JPH07263795A - Semiconductor laser - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] Regarding Fabry-Perot type semiconductor laser, prevent reflection surface contamination by solder, secure sufficient contact area with substrate for optical coupling, and reduce threshold current. . [Structure] Active layer 8 having at least one end face cleaved
And a groove 3 dividing the active layer 8 in the light traveling direction, and a reflective film 4 formed inside the groove 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser,
More specifically, it relates to a Fabry-Perot type semiconductor laser.

[0002]

2. Description of the Related Art Optical fiber communication is being developed from a trunk system to a network (subscriber system, LAN (local area network), in-device data transmission, etc.), but semiconductor lasers are used for such a wide range of applications. In order to improve performance,
That is, lower threshold current and lower price are required.

In order to reduce the cost of a semiconductor laser module in which an optical fiber and a semiconductor laser are combined, it is indispensable to reduce the cost required for the combination of such optical coupling members, but flip chip bonding mounting is a problem to be solved by this problem. On the other hand, it is expected to be a promising solution. Figure 3
FIG. 3 is a side view showing a semiconductor laser module in which a semiconductor laser is flip-chip bonded.

The semiconductor laser 31A is fixed on a silicon substrate 34 having a V groove 33 for fixing the optical fiber 32 so that the end face of the active layer 35 faces the core 36 of the optical fiber 32. Reference numeral 37 is the optical fiber 3
It is a clad of 2. When fixing the semiconductor laser 31A, an AuSn alloy 38 having a thickness of several μm is fusion-bonded onto the SiO ₂ insulating layer 39 on the surface of the silicon substrate 34. Then, the n-electrode 41 of the semiconductor laser 31A is connected to the electrode 43 on the SiO ₂ insulating film 39 via the gold (Au) wire 42. Reference numeral 40 is a high reflectance film formed on both end surfaces of the semiconductor A.

Reliability of solder fusion and positional accuracy (active layer 3
5 and the accuracy of optical coupling between the core 36 of the optical fiber 32)
In order to make it easier, soldering of the semiconductor laser 31A is necessary.
The surface that is flat and the larger the area is, the easier it is to handle. one
On the other hand, the threshold current density Jth of the semiconductor laser 31A is Jth =
{Α + ln (1 / R ₁R₂) / 2L} / β
(Α is the optical loss per unit length due to the laser medium, β is
Gain coefficient, L is resonator length, R₁And R₂Is the gap between the resonator ends.
Ra reflectance).

Therefore, in order to reduce the threshold current, the cavity length L is shortened, and the high reflectance films 40 are formed on both end faces of the semiconductor laser 31A to provide mirror reflectances R ₁ and R ₁ .
It is necessary to raise ₂ . However, since the cleavage surface is currently used as a reflection surface, the resonator length L is, for example, 100 μm.
If the length is shortened to less than 1, the handling will be troublesome.

Therefore, as a method of shortening the resonator length L, as shown in FIG. 4 (illustrated according to the mode before flip chip bonding mounting. The same elements as those in FIG. 3 are designated by the same reference numerals), and a semiconductor is used. An unnecessary portion is removed by dry etching so that the active layer 35 has a desired length without changing the overall size of the laser 31B, and the substantial cavity length L ₁ including the active layer 35 is shortened. There is an example.

[0008]

However, when the unnecessary active layer 35 is removed by such dry etching, a step 46 is formed around the active layer 35, so that the semiconductor laser 31B is annealed at about 300.degree. When the flip chip bonding mounting is attempted, the already formed solder layer 38 is melted, the solder material wraps around the vertical surface of the step 46 and touches the high reflectance film 40 to change the reflectance or film quality, or the device characteristics are changed. It may deteriorate.

Further, forming a step on the semiconductor laser reduces the contact area with the silicon substrate 34 involved in solder fusion in the first place, so that the reliability of fusion is reduced and the position accuracy is also reduced. . The present invention has been made in view of such a problem, and a semiconductor capable of preventing the reflection surface from being contaminated by solder, ensuring a sufficient contact area with the optical coupling substrate, and reducing the threshold current. The purpose is to provide a laser.

[0010]

As shown in FIG. 2, the above-mentioned problems are solved by an active layer 8 having an end face at least one of which is cleaved, and a groove 3 which divides the active layer 8 in the light traveling direction. The semiconductor laser is characterized in that it has a reflection film 4 formed inside the groove 3.

The reflection film 4 has a multi-layered structure and is solved by a semiconductor laser. The reflective film 4 having a multi-layered structure has material layers 11 and 1 having a coefficient of thermal expansion different from that of the active layer 3 by less than 1.0 × 10 ⁻⁶ / deg.
This is solved by a semiconductor device characterized by including 2 and 13.

The active layer 8 is formed of a multi-element material containing a group III element and a group V element, and the reflective film 4 is formed of layers 11 and 13 made of a dielectric material of aluminum nitride or zirconium oxide and chromium. The problem is solved by a semiconductor laser characterized by being formed by a combination of a layer 12 made of a metal of either tungsten or molybdenum.

[0013]

[Operation] According to the present invention, a groove that divides the active layer in the light traveling direction is formed, and a reflective film is formed in the groove.
Therefore, a resonator is formed between the cleavage plane of the active layer and the groove, whereby a resonator shorter than the semiconductor laser is formed, and the threshold current density can be reduced.

Since the cavity length is adjusted by the groove, no step is formed on the upper surface of the semiconductor laser,
A sufficient contact area with the optical coupling substrate is secured.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an outline of a semiconductor laser 1 of the present invention. The semiconductor laser 1 of the present embodiment belongs to a so-called buried stripe type and has a stripe-shaped active layer 2, and a groove 3 is formed in a portion near the center thereof by cutting the active layer 2 in the middle. The high reflectance film 3 is embedded in the inside. This semiconductor laser 1 has a length L ₀ along the light traveling direction of about 300 μm, and both end faces thereof are formed by cleavage.

The groove 3 has a length of about 2 μ along the light traveling direction.
m, width in the lateral direction perpendicular to the light traveling direction is about 8 μm, depth
Is about 5 μm. The active layer 2 is lighted by the groove 3.
100 μm semiconductor laser region and 200 μm in the traveling direction
Is divided into two extended areas. And A-A of FIG.
Referring to FIG. 2A, which is a sectional view taken along the line, a semiconductor laser 1
Is n⁺Type InP substrate 5, n⁺-Formed on InP substrate 5
N-type InP clad layer 6, band cap 1.31 μm
InGaAsP active layer 7, p-type InP clad layer 8, n ⁺Type In
A GaAsP contact layer 9 is formed. InP substrate 5
An n-electrode 10 having a two-layer structure of AuGe / Au is formed below
ing.

The above-mentioned groove 3 is formed by etching in a direction perpendicular to the substrate surface by reactive ion etching using ethane gas using a resist mask, and from the InGaAsP contact layer 9 to the upper part of the InP substrate 5. It is formed to a depth reaching. The high-reflectance film 4 in the groove 3 is composed of an aluminum nitride (AlN) layer 11, a chromium (Cr) layer 12, and an aluminum nitride (AlN) layer 13 which are sequentially stacked on the inner peripheral surface of the groove 3. It has a layered structure, and the first and second AlN films 11 and Cr layers 12 are U-shaped in cross section. The AlN film 11, the Cr layer 12 and the AlN layer 13 are formed by a method such as sputtering, ion plating and vapor deposition.

With the groove 3 filled with the high reflectance film 4, In
The upper surface of the GaAsP contact layer 9 is flat, and the opening 14a is formed in the semiconductor laser region I on it.
The SiO ₂ film 14 is formed to a thickness of 4000Å. A p-electrode 15 having a three-layer structure of Ti (lower layer) / Pt (intermediate layer) / Au (upper layer) is formed on the SiO ₂ insulating layer 14, and the p-electrode 15 is made of InGaAsP through the opening 14a.
It is connected to the contact layer 9.

Further, on the p-electrode 15, an AuSn solder layer 1 used for bonding to a silicon substrate (not shown).
6 is formed, and the upper surface of the AuSn solder layer 16 is formed substantially flat. Furthermore, from the above-mentioned InP substrate 5, InGa
A high reflectance film 17 (reflectance of 60 to 80%) made of a dielectric double layer film of TiON / SiO ₂ is formed on the light output end face on the semiconductor laser region I side of the cleavage surface up to the AsP contact layer 9. Has been done.

In the semiconductor laser 1 described above, since the distance between both end faces is formed to be about 300 μm, the size is not a hindrance to the handling, but in the groove 3 for cutting the InGaAsP active layer 8 and on the light output end face. Since the section between the two high-reflectance films 4 and 17 formed in the above becomes a substantial resonator,
A low threshold current can be realized by a resonator having a short length of about 100 μm.

Further, the high reflectance film 4 in the groove 3 is an intermediate layer thereof.
A high reflectance of 90% or more is achieved by the Cr layer 12 which is
Be done. In addition, the coefficient of thermal expansion of the AlN layers 11 and 13 is 4.5 ×
10 ^-6Since it is / deg, In forming the cladding layers 6 and 7 is In
P and the coefficient of thermal expansion of InGaAsP forming the active layer 2 (respectively
4.5 x 10^-6/ deg and about 5 × 10^-6/ deg)
Since it does not exist, when performing flip chip bonding later
The heat applied to the high reflectance film 4 and its surroundings
Deformation due to thermal stress does not occur between the semiconductor layer and
Reliability is maintained.

By the way, in order to minimize the stress acting between the active layer 2 and the high reflectance film 4, the volume of the high reflectance film 4 (that is, the volume of the groove 3) is preferably as small as possible. Is effective for dry etching. In this embodiment, after the high-reflectance film 4 is formed, but before the SiO ₂ insulating layer 14 and the p-electrode 115 are deposited and laminated, they are projected outside the groove 3 as shown in FIG. 2 (b). The residue of the high-reflectance film 4 is removed by dry etching using argon gas and freon gas (CHF ₃ ), so that a laminated structure having a flat surface in which the high-reflectance film 4 is embedded is obtained. According to this, the SiO ₂ insulating layer 14 and the p electrode 15 are formed on the surface.
The surface of the final semiconductor laser 1 on which the solder is formed is also flattened, and even when it is later soldered to a silicon substrate to which an optical fiber is fixed as shown in FIG. Combined with the width, the reliability and position accuracy of solder fusion are increased.

The semiconductor laser 1 has a highly reflective film 1 on the end face.
The wafer is divided into chips before forming 7. However, since the high reflectance film 4 at that time is not exposed on the side surface of the chip, there is no risk of film peeling. Therefore, in the semiconductor laser of the present embodiment, since no step is provided in order to shorten the cavity length, solder wraparound during flip-chip bonding mounting as described above cannot occur, and solder wraparound does not occur. There is no damage to the highly reflective film and deterioration of the position accuracy.

The embedded high reflectance film of the present invention is
Flip-chip bonding mounting semiconductor described here
Body lasers, semiconductor lasers for optoelectronic integrated circuits,
Semiconductor light emitting device using photon recycling effect
It can also be applied to equipment and optical waveguides. Also, in the groove 3
As the high-reflectance film 4 to be filled in, the coefficient of thermal expansion is 4.9 × 1
0^-6Thermal expansion coefficient of 4.5 instead of chrome layer 12 of / deg
× 10^-6/ deg tungsten (W), thermal expansion coefficient 3.7
× 10^-6~ 5.3 x 10^-6/ deg molybdenum (Mo) etc.
It may be applied and gold, silver or
Other metal layers are formed to a thickness of about 500 Å and mixed with chromium.
You may use together. Also, instead of AlN layers 11 and 13
Has a thermal expansion coefficient of 5.4 × 10^-6zirconium oxide / deg
(ZrO₂) May be used for the compound that constitutes the semiconductor laser.
Thermal expansion coefficient is 1.0 × 10 compared with semiconductors ^-6less than / deg
Any difference is acceptable.

Further, the materials constituting the semiconductor laser are
Not limited to InP and InGaAsP, but AlGaAs and Al
From multi-element semiconductors containing group III elements such as indium (In), gallium (Ga) and aluminum and group V elements such as arsenic (As), phosphorus (P) and antimony (Sb) such as GaSb and InGaAs It may be a semiconductor laser provided with such an active layer.

[0026]

As described above, according to the present invention, since the groove that divides the active layer in the light traveling direction is formed, and the reflective film is formed in the groove, the active layer is cleaved from the cleavage plane. A resonator is formed between the grooves, which forms a resonator shorter than the semiconductor laser, and can reduce the threshold current density.

Further, since the cavity length is adjusted by the groove, no step is formed on the upper surface of the semiconductor laser,
A sufficient contact area with the optical coupling substrate can be secured.

[Brief description of drawings]

FIG. 1 is a perspective view showing an outline of a semiconductor laser according to an embodiment of the present invention.

2 is a cross-sectional view taken along the line AA of the semiconductor laser shown in FIG.

FIG. 3 is a side view of a conventional semiconductor laser module.

FIG. 4 is a side view of a conventional semiconductor laser.

[Explanation of symbols]

1 semiconductor laser 2 active layer 3 groove 4 high reflectance film 5 InP substrate 6 InP clad layer 7 InGaAsP active layer 8 InP clad layer 9 InGaAsP contact layer 10 n electrode 11, 13 aluminum nitride layer 12 chromium layer 14 SiO ₂ insulating film 15 p electrode 16 AuSn solder layer 17 high reflectance film

Claims (4)

[Claims] 1. An active layer (8) having at least one cleaved end face, a groove (3) dividing the active layer (8) in the light traveling direction, and formed inside the groove (3). And a reflective film (4). 2. The semiconductor laser according to claim 1, wherein the reflection film (4) has a multi-layer structure. 3. The reflective film (4) having a multilayer structure has a coefficient of thermal expansion of 1.0 × 10 ⁻⁶ / d as compared with the active layer (3).
A semiconductor device according to claim 1, characterized in that it comprises material layers (11, 12, 13) having a difference of less than eg. 4. The active layer (8) is made of a multi-element material containing a group III element and a group V element, and the reflective film (4) is made of a dielectric material of aluminum nitride or zirconium oxide. 2. The semiconductor laser according to claim 1, wherein the semiconductor laser is formed by a combination of the layers (11, 13) and the layer (12) made of a metal of chromium, tungsten or molybdenum.