JPH06283803A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To realize a semiconductor light emission device having good optical coupling characteristics in which DFB lasers and modulators are integrated through simultaneous growth utilizing crystal growth on a ridge. CONSTITUTION:Two types of crystal layer having different emission characteristics are grown simultaneously in the direction of cavity by taking advantage of the fact that a multilayer semiconductor formed on a ridge of 1-3mum wide and 1-3mum high, which is formed between two grooves 5 of 1-10mum wide made in a semiconductor substrate 1, has variable emission characteristics. This method allows formation of a light, emitting part comprising a DFB laser having a distorted multiple quantum well structure in the active layer and an optical modulator part of multiple quantum well structure having an absorption end on the side closer by 50-80nm to the short wave side than the oscillation wavelength of the DFB laser through same process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device useful as a light source for optical communication of a long distance engine system requiring a large capacity,
In particular, it relates to a distributed feedback laser with an external modulator.

[0002]

2. Description of the Related Art As a light source element of a frequency division multiplexing transmission system (FDM) which requires high coherence, it is required that chirping (fluctuation of oscillation wavelength at the time of modulation) is small. A distributed feedback laser with an external modulator is used as a light source element of this type.
It is called B laser. ) And an optical modulator are separately manufactured and combined, but they have the advantage of reducing the device size and not requiring adjustment for optical coupling of the two, but on the other hand, they require multiple crystal growth and device manufacturing processes. Since it is necessary, the deterioration of the characteristics of the entire optical element including the loss in the optical coupling portion cannot be avoided.

An example of manufacturing a conventional DFB laser with an external modulator is shown in FIG. In this conventional example, first, an n-InP substrate 30 is formed by metalorganic vapor phase epitaxy (MOVPE).
An InGaAs layer 31, an n-In layer 32, an MQW layer 33, a DFB layer 34, a p-InP layer 35 and an InGaA layer are formed on the top.
After forming the substrate DFB laser structure composed of the s layer 36,
In order to form the optical modulator portion MD, the portions other than the laser portion LD are etched and removed up to the substrate 30 (FIG. 3A).
Next, using the molecular beam epitaxy method (MBE), n-I
The modulator MD portion including the nAlAs layer 37, the MQW layer 38, the p-InAlAs layer 39, and the InGaAs layer 40 is regrown (FIG. 3B). In this case, the boundary between the laser section LD and the modulator section MD is so-called butt joint coupling. The MOVPE method can also grow crystals exhibiting the quantum confined Stark effect, and the laser LD
The modulator unit MD may be formed only by the MOVPE method. Finally, the clad layer 43 composed of the p-InP layer 41 and the InGaAs layer 42 is regrown (FIG. 3C),
In order to obtain a high-speed response characteristic, a device structure as shown in FIG. 3D is obtained by embedding with polyimide 44 and attaching electrodes of the n electrode 45 and the p electrode 46. In addition, 47
Is an antireflection (AR) film. The coupling efficiency in this case is 80
It is estimated to be about%. There is also a structure in which the laser portion is a conventional bulk type, but the basic manufacturing process does not change. The device shown in FIG. 3 has a low process yield and poor reproducibility of characteristics. JP-A-2-229485
The publication describes a practical DFB laser with an external modulator in which the optical coupling characteristics are improved by forming the laser on the modulator. This method also requires removal of the laser structure in the modulator portion, regrowth of the cladding, and buried growth, which complicates the process.

An element in which a DFB laser and a modulator are integrated has been realized by Aoki et al. By utilizing the mask selective growth method (Research Report No. 445, P. of Applied Electronic Properties).
9-14 or ELECTRONICS Letters Vol.28, No.12.pp.1157
-1158). The element structure is shown in FIG. 4. In this element, the MQW-DFB laser section 50 and the MQW-EA modulator section 5 are shown.
No. 2 utilizes that the change in the mask width and the gap width between the masks causes the change in the well layer thickness due to the difference in the growth rate in each portion to change the light emission characteristics. Therefore, since there is a step in the cavity direction of this element, the optical coupling cannot be theoretical. Figure 4
In, the MQW-DFB laser unit 50 has a grating 51 as shown in an enlarged manner. Also MQW-E
As shown in an enlarged scale, the A modulator unit 52 has InGaAs /
It has an InGaAsP MQW structure 53 and an InGaAsP waveguide layer 54. 55 is an n-InP substrate, 56 is F
An e-doped InP layer, 57 is a reflective (HR) film, and 58 is a non-reflective (AR) film.

[0005]

DISCLOSURE OF THE INVENTION The present invention utilizes a crystal growth on a ridge to carry out batch growth with good optical coupling characteristics.
The main issue is to realize a semiconductor light emitting device in which a laser and a modulator are integrated.

[0006]

According to the present invention, the width of the shape of a ridge previously formed on a semiconductor, the interval (groove interval) between adjacent ridges or the width of the groove, and the height of the ridge are within a predetermined range. Set to metalorganic vapor phase growth (MOVP
According to the method E), the active layer is formed into a semiconductor multilayer film having a strained multiple quantum well (MQW) structure. That is, the semiconductor light emitting device of the present invention has a width of 1 to 1 formed on the semiconductor substrate.
Width 1-3 μm between two 10 μm grooves, height 1
In an optical device that utilizes the change in the light emission characteristics of a semiconductor multilayer film formed on a ridge of ~ 3 μm, by simultaneously growing two types of crystal layers having different light emission characteristics in the cavity direction, the light emitting portion and the light The modulator section is formed in the same step, and preferably, the light emitting section is a distributed feedback laser having a strained multiple quantum well structure in the active layer, and the optical modulator section is a distributed feedback laser. It is characterized by having a multiple quantum well structure having an absorption edge on the short wavelength side of 50 to 80 nm from the oscillation wavelength of the type laser.

[0007]

MOVP is formed on a semiconductor substrate having a pattern in which a ridge width, a groove width, and a ridge height are set in advance.
When a semiconductor multi-layer film having a strained quantum well structure is formed by the E method, due to the characteristic of crystal growth, a difference occurs in the moving speed of semiconductor constituent elements depending on the crystal plane, and the composition of the n-strained multiple quantum well film on the ridge is slightly different. While making changes. Therefore, an optical functional element having a slightly different thickness and composition of the active layer can be formed on the plurality of ridges, and its wavelength characteristic can be controlled in a wide range.

In controlling the wavelength characteristics, the main cause of the change is the change in the composition of the quantum well layer. 1 (A), (B), and (C) show In _1-X Ga _x , respectively.
It is a view showing changes in light emission characteristics from an As / InGaAsP (λg = 1.1 μm) quantum well layer depending on a ridge width, a groove width and a ridge height. Figure 1 (A)
Sets the ridge height to 2 μm and the ridge width to 1
The relationship between the amount of change in the emission wavelength when changing from .mu.m to 6 .mu.m is shown by using the groove width of the ridge side surface as a parameter. As can be seen from the figure, when the groove width is 3 μm or less, the shift amount of the emission wavelength significantly increases with respect to the ridge width. When the ridge width is 4 μm or more, the shift amount of the emission wavelength is extremely small. In FIG. 1B, the groove width on the side surface of the ridge is 1 with the height of the ridge being constant at 2 μm.
It shows the characteristics with the ridge width as a parameter with respect to the relationship with the amount of change in the emission wavelength when changing from μm to 10 μm. As you can see, the ridge width is 2
When the groove width is less than or equal to μm, the shift amount of the emission wavelength changes significantly with respect to the change in groove width, and is particularly remarkable when the groove width is 6 μm or less. FIG. 1C shows the relationship with the amount of change in the emission wavelength when the height of the ridge is changed from 1.2 μm to 2.2 μm with the groove width on the side surface of the ridge being constant at 1.5 μm.
The characteristics are shown with the ridge width as a parameter.
Although not shown, it can be seen that the shift amount of the emission wavelength is remarkable with respect to the height of the ridge in the height range of 1 to 3 μm. That is, from the characteristics of FIG. 1, the ridge width, height,
It is shown that in the case of a groove having a minute dimension of 10 μm or less, the amount of change in the emission wavelength is extremely large, and the emission wavelength can be controlled by a processing technique such as a ridge. Further, the emission characteristics shift to the longer wavelength side as the ridge width becomes narrower and the groove width becomes narrower.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. <Integrated Light Source of DFB Laser and Optical Modulator> An example of producing an integrated light source of DFB laser and optical modulator by keeping the ridge width and the groove depth constant and changing the groove interval or the groove width is shown in FIG. Shown in.

First, as shown in FIG. 2A, n-type In
Diffraction grating 2 is formed on a portion of P (100) substrate 1 which will be a DFB laser, using a laser interference exposure method or an electron beam exposure method. Next, the insulating film 3 made of an oxide film or a nitride film is processed by photolithography and dry etching to have a pattern (a ridge stripe portion and a step between the stripe portions as shown in FIG. 2B). Get the plateau mask). There is also a substrate 1 in which an optical waveguide layer (for example, InGaAsP layer) is crystal-grown before pattern formation, and in that case, a corresponding waveguide layer growth process is omitted in the subsequent crystal growth. Next, as shown in FIG. 2C, a groove width modulation type non-flat substrate 1'is formed by dry etching using chlorine gas. Here, the width dw
A ridge (mesa) 4 of 1.5 mm is formed in the <011> direction (so-called reverse mesa direction), the depth h of the groove 5 is 2 μm, and the groove width dg is 1.5 μm for the DFB laser and the modulator, respectively.
30 μm, and the length of each part is 3
It is 00 μm. Then, using trimethylindium, triethylgallium, arsine, and phosphine as source gases for the semiconductor, and hydrogen selenide and diethylzinc as doping gases, a metalorganic vapor phase epitaxy method was performed on the ridge at 630 ° C. and 0.1 atm. As shown in FIG.
GaAsP waveguide layer and 5 cycles of 30Å InGaAs
A light emitting layer 6 having a strained quantum well structure made of a P well / 150 Å InGaAsP barrier and a p-InP clad layer 7 are formed. As a result, the emission spectrum on the flat substrate observed by the photoluminescence method has a peak at 1.3 μm, while the adjacent groove widths are 1.5 μm and 3.
The peaks of light emission from the ridge, which is 0 μm, are 1.55 μm and 1.48 μm, respectively. By doing this, the oscillation wavelength of the DFB laser is 50 to 80 nm.
An optical modulator having a multiple quantum well structure having an absorption edge on the short wavelength side can be obtained. Further, according to FIG. 2 (E), p-InP clad layer 7'is additionally deposited by metalorganic vapor phase epitaxy, and then n-I is used as a buried layer for current blocking.
After growing the nP layer 8 and the p-InP layer 9, p-InG
The aAsP contact layer 10 is formed. The crystal growth of FIGS. 2D and 2E can be performed once depending on the conditions, but when the thickness of the buried layer, the doping control, and the like are accurately performed, the crystal growth is performed in two or three times. Finally Figure 2
As shown in (F), a p-electrode 11 and an n-electrode 11 'are formed on the upper and lower sides, and each portion on the ridge where the composition changes is D
A separation groove 12 is provided to separate the FB laser 15 and the optical modulator 16.

As a result, a width of 1 to 3 μ formed between the two grooves 5 and 5 formed in the semiconductor substrate 1 and having a width of 1 to 10 μm.
By utilizing the fact that the emission characteristics of the semiconductor multi-layer film formed on the ridge 4 having a height of m 3 and a height of 1 to 3 μm change, two kinds of crystal layers having different emission characteristics are simultaneously grown in the cavity direction. A light-emitting portion including a DFB laser 15 having a strained multiple quantum well structure in an active layer, and a DFB laser 1
An optical modulator 16 having a multiple quantum well structure having an absorption edge on the shorter wavelength side of 50 to 80 nm than the oscillation wavelength of 5 is formed in the same step.

The element thus manufactured is shown in FIG.
After mounting on the heat sink 13 as shown in (F) and further bonding the lead wire (wire) 14, I _LD
In the state where the DFB laser 15 is oscillated by injecting a constant current as, the current modulated as I _MOD is supplied to the optical modulator 16
To use.

[0013]

According to the present invention, an integrated light source of a DFB laser and an optical modulator can be easily manufactured, and the optical communication technology can be advanced by reducing the cost of the device.

[Brief description of drawings]

FIG. 1 In _1-X Ga _x As formed on a non-planar substrate
/ InGaAsP (λg = 1.1 μm) -based MQW layer emission wavelength shift amount (A): ridge width dependence of emission wavelength shift amount at various groove widths, (B): emission wavelength at various ridge widths The groove width dependence of the shift amount of (1), (C): the ridge height dependence of the emission wavelength shift amount in various ridge widths.

FIG. 2 is a diagram showing a method of manufacturing an integrated light source of a DFB laser and an optical modulator according to an embodiment of the present invention.

FIG. 3 is a diagram showing a conventional example of an integrated light source of a DFB laser and an optical modulator.

FIG. 4 is a diagram showing another conventional example of an integrated light source of a DFB laser and an optical modulator.

[Explanation of symbols]

 1 Substrate 2 Diffraction Grating 3 Oxide Film or Nitride Film 4 Ridge 5 Groove 6 InGaAs / InGaAsP Light-Emitting Layer and Optical Waveguide Layer 7, 7 ′ p-InP Clad Layer 8 n-Embedded Layer 9 p-InP Embedded Layer and Clad Layer 10 Contact Layer 11, 11 'Electrode 12 Element isolation groove 13 Heat sink 14 Lead wire 15 DFB laser 16 Optical modulator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuru Naganuma 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A width of 1 to 10 μm formed on a semiconductor substrate
Width 1-3 μm, height 1-3 μm between two grooves
In an optical device that utilizes the change in the emission characteristics of the semiconductor multilayer film formed on the ridge, the two types of crystal layers having different emission characteristics are simultaneously grown in the cavity direction so that the light emitting portion and the optical modulator are formed. A semiconductor light-emitting device, wherein the parts are formed in the same process. 2. The light emitting section according to claim 1, wherein the active layer is a distributed feedback laser having a strained multiple quantum well structure, and the optical modulator section is 50 to 80 wavelengths longer than the oscillation wavelength of the distributed feedback laser.
A semiconductor light emitting device comprising a multi-quantum well structure having an absorption edge on the short wavelength side.