JPS62165989A - Distributed feedback type semiconductor laser element - Google Patents

Abstract

PURPOSE:To concentrate a current only in an active layer on a V-shaped groove by forming a stripelike V-shaped groove from the surface of an internal current narrowing layer formed on a P-type InP substrate to the substrate, increasing the thickness of an active layer formed thereon on the groove and forming a corrugation layer for selecting a wave thereon. CONSTITUTION:An N-type InP layer 33 and a P-type InP layer 35 are laminated and grown as internal current narrowing layers on a P-type InP substrate 31 having a (100) face, an a groove 37 of V-shaped section is formed in (0, 1, -1) direction from the layer 35 to the surface of the substrate 31. Then, a P-type InP clad layer 39 is grown on the entire surface while burying the groove, and an InGaAsP active layer 41 is thickly grown on the groove 37, a waveshape forming layer 43 for selecting a wavelength becoming a corrugation layer on the surface and an N-type InGaAsP cap layer 45 are laminated and deposited thereon. Thus, a current flowing to the layer 41 is concentrated only on the groove 37 to obtain a single mode oscillation element with a low current.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an InP-based semiconductor laser device that oscillates in a single-l axis (longitudinal) mode.

(Prior art) Figure 3 shows, for example, the literature (Electronics Letters (E
lecLoronics LcLtcrs) 18 [
1] Conventional embedded D F B (DisLribu
FIG. 2 is a partially cutaway perspective view showing a t, ed-fecdback type (minute feedback type) semiconductor laser device. This element is well known as the basic structure of an axial mode single wavelength laser.

In FIG. 3, 11 is an n-type 1nP substrate (
(hereinafter also referred to as a substrate), this substrate 11
The upper surface of the wafer is patterned into corrugations of appropriate pitch and depth by conventional fluorographic lithography and chemical etching techniques.

Further, on the upper surface of the substrate +1, from the substrate 11 side, an n-type Ga1nAsP optical waveguide layer 13, a GaI nAsP active layer 15, a p-type 1nP cladding layer 17, and a p-type WGa
The width of the active layer 15 (in the direction P is not shown in FIG. 3 and the downward active +J[1, vX
I Lllll'ljuice>P,)h~')lt m Ft!
ffFte And A stacked body 21 having a striped inverted mesa structure is provided in a direction that intersects this Ichibatake.

This laminate 21 is obtained by forming each of the layers 13 to 19 on the substrate Il by the first liquid phase epitaxial growth, and after taking out the substrate 11 provided with each of these layers from the growth furnace.
It is obtained by chemically etching unnecessary portions of each layer using ordinary photolithography techniques.

Further, a p-type 1nP layer 23 and an n-type InP layer 25 are sequentially provided on the InP substrate 11 so as to be in contact with both side surfaces of the laminate 21 in the stripe direction, and each of these layers 2
3 and 25, the active layer I5 was buried to obtain a BH groove structure. Note that the p-type 1nP layer 23 and the n-type 1nP layer 25
is formed by the second liquid phase epitaxial growth.

Although not shown in the drawings, this semiconductor laser device has an n-side electrode on the lower side of the n-type 1nP substrate 11 and a p-side electrode on the negative side of the P-type GaT nAsP cap layer 19. has been done.

In such a semiconductor laser device, the p-n junction at the interface between the ρ-type 1nP layer 23 and the n-type 1nP layer 25 is reverse biased, so almost no current flows in this part, and the injected current is The current flows concentratedly in the region of the active layer 15 indicated by W in FIG. 3, thereby realizing a current confinement structure.

(Problems to be Solved by the Invention) However, the semiconductor laser device as described above has a structure in which a laminate is formed by mesa etching and the side surfaces of the laminate are embedded. Therefore, there is a problem in that leakage current is likely to occur along the side surfaces of the stack including the side surfaces of the active layer 15.

This leakage current causes deterioration of the characteristics of the semiconductor laser device, such as increasing the oscillation threshold current of the semiconductor laser device and increasing the operating current for obtaining a desired light emission output.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a distributed feedback semiconductor laser device that operates with low current and is capable of oscillating in a single axial mode.

(Means for solving the problem) In order to achieve this objective, according to the present invention, p-type 1
A striped V-groove with a depth extending from the surface of the internal current confinement layer provided on the nP underlayer to this underlayer, an active layer provided above the V-groove, and a V-groove provided close to the upper side of this active layer. The active layer portion above the V-groove described above is thicker than the active layer portion above the internal current confinement layer other than the V-groove. do.

(Function) According to the structure of the semiconductor laser device of the present invention, since the active layer is formed above the V-groove in a region wider than the width of the 2-groove, it does not have side surfaces as in the prior art. Furthermore, the current injected into the semiconductor laser device flows concentratedly in the active layer region formed in the V-groove, so that leakage current is difficult to occur. Since the waveform portion is provided, a portion of the light emitted from the active layer is Bragg-reflected by the waveform portion.

Furthermore, since the thickness of the active layer portion above the trench is thicker than the thickness of the active layer portion above the internal current confinement layer, stable oscillation is achieved in the transverse fundamental mode.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that these figures are only schematic illustrations to the extent that the present invention can be understood, and the shapes, dimensions, and arrangement relationships are not limited to the illustrated examples. Further, in these figures, the same components are designated by the same reference numerals.

FIG. 1 is a perspective view showing essential parts of a semiconductor laser element f of the present invention.

In FIG. 1, 31 is a P-type 1nP substrate (
(hereinafter also referred to as a substrate).

Incidentally, this base may be composed of a suitable material such as a p-type TnP substrate and a p-type 1nP buffer layer. On the (100) plane of this p-type 1nP substrate 31, an n-type 1nP layer 33 and a p-type 1np layer 35 are provided as an internal current confinement layer in the j-order. Moreover, between this current confinement layer, <01
Furthermore, a p-type InP layer 35 is formed in stripes in the 1> direction.
A V-shaped groove 37 is provided at a depth extending from the surface to the substrate 31 and having a cross section perpendicular to the stripe direction.

Further, in this groove 37 and the p-type 1nP layer 35, a ρ-type 1nP layer 39 as a lower crat layer and an In as an active layer are formed.
GaAsP layer 41 and n-type I as a P-layer cladding layer
An nGaAsP layer 113 is provided. In this case, in order to stably oscillate the semiconductor laser in the transverse fundamental mode, the thickness of the active layer in the area above the groove 37 (the area indicated by Wo in FIG. The thickness is set appropriately so that it is thicker than the active layer portion in other regions, that is, the active layer portion above the internal current confinement layer 33.

Further, for example, on the surface of the upper cladding layer 43 on the side opposite to the active layer, a wave 1 [3 shaped portion (corrugation layer) 43a having irregularities at a predetermined pitch, for example, a pitch of 2,000 to 3,000 people is provided. The layer thickness of this first-side cladding layer 43 is such that a part of the wave emitted from the active layer above the groove is guided through the surface of the L-side cladding layer, and is transmitted by the wave-shaped portion 43a on the surface of the first-side cladding layer. The layer thickness should be appropriate to ensure black reflection.

Moreover, the one L side → cut layer 4 having this wave-shaped portion 43a
:l k is provided with an n-type 1nGaAsP layer 45 as a cap layer, and p (H'l
7F+, the pole 47 is placed on the upper side of the cap layer 45 with n I
! I11 electrodes 49 are provided respectively to constitute the distributed feedback semiconductor laser device of the present invention.

The semiconductor laser device described above has a substrate 31 and an n-heli In.
Since the P layer 33, the p-type 1nP layer 35, and the p-type 1nP upper rat layer 39 form a current confinement structure, the current injected into the device is as shown by the dotted circle in FIG. It efficiently flows into the region indicated by W0 in the figure.

Incidentally, in the semiconductor device of the present invention, in order to obtain good characteristics as a distributed feedback type (DFB; I) laser device, a five-waveform portion (corrugation layer) 43a is provided very close to the active layer. There is a need. In addition, in order to stabilize the lateral fundamental moat, the thickness of the active layer in one of the -1 grooves 37 (region indicated by Wl in FIG. 1) is formed to be thicker than the thickness of the other active layer region. Is it necessary? For that purpose, W
. It is necessary that the shape of the active layer in the region is a sun-moon shape that is convex toward the substrate 31 side. Furthermore, in order to realize more reliable basic mode excavation, it is necessary to narrow the width of the crescent, and therefore it is desirable to make the groove 37 as small as possible. On the other hand, this groove 37 needs to have a depth that reaches the substrate 31, and therefore the p-type InP layer 35
Etching is performed from the surface of the substrate 31 to the substrate 31, but during this etching, etching is also performed in a direction parallel to the surface of the substrate 31. Therefore, the deeper the groove 37 is, the wider the groove 37 is. turn into. In such a case, if the thickness of the semiconductor layer for forming the current confinement layer formed on the substrate 31 can be made thinner, the groove 37 reaching the plate 31 can be formed even if the etching depth is shallow. 1. As in the present invention, the diffusion length of minority carriers can be shortened as a current confinement layer.11. When using JInP layer, p ”l l
The layer thickness can be made thinner than when using an nP layer,
Therefore, the groove 37 can be made smaller.

In addition, the lower crat layer 3 is formed by liquid phase epitaxial growth.
9, the active layer 41, and the upper crat layer 43 in the groove 3.
7 and in the p-type 1nP current confinement layer 35F,
Crystals grow quickly inside the grooves due to the plane orientation dependence of crystal growth. Roughly speaking, if the groove 37 can be made smaller as mentioned in No. 1 above, the thickness of each of these layer parts above the groove 37 can be easily reduced to J'5 even if there is a lack of thickness above the current confinement layer. I can do it. Therefore, -C', it is possible to make the thickness of the active layer portion above the groove (2) thicker than the thickness of the active layer portion other than the seven portions of the groove (2). Also, since the ■groove is small, the surface of the active layer portion above the ■groove 37 is flat without maintaining the V-groove shape.
! Since it is possible to approach th, the wavelength selection waveform section provided on the F- side of the active layer can be formed very close to the active layer.

Hereinafter, in order to deepen the understanding of this invention, -'L'r:1i
For an example of the manufacturing method for manufacturing the two-semiconductor element Y-, refer to FIG. 2(A), (E) and 11'A. (This will be explained as follows. In addition, Fig. 2 (A)
- (C) is a cross-sectional view corresponding to the cross section taken along the line I-I of the element shown in FIG.

First, an n-type InP layer 33 is formed as a semiconductor layer for forming an internal current confinement layer by first liquid phase epitaxial growth.
p-type 1nP layer 35 and p-type InP substrate 31 (100
) to obtain the wafer structure shown in FIG. 2(A). Note that this ρ-type InP layer 35 is provided to protect the surface of the mouth-type 1nP layer 33 in contact with this layer 35 from the outside air and the etching atmosphere in the next step, thereby maintaining reliability as a current confinement layer.

Next, using normal photoetching techniques, e.g.
A mask for etching the p-type InP layer 35 in stripes with a predetermined width parallel to the <011> direction of the substrate 31 is formed using iO2 as a mask material. Subsequently, using a suitable etchant, the p exposed by the window is
The InP layer 35 and the 1nP layer 33 below this layer are etched down to the substrate 31 to form a groove 37 with a V-shaped cross section perpendicular to the stripe direction and a width WA. The wafer structure shown in Figure (B) is obtained. In addition to forming this groove 37, a current confinement function can be constructed by the remaining portion of the ρ-type 1nP layer 35 and the remaining portion of the mouth-type 1nP layer 33.

Next, by a second liquid phase epitaxial growth, a P-type InP layer 39, for example, as a lower cladding layer, an InGaAsP layer 41, for example, as an active layer, and an n-type InGaAsP layer 43, for example, as a layer side 1 layer are formed. and,
The p-type 1nP current confinement layer 35 and the inner surface of the groove 37 are sequentially formed. In this invention, the formation of each of these layers consists of p-type 1
Rather than growing on a flat region such as the surface of the nP layer 35, the groove 3
7. It is necessary to ensure that the growth into the internal region is made thicker. The aforementioned liquid phase epitaxial growth method is well known as a method for selectively controlling the layer thickness in this manner. According to this method, since the crystal growth rate inside the groove 37 is faster than the crystal growth rate on the flat surface outside the structure, the layer thickness of the region above the groove 37 of each layer is equal to the layer thickness above the current confinement layer 33. The structure shown in FIG. 2(C) is obtained.

Next, a resist pattern is formed on the n-type 1nGaAsP upper cladding layer 4 by a normal photolithographic exposure method.
Then, unnecessary portions of the surface of the upper cladding layer 43 are etched using a chemical etching technique to form a corrugated portion (corrugation layer) 43a having an uneven surface with an appropriate pitch and depth. It is formed on the surface of this upper cladding layer 43 to obtain the structure shown in FIG. 2(D). In this embodiment, the waveform portion 43a is
It is constructed so that unevenness appears at a pitch of 2,000 to 3,000 people in the 011> direction. Note that the pitch depth of the unevenness, etc. can be changed depending on the element design.

Next, by a second liquid phase epitaxial growth, for example, the njllnGaAsP layer 45 as a cap layer is grown, and the upper cladding layer 43 with the corrugated portion 43a is removed.
J: to obtain a wafer structure B at the 21st'21(E). Here, it is not necessary to specifically limit the crystal growth method in Section 24 (1) to liquid phase epitaxial growth, such as metal organic pyrolysis vapor deposition (MOCVD).
It is also possible to use a growth method such as

Next, a p-side electrode 47 is formed on the lower surface of the p-type 1nP substrate 31, and an n-side electrode 49 is formed on the upper surface of the cap layer 45, so that the distribution return of the present invention as shown in FIG. type semiconductor laser device can be obtained.

In the above embodiment, the surface of the upper cladding layer is processed to have an uneven surface to form a waveform portion. A layer having a waveguiding function may be provided separately.

(Effects of the Invention) As is clear from the above description, according to the semiconductor laser device of the present invention, the active layer is formed above the V-groove in a region wider than the width of the V-groove, which is different from the conventional one. It does not have such aspects. Furthermore, the current injected into the semiconductor laser device flows concentratedly in the active layer region formed above the V-groove.

Therefore, leakage current is unlikely to occur.

Furthermore, since the wave-shaped portion for wavelength selection is provided close to the active layer, a portion of the light emitted from the active layer is Bragg-reflected by the wave-shaped portion. Therefore, single-longitudinal mode oscillation occurs.

Furthermore, since the thickness of the active layer portion above the trench is greater than the thickness of the active layer portion above the internal current confinement layer, stable oscillation is achieved in the transverse fundamental mode.

Therefore, it is possible to provide a distributed feedback semiconductor laser device that operates with a low current and is capable of oscillating in the axial mode.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the main parts of the semiconductor laser device of the present invention, FIGS. 2A to 2E are manufacturing process diagrams showing an example of the method for manufacturing the semiconductor laser device of the invention, and FIG. FIG. 2 is a partially cutaway perspective view showing a conventional semiconductor laser device. 3I...p-type 1nP substrate 33-n-type InP current confinement layer 35/P-type 1nP layer 37...stripe groove 39...p-type InP'l' side cladding layer 4l---1
nGaAsP active layer 43... n-type 1nGaAsP upper cladding layer 43a.
・Wave shaped part (corrugation layer) 45・n-type InG
aAsP cap layer 47・-”p-side electrode, 49・-n-side electrode. Patent applicant Oki Electric Industry Co., Ltd. jfP type InP
The foundation pile 33n type construction was carried out in a gorge manga written in this dynasty's history - Saikan 5 Beggar O Slope □□□ Part 1
Figure 2

Claims (1)

[Claims] (1) A striped V-groove with a depth extending from the surface of the internal current confinement layer provided on the p-type InP underlayer to the underlayer, an active layer provided above the V-groove, and an active layer above the active layer. and a waveform shaped part for wavelength selection provided adjacently, and the thickness of the active layer portion above the V-groove is thicker than the thickness of the active layer portion above the internal current confinement layer other than the V-groove. A distributed feedback semiconductor laser device characterized by: