KR101251042B1 - single-mode high-speed vertical-cavity surface-emitting laser - Google Patents

Abstract

Surface emitting lasers are used as light sources for short / medium distance optical wiring and optical communication, and the need for high speed modulated surface emitting lasers is increasing for low power consumption and large capacity short / medium distance as communication light sources. In particular, as the demand for high-capacity connections in the short / medium range increases rapidly as high-definition video, such as high-definition television, single-mode and high-speed high-modulation characteristics of 10 Gbps or more can increase the signal transmission distance using optical fibers. Required. The present invention relates to a single-mode high-speed modulation surface emission laser, and to minimize the capacitor between the electrode pads, consisting of two current and mode limited aperture for reducing the capacitor and mode control of the device is possible to enable single-mode oscillation and high-speed modulation It is an element of a single mode high speed modulated surface emitting laser.

Description

Single-mode high-speed vertical-cavity surface-emitting laser device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single mode high speed modulated surface emitting semiconductor laser device, and in particular, a surface emitting laser characterized by two current and mode limiting aperture structures for minimizing capacitors between electrode pads and reducing capacitors and mode control of the device. It relates to an element.

Surface-emitting lasers are used as light sources for short / medium distance communications, and their applications are rapidly increasing in optical connections, optical sensors, and optical communications. In particular, the high fiber-coupling efficiency of surface-emitting lasers, low unit cost by wafer-based fabrication process, low mounting cost, low electrical power consumption, and two-dimensional array Due to the characteristics of the array, it is expected to quickly establish itself as a light source for next generation optical communication and signal processing. In particular, in recent years, the demand for high-capacity connections in short / medium distances is rapidly increasing with the increase in high-definition video such as high-definition television. There is a need for a light source with properties. Accordingly, in order to improve the characteristics of transmission distance and all-optical conversion efficiency, it is based on the single-mode characteristic of low loss in optical fiber for signal transmission of surface emitting laser and no loss by dispersion for application as transmission device for medium and long distance. There is a need for the development of a high speed modulation surface emitting laser device structure.

In order to obtain the single mode and high speed modulation characteristics of the surface emitting laser, the coupling efficiency between the carrier distribution due to the current flow in the desired area and the fundamental transverse mode of the light with Gaussian intensity distribution formed inside during the laser oscillation are increased. In addition to the characteristics, there is a need for a low impedance characteristic that can reduce the loss during high-speed modulation by the capacitor between the electrode and the electrode pad for current injection. Therefore, there is a need for a structure between the electrodes to reduce the capacitance of the device as well as a structure for limiting the current and mode of the device.

Conventional surface-emitting laser structures and fabrication methods involve oxidizing a portion of the AlGaAs layer directly above the active layer by wet etching to implant ions such as protons and oxide-confined structures that allow current to flow through only unoxidized regions. There are ion-implanted structures that allow the current to flow to the desired area by acting as an insulating layer, air-gap structures that control the flow of current by etching some areas, and regrowth structures that control the current flow through regrowth.

Oxide-confined method has the advantage of effectively controlling the flow of current, but it is difficult to apply to various wavelength bands because it can be effectively applied only when using AlGaAs material of GaAs substrate.

In addition, the ion-implanted method has characteristics such as an increase in resistance due to ion-implantation, and it is difficult to accurately adjust the current aperture size.

The air-gap method can be used as a surface emitting laser structure of various wavelength bands because it can be applied to various materials that can be easily etched, but it has disadvantages such as leakage current generation through air-gap due to voltage increase.

In addition, the regrowth method is effective in controlling current flow, but has a disadvantage in that the structure is complicated and wafer growth must be performed more than once. In addition, such a structure is limited to current limiting and does not have a structure for current limiting and mode limiting.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to have a single mode and a low capacitor characteristic through two current and mode limit apertures, and to form a capacitor between electrode pads through etching to a semi-insulated substrate. It is to provide a single-mode high-speed modulation surface emission laser device characterized in that to minimize.

According to an aspect of the present invention, there is provided a high-efficiency, high-speed modulation surface emitting laser device comprising: a lower mirror layer composed of a semiconductor DBR (distributed Bragg reflector) sequentially stacked on a semi-insulated semiconductor substrate, and a lower contact layer composed of an n-type semiconductor; An active layer formed of a quantum well layer on the lower contact layer; A current injection layer composed of a semiconductor on the active layer; A limiting layer configured as a semiconductor on the current injection layer for limiting current; An upper contact layer composed of a semiconductor doped on the limiting layer; An upper mirror layer composed of a semiconductor or dielectric DBR sequentially stacked on the upper contact layer; It is made, including.

In the present invention, after etching a portion of the upper mirror layer and the upper contact layer, a part of the limiting layer is removed, and the insulating dielectric layer having a low refractive index is filled to form an insulating 2 layer for limiting the current and the mode. After etching some regions, a part of the active layer is removed and filled with an insulating dielectric layer having a low refractive index to form an insulating layer for current and mode limitation to optimize the coupling between the distribution of current and the resonant mode of internal light, Has a structure.

In addition, the upper electrode is connected to the upper contact layer from which a part of the upper mirror layer is removed, and the upper mirror layer, the upper contact layer, the limiting layer, the current injection layer, and the active layer are partially removed, and the lower electrode is connected to the lower contact layer. Allow current to be injected. And a portion of the upper mirror layer, the upper contact layer, the limiting layer, the current injection layer, the active layer, the lower contact layer, the lower mirror layer and the semi-insulating semiconductor substrate for low capacitance between the electrodes, and a dielectric for insulation between the electrodes. After forming the insulating layer on the portion except the upper mirror layer and the lower electrode of the region where the light is emitted, the upper electrode pad is connected to the upper electrode, and the lower electrode pad is connected to the lower electrode to form an electrode pad It has a structure of low impedance in the liver. Therefore, there is oscillation characteristic of low impedance single mode high speed modulated surface emitting laser.

The single-mode high-efficiency high-speed modulation surface emitting laser of the present invention minimizes the capacitor between the electrode pads, and consists of two current and mode limited apertures for reducing the capacitor and mode control of the device. It has an effect that can be utilized in the light source device for short / medium distance.

1 is a cross-sectional view showing a single mode high speed modulated surface emitting laser device of the present invention;
2 is a flow chart illustrating the current flow by two currents and the mode-limited aperture of the single mode high speed modulated surface emitting laser according to the present invention, and the carrier distribution and the intensity distribution of the emission beam.
3 is a diagram showing the impedance characteristics of the single-mode high-speed modulation surface emission laser of the present invention.

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 cross-sectional view of a single-mode high-speed modulation surface emitting laser device according to an embodiment of the present invention, 21 is a semi-insulating semiconductor substrate, 22 is a lower mirror layer composed of a semiconductor DBR, 23 is a bottom contact composed of n-type semiconductor Layer, 24 is an active layer consisting of multilayered quantum wells for gain, 25 is a current injection layer consisting of semiconductors, 26 is a limiting layer for current limiting consisting of semiconductors, 27 is an upper contact layer consisting of semiconductors, 28 is a semiconductor or dielectric An upper mirror layer composed of a DBR, 29 is an insulating layer 1 filled and removed a part of the active layer, 30 is an insulating layer 2 partially filled and removed a limiting layer, 31 is a lower electrode formed for current injection on the lower contact layer, 32 Denotes an upper electrode formed for current injection on the upper contact layer, and 33 denotes a dielectric insulating layer for insulation between the electrodes. 34 and 35 represent upper electrode pads and lower electrode pads connected to the upper electrode and the lower electrode, respectively.

2 illustrates a semi-insulating semiconductor substrate 21, a lower mirror layer 22, a lower contact layer 23, an active layer 24, a current injection layer 25, a limiting layer 26, and an upper contact layer in FIG. 1. 27, two of the single mode high-speed modulation surface emitting lasers shown by the upper mirror layer 28, the insulating one layer 29, the insulating two layer 30, the lower electrode 31, and the upper electrode 32 are shown. A cross-sectional view showing the current flow by the current and mode limited aperture, the carrier distribution and the intensity distribution of the emission beam.

A current is applied between the upper electrode 32 and the lower electrode 31 to drive a single mode high speed modulated surface emitting laser device, wherein the current injected into the upper electrode 32 is limited through the upper contact layer 27. In this case, since the current does not flow to the insulating second layer 30, current is injected through the aperture of the limiting layer 26 without the insulating second layer 30. The current through the limiting layer 26 is injected into the active layer 24 while the current spreads through the current injection layer 25, and no current flows into the insulating layer 1 of the active layer 24. Therefore, current is injected as indicated by arrow 43.

By the two current limiting apertures formed by the insulating 2 layer 30 and the insulating 1 layer 29, the current flow arrow 43 and the distribution of the carriers 44 have a basic transverse mode having a Gaussian light intensity distribution. Keep the same distribution. At this time, the current flow aperture formed by the insulating second layer 30 is formed to be smaller than the current flow aperture formed by the insulating first layer 29 so that the spread of the current forms a distribution by diffusion. In addition, the refractive indexes of the formed materials of the insulating 2 layer 30 and the insulating 1 layer 29 are smaller than those of the limiting layer 26 and the active layer 24 so that the optical mode is limited so that the light is emitted (41). The coupling between the single transverse mode of the Gaussian intensity distribution 42 and the carrier distribution is optimized to have a monomodal emission characteristic.

3 illustrates a semi-insulating semiconductor substrate 21, a lower mirror layer 22, a lower contact layer 23, an active layer 24, a current injection layer 25, a limiting layer 26, and an upper contact layer in FIG. 1. 27) the upper mirror layer 28, the insulating 1 layer 29, the insulating 2 layer 30, the lower electrode 31, the upper electrode 32, the dielectric insulating layer 33, the upper electrode pad 34 Fig. 1 is a cross-sectional view showing the impedance characteristics of a single mode high speed modulated surface emitting laser shown.

The impedance of the device is configured as follows. That is, the series resistance Rt for applying current to the active layer 24 from the upper contact layer 27 and the series resistance for applying current to the active layer 24 through the lower contact layer 27 from the lower electrode 31 ( Rb2), series resistance (Rb2), limiting layer (26), current injection layer (25), series resistance (Rj) and electrode in active layer (24) for applying current from lower contact layer (23) to active layer (24) The capacitance between the capacitor Cj in the active layer 24 and the capacitance Ci1 in the first insulating layer 29, the capacitance Ci2 in the second insulating layer 30, and the upper electrode pad 34 in the capacitance between them. And the capacitance Cp between the lower electrode 31. The main factor in determining the modulation rate is the response rate due to the high speed modulation signal applied by the impedance between the electrodes. That is, in order to reduce the loss due to the impedance and the reflected wave, it is necessary to reduce the series resistances (Rj, Rt, Rb1, Rb2), and in particular, reduce the capacitances (Cj, Ci1, Ci2, Cp). Among the capacitors, the largest contributions are Cp of the upper electrode pad 34 and Ci1 and Ci2 due to the insulating layer of the device. This single-mode high-speed modulation surface emitting laser has a top electrode pad ( 34) and the lower electrode 31 and the lower electrode pad 35 is configured to be connected to have a minimized capacitor (Cp) characteristics, and the capacitors Ci1 and Ci2 of the two insulator 1 and insulator 2 layers are connected in series Characterized in that it is configured to reduce the capacitor (Ci = (Ci1xCi2) / (Ci1 + Ci2)).

The preferred embodiment of the present invention will be described in more detail with reference to FIG. 1. As a lower mirror layer 22 on the semi-insulated InP semiconductor substrate 21, the semiconductor DBR layer is In _y (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w ) _1-z As s (0 < x, y, z, w < 1) or InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1), etc., on which the lower electrode The lower contact layer 23 for contact is composed of n-type InP, and In _y (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w ) is placed on InP for laser gain thereon. ) _1-z As s (0 < x, y, z, w < 1) or InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1) into a multi-quantum well layer The configured active layer 24 is formed. On the active layer 24 a current injection layer 25 consisting of doped InP for current application, In _y (Al _x Ga _1-x ) _1-y As (0 < x, The confinement layer 26 composed of y, z, w < 1, the InP doped with the upper contact layer 27 for upper electrode contact, and the like. The upper mirror layer 28 has a semiconductor or dielectric DBR layer of In _y (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w ) _1-z As s (0 < x , y, z, w < 1) or InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1) or TiO _x / SIO _x or Si / SiO _x , Si / TiO _{and x} . The limiting layer 26 is partially removed for current and mode limitation, and the removed part is filled with the insulating second layer 30 such as AlO _x or AlN _x . The active layer 24 is partially removed for current and mode limitation, and the removed portion is filled with an insulating layer 1 such as AlO _x or AlN _x . The upper electrode 32 is formed by depositing or removing a metal electrode on the upper contact layer 27 after partially etching or removing the upper mirror layer 28, and the lower electrode 31 is formed on the upper mirror layer 28 and upper contact. A portion of the layer 27, the limiting layer 26, the current injection layer 25, and the active layer 24 is removed and then formed by depositing a metal electrode on the lower contact layer 23. The upper mirror layer 28, the upper contact layer 27, the limiting layer 26, the current injection layer 25, the active layer 24, for low capacitance between the upper electrode pad 34 and the lower electrode 30, The lower contact layer 23, the lower mirror layer 22, and the semi-insulating semiconductor substrate 21 are partially etched to connect the upper electrode pad 34 and the upper electrode 32 to form the lower electrode 31 through the semi-insulating substrate. ) And impedance are formed.

Therefore, the current flows through the upper electrode pad 34-the upper electrode 32-the upper contact layer 27-the limiting layer 26-the current injection layer 25-the active layer 24-the lower contact layer 23-the lower part. The distribution of the current and the carrier and the intensity distribution of the internal resonant light are induced by the electrode 30, whereby the insulating 2 layer 30 and the insulating 1 layer 29 form the current and mode limiting aperture of the limiting layer 26. Coupling is made effectively by controlling the characteristics, and has a single mode characteristic, and the capacitor characteristics include the upper electrode pad 34, the semi-insulating semiconductor substrate 21, the lower mirror layer 22, the lower contact layer 23, and the lower electrode 30. Low Cp by the bottom electrode pad 35 and low Ci (Ci = (Ci1xCi2) / (Ci1 + Ci2)) characteristics through the series connection of the insulating 1 layer 29 and the insulating 2 layer 30 do.

The semiconductor DBR layer constituting the lower mirror layer 22 of the surface emitting laser has a lattice matched structure to InP (In _x (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w )). Semiconductors with different refractive indices, such as _1-z As s (0 < x, y, z, w < 1) or InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1) The thin film layers are alternately grown and fabricated so that the thickness of one cycle is half the laser oscillation wavelength at the optical length (refractive index in the thickness x oscillation wavelength of the material). The upper mirror layer 28 has a semiconductor or dielectric DBR layer of In _y (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w ) _1-z As s (0 < x, y, z, w < 1) or InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1) or TiO _x / SIO _x or Si / SiO _x , Si / TiO _x, etc. It is formed so that the semiconductor thin film layers having different refractive indices are alternately grown and manufactured so that the thickness of one cycle is half the laser oscillation wavelength at the optical length (thickness x refractive index of the oscillation wavelength). The active layer 24 is configured such that the total thickness is an integer multiple of half the oscillation wavelength in optical length.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

21: semi-insulating substrate
22: bottom mirror layer composed of semiconductor DBR
23: bottom contact layer composed of n-type semiconductor
24: active region
25: current injection layer composed of semiconductor
26: limited layer consisting of a semiconductor
27: top contact layer composed of semiconductor
28: top mirror layer
29: 1 layer of insulation for current and mode limitation
30: 2 layers of insulation for current and mode limitation
31: lower electrode
32: upper electrode
33: dielectric insulation layer for insulation between electrodes
34: upper electrode pad
35: lower electrode pad
41: Indication indicating the direction of light emission
42: display indicating the intensity distribution of light
43: display indicating the flow of current
44: display showing the distribution of carriers by the current
Rt: Series resistor for active layer current injection in upper contact layer
Rj: series resistor for current injection in active layer
Rb1: series resistance for active layer current injection in the bottom contact layer
Rb2: series resistance for current injection of the bottom contact layer and active layer in the bottom electrode
Cj: capacitance in the active layer
Ci1: Capacitance by 1 layer of insulation
Ci2: Capacitance by 2 layers of insulation
Cp: capacitance between electrodes by electrode pad

Claims (9)

In the surface emitting laser device,
A lower mirror layer composed of a semiconductor distributed Bragg reflector (DBR) sequentially stacked on a semi-insulating semiconductor substrate and a lower contact layer composed of an n-type semiconductor; An active layer formed of a quantum well layer on the lower contact layer; A current injection layer composed of a semiconductor on the active layer; A limiting layer composed of a semiconductor on the current injection layer; An upper contact layer formed of a semiconductor on the limit layer; An upper mirror layer composed of a semiconductor or dielectric DBR sequentially stacked on the upper contact layer; / RTI &gt;
An insulating two layer for limiting current and mode by etching portions of the upper mirror layer and the upper contact layer, removing portions of the limiting layer, and filling the gaps; An insulating one layer for limiting current and mode by etching portions of the upper mirror layer, the upper contact layer, the limiting layer, and the current injection layer, removing a portion of the active layer, and filling the gaps; An upper electrode which removes a part of the upper mirror layer and is connected on an upper contact layer; A lower electrode connected to the lower contact layer by partially removing the upper mirror layer, the upper contact layer, the limiting layer, the current injection layer, and the active layer; The upper mirror layer, the upper contact layer, the limiting layer, the current injection layer, the active layer, the lower contact layer, the lower mirror layer and a portion of the semi-insulating semiconductor substrate are removed and formed on the semi-insulating semiconductor substrate, the lower contact layer, and the upper contact layer. One dielectric insulating layer; And forming a top electrode pad and a bottom electrode pad connecting the top electrode and the bottom electrode, respectively, to perform high-speed modulation of high-speed capacitor characteristics between the electrodes through a semi-insulating semiconductor substrate. Claim 1
And the current flow aperture formed by the insulation two layer is smaller than the current flow aperture formed by the insulation one layer so that the spread of the current is distributed by diffusion. Claim 1
And the optical mode is limited such that the refractive indices of the insulating layer 2 and the insulating layer 1 are smaller than that of the limiting layer and the active layer. In the surface emitting laser device,
In _y (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w ) _1-z As s (0 < x, y, z, w < 1) or a lower mirror layer composed of a semiconductor DBR layer of InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1); A lower contact layer composed of n-type InP on the lower mirror layer; An active layer comprising a quantum well layer on InP on the lower contact layer; A current injection layer composed of a semiconductor doped on the active layer; A limiting layer composed of a semiconductor doped on the current injection layer; An upper contact layer composed of a semiconductor doped on the limiting layer; In _y (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w ) _1-z As s (0 < x, y, z, w < 1) on the upper contact layer or InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1) semiconductor DBR layer or TiO _x / SIO _x or Si / SiO _x , Si / TiO _x dielectric DBR layer An upper mirror layer; / RTI &gt;
Current and mode limited apertures are removed by removing the partial region of the limiting layer and the insulating layer 2 formed of a material having a lower refractive index than the limiting layer and the insulating first layer formed of a material having a lower refractive index than the active layer. Construct;
An upper electrode formed by partially etching the upper mirror layer and depositing a metal electrode on the upper contact layer; A lower electrode formed by depositing a metal electrode on the lower contact layer after removing a portion of the upper mirror layer, the upper contact layer, the current injection layer, and the active layer; The upper mirror layer, the upper contact layer, the limiting layer, the current injection layer, the active layer, the lower contact layer, the lower mirror layer and a portion of the semi-insulating semiconductor substrate are removed and formed on the semi-insulating semiconductor substrate, the lower contact layer, and the upper contact layer. One dielectric insulating layer; And forming a top electrode pad and a bottom electrode pad connecting the top electrode and the bottom electrode, respectively, to perform high-speed modulation of low capacitor characteristics between the electrodes through a semi-insulating semiconductor substrate. The method of claim 4,
The current injection layer is a single-mode high-speed modulation surface emission laser device, characterized in that composed of p-type InP. The method of claim 4,
The limiting layer is a p-type In _y (Al _x Ga _{1- x} ) _{1- y} As (0 < x, y < 1), characterized in that the single-mode high-speed modulation surface emitting laser device. The method of claim 4,
And the insulating 1 layer and the insulating 2 layer are made of a material comprising AlO _x or AlN _x . The method of claim 4,
The upper contact layer is a single-mode high-speed modulation surface emission laser device, characterized in that composed of n-type InP. The method of claim 4,
The active layer is In _y (Al _x Ga _1-x ) _1-y As / In _z (Al _w Ga _1-w ) _1-z As s (0 < x, y, z, w < 1) or InP / In _y (Al _x Ga _1-x ) _1-y As (0 < x, y < 1) A single mode high speed modulated surface emitting laser device, characterized in that composed of.

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