JP2006253235A - Laser diode chip, laser diode and process for fabricating laser diode chip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser diode chip outputting purple-blue laser light in which the yield can be enhanced while reducing the fabrication cost, and to provide a laser diode comprising the laser diode chip, and a process for fabricating a laser diode chip. <P>SOLUTION: Lateral opposite sides parallel with the cleavage plane and holding the central portion of a laser diode chip including a p-GaN cap layer 6 and a p-AlGaN clad layer 5 are cut by etching. The p-GaN cap layer 6 and the p-AlGaN clad layer 5, i.e. the end faces of a GaInN active layer 4, have a chevrony shape when viewed from the cleavage plane. The cut portion is provided with current constriction layers 7 and 7 composed of an oxide film produced by sintering a liquid oxide film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser diode chip that uses a GaN-based semiconductor substrate and outputs blue-violet laser light, a laser diode including the laser diode chip, and a method of manufacturing the laser diode chip.

  In recent years, optical discs have been used for recording data such as sound and images converted into digital signals. For example, in DVD, data is written and read using a laser beam having a wavelength of 6500 nm (red). ing. However, with the progress of video technology and image processing technology, an optical disk having a larger recording capacity is required. For example, for next-generation large-capacity optical disks such as next-generation DVDs, a blue-violet laser diode having a shorter wavelength is being studied as a light source for recording and reproduction.

  A laser diode chip that outputs blue-violet laser light has a structure in which an active layer of a GaInN semiconductor is sandwiched between a p-type AlGaN semiconductor and a clad layer of an n-type AlGaN semiconductor on an n-type GaN semiconductor substrate, n An n-electrode is provided on the surface of the p-type GaN-based semiconductor substrate, and a p-electrode is provided on the surface of the p-type GaN cap layer laminated on the p-type AlGaN-based semiconductor layer. By applying a voltage between the electrodes and passing a current through the active layer, a laser beam having a wavelength of, for example, 405 nm is cleaved as an end face of the active layer by the action of electrons and holes (carriers) coupled in the active layer. More release.

  In order to oscillate the laser beam efficiently, it is necessary to concentrate the current only in the active region, which is a spatially limited region of the active layer, and confine the light generated by the combination of electrons and holes in the active region. The structure of the laser diode chip for this purpose is roughly divided into two structures, a gain waveguide structure and a refractive index waveguide structure.

  In the gain waveguide structure, for example, by performing ion implantation, a resistance value is changed in the cladding layer of the p-type AlGaN-based semiconductor to form an insulating layer having a high resistance value, and a region where current flows is limited. It is a thing. When a voltage is applied between the electrodes, only the region where the current flows produces optical gain, and the refractive index is equivalently increased by the current, and the activated region has the effect of an optical waveguide and can confine light. it can. However, since the active region is determined by the current flow, the active region widens due to the current diffusion effect and the boundary of the active region is unstable. For this reason, there are disadvantages such as a large threshold current for starting laser oscillation and a large astigmatic difference.

  On the other hand, in the refractive index guided structure, both sides of the p-type AlGaN-based semiconductor cladding layer and GaInN-based semiconductor active layer in the lateral direction perpendicular to the stacking direction are vertically etched and the semiconductor layers are epitaxially grown on both sides. Then, the crystal is grown again to form a current confinement layer. This limits the active region. Since the active region is physically limited, light is strongly confined, the threshold current is reduced, and the astigmatic difference is also reduced as compared to the gain waveguide structure.

  FIG. 5 is an explanatory view showing a conventional manufacturing process of a laser diode chip by crystal growth. A wafer 50 on which different crystals are grown to have a predetermined layer structure by the epitaxial crystal growth method is taken out from the crystal growth furnace, and an insulating film 51 is formed on the growth surface by CVD (Chemical Vapor Deposition) (FIG. 5 (a)). Photoresist 52 is applied to the surface of insulating film 51, and a mask is overlaid for exposure, and the exposed portion is removed with a chemical solution (FIG. 5B).

  By dry etching, the insulating film 51 is removed except for the unexposed part (FIG. 5C). Further, both side portions of the cladding layer are cut out by etching (FIG. 5D). The wafer 50 from which both side portions of the clad layer are cut out is again put into the crystal growth furnace, and the semiconductor crystal 53 is grown in layers (FIG. 5E). The semiconductor crystal 53 is removed by etching until the insulating film 51 is exposed (FIG. 5F), and the exposed insulating film 51 is removed by etching (FIG. 5G). Thereby, a current confinement layer made of the semiconductor crystal 53 different from the cladding layer and the active layer is grown.

  However, in the conventional method, in order to form the current confinement layer, it is necessary to repeat the crystal growth process twice, which increases the manufacturing cost. In addition, since the crystal growth process requires precise layer thickness control and affects the yield of products, there is a problem that the yield of manufactured laser diode chips is reduced by repeating the crystal growth process.

  The present invention has been made in view of such circumstances, and a liquid oxide film is baked with a central portion (stripe) of a cladding layer of a p-type AlGaN-based semiconductor in a lateral direction substantially perpendicular to the stacking direction interposed therebetween. By providing a current confinement layer, the threshold current for starting laser oscillation is reduced, the astigmatic difference is reduced, the second crystal growth process is not required, and the yield is improved compared to the prior art. It is an object of the present invention to provide a laser diode chip that outputs blue-violet laser light capable of reducing costs, a laser diode including the laser diode chip, and a method of manufacturing the laser diode chip.

  Another object of the present invention is to confine light and carriers by increasing the thickness of the current confinement layer as the distance from the central portion (stripe) of the cladding layer of the p-type AlGaN-based semiconductor increases. Another object of the present invention is to provide a laser diode chip that can output blue-violet laser light and a laser diode including the laser diode chip.

  Another object of the present invention is to double the current confinement layer in the vertical direction and the horizontal direction of the laser diode chip by interposing the central portion (stripes) of the clad layer of the n-type AlGaN semiconductor in between. An object of the present invention is to provide a laser diode chip that forms a heterostructure and outputs an efficient blue-violet laser beam, and a laser diode including the laser diode chip.

  Another object of the present invention is that the GaInN-based semiconductor layer is a multiple quantum well layer in which quantum well layers and quantum barrier layers are alternately stacked, thereby outputting a high-power blue-violet laser beam. It is an object of the present invention to provide a diode chip and a laser diode including the laser diode chip.

  The laser diode chip according to the first aspect of the present invention is a laser in which at least a first cladding layer of an n-type AlGaN semiconductor, an active layer of a GaInN semiconductor, and a second cladding layer of a p-type AlGaN semiconductor are stacked in this order on a substrate. The diode chip is characterized in that a current confinement layer formed by firing a liquid oxide film is provided opposite to the central portion of the second cladding layer in a direction substantially perpendicular to the stacking direction.

  A laser diode chip according to a second invention is characterized in that, in the first invention, the thickness of the current confinement layer is increased as the distance from the center portion increases.

  In the laser diode chip according to a third aspect of the present invention, in the first or second aspect, the current confinement layer is opposed to the central portion of the first cladding layer in a direction substantially perpendicular to the stacking direction. It is characterized by that.

  A laser diode chip according to a fourth invention is characterized in that, in any one of the first to third inventions, the active layer is a multiple quantum well layer in which quantum well layers and quantum barrier layers are alternately laminated. To do.

  A laser diode according to a fifth aspect of the invention includes the laser diode chip according to any one of the first to fourth aspects of the invention.

  According to a sixth aspect of the present invention, there is provided a method of manufacturing a laser diode chip, comprising at least an n-type AlGaN-based semiconductor first cladding layer, a GaInN-based semiconductor active layer, and a p-type AlGaN-based semiconductor second cladding layer in this order. In the method for manufacturing a laminated laser diode chip, an insulating film is formed to cover a central portion of the second cladding layer in a direction substantially perpendicular to the stacking direction, and the second cladding layer not covered with the insulating film is formed. Part is removed by etching, a liquid oxide film is applied to the semiconductor layer and the insulating film exposed by the etching, the applied liquid oxide film is baked, and the baked oxide film is etched until the insulating film is exposed Then, it is planarized, and the exposed insulating film is removed by etching.

  In the first invention, the active region of the active layer of the GaInN semiconductor is physically limited by the current confinement layer obtained by baking the liquid oxide film, and confines light and carriers in the active region.

  In the second invention, the thickness of the current confinement layer is increased as the distance from the center (stripe) of the second cladding layer of the p-type AlGaN-based semiconductor in a direction substantially perpendicular to the stacking direction is increased. . Thus, a current confinement layer having a refractive index equal to or lower than that of the cladding layer is provided, and a double heterostructure is formed in the laser diode chip.

  In the third aspect of the invention, the current confinement layer is opposed to the central portion (stripe) of the first cladding layer of the n-type AlGaN-based semiconductor. Thereby, a double hetero structure is formed in the vertical direction and the horizontal direction of the laser diode chip, and carriers and light are more efficiently confined in the active region.

  In the fourth invention, the active layer of the GaInN-based semiconductor is a multiple quantum well layer in which quantum well layers and quantum barrier layers made of ultrathin films of 100 μm or less are alternately stacked. As a result, carriers confined in the active layer have discrete energy levels (sublevels) larger than the energy band from the energy band (band), and the carrier transition is between these sublevels. As a result, the energy of light emission increases, the amplification of light increases, and laser oscillation is performed more efficiently.

  In the fifth invention, the laser diode includes any one of the laser diode chips of the first invention to the fourth invention.

  In the sixth invention, an insulating film for covering the central portion (stripe) of the cladding layer of the p-type AlGaN-based semiconductor is formed. A part of the cladding layer of the p-type AlGaN-based semiconductor not covered with the insulating film is removed by etching. This forms a spatial structure for providing the current confinement layer. A liquid oxide film is applied to the semiconductor layer and the insulating film exposed by the etching, and the applied liquid oxide film is baked. Thereby, instead of crystal growth, a current confinement layer formed by firing the liquid oxide film is buried with the central portion of the clad layer of the p-type AlGaN semiconductor interposed therebetween. The fired oxide film is flattened by etching until the insulating film is exposed, and the exposed insulating film is removed by etching. As a result, a current confinement layer made of an oxide film is formed with the central portion of the cladding layer of the p-type AlGaN-based semiconductor in between.

  In the first invention and the sixth invention, the active region of the active layer is formed by providing a current confinement layer formed by firing a liquid oxide film with the central portion of the p-type AlGaN-based semiconductor layer as the cladding layer interposed therebetween. A current confining layer that is physically limited can be provided instead of crystal growth, and the threshold current for starting laser oscillation is reduced, the astigmatic difference is reduced, and the crystal growth process is not required twice. Thus, the yield can be improved and the manufacturing cost can be reduced.

  Further, when the depth of the cut-out portion of the cladding layer is deep, for example, it is impossible to provide a current confinement layer by forming an oxide film by vapor phase growth or the like, compared with the current confinement. Since the liquid oxide film is used to provide the layer, the current confinement layer can be easily provided regardless of the shape of the cut surface of the clad layer cut out by etching and the depth or size of the cut portion. A desired structure can be formed, and a structure that matches the desired characteristics of the laser diode can be easily realized.

  In the second invention, the thickness of the current confinement layer is increased with increasing distance from the central portion along the lateral direction of the cladding layer of the p-type AlGaN-based semiconductor. Thus, a double hetero structure can be formed to confine the laser beam and carriers.

  In the third invention, the current confinement layer is provided with the central portion of the clad layer of the n-type AlGaN-based semiconductor interposed therebetween, whereby the light output efficiency can be improved.

  In the fourth invention, the active layer of the GaInN-based semiconductor is a multiple quantum well layer in which quantum well layers and quantum barrier layers are alternately stacked so that a high-power red laser beam can be output. it can.

  In the fifth invention, by providing the laser diode chip of any one of the first to fourth inventions, the threshold current for starting the laser oscillation is reduced, the astigmatic difference is reduced, and the crystal twice. It eliminates the need for a growth process, improves yields, and reduces manufacturing costs. Further, the laser beam and the carrier can be confined, and a high-power red laser beam can be output.

Embodiment 1
Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments. FIG. 1 is a schematic diagram showing the structure of a laser diode chip according to the present invention. In the figure, reference numeral 1 denotes an n-GaN substrate made of an n-type GaN-based semiconductor crystal. The n-GaN substrate 1 has, for example, a rectangular parallelepiped shape with a width (width) of about 250 μm, a thickness (length) of about 100 μm, and a length of about 300 μm.

  On the n-GaN substrate 1, for example, an n-GaN buffer layer 2 made of an n-type GaN-based semiconductor crystal having a thickness of about 0.5 μm and an n-type AlGaN-based semiconductor crystal having a thickness of about 0.5 μm are formed. n-AlGaN cladding layer 3, GaInN active layer 4 made of GaInN semiconductor crystal having a thickness of about 0.1 μm, p-AlGaN cladding layer 5 made of p-type AlGaN semiconductor crystal having a thickness of about 0.5 μm, thickness A p-GaN cap layer 6 made of a p-type GaN-based semiconductor crystal having a thickness of about 0.5 μm is laminated in this order by an epitaxial crystal growth method. In FIG. 1, the thickness of each layer is emphasized in order to make the structure of the laser diode chip easier to understand, but the layers other than the n-GaN substrate 1 have a thickness of several μm or less.

  The lateral side portions of the p-GaN cap layer 6 and the p-AlGaN cladding layer 5 that are parallel to the cleavage plane across the central portion of the laser diode chip are cut out by etching, and from the cleavage plane that is the end face of the GaInN active layer 4. The shapes of the p-GaN cap layer 6 and the p-AlGaN cladding layer 5 as seen are mountain-shaped. Current confinement layers 7 and 7 made of an oxide film obtained by baking a liquid oxide film are provided in the cut out portion. Thus, the current confinement layers 7 and 7 are opposed to each other with the central portion in the direction perpendicular to the stacking direction of the p-GaN cap layer 6 and the p-AlGaN cladding layer 5 in between. That is, current confinement layers 7 and 7 having a refractive index equal to or lower than that of the n-AlGaN cladding layer 3 are provided to form a double heterostructure in the laser diode chip. A p-electrode 8 is formed on the surfaces of the current confinement layers 7 and 7 and the p-GaN cap layer 6, and an n-electrode 9 is formed on the surface of the n-GaN substrate 1.

  The laser diode chip is operated by passing a forward current between the p electrode 8 and the n electrode 9. The current flowing through the GaInN active layer 4 via the p-electrode 8 is limited by the current confinement layers 7 and 7 and is confined in a limited region (active region) of the GaInN active layer 4. The carriers (electrons and holes) injected by the current are concentrated in the active region, and light generated by the coupling of the carriers is reflected by the n-AlGaN cladding layer 3 and the p-AlGaN cladding layer 5 having a low refractive index. It is confined in the active region by a double heterostructure sandwiching the large GaInN active layer 4. When the forward current is increased and the threshold current is exceeded, laser oscillation occurs, and for example, laser light having a wavelength of 405 nm can be extracted from the tear interface.

  FIG. 2 is an explanatory view showing a manufacturing process of the laser diode chip according to the present invention. A crystal growth furnace comprising a wafer 50 in which an n-GaN buffer layer, an n-AlGaN cladding layer, a GaInN active layer, a p-AlGaN cladding layer, and a p-GaN cap layer are stacked in this order on an n-GaN substrate by an epitaxial crystal growth method. The insulating film 51 (for example, the width dimension is about 3 to 4 μm) is formed on the growth surface by CVD (Chemical Vapor Deposition) (FIG. 2A). Photoresist 52 is applied to the surface of the insulating film 51, the mask is overlaid and exposed, and the exposed portion is removed with a chemical solution (FIG. 2B).

  By dry etching, the insulating film 51 is removed except for the unexposed part (FIG. 2C). Further, both side portions are cut out by etching, leaving the central portions of the p-GaN cap layer and the p-AlGaN cladding layer (FIG. 2D). The cutout portion can be gradually cut out from the central portion toward the outside. A liquid oxide film 54 (for example, a coating liquid containing silicon oxide as a main component) is coated on the wafer 50 from which both sides of the p-GaN cap layer and the p-AlGaN cladding layer are cut out to cover the insulating film 51. And then baked (for example, baked at 80 ° C., 150 ° C. and 200 ° C. for about 1 minute, and then at 400 ° C. for about 30 minutes) (FIG. 2E).

  The fired oxide film 7 is removed by etching until the insulating film 51 is exposed, the surface is flattened (FIG. 2F), and the exposed insulating film 51 is removed by etching (FIG. 2G). . Thereby, instead of the crystal growth by the semiconductor crystal, the current confinement layer 7 formed by baking the liquid oxide film is formed.

  A metal film to be a p-electrode is formed on the surface of the wafer on which the current confinement layer is formed, and a metal film to be an n-electrode is also formed on the back surface of the substrate. The wafer on which the metal film is formed is cut into individual laser diode chips, and the two end faces forming the optical resonator are made to be flat and parallel (cleavage planes) parallel to each other. A laser diode chip is mounted on a package, and a laser diode is manufactured by bonding a wire for passing a current.

  As described above, the current confinement layer for confining carriers and light is replaced by a liquid oxide film instead of the conventional epitaxial crystal growth, and the central portion of the p-GaN cap layer and the p-AlGaN cladding layer ( By providing a stripe), a laser diode chip that has conventionally required two epitaxial crystal growth processes can be manufactured by a single epitaxial crystal growth process. Yield can be improved, the manufacturing process can be saved, and the manufacturing cost can be reduced. Further, there is no drawback that the threshold current for starting laser oscillation is increased and that the astigmatic difference is large by physically providing the current confinement layer on the p-GaN cap layer and the p-AlGaN cladding layer.

  In the above-described embodiment, the size of the substrate of the laser diode chip and the thickness of each semiconductor layer are examples, and are not limited to these. Needless to say, the composition of each element of the AlGaN semiconductor and the GaInN semiconductor can be set to a desired composition.

Embodiment 2
In the first embodiment, the lateral portions of the p-GaN cap layer 6 are removed by etching, the upper portions of the lateral sides of the p-AlGaN cladding layer 5 are removed by etching, and the current confinement layer 7 is formed in the removed portions. Although provided, the structure of the current confinement layer 7 is not limited to this.

  FIG. 3 is a schematic diagram showing the structure of the current confinement layer 7. As shown in FIG. 3A, both lateral portions of the p-GaN cap layer 6 and the p-AlGaN cladding layer 5 are removed by etching, and upper portions of both lateral sides of the GaInN active layer 4 are removed by etching. The dimension in the vertical direction of the portion to be removed is increased toward the outside in the horizontal direction of the laser diode chip. Current confinement layers 7 and 7 formed by firing a liquid oxide film are provided in the removed portion.

  Further, as shown in FIG. 3B, both sides of the p-GaN cap layer 6, the p-AlGaN cladding layer 5, and the GaInN active layer 4 are removed by etching, and both the n-AlGaN cladding layer 3 are removed. The upper part of the side is removed by etching. The dimension in the vertical direction of the portion to be removed is increased toward the outside in the horizontal direction of the laser diode chip. It is provided in a portion where the current confinement layers 7 and 7 formed by firing the liquid oxide film are removed. Thus, a double hetero structure can be formed in the vertical direction and the horizontal direction of the laser diode chip. As a result, a more efficient laser diode chip can be manufactured.

Embodiment 3
In the first and second embodiments described above, an active layer made of a GaInN-based semiconductor crystal is used, which is a laser diode chip that outputs blue-violet laser light having a laser light output of about several mW to several tens of mW. However, the present invention can also be applied to a laser diode chip that outputs a blue-violet laser beam with higher output.

  FIG. 4 is a schematic diagram showing the structure of a high-power laser diode chip according to the present invention. In the figure, 11 is an ultra-thin film having a thickness of about 100 mm or less, and a plurality of quantum well layers made of GaInN-based semiconductor crystals and quantum barrier layers are alternately stacked, and an MQW (Multi-quantum Well) having a thickness of about 500 mm. Quantum well layer) active layer. On the upper side of the MQW active layer 11, a p-AlGaN waveguide layer 12 made of a p-type AlGaN semiconductor crystal for confining light, and on the lower side, an n-AlGaN waveguide made of an n-type AlGaN semiconductor crystal. Layer 10 is provided. Note that parts similar to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The lateral portions of the p-GaN cap layer 6 are removed by etching, the upper portions of the lateral sides of the p-AlGaN cladding layer 5 are removed by etching, and current confinement layers 7 and 7 are provided in the removed portions. The dimension in the vertical direction of the current confinement layers 7 is increased outward in the lateral direction of the laser diode chip.

  As a result, carriers confined in the MQW active layer 11 have discrete energy levels (sublevels) larger than the energy band, and carrier transitions occur between these sublevels. The energy of the laser beam increases, the amplification of light increases, laser oscillation is possible with a low current, and high-power laser light can be output.

  In the first, second, and third embodiments described above, the p-AlGaN cladding layer 5 and the n-AlGaN cladding layer 3 have a single-layer structure. However, the present invention is not limited to this, and the composition of the semiconductor crystal is not limited to this. A configuration may be provided in which a plurality of modified p-AlGaN cladding layers and n-AlGaN cladding layers are provided.

It is a schematic diagram which shows the structure of the laser diode chip concerning this invention. It is explanatory drawing which shows the manufacturing process of the laser diode chip concerning this invention. It is a schematic diagram which shows the structure of a current confinement layer. 1 is a schematic diagram showing a structure of a high-power laser diode chip according to the present invention. It is explanatory drawing which shows the manufacturing process of the laser diode chip by the conventional crystal growth.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 n-GaN substrate 2 n-GaN buffer layer 3 n-AlGaN cladding layer 4 GaInN active layer 5 p-AlGaN cladding layer 6 p-GaN cap layer 7 Current confinement layer 8 p electrode 9 n electrode 10 n-AlGaN waveguide layer 11 MQW active layer 12 p-AlGaN waveguide layer

Claims (6)

In a laser diode chip in which at least a first cladding layer of an n-type AlGaN semiconductor, an active layer of a GaInN semiconductor, and a second cladding layer of a p-type AlGaN semiconductor are stacked in this order on a substrate.
A laser diode chip comprising a current confinement layer formed by firing a liquid oxide film with a central portion of the second cladding layer in a direction substantially perpendicular to the stacking direction therebetween. The current confinement layer has a thickness of
2. The laser diode chip according to claim 1, wherein the laser diode chip is increased as the distance from the center portion increases. The current confinement layer is
3. The laser diode chip according to claim 1, wherein a center portion of the first clad layer in a direction substantially perpendicular to the stacking direction is disposed between the laser diode chips. The active layer is
4. The laser diode chip according to claim 1, wherein the laser diode chip is a multiple quantum well layer in which quantum well layers and quantum barrier layers are alternately stacked.   A laser diode comprising the laser diode chip according to claim 1. In a method of manufacturing a laser diode chip, in which at least a first cladding layer of an n-type AlGaN-based semiconductor, an active layer of a GaInN-based semiconductor, and a second cladding layer of a p-type AlGaN-based semiconductor are stacked in this order on a substrate.
Forming an insulating film for covering the central portion of the second cladding layer in a direction substantially perpendicular to the stacking direction;
A portion of the second cladding layer not covered with the insulating film is removed by etching;
Applying a liquid oxide film to the semiconductor layer exposed by the etching and the insulating film,
Bake the applied liquid oxide film,
Etching the fired oxide film until the insulating film is exposed, and flattening,
A method of manufacturing a laser diode chip, wherein the exposed insulating film is removed by etching.

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