Vertical cavity surface emitting laser with metal grating structure

Abstract

The invention provides a vertical cavity surface emitting laser with a metal grating structure, and relates to the field of semiconductor photoelectrons. The vertical cavity surface emitting laser comprises a light emitting device comprising an ohmic contact layer and a first electrode layer; the grating layer is formed on the surface of the ohmic contact layer, the grating layer comprises a plurality of columnar grating protrusions and grating gaps, and the grating gaps are formed around the grating protrusions; wherein the grating protrusions are made of metal materials, and the grating protrusions are connected with the first electrode layer. The metal grating structure can be used as an electrode of the vertical-cavity surface-emitting laser, ohmic contact of a device is achieved, and meanwhile the vertical-cavity surface-emitting laser can have the polarization characteristic. According to the metal grating structure, the current density distribution of the device can be uniform while the electrode and polarization characteristics are considered, so that the device has a better temperature characteristic. Compared with a traditional grating structure, the metal grating structure is simpler in preparation method and lower in cost in device preparation.

Description

Technical Field

[0001] The invention relates to the field of semiconductor optoelectronics, and in particular to a vertical cavity surface emitting laser with a metal grating structure. Background Art

[0002] Vertical Cavity Surface Emitting Laser (VCSEL) is a laser whose light emission direction is perpendicular to the substrate surface. Its quantum well is usually grown in the (100) direction, and the gain in all polarization directions is isotropic.

[0003] At present, due to the large lateral size of vertical cavity surface emitting lasers, high-order transverse modes are prone to occur, and each of these modes contains two orthogonal polarization states. These two polarization states will jump during changes in temperature or bias current, making it difficult to achieve stable polarization selection characteristics. Therefore, vertical cavity surface emitting lasers with stable polarization selection characteristics have important applications in atomic sensor devices, optical communication systems, laser frequency doubling, gas detection and spectral analysis.

[0004] Traditional vertical cavity surface emitting lasers have serious internal heat generation and uneven current distribution. Self-heating will seriously affect the performance of VCSEL. The output power of VCSEL is severely limited by the thermal reversal effect caused by temperature rise. At the same time, the life and reliability of VCSEL will also decrease with the increase of temperature. Therefore, polarized vertical cavity surface emitting laser devices with good temperature characteristics are of great significance in the application research of atomic sensor devices, optical communication systems, laser frequency doubling, gas detection and spectral analysis. Summary of the invention

[0005] In order to solve the technical problems of traditional vertical cavity surface emitting lasers such as unstable polarization, serious heat generation inside the device, uneven current distribution, self-heating, etc., the present invention provides a vertical cavity surface emitting laser with a metal grating structure.

[0006] The present invention provides a vertical cavity surface emitting laser with a metal grating structure, comprising: a light emitting device, comprising an ohmic contact layer and a first electrode layer; a grating layer, formed on the surface of the ohmic contact layer, the grating layer comprising a plurality of columnar grating protrusions and grating gaps, the grating gaps being formed around the grating protrusions; wherein the grating protrusions are made of metal material, and each grating protrusion is connected to the first electrode layer.

[0007] According to an embodiment of the present invention, the arrangement and distribution of the grating protrusions and the grating gaps are periodic in at least one direction, and the shapes of the grating protrusions include straight bar columns and curved bar columns.

[0008] According to an embodiment of the present invention, the refractive index of the material of the grating protrusion is greater than that of the grating gap, and the material of the grating protrusion includes gold, silver, and copper.

[0009] According to an embodiment of the present invention, the grating gaps are filled with a medium, and the medium includes air or a material with a refractive index smaller than that of the grating protrusions.

[0010] According to an embodiment of the present invention, the first electrode layer is in the form of an annular boss, and an electrode hollow region is formed in the middle of the annular boss, which is used as a light exit hole of a vertical cavity surface emitting laser.

[0011] According to an embodiment of the present invention, the grating layer is disposed in the middle region of the first electrode layer and covers the light exit hole.

[0012] According to an embodiment of the present invention, the first electrode layer is formed on the surface of the ohmic contact layer and is disposed at the outer edge of the grating gap.

[0013] According to an embodiment of the present invention, the grating layer is manufactured by a photolithography process.

[0014] According to an embodiment of the present invention, the period and the grating width of the grating layer are determined by the polarization mode of the laser light emitted by the vertical cavity surface emitting laser.

[0015] According to an embodiment of the present invention, the light-emitting device further comprises: a P-type distributed Bragg reflector layer, an oxidation restriction layer, an active layer, an N-type distributed Bragg reflector layer, a substrate and a second electrode layer stacked in sequence from top to bottom on the bottom surface of the ohmic contact layer, wherein the oxidation restriction layer is a ring-shaped boss.

[0016] Compared with the prior art, the vertical cavity surface emitting laser with a metal grating structure provided by the present invention has at least the following beneficial effects:

[0017] (1) The metal grating structure can reduce the gain of one of the two modes, the transverse electric mode and the transverse magnetic mode, and has polarization selection characteristics;

[0018] (2) The metal grating structure can make the device temperature distribution more uniform through the good heat dissipation characteristics of metal;

[0019] (3) By setting the parameters of the metal grating structure, photolithography can be used instead of electron beam exposure, reducing costs and making the process simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0021] Figure 1 A cross-sectional view of a vertical cavity surface emitting laser having a metal grating structure according to an embodiment of the present invention is schematically shown;

[0022] Figure 2 Schematically shows Figure 1 A cross-sectional view of a metal grating structure in FIG.

[0023] Figure 3 A schematic diagram shows a structure of a vertical cavity surface emitting laser with a metal grating structure according to an embodiment of the present invention;

[0024] Figure 4 Schematically showing the calculation result of the reflection spectrum of the grating optical characteristics of the vertical cavity surface emitting laser according to the embodiment of the present invention;

[0025] Figure 5 A temperature comparison diagram of a vertical cavity surface emitting laser according to an embodiment of the present invention and a common vertical cavity surface emitting laser is schematically shown;

[0026] Figure 6 A current density comparison diagram between a vertical cavity surface emitting laser according to an embodiment of the present invention and a common vertical cavity surface emitting laser is schematically shown.

[0027] Description of reference numerals:

[0028] 1. Grating layer; 10. Grating gap; 11. Grating protrusion; 2. First electrode layer; 3. Ohmic contact layer; 4. P-type distributed Bragg reflector layer; 5. Oxidation restriction layer; 6. Active layer; 7. N-type distributed Bragg reflector layer; 8. Substrate; 9. Second electrode layer. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0030] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0031] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0032] When using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, and C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc. When using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, or C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.

[0033] It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are only reference directions of the drawings and are not intended to limit the scope of protection of the present invention. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations will be omitted when they may cause confusion in the understanding of the present invention.

[0034] When implementing the technical concept of the present invention, the inventors found that the polarization selection characteristics of the vertical cavity surface emitting laser can be realized by using a grating structure. By adjusting the grating period, duty cycle, thickness and other parameters to increase the reflectivity difference between the transverse electric (TE) and transverse magnetic (TM) modes, one of them can be suppressed, thereby achieving controllable polarization of the laser emitted by the vertical cavity surface emitting laser. The use of a metal polarization grating can, on the one hand, give the device the ability to control polarization, and on the other hand, make the device temperature distribution more uniform through the good heat dissipation characteristics of the metal. At the same time, the design of the metal grating parameters can also achieve the purpose of reducing process difficulty and reducing costs.

[0035] In view of this, the present invention provides a vertical cavity surface emitting laser with a metal grating structure, which is used to solve the problem of unstable polarization of the vertical cavity surface emitting laser, and at the same time solve the problems of serious heat generation inside the device, uneven current distribution, self-heating, etc.

[0036] Figure 1 A cross-sectional view of a vertical cavity surface emitting laser with a metal grating structure according to an embodiment of the present invention is schematically shown. Figure 2 Schematically shows Figure 1 Cross-sectional view of the metal grating structure in . Figure 3 The structure of a vertical cavity surface emitting laser with a metal grating structure according to an embodiment of the present invention is schematically shown.

[0037] like Figures 1 to 3 As shown, the vertical cavity surface emitting laser with a metal grating structure of this embodiment includes a light emitting device and a grating layer 1. The light emitting device includes an ohmic contact layer 3 and a first electrode layer 2. The grating layer 1 is formed on the surface of the ohmic contact layer 3, and the grating layer 1 includes a plurality of columnar grating protrusions 11 and grating gaps 10, and the grating gaps 10 are formed around the grating protrusions 11. Among them, the grating protrusions 11 are made of metal material, and each grating protrusion 11 is connected to the first electrode layer 2.

[0038] Through the embodiment of the present invention, the grating layer 1 is formed on the surface of the ohmic contact layer 3, and each grating protrusion 11 is connected to the first electrode layer 2, which can be used as a polarization structure of the light-emitting device, while uniformizing the current density and reducing Joule heat.

[0039] In this embodiment, the first electrode layer 2 is formed on the surface of the ohmic contact layer 3 and is disposed at the outer edge of the grating gap 10. The outer peripheral wall of the grating protrusion 11 is connected to the first electrode layer 2.

[0040] Please continue reading Figure 2 The arrangement and distribution of the grating protrusions 11 and the grating gaps 10 are periodic in at least one direction, and the shapes of the grating protrusions 11 include straight bar columns and curved bar columns.

[0041] Among them, T g is the height of the grating layer 1, H1 is the thickness of the ohmic contact layer 3, and T is the grating period. Considering the large grating width and period, the grating layer 1 can be made by photolithography.

[0042] In this embodiment, the refractive index of the material of the grating protrusions 11 is greater than that of the grating gaps 10 , and the grating protrusions 11 are made of metal materials with good electrical conductivity, such as gold, silver, and copper.

[0043] In this embodiment, the grating gap 10 is filled with a medium, and the medium includes air or a material with a refractive index smaller than that of the grating protrusion 11 .

[0044] Optionally, the material of the ohmic contact layer 3 includes gallium arsenide or aluminum gallium arsenide material with a lower aluminum component.

[0045] In this embodiment, the first electrode layer 2 is in the form of an annular boss, and an electrode hollow region is formed in the middle of the annular boss, which is used as a light exit hole of the vertical cavity surface emitting laser.

[0046] Furthermore, the grating layer 1 is arranged on one side of the laser emitting direction of the light emitting device. The grating layer 1 is arranged in the middle area of ​​the first electrode layer 2 and covers the light emitting hole.

[0047] In this embodiment, the period and grating width of the grating layer 1 are determined by the polarization mode of the laser emitted by the vertical cavity surface emitting laser.

[0048] In this embodiment, the light-emitting device further includes a P-type distributed Bragg reflector layer (Distributed Bragg Reflector, referred to as DBR) 4, an oxidation restriction layer 5, an active layer 6, an N-type distributed Bragg reflector layer 7, a substrate 8 and a second electrode layer 9 which are stacked in sequence from top to bottom on the bottom surface of the ohmic contact layer 3.

[0049] The oxidation limiting layer 5 is disposed on the active layer 6 and is in the form of an annular boss. The middle of the annular boss is a current limiting hole for limiting the current injected into the active layer 6.

[0050] Through the embodiments of the present invention, the metal grating structure can be used as an electrode of a vertical cavity surface emitting laser to achieve ohmic contact of the device, and at the same time, the vertical cavity surface emitting laser can have polarization characteristics. While taking into account both the electrode and polarization characteristics, the metal grating structure can evenly distribute the device current density, so that the device has better temperature characteristics.

[0051] The following is an experimental verification of the vertical cavity surface emitting laser with a metal grating structure proposed in this embodiment.

[0052] Specifically, this experiment uses a 795nm vertical cavity surface emitting laser with a cylindrical support platform and a circular light exit hole, and the grating layer 1 serves as the polarization structure of the light emitting device, while uniformizing the current density and reducing Joule heat.

[0053] It should be understood that the present invention does not limit the wavelength of specific light in the vertical cavity surface emitting laser, and it can be set according to the actual application scenario.

[0054] The vertical cavity surface emitting laser used in the experiment uses a strip columnar grating protrusion 11 made of gold, the refractive index of the material of the ohmic contact layer 3 is 3.55, and the height T of the grating layer 1 is g The thickness H1 of the ohmic contact layer 3 is 230 nm, the thickness H1 of the ohmic contact layer 3 is 60 nm, the grating width in the X direction (eg, the horizontal direction) is 1.8 µm, the grating period T is 3 µm, and the grating duty cycle is 0.6.

[0055] Figure 4 The calculation result of the reflection spectrum of the grating optical characteristic of the vertical cavity surface emitting laser according to the embodiment of the present invention is schematically shown.

[0056] Under the above conditions, this experiment simulated the grating layer 1 based on the Rigorous Coupled Wave Analysis (RCWA) algorithm. The incident light was a TE plane wave with the electric field component perpendicular to the incident surface. Figure 4The reflectance spectrum of the grating optical characteristics shown includes two curves, TE reflectivity and TM reflectivity. From these two curves, it can be seen that the TE mode reflectivity of the grating layer near the 795nm band is much higher than the TM mode reflectivity, which can achieve good polarization selection.

[0057] Figure 5 The temperature comparison diagram of the vertical cavity surface emitting laser according to the embodiment of the present invention and the common vertical cavity surface emitting laser is schematically shown.

[0058] like Figure 5 As shown, it can be seen that the temperature of the active region, P-type DBR, and N-type DBR of the vertical cavity surface emitting laser proposed by the present invention are lower than that of the ordinary vertical cavity surface emitting laser. The temperature of the single tube device is reduced by about 2K, where K is the Kelvin temperature.

[0059] Figure 6 A current density comparison diagram between a vertical cavity surface emitting laser according to an embodiment of the present invention and a common vertical cavity surface emitting laser is schematically shown.

[0060] like Figure 6 As shown, it can be seen that the current density distribution of the vertical cavity surface emitting laser proposed in the present invention is smoother, wherein the peak of the current density distribution in the active region at the oxidation aperture is smaller than the current density difference at the center, and the current density distribution uniformity of the P-type DBR far exceeds that of ordinary vertical cavity surface emitting lasers.

[0061] The following describes a method for preparing a vertical cavity surface emitting laser with a metal grating structure and a central wavelength of 795 nm in this embodiment. The preparation method includes the following steps 1 to 8.

[0062] Step 1: Growth of epitaxial structure. Using the Metal-organic Chemical Vapor Deposition (MOCVD) process, 39 pairs of N-type Al 0.22 Ga 0.78 As / Al 0.9 Ga 0.1 As distributed Bragg reflector layer 7, triple quantum well active region 6, wherein the material used for the active layer 6 is In 0.08 Ga 0.79 Al 0.13 As / Al 0.3 Ga 0.7 As,Al 0.98 Ga 0.02 As oxidation limiting layer 5,26 for P-type Al 0.22 Ga 0.78 As / Al 0.9 Ga 0.1As distributed Bragg reflector layer 4, p-type heavily doped GaAs ohmic contact layer 3.

[0063] Step 2: Use plasma enhanced chemical vapor deposition (PECVD) to grow a SiO2 mask to prepare for the subsequent ICP (Inductively Couple Plasma) etching of the distributed Bragg reflector mesa. Transfer the mesa pattern to the SiO2 mask for subsequent mesa etching in one lithography.

[0064] Step 3: ICP etches the cylindrical mesa to a depth sufficient to expose the Al that needs to be oxidized next. 0.98 Ga 0.02 As layer 5.

[0065] Step 4: Wet oxidation: oxidize the etched epitaxial wafer. At a high temperature of 440°C, use nitrogen as a carrier gas and introduce water vapor at about 92°C to oxidize the Al in the epitaxial wafer. 0.98 Ga 0.02 The As oxidation limiting layer 5 is oxidized to form a current limiting hole.

[0066] Step 5: Use PECVD to grow a SiO2 insulating layer, perform secondary photolithography to define and etch the light-emitting holes, and insulate the sidewalls.

[0067] Step 6: Prepare the grating structure and electrode layer 2 at the same time. Perform three photolithography steps and use negative photoresist stripping technology to make metal electrodes and grating structures.

[0068] Step 7: Thin and polish the back substrate and deposit the back electrode.

[0069] Step 8: The vertical cavity surface emitting laser is prepared by successively performing alloying, cleavage and dicing, preliminary testing, chip welding and packaging.

[0070] According to the embodiments of the present invention, the metal grating structure has a simpler preparation method and lower cost in device preparation compared with a traditional grating structure.

[0071] In summary, according to the vertical cavity surface emitting laser with a metal grating structure provided by the above embodiment of the present invention, the metal grating structure enables the device to have polarization selection characteristics, and the metal grating structure can make the current density uniform and reduce Joule heat. By selecting the period, duty cycle and other parameters of the grating layer, the polarization selection characteristics of the grating can be selected to achieve polarization selection and polarization-independent characteristics, so that it can be applied in many atomic sensor devices, communications and other fields.

[0072] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination. The scope of the present invention is defined by the appended claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A vertical cavity surface emitting laser having a metal grating structure, characterized in that: include: A light-emitting device comprising an ohmic contact layer (3) and a first electrode layer (2); A grating layer (1) is formed on the surface of the ohmic contact layer (3), the grating layer (1) comprising a plurality of columnar grating protrusions (11) and grating gaps (10), the grating gaps (10) being formed around the grating protrusions (11); Wherein, the grating protrusions (11) are made of metal material, and each of the grating protrusions (11) is connected to the first electrode layer (2).

2. The vertical cavity surface emitting laser according to claim 1, characterized in that: The arrangement and distribution of the grating protrusions (11) and the grating gaps (10) are periodic in at least one direction, and the shapes of the grating protrusions (11) include straight bar columns and curved bar columns.

3. The vertical cavity surface emitting laser according to claim 1, characterized in that: The refractive index of the material of the grating protrusion (11) is greater than that of the grating gap (10), and the material of the grating protrusion (11) includes gold, silver, and copper.

4. The vertical cavity surface emitting laser according to claim 1, characterized in that: The grating gap (10) is filled with a medium, wherein the medium comprises air or a material having a refractive index lower than that of the grating protrusion (11).

5. The vertical cavity surface emitting laser according to claim 1, characterized in that: The first electrode layer (2) is in the form of an annular boss, and an electrode hollow region is formed in the middle of the annular boss, serving as a light exit hole of the vertical cavity surface emitting laser.

6. The vertical cavity surface emitting laser according to claim 5, characterized in that: The grating layer (1) is arranged in the middle area of ​​the first electrode layer (2) and covers the light exit hole.

7. The vertical cavity surface emitting laser according to claim 1, characterized in that: The first electrode layer (2) is formed on the surface of the ohmic contact layer (3) and is arranged at the outer edge of the grating gap (10).

8. The vertical cavity surface emitting laser according to claim 1, characterized in that: The grating layer (1) is manufactured using a photolithography process.

9. The vertical cavity surface emitting laser according to claim 1, characterized in that: The period and grating width of the grating layer (1) are determined by the polarization mode of the laser light emitted by the vertical cavity surface emitting laser.

10. The vertical cavity surface emitting laser according to claim 1, characterized in that: The light emitting device further comprises: A P-type distributed Bragg reflector layer (4), an oxidation restriction layer (5), an active layer (6), an N-type distributed Bragg reflector layer (7), a substrate (8) and a second electrode layer (9) are stacked in sequence from top to bottom on the bottom surface of the ohmic contact layer (3), wherein the oxidation restriction layer (5) is in the form of an annular boss.

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