CN110048305B - Graphene-dielectric DBR single-mode vertical cavity surface emitting laser and preparation method thereof - Google Patents

Abstract

A graphene-dielectric DBR single-mode vertical cavity surface emitting laser and a preparation method thereof relate to the field of semiconductor lasers and graphene. The structure is obtained in a multi-chip integration mode, the half-VCSEL, the graphene and the upper DBR are respectively prepared, the graphene is transferred on the half-VCSEL after the half-VCSEL is prepared, and finally the upper DBR part with curvature is obtained to form the complete VCSEL structure. Confining the transverse optical field to the top increases the high order mode loss and threshold gain, resulting in high quality single mode while reducing the contact resistance of the device.

Description

Graphene-dielectric DBR single-mode vertical cavity surface emitting laser and preparation method thereof

Technical Field

The invention relates to the field of semiconductor lasers and graphene, in particular to a graphene-dielectric DBR single-mode vertical cavity surface emitting laser and a preparation method thereof.

Background

The development prospect of a vertical-cavity surface-emitting laser (VCSEL) in the field of functional integrated optics is particularly wide. A high-speed VCSEL having a single transverse mode is very important because it can be efficiently coupled with an optical fiber and prevent pulse broadening of a long transmission distance due to dispersion in the optical fiber, and the VCSEL generally needs to reduce a cavity sectional area to reduce a supported transverse mode, thereby realizing the single transverse mode. However, this reduces its effective volume, thereby limiting the output power of the fundamental mode.

The higher-order modes in the VCSEL can be controlled using techniques such as an antiresonance mode, a surface relief mode, a tunnel junction mode, and a photonic crystal mode, but these mode control techniques cause a problem of a high threshold current in addition to complicated process conditions and expensive techniques.

Therefore, high-power fundamental mode emission in the VCSEL has been a challenge, and an effective measure is needed to solve the deficiencies of the prior art.

Disclosure of Invention

The invention aims to provide a graphene-dielectric DBR single-mode vertical cavity surface emitting laser and a preparation method thereof. The device structure limits a transverse optical field to the top by using the dielectric DBR with a certain curvature, increases high-order mode loss and threshold gain, thereby generating a high-quality single mode, and simultaneously reduces the contact resistance of the device.

The structure of the graphene-dielectric DBR single-mode vertical cavity surface emitting laser is shown in figure 1; the structure mainly comprises a laser back electrode (1), a GaAs substrate (2), a lower DBR (3) and an active region (4) from bottom to top in sequence, wherein an oxidation limiting layer (6) array is arranged on the active region (4), and each oxidation limiting layer (6) unitThe upper layer of the P + + doped GaAs layer (5); a layer of SiO is encapsulated in the epitaxial structure of the product₂The upper end face and the side face of a passivation layer (7), namely an array comprising an oxidation limiting layer (6) and a P + + doped GaAs layer (5) and an active region (4) between the arrays are encapsulated with SiO₂A passivation layer (7) of SiO₂A passivation layer (7) is used for etching a hole A in the middle of the upper end face of the P + + doped GaAs layer (5) corresponding to each unit, namely the hole A corresponds to a light outlet of the laser, so that the P + + doped GaAs layer (5) is exposed; SiO of each cell in the array₂A VCSEL electrode (8) is arranged on the outer side of the periphery of the passivation layer (7), and the VCSEL electrode (8) is further connected with the P + + doped GaAs layer (5) through the inner side surface of the hole A, so that a half-VCSEL is formed; graphene layers (9) are arranged on the outer sides of the periphery of the VCSEL electrode (8) and the P + + doped GaAs layer (5) corresponding to the hole A, and the whole graphene layer (9) is of a complete encapsulation structure; be equipped with on top surface graphite alkene layer (9) of every unit in the array and go up DBR (10), go up DBR (10) whole arc layer spherical structure for having camber, spherical structure is upwards protruding, and spherical structure covers hole A simultaneously. The thicknesses of all points of the spherical surface of the arc layer are preferably consistent.

In the structure, the graphene layer part is transferred to a half-VCSEL (vertical cavity surface emitting laser) by coating PMMA (polymethyl methacrylate);

the upper DBR part in the structure of the invention is formed by alternately growing films on a glass substrate by utilizing a Metal Organic Chemical Vapor Deposition (MOCVD) or a vacuum electron beam evaporation coating machine.

The VCSEL electrode (8) is Ti/Au.

The structure is obtained in a multi-chip integration mode, the half-VCSEL, the graphene and the upper DBR are respectively prepared, the graphene is transferred on the half-VCSEL after the half-VCSEL is prepared, and finally the upper DBR part with curvature is obtained to form the complete VCSEL structure.

The invention also provides a preparation method of the graphene-dielectric DBR single-mode vertical cavity surface emitting laser, which comprises the following steps:

(1) firstly, alternately growing n-Al on an n-type GaAs substrate by Metal Organic Chemical Vapor Deposition (MOCVD)_0.12Ga_0.88As layer and n-Al_0.9Ga_0.1An As layer constituting a lower DBR; then growing GaAs/Al_0.3Ga_0.7The As quantum well structure forms an active region; then regrowing heavily doped p-type AlGaAs or Al_0.98Ga_0.02As forms a P + + doped GaAs layer (5) which is convenient for forming good ohmic contact with the injection electrode;

(2) finally, forming an oxidation limiting layer (6) at the bottom of the heavily doped p-type AlGaAs layer by an oxidation process, photoetching a laser graph on the epitaxial wafer grown in the step (1), corroding the photoetched epitaxial wafer into a mesa structure by using selective corrosion liquid, and corroding the epitaxial wafer to the depth of exposing Al_0.98Ga_0.02As oxidizes the side wall of the limiting layer; performing transverse oxidation on the obtained epitaxial wafer by a wet nitrogen oxidation method by using a high-temperature oxidation furnace to form an oxidation limiting layer, and manufacturing an injection current limiting hole;

(3) deposition of SiO using Plasma Enhanced Chemical Vapor Deposition (PECVD)₂Passivating layer, and photoetching and corroding to form laser light-emitting hole;

(4) sputtering Ti/Au to form a laser array injection electrode, and stripping photoresist to form a laser light outlet; completing the half-VCSEL;

(5) transferring a layer of graphene on the prepared formed half-VCSEL region;

(6) alternately growing Si on the other surface of the graphene by using Metal Organic Chemical Vapor Deposition (MOCVD) or vacuum electron beam evaporation coating machine₃N₄/SiO₂A thin film constituting an upper DBR of the laser;

(7) grinding the substrate to be thin, sputtering AuGeNi/Au to form a laser array back electrode, and annealing to form good ohmic contact between the metal layer and the semiconductor material;

(8) etching the upper DBR to expose the electrode, and growing the upper DBR at 350 deg.C and N₂And annealing for 30 seconds under gas to obtain the complete bent DBR VCSEL device.

Drawings

FIG. 1: the overall structure schematic diagram of the graphene-dielectric DBR single-mode vertical cavity surface emitting laser is shown;

FIG. 2: a schematic structural diagram of a graphene-dielectric DBR single-mode vertical cavity surface emitting laser epitaxial wafer;

FIG. 3: a table-board schematic diagram etched by the graphene-medium DBR single-mode vertical cavity surface emitting laser;

FIG. 4: forming an injection current limiting hole schematic diagram after the device oxidation limiting layer is transversely oxidized;

FIG. 5: device growth SiO₂A post-passivation structure schematic diagram;

FIG. 6: device etching SiO₂A post-passivation structure schematic diagram;

FIG. 7: sputtering Ti/Au to form a schematic diagram of an injection electrode of the laser;

FIG. 8: stripping the injection electrode schematic diagram of the Ti/Au laser;

FIG. 9: thinning the substrate to prepare a laser array back electrode schematic diagram;

FIG. 10: transferring a graphene schematic on a half-VCSEL;

FIG. 11: alternately growing films on the other side of the graphene to form an upper DBR schematic diagram;

FIG. 12: a schematic structure diagram of the annealed graphene-dielectric DBR single-mode vertical cavity surface emitting laser;

FIG. 13: and (3) transferring the graphene to a Half-VCSEL structure, and then carrying out planar scanning electron microscope image.

FIG. 14: an optical microscope image of a graphene-dielectric DBR single mode vertical cavity surface emitting laser.

FIG. 15: scanning electron microscope images of graphene-dielectric DBR single-mode vertical cavity surface emitting lasers.

FIG. 16: a single mode spectrogram of a graphene-dielectric DBR single mode vertical cavity surface emitting laser.

In fig. 1: 1. laser back electrode, 2 GaAs substrate, 3 lower DBR, 4 active region, 5P + + doped GaAs layer, 6 oxidation limiting layer, 7 SiO₂Passivation layer, 8.VCSEL electrode, 9. graphene layer, 10. upper DBR.

Detailed Description

The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the following examples.

Example 1

The preparation method, the object diagram and the spectrogram of the graphene-dielectric DBR single-mode vertical cavity surface emitting laser are described in detail below with reference to FIGS. 2-16:

step 1, adopting Metal Organic Chemical Vapor Deposition (MOCVD) to alternately grow n-Al on an n-type GaAs substrate_0.12Ga_0.88As layer and n-Al_0.9Ga_0.130 pairs of As layers form a lower DBR; then growing GaAs/Al_0.3Ga_0.7The As quantum well structure forms an active region; then growing Al_0.98Ga_0.02Forming an oxidation limiting layer on the As layer; finally, growing heavily doped p-type AlGaAs, which is convenient for forming good ohmic contact with the injection electrode;

step 2, photoetching a laser array pattern on the epitaxial wafer grown in the step 1, and corroding the photoetched epitaxial wafer into a mesa structure by using selective corrosion liquid until Al is exposed_0.98Ga_0.02As oxidizes the side wall of the limiting layer;

step 3, performing transverse oxidation on the epitaxial wafer in the step 2 by using a high-temperature oxidation furnace through a wet nitrogen oxidation method to form an oxidation limiting layer, and manufacturing an injection current limiting hole;

step 4, depositing SiO with thickness of 300nm by using Plasma Enhanced Chemical Vapor Deposition (PECVD)₂Passivating layer, and photoetching and corroding to form laser light-emitting hole;

step 5, sputtering Ti/Au to form a laser array injection electrode, and stripping photoresist to form a light outlet;

step 6, grinding the substrate to 200 mu m, sputtering AuGeNi/Au to form a laser array back electrode, annealing to enable the metal layer and the semiconductor material to form good ohmic contact, and finishing the manufacture of a laser half-VCSEL region;

7, transferring a layer of graphene on the prepared formed half-VCSEL region;

step 8, utilizing Metal Organic Chemical Vapor Deposition (MOCVD) or vacuum electron beam evaporation coating machine to alternately grow Si on the top graphene₃N₄/SiO₂Total 7 pairs of, Si₃N₄/SiO₂The lower surface of the film covers the light-emitting hole of the laser to form a flat upper DBR of the laser;

step 10, etching the upper DBR to expose the contact electrode, and performing N at 350 deg.C₂And annealing for 30 seconds under the atmosphere, and finishing the preparation of the complete device.

Figure 13 is a planar scanning electron micrograph of graphene after transfer onto a Half-VCSEL structure.

Fig. 14, 15 are optical microscope images and scanning electron microscope images of a graphene-dielectric DBR single mode vertical cavity surface emitting laser, which was mechanically surface scanned, showing a curvature of about 4.5 m.

Fig. 16 shows that the single-mode light output of the graphene-dielectric DBR single-mode vertical cavity surface emitting laser has a center wavelength of about 858.5 nm.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent structures or equivalent flow transformations made by using the contents of the specification and the drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims (5)

1. The graphene-dielectric DBR single-mode vertical cavity surface emitting laser is characterized by mainly comprising a laser back electrode (1), a GaAs substrate (2), a lower DBR (3) and an active region (4) from bottom to top, wherein an array of oxidation limiting layers (6) is arranged on the active region (4), and the upper layer of each oxidation limiting layer (6) unit is a P + + doped GaAs layer (5); a layer of SiO is encapsulated in the epitaxial structure of the product₂The upper end face and the side face of a passivation layer (7), namely an array comprising an oxidation limiting layer (6) and a P + + doped GaAs layer (5) and an active region (4) between the arrays are encapsulated with SiO₂A passivation layer (7) of SiO₂A passivation layer (7) is used for etching a hole A in the middle of the upper end face of the P + + doped GaAs layer (5) corresponding to each unit, namely the hole A corresponds to a light outlet of the laser, so that the P + + doped GaAs layer (5) is exposed; SiO of each cell in the array₂A VCSEL electrode (8) is arranged on the outer side of the periphery of the passivation layer (7), and the VCSEL electrode (8) is further connected with the P + + doped GaAs layer (5) through the inner side surface of the hole A, so that a half-VCSEL is formed; graphene layers (9) are arranged on the outer sides of the periphery of the VCSEL electrode (8) and the P + + doped GaAs layer (5) corresponding to the hole A, and the whole graphene layer (9) is of a complete encapsulation structure; the top surface of each unit in the array is provided with a graphene layer (9)The upper DBR (10) and the upper DBR (10) are integrally of arc-layer spherical structures with curvature, the spherical structures are upwards convex, and meanwhile the spherical structures cover the hole A.

2. The graphene-dielectric DBR single mode vertical cavity surface emitting laser according to claim 1, wherein the graphene layer sections are transferred to the half-VCSEL by PMMA coating.

3. The graphene-dielectric DBR single mode vertical cavity surface emitting laser of claim 1 wherein the upper DBR portion is structurally formed of thin films alternately grown on a glass substrate using a metal organic chemical vapor deposition or vacuum electron beam evaporation coater.

4. The graphene-dielectric DBR single-mode vertical-cavity surface-emitting laser according to claim 1, characterized in that the VCSEL electrodes (8) are Ti/Au.

5. The method of fabricating a graphene-dielectric DBR single mode vertical cavity surface emitting laser of claim 1, comprising the steps of:

(1) firstly, alternately growing n-Al on an n-type GaAs substrate by adopting metal organic chemical vapor deposition_0.12Ga_0.88As layer and n-Al_0.9Ga_0.1An As layer constituting a lower DBR; then growing GaAs/Al_0.3Ga_0.7The As quantum well structure forms an active region; then regrowing heavily doped p-type AlGaAs or Al_0.98Ga_0.02As forms a P + + doped GaAs layer (5) which is convenient for forming good ohmic contact with the injection electrode;

(2) finally, forming an oxidation limiting layer (6) at the bottom of the heavily doped p-type AlGaAs layer by an oxidation process, photoetching a laser graph on the epitaxial wafer grown in the step (1), corroding the photoetched epitaxial wafer into a mesa structure by using selective corrosion liquid, and corroding the epitaxial wafer to the depth of exposing Al_0.98Ga_0.02As oxidizes the side wall of the limiting layer; performing transverse oxidation on the epitaxial wafer obtained by wet nitrogen oxidation in a high-temperature oxidation furnace to form an oxidation limiting layer, and making injection current limitationAn aperture;

(3) deposition of SiO using plasma enhanced chemical vapor deposition₂Passivating layer, and photoetching and corroding to form laser light-emitting hole;

(4) sputtering Ti/Au to form a laser array injection electrode, and stripping photoresist to form a laser light outlet; completing the half-VCSEL;

(5) transferring a layer of graphene with the thickness of 3.6nm on the prepared formed half-VCSEL region;

(6) alternately growing Si on the other surface of the graphene by utilizing metal organic chemical vapor deposition or vacuum electron beam evaporation coating machine₃N₄/SiO₂A thin film constituting an upper DBR of the laser;

(7) grinding the substrate to be thin, sputtering AuGeNi/Au to form a laser array back electrode, and annealing to form good ohmic contact between the metal layer and the semiconductor material;

(8) etching and growing the upper DBR to expose the electrode, and growing the upper DBR at 350 degree N₂Annealing was performed under gas for 30 seconds to complete the fabrication of the fully bent DBRVCSEL device.

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