KR100224882B1 - Vertical cavity surface emitting laser and manufacturing method thereof - Google Patents

Abstract

A method for producing a surface light laser is disclosed.

The disclosed surface light laser manufacturing method includes the steps of preparing a substrate and alternately stacking semiconductor material layers to form a first reflector layer; Etching a portion of the upper surface of the first reflector layer; Oxidizing one semiconductor material layer forming an unetched layer of the first reflector layer to form an oxide layer; Depositing a first electrode layer on the first reflector layer; Forming an active layer on the first reflector layer; Alternately stacking two semiconductor material layers on the active layer to form a second reflector layer; Etching a portion of the upper surface of the second reflector layer to form a contact surface; Oxidizing the etched and partially removed layer of the second reflector layer; And depositing and forming a second electrode layer on the contact surface of the second reflector layer.

Description

Surface cavity laser and manufacturing method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a vertical cavity surface emitting laser (VCSEL), and more particularly, to a method for manufacturing a surface light laser having an improved structure for easily injecting current and emitting short wavelength light. .

In general, since the surface light laser emits a Gaussian beam close to a circular shape in the stacking direction of the semiconductor material layer unlike the edge emitting laser, 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, Ga`As ~ or the like doped with n-type impurities. 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 ~ having different compositions alternately. 20 to 30 layers are laminated. 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. In other words, p-type Al_x `Ga_1-x` As ~ having different compositions 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 energy band gap determined by the light emitting material of the active layer 14. That is, as the energy band gap increases, the oscillation wavelength is shortened. 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 therein, there is a limit to the increase and the increase in the resistance Thermal problems occur.

Accordingly, the present invention has been made to overcome the above-mentioned problems, and it is possible to increase the refractive index difference between the two material layers of each of the reflector layers, and to reduce the number of layers of the two material layers significantly. It is another object to provide a manufacturing method.

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

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

Figures 3a to 3i is a process diagram shown to explain the manufacturing method of the 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 36,66 Contact surface 37,67 Laminated surface

40 ... active layer 50 ... current limiting layer 60 ... second reflector layer

61 ... second insulating layer 65 ... second conductive layer 70 ... first electrode layer

80 second electrode layer

In order to achieve the above object, the method for manufacturing a surface light laser according to the present invention comprises the steps of preparing a substrate and alternately stacking two semiconductor materials having different refractive indices of the same semiconductor type on the prepared substrate to form a first reflector layer. Wow; Etching a portion of the upper surface of the first reflector layer to a predetermined depth to form an opening surface; Oxidizing one semiconductor material layer among the unetched semiconductor materials of the first reflector layer to form an oxide layer; Depositing and forming a first electrode layer on the opening surface; Forming an active layer on the first reflector layer; Forming a second reflector layer by alternately stacking two semiconductor materials having different refractive indices of the first reflector layer and another semiconductor type on the active layer; Etching a portion of the upper surface of the second reflector layer to a predetermined depth to form an opening surface; Forming an oxide layer by oxidizing one layer of the semiconductor material which is partially etched away from the second reflector layer; And depositing and forming a second electrode layer on the opening surface of the second reflector layer.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention;

2 is a cross-sectional view of a surface light laser according to the present invention. As shown, the laser beam is positioned between the substrate 20, the pair of first and second reflector layers 30 and 60, and the first and second reflector layers 30 and 60. The active layer 40 to be generated and the 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 is made of a semiconductor material containing an impurity, for example, Ga`As ~ or the like 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 stacking surface 37 on which the active layer 40 and the second reflector layer 60 are stacked, and is positioned around the stacking surface 37 on the upper surface thereof. It has a contact surface 36 on which one electrode layer 70 is formed. The first conductive layer 35 is formed by alternately stacking two semiconductor materials having different refractive indices, for example, Al_x Ga_1-x As and AlAs, on the stack surface 37 of the first insulating layer 31. 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 electrode layer 70 is formed on the contact surface 36 on the first insulating layer 31 to supply current to the first conductive layer 35. 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 ( The uppermost layer of 31) is preferably an Al_x Ga_1-x As layer through which electricity flows, or an AlAs layer.

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 different from the first reflector layer 30, for example, a p-type Al_x Ga_1-x As layer, an AlAs layer, and an Al_2 O_3 layer. The second conductive layer 65 is a layer formed on the active layer 40 in 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 to be described later is energized to the active layer 40. The second conductive layer 65 has a contact surface 66 on which the second electrode layer 80 is coupled and a stacking surface 67 on which the second insulating layer 61 is stacked. The second electrode layer 80 is stacked on the contact surface 66. 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 ion implanted into a portion of the active layer 40 except for a central portion thereof and a portion of the first and second conductive layers 35 and 65 facing the active layer 40. Formed by proton injection.

3A to 3I are views for explaining a method of manufacturing a surface light laser according to the present invention.

In the method of manufacturing a surface light laser, first, as shown in FIG. 3A, a substrate 20 is prepared, and two semiconductor materials having different refractive indices, for example, an Al_x Ga_1-x As layer and an AlAs layer, are prepared on the prepared substrate 20. Are alternately stacked to form a first reflector layer (30). At this time, the substrate 20 is preferably made of a semiconductor material, the substrate 20 and the first reflector layer 30 is an impurity semiconductor material of the same type. Thereafter, as shown in FIG. 3B, a portion of the upper surface of the first reflector layer 30 is etched to a predetermined depth by dry etching or the like to form the contact surface 36. As shown in FIG. 3C, the Al_2O_3 oxide layer is oxidized by oxidizing two to three layers of the semiconductor material adjacent to the substrate 20 of the first reflector layer 30, that is, the unetched AlAs layer through an oxidation process. Form. The oxidation process is carried out by exposing the layer to be oxidized to an oxygen atmosphere. Since this oxidation process is widely known, the detailed description is abbreviate | omitted. The refractive index of the region of the first reflector layer 30 in which the oxide layer is formed is lowered to about half or less than before the oxidation. Therefore, the difference in refractive index between the oxide material and the non-oxidized semiconductor material is increased, and the number of pairs of the first reflector layer 30 can be greatly reduced as compared with the conventional surface light laser. On the other hand, the oxidized portion becomes the first insulating layer 31. Here, the steps shown in FIG. 3B and the steps shown in FIG. 3C may be performed in a reversed order.

Next, as shown in FIG. 3D, the first electrode layer 70 is formed on the contact surface 36 of the first reflector layer 30. Therefore, the problem of electrode arrangement caused by the formation of the first insulating layer 31 in the first reflector layer 30 can be solved.

Thereafter, as shown in FIG. 3E, the active layer 40 is formed on the non-oxidizing conductive layer of the first reflector layer 30. Since the active layer 40 has been described with reference to FIG. 2, detailed description thereof will be omitted.

3F, the second reflector layer 60 is formed by alternately stacking two semiconductor materials having different refractive indices, for example, an Al_x Ga_1-x As layer and an AlAs layer, on the active layer 40. The second reflector layer 60 is formed of an impurity semiconductor material different from that of the first reflector layer 30. Thereafter, as shown in FIG. 3G, a portion of the upper surface of the second reflector layer 60 is etched to a predetermined depth by a dry etching method to form a contact surface 66. As shown in FIG. 3H, two to three layers of the upper semiconductor material layer of the second reflector layer 60, that is, the AlAs layer of the etched portion are oxidized to form an Al_2 O_3 oxide layer. This oxidation process is substantially the same as the process shown in Fig. 3C. Here, the process shown in FIG. 3G and the process shown in FIG. 3H may be interchanged.

Thereafter, as illustrated in FIG. 3I, protons or electrons are injected into portions of the active layer 40 and portions of the first and second reflector layers 30 and 60 that contact the active layer 40. The current limiting layer 50 is formed. The current limiting layer 50 is provided to guide the flow of current applied to the first electrode layer 70 and the second electrode layer 80 and to improve the mode characteristics of the laser light generated in the active layer 40. .

Finally, the second electrode layer 80 is formed on the contact surface of the second reflector layer 60 to manufacture a surface light laser as shown in FIG. 2.

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 (6)

Preparing a substrate, and alternately stacking two semiconductor material layers having different refractive indices of the same semiconductor type on the prepared substrate to form a first reflector layer; Etching a portion of the upper surface of the first reflector layer to a predetermined depth to form a first contact surface; Oxidizing one semiconductor material layer among the unetched semiconductor material layers of the first reflector layer to form an oxide layer; Depositing a first electrode layer on the first contact surface; Forming an active layer on the unetched portion of the first reflector layer; Alternately stacking two semiconductor material layers having different refractive indices of the first reflector layer and another semiconductor type on the active layer to form a second reflector layer; Etching a portion of the upper surface of the second reflector layer to a predetermined depth to form a second contact surface; Oxidizing one semiconductor material layer among the unetched semiconductor material layers of the second reflector layer to form an oxide layer; And depositing and forming a second electrode layer on the second contact surface. 2. The method of claim 1, further comprising forming a current limiting layer by implanting ions or protons in a portion of the active layer except for a central portion of the active layer and regions around the active layer of the first and second reflector layers. Surface light laser manufacturing method. The method of claim 1, wherein the first reflector layer comprises two semiconductor material layers alternately stacked with Al_x Ga_1-x As and AlAs, respectively. The method of claim 3, wherein the oxide layer of the first reflector layer is made of Al_2 O_3 formed by oxidation of AlAs. The method of claim 1, wherein the second reflector layer comprises two semiconductor material layers alternately stacked with Al_x Ga_1-x As and AlAs, respectively. The method of claim 5, wherein the oxide layer of the second reflector layer is made of Al_2 O_3 formed by oxidation of the AlAs.