JP4822244B2 - Semiconductor light-emitting device using self-forming quantum dots - Google Patents

Description

  The present invention relates to a semiconductor light emitting device using self-formed quantum dots, and is particularly characterized by a lateral mode control configuration in a semiconductor laser or a semiconductor optical amplifier (SOA) used as a light source in an optical communication system. The present invention relates to a semiconductor light emitting device using self-forming quantum dots.

  In recent years, optical communication systems are spreading to general households as high-speed transmission systems. However, a semiconductor laser or semiconductor optical amplifier used as a light source for optical communication or as a repeater is required to have a single transverse mode. .

  This unification of the transverse mode is important for stably operating the semiconductor laser and increasing the coupling efficiency of light to the fiber. In conventional semiconductor lasers or semiconductor optical amplifiers, the active layer is striped. In this way, the transverse mode is unified.

  In addition, with the recent increase in speed and functionality of optical communication systems, semiconductor light emitting devices such as semiconductor lasers and semiconductor optical amplifiers that are light sources are also required to have excellent wavelength stability. In order to secure a relatively large gain coupling coefficient compared to the configuration, a gain coupled DFB laser using a self-formed quantum dot as an active layer having a structure in which the state of electrons is quantized in three dimensions in all directions is also proposed. (For example, refer to Patent Document 1).

  Further, in such a semiconductor laser using self-forming quantum dots, a periodic structure made of a plurality of materials having different lattice constants is provided under the active layer, and the density or the size of the self-forming quantum dots grown on the periodic structure is increased. It has also been proposed to unify wavelengths by periodically changing at least one of them (for example, see Patent Document 2).

On the other hand, in a semiconductor laser or semiconductor optical amplifier using quantum dots, it is also proposed to control the beam shape of the transverse fundamental mode by controlling the density distribution of the quantum dots in the direction perpendicular to the resonator axis ( For example, see Patent Document 3).
JP 2001-326421 A JP 2003-309322 A JP-A-11-307860

  However, in any of the above proposals, the transverse fundamental mode is realized by patterning the active layer including quantum dots in a stripe shape. In these proposals, the active layer is cut directly by etching, so that a laser is used. There is a problem that the deterioration of is large.

  Accordingly, an object of the present invention is to control the transverse mode without directly etching the active layer.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
Reference numerals 1 and 6 in the figure denote a lower cladding layer and an upper cladding layer, respectively. To solve the above problem, the present invention provides a semiconductor light emitting device using self-forming quantum dots 4 as an active layer medium, having a ridge type optical waveguide, and perpendicular to the optical axis of the optical waveguide. The density of the self-forming quantum dots 4 in a simple cross section is larger in the central portion than in the peripheral portion.

In this way, by utilizing the density density of the self-forming quantum dots 4, an active layer structure is produced in which the density of the self-forming quantum dots 4 at both ends is smaller than that at the center in the direction perpendicular to the resonator. Thus, it is possible to suppress the occurrence of the lateral higher order mode without directly processing the active layer, and hence without reducing the reliability of the element.
In particular, since the ridge type optical waveguide which is the stripe structure 7 for controlling the transverse mode is provided in addition to the density distribution of the self-forming quantum dots 4, the oscillation mode can be surely set to the transverse fundamental mode.
The semiconductor light emitting element mainly means a semiconductor laser or a semiconductor optical amplifier, but also includes a light emitting diode (LED).

  In order to form a density close to the density of the self-forming quantum dots 4 described above, the lattice constant of the base semiconductor layer 2 in the central portion is set to be equal to that of the base semiconductor layer 3 in the peripheral portion in the cross section perpendicular to the optical axis in the optical waveguide. It may be larger than the lattice constant.

  Further, the above-described base semiconductor layers 2 and 3, the self-forming quantum dots 4 formed on the base semiconductor layers 2 and 3, and the barrier layer 5 covering the self-forming quantum dots 4 and the base semiconductor layers 2 and 3. Such a laminated structure may be configured so as to be laminated at least two layers, whereby a large light output can be obtained.

  In this case, the density of the self-forming quantum dots 4 is preferably about 1.5 times or more higher than the density of the self-forming quantum dots 4 in the peripheral portion. In this case, it is sufficient to make it more than twice, thereby effectively suppressing the occurrence of the transverse higher-order mode.

  In this case, the combination of InGaAs as the base semiconductor layer 2 having a large lattice constant, GaAs as the base semiconductor layer 3 having a low lattice constant, and InAs as the self-forming quantum dot 4 is the most typical combination. A semiconductor light emitting device that oscillates at a wavelength suitable for a light source for optical communication can be realized.

  According to the present invention, by utilizing the base dependency of the density of self-forming quantum dots, it is possible to suppress lateral higher-order modes without directly processing the active layer, thereby reducing the reliability of the device. There is nothing.

  The present invention makes use of the substrate dependence of the density of self-forming quantum dots, and in the cross section perpendicular to the resonator axis, the lattice constant of the underlying semiconductor layer in the central portion is made larger than the lattice constant of the underlying semiconductor layer in the peripheral portion. As a result, the density of the self-forming quantum dots at both end portions is reduced as compared with the central portion, and the lateral higher-order mode is controlled.

Here, with reference to FIG. 2 thru | or FIG. 7, although the semiconductor light-emitting device using the self-forming quantum dot of Example 1 of this invention is demonstrated, each figure is sectional drawing perpendicular | vertical to an optical axis.
See Figure 2
First, an n-type GaAs buffer layer 12 having a thickness of, for example, 500 nm and a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ is formed on the n-type GaAs substrate 11 using MOCVD (metal organic chemical vapor deposition). The n-type AlGaAs cladding layer 13 having a thickness of, for example, 1.4 μm, an Al composition of 0.4, and a doping concentration of 6.0 × 10 ¹⁷ cm ⁻³ , and a non-doped GaAs layer 14 having a thickness of, for example, 150 nm The non-doped InGaAs layer 15 having a thickness of, for example, 5 nm and an In composition ratio of 0.15 is sequentially grown.

See Figure 3
Next, after applying a resist on the non-doped InGaAs layer 15, for example, a resist pattern 16 having a stripe-shaped groove 17 having a width of 3.0 μm and a length of 300 μm is formed by using an electron beam exposure method or an interference exposure method, and then By depositing a SiO ₂ film 18 using a sputtering method, a stepped SiO ₂ pattern 19 is formed inside the stripe-shaped groove 17.

See Figure 4
Next, the SiO ₂ film 18 deposited on the resist pattern 16 is removed by removing the resist pattern 16 so that only the SiO ₂ pattern 19 remains, and the non-doped InGaAs layer 15 is selectively used with the SiO ₂ pattern 19 as a mask. To remove.

See Figure 5
Next, the removal portion of the non-doped InGaAs layer 15 is buried by growing the non-doped GaAs buried layer 20 by the MOCVD method using the SiO ₂ pattern 19 as it is as a selective growth mask.

See FIG.
Next, after removing the SiO ₂ pattern 19, for example, a method described in Japanese Patent Laid-Open No. 9-326506 is used, and an InAs forming source gas corresponding to a trimolecular layer is supplied at a growth temperature of 470 ° C., for example. Then, the InAs quantum dots 21 are self-formed.

The density of the InAs quantum dots 21 greatly depends on the underlying semiconductor layer, here the non-doped InGaAs layer 15 and the non-doped GaAs buried layer 20, and the density of the InAs quantum dots 21 grown on the non-doped InGaAs layer 15 in this case is 8 × 10 ¹⁰ / cm ² , and the density of InAs quantum dots 21 grown on the non-doped GaAs buried layer 20 is ˜3 × 10 ¹⁰ / cm ² , and a density distribution is formed.

See FIG.
Next, the MOCVD method is used again to embed the InAs quantum dots 21 with a non-doped GaAs barrier layer 22 having a thickness of, for example, 100 nm, and the thickness is, for example, 1.4 μm and the Al composition is 0.4. A p-type AlGaAs cladding layer 23 having a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ , a thickness of, for example, 20 nm, an Al composition of 0.2, and a doping concentration of 2.0 × 10 ¹⁹ cm ⁻³ The type AlGaAs layer 24 and the p-type GaAs contact layer 25 having a thickness of, for example, 400 nm and a doping concentration of 2.0 × 10 ¹⁹ cm ⁻³ are formed.

Next, although not shown, a dry etching method is performed using a striped SiO ₂ pattern as a mask to form a ridge mesa 26 having a height of 1.5 μm and a width of 3 μm, which coincides with the shape of the non-doped InGaAs layer 15. After that, the SiO ₂ pattern is removed, and then a p-side electrode 27 is formed on the p-type GaAs contact layer 25 and an n-side electrode 28 is provided on the back surface of the n-type GaAs substrate 11 to thereby form a self-forming quantum dot. The basic structure of the semiconductor light emitting device using the is completed.

  In the first embodiment of the present invention, since a density distribution is formed in the InAs quantum dots 21, a sufficient gain is obtained in the peripheral portion where the density of the InAs quantum dots 21 is small in the lateral high-order mode spreading in the peripheral portion. As a result, the oscillation of the transverse higher-order mode is suppressed, and the oscillation of the transverse fundamental mode is obtained in synergy with the transverse mode control effect by the ridge mesa 26.

  As described above, in Example 1 of the present invention, since the transverse mode is controlled by the density distribution of the self-forming quantum dots, it is not necessary to directly process the active layer, and the device characteristics may be deteriorated. Absent.

Next, with reference to FIG. 8, the semiconductor light-emitting device of Example 2 of the present invention will be described. Since the basic manufacturing process is the same as that of Example 1, the description is simplified.
See FIG.
FIG. 8 is a cross-sectional view perpendicular to the optical axis of the semiconductor light emitting device of Example 2 of the present invention. In this case, InAs quantum dots are provided in three layers.

  In the case of forming the quantum dot active layer in this case, after forming the first-stage InAs quantum dots 21 in exactly the same manner as in Example 1, the non-doped GaAs barrier layer 36 having a thickness of, for example, 20 nm and the thickness are formed. For example, a 10 nm non-doped InGaAs layer 37 is formed, this non-doped InGaAs layer 37 is patterned in the same manner as the non-doped InGaAs layer 15, and the removed portion is buried with a non-doped GaAs buried layer 38, and an InAs quantum dot is formed thereon. 39 is formed.

  Then, by repeating this process as many times as necessary, in this case, by repeating the process once more, a three-tiered quantum dot active layer is formed.

In Example 2 , since the quantum dot active layer has a three-tiered structure, the light output can be increased as compared with the quantum dot active layer having a one-stage structure.

  In the description of each of the above embodiments, the semiconductor light emitting device has been described for the sake of simplicity. However, when a semiconductor laser is formed, it is necessary after forming the resonator surface by cleaving. Accordingly, a reflective film may be provided on the cleavage surface, and when a semiconductor optical amplifier is formed, an antireflection film may be formed on the cleavage surface.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the conditions and configurations described in the embodiments, and various modifications are possible. For example, the width described in the embodiments Numerical values such as length, height, thickness, composition ratio and doping concentration are not limited to the numerical values described.

In the description of each of the above embodiments, the manufacturing method in the chip state is described from the beginning. However, the manufacturing method is usually performed in the wafer state, and therefore, when the underlying semiconductor layer is selectively etched. The length of the SiO ₂ pattern used as the mask is not 300 μm, but a length corresponding to the size of the wafer, and a large number of semiconductor light emitting elements are manufactured in a lump.

  In each of the above embodiments, the AlGaAs / GaAs system is described. However, the present invention is also applied to the InGaAsP / InP system. In this case, a quantum dot having a high density according to the manufacturing conditions is used. The formed semiconductor layer may be left in the central portion.

  In each of the above embodiments, the density ratio of the self-forming quantum dots is 8/3 (≈2.67), but the density ratio may be 3/2 (= 1.5) or more. More preferably, it should be 2/1 (= 2) or more.

  In each of the above embodiments, the MOCVD method is used as the crystal growth method. However, the present invention is not limited to the MOCVD method, and the MBE (except for the p-type AlGaAs buried layer growth step in the third embodiment) is used. Molecular beam epitaxial growth method) may be used.

The detailed features of the present invention will be described again with reference to FIG. 1 again.
See FIG. 1 again. (Supplementary note 1) In a semiconductor light emitting device using a self-forming quantum dot 4 as an active layer medium, the semiconductor light-emitting device has a ridge type optical waveguide and is self-formed in a cross section perpendicular to the optical axis in the optical waveguide. A semiconductor light emitting device using self-forming quantum dots, wherein the density of the type quantum dots 4 is greater in the center than in the periphery.
(Additional remark 2) In the cross section perpendicular to the optical axis in the optical waveguide, the base constant of the base semiconductor layer 2 in the central portion is larger than the lattice constant of the base semiconductor layer 3 in the peripheral portion, and the base semiconductor has a large lattice constant. The density of the self-forming quantum dots 4 formed on the layer 2 is higher than the density of the self-forming quantum dots 4 formed on the base semiconductor layer 3 having a small lattice constant. Semiconductor light-emitting device using self-formed quantum dots.
(Supplementary Note 3) The base semiconductor layers 2 and 3, the self-forming quantum dots 4 formed on the base semiconductor layers 2 and 3, and the barrier covering the self-forming quantum dots 4 and the base semiconductor layers 2 and 3 The semiconductor light-emitting device using self-formed quantum dots according to appendix 2, wherein at least two layers of the layered structure of layers 5 are stacked.
(Supplementary note 4) Any one of Supplementary notes 1 to 3, wherein the density of the self-forming quantum dots 4 in the central portion is 1.5 times or more higher than the density of the self-forming quantum dots 4 in the peripheral portion. A semiconductor light emitting device using the self-forming quantum dot according to 1.
(Supplementary Note 5 ) The base semiconductor layer 2 having a large lattice constant is made of InGaAs, the base semiconductor layer 3 having a small lattice constant is made of GaAs, and the self-forming quantum dots 4 are made of InAs. A semiconductor light-emitting device using the self-forming quantum dot according to any one of appendices 2 to 4 .

  Examples of utilization of the present invention include a semiconductor laser or a semiconductor optical amplifier as a light source for optical communication. However, the present invention is not limited to this example, and a semiconductor laser for an optical information processing light source such as a DVD light source. Alternatively, it may be used for transverse mode control or beam diameter control of a light emitting diode.

It is explanatory drawing of the fundamental structure of this invention. It is explanatory drawing of the manufacturing process to the middle of the semiconductor light-emitting device of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 2 of the semiconductor light-emitting device of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 3 of the semiconductor light-emitting device of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 4 of the semiconductor light-emitting device of Example 1 of this invention. It is explanatory drawing of the manufacturing process until the middle of FIG. 5 or subsequent of the semiconductor light-emitting device of Example 1 of this invention. It is explanatory drawing of the manufacturing process after FIG. 6 of the semiconductor light-emitting device of Example 1 of this invention. It is structure explanatory drawing of the semiconductor light-emitting device of Example 2 of this invention .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lower clad layer 2 Underlayer semiconductor layer 3 Underlayer semiconductor layer 4 Self-formation quantum dot 5 Barrier layer 6 Upper clad layer 7 Stripe structure 11 n-type GaAs substrate 12 n-type GaAs buffer layer 13 n-type AlGaAs clad layer 14 Non-doped GaAs layer 15 Non-doped InGaAs layer 16 Resist pattern 17 Striped groove 18 SiO ₂ film 19 SiO ₂ pattern 20 Non-doped GaAs buried layer 21 InAs quantum dot 22 Non-doped GaAs barrier layer 23 p-type AlGaAs cladding layer 24 p-type AlGaAs layer 25 p-type GaAs contact layer 26 Ridge mesa 27 p-side electrode 28 n-side electrode 29 p-type AlGaAs cladding layer
36 Non-doped GaAs barrier layer 37 Non-doped InGaAs layer 38 Non-doped GaAs buried layer 39 InAs quantum dot 40 Non-doped GaAs barrier layer 41 Non-doped InGaAs layer 42 Non-doped GaAs buried layer 43 InAs quantum dot

Claims (4)

In a semiconductor light emitting device using self-forming quantum dots as an active layer medium, it has a ridge-type optical waveguide, and the density of the self-forming quantum dots in the cross section perpendicular to the optical axis in the optical waveguide is centered from the periphery. Semiconductor light-emitting device using self-forming quantum dots characterized by being large in size.   In the cross section perpendicular to the optical axis of the optical waveguide, the lattice constant of the base semiconductor layer in the central portion is larger than the lattice constant of the base semiconductor layer in the peripheral portion and is formed above the base semiconductor layer having a large lattice constant. 2. The self-formed quantum dot according to claim 1, wherein the density of the self-formed quantum dot is higher than the density of the self-formed quantum dot formed on the upper part of the underlying semiconductor layer having a small lattice constant. Semiconductor light emitting device.   At least two or more stacked layers including the base semiconductor layer, the self-forming quantum dots formed on the base semiconductor layer, and the barrier layer covering the self-forming quantum dots and the base semiconductor layer are stacked. A semiconductor light emitting device using the self-forming quantum dot according to claim 2.   4. The density according to claim 1, wherein a density of the self-forming quantum dots in the central portion is 1.5 times or more higher than a density of the self-forming quantum dots in the peripheral portion. 5. A semiconductor light emitting device using self-forming quantum dots.

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