KR100766069B1 - Quantum Dot Laser Diode And The Manufacturing Method Thereof - Google Patents

Abstract

The present invention relates to a distributed feedback quantum dot laser diode and a method of manufacturing the same, comprising the steps of: forming a grating structure layer including a plurality of gratings on a substrate; Forming a first lattice matching layer on the grating structure layer; Forming at least one quantum dot layer having at least one quantum dot on the first lattice matching layer; Forming a second lattice matching layer on the quantum dot layer; Forming a cladding layer on the second lattice matching layer; And forming an ohmic contact layer on the clad layer. Accordingly, a high gain can be obtained at a desired wavelength without being affected by the uniformity of the quantum dots, thereby improving the characteristics of the laser diode.

Grating, quantum dot, laser diode

Description

Quantum dot laser diode and the manufacturing method thereof

1A to 1F are manufacturing process diagrams for explaining a manufacturing step of a quantum dot laser diode according to an exemplary embodiment of the present invention.

FIG. 2A is a cross-sectional view of a quantum dot laser diode according to an embodiment of the present invention taken by a scanning electron microscope (SEM).

2B is an image taken with an optical microscope of the surface of the quantum dot laser diode according to an embodiment of the present invention.

3 is a graph showing the emission spectrum of the quantum dot laser diode including the grating structure layer and the emission spectrum of the quantum dot laser diode without the grating structure layer according to the present invention.

Figure 4a is a graph showing the light output according to the current injection measured by the quantum dot laser diode manufactured in accordance with the present invention at room temperature continuous oscillation conditions.

4B is a graph showing a spectrum obtained by injecting a predetermined current into a quantum dot laser diode manufactured according to the present invention.

<Description of Signs of Major Parts of Drawings>

100: laser diode 110: substrate

120: grating structure layer 130: grating

140: first lattice matching layer 141: second lattice matching layer

150: In (Ga) As quantum dot layer 160: cladding layer

170: ohmic contact layer

The present invention relates to a distributed feedback quantum dot laser diode and a method of manufacturing the same, and more particularly, to a quantum dot laser diode having a grating structure formed below the quantum dot and a method of manufacturing the same.

Recently, quantum dot laser diodes using the quantum dots grown through the spontaneous formation method for active layers have been developed. Specifically, such quantum dot laser diodes have a broad-area shape, a ridge waveguide shape, and a buried hetero. Structural (Buried hetero-structure) form, and a pattern having a grating structure by externally patterning the metal grating has been developed.

However, according to a recent research trend of growing In (Ga) As quantum dots on a InP substrate through a spontaneous formation method, it is possible to form relatively uniform quantum dots compared to the In (Ga) As quantum dot structure formed on a GaAs substrate. The disadvantage is that it is not easy. In addition, when a quantum dot having somewhat less uniformity is applied to a laser diode, there is a limit in obtaining good device characteristics because the gain obtained at a desired oscillation wavelength is reduced. Accordingly, when fabricating a laser diode using In (Ga) As quantum dots as an active layer on an InP substrate, a method for improving device characteristics is to improve quantum dot uniformity in a desired wavelength region or to improve characteristics of a specific wavelength. The method is being studied.

The present invention has been devised to solve the above problems, and an object of the present invention is to form a grating structure on a substrate, whereby a high gain can be obtained in a desired wavelength region without being affected by the uniformity of quantum dots. The present invention provides a quantum dot laser diode and a method of manufacturing the same.

According to an aspect of the present invention, to achieve the above object, the present method of manufacturing a quantum dot laser diode comprises the steps of: forming a grating structure layer comprising a plurality of gratings on a substrate; Forming a first lattice matching layer on the grating structure layer; Forming at least one quantum dot layer having at least one quantum dot on the first lattice matching layer; Forming a second lattice matching layer on the quantum dot layer; Forming a cladding layer on the second lattice matching layer; And forming an ohmic contact layer on the clad layer.

In the forming of the quantum dots, one of an organic metal chemical vapor deposition method, a molecular beam vapor deposition method, and a chemical ray vapor deposition method is used. The quantum dot is formed using In (Ga) As. In the forming of the first and second lattice matching layers, the first and second lattice matching layers are formed using a group III-V compound.

In the forming of the first and second lattice matching layers, the first and second lattice matching layers are formed in a separate confinement hetero (SCH) structure having a wave guide having a spin index (SPIN) shape. In the case of forming the first and second lattice matching layers with the SPIN-type SCH structure, a quantum well is inserted into the SPIN SCH structure so as to surround the quantum dots symmetrically or asymmetrically.

In the forming of the first and second lattice matching layers, the first and second lattice matching layers are formed in a SCH (Separate confinement hetero) structure having a wave guide having a graded index (GRIN). In the case of forming the first and second lattice matching layers with the GRIN-type SCH structure, the quantum well is inserted into the GRIN SCH structure to form the quantum dot to symmetrically or asymmetrically surround the quantum dot.

According to another aspect of the invention, the present quantum dot laser diode includes a grating structure layer comprising a plurality of gratings formed on a substrate; A first lattice matching layer formed on the grating structure layer; At least one quantum dot layer including at least one quantum dot formed on the first lattice matching layer; A second lattice matching layer formed on the quantum dot layer; A cladding layer formed on the second lattice matching layer; And an ohmic contact layer formed on the clad layer.

Preferably, the substrate is an InP substrate or a GaAs substrate. The quantum dot is made of In (Ga) As. The first and second lattice matching layers are made of a group III-V compound. The first and second lattice matching layers have a separate confinement hetero (SCH) structure having wave guides having a spin index (SPIN) shape or a graded index (GRIN) shape.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1A to 1F are manufacturing process diagrams for explaining a manufacturing step of a quantum dot laser diode according to an exemplary embodiment of the present invention.

1A to 1F, in order to manufacture the quantum dot laser diode 100, first, a substrate 110 is prepared, and a grating structure layer 120 including a plurality of gratings 130 is prepared on the prepared substrate 110. ) Is formed (see FIG. 1A). In general, the grating 130 may be used for injection of light and induced emission of light. In the present embodiment, the layer including the grating 130 was referred to as the grating structure layer 120, but the grating structure layer 120 The silver may play a role similar to the cladding layer formed to confine the light. The substrate 110 constituting the quantum dot laser diode 100 uses an InP substrate or a GaAs substrate.

Referring to FIG. 1B, a first lattice matching layer 140 is formed on the grating structure layer 120. The first lattice matching layer 140 is a layer for growing In (Ga) As quantum dots on the InP substrate 110 on which the grating structure layer 120 is formed by using a spontaneous forming method. InAlGaAs, In (Ga, As) P Can be formed by lattice-matched. The first lattice matching layer 140 may include a material layer made of a group III-V compound (eg, Group 3 (In, Al, Ga, etc.), Group 5 (As, P, etc.)) or a Group III-V compound. It serves as a barrier layer with a heterojunction structure formed by stacking two or more layers. In addition, the first lattice matching layer 140 may be formed of a SCH structure with a wave guide in the form of a spin index (SPIN), or a SCH (Separate confinement hetero) with a wave guide in the form of a graded index (GRIN). It can be formed into a structure.

Referring to FIG. 1C, a quantum dot layer 150 made of In (Ga) As quantum dots is formed on the first lattice matching layer 140. The quantum dot layer 150 is composed of In (Ga) As quantum dots in which In (Ga) As is grown using a spontaneous formation mechanism, and the quantum dots are organometallic chemical vapor deposition (MOCVD), molecular beam deposition (MBE), and atomic beam deposition. It can be grown by using one of (ALE) and actinic vapor deposition (CBE). In the present embodiment, the quantum dots constituting the quantum dot layer are not spaced apart, but the quantum dot structure may be formed at a predetermined distance.

Although not disclosed in the present embodiment and the drawings, when the first lattice matching layer 140 is formed in a SCH structure having a SPIN shape, a quantum dot formed by inserting a quantum well into the SPIN SCH is formed. WELL, DWELL) can be symmetrically surrounded, or a quantum well can be inserted asymmetrically by inserting a quantum well in the SPIN SCH structure. Of course, even when the first lattice matching layer 140 is formed in a GRIN type SCH structure, the first lattice matching layer 140 inserts a quantum well shape into the GRIN type SCH to symmetrically surround the quantum dots or to form a GRIN type SCH A quantum well may be inserted into the structure to asymmetrically surround the quantum dot. Although one quantum dot layer is formed in this embodiment, a plurality of quantum dot layers having a plurality of quantum dots may be stacked.

Referring to FIG. 1D, after forming a quantum dot layer 150 including a plurality of quantum dots, a second lattice matching layer 141 is formed on the quantum dot layer 150. The second lattice matching layer 141 may be the same layer in structure and role as the first lattice matching layer 140, and the second lattice matching layer 141 may also be formed as a barrier layer or an SCH structure.

Referring to FIG. 1E, after the second lattice matching layer 141 is formed on the quantum dot layer 150 of the quantum dot structure, the clad layer 160 may serve to constrain the light emitted from the quantum dot layer 150. ) Is formed. The cladding layer 160 may be formed using InAl (Ga) As or In (Ga, As) P.

Referring to FIG. 1F, an ohmic contact layer 170 is formed on the cladding layer 160. The ohmic contact layer 170 is a layer for controlling ohmic contact, and is formed using InGaAs in this embodiment.

FIG. 2A is an image taken by a scanning electron microscope (SEM) of a cross section of a quantum dot laser diode according to an embodiment of the present invention, and FIG. 2B is an image taken by an optical microscope on a surface of a quantum dot laser diode according to an embodiment of the present invention. to be.

Referring to FIG. 2A, the quantum dot laser diode according to the present invention includes a grating structure layer 120 including grating 130 and a quantum dot layer including In (Ga) As quantum dots formed on the grating structure layer 120 ( 150) is included. FIG. 2B shows a ridge waveguide form after growing a distributed feedback laser diode using an In (Ga) As quantum dot structure formed on a grating structure layer and a quantum dot layer 150 and an InAlGaAs-InAlAs material system. The quantum dot laser diode produced by A) is shown.

3 is an emission spectrum graph of the quantum dot laser diode including the grating structure layer and the emission spectrum graph (ii) of the quantum dot laser diode without the grating structure layer according to the present invention. Emission spectrum experiments were conducted at room temperature (RT), and all other conditions (eg, quantum dot layer growth conditions) were the same except with or without grating (ii).

Referring to FIG. 3, the horizontal axis represents wavelength (μm) and the vertical axis represents intensity (arb. Units). The graph (i) is a light emission spectrum graph of a quantum dot laser diode including a grating structure layer, and seven quantum dot layers stacked on the grating structure layer, and the graph (ii) does not include the grating structure layer, and seven quantum dot layers It is a light emission spectrograph of this laminated quantum dot laser diode. From the graphs (i) and (ii), it can be seen that a quantum dot laser diode including grating at a wavelength of about 1.55 [mu] m or more can obtain a high gain in a desired wavelength range compared to a quantum dot laser diode without grating. Although the above experiment makes the number of quantum dots seven, it is not limited thereto. .

Figure 4a is a graph showing the light output according to the current injection in the quantum dot laser diode manufactured in accordance with the present invention at room temperature continuous wave (cw: continous wave) conditions, Figure 4b is a predetermined It is a graph showing the spectrum obtained by the injection of current.

First, referring to FIG. 4A, FIG. 4A is a graph illustrating a change in light output according to a current injected into a quantum dot laser diode according to the present invention at room temperature continuous oscillation conditions, and the horizontal axis represents the injected current I: The vertical axis represents the power output. 4A illustrates the results of experiments using a quantum dot laser diode of a ridge wave guide type including a quantum dot layer having In (Ga) As quantum dots manufactured according to the present invention. The ridge wave guide used in this experiment had a ridge width of 3 μm, was cut to have a cavity length of 1 mm, and then experimented at room temperature continuous oscillation conditions. According to the experimental results, the light output does not change until the current applied to the quantum dot laser diode reaches a predetermined value. However, when the current exceeds about 40 mA, the applied current and the light output show a proportional relationship. As a result, it can be seen that the light output in the quantum dot laser diode according to the present invention is proportional to the applied current, and is stable and uniform.

Referring to FIG. 4B, FIG. 4B is a spectrum of a quantum dot laser diode according to the present invention measured under the same condition as that of FIG. 4A. In FIG. 4B, the horizontal axis represents wavelength, and the vertical axis represents intensity. From the spectrum of Figure 4b it can be seen that a fairly high gain can be obtained at the desired oscillation wavelength. In the present embodiment, the intensity of the wavelength of about 1.564 μm is much higher than that of other wavelengths, and the intensity of about −15 dB is shown. This is approximately 42 kHz higher than at other wavelengths. As a result, when using the quantum dot laser diode according to the present invention, a relatively high gain can be obtained at a desired wavelength, thereby improving device characteristics.

Although the present invention has been described with reference to the embodiments illustrated in the accompanying drawings, it is merely an example, and those skilled in the art may understand that various modifications and equivalent other embodiments are possible. There will be.

According to the foregoing, by forming a grating structure under the quantum dot, that is, by adopting a grating (structure) as a variable affecting the quantum dot active layer, the quantum dot laser having a good gain at the desired oscillation wavelength without being affected by the quantum dot uniformity A diode can be provided.

Claims (13)

Forming a grating structure layer including a plurality of gratings on the substrate; Forming a first lattice matching layer on the grating structure layer; Forming at least one quantum dot layer having at least one quantum dot on the first lattice matching layer; Forming a second lattice matching layer on the quantum dot layer; Forming a cladding layer on the second lattice matching layer; And Forming an ohmic contact layer on the clad layer Quantum dot laser diode manufacturing method comprising a. The method of claim 1, In the forming of the quantum dot, A method of fabricating a quantum dot laser diode using one of an organometallic chemical vapor deposition method, a molecular beam deposition method, and a chemical ray deposition method. The method of claim 2, The quantum dot is formed using In (Ga) As quantum dot laser diode manufacturing method. The method of claim 1, In the forming of the first and second lattice matching layer, the method of manufacturing a quantum dot laser diode to form the first and second lattice matching layer using a group III-V compound. The method of claim 1, In the forming of the first and second lattice matching layers, a quantum dot laser diode is formed by forming the first and second lattice matching layers into a separate confinement hetero (SCH) structure having a wave guide having a spin index (SPIN) shape. Way. The method of claim 5, In the case of forming the first and second lattice matching layers with the SPIN-type SCH structure, a quantum dot laser diode is formed so as to symmetrically or asymmetrically surround the quantum dots by inserting a quantum well into the SPIN SCH structure. Way. The method of claim 1, In the forming of the first and second lattice matching layers, the quantum dot laser diode forming the first and second lattice matching layers in a SCH (Separate confinement hetero) structure having a wave guide having a graded index (GRIN) shape. Manufacturing method. The method of claim 7, wherein In the case of forming the first and second lattice matching layers with the GRIN-type SCH structure, a quantum dot laser diode is formed so as to symmetrically or asymmetrically surround the quantum dots by inserting a quantum well into the GRIN SCH structure. Way. A grating structure layer including a plurality of gratings formed on the substrate; A first lattice matching layer formed on the grating structure layer; At least one quantum dot layer including at least one quantum dot formed on the first lattice matching layer; A second lattice matching layer formed on the quantum dot layer; A cladding layer formed on the second lattice matching layer; And Ohmic contact layer formed on the clad layer Quantum dot laser diode comprising a. The method of claim 9, The substrate is a quantum dot laser diode of InP substrate or GaAs substrate. The method of claim 9 The quantum dot is a quantum dot laser diode made of In (Ga) As. The method of claim 9, The first and second grating matching layer is a quantum dot laser diode made of a group III-V compound. The method of claim 9, The first and second grating matching layers are SCH (Separate confinement hetero) structures having wave guides having a spin index (SPIN) shape or graded index (GRIN) shape.

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