JPH10233549A - Nitride semiconductor laser diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the heat-dissipating property of a nitride semiconductor laser diode by a method wherein, separately from a positive electrode and a negative electrode which are formed on a face which comprises a positive electrode and a negative electrode, a nitride semiconductor layer which is formed to be a shape capable of coming into contact with a heat-dissipating body is provided. SOLUTION: An n-type layer 2, an active layer 3 and a p-type layer 4 are laminated on a substrate 1, an n-ohmic electrode 11 as a negative electrode is installed on an n-type nitride semiconductor layer in a recess which is formed by an etching treatment, and a p-ohmic electrode 12 as a positive electrode is installed on a p-type nitride semiconductor layer in a protrusion which is not etched. Then, in addition to the formation of the n-ohmic electrode 11 and the p-ohmic electrode 12, a nitride semiconductor layer in the neighborhood on the left of the n-ohmic electrode 11 is not removed by an etching operation so as to be left, and a heat-dissipating part 30 which is formed to be a shape capable of coming into contact with a heat sink 40 is formed. Thereby, it is possible to obtain a nitride semiconductor laser diode whose heat-dissipating property is improved, which restrains a rise in a threshold value and whose life characteristic can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (I).
_{n X Al Y Ga 1-XY} N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1)
More particularly, the present invention relates to a nitride semiconductor laser diode (LD) having excellent heat dissipation.

[0002]

2. Description of the Related Art A semiconductor laser diode (hereinafter sometimes simply referred to as a "semiconductor laser") has its characteristics and reliability greatly affected by heat. Therefore, Joule heat due to a high current density is dissipated to drive the semiconductor laser. That is very important in practice. Dissipation of heat 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 extracted 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 the electrodes are formed by etching the p-type layer and the active layer. It is provided on the exposed n-type layer and the uppermost p-type layer. In such a structure, the nitride semiconductor laser has a step between the exposed n-type layer and the uppermost p-type layer. FIG. 1 is a schematic cross-sectional view showing an example of a semiconductor laser chip having such a structure. 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, 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 a concave portion on the nitride semiconductor layer, and a A p-ohmic electrode 12 (positive electrode) is provided, and an insulating film 13, a p-pat electrode 15, and an n-pat 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]

However, since the nitride semiconductor laser of FIG. 1 has two electrodes on one surface as described above, the p-side having the positive electrode and the n-side forming the negative electrode are formed at the time of forming the negative electrode. A height difference (step) is generated on the surface in contact with the heat sink, 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 be sufficiently contacted. As a result, the heat dissipation of the nitride semiconductor laser deteriorates, the threshold value increases, and the lifetime characteristics deteriorate.
SUMMARY OF THE INVENTION It is an object of the present invention to improve the heat dissipation of a nitride semiconductor laser, suppress a rise in threshold voltage, and achieve an improvement in life characteristics.

[0004]

That is, the object of the present invention is to
This can be achieved by the following configuration. (1) In a nitride semiconductor laser diode in which a pair of positive and negative electrodes are provided on the same surface side, a radiator is provided separately from forming the positive and negative electrodes on the surface having the positive and negative electrodes. A nitride semiconductor laser diode comprising: a nitride semiconductor layer (hereinafter, sometimes referred to as a heat radiating portion) formed in a contactable shape.

Further, other preferred embodiments (2) and (3) of the present invention are shown below. (2) The nitride semiconductor laser diode according to (1), wherein a height difference between the positive electrode and the nitride semiconductor layer formed separately from the positive electrode and the negative electrode is within 0 to 2 μm. (3) A conductive material electrically contacting the negative electrode is formed on the nitride semiconductor layer formed separately from the positive electrode and the negative electrode, and the conductive material is mounted on the heat radiator face down. 3. The nitride semiconductor laser diode according to 1 or 2.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In other words, according to the present invention, there is provided a nitride semiconductor layer formed in a shape capable of contacting a heat radiator, separately from forming a positive electrode and a negative electrode on a surface having a positive electrode and a negative electrode. (Hereinafter, it may be referred to as a heat radiating portion.) By increasing the contact area of the nitride semiconductor laser diode with the heat radiator, the Joule heat due to a high current density, which is extremely problematic in driving the semiconductor laser, can be improved. Can be dissipated. As a result, a rise in the threshold value is suppressed, and the life characteristics are significantly improved. Such a heat radiating part of the present invention,
After laminating a nitride semiconductor layer of a semiconductor laser, when a resist is applied and the resist is irradiated with light to determine a portion to be etched, a desired shape, that is, a shape that can be brought into contact with a radiator (for example, a heat sink) is used. In addition, it is formed by etching without exposing a portion that can be a heat radiation portion.
Therefore, it is possible to provide the heat radiating portion of the present invention by a simple method without requiring a special new process for manufacturing a semiconductor laser requiring many processes.

The heat radiator is a heat absorbing material that absorbs and dissipates Joule heat generated in the nitride semiconductor laser diode, and is, for example, a heat sink, a submount, a stem, or the like, and a material having good heat conductivity for dissipating heat. As diamond, BeO, CuW, AlN, cBN,
Si, SiC, GaAs, Al ₂ O _{3 and the} like can be mentioned. 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. The heat radiating portion is formed in a shape capable of contacting the heat radiator in order to conduct the Joule heat generated in the nitride semiconductor laser diode to the heat radiator, and is a portion for contacting the heat radiator and dissipating the heat. Consisting of semiconductors. Here, that the heat radiating portion is formed in a shape capable of contacting the heat radiating body means that
It is sufficient that the heat radiating portion can contact at least the heat radiator. Preferably, the uppermost layer of the heat radiating portion is higher than the upper portion of the negative electrode provided in the concave portion of the nitride semiconductor layer, that is, the heat radiating portion contacts the heat radiator more than the negative electrode. The height difference between the uppermost layer of the heat radiating portion and the uppermost layer of the convex portion of the nitride semiconductor layer on which the positive electrode is provided is more preferably 0 to 2 μm, and is particularly preferably horizontal to the heat radiator. A heat radiating portion is formed so as to be able to contact the surface.

The radiating portion of the present invention can be installed in any position as long as it can be in contact with the radiator. However, in order to enhance the radiating efficiency, the radiating portion is formed on the negative electrode formed in the concave portion and / or on the convex portion. Preferably, it is formed adjacent to the positive electrode. By doing so, heat can be efficiently transmitted from the electrode, which easily accumulates Joule heat due to the high current density, to the heat radiating portion. Further, the heat radiating portion may be formed at two or more places on the nitride semiconductor layer of one unit of the nitride semiconductor laser diode, and can be formed within one unit of a generally preferable size of the nitride semiconductor laser diode. Any number may be formed. Here, "may be formed as much as possible" means that a nitride semiconductor layer on which an electrode is not formed is formed as a heat radiating portion within a range that does not cause a decrease in performance of the nitride semiconductor laser. Further, 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 radiating portion is within 0 to 2 μm, there is no significant step unlike the conventional nitride semiconductor laser diode. Even when the surface of the nitride semiconductor laser diode having the positive and negative electrodes is brought into contact with the heat radiator, the surface can be satisfactorily contacted without being inclined, and the heat radiation is significantly improved. Further, since the heat radiating portion is made of a nitride semiconductor, the heat radiating portion is excellent in thermal conductivity. In this respect, the heat radiating portion is suitable for dissipating heat.

The present invention is applicable only to a nitride semiconductor laser diode having a heat radiating portion made of a nitride semiconductor layer at at least one position on the same surface having a positive electrode and a negative electrode. Other configurations (layer configuration of the nitride semiconductor layer, shape and material of the electrodes, etc.) other than the heat radiating section in [1] are not particularly limited, and configurations of various known nitride semiconductor laser diodes can be applied.

Hereinafter, a nitride semiconductor laser diode having a heat radiating portion of the present invention will be specifically described with reference to the drawings. FIG. 2 is a schematic sectional view of a nitride semiconductor laser diode according to one embodiment of the present invention. FIG. 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 a substrate 1. ) Are stacked, and the n-ohmic electrode 11 (negative electrode) is formed on the n-type nitride semiconductor layer in the concave portion formed by the etching process, and the p-ohmic electrode 12 is formed on the p-type nitride semiconductor layer in the convex portion which is not etched.
(Positive electrodes) are provided, and an insulating film 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. 1
3 is formed, a p-pat electrode 15 is formed on the p-side p-ohmic electrode 12, and the n-side n-ohmic electrode 11 is formed.
An n-pat electrode 14 is formed as shown in FIG. 2 on the heat radiating portion 30 of the nitride semiconductor layer which is adjacent to the n-ohmic electrode 11 and which is not removed by etching, as shown in FIG. Pad electrode 14 and lead electrode 4
1 and conductive materials 52 and 51 respectively.
This is a nitride semiconductor laser diode 101 directly bonded to a semiconductor laser diode 101.

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 as viewed in the drawing is left without being removed by etching and can contact the heat sink 40. The heat radiating part 30 is an n-ohmic electrode
Is provided on the left side, and Joule heat generated in the electrodes can be efficiently dissipated to the heat sink 40. Also, the height of the heat radiating portion 30 is adjusted to the p-ohmic electrode 12.
By providing an insulating film 13 on both sides of the p-ohmic electrode 12 so as to have the same thickness as that of the p-ohmic electrode 12, the positive and negative sides of the nitride semiconductor laser diode 101 can be formed. The surface having the electrodes can be in good contact with the heat sink 40. Further, by providing the n-pat electrode 14 electrically connected to the n-ohmic electrode 11 and the p-pat electrode 15 electrically connected to the p-ohmic electrode 12 in the heat radiating portion 30 in consideration of the thickness, respectively. , The height difference between the p-side and the n-side is almost 0 μm
, And the nitride semiconductor laser diode 101 and the heat sink 40 can be in horizontal contact with each other, so that heat can be more efficiently dissipated.

As described above, the semiconductor laser diode 10
When the heat sink 1 is brought into contact with the heat sink 40, the semiconductor laser diode 101 can contact the heat sink 40 substantially horizontally without any step difference between the p-side and the n-side because the heat-dissipating portion 30 is formed. Further, since the heat radiating portion 30 is made of the same material as the nitride semiconductor, heat generated by the active layer 3 is quickly transmitted to the heat radiating portion 30. Further, since the heat radiating portion 30 is provided with the n-pat electrode 14 made of a metal material having good thermal conductivity, such as Au, Ag, or Au / Ge, heat is efficiently transmitted to the heat sink 40 via this member. You.

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 radiating portion 30 is 0 to 2 μm, preferably 0 to 1 μm, the contact with the heat sink 40 is good. And the thermal conductivity is further improved,
Further, since the bonding can be performed substantially horizontally to the heat sink 40, the fractionation is improved in the production of the nitride semiconductor laser, which is advantageous. As the conductive materials 51 and 52 for directly bonding the p-pat electrode 15 and the n-pat electrode 14, solder materials such as In, PbSn, AuSn, and AuSi, silver paste, In paste, and the like can be used.

FIG. 3 is a schematic sectional view of a nitride semiconductor laser diode according to one embodiment of the present invention. FIG.
Comprises 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 a substrate 1. The p-ohmic electrode 12 is provided on the uppermost layer of the p-type nitride semiconductor layer that has been laminated and formed into a ridge shape by the etching process, and the n-type nitride semiconductor in the concave portion formed in the n-type nitride semiconductor layer by the etching process An n-ohmic electrode 11 is provided on the layer, and a heat-radiating portion 31 is provided on the p-side nitride semiconductor layer other than the heat-radiating portion 30 and the p-side ridge formed adjacent to the n-ohmic electrode 11, respectively. A nitride semiconductor laser diode 102 in which the pad electrode 15 and the lead electrode 42, and the n-pat electrode 14 and the lead electrode 41 are directly bonded to the heat sink 40 with conductive materials 52 and 51, respectively. . According to the present invention, when a ridge is conventionally formed 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 heat conductivity to the heat sink 40 in addition to the heat radiating portion 30 is improved. Further, by considering the ridge formation position in consideration of the configuration of the laser and the like, and appropriately selecting the position each time, for example, by selecting the center or the end of the p-type nitride semiconductor layer, the heat radiating portion 31 can be easily formed. In addition, the performance of the heat radiating portion 31 can be sufficiently exhibited. As described above, when the ridge is at the left end on the p-side, the center extends from the center to the right end of the p-side nitride semiconductor layer. By providing a heat radiating portion, the heat radiating portion can be formed as much as possible on the p-side and n-side nitride semiconductor layers where no electrodes are formed.

It is preferable that the height of the uppermost layer of the nitride semiconductor of the heat radiating portion 31 in FIG. 3 and the height of the uppermost layer of the nitride semiconductor of the ridge are made equal, and furthermore, the uppermost layer of the heat radiating portion 31, the uppermost layer of the ridge and the heat radiating portion. More preferably, the heights of the 30 are matched.
This improves the contact between the positive and negative electrodes on the nitride semiconductor layer and the heat sink, and improves the heat dissipation.
In FIG. 3, an insulating film 13 is provided on both sides of the ridge electrode 12, a p-pat electrode 15 is provided on the p-side, and an n-pat electrode 14 is provided on the n-side, so that the height difference between the p-side and the n-side is 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]

The gallium nitride based compound semiconductor laser device of the present invention is manufactured by the metalorganic chemical vapor deposition method. And a comparative example. [Comparative Example] A GaN-based compound semiconductor blue light emitting device grown on a sapphire substrate by MOCVD was fabricated using a p-type GaN layer and n-type InG such that the p-layer shape as shown in FIG.
After a part of the aN layer is removed by etching, a 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.
, And die-bonded face down, and thereafter a laser diode was formed according to a conventional method. When the device was oscillated with a pulse, the threshold current density was 5 KA / c.
The output after one hour at m ² was reduced by 60%. [Embodiment] In the embodiment, as shown in FIG. 3, heat radiating portions 30 and 31 having the same ridge height are provided on the p-side and the n-side (p-G).
aN is not etched and remains in a desired shape), and the height difference between the p-side and the n-side is eliminated.
A laser diode was manufactured in the same manner as in the comparative example except that the pad electrode was changed to 31. When the device was oscillated with a pulse, the threshold current density was 3.5.
The output after one hour at KA / cm ² was reduced by 10%.

As described above, in the embodiment in which the heat radiating portion is provided, the threshold current density is low, the output is not reduced, and the life characteristics are good as compared with the comparative example having no heat radiating portion.

[0018]

As described above, according to the present invention, by forming the heat radiating portion on the surface having the positive electrode and the negative electrode, the heat radiating property is improved, the rise in the threshold value is suppressed, and the life characteristics are remarkably improved. . Further, in 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 heat radiating portion on the n side are high and low. When the difference is 0 to 2 μm, the contact with the heat radiator is further improved, and a more preferable effect is obtained. Further, as another effect, in the present invention, since the semiconductor laser diode and the heat radiator are in substantially parallel contact with each other, it is easy to design a lens for condensing the laser light. Furthermore, as another effect, the present invention provides a method of reducing the height difference between the p-side and the n-side on the surface having the electrode of the nitride semiconductor layer, which reduces the amount of the conductive material to be directly bonded. The probability of short circuit between the electrodes is reduced, and the industrial utility value is increased.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a conventional nitride semiconductor laser diode.

FIG. 2 is a schematic cross-sectional view of a nitride semiconductor laser diode according to one embodiment of the present invention.

FIG. 3 is a schematic sectional view of a nitride semiconductor laser diode according to 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-pat electrode 15 ··· p-pat electrode 30 and 31 · · · radiator 40 · heat sink 41 and 42 · · lead electrode 51 and 52 ... conductive material

Claims (1)

[Claims] 1. A nitride semiconductor laser diode having a pair of positive and negative electrodes provided on the same surface side, in addition to forming a positive electrode and a negative electrode on a surface having a positive electrode and a negative electrode, dissipating heat. A nitride semiconductor laser diode comprising a nitride semiconductor layer formed in a shape capable of contacting a body.