JPH09129969A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably improve the high-temperature operating characteristic of a long-wavelength semiconductor laser by forming an InAlGaAs MQW active layer on an InP substrate and side barrier layers on both sides of the active layer. SOLUTION: A mesa stripe 5 is formed on an n-type InP substrate 1 by successively growing an n-type InP buffer layer 2, an InAlGaAS MQW active layer 3, and a p-type InP clad layer 4 on the substrate 1. Then an insulating film mask is formed on the upper surface of the stripe 5 and p-type InAlAs side barrier layers 6, p-type current blocking layers 7, and n-type current blocking layers 8 are successively grown on the substrate 1 except the area of the stripe 5. Moreover, the mask on the upper surface of the stripe 5 is removed and electrodes are formed by successively forming a p-type InP clad layer 9 and a p-type InGaAs contact layer 10 on the entire surface of the laminated body including the stripe 5. Finally, a desired semiconductor laser is obtained by cutting the laminated body into individual laser chips.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly, to a semiconductor laser having a buried structure suitably used for optical communication and the like.

[0002]

2. Description of the Related Art Nowadays, multimedia is becoming a major part of the society, and the development of optical communication systems that are effective in transmitting large amounts of information is remarkable. Semiconductor lasers are the most important key devices among various optical components used in optical communication systems. In particular, in an optical subscriber communication system in which a large amount of signal is transmitted to each home, a semiconductor laser capable of operating over a wide temperature range without using a peltier cooler is strongly demanded.

As a semiconductor laser suitable for optical communication such as an optical fiber, an InGaAsP-based or InAlGaAs-based multiple quantum well is presently provided on an InP substrate.
An element having a wavelength band of 1.3 to 1.6 μm formed by forming an active layer having an MQW) structure is often used.

As an example of this type of conventional semiconductor laser, an InGaAsP strained multiple quantum well (M
QW) Semiconductor lasers are described in Aoki et al.
Photonics Technology Letters Magazine, Volume 7, Volume 1
3-15, published in 1995).

In this conventional semiconductor laser, as shown in FIG. 5, a strained MQW active layer 3 is formed on a flat InP substrate 1.
The p-InP cladding layers 4 and 9 and the p-InGaAs contact layer 10 are sequentially grown, and a p-InP
The clad layer 9 is processed into an inverted mesa structure by etching.

The MQW active layer 3 has an InGaAsP quantum well layer having a lattice constant larger than about 1% InP, and the width at the bottom of the mesa stripe 5 is set to 2.6 μm.

In the device having this structure, 85 ° C.-5 mW
The operating current at the time of output is about 35 mA, and good characteristics are obtained as a long wavelength light source for a subscriber system.

A semiconductor laser (ridge waveguide structure) using an InAlGaAs-based material as an active layer in a device having a similar laser structure has also been reported.
E. FIG. ZAH et al. (IEEE Journal of Quantum Electronics, Vol. 30, pp. 511-523, 1994).

In the InAlGaAs-based semiconductor material, the band offset on the conduction band side is larger than the band offset on the valence band side, so that the overflow of electrons is suppressed particularly in a high-temperature environment, and more excellent high-temperature operation characteristics are obtained. It is believed to be obtained.

Further, for example, Japanese Patent Application Laid-Open No. 63-229975
Japanese Patent Application Laid-Open Publication No. H11-163873 discloses a buried heterostructure (bu) in a semiconductor laser having an active layer made of InGaAsP-based material.
Al as a current blocking layer (embedding layer) for forming a written hetero structure
A configuration has been proposed in which a low threshold current and high efficiency are achieved by using a GaInAs-based material.

[0011]

However, the required performance of the semiconductor laser is unavoidable, and further lower current operation is desired.

In particular, if the current value required to obtain an optical output of 5 mW at 85 ° C., which is considered to be the maximum temperature without temperature adjustment, can be reduced to about 20 mA, no bias drive or APC (Auto Power Control) The load on the laser drive circuit, such as free operation, is greatly reduced.

For this purpose, it is effective to use a buried structure instead of the ridge waveguide structure described as a conventional semiconductor laser. There is a limit to current reduction.)

The active layer has a higher barrier energy with respect to electrons and a lower InAlGaP with less electron carrier leakage than the InGaAsP system which has been widely used in the past.
As-based materials are desirable.

However, in an InAlGaAs material system which is promising as a high-temperature operating LD, InP
A semiconductor multi-layer structure such as an active layer is formed on the substrate, and as shown in FIG.
There is a high energy barrier for electrons between the P layer and the n-InAlAs layer.

Accordingly, even if an InAlGaAs-based quantum well structure active layer of good quality is formed and a buried structure is formed using an InP material by an ordinary method, n-InP and n-In
Electrons that reach the interface with AlAs are not effectively injected into the active layer but leak out in the lateral direction.

For this reason, even if buried growth can be performed in a good shape, there may be a case where only characteristics inferior to those of the ridge waveguide structure element can be obtained.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-mentioned problems, and has an excellent performance of a buried structure semiconductor laser which greatly improves the characteristics of a conventional semiconductor laser.
In particular, it is an object of the present invention to provide a long-wavelength buried semiconductor laser having an InAlGaAs-based material.

[0019]

To achieve the above object, the present invention provides a semiconductor laser having a buried structure in which an active layer for radiative recombination is covered with a semiconductor material having a larger energy gap and a smaller refractive index. 2. A semiconductor laser having a buried structure, characterized in that a semiconductor layer having a conduction band energy higher than that of the active layer is formed beside the active layer.

The semiconductor laser according to the present invention preferably has an InAlGaAs-based buried structure active layer, and an InAlGaAs-based semiconductor layer is formed next to it.

[0021]

The principle and operation of the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing an energy band around an InAlGaAs-based MQW active layer constituting a 1.3 μm band semiconductor laser, as an example.

Referring to FIG. 2, the wavelength composition is 1.36 μm,
InAlGaAs quantum well layer 13 having a distortion amount of + 1.2%
(Thickness: 7 nm) were formed, and the emission wavelength composition was 1.0
6 μm InAlGaAs barrier layer 14 (film thickness 10 n
m).

The entire MQW active layer has a wavelength composition of 1.06 μm.
InAlGaAs optical confinement layer 12 (50 n thick)
m) and n-InAlAs cladding layer 11 (thickness 1
00 nm), p-InAlAs cladding layer 15 (thickness 1
00 nm).

When a current is injected, electrons are injected from the n-InP buffer layer 2 through the n-InAlAs layer 11 into the MQW active layer.

However, as described above, since a high energy barrier exists between the n-InP buffer layer 2 and the n-InAlAs layer 11, electrons cannot easily cross this energy barrier.

At this time, if the p-InP layer is formed beside the active layer as in a semiconductor laser having a normal buried structure, a part of the injected electrons will not reach the active layer but extend in the lateral direction. Will leak out.

The present invention employs a method of forming a barrier semiconductor layer having a high energy barrier in the lateral direction and suppressing carrier leakage in the lateral direction.
In the case of an As-based semiconductor laser, an InAlAs layer or an InAlGaAs layer having a composition similar thereto may be formed beside the active layer.

According to the present invention, as described above,
By forming a side barrier layer serving as a barrier or a semiconductor layer corresponding to the side barrier layer beside the MQW active layer of the system, electrons leak laterally due to the influence of a hetero barrier between the InP substrate and the InAl (Ga) As layer. By suppressing the phenomenon and effectively injecting carriers into the active layer, for example, an operating current of 20 to 25 m at an output of 85 ° C. and 5 mW is output.
A, and to provide a semiconductor laser whose performance is particularly improved as compared with the conventional device.

[0029]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 schematically shows a cross section of a buried structure type semiconductor laser according to an embodiment of the present invention. In FIG. 1, 1 is an n-InP substrate, 2 is an n-InP buffer layer, 3 is an InAlGaAs-based MQW active layer, and 4 is p-I
nP cladding layer, 6 is a p-InAlAs side barrier layer, 7 is a p-InP current blocking layer, 8 is an n-InP current blocking layer, 9 is a p-InP cladding layer, and 10 is a p-InP cladding layer.
3 shows an InGaAsP contact layer.

Such a semiconductor laser is manufactured, for example, according to the following manufacturing process.

First, two stripe-shaped SiO ₂ insulating film masks are formed on the n-InP substrate 1 with an interval of about 1.5 μm, and a semiconductor multilayer structure including an active layer or the like in the interval is formed, for example. It is selectively grown by MOVPE (metal organic vapor phase epitaxy) or the like.

By the selective growth method, the n-InP buffer layer 2 (thickness: 100 nm), the MQW active layer 3 (total thickness: about 400 nm), the p-InP cladding layer 4 (thickness: 200 nm)
nm) are sequentially grown to form a mesa stripe 5.

The MQW active layer 3 has an n-InAlAs layer 11 (thickness 1) as shown in the energy band structure of FIG.
00 nm), InAlGaAs optical confinement layers 12 (50 nm each, both sides), 10 layers of InAlGaAs
Quantum well layer 13 (wavelength composition 1.36 μm, strain amount + 1.
9% InAlGaAs barrier layer 14 (wavelength composition 1.06 μm, no distortion, thickness 10 n)
m) and a p-InAlAs layer 15 (100 nm thick).

During the selective growth, the crystal grows also in the region outside the insulating film mask, but is omitted in the figure.

After forming such a mesa stripe 5, an insulating film mask is formed only on the upper surface of the mesa stripe 5, and the p-InAlAs side barrier layer 6 is formed in a region other than the mesa stripe 5 by a second crystal growth process. (Thickness 1
00 nm), p-InP current blocking layer 7 (thickness 400
nm), n-InP current blocking layer 8 (400 n thick)
m) are sequentially grown, and finally, the mask on the upper surface of the mesa stripe 5 is removed, and the entire surface of the p-InP cladding layer 9 (thickness: 1.3 μm) and the p-InGaAsP contact layer 10 are removed.
(Thickness: 0.3 μm) are laminated, electrodes are formed, and then cut into individual laser chips to obtain a desired semiconductor laser.

FIG. 3 shows the energy band structure viewed from the n-InP buffer layer 2 in the lateral direction when the p-InAlAs side barrier layer 6 is provided (see the solid line) and when it is not provided (see the broken line).

When the p-InAlAs side barrier layer 6 is not provided, a part of the electrons injected from the substrate 1 side is nI
A large energy barrier of the nAlAs layer 11 (see FIG. 2) (does not serve as a barrier except at the interface because of n-type doping). ) May leak into the p-InP (p-block layer 7) side of the buried layer. By forming the InAlAs side barrier layer 6 in the lateral direction of the active layer 3, such carrier leakage can occur. Was significantly suppressed, and carriers were effectively injected into the active layer 3.

As a result of forming a high-reflection film having a device length of 250 μm and 70% and 95% on the end face of the device and evaluating the characteristics, the operating current at 85 ° C.-5 mW output was 20 to
The result was 25 mA, which is a significantly improved performance as compared with the conventional device.

As a comparative example, a device having no side barrier layer was manufactured by the same method as above, and its characteristics were evaluated. The operating current under the same conditions was 40 to 50 mA. It can be seen that the operating current is almost halved.

Further, instead of the n-InAlAs layer 11, an n-InAlGaAs having an emission wavelength of 1.06 μm is used.
When an element using the layer was manufactured, almost the same performance was obtained.

FIG. 4 is a diagram schematically showing a cross section of a mesa stripe portion of a semiconductor laser according to a second embodiment of the present invention.

With reference to FIG. 4, in the present embodiment,
When growing the p-InAlAs layer 15 on the MQW active layer 3 including up to the InAlGaAs optical confinement layer 12 (see FIG. 2), the growth temperature in the lateral direction is increased by increasing the growth temperature from the normal 630 ° C. to 670 ° C. Was increased.

By growing under these conditions, pI
The nAlAs layer 15 was grown to a thickness of 150 nm in the vertical direction and 50 nm in the horizontal direction.

In this case, the p-InAlAs layer 15 itself functions as a side barrier layer. Therefore, excellent characteristics similar to those of the first embodiment can be realized without growing the side barrier layer 6 during the burying growth.

[0046]

As described above, the present invention is particularly applicable to I
In a semiconductor laser in which an InAlGaAs-based MQW active layer is formed on an nP substrate, a side barrier layer serving as an electron barrier or a semiconductor layer corresponding to the side barrier layer is formed next to the active layer, so that electrons become InP and InAl (G).
a) The phenomenon of lateral leakage due to the effect of the hetero barrier with the As layer is suppressed, and carriers are effectively injected into the active layer. Therefore, excellent high-temperature operation characteristics far exceeding conventional semiconductor lasers are achieved. It has an effect that can be realized.

[Brief description of the drawings]

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

FIG. 2 is an energy band diagram of an active layer according to the first embodiment of the present invention.

FIG. 3 is a lateral energy band diagram in the first embodiment of the present invention.

FIG. 4 is a cross-sectional structure diagram at the time of a first growth according to a second embodiment of the present invention.

FIG. 5 is a sectional structural view of a conventional semiconductor laser.

[Explanation of symbols]

Reference Signs List 1 substrate 2 buffer layer 3 active layer 4, 9 clad layer 5 mesa stripe 6 side barrier layer 7 p block layer 8 n block layer 10 contact layer 11 n-InAlGaAs layer 12 optical confinement layer 13 quantum well layer 14 barrier layer 15 p- InAlGaAs layer 21 SiO ₂ film 22 Polyimide

Front page continuation (72) Inventor Bidens Look 5-7-1, Shiba, Minato-ku, Tokyo NEC Corporation

Claims (5)

[Claims] 1. A semiconductor laser having a buried structure in which an active layer for radiative recombination is covered with a semiconductor material having a larger energy gap and a smaller refractive index than that of the active layer. A semiconductor laser having a buried structure, characterized in that a semiconductor layer having high energy is formed. 2. A semiconductor laser having a buried structure in which an active layer for radiative recombination is covered with a semiconductor material having a larger energy gap and a smaller refractive index, wherein the active layer contains at least an InAlGaAs semiconductor material. A semiconductor laser having a buried structure, characterized in that an InAlGaAs layer is formed beside the active layer. 3. A semiconductor laser having a buried structure in which an active layer for radiative recombination is covered with a semiconductor material having a larger energy gap and a smaller refractive index, wherein the active layer contains at least an InAlGaAs-based semiconductor material, The p-type InAlGaAs-based cladding layer has a larger energy gap than the n-type InAlGaAs-based cladding layer, and a p-type InAlGaAs-based semiconductor layer is formed next to the active layer. 2. A semiconductor laser having a buried structure according to 2. 4. The buried structure semiconductor according to claim 1, wherein the active layer is an InAlGaAs-based quantum well active layer, and a side barrier layer made of an InAlAs layer is provided on a side surface of the active layer. laser. 5. A p-type InAlG covering at least a side surface of the active layer instead of providing the side barrier layer.
5. The embedded semiconductor laser according to claim 4, further comprising an aAs semiconductor layer.