JPH08148754A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE: To provide a semiconductor laser which allows less leak current, excellent light emission efficiency and high-speed modulation. CONSTITUTION: The n-type InP substrate 11 of a semiconductor laser is provided with a mesa-shaped stripe 13, which is formed by subsequently depositing an n-type InP clad layer 13a, an active layer 13b and a p-type InP clad layer 13c which contains zinc-(Zn) as a p-type impurity, and current block layers 15, which are provided on the sides of the mesa-shaped stripe and are formed of an iron (Fe) doped InP layer. The p-type InP clad layer 13c is formed of an InP layer that contains silicon(Si) as well as Zn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having an Fe-doped semiconductor layer as a current blocking layer and a method for manufacturing the same.

[0002]

2. Description of the Related Art Iron (Fe) is a type of semiconductor laser.
There is a type of semiconductor laser in which a current blocking layer is constituted by a semiconductor layer doped with. Its typical structure is InP
Explaining with an example of a semiconductor laser of the system, it is formed by having an n-type InP clad layer, an active layer, and a p-type InP clad layer in this order on an InP substrate of the first conductivity type, for example, n-type (hereinafter, the same). InP having a laser stripe in the shape of a mesa, and Fe doped on the side surface of the laser stripe.
The current blocking layer is composed of (also referred to as Fe-doped InP layer). In this type of semiconductor laser, p
The device capacitance can be made smaller than that of the type of semiconductor laser in which the stacked body of the n-type semiconductor layer and the n-type semiconductor layer is provided on the side surface of the laser stripe so as to have a reverse bias, and thus the element capacitance can be made smaller, so high-speed modulation operation is possible. become.

[0003]

By the way, zinc is generally used as a p-type impurity (p-type dopant) when manufacturing a semiconductor laser. In that case, the p-type clad layer in the mesa-shaped stripe is also composed of a layer containing zinc (Zn). In such a case, in the semiconductor laser of the type using the Fe-doped InP layer as the current blocking layer, the p-type InP cladding layer containing zinc and the F-type InP cladding layer are used.
It is always in contact with the e-doped InP layer. Then, the p-type InP clad layer containing Zn and the Fe-doped In
Since Zn and Fe interdiffuse with the P layer, Fe, which is a level group that traps electrons in the Fe-doped InP layer, is reduced, and as a result, the function as a current blocking layer is deteriorated. The problem arises that

[0004]

Therefore, according to the first invention of this application, a mesa stripe composed of a p-type cladding layer containing zinc as a p-type impurity, an active layer and an n-type cladding layer, In a semiconductor laser comprising a current blocking layer made of a semiconductor layer doped with iron (Fe), which is provided on a side surface of the mesa-shaped stripe, a p-type clad layer is made to contain silicon (Si) together with Zn. It is characterized by being composed of different layers.

According to the second invention of this application, a mesa-shaped stripe formed of a p-type cladding layer containing zinc as a p-type impurity, an active layer and an n-type cladding layer, and the mesa-shaped stripe of In manufacturing a semiconductor laser having a current blocking layer made of a semiconductor layer provided on a side surface and doped with iron (Fe), when a p-type cladding layer is formed, silicon (Si) is also contained together with Zn. Then, the layer is formed, and then a current blocking layer made of a semiconductor layer doped with Fe is formed.

In these first and second inventions, the doping amount of silicon (Si) contained in the p-type cladding layer together with Zn does not impair the p-type of the cladding layer because it constitutes a pair of zinc and iron. It is considered that it is better to be close to the doping amount of zinc within the range.

In the second invention, forming the p-type clad layer by containing silicon (Si) together with Zn means that the p-type semiconductor layer contains zinc on the underlying layer (eg, compound semiconductor substrate). A p-type semiconductor layer including silicon, a semiconductor layer for forming an active layer, and an n-type semiconductor layer are formed (the p-type and n-type semiconductor layers may be upside down), and these semiconductor layers are processed into mesa-shaped stripes. It is considered that either the case where the p-type clad layer is obtained or the case where both or one of Zn and Si is contained in the portion corresponding to the p-side clad layer after the mesa-shaped stripe is first obtained.

In implementing the first invention, it is preferable to provide n-type semiconductor layers above and below the Fe-doped semiconductor layer. The reason is as follows. The Fe-doped semiconductor layer (for example, Fe-doped InP layer) has a level for trapping electrons and thus functions as a blocking layer for electron injection. However, since it does not have a level for trapping holes, a p-type semiconductor layer is added thereto. When in contact with each other, holes are injected into this Fe-doped semiconductor layer. The holes recombine with the electrons injected into the Fe-doped semiconductor layer, which causes a current to flow in the Fe-doped semiconductor layer and deteriorates the function as a block layer. Such a phenomenon is, for example, F
When a p-type clad layer or a p-type contact layer is provided on the e-doped InP layer, or Fe-doped InP on the p-type substrate
This occurs when a layer is provided. However, if the n-type semiconductor layers are provided above and below the Fe-doped InP layer as in this preferred example, the problem of hole injection can be avoided. Here, the lower layer of the n-type semiconductor layers provided above and below the Fe-doped semiconductor layer may be the n-type semiconductor substrate itself.

[0009]

According to the first invention of this application, the p-type cladding layer is composed of a layer doped with Zn and Si. Zn
Z in layers containing both (and co-doped) with Si
Since n and Si form a pair, they do not move or become hard to move in the layer. Therefore, as compared with the case where Si is not contained in the p-type clad layer, Zn and Fe between the p-type clad layer containing Zn and the Fe-doped semiconductor layer are
Mutual diffusion with and is prevented or reduced.

Further, according to the second invention of this application, the Fe-doped semiconductor layer is in contact with the p-side cladding layer in a state where Zn and Si are doped. Therefore, the mutual diffusion of zinc and iron between both layers can be continuously prevented or reduced immediately after the p-side clad layer and the Fe-doped semiconductor layer are in contact with each other.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the first invention and the second invention of this application will be described below with reference to the drawings. It should be noted that the drawings used for the description schematically show the dimensions, shapes, and arrangement relationships of the respective constituents to the extent that the present invention can be understood. Further, in the following embodiments, an example will be described in which these inventions are applied to a semiconductor laser made of an InP-based material and having a base made of an n-type InP substrate.

FIG. 1 is a diagram for explaining a semiconductor laser according to an embodiment of the first invention. More specifically, it is a cross-sectional view of the semiconductor laser of the example when cut along a direction orthogonal to the stripe direction of a mesa-shaped stripe provided therein.

The semiconductor laser 10 of this embodiment has an n-type I
On the nP substrate 11, there are provided mesa-shaped stripes 13 that form a laser cavity, and a current block layer 15 that is provided on the side surface of the mesa-shaped stripes 13 and that is composed of an Fe-doped InP layer. However, the mesa-shaped stripe 13 is
It is composed of an n-type InP clad layer 13a, an active layer 13b, and a p-type InP clad layer 13c containing Zn and silicon (Si), which are sequentially stacked from the n-type InP substrate 11 side. Here, the n-type InP clad layer 13a
Is, but not limited to, tin (Sn) at 1 × 10 ¹⁸ / c
It is composed of an InP layer doped with m ³ . Also, p
The type InP clad layer 13c is InP doped with, but not limited to, zinc 5 × 10 ¹⁷ / cm ³ and silicon, but not limited to 4 × 10 ¹⁷ / cm ^3.
It consists of layers. In addition, this mesa-shaped stripe 13
The width of is determined according to the design, but is generally set to a width in which transverse mode single operation is obtained.

Further, the semiconductor laser 10 of this embodiment is
In order to eliminate the influence of holes on the Fe-doped InP layer 15, the n-type InP layer 1 is formed above and below the Fe-doped InP layer 15.
3a and n-type InP layer 17. Where layer 13
a may be the n-type InP substrate 11 itself.

Further, the semiconductor laser 10 has p-type In on the mesa-shaped stripe 13 and the n-type InP layer 17.
It comprises a P clad layer 19 and a p-type InGaAs (P) contact layer 21. Here, the p-type InP clad layer 19
Is composed of an InP layer doped with 5 × 10 ¹⁷ zinc, although not limited thereto.

Further, the semiconductor laser 10 has a p-side electrode 23 on the contact layer 21, and also has n-type InP.
An n-side electrode 25 is provided on the back surface of the substrate. However, the electrode 23 on the p-side is provided on the contact layer 21 with the insulating film 27 sandwiched in the portion other than the portion corresponding to the mesa-shaped stripe 13.

The semiconductor laser 10 of this embodiment has a structure in which the p-type InP clad layer 13c and the Fe-doped InP layer 15 are in contact with each other as in the conventional case, but the p-type InP clad layer 13c is doped with silicon in addition to zinc. Since silicon and zinc are paired with each other, zinc does not move or is hard to move in the InP layer 13. Therefore, p-type I
Since the mutual diffusion of Fe and Zn between the nP clad layer 13c and the Fe-doped InP layer 15 can be reduced as compared with the conventional case, the function of the current blocking layer 15 is less likely to deteriorate. Therefore, the leakage current due to the iron-zinc mutual diffusion can be suppressed as compared with the conventional one, and the threshold current can be reduced, the luminous efficiency can be improved, the maximum luminous efficiency can be improved, and the like.

Next, an embodiment of the method for manufacturing a semiconductor laser according to the second invention will be described with reference to FIGS. 2 (A) to 2 (C) and FIG. Here, FIGS. 2A to 2C are process diagrams for explaining the manufacturing method of the example. Both figures are shown by a sectional view at a position corresponding to FIG.

First, on the n-type InP substrate 11, n-type In
P layer 13x, active layer forming semiconductor layer 13y, p-type InP
The layer 13z and the p-type InGaAs (P) layer 31 are formed in this order by, for example, the MOVPE method (FIG. 2).
(A)). However, in this embodiment, the n-type InP layer 13x is assumed to be doped with tin (Sn) at 1 × 10 ¹⁸ / cm ³ . The active layer forming semiconductor layer 13y is
It is determined according to the structure of the active layer 13b, and may be a single layer, a layer to which a diffraction grating or the like is added, or a layer having a multiple quantum structure. In this embodiment, the p-type InP layer 13z is doped with zinc at 5 × 10 ¹⁷ / cm ³ and silicon is doped at 4 × 10 ¹⁷ / cm ^3, for example. In addition,
The p-type InGaAs (P) 31 is a mesa stripe 1
3 is formed so that the formed stripes become desired mesa stripes 13 having a substantially rectangular cross section. However, this layer 31 is not essential.

Next, on the p-type InGaAs (P) 31, a stripe-shaped etching mask 33 having a stripe direction of <011> and a stripe width of, for example, 3.5 μm, which is, for example, a SiO ₂ film is formed. The etching mask 33 made of is formed by a known film forming technique, photolithography technique, and etching technique.

Next, the layers 31, 13z, 13y, 13x
The portion not covered with the etching mask 33 is removed to a depth which reaches the n-type InP layer 13x here but does not reach the n-type InP substrate 11 by using, for example, a hydrobromic acid-based etching solution. As a result, the mesa-shaped stripe 13 is obtained (FIG. 2 (B)). Next, the side surface of the mesa-shaped stripe 13 is filled with the Fe-doped InP layer 15 by, for example, the MOVPE method, and the n-type InP layer 17 is formed on the Fe-doped InP layer 15 (FIG. 2B).

Next, for example, hydrofluoric acid (HF) and nitric acid (HN
After removing the etching mask 33 and the InGaAs (P) layer 31 with an etching solution containing O ₃ ) and water (H ₂ O), respectively, on the mesa-shaped stripe 13 and n.
P on the type InP layer 17 by, for example, the MOVPE method.
Type InP clad layer 19 and p type InGaAsP contact layer 21 (however, the contact layer below the insulating film 27 shown in FIG. 1) are sequentially formed (FIG. 2).
(C)).

Next, the insulating film 27, p is formed by a known method.
A InGaAsP contact layer 21 (however, the contact layer above the insulating film 27 shown in FIG. 1) is formed,
Further, the n-side contact layer 29 and the electrode 25 are formed. Thereafter, the semiconductor laser 10 of the embodiment shown in FIG. 1 is divided by dividing each semiconductor laser from the wafer by a suitable method.
Is obtained.

In the method of the second embodiment of the present invention, the mesa stripe 13 having the p-side cladding layer 13c doped with Zn and Si is filled with the Fe-doped semiconductor layer 15. Thus, the semiconductor laser 10 is manufactured. Therefore, the p-side cladding layer 13
Immediately after the contact between c and the Fe-doped semiconductor layer 15,
The effect of silicon of 13c in the side clad layer is developed, and mutual diffusion of zinc and iron between both layers 13c and 15 can be prevented or reduced.

Although the embodiments of the first invention and the second invention of this application have been described above, these inventions are not limited to the above-mentioned embodiments.

For example, in the structure shown in FIGS. 1 and 2, a p-type InP substrate is used instead of the n-type InP substrate,
In containing zinc and silicon in the position of the lower cladding layer
P-cladding layer is arranged, and n-type I
Even when the np clad layer is arranged, the same effect as that of the embodiment can be obtained. Further, when the present invention is applied to a GaAs semiconductor laser, the same effect as that of the embodiment can be expected.

[0027]

As is apparent from the above description, according to the semiconductor laser of the first invention of this application, zinc (Zn)
A mesa-shaped stripe formed of a p-type clad layer containing p as a p-type impurity, an active layer, and an n-type clad layer, and a semiconductor layer provided on the side surface of the mesa-shaped stripe and doped with iron (Fe). In the semiconductor laser having the current blocking layer, the p-type clad layer is composed of a layer containing not only Zn but also silicon (Si). Therefore, the mutual diffusion of zinc and iron between the p-type cladding layer containing zinc and the Fe-doped semiconductor layer can be prevented or reduced as compared with the conventional case, so that the function of the current blocking layer made of the Fe-doped semiconductor layer is maintained. Therefore, the leak current can be suppressed. Therefore, it is expected to provide a semiconductor laser having a reduced oscillation threshold current, improved emission efficiency and maximum emission output.

Further, according to the method for manufacturing a semiconductor laser of the second invention of this application, a mesa-shaped structure composed of a p-type cladding layer containing zinc (Zn) as a p-type impurity, an active layer and an n-type cladding layer is provided. In manufacturing a semiconductor laser including a stripe and a current blocking layer formed of a semiconductor layer provided on a side surface of the mesa-shaped stripe and doped with iron (Fe), when forming a p-type cladding layer, Zn
Together with silicon (Si) to form the layer,
After that, a current blocking layer made of a semiconductor layer doped with Fe is formed. Therefore, the p-side cladding layer and Fe
Immediately after the contact with the doped semiconductor layer, the mutual diffusion of zinc and iron between both layers can be continuously prevented or reduced, so that the semiconductor having improved oscillation threshold current, emission efficiency and maximum emission output can be obtained. We can expect to provide lasers.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the first invention.

FIG. 2A to FIG. 2C are process drawings for explaining an embodiment of the second invention.

[Explanation of symbols]

10: Semiconductor laser of Example 11: Base (n-type InP substrate) 13: Mesa stripe 13a: n-type InP clad layer 13b: active layer 13c: p-type InP containing Zn as p-type impurity
Cladding layer 15: current blocking layer composed of Fe-doped InP layer 17: n-type InP layer 19: p-type InP clad layer 21: p-type InGaAs (P) contact layer 23: p-side electrode 25: n-side electrode 27: Insulating film 29: n-side contact layer

Claims (2)

[Claims] 1. A p containing zinc (Zn) as a p-type impurity
A mesa-shaped stripe composed of a clad layer, an active layer, and an n-type clad layer, and a current blocking layer formed of a semiconductor layer provided on a side surface of the mesa-shaped stripe and doped with iron (Fe). The semiconductor laser according to claim 1, wherein the p-type clad layer is composed of a layer containing not only Zn but also silicon (Si). 2. A p containing zinc (Zn) as a p-type impurity
A mesa-shaped stripe composed of a clad layer, an active layer, and an n-type clad layer, and a current blocking layer formed of a semiconductor layer provided on a side surface of the mesa-shaped stripe and doped with iron (Fe). In manufacturing such a semiconductor laser, when a p-type clad layer is formed, Zn (Si) is also contained together with the layer to form the layer, and then a current blocking layer composed of a Fe-doped semiconductor layer is formed. A method for manufacturing a semiconductor laser, which comprises forming the semiconductor laser.