JP2016092124A - Optical modulator integrated semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical modulator integrated semiconductor laser capable of obtaining high optical output with low power consumption.SOLUTION: A semiconductor laser section 2 and a field absorption optical modulation section 3 are formed on an n-type InP substrate 1. The field absorption optical modulation section 3 includes an optical absorption layer 4 formed on the n-type InP substrate 1. The semiconductor laser section 2 includes: a stripe-shaped active layer 10 formed on the n-type InP substrate 1; and a p-type InP clad layer 5 formed on the active layer 10. A ridge is formed on the p-type InP clad layer 5. The active layer 10's width Wld is narrower than the p-type InP clad layer 5's ridge width Wrg. The active layer 10 exists only in an area below the ridge of the p-type InP clad layer 5. The optical absorption layer 4 covers a side surface of the active layer 10 and has band gap energy larger than that of the active layer 10.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical modulator integrated semiconductor laser (EML-LD) used as a light source for optical fiber communication.

  2. Description of the Related Art An optical modulator integrated semiconductor laser in which a semiconductor laser unit that emits laser light and an electroabsorption optical modulator that modulates laser light are integrated on a semiconductor substrate is known (for example, see Patent Document 1).

JP 2014-63052 A

  In a laser in which a ridge is formed in the cladding layer on the active layer, conventionally, the width of the active layer is wider than the ridge width, and the active layer protrudes from the region below the ridge of the cladding layer. When a current is injected into the semiconductor laser portion, a leakage current flows through the protruding portion of the active layer. Further, since the current density in that portion is relatively small, the laser light is absorbed.

  In particular, in a laser that requires an optical output with a wavelength of 1.55 to 1.63 μm, the difference in band gap energy between the active layer and the InP cladding layer is large, so that leakage current and optical absorption are in the 1.53 to 1.55 μm band It is difficult to obtain a high light output with low power consumption, which is larger than the EML.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain an optical modulator integrated semiconductor laser capable of obtaining a high optical output with low power consumption.

  An optical modulator integrated semiconductor laser according to the present invention includes a semiconductor substrate, a semiconductor laser portion that is formed on the semiconductor substrate and emits laser light, and an electric field absorption that is formed on the semiconductor substrate and modulates the laser light. A light-absorbing layer formed on the semiconductor substrate, and the semiconductor laser portion is a stripe-shaped active layer formed on the semiconductor substrate. And a clad layer formed on the active layer, the ridge is formed on the clad layer, the width of the active layer is narrower than the ridge width of the clad layer, and the active layer is the clad It exists only in the lower region of the ridge of the layer, and the light absorption layer covers a side surface of the active layer and has a band gap energy larger than the band gap energy of the active layer.

  In the present invention, the active layer exists only in the lower region of the ridge through which current flows. The side surface is covered with a light absorption layer having a larger band gap energy than the active layer. For this reason, leakage current and light absorption to the outside from the lower region of the ridge are small. As a result, high light output can be obtained with low power consumption.

1 is a perspective view showing an optical modulator integrated semiconductor laser according to an embodiment of the present invention. It is sectional drawing which shows the electroabsorption type optical modulation part of FIG. It is sectional drawing which shows the semiconductor laser part of FIG. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. 1 is a plan view showing an optical modulator integrated semiconductor laser according to an embodiment of the present invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the optical modulator integrated semiconductor laser which concerns on embodiment of this invention. It is sectional drawing which shows the semiconductor laser part of the optical modulator integrated semiconductor laser which concerns on a comparative example. It is a top view which shows the optical modulator integrated semiconductor laser which concerns on a comparative example.

  FIG. 1 is a perspective view showing an optical modulator integrated semiconductor laser according to an embodiment of the present invention. A semiconductor laser part 2 that emits laser light and an electroabsorption optical modulation part 3 that modulates the laser light are formed on an n-type InP substrate 1, and both are butt-jointed.

FIG. 2 is a cross-sectional view showing the electroabsorption optical modulator of FIG. On the n-type InP substrate 1, a light absorption layer 4, a p-type InP clad layer 5, and a p-type contact layer 6 made of an InGaAs / InGaAsP multilayer film are sequentially formed. The light absorption layer 4 has an AlGaInAs multiple quantum well. A ridge is formed in the p-type InP cladding layer 5 and the p-type contact layer 6, and the side surface of the ridge is covered with an insulating film 7 such as SIO ₂ or SiN. An anode electrode 8 made of Cr / Au, Ti / Pt / Au or the like is connected to the p-type contact layer 6. A cathode electrode 9 made of an Au / Ge material is connected to the back surface of the n-type InP substrate 1.

  FIG. 3 is a cross-sectional view showing the semiconductor laser portion of FIG. A stripe-shaped active layer 10 is formed on the n-type InP substrate 1. The active layer 10 has an InGaAsP multiple quantum well, InGaAsP-SCH, and InGaAsP / InP diffraction grating. A p-type InP cladding layer 5 and a p-type contact layer 6 are sequentially formed on the active layer 10.

  A ridge is formed in the p-type InP clad layer 5 and the p-type contact layer 6, and the side surfaces of the ridge are covered with an insulating film 7. An anode electrode 11 made of Cr / Au, Ti / Pt / Au, or the like is connected to the p-type contact layer 6.

  The width Wld of the active layer 10 is narrower than the ridge width Wrg of the p-type InP cladding layer 5 (Wld <Wrg). The ridge width Wrg is 1.7 μm to 2.7 μm. The active layer 10 exists only in the region below the ridge of the p-type InP cladding layer 5. The width Wld of the active layer 10 is 1.3 to 1.8 μm, which is the same as that of the buried laser diode, and the width of the waveguide of the semiconductor laser unit 2 satisfying the higher-order mode cutoff condition with respect to the oscillation wavelength. To do.

  The light absorption layer 4 having a band gap energy larger than the band gap energy of the active layer 10 covers the side surface of the active layer 10. The oscillation wavelength of the semiconductor laser unit 2 is 1.55 to 1.63 μm, and the light absorption layer 4 is transparent to light having this oscillation wavelength.

  Next, a method for manufacturing the optical modulator integrated semiconductor laser according to the present embodiment will be described. 4, 5, and 7-13 are cross-sectional views showing the optical modulator integrated semiconductor laser according to the embodiment of the present invention. FIG. 6 is a plan view showing an optical modulator integrated semiconductor laser according to an embodiment of the present invention.

First, as shown in FIG. 4, the active layer 10 is crystal-grown on the n-type InP substrate 1 by MOCVD. Next, as shown in FIGS. 5 and 6, a selective growth mask 12 made of SiO _{2 is} formed by sputtering and patterned. The width of the selective growth mask 12 is Wld. The active layer 10 is etched using the selective growth mask 12 as a mask.

Next, as shown in FIG. 7, the light absorption layer 4 is crystal-grown in a portion not covered with the selective growth mask 12 by MOCVD (butt joint growth). Next, as shown in FIG. 8, the selective growth mask 12 is removed by dry etching using CF _{4 or the} like.

  Next, as shown in FIG. 9, a p-type InP cladding layer 5 having a thickness of about 2 μm and a p-type contact layer 6 having a thickness of about 0.5 μm are sequentially formed on the entire surface of the wafer. Zn, Mg, C or the like is added to the p-type InP clad layer 5 and the p-type contact layer 6 as a p-type dopant.

Next, as shown in FIG. 10, a mask 13 made of SiO ₂ is patterned. Next, as shown in FIG. 11, unnecessary portions of the p-type InP cladding layer 5 and the p-type contact layer 6 are removed by at least one of dry etching and wet etching using the mask 13 as a mask. Thereafter, as shown in FIG. 12, the mask 13 is removed.

Next, as shown in FIG. 13, an insulating film 7 such as SiO ₂ or SiN is formed on the entire surface. Then, the insulating film 7 is etched in a region where an electrode contact is obtained. Thereafter, anode electrodes 8 and 11 are formed on the electroabsorption optical modulation unit 3 and the semiconductor laser unit 2, respectively, and a cathode electrode 9 is formed on the back surface of the n-type InP substrate 1.

  Next, the effect of this embodiment will be described in comparison with a comparative example. FIG. 14 is a cross-sectional view showing a semiconductor laser portion of an optical modulator integrated semiconductor laser according to a comparative example. FIG. 15 is a plan view showing an optical modulator integrated semiconductor laser according to a comparative example. In the comparative example, the width of the selective growth mask 12 is thick, the width Wlg of the active layer 10 is wider than the ridge width Wrg, and the active layer 10 protrudes from the lower region of the ridge. For this reason, when a current is injected into the semiconductor laser section 2, a leakage current flows through the protruding portion of the active layer 10. Further, since the current density in that portion is relatively small, the laser light is absorbed.

  On the other hand, in the present embodiment, the active layer 10 exists only in the lower region of the ridge through which current flows. The side surface is covered with a light absorption layer 4 having a band gap energy larger than that of the active layer 10. For this reason, leakage current and light absorption to the outside from the lower region of the ridge are small. As a result, a high light output can be obtained with low power consumption as compared with the comparative example.

  In the present embodiment, the active layer 10 is made of an InGaAsP-based material, and the light absorption layer 4 is made of an AlGaInAs-based material. However, the material of the light absorption layer 4 is not limited to this. For example, even when the light absorption layer 4 includes a layer made of an AlGaInAs-based material and a layer made of InP or InGaAsP formed on or under the layer made of an AlGaInAs-based material, the same effect can be obtained. Since InP or InGaAsP has a larger band gap energy than the AlGaInAs-based material, leakage current and light absorption are further reduced. The same effect can be obtained even when the light absorption layer 4 is made of an InGaAsP material having a band gap energy larger than that of the active layer 10.

1 n-type InP substrate (semiconductor substrate), 2 semiconductor laser part, 3 electroabsorption light modulation part, 4 light absorption layer, 5 p-type InP clad layer (clad layer), 10 active layer

Claims (5)

A semiconductor substrate;
A semiconductor laser part formed on the semiconductor substrate and emitting laser light;
An electroabsorption optical modulator that is formed on the semiconductor substrate and modulates the laser beam;
The electroabsorption light modulator has a light absorption layer formed on the semiconductor substrate,
The semiconductor laser part has a stripe-shaped active layer formed on the semiconductor substrate, and a cladding layer formed on the active layer,
A ridge is formed in the cladding layer,
The width of the active layer is narrower than the ridge width of the cladding layer,
The active layer is present only in the lower region of the ridge of the cladding layer;
The optical modulator integrated semiconductor laser, wherein the light absorption layer covers a side surface of the active layer and has a band gap energy larger than a band gap energy of the active layer. The active layer is made of an InGaAsP-based material,
2. The optical modulator integrated semiconductor laser according to claim 1, wherein the light absorption layer is made of an AlGaInAs-based material. The active layer is made of an InGaAsP-based material,
2. The light according to claim 1, wherein the light absorption layer includes a layer made of an AlGaInAs-based material and a layer made of InP or InGaAsP formed on or under the layer made of the AlGaInAs-based material. Modulator integrated semiconductor laser.   2. The optical modulator integrated semiconductor laser according to claim 1, wherein the active layer and the light absorption layer are made of an InGaAsP-based material.   5. The optical modulator integrated semiconductor laser according to claim 1, wherein an oscillation wavelength of the semiconductor laser unit is 1.55 to 1.63 μm.

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