JPH02252284A - Semiconductor laser array and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the laser characteristics due to the slips in the oscillation wavelength and the gain peak from occurring by a method wherein mesastripes in different widths are formed on multiple regions on a substrate while active layers etc., including quantum well layers are formed cn the mesastripes by specific process. CONSTITUTION:A diffraction lattice 100 in specific thickness is formed on an n-type InP substrate 11. Next, multiple mesa stripes 35, 36 in different widths of S1, S2 are formed by photolithography in the perpendicular direction to the lattice 100. Next, an InGaAsP photowaveguide layer 12, an InGaASPMQW active layers 31, 32 and a P-InP layer 14 are successively formed on the mesa substrate by liquid epitaxial deposition process. At this time, the thickness of the layers on the mesastripes 35, 36 thinner than that of flat parts is notably dependent upon the widths of the mesastripes 35, 36 while the thickness of the quantum well layers included in the active layers is also differentiated in respec tive regions on the substrate 11. Through these procedures. the slips in the oscillation wavelength and the gain peak can be prevented from occurring so that the laser array in the least dispersion in characteristics may be displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an integrated multi-wavelength distributed feedback semiconductor laser array, which is a light source necessary for wavelength division multiplexing optical communication, and a method for manufacturing the same.

2. Description of the Related Art In recent years, optical multiplex communication has been actively researched and developed as a high-capacity optical communication. Such light sources for wavelength division multiplexing communication require multiple semiconductor lasers with different oscillation wavelengths, but in order to miniaturize the light source and adjust the optical axis, it is necessary to integrate lasers with different oscillation wavelengths on the same substrate. Research and development of multi-wavelength integrated laser arrays is also gaining momentum. In order to increase the multiplexing density, such a multi-wavelength light source is preferably configured with a distributed feedback semiconductor laser (hereinafter referred to as DFB-LD) that has stable single-axis mode oscillation even during high-speed modulation.

In DFB-LD play, a relatively easy method for changing the oscillation wavelength of each LD is to change the pitch 71 of the diffraction grating that constitutes each LD [References H, 0kuda, et. aj.

Japan J Applied Physics (JI
)n, J, Appl, Phys, ) 23
(1984) L9o4).

FIG. 6A is a plan view of an LD array in which a plurality of LDs are integrated on the same substrate. Here, two representative LDs (
Only 1 and 2) are shown. Figure 6 B and C are each L
Cross section a-a', b in the capitivity direction of Dl, 2
-b' is an epitaxial structure diagram. Here 11 is n
InP type substrate, 12 is an n-InGaAsP optical waveguide layer (bandgap wavelength λ = 1.1 μm), 13 is In
GaAsP active layer (λ9=1.3 μm), 14 is p-type I
It is an nP cladding layer.

On the n-type InP substrate 11, there is a pitch/f1=39.
Diffraction gratings 20.21 to 40 and A2=3860 are formed.

The oscillation wavelength λ of the LD is ``If off is the effective refractive index and N is the diffraction order, λ = 2 n - Δ7menN ・A...・mark・
...(1) Determined by ff. Here, N=2, "off" is 3°3o
Then, the oscillation wavelength of each LD is λ1=1.30μ
m.

With λ2=1.27 μm, an oscillation wavelength difference of 30 nm can be obtained with two LDs. In this way, by changing the pitch of the diffraction grating in each LD, the oscillation wavelength of the pDFB-LD can be changed.

However, each LD1 of this DFB-LD array
; Since the bandgap wavelength λ9°, that is, the gain peak, of the active layer 13 in No. 2 is the same as 1.3 μm, the deviation between the oscillation wavelength and the gain peak becomes a problem. In other words, Figures 7A and 7B show the oscillation spectra of LD1 and LD2. In LD1, the oscillation wavelength corresponds to the gain peak, whereas in LD2, the oscillation wavelength determined by the diffraction grating pitch is much larger than the gain peak. It can be seen that there is a shift to the shorter wavelength side. Such a deviation causes an increase in the oscillation threshold current, a decrease in the luminous efficiency, and a deterioration in the temperature characteristics. Furthermore, when the difference between the two becomes larger, oscillation in the DFB mode no longer occurs.

In addition, as a manufacturing problem, in order to fabricate diffraction gratings with different pitches in different areas on the same substrate using the commonly used two-beam interference exposure method, a multi-step masking process for areas other than the selected area and a two-beam interference exposure process are required. This means that it has to be made repeatedly. Such a complicated process not only reduces yield but also causes deterioration and variation in device characteristics.

Problems to be Solved by the Invention In the DFB-LD array using the conventional method of changing the diffraction grating pitch to obtain the oscillation wavelength difference,
Due to the deviation between the oscillation wavelength of the LD determined by the diffraction grating pitch and the gain peak determined by the active layer bandgap, deterioration and variation in the characteristics of the LDs forming the array become a problem. Furthermore, forming diffraction gratings with different pitches in selected areas requires a very complicated process, resulting in lower yields and deterioration of characteristics.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a plurality of regions in an array on the main surface of the same semiconductor substrate of the first conductivity type, each region having a different effective refractive index and bandgap energy. After forming mesa stripes in an array, which is a semiconductor laser array, each having an active layer including a quantum well layer, a diffraction grating, and a cladding layer of a second conductivity type, an MQW layer is formed on the mesa array substrate. A method of manufacturing a semiconductor laser array is characterized in that it includes a step of forming an epitaxial layer.

Operation By using the above-mentioned means, the oscillation wavelength difference is obtained by the effective refractive index difference in each distributed feedback laser cavity constituting the play, and the gain peak also shows a shift similar to the oscillation wavelength shift due to the quantum size effect, and the oscillation wavelength and gain peak Therefore, it is possible to provide a distributed feedback laser array that suppresses deterioration of laser characteristics due to deviation of the laser beam by a very simple means.

EXAMPLE Hereinafter, an example will be described in which a distributed feedback (DFB) LD array according to the present invention is made of InGaAsP/InP material. FIG. 1 shows this array structure, and A-C is a plan view A of two LDs (LDl, LD2) and a cross-sectional basic structure diagram B in the cavity direction, as in the case of FIG. 6 showing the conventional example. ,C. Same as the conventional example (diffraction grating 100 on n-InP substrate 11, InG
aAsP optical waveguide layer 12° active layer 31, 32, p
-Mainly composed of an InP cladding layer. Here, the difference from the conventional example is that in the conventional example, the pitch of the diffraction gratings 20 and 21 is /11. ．． Unlike No. 42, the composition and thickness of the active layer 13 were the same, whereas in this example, the active layer was composed of InGaAsP well layers (λ9
= 1.3 μm) and InGaAsP barrier layer (λ = 1.Q
A multi-quantum well (MQW) structured active layer 3 consisting of
It is 1°32. Here, the MQW active layer 31 consists of 60 well layers 33 and 50 barrier layers 3406 pairs, as shown in an enlarged view in Figure 1, and the MOW active layer 32 is shown in an enlarged view in Figure 1E. Like 100 well layers 36 and 1
It consists of 3605 pairs of barrier layers to 00. The pitch of the diffraction gratings is the same in both cases, Ao=4000.

The oscillation wavelength in DFB-LD is (1) in the conventional example.
According to the formula, it depends on the effective refractive index of the guided mode of the LD (
Figure 2A). In FIG. 1, n of LDl. ff is 3.
18, whereas in LD2 it is 3.26. This n. Due to the ffO difference, the respective oscillation wavelengths are 1.27 μm for LDl and 1.27 μm for LDl, as shown in Figure 2.
For I and D2, a difference of 1.30 μm and 30 nm was obtained.

On the other hand, in the structure of the present invention, the active layers 31 and 32 of LDl and LD2 are MQW layers with well layer thicknesses of 50A and 100A, respectively, so the band gap energy, that is, the gain peak of both, is as shown in FIG. 2B. Depends on size effect.

That is, while it is 1.27 μm in LD1, it is 1.30 μm in LD2. FIG. 3 shows the oscillation vectors of two LDs of the present invention.

A corresponds to LD1, and B corresponds to LD2. The gain peak almost coincides with the oscillation wavelength, and there is almost no deviation between the two as in the conventional example shown in FIG. This is because the oscillation wavelength shift due to the 5sff change and the gain peak shift due to the quantum size effect occur in the same direction with respect to a change in the well layer thickness.

As described above, in the DFB-LD array of the present invention, the deviation between the oscillation wavelength and the gain peak is small, the variation in characteristics of each LD in the array is small, and all have good current-light output characteristics.
Indicates temperature characteristics.

Next, a process for manufacturing a DFB-LD array having the structure of the present invention will be described. First, as shown in Figure 4A, the n-type I
Bitch Δ on nP substrate by two-beam interference exposure method. =40
Form a diffraction grating of 00 people.

Next, as shown in FIG. 4B, a width s1. A plurality of mesa stripes 35 and 36 with different S2 are formed by normal photolithography.

On this mesa substrate, the liquid phase epitaxial growth method is applied to
As shown in ↓, InGaAsP optical waveguide layer 11, InG
An aAsP MQW active layer (31°32) and a p-InP layer 14 are sequentially formed. According to the liquid growth method, the thickness of the epitaxial layer on the mesa stripe is thinner than on the flat part and largely depends on the width of the mesa stripe. MQ in Figure 6
The dependence of the well layer Lz of the W active layer and the effective refractive index on the mesa stripe width S is shown. As the mesa stripe width decreases, both the well layer thickness and the effective refractive index decrease.

If S is 10 μm and S2 is 20 μm, the first diagram.

Well layer thickness 33.3 in MQW layer 31,3≧ shown in E
5 are 60 and 100, respectively, and the effective refractive index n of the active layer. ff is 3.1B each.

3.26 is different. According to Figures 2 and 3, the oscillation wavelength shift due to the difference in effective refractive index and the gain peak shift due to the difference in well layer thickness exhibit similar behavior. DFB-
An LD array can be obtained.

As described above, in this manufacturing method, an integrated multi-wavelength DFB-LD array with small variations in characteristics can be obtained by a very simple process of one diffraction grating formation process and basically one epitaxial growth process.

By the way, in this embodiment, for the sake of simplicity, a two-wavelength integrated device has been described as an example, but the same applies to a multi-wavelength LD array having three or more wavelengths. Furthermore, although the structure of the DFB-LD has a diffraction grating under the active layer, the DFB-4D structure having a diffraction grating on the active layer is exactly the same. Although the liquid phase method has been described as an epitaxial growth method, similar effects can be obtained by other methods such as MOVPE and MBE if conditions are selected. Further, although the InGaAsP/InP system material has been described, other 2-v group semiconductors such as AlGaAs/GaAs, 1%, etc. can be similarly applied.

More than the effects of the invention, the present invention provides an active layer including a quantum well layer having a different layer thickness in each region, a diffraction grating, and a second conductive layer in a plurality of regions in an array on the main surface of the same semiconductor substrate of the first conductivity type. It is an integrated semiconductor laser array characterized by having a cladding layer of the same type, and has good single-axis mode oscillation with little variation in characteristics due to small deviation of the gain peak of each I and D oscillation wavelength. It is possible to provide a multi-wavelength LD array. There is also a step of forming a diffraction grating on a semiconductor substrate, and a step of forming an array of mesa stripes with different widths in multiple regions on the substrate, and then forming a growth layer including a fiMQW layer by liquid phase epitaxial growth. This is a method for manufacturing a semiconductor laser array characterized by including the above-mentioned integrated element by a very simple manufacturing process of basically forming a diffraction grating once and epitaxially growing it once. be.

[Brief explanation of drawings]

FIG. 1 shows the structure of a DFB-LD array according to an embodiment of the present invention, and FIG. 1A is a plan view thereof, and FIG. 1B is a plan view thereof. C is a cross-sectional view along the optical axis direction a-a', bb'line;
In the same figure, E is an enlarged cross-sectional view of the MQW layer in B and C of the same figure, respectively. Figure 2A shows the dependence of the oscillation wavelength on the effective refractive index, B shows the dependence of the gain peak on the well layer thickness, and Figure 3 shows the dependence of the gain peak on the well layer thickness.
Figures A and B are diagrams showing the oscillation spectra of two typical LDs in the array of the present invention, and Figures 4A, B, and C are perspective views and cross-sectional views showing the manufacturing proscene of the DFB-LD array according to the present invention. FIG. 5 is a diagram showing the dependence of the effective refractive index and the well layer thickness on the mesa stripe width. FIG. 6 shows the structure of a conventional laser; FIG. 6A is a plan view thereof, FIGS.
is a diagram showing the oscillation spectrum of FIG. 6; 1...LDl, 2...LD2.11.
......n-type InP substrate, 12-...-InGaAa
P optical waveguide layer, 14... p-type InP cladding layer,
100... Diffraction grating, 31.32...
MQW active layer, 33; 35...Well layer. Name of agent: Patent attorney Shigetaka Awano (1 person)
・-LDI 2・-LD 2 FIG. @36″-7II M, 71 (β) lρθ I7-layer thickness Lz (A) J, f5 Large difference. Fig. pρ 35.3g - Medium length stripe. / Fig. Medium length stripe ° Width δ (P/WL) Fig. Kumacho

Claims (2)

[Claims] (1) An active layer including a quantum well layer having a different layer thickness in each region, a diffraction grating, and a cladding layer of a second conductivity type are formed in a plurality of regions in an array on the same semiconductor substrate of a first conductivity type. A semiconductor laser array comprising: (2) Forming a diffraction grating on a semiconductor substrate or epitaxial substrate, forming mesa stripes with different widths in an array in multiple regions on the semiconductor substrate or epitaxial substrate, and then epitaxially growing on the mesa array substrate. A method of manufacturing a semiconductor laser array, comprising the step of forming an epitaxial layer including an active layer constituted by a quantum well layer.