KR100224881B1 - Vertical cavity surface emitting laser - Google Patents

Abstract

Surface light lasers are disclosed. This disclosed surface light laser comprises a substrate; A semiconductor material layer of one semiconductor type, an oxide layer is formed by alternately stacking a substrate, and a first insulating layer having a first contact surface and a first stacked surface thereon, and a first insulating layer on the first stacked surface. A first reflector layer having a first conductive layer formed by laminating two semiconductor material layers, such as a layer; A first electrode layer formed on the first contact surface; An active layer formed on the first conductive layer and generating laser light; A second conductive layer formed by alternately stacking two semiconductor material layers of a different semiconductor type from the first reflector layer on the active layer, and a second conductive layer having a second contact surface and a second stacked surface thereon; A second reflector layer having a second insulating layer formed by laminating a semiconductor type semiconductor material layer such as a conductive layer and an oxide layer; A second electrode layer formed on the second contact surface; A buffer layer formed between the first contact surface and the first electrode layer and / or between the second contact surface and the second electrode layer to prevent supplementation and oxidation of crystal defects; And a cap layer formed on the buffer layer to diffuse current injected through the first electrode layer and / or the second electrode layer.

Description

Surface cavity laser

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical cavity surface emitting laser (VCSEL), and more particularly, to a surface light laser whose structure is improved to facilitate current injection and to emit short wavelength light.

In general, unlike the edge-emitting laser, the surface light laser emits a Gaussian beam close to a circular shape in the stacking direction of the semiconductor material layer, so that an optical system for shape correction of the emitted light is unnecessary. And since the size can be made small, a plurality of surface light lasers can be integrated on one semiconductor wafer. Therefore, two-dimensional array is easy. Due to these advantages, the VCSEL can be widely applied in optical applications such as electronic calculators, acoustic imaging devices, laser printers, laser scanners, medical equipment, and communication fields.

1 shows a conventional surface light laser.

The surface light laser includes a substrate 12, a first reflector layer 13, an active layer 14, a second reflector layer 16 and an upper electrode layer 17 sequentially formed on the substrate 12, and the substrate. And a lower electrode layer 11 attached to the lower surface of the 12.

The substrate 12 is made of a semiconductor material containing n-type impurities, for example, n-type Ga` As. The first reflector layer 13 is formed on the substrate 12, and impurities of the same type as the substrate 12, for example, n-type Al_x `Ga_1-x` As ~ and Al`As ~ 20 to 30 layers are alternately stacked. The first reflector layer 13 has a high reflectance of approximately 99.9% or more as a whole, and transmits some of the light that is lasered in the active layer 14. The second reflector layer 16 is made of the same kind of impurity semiconductor material containing impurities of the opposite type to the first reflector layer 13. That is, p-type Al_x `Ga_1-x` As ~ and Al`As ~ are alternately stacked on the active layer 14. The second reflector layer 16 has a reflectance of approximately 99.6%, which is lower than that of the first reflector layer 13, so that the light emitted from the active layer 14 can be emitted. In addition, the first reflector layer 13 and the second reflector layer 16 respectively face the active layer 14 by a voltage applied through the lower electrode layer 11 and the upper electrode layer 17 connected to an external power source. Induce the flow of electrons and holes. The active layer 14 generates light by energy transition due to recombination of electrons and holes.

The upper electrode layer 17 is provided with a window 18 so that the outgoing light passing through the second reflector layer 16 can pass therethrough. The upper electrode layer 17 is made of a metal having high electrical conductivity to facilitate electrical transfer with an external power source. Power is applied between the upper electrode layer 17 and the lower electrode layer 11 so that a current flows into the surface light laser.

In order to improve the light output emitted from the window 18, the current limiting layer 15 is formed by ion implantation or proton injection into the first reflector layer 13 and the active layer 14 except the bottom of the window 18. ) Is formed. The current limiting layer 15 restricts the flow of current in the surface light laser to improve the output of light that is lasered in the active layer 14 and exits the window 18.

Here, the oscillation wavelength of the surface light laser is determined by the wavelength due to the energy band gap of the active layer and the thickness of the resonator composed of the second reflector layer 16. The oscillation wavelength becomes shorter as the energy band gap increases. In order to increase the recording density of the recording medium, short wavelength of the used light source is required, and in order to oscillate the short wavelength laser efficiently at room temperature, it is important to form a reflector layer having a high reflectance and a wide wavelength band. The reflectance and the wavelength band are proportional to the refractive index difference between the two material layers forming the reflector layer.

Therefore, it is necessary to increase the refractive index difference between Al_x'Ga_1-x'As and Al'As as a condition for generating a laser of short wavelength, for example, a wavelength region of 650 nm. To this end, if the refractive index difference is increased by changing the composition ratio of Al_x `Ga_1-x` As ~ with 20 to 30 pairs of the two material layers stacked, a thermal problem occurs due to the increase of the resistance.

The present invention has been made in view of the above problems, and increases the refractive index difference between the two material layers of each reflector layer, and reduces the number of stacked layers of the two material layers so that short wavelength light can be generated and emitted. It is an object of the present invention to provide a surface light laser.

1 is a cross-sectional view showing a schematic configuration of a conventional surface light laser.

2 is a cross-sectional view showing a schematic configuration of a surface light laser according to the present invention.

Explanation of symbols for the main parts of the drawings

20 ... substrate 30 ... first reflector layer 31 ... first insulating layer

35 first conductive layer 36 first contact surface 37 laminated surface

38 first buffer layer 39 first cap layer 40 active layer

50 ... current limiting layer 60 ... second reflector layer 61 ... second insulating layer

65 second conductive layer 66 second contact surface 67 second laminated surface

68. Second buffer layer 69 ... Second cap layer 70 ... First electrode layer

80 second electrode layer

The present invention, in order to achieve the object as described above; A semiconductor material layer of one semiconductor type and an oxide layer are alternately stacked on the substrate, and a first insulating layer having a first contact surface and a first stacked surface thereon and the first stacked surface on the substrate. A first reflector layer having a first conductive layer formed by laminating two semiconductor material layers of the same semiconductor type as the first insulating layer; A first electrode layer formed on the first contact surface; An active layer formed on the first conductive layer and generating laser light; A second conductive layer formed by alternately stacking two semiconductor material layers of a different semiconductor type from the first reflector layer and having a second contact surface and a second stacked surface on the active layer, and on the second laminated surface A second reflector layer having a second insulating layer formed by laminating a semiconductor type semiconductor material layer such as the second conductive layer and an oxide layer; In the surface light laser including; the second electrode layer formed on the second contact surface,

A buffer layer formed between the first contact surface and the first electrode layer and / or between the second contact surface and the second electrode layer to prevent supplementation and oxidation of crystal defects; And a cap layer formed on the buffer layer to diffuse current injected through the first electrode layer and / or the second electrode layer.

Hereinafter, a surface light laser according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view of a surface light laser according to an embodiment of the present invention. As shown, the surface light laser is positioned between the substrate 20, the first and second reflector layers 30 and 60, and the first and second reflector layers 30 and 60, and the laser light. And an active layer 40 for generating a first electrode, and first and second electrode layers 70 and 80 for supplying current to the first and second reflector layers 30 and 60, respectively.

The substrate 20 uses a semiconductor material containing impurities, such as Ga`As ~ doped with n-type.

The first reflector layer 30 includes a first insulating layer 31 and a first conductive layer 35 sequentially stacked on the substrate 20. The first insulating layer 31 is formed by alternately stacking a semiconductor material of the same type as the substrate 20 and an oxide material. That is, the first insulating layer 31 includes Al_x `Ga_1-x` As ~ and Al_2 O_3 as alternating semiconductor material layers 32 and oxide layers 33, respectively. Here, the Al_2 O_3 oxide layer 33 is formed by oxidation of AlAs, and its refractive index drops to about half or more as compared with the case of employing a conventional AlAs semiconductor material. Therefore, when the Al_x `Ga_1-x` As ~ and Al_2 O_3 are alternately stacked as part of the first reflector layer 30, a high reflectance of about 99.9% or more can be obtained despite the drastically reduced pair number. have. The first insulating layer 31 has a first stacked surface 37 on which the first conductive layer 35, the active layer 40, and the second reflector layer 60 are stacked. The first contact surface 36 is positioned around the first stacked surface 37 and on which the first electrode layer 70 is formed. The first contact surface 36 is formed by substantially removing the peripheral portion of the first conductive layer 35 through an etching process, for example, a dry etching process. Therefore, the first contact surface 36 is mechanically damaged during the etching process. In addition, since the oxidation progresses on the surface of the first contact surface 36 for a time delayed until the formation of the first electrode layer 70, the contact resistance is greatly decreased. In view of such points, a first buffer layer 38 and a first cap layer 39 are formed between the first contact surface 36 and the first electrode layer 70. The first buffer layer 38 is formed on the first contact surface 36 by a second epitaxial growth method, and serves to buffer and oxidize a mechanical defect of the first contact surface 36. Layer to prevent. The first cap layer 39 in the first buffer layer 38 is in a position on, the current injected through the first electrode to be easily diffused layer, for example, ~10 ^ 19 / cm ³ or more higher doping level Doped. Therefore, mechanical damage and oxidation of the first contact surface can be prevented.

The first conductive layer 35 is formed by alternately stacking two semiconductor materials having different refractive indices, eg, Al_x Ga_1-x As and AlAs, on the first insulating layer 31 and the first stacked surface 37. The first conductive layer 35 is a layer provided to compensate for the fact that the first insulating layer 31 causes a large difference in refractive index to maintain a high reflectance, while being electrically insulated so that the electrode layer is not energized. The first conductive layer 35 is supplied with current through the current injected through the first electrode layer 70. The first insulating layer in which the first electrode layer 70 is formed such that a current is directed to the active layer 40 via the first conductive layer 35 by the voltage applied to the first electrode layer 70 ( 31 is an Al_x Ga_1-x As layer through which electricity flows.

The active layer 40 is stacked on the first conductive layer 35 of the first reflector layer 30. The active layer 40 generates light by energy transition by recombination of electrons and holes, and has a single or multiple quantum-well structure or a superlattice structure.

The second reflector layer 60 is stacked on the active layer 40 and includes a second conductive layer 65 and a second insulating layer 61. The second reflector layer 60 is formed of a semiconductor material layer of a different type from the first reflector layer 30, for example, a p-type Al_x Ga_1-x As layer and an AlAs layer. The second conductive layer 65 is a layer formed on the active layer 40 and has the same structure as the first conductive layer 35. That is, the Al_x Ga_1-x As layer and the AlAs layer are formed by alternately stacking a plurality of pairs, and the power applied to the second electrode layer 80 described later is energized to the active layer 40. The second conductive layer 65 has a second contact surface 66 on which the second electrode layer 80 is coupled and a second stacked surface 67 on which the second insulating layer 61 is stacked. Have The second electrode layer 80 is stacked on the second contact surface 66. In this case, since the second contact surface 66 is formed by an etching process similarly to the first contact surface 66, mechanical damage by etching is caused. In addition, there is a problem of being oxidized by a time delayed until the deposition of the second electrode layer 80. Therefore, after forming the second buffer layer 68 and the second cap layer 69 on the second contact surface 66, the second electrode layer 80 is deposited. Since each of the second buffer layer 68 and the second cap layer 69 is substantially the same as each of the first buffer layer 38 and the second cap layer, a detailed description thereof will be omitted.

The second insulating layer 61 is a layer provided to reduce the number of pairs of the second reflector layer 60 and is substantially made of the same semiconductor material as the first insulating layer 31, and thus a detailed description thereof will be omitted. do.

Here, the first reflector layer 30 is described as an n-type semiconductor material, and the second reflector layer 60 is described as an example of a p-type semiconductor material, but may be changed to semiconductor materials of opposite types to each other.

As a means for preventing the deterioration of the mode characteristic of the laser beam transmitted through the second reflector layer 60 by the current applied to each of the first electrode layer 70 and the second electrode layer 80 is supplied through the shortest path. It is preferable to further include a current limiting layer (50).

The current limiting layer 50 may be used for ion implantation or proton implantation in a portion of the active layer 40 except for the center portion and a portion of the first and second conductive layers 65 facing the active layer 40. Is formed by.

In the surface light laser provided as described above, first and second insulating layers 31 and 61 in which two material layers having a large refractive index difference are alternately stacked on each of the first reflector layer 30 and the second reflector layer 60. Since the number of pairs for obtaining high reflectance can be greatly reduced, the increase in resistance and thermal problems caused by the stacked pairs can be solved. In addition, since the laser light is generated in the center portion of the active layer 40 by the formation of the current limiting layer 50, it is possible to obtain a laser light with improved mode characteristics.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible therefrom.

Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the claims.

Claims (5)

A substrate; A semiconductor material layer of one semiconductor type and an oxide layer are alternately stacked on the substrate, and a first insulating layer having a first contact surface and a first stacked surface thereon and the first stacked surface on the substrate. A first reflector layer having a first conductive layer formed by laminating two semiconductor material layers of the same semiconductor type as the first insulating layer; A first electrode layer formed on the first contact surface; An active layer formed on the first conductive layer and generating laser light; A second conductive layer formed by alternately stacking two semiconductor material layers of a different semiconductor type from the first reflector layer and having a second contact surface and a second stacked surface on the active layer, and on the second laminated surface A second reflector layer having a second insulating layer formed by laminating a semiconductor type semiconductor material layer such as the second conductive layer and an oxide layer; In the surface light laser including; the second electrode layer formed on the second contact surface, A buffer layer formed between the first contact surface and the first electrode layer and / or between the second contact surface and the second electrode layer to prevent supplementation and oxidation of crystal defects; And a cap layer formed on the buffer layer to diffuse current injected through the first electrode layer and / or the second electrode layer. The method of claim 1, And the capping layer is doped with a doping level of approximately ~ 10 ^ 19 / cm ³ or more. The method according to claim 1 or 2, And a current limiting layer formed by ion implantation or proton implantation in a partial region except the central portion of the active layer and a partial region facing the active layer of the first and second conductive layers. The method according to claim 1 or 2, The first insulating layer includes Al_x Ga_1-x As and Al_2 O_3 as alternating semiconductor material layers and oxide layers, respectively, The first conductive layer is a surface light laser, characterized in that each of the two semiconductor material layers stacked alternately comprising Al_x Ga_1-x As and Al As. The method according to claim 1 or 2, The second conductive layer is two semiconductor material layers stacked alternately with Al_x Ga_1-x As and Al As, respectively. And the second insulating layer comprises Al_x Ga_1-x As and Al_2 O_3 as alternating semiconductor material layers and oxide layers, respectively.