KR101433361B1 - polarization-control vertical-cavity surface-emitting laser - Google Patents

Abstract

Surface emitting lasers are used as light sources for short distance communication and optical sensors, and their application to optical connection, optical sensor and optical communication is increasing rapidly. Especially, various optical sensor applications such as free space gas, image, and light source for displacement sensor have been progressed, and stable beam emission characteristics without change of polarization according to current and time are required for accurate sensing. The present invention relates to a surface emitting laser element characterized in that the polarization direction is adjusted by generating a difference between a gain difference and a oscillation wavelength between polarizations due to strains caused by strained quantum wells and anisotropic electrodes.

Description

A polarization-controlled vertical-cavity surface-emitting laser

The present invention relates to a surface emitting semiconductor laser device with polarization control, and more particularly, to a semiconductor laser device with a polarization controlled surface emitting semiconductor laser device, in which strain caused by strained multiple quantum wells and anisotropic electrodes causes a difference in gain and oscillation wavelength between polarizations Thereby adjusting the polarization direction of the laser beam.

Surface emitting lasers are used as light sources for short distance communication and optical sensors, and their application to optical connection, optical sensor and optical communication is increasing rapidly. Particularly, the characteristics of the surface emitting laser in the longitudinal direction, such as the single mode spectrum characteristic, the circular beam emission characteristic, the low unit cost by the wafer-based manufacturing process, the low mounting cost, the low electrical power consumption, dimensional array, etc., various applications are being made for a light source for data communication such as optical connection, a gas in free space, an image, a light source for a displacement sensor, and the like. In particular, recently, demand for sensors such as high-resolution optical mice and atomic clocks is rapidly increasing. However, in order to reduce the error rate and precise sensing of such an application, a stable beam emission characteristic without change of polarization according to current and time is required. In general, optical sensors utilize the characteristics of transmission, reflection, and absorption of light, and most optical components have properties in which the characteristics change according to the polarization direction of the beam in transmission, reflection, and absorption. Therefore, the amount of transmission, reflection, and absorption changes due to the polarization change of the light source, which causes a change in the amount of signal detection, which causes the accuracy of the optical sensor to deteriorate. Therefore, it is necessary to develop a polarization-controlled surface emitting laser device which does not change the polarization characteristics depending on the operating current, temperature and time.

Conventional polarization-controlled surface emitting laser devices include a structure in which a shape of an oscillating laser beam is formed to have anisotropy and a structure in which a laser beam is tilted to be anisotropy to form an anisotropic structure. A structure for growing a surface emitting laser, and a structure in which a grating is formed on a laser column to adjust reflectance for each polarization.

The anisotropic structure of the laser pillar shape or the structure in which the laser pillar is inclined is advantageous in that the device is relatively easy to fabricate, but the size of the laser beam having anisotropy is larger than that of the oscillation wavelength (0.85 μm band) (Diameter: 10 to 50 탆). Thus, it has a disadvantage that polarization control characteristics are poor due to insufficient effect on polarization control.

In the structure using the substrate, the difference in gain characteristics due to the polarization of the surface emitting laser is relatively large, so that the polarization control property is excellent. However, it is difficult to grow the surface emitting laser structure on the substrate, It has disadvantages.

The method of forming the grating on the laser pillar has a disadvantage in that the manufacturing process is complicated and the yield is low due to the need to form a fine pattern of about 0.1 탆 on the pillar, although the polarization control property is excellent.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a method and apparatus for compensating for a difference between a gain difference between polarizations and an oscillation wavelength by stresses caused by strained multiple quantum wells and anisotropic electrodes. And the polarization direction is controlled by controlling the polarization direction of the laser beam. That is, it is an object of the present invention to provide a device capable of adjusting polarization with a simple structure by growing a strained structure in a multi-quantum well and causing a gain and a wavelength difference according to polarization to be generated in a strained gain layer by stress of an anisotropic electrode structure.

According to an aspect of the present invention, there is provided a polarization-controlled surface emitting laser element comprising: a lower mirror layer composed of an n-type semiconductor DBR (distributed Bragg reflector) sequentially stacked on a semiconductor substrate; A lower cladding layer made of a semiconductor on the lower mirror layer; A gain layer formed of a multiple quantum well layer strained on the lower clad layer; An upper clad layer made of a semiconductor on the gain layer; An upper first mirror layer composed of a p-type semiconductor DBR stacked on the upper clad layer; A current confining layer for current confinement on the upper first mirror layer; An upper second mirror layer composed of a p-type semiconductor DBR layered on the current confined layer; .

In the present invention, a part of the upper second mirror layer, the current confined layer, the upper first mirror layer, the upper clad layer, the gain layer and the lower clad layer is etched, and then a part of the current confined layer is oxidized to form an oxide layer An upper electrode is formed on the upper second mirror layer, a dielectric thin film is formed on the portion except for the laser column to form a dielectric insulating layer, and an electrode pad for the upper electrode and wiring is formed. So that stress due to the electrode connecting metal pad acts on the laser pillar.

The present invention has oscillation characteristics of polarization control so that the gain characteristic and the oscillation wavelength according to polarization are made different by the stress caused by the anisotropic electrode connecting metal pad in the gain layer of the laser column.

The polarization-controlled surface emitting laser according to the present invention is characterized in that the stress caused by the anisotropic property of the gain layer of the multi-quantum well and the anisotropic property of the polarization-controlled surface emitting laser causes a difference in gain and oscillation wavelength depending on the polarization direction, Beam emission characteristics of polarization control with stable polarization characteristics and optical sensing using characteristics such as transmission, reflection and absorption in free space. Stable output characteristic according to operating current, temperature and time. .

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side sectional view showing a polarization-controlled fast modulation surface emitting laser element of the present invention,
Fig. 2 is a cross-sectional view of the polarization-controlled surface emitting laser element of the present invention viewed from the direction in which the beam is emitted. Fig.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in order to facilitate a person skilled in the art to easily carry out the technical idea of the present invention. do.

1 is a side cross-sectional view of a wavelength-tunable surface emitting laser element according to a preferred embodiment of the present invention, in which reference numeral 21 denotes a (001) semiconductor substrate, 22 denotes a lower mirror layer composed of laminated n-type doped semiconductor DBR, 24 is a gain layer formed of strained multiple quantum well layers, 25 is an upper cladding layer composed of semiconductors, 26 is an upper first mirror layer composed of stacked p-type semiconductor DBRs, 27 is an upper cladding layer made of p- An upper second mirror layer 28 composed of stacked p-type semiconductor DBRs, 29 an oxide layer formed by oxidizing a part of the current confined layer, 41 an upper second mirror layer A dielectric layer for insulation between the electrodes; 31, a dielectric layer for insulation between the electrodes; 31, a dielectric layer for protecting the upper part of the upper mirror layer, the upper cladding layer, the gain layer and the lower cladding layer; The upper electrode formed, 32, Sub-electrode electrode pad 33 to give a stress to the laser pillar 41 according to the current application and is associated with an anisotropic (30) shows a lower electrode formed on the back of the semiconductor substrate 21.

2 is a sectional view of the laser device viewed from the direction in which the beam is emitted so that the electrode pad 32 connected to the upper electrode 32 has a smaller width w of the electrode pad 32 than the diameter d of the laser column 41 , The electrode pad 32 is formed to be long in one direction so as to have anisotropy, and the direction is set to [110] or [1-10] in the crystal direction.

The difference in gain and oscillation wavelength between the [110] or [1-10] direction, which is the general polarization direction that the surface emitting laser can have due to the stresses in the strained multi-quantum well and the electrode pad, A difference is generated and the beam is emitted only in one direction of polarized light. Therefore, it has characteristics of stable polarization-controlled surface emitting laser.

A preferred embodiment of the present invention will be described in more detail with reference to FIGS. 1 and 2. FIG. (001) as a lower over-doped GaAs semiconductor substrate 21, a mirror layer (22) n-type doped semiconductor DBR layer is of Al _x Ga _{1 - x As / Al y Ga 1} -y As (0 <x, y < 1), and a lower cladding layer 23 made of Al _x Ga _{1 -x} As (0 < x < 1) is formed thereon. On the GaAs substrate 1 for generating a gain difference by laser gain and stress, a tense (strained) Al _x Ga _{1 -} is _{x as / in y Ga 1 -y} as (0 <x, y <1) the gain layer (24) consisting of a multi-quantum well is formed. On the gain layer 24, an upper cladding layer 25 made of Al _x Ga _{1 -x} As (0 < x < 1) is formed, and a p-type doped semiconductor DBR layer is formed of Al _x Ga _{1 - x} As / Al _y An upper first mirror layer 26 formed of Ga _{1 -y} As (0 < x, y < 1), and a p-type Al _x Ga _{1 -x} As (0 < x an upper that is formed with _{x as / Al y Ga 1 -y} as (0 <x, y <1) the _<1), the current confining layer 27 and the p-type doped semiconductor DBR layer is Al _x Ga ₁ consisting of 2 mirror layer 28 and the like.

Then, a part of the upper second mirror layer 28, the current confining layer 27, the upper first mirror layer 26, the upper clad layer 25, the gain layer 24 and the lower clad layer 23 is etched An upper electrode 31 for applying a current is formed on the upper part of the upper second mirror layer 28 of the laser column 41 and a current limiting layer 27 are oxidized to form an oxide film layer 29 for insulation. The formation of the laser column is formed by a dry etching method using Cl ₂ gas or a wet etching method using a phosphoric acid or a sulfuric acid solution. The oxide film layer 29 is formed by oxidizing a part of the current confining layer 27 using a wet oxidation method.

An electrode pad 32 connected to the upper electrode 31 for stressing the laser column 41 by current application and anisotropy is formed in an anisotropic manner after forming the dielectric insulating layer 30 for insulation between the electrodes Ti / Pt / Au or Ti / Au. The electrode pads 32 are formed such that the width w of the electrode pads 32 is smaller than the diameter d of the laser pillar 41 and the electrode pads are formed long in one direction so as to have anisotropy, ] Or [1-10]. The thickness of the electrode pad 32 is set to be not less than 2 탆 and not more than 6 탆 in order to impart stress.

The semiconductor DBR layers constituting the lower mirror layer 22 of the surface-emitting laser is an n-type doped with a lattice matched structures on _{GaAs Al x Ga 1 - x As} / Al y Ga 1 - y As (0 <x, y &Lt; 1) and the like, and the thickness of one period is half of the laser oscillation wavelength with the optical length (the thickness of the material x the refractive index at the oscillation wavelength) in order to fabricate alternately growing semiconductor thin film layers having different refractive indexes. First upper mirror layer 26, the upper second mirror layer 28 is p-type doped Al _x Ga _{1 -} is formed by _{x As / Al y Ga 1-} y As (0 <x, y <1) , etc. The semiconductor thin film layers having different refractive indexes are alternately grown and fabricated so that the thickness of one period is half the wavelength of the laser oscillation at the optical length (thickness of the material x refractive index at the oscillation wavelength). The total thickness of the lower clad layer 23, the gain layer 24, and the upper clad layer 25 is set to be an integral multiple of the oscillation wavelength half with the optical length.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it is to be understood that the embodiments are for the purpose of illustration only and are not to be construed as limitations. In addition, it will be understood by those of ordinary skill in the art that various embodiments are possible within the scope of the technical idea of the present invention.

21: semiconductor substrate
22: lower mirror layer
23: Lower clad layer
24: gain layer
25: upper cladding layer
26: upper first mirror layer
27: current limiting layer
28: upper second mirror layer
29: oxide layer
30: dielectric insulating layer
31: upper electrode
32: Electrode pad
33: Lower electrode
41: laser pillar
d: diameter of the laser column
w: width of electrode pad

Claims (5)

a lower cladding layer made of a semiconductor and a lower mirror layer composed of an n-type doped semiconductor DBR (distributed Bragg reflector) sequentially stacked on an n-type doped (001) semiconductor substrate; A gain layer formed on the lower clad layer; An upper clad layer made of a semiconductor on the gain layer; An upper first mirror layer composed of a p-type doped semiconductor DBR on the upper clad layer; A current confined layer made of a semiconductor on the upper first mirror layer; An upper second mirror layer composed of a p-type doped semiconductor DBR on the current confined layer; A laser column formed by etching the upper second mirror layer, the current confined layer, the upper first mirror layer, the upper clad layer, the gain layer, and a part of the lower clad layer; An oxide film layer formed by oxidizing a part of the current confined layer of the laser column; An upper electrode formed on the upper second mirror layer; A dielectric insulating layer formed of a dielectric thin film at a portion except the upper portion of the laser column; An electrode pad connected to the upper electrode; Wherein the polarization-controlled surface emitting laser element comprises:
Wherein the gain layer is formed of a strained multiple quantum well layer capable of changing a gain according to a stress and the electrode pad is formed to be long in one direction so as to have anisotropy in order to stress the laser column, To [110] or [1-10].
delete The method according to claim 1,
Wherein the width of the electrode pad is smaller than the diameter of the laser column.
A lower mirror layer in which an n-type doped semiconductor DBR layer is formed of Al _x Ga _{1 -x} As / Al _y Ga _{1 -y} As (0 < x, y < 1) on a doped GaAs semiconductor substrate of (001); A lower cladding layer made of Al _x Ga _{1 -x} As (0 < x < 1) on the lower mirror layer; An upper clad layer formed on the lower clad layer; An upper cladding layer made of Al _x Ga _{1 -x} As (0 < x < 1) on the gain layer; An upper first mirror layer formed on the upper cladding layer such that a p-type doped semiconductor DBR layer is formed of Al _x Ga _{1 -x} As / Al _y Ga _{1 -y} As (0 < x, y < 1); A current confined layer made of p-type Al _x Ga _{1 -x} As (0 < x < 1) on the upper first mirror layer; An upper second mirror layer on which a p-type doped semiconductor DBR layer is formed of Al _x Ga _{1 -x} As / Al _y Ga _{1 -y} As (0 < x, y < 1) on the current confining layer; A laser pillar formed by etching a part of the upper second mirror layer, the current confined layer, the upper first mirror layer, the upper clad layer, the gain layer, and the lower clad layer; An upper electrode formed on an upper portion of the upper second mirror layer of the laser column; An oxide film layer formed by oxidizing a part of the current confined layer of the laser column; A dielectric insulating layer formed of a dielectric thin film at a portion except the upper portion of the laser column; And an electrode pad connected to the upper electrode,
The gain layer may be strained Al _x Ga _{1 -x} As / In _y Ga _{1 -y} As (0 < x, y < 1) on a GaAs substrate for generating gain differences by laser gain and stress, Ti / Pt / Au or the like so that the direction of the electrode pad is [110] or [1-10] in the crystal direction, and the electrode pad is formed in a long direction so as to have anisotropy for stressing the laser column. Ti / Au. &Lt; / RTI &gt;
The method of claim 4,
Wherein the thickness of the electrode pad is in the range of 2 占 퐉 to 6 占 퐉.

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