CN101179177A - Structure and Fabrication Method of Long Wavelength Vertical Cavity Surface Emitting Laser - Google Patents

Abstract

A structure of a long-wavelength vertical cavity surface-emitting laser, comprising: an N-type GaAs substrate; a plurality of periods of lower Bragg reflectors, the plurality of periods of lower Bragg reflectors are fabricated on the substrate; an active region and The lower Bragg reflectors of multiple periods are connected; the upper Bragg reflectors of multiple periods are fabricated in the middle position on the active area; a SiO ₂ mask is deposited on the upper surface of the lower Bragg reflectors of multiple periods, and the active area Part of the upper part and the side wall and the part of the upper part and the side wall of the upper Bragg reflector; a P electrode is made on the _SiO2 mask of the active area and the exposed active area surface; an N electrode is made on the substrate below.

Description

Structure and Fabrication Method of Long Wavelength Vertical Cavity Surface Emitting Laser

technical field

The invention relates to the structure and manufacturing method of a long-wavelength vertical cavity surface-emitting laser, which adopts a combination of GaAs/AlGaAs material system as a lower Bragg reflector, and adheres the lower Bragg reflector to the active area by bonding. The invention also relates to processes and methods of making the structure.

Background technique

Due to its low threshold, circular beam, easy coupling and easy two-dimensional integration, vertical cavity surface emitting laser has become a research hotspot in the field of optoelectronics. In the optical fiber communication system, the long-wavelength vertical cavity surface-emitting laser source with dynamic single-mode operation is an indispensable key component. It is mainly used for medium-distance and long-distance high-speed data communication and optical interconnection, optical parallel processing, and optical identification system, and has important applications in both metropolitan area network and wide area network.

The wavelengths of 1.3μm and 1.55μm are in the low dispersion and low attenuation windows of optical fibers, making 1.3μm and 1.55μm VCSELs have incomparable advantages over short-wavelength VCSELs in medium and long-distance ultra-high parallelism optical fiber communications. Some communication standards and mature technologies make long-wavelength VCSELs have broad application prospects in parallel optical transmission, optical communications and wavelength division multiplexing (WDM) systems, and have great pre-market potential. In the region around the wavelength of 1.3μm and 1.55μm, the materials that can provide high gain are mainly based on InP substrate materials. A major difficulty of InP-based InGaAsP QW and AlGaInAs QW VCSELs is the Bragg lattice matching with the active layer material. Reflector materials, InGaAsP/InP, AlGaInAs/InP, InAlGaAs/InAlAs and other materials have relatively small refractive index difference. Therefore, to make the DBR achieve a reflectivity of more than 99%, more cycles are required, thereby increasing the epitaxial growth. Difficulties. Moreover, thicker DBRs also lead to greater series resistance, more severe thermal effects, and greater optical loss. On the other hand, the low thermal conductivity of quaternary alloy materials makes it difficult to reduce the thermal resistance of devices. These factors make the research progress of InP-based long-wavelength VCSELs significantly slower than that of short-wavelength VCSELs. The Bragg reflector composed of GaAs/AlGaAs material system has a large refractive index difference, so it can achieve very high reflectivity through relatively few cycles, which improves the traditional long-wavelength vertical cavity surface emitting laser distributed Bragg reflector. The number of layers is large, the thermal resistance is large, it is difficult to achieve high reflectivity, and the disadvantages of epitaxial growth are difficult.

Contents of the invention

The object of the present invention is to provide a structure and manufacturing method of a long-wavelength vertical-cavity surface-emitting laser, which improves the traditional long-wavelength vertical-cavity surface-emitting laser with many layers of distributed Bragg mirrors, large thermal resistance, and difficulty in achieving high reflectivity. Disadvantages of difficult growth.

A structure of a long-wavelength vertical cavity surface emitting laser according to the present invention is characterized in that the structure comprises:

A substrate, the substrate is an N-type GaAs substrate;

A lower Bragg reflector with multiple periods, the lower Bragg reflector with multiple periods is fabricated on the substrate, and the lower Bragg reflector with multiple periods is used to reflect the light in the laser cavity to form laser oscillation;

An active region, the active region is connected with a plurality of periodic lower Bragg reflectors by bonding to form optical gain;

A multi-period upper Bragg reflector, the multi-period upper Bragg reflector is fabricated in the middle of the active area, and forms a light exit window at the same time, and is used to reflect the light in the laser cavity to form laser oscillation;

A SiO ₂ mask, deposited on the top of the lower Bragg reflector, part of the upper part and side walls of the active region, and part of the upper part and side walls of the upper Bragg reflector, plays the role of forming a light exit window and preventing short circuits ;

a P electrode fabricated on the _SiO2 mask of the active area and the exposed surface of the active area to form a cavity contact for current injection;

An N electrode, the N electrode is fabricated under the substrate.

Among them, the lower Bragg reflector with multiple periods includes 32 periods of Al _0.9 Ga _0.1 As layer and GaAs layer and one period of Al _0.9 Ga _0.1 As layer, Al _0.98 Ga _0.002 As layer and GaAs layer; among them, Al _0.98 Ga _0.02 As The layer is used for oxidation, forming oxidation holes to form insulating regions for current confinement.

The diameter of the oxidation pores is about 10-20 microns.

The upper Bragg reflector includes 3.5 periods of Si dielectric film and SiO ₂ dielectric film.

A method for manufacturing a long-wavelength vertical cavity surface-emitting laser structure of the present invention is characterized in that the method comprises the following steps:

(1) The lower Bragg reflector is grown on the substrate for multiple cycles by the metal-organic chemical vapor deposition method of the epitaxial process;

(2) The active region is grown on the InP substrate by molecular beam epitaxy;

(3) The active region and the Bragg reflector are bonded by bonding technology, the bonding interface is InP/GaAs, and then the InP substrate is removed by chemical etching;

(4) A mask is formed by a standard photolithography process, with a photoresist electron beam cyclotron resonance deposition or electron beam evaporation on a Bragg mirror;

(5) A mask is formed by a standard photolithography process, and a mesa is formed by chemically etching the active region and the lower Bragg reflector, exposing the Al _0.98 Ga _0.02 As layer and the GaAs layer of the lower Bragg reflector;

(6) Partially oxidize the Al _0.98 Ga _0.02 As layer through an oxidation process to form oxidation holes and insulating regions to play a role in current confinement;

(7) Thermally deposited _SiO2 mask, through standard photolithography and etching, to expose the light exit window, and at the same time form a mask on the upper Bragg reflector and the side wall of the active region to prevent current short circuit;

(8) Evaporate the P electrode, then form a mask through a standard photolithography process, then corrode to form the P electrode shape, and then carry out alloying treatment;

(9) Thinning and polishing the N-type InP substrate, evaporating the N electrode, and then performing alloying treatment to complete the fabrication of the device.

The lower Bragg reflector includes 32 periods of Al _0.9 Ga _0.1 As layer and GaAs layer and one period of Al _0.9 Ga _0.1 As layer, Al _0.98 Ga _0.02 As layer and GaAs layer.

The optical thickness of the active region is 1.5λ, where λ is the lasing wavelength.

Wherein the upper Bragg reflector is formed by a peel-off process with glue, including 3.5 cycles of dielectric film Si layer and _SiO2 layer deposited or evaporated in sequence.

Wherein the oxidized pores have a diameter of 10-20 microns.

Description of drawings

For further illustrating content and characteristics of the present invention, below in conjunction with example and accompanying drawing, describe in detail as follows, wherein:

Fig. 1 is the schematic diagram of long-wavelength surface-emitting laser of the present invention;

Fig. 2 is the optical photograph of InP substrate corrosion;

Fig. 3 is the scanning electron microscope picture of the upper Bragg reflector 5 of electron beam evaporation after the lower Bragg reflector 3 of the present invention is bonded to the active region 4;

Fig. 4 is the optical microscope picture after the upper Bragg reflector 5 is peeled off with glue;

The optical photo of the active region 4 and the lower Bragg reflector 3 after wet etching in Fig. 5;

FIG. 6 is an optical micrograph of the Al _0.98 Ga _0.02 As layer 33 after partial oxidation.

Detailed ways

The present invention utilizes the GaAs/AlGaAs material system as the lower Bragg reflector 4, and the Si layer 51 and SiO ₂ layer 52 dielectric films of 3.5 cycles as the upper Bragg reflector 5 to realize the structure of the long-wavelength surface-emitting laser. Fig. 1 is a schematic diagram of a long-wavelength surface-emitting laser of the present invention. Including N electrode 1, N-type GaAs substrate 2, lower Bragg reflector 3, including 32 periods of Al _0.98 Ga _0.1 As layer 31 and GaAs layer 32 and one period of Al _0.9 Ga _0.1 As layer 31, Al _0.98 Ga _0.02 As layer 33 and GaAs layer 32, strained quantum well active region 4, upper Bragg reflector 5, composed of 3.5 periodic Si/ _SiO2 multilayer dielectric films 51 and 52, which are also light exit windows, _SiO2 mask 6, P electrode 7. The main features of this structure are as follows:

1. The lower Bragg reflector 3 includes 32 periods of Al _0.9 Ga _0.1 As layer 31 and GaAs layer 32 and one period of Al _0.9 Ga _0.1 As layer 31 , Al _0.98 Ga _0.02 As layer 33 and GaAs layer 32 . Among them, the Al _0.98 Ga _0.02 As layer 33 is used for oxidation to play a role of current confinement, and the oxidation pore diameter is about 10-20 microns.

2. Wherein the upper Bragg reflector 5 includes 3.5 periods of Si/SiO ₂ multilayer dielectric films 51 and 52;

3. The lower Bragg reflector 3 and the active region 4 are grown on different substrates using different epitaxial methods, and then bonded together by bonding;

4. The optical thickness of the active region is designed to be 1.5λ, where λ is the lasing wavelength;

5. The P electrode 7 of this structure is fabricated on the active region 4, and the N electrode 1 is fabricated on the substrate 2, which is a typical intracavity contact vertical cavity surface emitting laser.

During the epitaxial growth, the epitaxial growth of the lower Bragg reflector 3 and the active region 4 is respectively performed on the two substrates by using two growth methods. Wherein, the lower Bragg reflector 3 is grown on the GaAs substrate 2 by molecular beam epitaxy growth method, and the active region 4 is grown on the InP substrate by the metal organic chemical vapor deposition method of the epitaxial process.

The active region 4 and the Bragg reflector 3 are adhered by bonding technology, the bonding interface is InP/GaAs, and then the InP substrate and the etching stop layer InGaAs are removed by chemical etching, and the etching solution for removing the substrate is 3HCl: 1H ₂ O, the etching stop layer InGaAs is removed using 1H ₃ PO ₄ : 5H ₂ O ₂ : 5H ₂ O etching solution. Figure 2 is an optical photo of the InP substrate and the etch stop layer InGaAs after removal. It can be seen from the figure that the corroded surface is very smooth and bright.

A mask is formed by a standard photolithography process, with photoresist electron beam cyclotron resonance deposition or electron beam evaporation on the Bragg reflector 5, including 3.5 cycles of dielectric film Si layer 51 and _SiO2 layer 52 deposited or evaporated in sequence , FIG. 3 is a transmission electron micrograph of the upper Bragg mirror 5 after electron beam evaporation. Then carry out stripping with glue to form the upper Bragg reflector 5, and the pattern formed by stripping with glue is shown in Figure 4;

A mask is formed by a standard photolithography process, and a mesa is formed by chemically etching the active region 4 and the lower Bragg reflector 3, exposing the Al _0.98 Ga _0.02 As layer 33 and the GaAs layer 32 of the lower Bragg reflector 3, the active region 4 and the lower Bragg reflector 3 The optical photo of the corrosion of Bragg reflector 3 is shown in Fig. 5;

The Al _0.9 Ga _0.02 As layer 33 is partially oxidized by an oxidation process to play a role of current confinement, and the oxidation aperture 35 is controlled at about 10-20 microns; for the Al _0.98 Ga _0.02 As layer 33 with a thickness of 50 nm, at a temperature of 420°C, When the water temperature is kept at 88°C and the nitrogen flow rate is 1L/min, the oxidation rate is about 1 micron/min. FIG. 6 is an optical microscope image of the partially oxidized Al _0.98 Ga _0.02 As layer 33 .

Thermally deposited _SiO2 mask 6, through standard photolithography, etching, exposes the light window, and forms a mask on the upper Bragg reflector 5 and the side wall of the active region 4 at the same time to prevent current short circuit;

Evaporate the P electrode 7, then form a mask through a standard photolithography process, and then corrode to form the shape of the P electrode 7, and then carry out alloying treatment;

The upper Bragg reflector 5 is prepared through the following steps. Firstly, a mask is formed by standard photolithography process, and then the upper Bragg reflector 5 is deposited or evaporated by electron beam cyclotron resonance at low temperature with photoresist, including sequential deposition or evaporation. 3.5 periods of the dielectric film Si layer 51 and SiO ₂ layer 52 are then stripped with adhesive to form the upper Bragg reflector 5 . FIG. 3 is a scanning electron microscope image of the overall structure, and FIG. 4 is an optical microscope image of the upper Bragg reflector 5 after stripping the glue.

Thinning and polishing the N-type InP substrate 2, then evaporating the N electrode 1, and finally performing alloying treatment.

Claims (9)

1. the structure of a long-wavelength vertical cavity surface emitting laser is characterized in that, this structure comprises:

One substrate, this substrate are N type GaAs substrate;

The lower Bragg reflector in a plurality of cycles, the lower Bragg reflector in these a plurality of cycles is produced on the substrate, and the light that the lower Bragg reflector in these a plurality of cycles is used in the reflector laser chamber forms laser generation;

One active area, this active area connects by the bonding mode and the lower Bragg reflector in a plurality of cycles, is used for forming the gain of light;

The last Bragg mirror in a plurality of cycles, the last Bragg mirror in these a plurality of cycles is produced on the centre position on the active area, forms light window simultaneously, and the light that is used in the reflector laser chamber forms laser generation;

-SiO ₂Mask, the part top and the sidewall that are deposited on the part top of top, active area of lower Bragg reflector in a plurality of cycles and sidewall and go up Bragg mirror play the effect that forms light window and prevent short circuit;

One P electrode, this P electrode is produced on the SiO of active area ₂With the surfaces of active regions that exposes, form the inner chamber contact on the mask, be used for electric current and inject;

One N electrode, this N electrode be produced on substrate below.

2. the structure of novel long-wavelength vertical cavity surface emitting laser according to claim 1 is characterized in that, wherein the lower Bragg reflector in a plurality of cycles comprises the Al in 32 cycles _0.9Ga _0.1The Al of As layer and GaAs layer and one-period _0.9Ga _0.1As layer, Al _0.98Ga _0.02As layer and GaAs layer; Al wherein _0.98Ga _0.02The As layer is used for oxidation, forms the oxidation hole, to form insulating regions with the flow restriction effect that electrifies.

3. the structure of novel long-wavelength vertical cavity surface emitting laser according to claim 2 is characterized in that, wherein the aperture in oxidation hole is about 10～20 microns.

4. the structure of novel long-wavelength vertical cavity surface emitting laser according to claim 1 is characterized in that, wherein goes up Si deielectric-coating and SiO that Bragg mirror comprises 3.5 cycles ₂Deielectric-coating.

5. the manufacture method of a long-wavelength vertical cavity surface emitting laser structure is characterized in that, this method comprises the steps:

(1) adopt the epitaxy technique mocvd method at the grow lower Bragg reflector in a plurality of cycles of substrate;

(2) adopt molecular beam epitaxy accretion method at InP substrate growth active area;

(3) active area and Bragg mirror are adopted the bonding techniques adhesion, bonded interface is InP/GaAs, adopts the method for chemical corrosion to remove the InP substrate then;

(4) form mask by standard photolithography process, Bragg mirror on band photoresist electron beam cyclotron resonance deposit or the electron beam evaporation;

(5) form mask by standard photolithography process, form table top, expose the Al of lower Bragg reflector by chemical corrosion active area and lower Bragg reflector _0.98Ga _O.02As layer and GaAs layer;

(6) make Al by oxidation technology _0.98Ga _0.02The oxidation of As layer segment forms oxidation hole and insulating regions to play the electric current restriction;

(7) heat deposition SiO ₂Mask by standard photoetching, corrosion, exposes light-emitting window, forms mask at last Bragg mirror and active area sidewall simultaneously, to prevent short circuit current;

(8) evaporation P electrode forms mask by standard photolithography process again, and corrosion forms the P electrode shape then, carries out Alloying Treatment then;

(9) attenuate, polishing N type InP substrate, evaporation N electrode carries out Alloying Treatment then, finishes the making of device.

6. the manufacture method of novel long-wavelength vertical cavity surface emitting laser according to claim 5 is characterized in that, wherein lower Bragg reflector comprises the Al in 32 cycles _0.9Ga _0.1The Al of As layer and GaAs layer and one-period _0.9Ga _0.1As layer, Al _0.98Ga _0.02As layer and GaAs layer.

7. the manufacture method of novel long-wavelength vertical cavity surface emitting laser according to claim 5 is characterized in that, wherein the optical thickness of active area is 1.5 λ, and λ is an excitation wavelength.

8. the manufacture method of novel long-wavelength vertical cavity surface emitting laser according to claim 5 is characterized in that, wherein going up Bragg mirror is to form by band glue stripping technology, comprises the deielectric-coating Si layer and the SiO in 3.5 cycles of deposit successively or evaporation ₂Layer.

9. the manufacture method of novel long-wavelength vertical cavity surface emitting laser according to claim 5 is characterized in that, wherein the aperture in this oxidation hole is 10～20 microns.

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