Low-loss dfb laser and method of manufacturing the same

Abstract

The application discloses a low-loss DFB laser, two P-AlGaInAs epitaxial layers are grown on the epitaxial structure of the low-loss DFB laser, and a P-AlGaInAs oxidation confinement layer is formed through chip process oxidation; the width of the ridge strip can be wider by adopting the structure, the ohmic contact resistance of the DFB laser can be reduced, the light field width of the DFB laser can be adjusted by adopting the oxidation confinement layer, meanwhile, the light field mode of the DFB laser can be compressed by utilizing the low refractive index characteristic of the oxidation confinement layer, the proportion of the light field in the P-InP ridge waveguide is reduced, and the light absorption loss is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser manufacturing, and particularly relates to a low-loss DFB laser and a manufacturing method of the laser. BACKGROUND

[0002] A distributed feedback laser (DFB) has a grating modulation with a periodical refractive index, has a good single longitudinal mode characteristic, a line width less than 1MHz, and a side mode suppression ratio up to 50dB or more, and is widely applied in optical fiber communication networks and optical fiber sensors. The DFB laser is divided into a ridge-waveguide confinement structure DFB (Ridge-DFB) and a buried heterostructure confinement DFB (BH-DFB) according to different structures.

[0003] The Ridge-DFB has a simple structure, uses a ridge strip with a width of about 2um to confine the optical field and the electric field of the DFB laser, and only needs to be subjected to twice epitaxial growth, so that the manufacturing process is simple. However, after the current is injected through the ridge strip, the DFB laser is subjected to lateral leakage through the etching stop layer, so that the threshold of the DFB laser is increased and the power is reduced. The BH-DFB laser uses a lateral confinement of a semi-insulating material to reduce the lateral leakage of the current of the DFB laser, so that a DFB laser with a low threshold and high power can be obtained. However, the BH-DFB laser needs to be subjected to four times of epitaxial growth, so that the cost is high and the yield is low. In addition, when the BH structure is used to confine the current of the DFB laser, the optical field of the DFB laser cannot be confined, so that the free carrier absorption loss of the light is large, and especially for a long-cavity long-power DFB laser and a long-wave DFB laser, the application of the performance of the DFB laser is limited.

[0004] In order to overcome the defects of the above laser, it is necessary to improve the existing DFB laser, and design a DFB laser with low ohmic contact resistance and low optical absorption loss. SUMMARY

[0005] In order to overcome the defects of the above laser, it is necessary to improve the existing DFB laser, and design a DFB laser with low ohmic contact resistance and low optical absorption loss.

[0006] The application discloses a low-loss DFB laser, which comprises an InP substrate, a buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well, an upper waveguide layer, an upper confinement layer, a buffer layer and an etching blocking layer are sequentially grown on the InP substrate from bottom to top, a longitudinal ridge strip is arranged on the etching blocking layer, and the ridge strip comprises an oxidation confinement layer, an InP connecting layer, a grating layer, an oxidation confinement layer, a potential barrier gradient layer and an ohmic contact layer.

[0007] Preferably, the N-InP buffer layer, the N-AlGaInAs lower confinement layer, the N-AlGaInAs lower waveguide layer, the AlGaInAs quantum well, the P-AlGaInAs lower waveguide layer, the P-AlGaInAs upper confinement layer, the P-InP buffer layer, and the P-InGaAsP etching stop layer are sequentially grown on the InP substrate, the ridge includes the P-AlGaInAs oxidation confinement layer, the InP bonding layer, the P-InGaAsP grating layer, the P-AlGaInAs oxidation confinement layer, the P-InGaAsP potential barrier overlayer, and the P-InGaAs ohmic contact layer.

[0008] Preferably, the width of the ridge is greater than 3 μm.

[0009] Preferably, the P-AlGaInAs oxidation confinement layer has a thickness ranging from 13 nm to 18 nm, a wavelength ranging from 916 nm to 925 nm, and a doping concentration ranging from 2.5E18 cm -3 -3.5E18 cm -3 .

[0010] Preferably, the oxidation depth of the P-AlGaInAs oxidation confinement layer is L=(W-d) / 2, W is the width of the ridge, and d is the desired aperture width.

[0011] The application also discloses a preparation method of the low-loss DFB laser, which comprises the following steps: 1) sequentially depositing, from bottom to top, the N-InP buffer layer, the N-AlGaInAs lower confinement layer, the N-AlGaInAs lower waveguide layer, the AlGaInAs quantum well, the P-AlGaInAs lower waveguide layer, the P-AlGaInAs upper confinement layer, the P-InP buffer layer, the P-InGaAsP etching stop layer, the P-AlGaInAs epitaxial layer, the InP bonding layer, the P-InGaAsP grating layer, the P-AlGaInAs epitaxial layer, the P-InGaAsP potential barrier overlayer, and the P-InGaAs ohmic contact layer on the InP substrate by using MOCVD to form a laser epitaxial wafer; 2) processing the P-AlGaInAs epitaxial layer, the InP bonding layer, the P-InGaAsP grating layer, the P-AlGaInAs epitaxial layer, the P-InGaAsP potential barrier overlayer, and the P-InGaAs ohmic contact layer on the laser epitaxial wafer by using an etching process to form a longitudinal ridge on the etching stop layer; and 3) performing oxidation treatment on the P-AlGaInAs oxidation confinement layer on the laser epitaxial wafer on which the ridge is formed.

[0012] Preferably, in step 2), the P-AlGaInAs oxidation confinement layer is etched by using a citric acid solution.

[0013] Preferably, in step 3), the oxidation depth of the P-AlGaInAs epitaxial layer on the laser epitaxial wafer is L=(W-d) / 2, W is the width of the ridge, and d is the desired aperture width.

[0014] Preferably, the thickness of the P-AlGaInAs oxidation confinement layer is in the range of 13-18 nm, the wavelength is in the range of 916-925 nm, and the doping concentration is in the range of 2.5E18 cm -3 -3.5E18 cm -3 .

[0015] Preferably, the width of the ridge is >3 μm.

[0016] The technical solution has the following beneficial effects: two P-AlGaInAs epitaxial layers are grown on the epitaxial structure of the low-loss DFB laser, and a P-AlGaInAs oxidation confinement layer is formed by chip process oxidation. This structure can make the width of the ridge wider, can reduce the ohmic contact resistance of the DFB laser, can adjust the light field width of the DFB laser by using the oxidation confinement layer, and can compress the light field mode of the DFB laser by using the low refractive index characteristic of the oxidation confinement layer, reduce the proportion of the light field in the P-InP ridge waveguide, and reduce the optical absorption loss. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Fig. 1 is a structure schematic diagram of an epitaxial wafer of an embodiment of the present application;

[0018] Figure 2 Fig. 2 is a structure schematic diagram of a ridge on an epitaxial wafer of an embodiment of the present application;

[0019] Figure 3 Fig. 3 is a structure schematic diagram of the oxidation depth and width of an oxidation confinement layer of an embodiment of the present application. DETAILED DESCRIPTION

[0020] The following describes the embodiments of the present application by specific specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification.

[0021] Example implementations are now described with reference to the drawings. Example implementations can be implemented in any of various forms, and are not limited to the examples described herein; rather, the example implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the example implementations to those skilled in the art. Features, components, or aspects described in conjunction with one example implementation can be implemented in any other example implementation unless the context clearly dictates otherwise. The examples described herein are not meant to be limiting. Stated optional features can be replaced with any suitable features, and combinations of stated features can be interchanged, unless the context clearly dictates otherwise. The terms "comprising," "including," containing," and "having" are used interchangeably and mean that other components can also be present. The terms "coupled" and "connected," along with derivatives thereof, are used to indicate that there is a direct connection between components, but can also mean that an indirect connection is made between components in the absence of an actual direct connection. The term "directly connected" is understood to mean that components are connected without any intermediary components. The terminology used herein is for the purpose of describing specific implementations only and is not intended to be limiting. Other implementations can be employed.

[0022] As Figure 1 , 2 illustrated, the patent discloses a low-loss DFB laser, comprising an InP substrate 001, sequentially grown on the InP substrate 001 from bottom to top are a buffer layer 002, a lower confinement layer 003, a lower waveguide layer 004, a quantum well 005, an upper waveguide layer 006, an upper confinement layer 007, a buffer layer 008, and an etching stop layer 009, a longitudinal ridge is provided on the etching stop layer 009, and the ridge comprises an oxidation confinement layer 010, an InP connecting layer 011, a grating layer 012, an oxidation confinement layer 013, a potential barrier gradient layer 014, and an ohmic contact layer 015.

[0023] As a preferred embodiment of the patent, the low-loss DFB laser sequentially grown on the InP substrate 001 are an N-InP buffer layer 002, an N-AlGaInAs lower confinement layer 003, an N-AlGaInAs lower waveguide layer 004, an AlGaInAs quantum well 005, a P-AlGaInAs upper waveguide layer 006, a P-AlGaInAs upper confinement layer 007, a P-InP buffer layer 008, a P-InGaAsP etching stop layer 009, and the ridge comprises a P-AlGaInAs oxidation confinement layer 010, an InP connecting layer 011, a P-InGaAsP grating layer 012, a P-AlGaInAs oxidation confinement layer 013, a P-InGaAsP potential barrier gradient layer 014, and a P-InGaAs ohmic contact layer 015. The width of the ridge is generally greater than 3 μm.

[0024] As Figure 3As shown, as another preferred embodiment of the present application, the oxidation depth of the oxide layer 100 in the P-AlGaInAs oxidation confinement layer 010, 013 is L = (W - d) / 2, W is the width of the ridge, and d is the desired aperture width. The thickness of the P-AlGaInAs oxidation confinement layer 010, 013 ranges from 13 to 18 nm, the wavelength ranges from 916 to 925 nm, and the doping concentration ranges from 2.5E18 cm -3 -3.5E18cm -3 .

[0025] The present patent also discloses a manufacturing method of the above low-loss DFB laser, taking a 1653 nm DFB laser as an example, which comprises the following steps:

[0026] First, the N-InP substrate 001 with a conductivity of 2-8 x 10 18 cm -2 is placed into the MOCVD system of Aixtron Company for growth. The reaction chamber pressure is 50 mbar, the growth temperature is 670°C, H 2 is used as the carrier gas, and trimethylindium (TMIn), trimethylgallium (TMGa), trimethylaluminum (TMAl), diethyl zinc (DeZn), silane (SiH 4 ), arsine (AsH 3 ), and phosphine (PH 3 ) are used as the reaction source gas. The N-InP buffer layer 002, N-AlGaInAs lower confinement layer 003, N-AlGaInAs lower waveguide layer 004, AlGaInAs quantum well 005, P-AlGaInAs upper waveguide layer 006, P-AlGaInAs upper confinement layer 007, P-InP buffer layer 008, P-InGaAsP etching stop layer 009, P-AlGaInAs oxidation confinement layer 010, P-InP buffer layer 011-1, and P-InGaAsP grating fabrication layer are sequentially grown according to the material composition shown in Table 1.

[0027] Next, the epitaxial wafer is taken out, and the grating is fabricated on the InGaAsP grating fabrication layer on the semi-finished epitaxial wafer by holographic lithography or electron beam lithography, forming a P-InGaAsP grating layer 12. Then, the P-InP coupling layer 011, P-AlGaInAs oxidation confinement layer 013, P-InGaAsP potential barrier overlayer 014, and P-InGaAs ohmic contact layer 015 are grown by pulse deposition method.

[0028] The specific method for growing the P-InP buffer layer 011-1 by the above pulse deposition method is as follows: after the semi-finished wafer with the processed P-InGaAsP grating layer 12 is cleaned, it is placed into the reaction chamber of the MOCVD system, the pressure in the reaction chamber is controlled to be 50 mbar, H2 is used as the carrier gas, the reaction chamber is supplied with PH3 gas with a flow rate of 900 sccm to protect the semi-finished wafer, the reaction chamber is slowly heated to 550°C, then TMIn source gas with a flow rate of 10 sccm is supplied to the reaction chamber within t1 = 2 seconds to grow the nucleation layer of the P-InP buffer layer 011-1 on the P-InGaAsP grating layer 12, at the same time, DeZn dopant gas with a flow rate of 0.36 sccm is supplied to the reaction chamber through the double dilution pipeline; then the TMIn source gas supplied to the reaction chamber is closed within t2 = 2 seconds, the DeZn dopant gas is also closed at the same time, time is provided for atomic migration in the nucleation layer of the P-InP grating cover layer that has been grown, so that the atoms in the nucleation layer of the P-InP buffer layer 011-1 that has been grown migrate to the lowest energy point, and the nucleation layer of the P-InP buffer layer 011-1 that has been grown is stabilized; then TMIn source gas with a flow rate of 10 sccm is supplied to the reaction chamber within t3 = 15 seconds to continue growing the base layer of the P-InP grating cover layer on the nucleation layer of the P-InP buffer layer 011-1 that has been grown, at the same time, DeZn dopant gas with a flow rate of 0.36 sccm is supplied to the reaction chamber through the double dilution pipeline; then the TMIn source gas and the DeZn dopant gas supplied to the reaction chamber are closed within t4 = 2 seconds, time is provided for atomic migration in the base layer of the P-InP buffer layer 011-1 that is to be grown later, so as to improve the crystal quality of the base layer of the P-InP buffer layer 011-1 and stabilize the base layer of the P-InP buffer layer 011-1; in this way, t1 + t2 + t3 + t3 = t5 = 21 seconds is used as a growth cycle to grow the P-InP buffer layer 011-1, and the growth of the P-InP buffer layer 011-1 is stopped after the total thickness of the P-InP buffer layer 011-1 is greater than the thickness of the P-InGaAsP grating layer 12.

[0029] Then, the pressure in the reaction chamber is kept at 50 mbar, the flow rate of the PH3 gas introduced into the reaction chamber is kept at 900 sccm, the temperature of the reaction chamber is raised to 670°C, H2 is used as the carrier gas, then the TMIn source gas with a flow rate of 720 sccm is introduced into the reaction chamber, the TMIn source gas can be introduced into the reaction chamber through two pipes, while the TMIn source gas is introduced into the reaction chamber, the DeZn dopant gas with a flow rate of 37.5 sccm is also introduced into the reaction chamber through the double dilution pipe, the N-InP coupling layer 011-2 is grown on the P-InP buffer layer 011-1 which has been grown, at this time, the average growth rate of the N-InP coupling layer 011-2 is 0.2 nm / s, and the N-InP coupling layer 11 is grown to a set thickness and then stopped growing.

[0030] Finally, the temperature of the reaction chamber is kept at 670°C, H2 is used as the carrier gas, and the corresponding source gas is introduced, the P-AlGaInAs oxidation confinement layer 013, the P-InGaAsP potential barrier excess layer 014, and the P-InGaAs ohmic contact layer 015 are sequentially grown on the N-InP coupling layer 11 which has been grown. The thickness and material of each layer of the above laser are shown in the following table.

[0031]

[0032] After the epitaxial wafer is grown, an etching process is used to form a laser ridge with a width of W. The difference between the present application and the traditional DFB laser structure is that there are two AlGaInAs oxidation confinement layers 010 and 013. For the 013 oxidation confinement layer, the same ICP dry etching process as the traditional DFB laser process can be used to etch it; for the 010 oxidation confinement layer, the solution for etching the InP ridge in the wet etching process cannot etch the AlGaInAs oxidation confinement layer, and the present application uses citric acid solution to etch the AlGaInAs, forming a structure as shown in Figure 2 The ridge width is 3.2 μm.

[0033] Then, the wafer with the ridge structure is placed in an oxidation furnace, and a similar oxidation process as the VCSEL laser process is used to wet-oxidize the two AlGaInAs oxidation confinement layers 010 and 013 using nitrogen and water vapor as the source gas. The oxidation depth is calculated using the following formula: L=(W-d) / 2. When W=3.2 μm and d=1.6 μm, the oxidation depth is 0.8 μm. W is the width of the ridge, and d is the desired aperture width. Finally, the same processes as the traditional DFB laser, such as coating, etching, scribing, and cleaving, are used to form a low-loss DFB laser.

[0034] The low-loss DFB laser is an edge-emitting laser, two P-AlGaInAs epitaxial layers are grown on the epitaxial structure of the laser, and a P-AlGaInAs oxidation confinement layer is formed by chip process oxidation. The width of the ridge is wider, and the ridge width is greater than 3μm. The wider ridge can reduce the ohmic resistance of the DFB laser. The light field width of the DFB laser can be adjusted by the oxidation confinement layer. Meanwhile, the refractive index of the oxidation confinement layer is relatively low. For example, the refractive index of the AlGaInAs oxidation confinement layer 010 and 013 is about 3.452. After wet oxidation, the refractive index sharply decreases to about 1.7. The refractive index of the epitaxial layer InP is about 3.221. The light field of the MQW active region is compressed under the low-refractive oxidation confinement layer in the longitudinal direction. The proportion of the light field in the P-InP ridge waveguide is sharply reduced, and the optical absorption loss can be effectively reduced.

[0035] The above embodiments only illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea of the present application should be covered by the claims of the present application.

Claims

1. A low-loss DFB laser, comprising an InP substrate (001), sequentially grown on the InP substrate (001) from bottom to top are an N-InP buffer layer (002), an N-AlGaInAs lower confinement layer (003), an N-AlGaInAs lower waveguide layer (004), an AlGaInAs quantum well (005), a P-AlGaInAs upper waveguide layer (006), a P-AlGaInAs upper confinement layer (007), a P-InP buffer layer (008), and a P-InGaAsP etching stop layer (009), characterized in that: The corrosion stop layer (009) is provided with a longitudinal ridge, the ridge includes a P-AlGaInAs oxidation limiting layer (010), an InP connecting layer (011), a P-InGaAsP grating layer (012), a P-AlGaInAs oxidation limiting layer (013), a P-InGaAsP potential barrier excess layer (014), a P-InGaAs ohmic contact layer (015), the thickness of the P-AlGaInAs oxidation limiting layer (010, 013) ranges from 13-18nm, the wavelength ranges from 916-925nm, and the doping concentration ranges from 2.5E18cm -3 -3.5E18cm -3 -3.5E18cm The P-AlGaInAs oxidation limiting layer (013) can be etched by using ICP dry etching process, the P-AlGaInAs oxidation limiting layer (010) is etched by using citric acid solution, and the width of the ridge is greater than 3µm. The oxidation depth of the P-AlGaInAs oxidation confinement layer (010, 013) is L=(W-d) / 2, W is the width of the ridge, and d is the desired aperture width.

2. A method of manufacturing a low-loss DFB laser, characterized by, It comprises the following steps: Step 1), on an InP substrate (001), N-InP buffer layer (002), N-AlGaInAs lower confinement layer (003), N-AlGaInAs lower waveguide layer (004), AlGaInAs quantum well (005), P-AlGaInAs upper waveguide layer (006), P-AlGaInAs upper confinement layer (007), P-InP buffer layer (008), P-InGaAsP etching stop layer (009), P-AlGaInAs epitaxial layer, InP bonding layer (011), P-InGaAsP grating layer (012), P-AlGaInAs epitaxial layer, P-InGaAsP barrier overlayer (014), P-InGaAs ohmic contact layer (015) are sequentially deposited from bottom to top by MOCVD to form a laser epitaxial wafer; Step 2), using etching process to process P-AlGaInAs oxidation confinement layer (010), InP bonding layer (011), P-InGaAsP grating layer (012), P-AlGaInAs oxidation confinement layer (013), P-InGaAsP barrier overlayer (014), P-InGaAs ohmic contact layer (015) on the laser epitaxial wafer, to form a longitudinal ridge in the etching stop layer (009), P-AlGaInAs oxidation confinement layer (013) can be etched by ICP dry etching process, and P-AlGaInAs oxidation confinement layer (010) is etched by citric acid solution; Step 3), the P-AlGaInAs epitaxial layer on the ridge-forming laser epitaxial wafer is subjected to oxidation treatment to form a P-AlGaInAs oxidation confinement layer (010, 013), the P-AlGaInAs oxidation confinement layer (010, 013) has a thickness range of 13-18 nm, a wavelength range of 916-925 nm, and a doping concentration range of 2.5E18 cm -3 -3.5E18 cm -3 , and the width of the ridge is >3 µm; In step 3), when the P-AlGaInAs epitaxial layer on the laser epitaxial wafer is subjected to oxidation treatment, the oxidation depth is L=(W-d) / 2, W is the width of the ridge, and d is the desired aperture width.

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