JP2514096B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device that oscillates in a single longitudinal mode, a low return optical noise and high output semiconductor laser device, and the same. It relates to a manufacturing method.

(Prior Art) Conventionally, as a laser structure that oscillates in a single longitudinal mode, C ³
There is a (Cleaved-Couple-Cavity) laser.

FIG. 3 is a schematic perspective view showing the structure of a conventional C ³ laser 10.

In the figure, 11 and 12 are different resonator lengths.
L ₁ and L ₂ lasers, which are optically coupled via a gap 13. Further, 14 is a light emitting region, which is composed of an active layer.

The reason why this conventional C ³ laser oscillates in a single longitudinal mode is explained below.

4 (A) to 4 (F) are spectrum diagrams for explaining single longitudinal mode oscillation. FIG. 4 (A) is a resonance mode of the laser 11, and FIG. 4 (B) is a resonance mode of the laser 12. ,
(C) is a resonance mode common to the laser 11 and the laser 12,
(D) shows the gain of the laser 10, and (E) shows the oscillation mode of the laser 10.

The resonance wavelength intervals of the lasers 11 and 12 as shown in FIGS. 9A and 9B are approximately Δλ ₁ = λ ₀ ² / 2nL ₁ (1), Δλ ₂ = λ ₀ ² / 2nL ₂ (2) (where Δλ ₁ and Δλ ₂ are resonator intervals of the lasers 11 and 12, λ ₀ is the oscillation wavelength, n is the refractive index, and L ₁ and L ₂ are the resonators of the lasers 11 and 12 Long) | Δλ ₁ −Δλ ₂ | << Δλ ₁ and Δλ ₂ , the resonant wavelength interval Λ that simultaneously satisfies the two resonator conditions is Λ = Δλ ₁ · Δλ ₂ / | Δλ ₁ −Δλ ₂ | λ ₀ ² / 2n | L ₁ −L ₂ | (3) At this time, it is easy to set | L ₁ −L ₂ | to about 1/10 of L ₁ or L ₂ and then (3 ), The resonance wavelength interval Λ becomes about 10 times, and only one wavelength resonates in the gain range (wavelength range in which oscillation is possible) of the laser 10, so that the laser 10 performing single longitudinal mode oscillation can be obtained. Is.

This conventional C ³ laser 10 was obtained by manufacturing each laser separately and optically coupling them via a gap 13.

(Problems to be Solved by the Invention) In such a conventional laser 10, it is difficult to optically couple two independent lasers 11 and 12.
In addition, this structure has a drawback that it is difficult to make the end face on which the gap 13 is formed a low-reflectance end face when a laser having high output and strong resistance to return light noise is manufactured by lowering the reflectance of the end face. It was

(Means for Solving the Problems) The present invention has been made to solve the above problems, and a semiconductor multilayer film having a half mirror function and a semiconductor multilayer film having a total reflection function are provided in a resonator. A semiconductor laser device for oscillating a single longitudinal mode, comprising: a semiconductor laser device and a method of manufacturing the same, wherein two kinds of semiconductor multilayer films form two resonators having different optical path lengths. It is the one we are trying to provide.

(Embodiment) FIG. 1 is a partial schematic sectional view showing the structure of a semiconductor laser 20 according to the present invention.

In the figure, reference numeral 21 denotes a substrate having a 45 ° inclined surface 21a at the upper part of the table, which is made of GaAs or the like. Reference numeral 22 denotes a multilayer film having a total reflection function, which is formed on the substrate 21.

Further, 23 is a clad layer, which is formed on the multilayer film 22. 24 is an active layer formed on the clad layer 23, on which a clad layer 25 is formed in the same manner as described above. A multilayer film 26 having a half mirror function is further formed on the clad layer 25.

The multilayer film 22 having the total reflection function and the multilayer film 26 having the half mirror function are both formed by laminating two kinds of semiconductors having different refractive indexes in a multilayer.

For example, the refractive index of the semiconductor a is n ₁ , and the refractive index of the semiconductor b is
If n ₂ and the oscillation wavelength of the semiconductor laser are λ, the film thickness
When the semiconductors a and b in which d ₁ and d ₂ are d ₁ = λ / 4 · n ₁ (4) d ₂ = λ / 4 · n ₂ (5) are overlaid by 2k layers, the reflectance Rk is
Is Becomes Here, n _s and n _c are the refractive indices of the substrate and the cladding layer.

In addition, the multilayer film 26 having the half-mirror function has d ₁ = 2 ^1/2 · λ / 4 · n ₁ (6) d ₂ = 2 ^1/2 in consideration of the incident angle of 45 °.・ Λ / 4 ・ n ₂ (7), and determine the number of layers so that the desired reflectance can be obtained.

Further, a window layer 27 that does not absorb light and a gap layer 28 for establishing conduction with the electrodes are formed on the multilayer film 26.

The end faces 29 and 30 of the semiconductor laser 20 according to the present invention formed by laminating in this manner have a high reflectance film on one side and a low reflectance film on the other side.

As described above, when using the semiconductor laser 20 according to the present invention, the light that travels straight through the active layer 24 is partially reflected by the inclined surface 26a of the multilayer film 26 having a half mirror function, and faces downward. Total reflection is performed by the multilayer film 22. On the other hand, the multilayer film 26
The light traveling straight without being reflected by the light travels as it is, is reflected by the end face 30 and returns to the original state, forming a resonator having a resonator length L ₁ + L ₀ . Further, since the multilayer film 26 has an angle of 45 ° on the inclined surface 26a with respect to the light traveling straight through the active layer 24, the totally reflected light returns to the original state and the resonator having the resonator length L ₂ + L ₀ . To form.

As in the conventional case, it is easy to set the cavity length difference L ₁ -L ₂ to about 10 μm, so that the resonance mode interval is several tens of times that of the ordinary laser structure, and single mode oscillation can be realized.

Next, a method of manufacturing the semiconductor laser 20 according to the present invention will be described.

By the way, generally in III-V semiconductors, when a part of the substrate is masked with photoresist or the like and anisotropically etched, the etching rate of the (111) plane in the crystal plane is higher than that of other planes. It is known that the (111) plane appears because it is slow.

At this time, the (100) and (111) planes, which are the bottom surfaces, form an angle of 54.7 °.

2A to 2D are schematic cross-sectional views for explaining the method for manufacturing the semiconductor laser 20.

 Hereinafter, description will be made in the order of numbers using the same drawing.

(1) First, from the crystal plane (100) plane, the crystal axis, <110
Using a GaAs substrate 21 sliced in a direction tilted by 9.7 ° to the> direction and masking part of it with photoresist or the like, and etching with a sulfuric acid-based etching solution, for example, one side is 45 ° with respect to the (100) plane. , The other is 63 ° inclined surface 21a
A trapezoidal convex portion having is formed. ((A) in the same figure) (2) A multilayer film having a total reflection function is formed on the substrate 21 by using, for example, a metal organic chemical vapor deposition method or a thin film growth method capable of maintaining the substrate shape such as MBE method. 22, a clad layer 23, an active layer 24, a clad layer 25, a multilayer film 26 having a half mirror function, a window layer 27, and a gap layer 28 are sequentially formed.
((B) in the figure) (3) Next, for example, by using a dry etching method or the like,
The upper surface of the trapezoidal convex portion is cut perpendicularly to form a resonator. ((C) in the figure) (4) Subsequently, the reflective film 29 having a low reflectance and the reflective film having a high emission rate
30 is formed on both end faces of the resonator. ((D) of the same figure) As described above, according to the method for manufacturing a semiconductor laser of the present invention, it is not necessary to optically couple two lasers, and the above-mentioned resonator length L can be obtained by a single crystal growth method. It is possible to form a resonator with ₁ and resonator length L ₂ .

Example 1 GaAs was used as the active layer 24, Ga Al As was used as the cladding layer 23, and a multilayer film 22 having a total reflection function was used.
A total of 40 layers of Al As are alternately laminated to create a reflectance of 90%, and as a multilayer film 26 having a half mirror function, 90 nm
A total of 12 layers of AlAs and 91 nm Ga Al As were alternately laminated to form a film having a reflectance of about 50%.

The semiconductor laser according to the present invention produced as described above oscillated in a single longitudinal mode at an oscillation wavelength of about 900 nm.

Although the reflectance of the multilayer film 26 having the half mirror function is set to about 50% in this embodiment, it is needless to say that the reflectance is not necessarily limited to this value.

(Effects of the Invention) As described above, in the present invention, a semiconductor laser that has a semiconductor multi-layer film having a half mirror function and a semiconductor multi-layer film having a total reflection function in a resonator and performs single longitudinal mode oscillation is provided. Since the two kinds of semiconductor multilayer films form two resonators having different optical path lengths, it is possible to provide a semiconductor laser with low optical feedback noise and high output. Since it can be manufactured by a single growth method, it is possible to provide a highly reliable manufacturing method.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a semiconductor laser according to the present invention, and FIG.
FIGS. 4A to 4D are schematic cross-sectional views for explaining a method for manufacturing a semiconductor laser, FIG. 3 is a schematic perspective view showing the structure of a conventional C ³ laser, and FIGS. 4A to 4E. FIG. 4 is a spectrum diagram for explaining single longitudinal mode oscillation. 20 ... Semiconductor laser, 21 ... Substrate, 21a, 26a ... Inclined surface, 22 ... Multi-layer film having total reflection function, 23, 25 ... Cladding layer, 24 ... Active layer, 26 ... Half mirror function Multi-layer film having 27, ... window layer, 28 ... cap layer, 29
…… Low reflectivity film, 30 …… High reflectivity film.

Claims (3)

(57) [Claims] 1. A semiconductor laser which has a semiconductor multilayer film having a half-mirror function and a semiconductor multilayer film having a total reflection function in a resonator and performs single longitudinal mode oscillation. A semiconductor laser device comprising a resonator having two different optical path lengths formed by a film. 2. The semiconductor laser device according to claim 1, wherein the high-reflectance end face and the low-reflectance end face are formed perpendicularly to the semiconductor multilayer film having a total reflection function. 3. A (100) plane of a III-V group semiconductor crystal
110> A step of forming a substrate having a tilted surface forming an angle of 45 ° with a bottom surface by performing wet etching with a predetermined angle in the axial direction, and a semiconductor multilayer having a total reflection function sequentially on the substrate. A step of forming a film, a clad layer, an active layer, a clad layer, a semiconductor multilayer film having a half mirror function, a window layer and a cap layer by a single crystal growth method, and a step of forming a cavity end face by dry etching And a step of forming a reflective film on the end face of the resonator, the method of manufacturing a semiconductor laser device.