JP2007027181A - Nitride semiconductor laser apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser apparatus with good heat dissipation properties and with high reliability by preventing a ridge strive from being damaged in the apparatus. <P>SOLUTION: In the nitride semiconductor laser apparatus where a nitride semiconductor laser element is joined with a submount or a stem junction down; the nitride semiconductor laser element comprises a p-type nitride semiconductor layer, a p-type electrode, and a metal film. A double channel structure is provided, in which a narrowed ridge strive is formed in an upper surface of the p-type nitride semiconductor layer, and a trench is provided on opposite sides along the ridge strive. The p-type electrode makes contact with the top of the ridge strive and is formed, adapted to the shape of the upper surface of the p-type nitride semiconductor layer. The metal film is formed on the p-type electrode without having a cavity between the metal film and the p-type electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor laser device, and more particularly, to a nitride semiconductor laser device in which grooves formed on both sides of a ridge stripe are filled with a metal film.

  Junction-down junction is known as a method for improving the heat dissipation of a semiconductor laser device. The junction down junction is a method of joining the surface on which the ridge stripe is formed to the submount.

  As a first example, a schematic cross-sectional view of a conventional nitride semiconductor laser device is shown in FIG. In FIG. 3, in the conventional nitride semiconductor laser device, an n-type nitride semiconductor layer 110, a nitride semiconductor active layer 120, and a p-type nitride semiconductor layer 130 are formed in this order on a substrate 100. Further, a convex ridge stripe 140 is formed on the p-type nitride semiconductor layer 130, and the p-type nitride semiconductor layer 130 is covered with an insulating film 170 except for a portion immediately above the ridge stripe 140.

  Further, a p-type electrode 180 is formed so as to cover the portion immediately above the ridge stripe and the surrounding insulating film 170, and an n-type electrode 200 is formed on the bottom surface of the substrate 100. The p-type electrode 180 and the submount 210 are joined by junction-down. Solder 220 is used for joining the p-type electrode 180 and the submount 210.

In the first example, the nitride semiconductor laser device, by bonding to a submount 210 of larger material than the thermal expansion coefficient of the substrate, prestressed to the nitride semiconductor laser device, the threshold current I _th is reduced Is done.

  As a second example, Patent Document 2 describes a method for preventing current leakage caused by solder wrapping around a side surface of a semiconductor laser element during junction down junction of an AlGaInAs / InP semiconductor laser device. ing.

  An example of the AlGaInAs / InP semiconductor laser device described in Patent Document 2 is shown in FIG. In FIG. 4, an n-type semiconductor layer 510, an active layer 520, and a p-type semiconductor layer 530 are sequentially stacked on a substrate 500. Further, a ridge waveguide 540 and grooves 550 are formed on both sides of the ridge waveguide 540 in the p-type semiconductor layer to form a double channel structure.

Further, an insulating film 560 made of SiO ₂ is formed except for the portion directly above the ridge-type waveguide 540, and a p-electrode 570 is formed on the upper surface of the region excluding the groove 550. An n-electrode 580 is formed on the substrate side of the semiconductor laser. Subsequently, an air bridge type p-type plated electrode 590 having a cavity 620 formed so as not to fill the groove 550 is formed on the surface having the ridge-type waveguide 540, and the p-type plated electrode 590 and the submount 600 are joined to each other. Down joined. Solder 610 is used to join the p-type plating electrode 590 and the submount 600.

  In the semiconductor laser device of the second example, by joining to the submount 600 through the air bridge type p-type plating electrode 590, current leakage due to the rise of the solder is prevented and the groove 550 is embedded in the solder 610. It is preventing. Further, the stress received by the ridge waveguide 540 due to the difference in thermal expansion coefficient between the semiconductor layer and the solder 610 is suppressed.

  The semiconductor laser device bonded in this way has excellent heat dissipation because it can radiate heat from the surface of the semiconductor laser element on which the nitride semiconductor layers are laminated.

  However, since the ridge stripe is narrow and easily damaged because current is confined, if it is damaged, it causes a decrease in the reliability of the nitride semiconductor laser device, such as a decrease in light emission characteristics. In addition, as the output of the nitride semiconductor laser device is increased, the temperature rise is particularly noticeable in the vicinity of the light emitting region immediately below the ridge stripe, which causes a decrease in reliability such as promoting the deterioration of the nitride semiconductor laser device. .

  For example, in the nitride semiconductor laser device of the first example, in the process of manufacturing a nitride semiconductor laser element, after a protruding ridge stripe is formed, the wafer is divided into individual nitride semiconductor laser elements (chips). In addition, in the process of scribing or dividing the wafer, the ridge stripe may be damaged by bringing the surface on which the ridge stripe is formed into contact with a stage or applying pressure.

  In addition, when performing junction-down bonding, a certain pressure is applied from the n-electrode side of the nitride semiconductor laser element to bond it to the submount, so that the ridge stripe having a convex shape is damaged by applying unnecessary stress. May end up. Furthermore, the nitride semiconductor laser element is tilted and joined to the submount, which causes the element characteristics to deteriorate. Further, the direction and degree of inclination of this tilt differs for each nitride semiconductor laser device. Due to the mismatch of the tilt, a difference in heat dissipation occurs, which causes variations in light emission characteristics.

In the semiconductor laser device of the second example, an air bridge type p-type plating electrode having a double channel structure in which a groove 550 is formed on both sides of the ridge waveguide 540 and a cavity in the groove 550 above the ridge waveguide 540. 590 is formed. In the case of an air bridge shape in which the groove portion 550 is not embedded as in the second example, or when the plating electrode is not formed in contact with the bottom surface of the groove portion 550 and is hollow, most of the heat generated in the light emitting region is Since it only conducts to the p-type plating electrode through the semiconductor layer of the ridge-type waveguide, and the heat dissipation is not good, the temperature rises remarkably and the deterioration of the semiconductor layer is promoted, leading to a reduction in the device life.
JP 2004-140141 A

  The present invention has been made to solve the above-described problems. An object of the present invention is to provide a nitride semiconductor laser device that prevents damage to the ridge stripe and has good heat dissipation and high reliability in the nitride semiconductor laser device.

  According to one aspect of the present invention, in a nitride semiconductor laser device in which a nitride semiconductor laser element is joined to a submount or a stem by junction down, the nitride semiconductor laser element includes a p-type nitride semiconductor layer, a p-type nitride semiconductor layer, and a p-type nitride semiconductor layer. A double channel structure including a constricted ridge stripe formed on the upper surface of the p-type nitride semiconductor layer and a groove provided on both sides along the ridge stripe. The p-type electrode is in contact with the top of the ridge stripe and is formed to match the shape of the upper surface of the p-type nitride semiconductor layer, the metal film is formed on the p-type electrode, and the metal film and the p-type electrode There is provided a nitride semiconductor laser device characterized in that there is no cavity therebetween.

Preferably, the width of the groove is 10 μm or more.
Preferably, the thickness of the metal film is 1 μm or more and 10 μm or less.

  Preferably, the outermost surface of the p-type electrode is formed of any one of Au, Ag, Cu, Al, or Mo.

  Preferably, the metal film is a plating containing at least one material of Au, Ag, Cu, or Al, or a metal film made of any of Au, Ag, Cu, Al, or Mo.

  Preferably, the outermost surface of the p-type electrode and the metal film are made of the same material.

  According to the nitride semiconductor laser device of the present invention, it is possible to provide a nitride semiconductor laser device that prevents damage to the ridge stripe, has good heat dissipation, and is highly reliable.

  According to the nitride semiconductor laser device of the present invention, the nitride semiconductor laser element is joined to the submount or the stem by junction down, and the nitride semiconductor laser element includes a p-type nitride semiconductor layer, a p-type electrode, a metal A double channel structure in which a narrowed ridge stripe is formed on the upper surface of the p-type nitride semiconductor layer and grooves are provided on both sides along the ridge stripe. The metal film is formed on the p-type electrode and is in contact with the top of the ridge stripe and conforms to the shape of the upper surface of the p-type nitride semiconductor layer, and a cavity is formed between the metal film and the p-type electrode. It is characterized by not having.

  As a result, the narrowed ridge stripe is prevented from being damaged, the heat released from the light emitting region is efficiently released, and the heat dissipation characteristics are improved, thereby improving the reliability of the nitride semiconductor laser device. Obtainable.

  Hereinafter, the nitride semiconductor laser device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view of a nitride semiconductor laser device of the present invention.

  In FIG. 1, an n-type nitride semiconductor layer 110, a nitride semiconductor active layer 120, and a p-type nitride semiconductor layer 130 are formed on a substrate 100 in this order. Here, the p-type nitride semiconductor layer 130 includes a ridge stripe 140, hill portions 160 formed on both sides of the ridge stripe 140, and a space between the ridge stripe 140 and the hill portion 160. A groove 150 is formed.

  The upper surface of the p-type nitride semiconductor layer 130 is covered with an insulating film 170 except for the top of the ridge stripe 140. Subsequently, the p-type electrode 180 and the metal film are formed on the ridge stripe 140 and on the insulating film 170. 190 are covered in this order, and an n-type electrode 200 is formed on the bottom surface of the substrate 100. Further, the metal film 190 is joined to the submount 210 by junction down. Solder 220 is used for joining.

  The insulating film 170 is an insulating film provided so that a current is constricted and injected only into the ridge stripe 140.

  In FIG. 1, the double channel structure refers to a structure formed on the upper surface of the p-type nitride semiconductor layer 130 and provided with groove portions 150 on both sides along the ridge stripe 140. The p-type electrode 180 is formed so as to be in contact with the top of the ridge stripe 140 and conform to the shape of the upper surface of the p-type nitride semiconductor layer 130. Here, being formed so as to conform to the shape means that the shape is substantially the same as the shape of the upper surface of the p-type nitride semiconductor layer 130. Specifically, the shape of the upper surface of the p-type nitride semiconductor layer 130 has a shape of a hill portion 160, a groove portion 150, a ridge stripe 140, a groove portion 150, and a hill portion 160 in order from the left side of FIG. This means that the shape of the electrode 180 has a similar uneven shape. As can be seen from FIG. 1, the metal film 190 is formed on the p-type electrode 180 and there is no cavity between the metal film 190 and the p-type electrode 180.

  Next, a procedure for manufacturing the nitride semiconductor laser device of the present invention shown in FIG. 1 will be described with reference to FIG.

  FIG. 2A is a cross-sectional view schematically showing an embodiment before an insulating film is formed on a nitride semiconductor laser element provided with a ridge stripe 140. In the nitride semiconductor laser device of FIG. 2A, the n-type nitride semiconductor layer 110, the nitride semiconductor active layer 120, and the p-type nitride semiconductor layer 130 are formed on the substrate 100 by a procedure known in the art. It is formed in order.

  Further, the p-type nitride semiconductor layer 130 has a ridge stripe 140, hill portions 160 formed on both sides of the ridge stripe 140, and a groove portion 150 between the ridge stripe portion 140 and the hill portion 160. Is formed. The groove 150 has a double channel structure. Examples of these forming methods include reactive ion etching (RIE) and ICP (Inductively Coupled Plasma).

  Next, as shown in FIG. 2B, the upper surface of the p-type nitride semiconductor layer 130 except the top of the ridge stripe 140 is covered with an insulating film 170 so as to conform to the shape of the semiconductor layer 130, and then Then, the entire surface of the nitride semiconductor laser element is covered with the p-type electrode 180 so as to match the shape of the upper surface of the semiconductor layer 130, and the metal film 190 is further covered. Here, conforming is as described above, and has substantially the same shape as the upper surface of the semiconductor layer 130.

  In FIG. 2B, the light emitting region 300 is a region that substantially contributes to light emission in the nitride semiconductor active layer 120 located near the bottom of the ridge stripe 140.

  One feature of the nitride semiconductor laser device according to the present invention formed as described above is that the trench 150 is filled with a metal film 190 so that a cavity is not formed. By forming the metal film 190, even if the surface on which the ridge stripe 140 is formed is damaged in the manufacturing process of the nitride semiconductor laser element, the metal film 190 is only damaged. It is possible to prevent damage to the ridge stripe.

  In the present invention, the width Wb of the groove 150 shown in FIG. 2A is preferably 10 μm or more. For example, when the width Wb of the bottom surface of the groove 150 is less than 10 μm, the groove 150 is not embedded and a cavity is generated, so that heat is cut off, heat dissipation efficiency is deteriorated, and the temperature rise of the nitride semiconductor laser device becomes remarkable. Because. Even when the groove 150 is buried and no cavity is formed, it is not preferable because the heat capacity of the metal film near the active layer is poor and the heat dissipation efficiency is not good.

  Although the width Wb of the groove 150 has a sufficient width, the heat dissipation efficiency is superior. For example, even if the width of the groove width 150 exceeds 50 μm, the heat dissipation efficiency is not significantly improved.

  Furthermore, in the present invention, as shown in FIG. 2A, the relationship between the width Wb of the bottom surface of the groove 150 and the width Rb of the bottom surface of the ridge stripe 140 preferably satisfies Rb / Wb ≦ 0.1. This is because good heat dissipation is obtained. The reason why good heat dissipation can be obtained is that the heat capacity of the metal film having good thermal conductivity is increased by forming a region having a metal film over a wide range from the vicinity of the light emitting region 300 where heat is generated. This is because most of the heat generated in the step can be released to the metal film 190.

  The width Rb of the ridge stripe 140 indicates the width of the bottom of the ridge stripe, that is, the interval from the end of one groove bottom across the ridge stripe to the end of the other groove bottom.

  The upper limit of the width Wp of the groove 150 is not particularly specified, but the width of the hill 160 is preferably at least 50 μm or more from the viewpoint that the submount 210 and the nitride semiconductor laser element are evenly bonded. The width Wp of the groove 150 may be sufficient considering the width of the nitride semiconductor laser element chip and the width of the hill.

  The width Rb of the ridge stripe 140 is preferably at least 1.8 μm or less. This is because it is necessary to improve the kink level as the output of the nitride semiconductor laser element increases. Further, the shape of the side surface of the groove 150 may be any of a rectangular shape, a forward mesa shape, and a reverse mesa structure.

  In FIG. 2B, the insulating film 170 is covered except for the top of the ridge stripe 140, and then the entire surface of the nitride semiconductor laser element is covered in the order of the p-type electrode 180 and the metal film 190. ing. One feature of the nitride semiconductor laser device according to the present invention is that the groove 150 is filled with the metal film 190 so that a cavity is not formed.

The insulating film 170 may be silicon oxide (SiO ₂ or the like) or silicon nitride (SiN _x or the like), or an oxide or nitride such as silicon, titanium, zirconia, tantalum, or aluminum.

  In addition, the thickness of the metal film 190 is preferably 1 μm or more and 10 μm or less. When the metal film 190 has a thickness of 1 μm or more, the stress applied to the ridge stripe by the metal film 190 can be buffered. For example, even if the surface of the metal film 190 is damaged during the manufacturing process, the insulating film 170, the p-type electrode 180, and the ridge stripe 140 are not easily damaged, so that the current can be injected normally. Further, in the case of a general nitride semiconductor laser element, since the height of the ridge stripe is about 0.4 to 0.6 μm, the groove 150 can be completely filled, and good heat dissipation can be obtained. I can do it. Further, if the metal film 190 is too thick, it becomes difficult to cleave the nitride semiconductor laser element wafer.

  The insulating film 170 can be formed by the following method, for example. First, the ridge stripe 140 is formed in the p-type nitride semiconductor layer 130. Next, after forming a resist mask only on the upper surface of the ridge stripe 140, silicon nitride is formed by sputtering or the like. Finally, the resist is removed to complete the insulating film 170.

  The p-type electrode 180 is formed in contact with the top surfaces of the ridge stripe portion 140 and the insulating film 170, and then a metal film 190 is formed. The p-type electrode 180 is preferably formed over the entire surface where the ridge stripe 140 is formed. This is because the p-type electrode 180 has the function of promoting the growth of the metal film in addition to the function as an electrode for injecting current into the ridge stripe 140. In order to preferably use this action, it is preferable that the outermost surface of the p-type electrode 180 is made of the same metal as the metal film 190.

  For example, a preferable metal film is Au when using Pd / Mo / Au, Ni / Au, Pd / Pt / Au, Pd / Au, or the like in which the outermost surface of the p-type electrode 180 is coated with Au. Further, even when the outermost surface of the p-type electrode 180 is any one of Ag, Cu, Al, Mo, etc., the metal film 190 is the same as the p-electrode 180, and is gold (Au), silver (Ag), copper (Cu). It is preferable to form a plating containing at least one of the above materials or any metal film such as Ag, Cu, Al, or Mo.

  Such p-type electrode 180 and metal film 190 can be formed as follows, for example. After forming the insulating film 170, the p-type electrode 180 is formed by EB vapor deposition. Subsequently, a metal film (plating) 190 having a thickness of 5 μm is completed by electroplating.

  As a method for forming the metal film 190, electroplating, immersion plating, alloy plating, EB deposition, sputtering, ECR, or the like can be used.

  By making the upper surface of the metal film 190 on the ridge stripe 140 lower than the upper surface of the metal film 190 on the hill portion 160, the ridge stripe 140 may be damaged when the ridge stripe 140 is damaged in the manufacturing process or when the junction is bonded to the submount 210. 140 is more preferable because damage to 140 can be prevented. In addition, since the metal film 190 is formed on the ridge stripe 140 when joining to the submount 210 by junction down, the heat dissipation efficiency is also good.

  Next, the substrate 100 is polished or etched from the back surface to remove a part of the substrate 100 and reduce the thickness of the wafer to about 80 to 200 μm. Thereafter, Hf / Al is formed on the n-type electrode 200 by, for example, EB vapor deposition.

  The material used for the n-electrode 200 is not limited to this, and Hf / Al / Mo / Au, Hf / Al / Pt / Au, Hf / Al / W / Au, Hf / Au, Hf / Mo / Au or the like may be used. Alternatively, an electrode material in which Hf is replaced with Ti or Zr with these materials may be used.

  Subsequently, the nitride semiconductor laser element thus formed is bonded to the submount 210 (or stem). At this time, the submount 210 and the metal film 190 are joined by junction down using the solder 220 so as to face each other.

  In the present invention, SiC or AlN is preferably used mainly for the submount, and since these have poor adhesion to metal, a glossy metal film is effective. In the present invention, the submount and the metal film can be joined via solder. The solder used at this time can be one containing at least one of In, Sn, Pd, and Au, and is preferably Au—Sn. The ratio is preferably about Au: Sn = 70: 30.

  In the above-described bonding, the case where the nitride semiconductor laser element is bonded to the submount has been described. However, the nitride semiconductor laser element may be directly bonded to the stem.

  In the present invention, a GaN substrate or an AlN substrate can be used as the substrate. Further, the nitride semiconductor is specifically AlGaN, InGaN, GaN, or the like. The metal film (plating) can be cyan gold plating or sulfite gold plating. Sulfurous acid gold plating is particularly preferable because it has high hardness and hardly causes deformation. Moreover, since the surface particle | grains become finer when glossy gold plating is performed, since adhesiveness with a submount becomes favorable, it is suitable.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic sectional drawing of the nitride semiconductor laser element of this invention. It is a schematic sectional drawing which shows the manufacturing process of the nitride semiconductor laser element of this invention. It is a schematic sectional drawing of the conventional nitride semiconductor laser apparatus. It is a schematic sectional drawing of the conventional semiconductor laser apparatus.

Explanation of symbols

  100, 500 substrate, 110 n-type nitride semiconductor layer, 120 nitride semiconductor active layer, 120 p-type nitride semiconductor layer, 140 ridge stripe portion, 150,550 groove portion, 160 hill portion, 170,560 insulating film, 180, 570 p electrode, 190 metal film, 200,580 n electrode, 210,600 submount, 220,610 solder, 300 light emitting region, 510 n-type semiconductor layer, 520 active layer, 530 p-type semiconductor layer, 540 ridge-type waveguide 590 p-type plated electrode, 620 cavity.

Claims (6)

In a nitride semiconductor laser device in which a nitride semiconductor laser element is joined to a submount or a stem by junction down,
The nitride semiconductor laser element includes a p-type nitride semiconductor layer, a p-type electrode, and a metal film,
A narrow channel ridge stripe is formed on the upper surface of the p-type nitride semiconductor layer, and a double channel structure in which grooves are provided on both sides along the ridge stripe is provided.
The p-type electrode is in contact with the top of the ridge stripe and is formed to match the shape of the upper surface of the p-type nitride semiconductor layer,
The nitride semiconductor laser device, wherein the metal film is formed on a p-type electrode, and there is no cavity between the metal film and the p-type electrode.   The nitride semiconductor laser device according to claim 1, wherein a width of the groove is 10 μm or more.   The nitride semiconductor laser device according to claim 1, wherein the metal film has a thickness of 1 μm to 10 μm.   The nitride semiconductor laser device according to claim 1, wherein an outermost surface of the p-type electrode is formed of any one of Au, Ag, Cu, Al, or Mo.   The metal film is a plating containing at least one material of Au, Ag, Cu, or Al, or a metal film made of any of Au, Ag, Cu, Al, or Mo. The nitride semiconductor laser device according to claim 1.   6. The nitride semiconductor laser device according to claim 1, wherein the outermost surface of the p-type electrode and the metal film are made of the same material.

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