulator and a distributed feedback laser diode (hereinafter referred to as D)
FB-LD. ) And semiconductor devices that have been integrated are attracting attention as key devices for next-generation optical transmission systems for trunk lines, and in recent years, research aimed at their practical application has been actively conducted. Further, in such a semiconductor laser, a buried structure in which an active layer extending on a substrate is covered with a clad layer and high luminous efficiency is obtained at a low threshold current is generally known. Also, especially 10G
In a device for b / s transmission, a current constriction structure including a semi-insulating layer such as InP doped with Fe (iron) and an n-type InP hole trap layer is used to reduce the capacitance of a modulator. There is.

FIG. 6 (a) is shown, for example, in the Proceedings of the IEICE General Conference 1995 (page 346).
It is a perspective view which shows the structure of the conventional semiconductor device which integrated the modulator and DFB-LD. Further, FIG.
6A is a partially enlarged cross-sectional view of a portion surrounded by a dashed line B in FIG. 6A, showing a heterojunction structure used in the conventional semiconductor device of FIG. In FIG. 6, 1
Is an n-type InP substrate doped with S (sulfur), and 2 and 4 are semi-insulating materials such as InP doped with Fe (iron) (Semi-Ins
Sulating: S.I.) layer, 3 is n-type InP doped with S
The hole trap layers 5 are p-type InP clad layers doped with Zn (zinc) (carrier concentration 7 ± 2 × 10 ¹⁷ c
m ^-3 ), 6 is Zn-doped p-type InGaA
s contact layer (carrier concentration 1 × 10 ¹⁹ cm ⁻³ or more), 7 is InGaA provided on the n-type InP substrate 1.
sP / InGaAs Multiple Quantum Well
ell: MQW) absorption layer (12 wells) (hereinafter referred to as MQW absorption layer), 8 is also MQ on the n-type InP substrate 1.
InGaAsP / InG provided integrally with the W absorption layer 7
aAs multiple quantum well active layer (hereinafter referred to as MQW active layer), 9 is a single wavelength laser diode, for example, DFB-.
Reference numeral 10 denotes an LD, and 10 denotes an EA external modulator such as an EA optical modulator.

In such a DFB-LD 9, laser light is emitted from the MQW active layer 8, but the semi-insulating layers 2 and 4 and the n-type InP hole trap layer 3 act as a current blocking layer. , The injection current is MQW active layer 8
And the MQW absorption layer 7 are concentrated (current constriction) and no current flows in the current blocking layers 2, 3 and 4, so that high emission efficiency can be obtained with a low threshold current. The MQW active layer 8, the MQW absorption layer 7, the semi-insulating layers 2 and 4, and the n-type InP hole trap layer 3 are n-type I.
It is provided on the nP substrate 1 and constitutes a current constricting means for confining a current.

Further, the active layer of the conventional DFB-LD 9 and the absorption layer of the EA external modulator 10 are the MQW active layer 8 and the MQW absorption layer 7, respectively, and the modulator length is 100 μm.
m. In this conventional semiconductor device, in order to improve the electrical isolation between the EA external modulator 10 and the DFB-LD 9, the current confinement structure has the p / SI / n / S. I./n structure. With such a structure, the capacitance C between the p-type InP clad layer 5 and the n-type InP hole trap layer 3 is reduced so that the signal applied to the EA external modulator 10 is n-type InP.
This is intended to suppress leakage to the DFB-LD 9 side via the hole trap layer 3.

[0006]

If the structure shown in FIG. 6 can be obtained ideally, good device characteristics should be obtained. However, in practice, Zn, which is a p-type dopant, is grown during epitaxial growth. In addition, thermal diffusion occurs from the doped p-type InP clad layer 5 and the p-type InGaAs contact layer 6 to the undoped MQW active layer 8, and desired characteristics cannot be obtained. The signal applied to the EA external modulator 10 is n-type InP
There is a possibility of leaking to the DFB-LD 9 side through the hole trap layer 3, and further, the doping concentration is reduced by the amount diffused, and there is a problem that a desired concentration cannot be obtained.

FIG. 7 shows the MQW in the semiconductor device of FIG.
7 is a graph showing the relationship between the concentration of impurities in the absorption layer 7 and the extinction ratio. As shown in FIG. 7, when impurities such as Zn enter the MQW absorption layer 7 and the concentration of the impurities increases, the extinction ratio, which is one of the important device characteristics, decreases. . In addition, FIG. 8 shows an actual Zn ion diffusion state (Secondary Ion Mass Spectroscopy).
This is a result of examination by Spectroscopy (SIMS). As shown in FIG. 8, Zn, which is a dopant, is added to the doped p-type InP clad layer 5 and p.
It can be seen that the type InGaAs contact layer 6 is thermally diffused to the undoped MQW absorption layer 7 and the MQW active layer 8.

Further, as described in JP-A-61-139082 and JP-A-7-86683, a method of using Be (beryllium) as a dopant instead of Zn can be considered, but in this case. Shows that it is difficult to obtain a desired doping concentration and a good mirror surface in the semiconductor device according to the present invention, and it is not possible to obtain the desired characteristics, based on an independent experimental result described later, that is, However, there is a problem that practical application cannot be achieved simply by doping Zn, Be or Zn.

The present invention has been made to solve the above problems, and it is possible to prevent unnecessary thermal diffusion of the dopant and obtain desired characteristics without lowering the extinction ratio and the like. At the same time, it is an object of the present invention to obtain a high-quality semiconductor device capable of obtaining a desired doping concentration and a good mirror surface.

[0010]

According to another aspect of the present invention, there is provided a semiconductor device, a substrate, a current constricting means provided on the substrate for constricting a current, and a Be-doped InP provided on the current constricting means. A cladding layer and an InGaAs contact layer provided on the InP cladding layer and doped with Zn and Be are provided.

The InGaAs contact layer is made of Zn.
And InG doped with Be and Be at a predetermined concentration.
It is composed of an aAs layer.

The InGaAs contact layer is made of Be.
A first layer formed of an InGaAs layer doped with Zn and provided on the InP clad layer, and a second layer formed of an InGaAs layer doped with Zn and provided on the first layer. , Are provided.

Further, B in the InGaAs contact layer
The concentration of e is 3 × 10 ¹⁸ cm ⁻³ or less.

The thickness t (μm) of the second layer and the Zn concentration [Zn] (cm ⁻³ ) in the second layer are the Be concentration (cm ⁻ ) in the first layer. ³ ) is [Be] (cm ⁻³ ), the following formula [Zn] t + [Be] (1-t) = 1 × 10 ¹⁵ (cm ⁻² ) is satisfied.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. The semiconductor device of the present invention is provided with a heterojunction structure as shown in FIG. 1 based on the result of an independent experiment described later, and also has an EA external modulator 10 and a DFB-LD 9 as shown in FIG. It is an integrated structure.

Before describing the structure of the semiconductor device of the present invention, first, the results of an experiment conducted independently will be described. In order to prevent Zn diffusion from the p-type InGaAs contact layer 6 doped with Zn of about 1 × 10 ¹⁹ cm ⁻³ to the lower layer, Be, which is expected to have small diffusion, is used as a dopant instead of Zn. In consideration of the metal-organic chemical vapor deposition method.
or Deposition: MOCVD) to bis-methylcyclopentadienyl beryllium (Be (CH ₃ C ₅
Be doping experiment with H ₄ ) ₂ : Cp ₂ Be)
Type InP clad layer 5 specification 7 × 10 ¹⁷ cm ^-3 and p type In
It was investigated whether or not the specifications of the GaAs contact layer 6 satisfy 1 × 10 ¹⁹ cm ⁻³ . As a result, the p-type InP clad layer 5
It was found that a high quality product satisfying the specifications can be obtained, while the p-type InGaAs contact layer 6 satisfies the specifications, but becomes cloudy due to doping of about 4 × 10 ¹⁸ cm ⁻³ or more. It turned out to make things worse. At this point, it was understood that simply changing Zn to Be was not enough. In addition, by this experiment, B
It was also confirmed that e diffuses into the Zn-doped layer but hardly diffuses into other layers.

Next, the structure of the semiconductor device of the present invention will be described. In the embodiment of the present invention shown in FIG. 1,
The difference from the conventional example of FIG. 6 is that p-type In doped with Zn is used.
A Be-doped p-type InP clad layer 11 doped with Be was used instead of the P-clad layer 5, and Z was used instead of the p-type InGaAs contact layer 6 doped with Zn.
The use of a p-type InGaAs contact layer 12 doped with both n and Be is two points. Since the other structure is the same as the conventional example of FIG. 6, refer to FIG.
The description is omitted here.

In this embodiment, Be-doped I
The carrier concentration of the nP clad layer 11 is 7 × 1 as specified.
It is set to 0 ¹⁷ cm ^-3 . Further, the carrier concentration of the InGaAs contact layer 12 doped with both Be and Zn is set to 1 × 10 ¹⁹ cm ⁻³ as specified, but the content is that the Be concentration is about 3 × 10 ¹⁸ cm ⁻³ and the Zn concentration is about 3 × 10 ¹⁸ cm ^−3. Is 7 × 10 ¹⁸ cm ^-3 . From the above experimental results, it was found that doping with Be concentration of about 4 × 10 ¹⁸ cm ⁻³ or more causes cloudiness and deteriorates the surface condition. Therefore, the Be concentration is set to the maximum value that does not cause cloudiness. That is, about 3 × 10 ¹⁸ cm ^-3 is suppressed to obtain a good mirror surface. Further, since the content of Zn causing diffusion is reduced and the amount of Be with less diffusion is used as much as possible, the thermal diffusion of the dopant can be prevented and suppressed, and the extinction ratio lowers due to the penetration of the dopant due to the thermal diffusion. And the like, and desired characteristics can be obtained.

Further, in this embodiment, in order to improve the electrical isolation between the EA external modulator 10 and the DFB-LD 9, the current confinement structure is p / p as in the conventional example of FIG. Since it is configured to have the SI / n / SI / n structure, the p-type Be-doped InP cladding layer 1
1 and the capacitance C ₁ between the n-type InP hole trap layer 3 and the signal applied to the EA external modulator 10 leaks to the DFB-LD 9 side through the n-type InP hole trap layer 3. This can be suppressed, and unlike the conventional example shown in FIG. 6, thermal diffusion of the dopant can be prevented as described above, so that desired favorable device characteristics can be obtained.

According to this embodiment of the present invention, the Be-doped InP cladding layer 11 has the structure as described above.
Since the InGaAs contact layer 12 doped with Zn and Be is used, unnecessary thermal diffusion of the dopant can be prevented, and the extinction ratio can be prevented from lowering due to the thermal diffusion of the dopant. It is possible to obtain a high-quality semiconductor device that can obtain desired characteristics, obtain a desired doping concentration and a good mirror surface, and prevent thermal diffusion while maintaining high quality.

Embodiment 2 FIG. An example of another embodiment of the present invention is shown in FIG. In the heterojunction structure of the embodiment shown in FIG. 2, the difference from the first embodiment of FIG.
p-type InGaAs of FIG. 1 doped with both e and Zn
InG doped with Be instead of the contact layer 12
p-type InGaAs contact layer 12 formed of aAs layer and provided on Be-doped InP clad layer 11
p-type InGaAs formed on the p-type InGaAs contact layer 12aa (first layer), which is composed of an aa (first layer) and a Zn-doped InGaAs layer.
This is the point that the p-type InGaAs contact layer 12a composed of two layers including the contact layer 12ab (second layer) is used. Since other structures are the same as those of the first embodiment shown in FIG. 1, the description thereof will be omitted here.

With such a structure, Zn and Be are formed between the uppermost Zn-doped p-type InGaAs contact layer 12ab and the Be-doped InGaAs contact layer 12aa immediately below the uppermost Zn-doped InGaAs contact layer 12ab by heat application during epitaxial growth. Mutual diffusion occurs. FIG. 3 and FIG.
The respective concentration profiles of Zn and Be in the respective layers before and after thermal diffusion are shown. As can be seen from FIG. 4, interdiffusion occurs between the Zn-doped p-type InGaAs contact layer 12ab and the Be-doped InGaAs contact layer 12aa.
Does not diffuse into the InP clad layer 11 doped with. Thus, Be diffuses into the Zn-doped layer, but does not diffuse into the other layers, as described above, as confirmed by the above experimental results.

Generally, the p-type InGaAs contact layer is suitable to have a thickness of about 1 μm. Therefore, also in this embodiment, the total thickness of the p-type InGaAs contact layer 12a including the two layers 12aa and 12ab is about 1 μm. To form. In addition, the p-type InGaAs contact layer 1
The specification of the carrier concentration of 2a is 1 × 10 ¹⁹ as described above.
Since it is (cm ⁻³ ), the minimum required Zn concentration in this case can be defined by the following equation (1). [Zn] t + [Be] (1-t) = 1 × 10 ¹⁵ (cm ⁻² ) ... (1) where [Zn] and [Be] are the concentrations of Zn and Be (cm ⁻³ ), respectively. And t is InGaA doped with Zn.
The thickness (μm) of the s contact layer 12ab.

FIG. 5 shows the necessary Zn concentration plotted against t. Here, regarding the Be concentration [Be], it was found from the above experimental results that it becomes cloudy with a doping of about 4 × 10 ¹⁸ cm ⁻³ or more and deteriorates the surface condition. The maximum value is [Be] = 3 × 10 ¹⁸ (cm ⁻³ ). At this time, for example, the thickness t of the InGaAs contact layer 6 is t = 0.
In the case of 5 μm, the Zn concentration [Zn] is calculated as [Zn] = 1.7 × 10 ¹⁹ cm ⁻³ from the above formula (1), and t =
In the case of 0.3 μm, [Zn] = 2.6 × 10 ¹⁹ cm ⁻³ is obtained. Thus, the combination obtained from these equations (1) may be used.

According to this embodiment, p-type In doped with both Be and Zn used in Embodiment 1 of FIG. 1 is used.
Instead of the GaAs contact layer 12, a layer having a two-layer structure of a Be-doped p-type InGaAs layer 12aa and a Zn-doped p-type InGaAs contact layer 12ab is used. The Zn-doped InGaAs contact layer 12 has the same effects as the Zn-doped InGaAs contact layer 12 because the structure has Zn only on the outermost surface.
Since Zn only thermally diffuses during the growth of ab, MQ
Diffusion of Zn into the W active layer 8 can be surely suppressed, a decrease in extinction ratio or the like caused by thermal diffusion of a dopant can be prevented, desired characteristics can be obtained, and a desired doping concentration or a favorable doping concentration can be obtained. A mirror surface can be obtained, and a high quality semiconductor device can be obtained.

Since the present invention is constructed as described above, it has the following effects.

On the Be-doped InP clad layer,
By providing the InGaAs contact layer doped with Zn and Be, the content of Be with small diffusion was increased and the content of Zn was reduced, so that unnecessary thermal diffusion of the dopant can be prevented. In addition, it is possible to prevent a decrease in extinction ratio caused by thermal diffusion of a dopant and obtain desired characteristics, and
It is possible to obtain a semiconductor device capable of preventing thermal diffusion while maintaining high quality.

The InGaAs contact layer is made of Zn and Be.
InGaAs each doped with a predetermined concentration
Since it is composed of layers, the above-mentioned effects are exhibited and the manufacturing process is also easy.

The InGaAs contact layer is composed of a Be-doped InGaAs layer and is provided on the InP clad layer, and a Zn-doped In layer.
Since the structure is composed of the GaAs layer and the second layer provided on the first layer, and the structure has Zn only on the outermost surface, during the growth of the Zn-doped InGaAs layer, Since only Zn thermally diffuses, it is possible to reliably suppress the diffusion of Zn into the active layer, prevent the extinction ratio from decreasing due to thermal diffusion of the dopant, and obtain desired characteristics. A high quality semiconductor device can be obtained.

Also, Be in the InGaAs contact layer
Since the concentration of ³ was suppressed to 3 × 10 ¹⁸ cm ⁻³ or less, which is the maximum value at which a good mirror surface can be obtained without clouding, a good mirror surface can be obtained.

Furthermore, the thickness t (μm) of the second layer and the Zn concentration [Zn] (cm ⁻³ ) in the second layer are the Be concentration (cm ⁻ ) in the first layer. ³ ) is [Be] (cm ^-3 ),
Since the following formula [Zn] t + [Be] (1-t) = 1 × 10 ¹⁵ (cm ⁻² ) is satisfied, the dopant concentration of 1 × 10 ¹⁹ (cm ⁻³⁾ which is the specification of the InGaAs contact layer. ) And the thickness of 1 μm, the diffusion of Zn can be suppressed, whereby the extinction ratio can be prevented from lowering due to thermal diffusion of the dopant, and desired characteristics can be obtained, and a high-quality semiconductor can be obtained. The device can be obtained.

[Brief description of drawings]

FIG. 1 is a partially enlarged cross-sectional view showing a heterojunction structure of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a partial enlarged cross-sectional view showing a heterojunction structure of a semiconductor device according to a second embodiment of the present invention.

3 is Zn and Be before thermal diffusion in the structure of FIG.
It is the figure which showed the graph by SIMS measurement which shows the profile of FIG.

4 is Zn and Be after thermal diffusion in the structure of FIG.
It is the figure which showed the graph by SIMS measurement which shows the profile of FIG.

5 is a Zn-doped InGaAs in the structure of FIG.
It is a figure showing the relation between layer thickness and required Zn concentration.

FIG. 6 is a perspective view and a partially enlarged cross-sectional view showing a conventional semiconductor device.

FIG. 7 is a graph showing the impurity concentration dependence of the extinction ratio of the MQW absorption layer in the conventional semiconductor device.

FIG. 8 shows Zn in the InP clad layer doped with Zn and the undoped MQW absorption layer and active layer.
It is the figure which showed the graph by SIMS measurement which shows the diffusion profile of.

[Explanation of symbols]

1 S-doped n-type InP substrate, 2,4 Fe-doped In
P semi-insulating layer, 3 n-type InP hole trap layer, 5
Zn-doped p-type InP clad layer, 6 Zn-doped p-type InGaAs contact layer, 7 MQW absorption layer, 8 M
QW active layer, 9 single wavelength laser diode (DFB-L
D) 10 EA external modulation, 11Be-doped p-type In
P clad layer, 12,12a p-type InGaAs contact layer, 12aa Be-doped p-type InGaAs contact layer, 12ab Zn-doped p-type InGaAs contact layer.

Claims (5)

[Claims] 1. A substrate, a current confinement means provided on the substrate for constricting a current, and a Be-doped I provided on the current confinement means.
A semiconductor device comprising an nP clad layer and an InGaAs contact layer provided on the InP clad layer and doped with Zn and Be. 2. The semiconductor device according to claim 1, wherein the InGaAs contact layer comprises an InGaAs layer doped with Zn and Be at predetermined concentrations. 3. The InGaAs contact layer comprises a Be-doped InGaAs layer, a first layer provided on the InP clad layer, and a Zn-doped InGaAs layer. The semiconductor device according to claim 1, further comprising a second layer provided on the one layer. 4. The semiconductor device according to claim 1, wherein the concentration of Be contained in the InGaAs contact layer is 3 × 10 ¹⁸ cm ⁻³ or less. 5. The thickness t (μm) of the second layer and the concentration [Zn] (cm ⁻³ ) of Zn in the second layer are the concentration of Be in the first layer. When (cm ⁻³ ) is [Be] (cm ⁻³ ), the following formula [Zn] t + [Be] (1-t) = 1 × 10 ¹⁵ (cm ⁻² ) is satisfied. The semiconductor device according to claim 3 or 4.