JP3593441B2 - Nitride-based compound semiconductor light emitting device and method of manufacturing the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light-emitting device using a nitride-based compound semiconductor material, and more particularly to a nitride-based compound semiconductor light-emitting device made of a nitride-based compound semiconductor such as GaN, AlGaN, and InGaN, and a method of manufacturing the same.
[0002]
[Prior art]
In recent years, semiconductor lasers have been used in various fields such as home appliances, OA equipment, communication equipment, and industrial measuring instruments. Above all, development of short-wavelength semiconductor lasers has been focused on for the purpose of application to high-density optical disk recording, which is expected to be used in many fields. At present, a red semiconductor laser is used, and the recording density has been improved as compared with the infrared semiconductor laser up to that time. However, there are many material problems such as difficulty in reducing defects and high operating voltage for application to next-generation optical disk recording and the like. Further, the oscillation wavelength is about 460 nm even if it is short, and oscillation in the order of 420 nm required by the system is difficult due to physical properties.
[0003]
On the other hand, a nitride-based semiconductor laser containing GaN can shorten the wavelength to 350 nm or less in principle, and an oscillation operation at 400 nm has been reported. Regarding reliability, reliability of 10,000 hours or more has been confirmed for LEDs. As described above, the nitride semiconductor material is a material having excellent characteristics that satisfy the conditions required as a next-generation optical disk recording light source.
[0004]
[Problems to be solved by the invention]
Here, the laser oscillation operation requires a resonator. In a normal semiconductor laser, a mirror is formed using a naturally cleaved surface to form a resonator. This is based on the fact that a plane having small binding energy, that is, a cleavage plane exists in the [011] or [0-11] direction in the cubic zinc-zinc structure. In the nitride semiconductor system, the cubic type and the hexagonal type exist as described above, and the hexagonal type crystal growing on sapphire has at present obtained the best crystal, but unfortunately, In the hexagonal type, the mode of the natural cleavage plane used when forming a normal semiconductor laser does not exist clearly, so it is guided to the cleavage plane of sapphire, and the nitride semiconductor is also broken in that direction, forming a resonator mirror. Is very difficult, and the yield of the device manufacturing process is low.
[0005]
In addition, there is a problem that the resonator mirror is suddenly deteriorated during operation at high output, and a problem that heat is generated during the operation causes distortion between the substrate and the substrate, dislocations multiply and the end face is deteriorated. I was.
When used as a light source for an optical recording disk, it is necessary to control the transverse mode to narrow the laser spot and oscillate only in the basic mode. This has a problem that it is difficult to control even a high-power laser used for recording, but it is difficult.
[0006]
As described above, the conventional nitride-based semiconductor light-emitting device has a number of problems such as extremely difficult formation of a resonator mirror, a problem in reliability, and difficulty in transverse mode control.
[0007]
The present invention has been made in view of such a problem. That is, an object of the present invention is to provide a nitride-based compound semiconductor light-emitting device capable of forming a good cleavage surface in a simple process and a method of manufacturing the same.
[0008]
[Means for Solving the Problems]
The gist of the present invention is that the light emitting layer is cleaved without being affected by the cleaving property of the substrate to form a resonator mirror, and a part of the end face is separated from the substrate to make it less likely to receive distortion from the substrate. The lateral mode is controlled by preventing the deterioration due to light emission, lowering the reflectance of a part of the emission end face, and making the part of the end face not parallel to the opposite face so as not to form a resonator. It is to improve the performance as a light source for a recording disk.
[0009]
More specifically, the nitride-based compound semiconductor light-emitting device of the present invention comprises a first contact layer formed on a substrate, a current confinement layer formed on the first contact layer, and a current confinement layer formed on the first contact layer. A light-emitting layer formed of a compound containing nitrogen, which is formed on the light-emitting layer, a second contact layer formed on the light-emitting layer, and the first contact layer and the second contact layer. The current constriction layer includes first and second electrodes formed, and a side surface of the current confinement layer recedes inward with respect to a side surface of the light emitting layer, and a recess is formed between the substrate and the side surface of the light emitting layer. It is characterized by having been done.
[0010]
Further, in the nitride-based compound semiconductor light emitting device of the present invention, a side surface of the light emitting layer including a concave portion formed by a side surface of the current confinement layer is covered with an insulator.
[0011]
Alternatively, the nitride-based compound semiconductor light-emitting device of the present invention comprises a substrate, an intermediate layer deposited on the substrate, and a first clad layer made of the nitride-based compound semiconductor deposited on the intermediate layer. An active layer made of a nitride-based compound semiconductor deposited on the first clad layer; and a second clad layer made of a nitride-based compound semiconductor deposited on the active layer. A nitride-based compound semiconductor light-emitting device, wherein the side surface of the intermediate layer recedes into the device from the side surface of the active layer on the light emission side surface of the light-emitting device, and the substrate and the active layer A concave portion is formed between the side surface and the side surface.
[0012]
Here, it is desirable to use any of AlN, AlGaN, InAlGaN, ZnO, and InGaN for the intermediate layer.
[0013]
Further, the light emitting element is configured to emit a laser beam by a resonator having a part of the side face opposed to the active layer as a light reflecting surface, and the light emitting side face of the light emitting element further includes the laser Cleaved surface of the nitride-based compound semiconductor including a portion where light intensity is most strongly emitted, and disposed on both sides of the cleaved surface, the reflectance at the wavelength of the laser light is the wavelength of the laser light of the cleaved surface And a surface that is relatively smaller than the reflectance in the above.
[0014]
Further, the side surface on the light emission side of the light emitting element includes a cleavage surface of the nitride-based compound semiconductor including a portion where the intensity of the laser light is emitted most strongly, and the cleavage surface arranged on both sides of the cleavage surface. And an inclined surface having an inclination.
[0015]
Further, in the method for manufacturing a nitride-based compound semiconductor light emitting device of the present invention, a step of forming a first contact layer on a substrate, a step of laminating and forming a current confinement layer on the first contact layer, Laminating a light emitting layer made of a compound containing nitrogen on the current confinement layer, laminating a second contact layer on the light emitting layer, and forming the second contact layer on the first contact layer and the second contact layer. Forming a first electrode and a second electrode that are in contact with each other, and forming a mesa-type laminate by etching the laminate from the first contact layer to the second contact layer using a mask. And a step of dicing the substrate on which the mesa-type laminated body is formed into element units by dicing, and, after installing the separated elements on a pedestal, immersing the element in an etchant to remove the current constriction layer. Selective etching from the periphery of the surface to form a concave portion on the side surface of the mesa-type laminate, and cleaving by applying an external force to the laminate in which the concave portion is formed. You.
[0016]
Alternatively, a step of depositing an intermediate layer on a substrate, a first cladding layer made of a nitride-based compound semiconductor, an active layer made of a nitride-based compound semiconductor, and a nitride-based compound semiconductor on the intermediate layer Depositing a second cladding layer consisting of: a step of forming an etching mask on the second cladding layer; and forming a mask on the substrate through the etching mask until a side surface of the intermediate layer is exposed. A first etching step of etching in a direction substantially perpendicular to the first etching step, a second etching step of forming a recess by selectively etching a side surface of the intermediate layer exposed in the first etching step, Removing the semiconductor layer portion including the active layer protruding above by cleaving to form an end face of the semiconductor laser.
[0017]
Here, the etching mask is at least one for concentrating stress along a cleavage plane of the nitride-based compound semiconductor so as to facilitate cleavage of the nitride-based compound semiconductor constituting the active layer. It is desirable to have a configuration characterized by having a wedge shape.
[0018]
Further, it is preferable that the intermediate layer is made of any one of AlN, AlGaN, ZnO, and InGaN.
[0019]
Further, it is desirable that the first etching step is configured to be performed by a dry etching method.
[0020]
Further, it is preferable that the second etching step is configured to be performed by a wet etching method using an etching solution.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, a good mirror can be formed by natural cleavage of the light emitting layer without cleavage being guided to the substrate. In addition, by separating a part of the end face from the substrate, it is difficult to receive distortion from the substrate, and deterioration due to the distortion can be prevented. Further, according to the present invention, the lateral mode is reduced by lowering the reflectance of a part of the laser light emitting end face or configuring the end face not to be parallel to the opposite face so that a part of the end face is not formed as a resonator. By controlling the light source, it is possible to provide a good light emitting element as a light source for an optical recording disk.
[0022]
Hereinafter, embodiments of the present invention will be described with reference to examples.
FIG. 1 is for explaining a schematic configuration of a blue semiconductor laser device according to a first embodiment of the present invention. On a sapphire substrate 10, an n-GaN buffer layer 11 (Si-doped, 3 to 5 × 10 ¹⁸ cm ^-3 , 2 μm), n-GaN contact layer 12 (Si-doped, 3 to 5 × 10 ¹⁸ cm ^-3 , 4 μm), n-AlN current confinement layer 13 (Si-doped, 3 to 5 × 10 ¹⁸ cm ^-3 , 1 μm), n-GaN cladding layer 14 (Si-doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), In _0.2 Ga _0.8 N active layer 15 (andove, 2 nm), p-GaN cladding layer 16 (Mg-doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), GaN contact layer 17 (Mg doped, 1-3 × 10 ¹⁸ cm- ³ , 0.1 μm) are sequentially formed by MOCVD, a mask covering a predetermined region is formed thereon, and the other portion is etched until the n-type contact layer 12 is reached. To form Next, a p-side electrode 18 is provided on the GaN contact layer 17 which is the uppermost layer of the stack, and an n-side electrode 19 is provided on the n-GaN contact layer 12.
[0023]
After that, the wafer is cut into individual elements by dicing from the back surface of the wafer constituting the substrate 10 and separated. Although not shown, the separated elements are placed on a pedestal with an interval enough to allow the etchant to penetrate, and are immersed in an etchant containing phosphoric acid and fluorine to selectively etch the AlN layer 13 from the side. That is, since the AlN layer 13 contains Al, it is selectively over-etched with respect to the other layers constituting the multilayer body M. As a result, the side surface of the AlN layer 13 recedes inside the device as compared with the side surfaces of the other layers, and a groove-shaped concave portion is formed around the stacked body M. This structure is a so-called current confinement structure. When the current is injected by the electrodes 18 and 19, the current is constricted by the AlN layer 13 and the density of the current injected into the active layer 15 can be increased. Next, each element thus etched is washed with water, and as shown in FIG. 2, a force F is applied to the end portions M1 and M2 near the side surfaces of the multilayer body M which are to be the resonator surfaces. As a result, the multilayer body M was easily cleaved along the groove-shaped concave portion irrespective of the cleavage direction of the substrate 10, and the formed cleavage surface was also good. This is because the light emitting layer In is not guided to the cleavage surface of the sapphire substrate 10. _0.2 Ga _0.8 This is considered to be due to clear natural cleavage of the GaN layers such as the N active layer 15, the n-GaN cladding layer 14, the p-GaN cladding layer 16 and the GaN contact layer 17 on both sides thereof.
[0024]
The laser of this example oscillated continuously at room temperature at a threshold value of 30 mA. The oscillation wavelength was 417 nm, and the operating voltage was 8V. Further, as shown in FIG. 3, the oscillation threshold value of this embodiment (Q) was 30 mA lower than that of the conventional device (P) without the current confinement structure, as shown in FIG. In addition, because of the good cleavage surface, deterioration and the like were suppressed, and the light emission pattern was also good. As a result, the luminous efficiency was improved more than twice as compared with the conventional one.
[0025]
The AlN current confinement layer 13 may be replaced with ZnO, and the etchant may be a solution containing sulfuric acid or an alkaline solution containing ammonia. When ZnO was used, not only crystals with better crystallinity were formed, but also etching was easy, the process was easy, and the yield was improved.
[0026]
The crystal growth may be performed by MBE.
[0027]
FIG. 4 is a diagram showing a schematic configuration of a blue semiconductor laser device according to a second embodiment of the present invention.
[0028]
On a sapphire substrate 20, an AlN buffer layer 21 (3 to 5 × 10 ¹⁸ cm ^-3 , 0.1 μm), n-GaN contact layer 22 (Si-doped, 1 × 10 ¹⁹ cm ^-3 , 4 μm), Zn0 layer 23 (1 μm), n-Al _0.5 Ga _0.5 N cladding layer 24 (Si-doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), GaN optical confinement layer 25 (Si-doped, 0.1 μm), In _0.1 Ga _0.9 N active layer 26 (Si doped, 3 nm), GaN light confinement layer 27 (Si doped, 0.1 μm), p-Al _0.5 Ga _0.5 N cladding layer 28 (Mg doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), GaN contact layer 29 (Mg-doped, 1-3 × 10 ¹⁸ cm ^-3 , 0.1 μm) are sequentially formed by the MBE method, a mask covering a predetermined region is formed thereon, and the other portion is etched until reaching the n-type contact layer 22 to form a mesa-type stacked body M. Form '. Next, a p-side electrode 30 is provided on the GaN contact layer 29 which is the uppermost layer of the stacked body M ′, and an n-side electrode 31 is provided on the n-GaN contact layer 22.
[0029]
Thereafter, the wafer is cut from the back surface of the wafer constituting the substrate 20 into individual elements by dicing and separated. Although not shown, each of the separated elements is mounted on a pedestal, and wiring is performed to terminals of the pedestal by Au wires 33 and 34 for both n-type and p-type. Next, the elements mounted on these pedestals are immersed in an etchant, and the Zn0 layer 23 is selectively etched from the side. As a result, the Zn0 layer 23 is over-etched, and the side surface thereof recedes inside the mesa-type laminate M ′ as compared with the side surface of the other layers, thereby forming a groove-shaped recess around the laminate M ′. Thereafter, the elements mounted on the pedestal are washed with water, and as shown in FIG. 5, an appropriate amount of a liquid silanol compound 32 is applied around the mesa-type laminate M 'of each element, and cured by heating to obtain a laminate M. Around the 'as shown in FIG. ₂ A film 32 is formed. Thereafter, when the element mounted on the pedestal is immersed in a liquid and subjected to ultrasonic waves, the end face portions M1 'and M2' serving as resonator surfaces shown in FIG. 5 are cleaved as shown in FIG. By this operation, a current confinement structure can be formed by the ZnO layer 23, and the side surface thereof is formed of SiO. ₂ Because of this, the leakage current flowing along the surface could be prevented.
[0030]
The laser device of this example continuously oscillated up to 80 ° C. at a threshold value of 10 mA as shown by a curve Q in FIG. The oscillation wavelength was 383 nm, the fundamental transverse mode was oscillated, and stable operation up to 5000 hours was confirmed as shown in FIG. The operating voltage of this laser device was 4V. In this element structure, the adjacent surface of the resonator mirror is etched when the Zn0 layer 23 is etched to form a current confinement structure, so that the threshold current decreases as shown in FIG. Since no leakage current flows on the surface, the luminous efficiency is also improved. Further, since no current flows near the resonator mirror surface, the resonator mirror is not damaged, and the distortion of the light emitting layer is reduced, thereby improving the reliability (FIG. 8). When the thickness of the AlN buffer layer 21 was increased to 20 μm, the function as a heat sink was added, the temperature characteristics were improved, and continuous oscillation was performed up to 100 ° C. Also, n-A1 _0.5 Ga _0.5 When the N cladding layer 24 was thinned to 0.1 μm, the cladding layer 24 and SiO ₂ The control of the transverse mode was maintained even at high power due to the difference in refractive index between the layer 32 and the layer 32.
[0031]
9 to 11 show a third embodiment of the present invention. FIGS. 9 and 11 are plan views and FIG. 10 is a side view.
[0032]
On the sapphire substrate 40, an AlN buffer layer 41 (3 to 5 × 10 ¹⁸ cm ^-3 , 0.01 μm), n-GaN contact layer 42 (Si-doped, 1 × 10 ¹⁹ cm ^-3 , 2 μm), n-Zn0 layer 43 (1 μm), n-GaN layer 44 (Si-doped, 1 × 10 ¹⁹ cm ^-3 , 1 μm), n-Al _0.5 Ga _0.5 N clad layer 45 (Si-doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), GaN optical confinement layer 46 (Si-doped, 0.1 μm), In _0.1 Ga _0.9 N active layer 47 (Si doped, 3 nm), GaN light confinement layer 48 (Si doped, 0.1 μm), p-Al _0.5 Ga _0.5 N cladding layer 49 (Mg doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), GaN contact layer 50 (Mg-doped, 1-3 × 10 ¹⁸ cm ^-3 , 0.1 μm) are sequentially grown and formed by MBE. Thereafter, the substrate 40 on which these growth layers are stacked is taken out of the growth chamber, and SiO 2 is deposited on the p-GaN contact layer 50. ₂ An insulating film 51 is formed, a part thereof is etched in a stripe shape (a part shown by a broken line in FIG. 9) so as to reach the p-GaN contact layer 50, and Ni is deposited thereon by 50 nm. Thereafter, a mask having a shape as shown in FIG. 11 is formed using Ti, and etching is performed by dry etching until the n-GaN contact layer 42 is reached. Next, a mask is formed in a portion other than the portion to be the n-type electrode 53, and then, p-type electrode 52 can be formed by evaporating Ti. Thereafter, the mask is removed. Next, the whole portion is etched until the other portion reaches the n-type contact layer 42 to form an n-type electrode 53. A p-side lead wire 54 is connected to the p-type electrode 52, and an n-side lead wire 55 is connected to the n-type electrode 53.
[0033]
A schematic diagram of the shape at this point is shown in FIG. This figure is a top view of a single light-emitting element region, which is composed of a p-type electrode 52 region to which a p-side lead wire 54 is connected, a laser element body 55 connected to the region, and an n-type electrode 53 region. ing. Comparing the completed top views of FIG. 11 and FIG. 9, it can be seen that the cleavage surface 56 serving as the resonator surface of the laser element body 55 is not formed. Thereafter, as in the case of the above-described embodiment, the entire substrate 40 is immersed in an etchant, and the Zn0 layer 43 is selectively etched from the side. As a result, the Zn0 layer 43 is over-etched, and its side surface recedes with respect to the entire side surface of the mesa-type laminated body M ″, and a groove-shaped concave portion 56 is formed around the laminated body M ″. In FIG. 10, a through-hole 57 which has been etched away is also formed inside the Zn0 layer 43. This is a p-type electrode to which the laser element body 55 and the p-side lead wire 54 of FIG. 10 or 11 are connected. Through holes 57 are formed by overetching in the grooves 59 on both sides of the connection with the 52 region.
[0034]
After the completion of the etching, the substrate is washed with water, cut out from the back surface of the wafer constituting the substrate 40 by dicing into element units, and separated. Next, each of the separated elements is mounted on a pedestal (not shown), and the n-type electrode 53 and the p-type electrode 54 are connected to the terminals of the pedestal by Au wire lead wires 54 and 55. Thereafter, although not shown, when ultrasonic waves are applied in a liquid, the end face portions M1 "and M2" of the mesa-type laminated body M "to be the resonator surface shown in FIG. 11 are cleaved to complete the structure as shown in FIG. Next, as shown in Fig. 9, an appropriate amount of a liquid silanol compound 58 is applied around the mesa-type laminate M "portion of the laser element, and cured by heating to oxidize the cyanol compound. As shown in FIG. 10, Si0 covering the side portions of the mesa-type laminate M " ₂ A film 58 is formed.
[0035]
In the laser device completed in this way, as shown in FIG. 10, a current confinement structure can be formed by the Zn0 layer 43, and the side surface thereof is made of SiO.sub. ₂ Since the film 58 was covered, the leakage current flowing along the surface could be prevented. Most importantly, the length between the end faces M1 "and M2" of the mesa-type laminated body M ", which is the cavity length of the laser element main body 55, and the stripe shape extended between them are the resonator length of the laser element main body 55. This means that the width of the Zn0 layer 43 can be reduced, whereby the threshold current and operating power can be reduced, and when the resonator length is 100 μm and the stripe width is 5 μm, the threshold current becomes 1 mA. Reliability has also improved.
In the laser device of this example, continuous oscillation was performed up to 80 ° C. at a threshold value of 3 mA. The oscillation wavelength was 390 nm, the fundamental transverse mode was oscillated, and stable operation up to 5000 hours was also confirmed. The operating voltage was 3.8V.
[0036]
Next, a fourth embodiment of the present invention will be described.
[0037]
FIG. 12 is a schematic diagram illustrating a cross-sectional structure of a blue semiconductor laser device according to a fourth embodiment of the present invention. In the figure, 60 is a sapphire substrate, 61 is an n-AlN buffer layer (Si-doped, carrier concentration: 3 to 5 × 10 ¹⁸ cm ^-3 , A layer thickness: 100 nm), and 62 is an n-GaN contact layer (Si-doped, 3 to 5 × 10 ¹⁸ cm ^-3 , 4 μm), 63 is n-Al _0.5 Ga _0.5 N cladding layer (Si doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), 64 is In _0.2 Ga _0.8 N active layer (undoped, 3 nm), 65 is p-Al _0.5 Ga _0.5 N cladding layer (Mg doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm) and 66 are p-GaN contact layers (Mg-doped, 1-3 × 10 ¹⁸ cm ^-3 , 0.1 μm), 67 is a p-side electrode, and 68 is an n-side electrode. The crystal growth of each semiconductor layer indicated by 61 to 66 in the same figure was performed by the MOCVD method.
[0038]
Also in this example, an element-forming step was performed after crystal growth of the laminated structure shown in FIG.
[0039]
FIG. 13 is a schematic diagram illustrating the shape of the etching mask used in this embodiment. That is, after the above-described crystal growth step, first, a mask having a shape as shown in FIG. 13 is formed on the contact layer 66, and an unmasked portion is etched until it reaches the substrate 60. This etching is desirably an etching method capable of etching vertically to the substrate without having selectivity depending on the composition of each of the semiconductor layers 61 to 66, and specifically, a dry etching method is used. Is desirable. More specifically, for example, CF is used as an etching gas. ₄ , SF ₆ , BCl ₃ , Cl ₂ Reactive ion beam etching can be performed using an ECR (Electron Cyclotron Resonance) etching apparatus using a mixed or single gas containing any one of the above.
[0040]
Further, when forming a mask on the gallium nitride crystal, as will be described later, the mask is formed such that the line AA in the figure is parallel to the cleavage plane of the gallium nitride-based compound semiconductor. Here, the cleavage plane of the gallium nitride-based compound semiconductor is specifically (1-100), (10-10), (01-10), (-1100), (-1010), or (0-10). 110). These planes are different from the cleavage planes of sapphire, and the method of the present invention allows cleavage of the gallium nitride-based compound semiconductor on a plane different from that of sapphire.
[0041]
FIG. 14 is a schematic perspective view showing the shape after the etching. As shown in the figure, the semiconductor layers 61 to 66 have side surfaces etched in a shape cut into a wedge shape in the depth direction.
Next, the AlN layer 61 exposed on the side surface of the semiconductor layer is selectively etched. As the etching method, for example, a wet etching method using an etching solution such as phosphoric acid, aqua regia, or SH (sulfuric acid: hydrogen peroxide solution: water = 5: 1: 1) can be used. That is, since the AlN layer 61 contains aluminum, it is selectively etched by these etching solutions. In addition, by increasing the temperature of the etching solution, the etching rate is increased, and a faster process can be performed.
[0042]
FIGS. 15A and 15B are explanatory views showing the shape of the semiconductor layer after this etching step. That is, FIG. 2A is a schematic perspective view, and FIG. 2B is a schematic front view as seen from the direction of the arrow shown in FIG. As shown in these figures, in this etching step, etching is performed until the AlN layer 61 below the edge E of the semiconductor layer cut from both sides by the wedge-shaped groove is removed by etching. By etching and removing the AlN layer 61 in this manner, the end portion E is separated from the substrate 60 and floats in the air, so that cleavage, which will be described later, can be easily performed.
[0043]
Next, a portion to be a p-electrode is masked and etched until the n-GaN layer 62 is exposed. Further, an n-side electrode 68 is formed by depositing an electrode material. Thereafter, by immersing in a solution and transmitting ultrasonic waves to the solution, the end face portion is cleaved to form a mirror-like end face.
[0044]
FIG. 16 is a schematic diagram illustrating a state where the end face portion is cleaved. According to the present invention, as described above, the wedge shape of the mask shown in FIG. 13 is aligned and etched along the natural cleavage plane of the gallium nitride based semiconductor. Therefore, stress can be concentrated along the cleavage plane of the gallium nitride based semiconductor, and cleavage can be easily caused. Further, according to the present invention, since the cleaved end portion E is separated from the substrate 60 by etching and removing the lower AlN layer 61 and floats in the air, the cleaved plane orientation of the substrate 60 Regardless, the gallium nitride based semiconductor can be cleaved.
[0045]
Thereafter, the substrate 60 is further diced, and each element is cut together with the substrate 60.
[0046]
FIG. 17 is a schematic perspective view of the completed semiconductor light emitting device. In the end face S of the completed device, there is a portion in which the layer containing aluminum is depressed from the periphery and has a concave shape. This depression is larger as the content of aluminum is larger. For this reason, not only the AlN layer 61 on the substrate 60 but also the cladding layers 63 and 65 are etched, so that the side surface is depressed to form a concave portion. However, the vicinity SL of the laser light emission end face is not exposed at the time of etching the AlN layer, and is exposed after cleavage by applying ultrasonic waves. Therefore, no dent due to this etching occurs, and the laser oscillation operation is not affected. Absent.
[0047]
The step of etching with a mask having a wedge shape may be after the step of exposing the n-side contact layer by etching to form an n-side electrode.
[0048]
Other steps can be performed in an order different from that of this embodiment. However, in that case, it is necessary to appropriately change the mask shape. Further, in the mask illustrated in FIG. 13, one element has an independent shape separated from other elements. However, the present invention is not limited to this. For example, adjacent elements on a wafer may be contacted. A mask having such a shape can also be used.
[0049]
As a result of trial production by the present inventor, when the light emitting device according to this example was fixed to an evaluation jig and operated, room temperature continuous oscillation was performed at a threshold value of 150 mA. The oscillation wavelength was 422 nm, and the operating voltage was 4V. In addition, the lifetime of the element is at least 10 times longer and extremely longer than that of an element having an end face formed by ordinary dry etching or an element having an end face formed by damaging a substrate or a growth surface and dividing it along the surface. It was found to have a lifetime.
[0050]
Further, looking at the light emission pattern of the laser beam, only one portion where the light intensity was maximum was found, which was optimal for reading and writing on an optical recording disk. This reflects that the light emitting device according to the present embodiment oscillates in the fundamental transverse mode. As a reason, it was confirmed that a portion having a low reflectivity was present on the end face, whereby the outer higher-order mode was cut, and oscillation was performed only in the fundamental mode.
[0051]
That is, in the present embodiment, since etching is performed in a wedge shape using a mask as illustrated in FIG. 13, the left and right surfaces SS, SS of the cleavage surface SL are, as shown in FIG. Since it was inclined and did not have a parallel surface that could act as a resonator, it was found that oscillation did not occur in a high-order mode near this even at high output.
[0052]
On the other hand, in the present invention, the shape of the mask may be changed so that the end face of the laser becomes flat.
[0053]
FIG. 18 is a schematic view illustrating such a mask. That is, a wedge shape C in which the end face side of the light emitting element is flat can be adopted. Even at the end face of the light emitting element formed by using such a mask in the same process as described above, the light reflectance can be made different between the cleaved face and the left and right faces. The reason is that the etching surface formed after the etching in the form of a wedge can be not a mirror surface but a "rough" surface having fine irregularities. Such a "rough" etched surface can be easily obtained by appropriately adjusting etching conditions in a dry etching method or the like.
[0054]
That is, when an etching mask as shown in FIG. 18 is used, the end face of the light emitting element can be made substantially flat, and the laser light emitting portion has a mirror surface formed by a cleavage plane. On the other hand, it can be formed so that etched surfaces with low reflectivity exist on the left and right sides. Also in this case, since the left and right surfaces of the cleavage surface are not surfaces that can function as a resonator, oscillation does not occur in a high-order mode even at a high output in the vicinity, and the fundamental transverse mode is maintained. be able to.
[0055]
On the other hand, also in the present embodiment, the AlN buffer layer 61 may be replaced with ZnO, and when ZnO is used, each layer grown thereon becomes a crystal having better crystallinity, thereby improving the characteristics of the light emitting element. Can be improved. In this case, aqua regia or a hydrochloric acid-based etching solution can be used as an etching solution for forming the recess.
[0056]
Further, instead of the AlN buffer layer 61, an InGaN layer may be used. In this case, the amount of strain of the crystal layer grown thereon is adjusted, and the effect of preventing cracks in the crystal even when the aluminum composition of the AlGaN layer is increased is obtained. Further, the InGaN layer functions as a light absorption layer, and has an advantage that self-excited oscillation occurs together with mode control, thereby facilitating high-frequency driving. In this case, a bromine-based or hydrochloric acid-based etching solution can be used.
[0057]
In this embodiment, the MOCVD method is used as a crystal growth method, but other methods such as an MBE method, a chemical beam epitaxial (CBE) method, an organic metal molecular beam epitaxial (MOMBE) method, and a hydride CVD method are used. Can also be used.
[0058]
Further, as the shape of the etching mask as shown in FIG. 13, the wedge-shaped portion can oscillate at an angle α = 0 to 45 ° with respect to the emission end face of the laser beam, and when α = 0 ° Although the output with respect to the current value was large, the transverse mode control could be held most when α = about 10 °. When the angle α is further increased, the lateral mode control can be maintained, but the output tends to decrease.
[0059]
Next, a fifth embodiment of the present invention will be described.
[0060]
FIG. 19 is a schematic diagram illustrating a cross-sectional structure of a blue semiconductor laser device according to a fifth embodiment of the present invention. That is, the laser device shown in the figure has a GaN buffer layer 81 (3 to 5 × 10 ¹⁶ cm ^-3 ), N-GaN contact layer 82 (Si-doped, 1 × 10 ¹⁸ cm ^-3 ), N-ZnO layer 83 (Cl doped, 1 × 10 ¹⁹ cm ^-3 , 1 μm), n-Al _0.5 Ga _0.5 N cladding layer 84 (Si-doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), GaN optical confinement layer 85 (undoped, 0.1 μm), In _0.2 Ga _0.8 N / GaN 3 MQW active layer 86 (undoped, well layer 2 nm, barrier layer 4 nm), GaN light confinement layer 87 (undoped, 0.1 μm), p-Al _0.5 Ga _0.5 N cladding layer 88 (Mg doped, 5 × 10 ¹⁷ cm ^-3 , 0.3 μm), GaN contact layer 89 (Mg doped, 1-3 × 10 ¹⁸ cm ^-3 , 0.1 μm) has a layered structure that is sequentially grown. Reference numeral 91 denotes a p-side electrode, and 92 denotes an n-side electrode.
[0061]
The crystal growth was performed by the MBE method. Thereafter, a mask as shown in FIG. 13 is formed on a portion to be a p-type electrode, and the other portion is etched until reaching the n-type contact layer 82 to form an n-type electrode 92. Next, the ZnO layer 83 is etched from the side by immersion in an etchant. As the etching solution, aqua regia or a hydrochloric acid-based etching solution can be used. As a result, the ZnO layer 83 is etched, and a structure is created in which the side surface of the ZnO layer 83 is recessed inside the element as compared with the side surfaces of the other layers. Further, at the time of washing after the etching, by washing with a strong water flow, the tip side is cleaved and removed from the wedge-shaped cut. Alternatively, the cleavage may be performed by applying ultrasonic waves in water. If such a wedge-shaped cut is not made, the intended end face could not be formed, and the yield was reduced.
[0062]
FIG. 20 is a schematic perspective view of a main part showing a shape before the cleavage described above.
[0063]
As a result of the prototype of the inventor, the light emitting device of this example continuously oscillated up to 80 ° C. at a threshold of 100 mA. The oscillation wavelength was 418 nm, and the fundamental transverse mode was oscillated, and stable operation up to 5000 hours could be confirmed. The operating voltage of the device was 4V.
[0064]
Here, in the present embodiment, as shown in FIG. 20, the ZnO layer 83 is recessed from the side surface of the element by etching. That is, the current is confined, and a current structure does not flow near the mirror surface which is the end face of the laser resonator, which is a so-called window structure. As a result, according to the present embodiment, optical damage (COD: catastrophic optical damage) due to current injection into the vicinity of the resonator surface is suppressed, and the effect of improving the reliability of the light emitting element is obtained. Can be.
Also in this embodiment, the crystal growth method is not limited to the MBE method, but may be MOCVD, chemical beam epitaxy (CBE), metalorganic molecular beam epitaxy (MOMBE), hydride CVD, or the like. You can also.
[0065]
【The invention's effect】
The present invention is embodied in the form described above, and has the effects described below.
[0066]
First, according to the present invention, it is possible to provide a semiconductor laser device capable of forming a high current injection density, a high luminous efficiency, a good mirror, and simplifying an element structure.
[0067]
Further, according to the present invention, the reliability of the light emitting layer is improved because the strain of the light emitting layer is relaxed, and the current injection to the end face is reduced, so that the optical sudden deterioration at the end face is less likely to occur, and the output is high and the reliability is excellent. Element can be obtained.
[0068]
Further, the above-described structure can be manufactured by a simple process with good reproducibility, and its usefulness is enormous.
[Brief description of the drawings]
FIG. 1 is a sectional view of a light emitting device according to a first embodiment of the present invention.
FIG. 2 is a perspective view showing a method for manufacturing the light emitting device shown in FIG.
FIG. 3 is a graph showing a relationship between an injection current and light emission intensity of the light emitting device shown in FIG. 1 in comparison with a conventional light emitting device.
FIG. 4 is a sectional view of a light emitting device showing a second embodiment of the present invention.
FIG. 5 is a perspective view of a light emitting device showing a method for manufacturing the light emitting device shown in FIG. 4;
FIG. 6 is a perspective view of a light emitting device showing a method for manufacturing the light emitting device shown in FIG.
7 is a graph showing the relationship between the injection current and the light emission intensity of the light emitting device shown in FIG. 4 in comparison with a conventional light emitting device.
8 is a graph showing a relationship between an operation time and an operation current of the light emitting device shown in FIG. 4 in comparison with a conventional light emitting device.
FIG. 9 is a top view of a light emitting device showing a third embodiment of the present invention.
FIG. 10 is a cross-sectional view of the light emitting device shown in FIG.
FIG. 11 is a schematic view showing a method for manufacturing the light emitting device shown in FIG.
FIG. 12 is a schematic diagram illustrating a cross-sectional structure of a blue semiconductor laser device according to a fourth embodiment of the present invention.
FIG. 13 is a schematic diagram showing the shape of an etching mask used in the fourth embodiment.
FIG. 14 is a schematic perspective view showing a shape after etching.
FIGS. 15A and 15B are explanatory views showing the shape of the semiconductor layer after this etching step. That is, FIG. 2A is a schematic perspective view, and FIG. 2B is a schematic front view as seen from the direction of the arrow shown in FIG.
FIG. 16 is a schematic diagram illustrating a state where an end face portion is cleaved.
FIG. 17 is a schematic perspective view of a completed semiconductor light emitting device according to a fourth embodiment.
FIG. 18 is a schematic view illustrating a mask.
FIG. 19 is a schematic diagram illustrating a cross-sectional structure of a blue semiconductor laser device according to a fifth embodiment of the present invention.
FIG. 20 is a schematic perspective view showing a main part of a light emitting device according to a fifth embodiment before cleavage.
[Explanation of symbols]
10, 60, 80 Sapphire substrate
11 n-GaN buffer layer
12,62,82 n-GaN contact layer
13 n-AlN current confinement layer
14, 63, 85 n-GaN cladding layer
15,64,86 InGaN active layer
16, 65, 87 p-GaN cladding layer
17, 66, 89 GaN contact layer
18, 67, 91 p-side electrode
19, 68, 92 n side
20 Sapphire substrate
21 AlN buffer layer
22 n-GaN contact layer
23 Zn0 layer
24 n-AlGaN cladding layer
25 GaN optical confinement layer
26 InGaN active layer
27 GaN optical confinement layer
28 p-AlGaN cladding layer
29 GaN contact layer
30 p-side electrode
31 n-side electrode
32 Si0 ₂ Insulating film

Claims (7)

A substrate, a first contact layer formed on the substrate, a current confinement layer formed on the first contact layer, and a light emitting layer made of a nitride-based compound semiconductor formed on the current confinement layer And a second contact layer formed on the light emitting layer, and first and second electrodes formed to contact the first contact layer and the second contact layer,
The current constriction layer has a side surface receding inward with respect to the side surface of the light emitting layer, and a recess is formed between the substrate and the side surface of the light emitting layer .
Laser light is emitted by a resonator having a part of the side surface opposed to the light emitting layer as a light reflecting surface, and the light emitting side surface of the light emitting layer is a nitride including a portion where the laser light is emitted most strongly. A nitride-based compound semiconductor light emitting device , comprising: a cleavage surface of a compound semiconductor; and inclined surfaces disposed on both sides of the cleavage surface and inclined with respect to the cleavage surface . A substrate, an intermediate layer formed on the substrate, a first cladding layer made of a nitride-based compound semiconductor formed on the intermediate layer, and a nitride layer formed on the first cladding layer. A nitride-based compound semiconductor light emitting device comprising at least an active layer made of a nitride-based compound semiconductor and a second clad layer made of a nitride-based compound semiconductor formed on the active layer,
On the side of the light emitting side of the light emitting element, the side of the intermediate layer recedes into the element from the side of the active layer, and a recess is formed between the substrate and the side of the active layer ,
The light emitting element emits laser light by a resonator having a part of a side surface facing the active layer as a light reflecting surface,
Side faces of the light emitting element on the light emission side are cleaved faces of the nitride-based compound semiconductor including a portion where the laser light is emitted most strongly, and are disposed on both sides of the cleaved faces and are inclined with respect to the cleaved faces. A nitride-based compound semiconductor light-emitting device having an inclined surface . The nitride compound semiconductor light emitting device according to claim 2, wherein the intermediate layer is made of a material selected from the group consisting of AlN, AlGaN, InAlGaN, ZnO, and InGaN. The inclined surface of the side of the light emitting side of the light emitting device, according to claim reflectance at the wavelength of the laser light, wherein the go smaller relatively than the reflectance at the wavelength of the laser beam of the cleavage plane 4. The nitride-based compound semiconductor light-emitting device according to any one of items 1 to 3. A method for manufacturing a nitride-based compound semiconductor light-emitting device having a single optical resonator and a cleavage surface from which laser light is emitted,
Forming a first contact layer on the substrate;
Forming a current confinement layer on the first contact layer;
Forming an active layer made of a nitride-based compound semiconductor on the current confinement layer;
Forming a second contact layer on the active layer;
Etching the second contact layer, the active layer, and the current confinement layer using a mask until the first contact layer is exposed, to form a mesa-type laminated structure;
Forming a first electrode in contact with the first contact layer;
Forming a second electrode in contact with the second contact layer;
A step of separating into element units by dicing,
After installing the separated element on a pedestal, the current confinement layer is selectively etched from the periphery of the side surface of the mesa-type laminated structure, and the laser beam is confined to the optical resonator so that the current is confined. Forming a concave portion on the side surface of the parallel mesa-type laminated structure, and forming a concave portion also on the side surface of the mesa-type laminated structure perpendicular to the laser beam;
The mesa-type stacked structure including the active layer protruding above a recess in a direction perpendicular to the laser beam by applying an external force to the stacked body in which the concave portion is formed to form the cleavage surface. Cleaving the upper end of the body;
A method for manufacturing a nitride-based compound semiconductor light emitting device, comprising: A method for manufacturing a nitride-based compound semiconductor light emitting device having a cleavage surface from which laser light is emitted,
An intermediate layer, a first clad layer made of a first nitride compound semiconductor, an active layer made of a second nitride compound semiconductor, and a second clad layer made of a third nitride compound semiconductor And depositing a laminate having on the substrate,
At least one wedge type having, on the laminate, an inclined surface inclined toward the laminate with respect to the cleavage surface, for concentrating stress along a natural cleavage surface of the second nitride-based compound semiconductor. Forming an etching mask having a notch,
A first etching step of forming a mesa-type laminated structure by etching through the etching mask until a side surface of the intermediate layer is exposed in a direction perpendicular to the substrate;
A second etching step of forming a concave portion by selectively etching the side surface of the intermediate layer exposed in the first etching step;
Forming the cleavage surface by cleaving a portion of the mesa-type laminated structure including the active layer protruding above the concave portion near a tip of the wedge-shaped notch;
A method for manufacturing a nitride-based compound semiconductor light emitting device, comprising: The etching mask has a pair of wedge-shaped notches opposed to concentrating the stress along the natural cleavage plane of the second nitride-based compound semiconductor constituting the active layer, forming the active layer 7. The method according to claim 6, wherein the second nitride-based compound semiconductor is cleaved along a straight line connecting the bottoms of the notches.

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