JP3786000B2 - Nitride semiconductor laser diode and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, nitride semiconductor _{(In X Al Y Ga 1-} X-Y N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) relates than consisting nitride semiconductor a laser diode (LD), a particularly excellent heat dissipation The present invention relates to a nitride semiconductor laser diode.
[0002]
[Prior art]
Semiconductor laser diodes (hereinafter sometimes referred to simply as “semiconductor lasers”) are significantly affected in their characteristics and reliability by heat. Therefore, it is practically necessary to dissipate Joule heat due to high current density when driving a semiconductor laser. Is very important. Heat dissipation is performed by bringing a semiconductor laser into contact with a heat sink.
Since the nitride semiconductor laser is grown on an insulating substrate such as sapphire or spinel, it is a so-called flip chip type in which positive and negative electrodes are taken out from the nitride semiconductor layer side. For example, a nitride semiconductor laser has a basic structure in which an insulating substrate, an n-type layer, an active layer, and a p-type layer are stacked, and an electrode is etched by etching the p-type layer and the active layer. The exposed n-type layer and the uppermost p-type layer are provided. In such a structure, the nitride semiconductor laser has a step between the exposed n-type layer and the uppermost p-type layer. An example of a semiconductor laser chip having such a structure is shown in a schematic cross-sectional view in FIG. 1. FIG. 1 shows a substrate 1 and an n-type layer 2 (having a laminated structure such as a light guide layer and a light confinement layer). , An active layer 3 and a p-type layer 4 (having a laminated structure such as a light guide layer and a light confinement layer), an n-ohmic electrode 11 (negative electrode) in the concave portion on the nitride semiconductor layer, and a convex portion A p-ohmic electrode 12 (positive electrode) is provided, and an insulating film 13, a p-pad electrode 15, and an n-pad electrode 14 are formed. The Joule heat due to the high current density is dissipated by bringing the surface having the electrodes into contact with the heat sink 40 having the lead electrodes 41 and 42.
[0003]
[Problems to be solved by the invention]
However, since the nitride semiconductor laser shown in FIG. 1 has one surface and two electrodes as described above, the surface that contacts the heat sink between the p side having the positive electrode and the n side forming the negative electrode when forming the negative electrode. As a result, there is a difference in level (step), and good direct bonding to the heat sink cannot be performed face down, and the electrode of the nitride semiconductor laser and the heat sink cannot sufficiently contact each other. As a result, the heat dissipation of the nitride semiconductor laser is deteriorated, the threshold value is increased, and the life characteristics are deteriorated.
Therefore, an object of the present invention is to improve the heat dissipation of the nitride semiconductor laser, to suppress the increase in threshold value and to improve the life characteristics.
[0004]
[Means for Solving the Problems]
That is, the object of the present invention can be achieved by the following configuration.
(1) A method of manufacturing a nitride semiconductor laser diode according to the present invention includes p-type nitridation in which an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are stacked on a substrate, and a ridge is formed by etching. A nitride semiconductor laser diode manufacturing method comprising a semiconductor layer and having a pair of positive and negative electrodes provided on the same side, wherein the negative electrode is formed on the exposed n-type nitride semiconductor layer by etching, A positive electrode is provided on the ridge of the p-type nitride semiconductor layer, and the heat dissipation portion is formed by leaving the p-type nitride semiconductor layer on the side of the ridge without being removed by etching.
(2) Further, the method for manufacturing a nitride semiconductor laser diode according to the present invention is the above-described method for manufacturing a nitride semiconductor laser diode, further comprising a positive electrode and a negative electrode on a surface having a positive electrode and a negative electrode. A heat dissipating portion made of a nitride semiconductor layer that is adjacent to the negative electrode and is not removed by etching is formed.
(3) The nitride semiconductor laser diode according to the present invention is a p-type nitride in which an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are stacked on a substrate, and a ridge is formed by etching. In a nitride semiconductor laser diode having a semiconductor layer and provided with a pair of positive and negative electrodes on the same surface side, a negative electrode and a p-type nitride semiconductor layer are formed on the exposed n-type nitride semiconductor layer by etching. A positive electrode is provided on the ridge of the p-type nitride semiconductor, and a heat dissipation portion is provided by leaving the p-type nitride semiconductor ridge without removing the side p-type nitride semiconductor layer.
[0005]
(2) Further, in the method for manufacturing a nitride semiconductor laser diode according to the present invention, in the method for manufacturing a nitride semiconductor laser diode, further, a heat dissipating portion made of a nitride semiconductor layer adjacent to the negative electrode and not removed by etching is provided. It is characterized by forming.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
That is, according to the present invention, a nitride semiconductor layer (hereinafter, referred to as a heat dissipation portion) formed in a shape that can contact a heat dissipator is formed separately from forming the positive electrode and the negative electrode on the surface having the positive electrode and the negative electrode. In other words, the contact area of the nitride semiconductor laser diode to the heat radiating body can be increased, and Joule heat due to high current density, which is very problematic in driving the semiconductor laser, can be dissipated well. As a result, the rise in threshold value is suppressed, and the life characteristics are remarkably improved.
Such a heat radiating portion of the present invention has a desired shape, that is, a heat radiating body (for example, a heat sink), when a nitride semiconductor layer of a semiconductor laser is stacked, a resist is applied, and a portion to be etched is irradiated with light. Etc.) is formed by etching without exposure to a portion that can be a heat radiating portion. For this reason, a special new process is not required for the manufacture of a semiconductor laser that requires a large number of processes, and the heat dissipating part of the present invention can be provided by a simple method.
[0007]
A radiator is an endothermic material that absorbs and dissipates Joule heat generated in a nitride semiconductor laser diode, for example, a heat sink, a submount, a stem, and the like. As a material having good thermal conductivity for dissipating heat, Examples include diamond, BeO, CuW, AlN, cBN, Si, SiC, GaAs, and Al ₂ O ₃ . In particular, when the radiator is diamond, the thermal conductivity is good, and when combined with the radiator of the present invention, a better effect can be obtained.
Further, the heat radiating portion is a part that is formed in a shape that can contact the heat radiating body so as to conduct Joule heat generated in the nitride semiconductor laser diode to the heat radiating body, and that dissipates heat by contacting the heat radiating body. It consists of a physical semiconductor. Here, the heat radiating portion is formed in a shape that can contact the heat radiating body as long as the heat radiating portion can contact at least the heat radiating body. Preferably, the uppermost layer of the heat radiating portion is provided in the recess of the nitride semiconductor layer. It is higher than the upper part of the negative electrode, that is, the heat radiating part is formed more easily to contact the heat radiating body than the negative electrode, and more preferably the uppermost layer of the heat radiating part and the uppermost layer of the convex part of the nitride semiconductor layer provided with the positive electrode And a heat radiating portion is preferably formed so as to be in horizontal contact with the heat radiating body.
[0008]
The installation position of the heat radiating portion of the present invention may be any as long as it is in contact with the heat radiating body, but in order to increase the heat radiating efficiency, the negative electrode formed in the concave portion and / or the positive electrode formed in the convex portion is provided. It is preferable to form them adjacent to each other. By doing so, heat can be efficiently conducted from the electrode that easily accumulates Joule heat due to high current density to the heat radiating portion. Two or more heat radiation portions may be formed on the nitride semiconductor layer of one unit of the nitride semiconductor laser diode, and can be within one unit of a generally preferred size of the nitride semiconductor laser diode. It may be formed as much as possible. Here, “may be formed as much as possible” means that a nitride semiconductor layer on which no electrode is formed is formed as a heat dissipation portion within a range that does not cause a decrease in the performance of the nitride semiconductor laser.
In addition, when the height of the uppermost layer of the nitride semiconductor layer having the positive electrode provided on the convex portion and the uppermost layer of the heat dissipation portion is within 0 to 2 μm, there is no significant step difference as in the conventional nitride semiconductor laser diode. Even if the surface having the positive and negative electrodes of the nitride semiconductor laser diode is brought into contact with the heat dissipator, it can be satisfactorily contacted without being inclined, and the heat dissipation is remarkably improved. Further, since the heat radiating portion is a nitride semiconductor, it has excellent thermal conductivity, and this is also suitable for the heat radiating portion to dissipate heat.
[0009]
The present invention only needs to be a nitride semiconductor laser diode having a heat radiating portion made of a nitride semiconductor layer in at least one place on the same surface having the positive electrode and the negative electrode, and the heat radiating portion in the nitride semiconductor laser diode Other configurations (layer configuration of nitride semiconductor layer, electrode shape and material, etc.) are not particularly limited, and configurations of various types of known nitride semiconductor laser diodes can be applied.
[0010]
Hereinafter, a nitride semiconductor laser diode having a heat dissipation part of the present invention will be specifically described with reference to the drawings.
FIG. 2 is a schematic cross-sectional view of a nitride semiconductor laser diode which is an embodiment of the present invention.
2 shows an n-type layer 2 (having a laminated structure such as a light guide layer and a light confinement layer), an active layer 3 and a p-type layer 4 (having a laminated structure such as a light guide layer and a light confinement layer) on the substrate 1. ) And an n-ohmic electrode 11 (negative electrode) on the concave n-type nitride semiconductor layer formed by etching, and a p-ohmic electrode 12 (positive electrode) on the non-etched p-type nitride semiconductor layer. ) And the insulating film 13 is formed on the surface of the p-type nitride semiconductor layer having the p-ohmic electrode 12 and on the n-type layer exposed from the side surface of the nitride semiconductor layer as shown in FIG. Then, a p-pad electrode 15 is formed on the p-ohmic electrode 12 on the p-side, and the heat radiating portion of the nitride semiconductor layer that is adjacent to the n-ohmic electrode 11 from the n-ohmic electrode 11 on the n-side and is not removed by etching 30 to n-pad electrode 14 A nitride semiconductor formed as shown in FIG. 2 and formed by directly bonding the p-pad electrode 15 and the lead electrode 42, and the n-pad electrode 14 and the lead electrode 41 to the heat sink 40 with the conductive materials 52 and 51, respectively. This is a laser diode 101.
[0011]
The heat radiating portion 30 is formed in such a shape that the nitride semiconductor layer on the left side of the n-ohmic electrode 11 is left without being removed by etching and can contact the heat sink 40 as viewed in the drawing. By providing the heat radiating part 30 on the left side of the n-ohmic electrode 11, Joule heat generated in the electrode can be efficiently dissipated to the heat sink 40. In addition, the height of the heat radiating portion 30 is made the same as that of the p-side nitride semiconductor layer having the p-ohmic electrode 12, and the insulating film 13 is formed on both sides of the p-ohmic electrode 12 with the same thickness as the p-ohmic electrode 12. By providing, the surface having the positive and negative electrodes of the nitride semiconductor laser diode 101 can be in good contact with the heat sink 40. Also, by providing the n-pad electrode 14 that is in electrical contact with the n-ohmic electrode 11 and the p-pad electrode 15 that is in electrical contact with the p-ohmic electrode 12 in the heat radiation portion 30 in consideration of the thickness, respectively. The height difference between the p-side and the n-side can be adjusted to approximately 0 μm, the nitride semiconductor laser diode 101 and the heat sink 40 can be in horizontal contact, and heat can be more efficiently dissipated.
[0012]
As described above, when the semiconductor laser diode 101 is brought into contact with the heat sink 40, no step is generated between the p side and the n side because the heat radiating portion 30 is formed, so that the semiconductor laser diode 101 is substantially horizontal with the heat sink 40. Can touch. Furthermore, since the heat radiating portion 30 is made of the same material as the nitride semiconductor, the heat generated in the active layer 3 is quickly transmitted to the heat radiating portion 30. Furthermore, since the n-pad electrode 14 made of a metal material such as Au, Ag, or Au / Ge having good thermal conductivity is provided in the heat radiating portion 30, heat is efficiently conducted to the heat sink 40 through this member. The
[0013]
When the height difference between the uppermost layer of the p-type nitride semiconductor layer having the p-ohmic electrode 12 and the uppermost layer of the heat dissipation portion 30 is 0 to 2 μm, preferably 0 to 1 μm, the contact with the heat sink 40 becomes good, The conductivity is further improved, and since it can be bonded almost horizontally to the heat sink 40, the fractional distillation is advantageously improved in the manufacture of the nitride semiconductor laser.
As the conductive materials 51 and 52 for directly bonding the p-pad electrode 15 and the n-pad electrode 14, solder materials such as In, PbSn, AuSn, and AuSi, silver paste, In paste, and the like can be used.
[0014]
FIG. 3 is a schematic cross-sectional view of a nitride semiconductor laser diode that is one embodiment of the present invention.
3 shows an n-type layer 2 (having a laminated structure such as a light guide layer and a light confinement layer), an active layer 3 and a p-type layer 4 (having a laminated structure such as a light guide layer and a light confinement layer) on the substrate 1. ), P-ohmic electrode 12 is placed on the uppermost layer of the p-type nitride semiconductor layer ridge-shaped by etching treatment, and n-type nitridation of the recess formed in the n-type nitride semiconductor layer by etching treatment The n-ohmic electrode 11 is disposed on the metal semiconductor layer, and the heat dissipation portions 31 are provided on the p-side nitride semiconductor layers other than the heat dissipation portion 30 and the p-side ridge formed adjacent to the n-ohmic electrode 11, respectively. The nitride semiconductor laser diode 102 is formed by directly bonding the p-pad electrode 15 and the lead electrode 42 and the n-pad electrode 14 and the lead electrode 41 with conductive materials 52 and 51 with the heat sink 40, respectively. A.
In the present invention, when forming a ridge as shown in FIG. 1, the p-side nitride semiconductor layer is etched like the p-type layer 4 in FIG. By forming the heat radiating portion 31 by leaving the side nitride semiconductor without being removed by etching, the thermal conductivity to the heat sink 40 in addition to the heat radiating portion 30 is improved. Furthermore, the heat sink 31 can be easily formed by selecting the center and end of the p-type nitride semiconductor layer, for example, by appropriately selecting the ridge formation position in consideration of the laser configuration and the like each time. In addition, the performance of the heat radiating portion 31 can be sufficiently exhibited. Thus, when the ridge is at the left end on the p side, from the center to the right end of the p side nitride semiconductor layer, and not shown, when the ridge is at the center on the p side, A heat dissipating part can be formed as much as possible on the p-side and n-side nitride semiconductor layers where electrodes are not formed, such as providing a heat dissipating part.
[0015]
It is preferable that the height of the uppermost layer of the nitride semiconductor of the heat dissipating part 31 and the uppermost layer of the nitride semiconductor of the ridge in FIG. More preferably, the lengths are matched. By doing so, the contact between the positive and negative electrodes on the nitride semiconductor layer and the heat sink is improved, and the heat dissipation is improved. In FIG. 3, an insulating film 13 is provided on both sides of the ridge electrode 12, a p-pad electrode 15 is provided on the p side, an n-pad electrode 14 is provided on the n side, and the height difference between the p side and the n side is made substantially the same. It is.
Further, according to the present invention, when the height difference between the p-side and the n-side is reduced, the amount of the conductive material to be directly bonded can be reduced, so that the probability of short-circuiting between the positive and negative electrodes is reduced and the industrial utility value is increased. .
[0016]
【Example】
Hereinafter, the gallium nitride-based compound semiconductor laser device of the present invention is manufactured by metal organic vapor phase epitaxy, and the increase in the threshold and the life characteristics due to the improvement in heat dissipation are described below. Shown and compared.
[Comparative example]
After removing part of the p-type GaN layer and the n-type InGaN layer from the GaN-based compound semiconductor blue light emitting device grown on the sapphire substrate using MOCVD so that the p-layer shape as shown in FIG. 1 remains. Then, p-type treatment is performed to further reduce the resistance of the uppermost p-type GaN layer. As shown in FIG. 1, a p-ohmic electrode 12 is formed on the p-type layer, and an n-ohmic electrode 11 is formed on the n-type layer, which is heat-treated at 500 ° C. and die-bonded face-down. A laser diode was used.
When this device was oscillated with a pulse, the threshold current density was 5 KA / cm ² and the output after 1 hour was reduced by 60%.
[Example]
In the embodiment, as shown in FIG. 3, the heat radiation portions 30 and 31 having the same height as the ridge are provided on the p side and the n side (p-GaN is not etched and left in a desired shape), and the heights of the p side and the n side are increased. A laser diode was made in the same manner as in the comparative example except that the difference was eliminated and the pad electrodes were formed so as to form the p and n side heat radiation portions 30 and 31.
When this device was oscillated with a pulse, the threshold current density was 3.5 KA / cm ² and the output after 1 hour decreased by 10%.
[0017]
As described above, the example in which the heat dissipating part is installed has a lower threshold current density and a lower output, and has better life characteristics than the comparative example having no heat dissipating part.
[0018]
【The invention's effect】
As described above, according to the present invention, the heat radiation portion is formed on the surface having the positive electrode and the negative electrode, thereby improving the heat radiation property, suppressing the rise of the threshold value, and significantly improving the life characteristics.
Further, according to the present invention, the height of the p-side nitride semiconductor layer having the positive electrode, the height of the heat radiating portion when the heat radiating portion is provided on the p side having the positive electrode, and the height of the n-side radiating portion are high and low. When the difference is 0 to 2 μm, the contact with the heat radiating body is further improved, and further preferable effects are obtained.
Further, as another effect, the present invention makes it easy to design a lens for condensing the laser light because the semiconductor laser diode and the heat radiating body are in contact with each other in almost parallel. Furthermore, as another effect, the present invention reduces the amount of conductive material to be directly bonded when the difference in height between the p-side and the n-side on the surface having the nitride semiconductor layer electrode is reduced. The probability of short-circuiting between electrodes is reduced and the industrial utility value is increased.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a conventional nitride semiconductor laser diode.
FIG. 2 is a schematic cross-sectional view of a nitride semiconductor laser diode that is one embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view of a nitride semiconductor laser diode that is one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... N-type layer 3 ... Active layer 4 ... P-type layer 11 ... N-ohmic electrode 12 ... P-ohmic electrode 13 ... Insulating film 14 ... · N-pad electrode 15 ··· p-pad electrodes 30 and 31 · · · heat dissipation portion 40 · · · heat sink 41 and 42 · · · lead electrodes 51 and 52 · · · conductive material

Claims (3)

An n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are stacked on a substrate, and has a p-type nitride semiconductor layer in which a ridge is formed by etching. A method of manufacturing a nitride semiconductor laser diode provided with an electrode,
By etching, a negative electrode is provided on the exposed n-type nitride semiconductor layer and a positive electrode is provided on the ridge of the p-type nitride semiconductor layer, and the p-type nitride semiconductor layer on the side of the ridge is removed without etching. A method of manufacturing a nitride semiconductor laser diode, characterized by forming a heat dissipation portion by remaining. The heat radiation part which consists of a nitride semiconductor layer which is adjacent to the negative electrode and is not removed by etching is formed on the surface having the positive electrode and the negative electrode separately from the positive electrode and the negative electrode. The manufacturing method of the nitride semiconductor laser diode of description. An n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are stacked on a substrate, and has a p-type nitride semiconductor layer in which a ridge is formed by etching. In a nitride semiconductor laser diode provided with an electrode,
A negative electrode is provided on the exposed n-type nitride semiconductor layer by etching, and a positive electrode is provided on the ridge of the p-type nitride semiconductor layer, and the p-type nitride semiconductor layer on the side of the ridge of the p-type nitride semiconductor is provided. A nitride semiconductor laser diode having a heat dissipating portion provided by leaving without being removed.

Images