JPH06244492A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser whose characteristic deterioration by the diffusion of p-type impurities into an active layer can be suppressed. CONSTITUTION:Concerning to a semiconductor laser having SCH structure, photoconfinement layers 3 and 5 provided on both sides of an active layer 4 are both n-type doped ones. The diffusion of impurities in a p-type clad layer into the active layer is suppressed by the n-type photoconfinement layer 3 arranged between the active layer 2, ad it becomes possible to prevent the deterioration of the laser characteristics such as the increase of threshold current, decrease of the efficiency, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used as a light source for optical fiber communication.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional DH (Double Heterostruct
FIG. 3 is a schematic sectional view showing a semiconductor laser having a (ure) structure. In the figure, 1 is Z with an impurity concentration of 5 × 10 ¹⁸ cm ^-3
n-doped p-type InP substrate, 2 has an impurity concentration of 1 to 3 × 1
0 ¹⁸ cm ^-3 , Zn-doped p-type InP clad layer with a thickness of 2 μm, 101 is undoped InG with a thickness of about 100 nm.
The aAsP active layer 6 is an S-doped n-type InP clad layer having an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ and a thickness of 1 μm.

FIG. 4 shows a conventional SCH (Separated Coordinate).
FIG. 3 is a schematic cross-sectional view of a semiconductor laser having an nfinement heterostructure structure and including a multi-quantum well (MQW) active layer. In the figure, 1,
Reference numerals 2 and 6 denote the same or corresponding portions as those in FIG. 3, and 103 has an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ and a thickness of about 5
0 nm Zn-doped p-type InGaAsP optical confinement layer, 4 is undoped M made of InGaAs and InGaAsP
The QW active layer 105 is an S-doped n-type InGaAsP optical confinement layer having an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ and a thickness of about 50 nm.

As described above, in the conventional semiconductor laser, Zn is most commonly used as the dopant for the p-type layer, and the p-type layer has a higher resistance than the n-type layer. It is desired to dope to a concentration of about 1 × 10 ¹⁸ cm ⁻³ or more.

Next, the operation will be described. D in Figures 3 and 4
When a voltage is applied to the H structure so that the p-type layer 1 side becomes positive, the potential barrier of the pn junction formed at the interfaces of the active layer 101 and the cladding layer 2, the active layer 4 and the cladding layer 103 becomes small, Electrons and holes are injected into the active layers 4 and 101 to cause laser oscillation. In the SCH structure of FIG. 4, carriers such as electrons and holes are confined in the active layer 4, but generated light is generated by the light confinement layers 103 and 105.
Spreads and is trapped.

[0006]

As described above, in the conventional semiconductor laser, the p-type layer has a Zn doping concentration of 1 × 10 ¹⁸ cm ^-3.
More layers are used. However, p-type dopants such as Zn easily diffuse due to heat, and metal organic chemical vapor deposition (MOC)
During the growth of the DH structure by VD) or the like, or during the buried growth for manufacturing the buried laser, it diffuses into the active layer. When Zn diffuses into the active layer to increase the hole concentration, absorption loss due to valence band absorption, free carrier absorption, etc., increases, and deterioration of laser characteristics such as increase in threshold current and decrease in efficiency occurs. There was a problem.

The present invention has been made to solve the above problems, and an object thereof is to obtain a semiconductor laser having a structure in which the diffusion of Zn into the active layer is suppressed and the laser characteristics are not deteriorated. .

[0008]

The semiconductor laser according to the present invention has an SCH structure, and the optical confinement layers on both sides of the active layer are each doped with n-type.

[0009]

In the present invention, the light confinement layer containing the n-type dopant capable of suppressing the diffusion of Zn is provided on both sides of the active layer to prevent the diffusion of Zn in the p-type cladding layer into the active layer. It is possible to prevent deterioration of laser characteristics such as increase of threshold current and decrease of efficiency.

[0010]

EXAMPLES Example 1. FIG. 1 is a sectional view showing the structure of the main part of a semiconductor laser according to the first embodiment of the present invention. In the figure, 1 is a Zn-doped p-type InP substrate having an impurity concentration of 5 × 10 ¹⁸ cm ⁻³ , and 2 is an impurity concentration of 1 to 3 × 10 ¹⁸ cm 3.
^-3 , Zn-doped p-type InP clad layer with a thickness of 2 μm,
4 is an undoped MQW active layer made of InGaAs and InGaAsP, 6 is an S-doped n-type InP cladding layer having an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ and a thickness of 1 μm, and 3 and 5
Has an impurity concentration of 1 × 10 ¹⁸ cm ^-3 and a thickness of about 50 nm.
It is a doped n-type InGaAsP optical confinement layer.

In the laser structure of this embodiment, the S-doped n-type optical confinement layer 3 exists between the Zn-doped p-type cladding layer 2 and the MQW active layer 4. Zn has a property that diffusion does not proceed in a region where an n-type dopant such as S exists. FIG. 5 shows it, and is the SIMS measurement result of the doping profile of Zn and S in the structure of FIG. As shown in FIG. 5, Zn diffuses from the p-type cladding layer 2 to the active layer 4, but does not diffuse much into the n-type cladding layer 6 containing S even after the buried growth. Therefore, in the structure according to the present embodiment, Zn remains at the interface with the n-type optical confinement layer 3 and does not diffuse to the active layer 4.

Thus, in this embodiment, the SCH
In the semiconductor laser having the structure, the light confinement layers disposed above and below the active layer are both n-type doped, so that diffusion of Zn into the active layer in the manufacturing process can be suppressed, and laser characteristics deteriorate. It is possible to obtain a semiconductor laser in which

In the semiconductor laser according to this embodiment,
The pn junction is p-type InP clad layer 2 and n-type InGaAs
It is formed at the interface with the P light confinement layer 3, but when a voltage is applied, the potential barrier of the pn junction is lowered and carriers are injected, and the carriers are confined in the active layer 4 to cause laser oscillation.

FIGS. 2 (a) to 2 (c) show energy bands in a non-biased state in a semiconductor laser having an SCH structure, and FIG. 2 (a) shows both sides of the optical confinement layer of the SCH layer. In the n-doped state, FIG. 2 (b) shows that the optical confinement layer on the n-type cladding layer side of the SCH layer is n-doped,
A state in which the p-type cladding layer side is p-doped, FIG. 2 (c)
Shows the state in which the optical confinement layer of the SCH layer is undoped.

2 (d) and 2 (e) show the energy band in the non-biased state in the semiconductor laser having the DH structure, and FIG. 2 (d) shows the n-type cladding layer on both sides of the active layer. 2 (e) is an ordinary DH structure including a p-type clad layer and a p-type clad layer.

In general, the height of the potential barrier of the pn junction when there is no bias is approximately the same as the forbidden band width,
The potential barrier in the case of a heterojunction is close to the value of the narrower bandgap of the layers forming the heterojunction.

The conventional DH structure active layer 10 shown in FIG.
When the cladding layers 2 on both sides of 1 are n-type doped,
As shown in Fig. 2 (e), the pn junction is the InP clad layer 2
The state becomes a so-called remote junction formed inside, and the height of the potential barrier of the pn junction has a large value close to the band gap of InP. Therefore, the potential barrier of the remote junction is high, carriers are less likely to be injected into the active layer 101, and the laser characteristics are deteriorated.

On the other hand, in the case of the SCH structure, as shown in FIGS. 2 (a) to 2 (c), in any case, that is, as in this embodiment, the optical confinement layers on both sides of the active layer are n. The potential barrier is InGa even when doped in the
The value is almost the same as the forbidden band width of the AsP optical confinement layer, which is sufficiently smaller than the value of the potential barrier (InP forbidden band width) in the case of the remote junction. Therefore, carriers are sufficiently injected into the active layer.

FIG. 6 is a sectional view showing the structure of a buried heterostructure laser. In the figure, 7 is a p-type InP clad layer, 8 is an n-type InP current blocking layer, 9 is a p-type InP current blocking layer, 10 and 12 are n-type InP clad layers,
Reference numeral 11 is an active layer.

In the conventional buried heterostructure laser, as shown in FIG.
As shown in, the pn junction exists between the InP current block layer and the pn junction in the active layer in parallel. When a voltage is applied to this semiconductor laser, carriers are usually intensively injected into the pn junction in the active layer portion where the potential barrier is relatively low. However, in the remote junction in which the cladding layers 7 and 12 on both sides of the active layer 11 are n-type doped, the height of the potential barrier of the pn junction has a large value close to the band gap of InP as described above. Carriers pass through the current block layer and clad layer 1
Since it is injected to 0, it becomes difficult to inject it into the active layer 11, and the laser characteristics are deteriorated.

On the other hand, in the case of the SCH structure according to this embodiment, since the potential barrier of the pn junction is sufficiently smaller than the potential barrier of the pn junction of InP as described above, the current blocking layer leads to the cladding layer. The amount of injected carriers is small and the laser characteristics do not deteriorate. Therefore, in the SCH structure, it becomes possible to dope the optical confinement layers on both sides of the active layer into n-type without causing a decrease in carrier injection efficiency, and carrier injection is hindered like a remote junction to deteriorate laser characteristics. There is no fear of doing it.

Example 2. In the first embodiment described above, Zn is used as the p-type dopant and S is used as the n-type dopant, but other dopants may be used. For example, p-type is Mg and n-type is Se. ，
It may be Te or the like.

Example 3. In the first embodiment, InG
The case of a semiconductor laser using an aAsP / InP-based material has been described, but other material systems such as AlGa are used.
A semiconductor laser of As / GaAs system or AlGaInP / GaAs system may be used, and the same effect can be obtained.

[0024]

As described above, according to the present invention, the SC
In the H structure semiconductor laser, the optical confinement layers on both sides of the active layer are n-type doped.
There is an effect that the diffusion of n can be suppressed, and a semiconductor laser can be obtained without a decrease in threshold current and efficiency.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a DH structure of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a diagram showing energy bands in a non-biased state in a semiconductor laser having an SCH structure and a semiconductor laser having a DH structure.

FIG. 3 is a schematic sectional view showing a DH structure of a conventional semiconductor laser.

FIG. 4 is a schematic sectional view showing a structure of a conventional semiconductor laser having an SCH structure.

FIG. 5 is a graph showing SIMS measurement results of Zn and S doping profiles in a DH structure of a conventional semiconductor laser.

FIG. 6 is a sectional view showing a structure of a conventional semiconductor laser having a buried structure.

[Explanation of symbols]

 1 p-type InP substrate 2 p-type InP clad layer 3 n-type InGaAsP optical confinement layer 4 MQW active layer 5 n-type InGaAsP optical confinement layer 6 n-type InP clad layer 7 p-type InP clad layer 8 n-type InP current blocking layer 9 p-type InP current blocking layer 10 n-type InP clad layer 11 active layer 12 n-type InP clad layer 101 undoped InGaAsP active layer 103 Zn-doped p-type InGaAsP optical confinement layer 105 S-doped n-type InGaAsP optical confinement layer

Claims (1)

[Claims] 1. An optical confinement layer having a forbidden band width between the active layer and the clad layer, respectively, between the clad layer disposed above and below the active layer with the active layer sandwiched therebetween. SCH (Separated Confinement Heterostruct)
A semiconductor laser having a ure) structure, wherein the light confinement layers provided on both sides of the active layer are all n-type doped.