CN101132120A - Dual-capacitance micromachined tunable vertical-cavity surface-emitting laser and its preparation method - Google Patents

Abstract

A dual-capacitance micromachine tunable vertical cavity surface-emitting laser and a preparation method thereof belong to the field of semiconductor optoelectronic devices. The laser includes from top to bottom: a tuning electrode (1), an insulating dielectric film (70), an upper distributed feedback Bragg reflector (20), a hollow sacrificial layer (40), and the hollow part is an air gap layer (30), an injection electrode (3), ohmic contact layer (2), middle distributed feedback Bragg reflector (90), oxidation confinement layer (4), active region layer (5), lower distributed feedback Bragg reflector (50), substrate (6 ) and ohmic contact electrodes (7), the insulating dielectric film (70) forms a double capacitor structure with the upper distributed feedback Bragg reflector (20) and the hollow sacrificial layer (40), and the upper distributed feedback Bragg reflector ( 20) and the middle distributed feedback Bragg reflector (90) are doped p ⁺ type, and the lower distributed feedback Bragg reflector (50) is n ⁺ type. The invention effectively improves the wavelength tuning range of the device.

Description

Dual-capacitance micromachined tunable vertical-cavity surface-emitting laser and its preparation method

technical field

A dual-capacitance micromachine tunable vertical-cavity surface-emitting laser belongs to the field of semiconductor optoelectronic devices, and relates to a structural design and preparation method of a wavelength-tunable surface-emitting laser.

Background technique

The application of multimode broadband fiber and dense wavelength division multiplexing (DWDM) system in the field of optical communication is becoming more and more important, which also requires the traditional VCSEL light source to provide an increasing wavelength range, so people are interested in wide-range wavelength tunable VCSEL demand is growing stronger. At present, it is widely used to prepare micro-mechanical tunable VCSELs by combining micro-mechanical systems (MEMS) and traditional VCSELs. VCSELs tuned by electrostatic force not only have the characteristics of large tuning range, fast response speed, and easy continuous tuning without mode hopping, but also are simple to operate and low in production cost, and have received extensive attention and research.

The tuning method adopted by semiconductor tunable VCSEL is electrostatic force mechanical tuning. When a voltage is applied to the upper electrode, a potential difference will be generated between the movable upper distribution feedback Bragg reflector and the injection electrode, thereby forming a flat plate capacitor between the upper electrode and the lower electrode, generating electrostatic force, thereby making the movable upper distribution The feedback Bragg mirror produces a displacement, which in turn changes the width of the resonant cavity and shifts the wavelength. However, the material used in the tunable VCSEL is GaAs-based materials. The energy of the GaAs material is only 2.59eV, and the dielectric strength is 3.5×70e4V/cm. Therefore, the highest tuning voltage for the micromechanical part of the tunable VCSEL is limited to about 15V. Otherwise, it is easy to cause device breakdown and emission due to excessive voltage. This restriction on the tuning voltage will greatly affect the displacement of the movable distributed feedback Bragg reflector, thereby reducing the wavelength tuning range and preventing the intrinsic large-range tuning characteristics of the tunable VCSEL from being fully utilized.

Contents of the invention

The purpose of the present invention is to provide a VCSEL capable of effectively increasing the displacement of the movable distributed feedback Bragg reflector and continuously tuning the wavelength in a wide range.

The invention discloses a dual capacitive micromachine tunable vertical cavity surface emitting laser, comprising

Tuning electrode 1, insulating dielectric film 70, upper distributed feedback Bragg reflector 20, hollow sacrificial layer 40, the hollow part is an air gap layer 30, injection electrode layer 3, ohmic contact layer 2, middle distributed feedback Bragg reflector 90, oxidation limitation Layer 4, active region layer 5, lower distributed feedback Bragg reflector 50, substrate 6 and ohmic contact electrode 7, the insulating dielectric film 70, upper distributed feedback Bragg reflector 20, and hollow sacrificial layer 40 form a double capacitance structure , the thickness of the hollow sacrificial layer 40 is 5-7 times of a quarter of the laser lasing wavelength, the upper distributed feedback Bragg reflector 20 and the middle distributed feedback Bragg reflector 90 are doped p ⁺ type, the lower The distributed feedback Bragg reflector 50 is n ⁺ type.

The material of the aforementioned hollow sacrificial layer 40 is one of semiconductor compounds GaAs, AlGaAs, GaInP, AlAs;

The aforementioned insulating dielectric film 70 is made of SiO2 or Si3N4;

The aforementioned upper distributed feedback Bragg reflector 20 and lower distributed feedback Bragg reflector 50 are obtained by growing 20 to 26 pairs of periods of two semiconductor compound materials with different refractive indices, and the middle distributed feedback Bragg reflector 90 is made of two different refractive indices. The semiconductor compound material is grown in 2-4 pairs of periods.

A method for preparing a dual-capacitance micromachine tunable vertical-cavity surface-emitting laser structure, comprising the following steps:

Step 1. Using metal organic chemical vapor deposition or molecular beam epitaxy system to sequentially epitaxially grow the distributed feedback Bragg reflector 50, the active region 5, the oxidation confinement layer 4, and the distributed feedback Bragg reflector 90 on the substrate 6, p-type ohmic contact layer 2;

Step 2, using metal organic chemical vapor deposition or molecular beam epitaxy system to epitaxially grow a sacrificial layer and a distributed feedback Bragg mirror 20 on the p-type ohmic contact layer 2, and prepare an insulating dielectric film by using a plasma-enhanced chemical vapor deposition method 70;

Step 3. Using a combination of photolithography and selective wet etching, the insulating dielectric film 70 and the upper distributed feedback Bragg reflector 20 are selectively etched to prepare a three-dimensional outline of the cantilever beam. For the specific description of the cantilever beam, see (application number: 200710175248.1, title: cantilever beam wavelength tunable vertical cavity surface emitting laser structure and preparation method, unit: Beijing University of Technology);

Step 4, performing secondary photolithography to corrode the ohmic contact layer 2 and the mid-distributed feedback Bragg reflector 90 to form a mesa structure and expose the sidewall of the oxidation limiting layer 4;

Step 5, using an oxidation furnace to oxidize at 440° C. for 30 minutes to oxidize the oxidation limiting layer 4 to form an injection current limiting aperture of 20 μm;

Step 6, selectively etching the sacrificial layer to expose the p-type ohmic contact layer 2;

Step 7, sputtering the tuning electrode 1 on the insulating dielectric film 70, and sputtering the TiAu injection electrode 3 on the surface of the p-type ohmic contact layer 2;

Step 8, sputtering AuGeNiAu ohmic contact electrodes 7 on the lower surface of the substrate 6 .

Step 9, selectively etching the sacrificial layer, the hollow part of the hollow sacrificial layer 40 is composed of the air gap layer 30 .

After the bias voltage is applied to the tuning electrode 1, the insulating dielectric film 70 and the injection electrode 3 are distributed as the two poles of the capacitor, and the dielectrics of the capacitor are two kinds of media, the upper distributed feedback Bragg reflector 20 and the air gap layer 30, respectively. The interior is equivalent to the series connection of two capacitors formed by the upper distributed feedback Bragg reflector 20 and the air gap layer 30 . The movable distributed feedback Bragg reflector 20 is manipulated by electrostatic force, so that the thickness of the resonant cavity is reduced, and the resonant wavelength is blue-shifted. After the voltage is turned off, under the action of elastic restoring force, the movable upper distributed feedback Bragg reflector 20 returns to Its original position state, so as to achieve adjustable lasing wavelength.

The tunable laser obtained by adopting the structural design and process preparation method of the present invention has the characteristics of high tuning voltage, meeting the requirement of large displacement of the movable film, and wide tuning range of lasing wavelength. Avoiding the limitation of the easy-to-tune voltage of the device and the small displacement range of the movable film on the tuning wavelength range.

Description of drawings

Figure 1: Schematic diagram of the device layer structure of the dual-capacitance micromachined tunable vertical-cavity surface-emitting laser structure proposed in the present invention;

Figure 2: Schematic diagram of the tuning voltage and displacement of the movable upper distributed feedback Bragg reflector in the structure of the present invention.

Detailed ways

The invention discloses a dual capacitive micromachine tunable vertical cavity surface emitting laser, comprising

Tuning electrode 1, insulating dielectric film 70, upper distributed feedback Bragg reflector 20, hollow sacrificial layer 40, the hollow part is an air gap layer 30, injection electrode layer 3, ohmic contact layer 2, middle distributed feedback Bragg reflector 90, oxidation limitation Layer 4, active region layer 5, lower distributed feedback Bragg reflector 50, substrate 6 and ohmic contact electrode 7, the insulating dielectric film 70, upper distributed feedback Bragg reflector 20, and hollow sacrificial layer 40 form a double capacitance structure , the thickness of the hollow sacrificial layer 40 is 5-7 times of a quarter of the laser lasing wavelength, the upper distribution feedback Bragg reflector 20 and the middle distribution feedback Bragg reflector 90 are doped p+ type, and the lower distribution The feedback Bragg reflector 50 is of n+ type.

Specific steps are as follows:

1. Use metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) system crystal-direction epitaxy to sequentially grow 26 pairs of GaAs and AlGaAs periodic growth structures on the n-gallium arsenide substrate 6 under the n+ type distribution Feedback Bragg reflector 50, active region 5, AlGaAs oxidation confinement layer 4, p-type ohmic contact layer 2, 3 pairs of GaAs and AlGaAs periodic growth structure mid-distributed feedback Bragg reflector 90, AlGaAs hollow sacrificial layer 40, 23 pairs of GaAs and an upper distributed Bragg reflector 20 of an AlGaAs periodic growth structure;

2. The SiO2 insulating dielectric film 70 is prepared by ion-enhanced chemical vapor deposition PECVD, with a thickness of 100 nm, and formed on the upper surface of the upper distributed Bragg reflector 20;

3. Using a combination of photolithography and selective wet etching, the insulating dielectric film 70 and the upper distributed feedback Bragg reflector 20 are selectively etched to prepare a three-dimensional contour pattern of the cantilever beam;

4. Carry out secondary photolithography to corrode the ohmic contact layer 2 and the mid-distributed feedback Bragg reflector 90 to form a mesa structure and expose the sidewall of the oxidation limiting layer 4;

5. Using oxidation furnace equipment to oxidize at 440°C for 30 minutes to oxidize the oxidation limiting layer 4 to form an injection current limiting pore size of 20um;

6. Selectively etch the sacrificial layer to expose the p-type ohmic contact layer 5;

7. Prepare the tuning electrode 1 on the insulating dielectric film 70, and prepare the TiAu injection electrode 3 on the surface of the p-type ohmic contact layer 2;

8. Prepare AuGeNiAu ohmic contact electrodes 7 on the lower surface of the substrate 6;

9. Selectively corrode the sacrificial layer, the hollow part of the hollow sacrificial layer 40 is the air gap layer 30, and the thickness is five quarters of the lasing wavelength;

The sacrificial layer is selectively etched to obtain a hollow sacrificial layer 40 , the hollow part is composed of an air gap 30 , so that the upper DBR 20 is suspended above the active region 5 . The air-gap layer 30 is a part of the resonant cavity, and the contact surface between the air and the adjacent semiconductor material has a great influence on the light output effect of the laser. Therefore, the sacrificial layer 40 is finally selectively etched with two materials with a large ratio of numbers, such as GaAs and AlGaAs.

FIG. 2 is a displacement curve of the upper distributed feedback Bragg reflector 20 as the tuning voltage changes. Reference signs D1 and D2 correspond to tuning voltage points of 15V and 30V, respectively. They represent the amount of displacement of the upper distributed feedback Bragg reflector 20 corresponding to different tuning voltages.

The situation shown in D1 is: without the insulating dielectric film 70, the maximum tuning voltage is about 15V, and under the electrostatic force between the tuning electrode 1 and the injection electrode 3, the displacement of the upper distributed feedback Bragg mirror 20 is only 50nm;

The situation shown in D2 is: in the case of using the insulating dielectric film 70 of the present invention, the tuning voltage can be increased to more than 30V. The insulating dielectric film 70, the tuning electrode 1, the upper distributed feedback Bragg reflector 20, the hollow sacrificial layer 30 and the injection electrode 3 form a double capacitor structure. Under the electrostatic force, the displacement of the upper distributed feedback Bragg reflector 20 reaches 250nm.

Claims (5)

1. A dual capacitive micromachine tunable vertical cavity surface emitting laser, characterized in that, from top to bottom, it includes: Tuning electrode (1), insulating dielectric film (70), upper distributed feedback Bragg mirror (20), hollow sacrificial layer (40), the hollow part of the hollow sacrificial layer (40) is an air gap layer (30), injection electrode ( 3), ohmic contact layer (2), middle distributed feedback Bragg reflector (90), oxidation confinement layer (4), active region layer (5), lower distributed feedback Bragg reflector (50), substrate (6) And ohmic contact electrode (7), described insulating medium thin film (70) and upper distributed feedback Bragg reflector (20), hollow sacrificial layer (40) constitute double capacitor structure, and described hollow sacrificial layer (40) thickness is 5-7 times of the lasing wavelength of the quarter laser, the upper distributed feedback Bragg reflector (20) and the middle distributed feedback Bragg reflector (90) are doped p ⁺ type, and the lower distributed feedback Bragg reflector ( 50) is n ⁺ type. 2. The dual capacitive micromachine tunable vertical cavity surface emitting laser according to claim 1, characterized in that: the material of the hollow sacrificial layer (40) is one of semiconductor compounds GaAs, AlGaAs, GaInP, AlAs. 3. The dual-capacitance micromachine tunable vertical cavity surface emitting laser according to claim 1, characterized in that: the material of the insulating dielectric film (70) is SiO ₂ or Si ₃ N ₄ . 4. The double capacitive micromachine tunable vertical cavity surface emitting laser according to claim 1, characterized in that: the upper distributed feedback Bragg reflector (20) and the lower distributed feedback Bragg reflector (50) are formed by refraction Two semiconductor compound materials with different refractive indices are grown for 20-26 pairs of periods, and the mid-distributed feedback Bragg reflector (90) is obtained by growing two semiconductor compound materials with different refractive indices for 2-4 pairs of periods. 5. The preparation method of the dual capacitive micromachine tunable vertical cavity surface emitting laser according to claim 1, comprising the following steps Step 1. Using metal organic chemical vapor deposition or molecular beam epitaxy system to sequentially epitaxially grow distributed feedback Bragg reflector (50), active region (5), oxidation confinement layer (4) on substrate (6), Middle distributed feedback Bragg reflector (90), p-type ohmic contact layer (2); Step 2, using metal-organic chemical vapor deposition or molecular beam epitaxy system to epitaxially grow the sacrificial layer and the upper distributed feedback Bragg mirror (20) on the p-type ohmic contact layer (2), and adopt the plasma enhanced chemical vapor deposition method Prepare an insulating dielectric film (70); Step 3, using a combination of photolithography and selective wet etching to selectively etch the insulating dielectric film (70) and the upper distributed feedback Bragg reflector (20) to prepare a three-dimensional contour pattern of the cantilever beam; Step 4, performing secondary photolithography, corroding the ohmic contact layer (2) and the distributed feedback Bragg mirror (90), forming a mesa structure, and exposing the sidewall of the oxidation limiting layer (4); Step 5. Oxidize the oxidation limiting layer (4) at 440° C. for 30 minutes using oxidation furnace equipment to form an injection current limiting aperture of 20 μm; Step 6, selectively etching the sacrificial layer to expose the p-type ohmic contact layer (2); Step 7, sputtering the tuning electrode (1) on the insulating dielectric film (70), and sputtering the TiAu injection electrode (3) on the surface of the p-type ohmic contact layer (2); Step 8, sputtering AuGeNiAu ohmic contact electrodes (7) on the lower surface of the substrate (6); Step 9, selectively etching the sacrificial layer, the hollow part of the hollow sacrificial layer (40) is the air gap layer (30).

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