JP4574413B2 - Reliability test method for semiconductor light emitting device for external cavity laser - Google Patents

Description

  The present invention relates to a reliability test method for a semiconductor light emitting device for an external cavity laser, and in particular, a semiconductor light emitting device having a window region (hereinafter referred to as a window structure type semiconductor light emitting device) and at least one end face of an optical waveguide. The present invention relates to a reliability test method for a semiconductor light emitting device for an external resonator type laser using a diagonally crossed semiconductor light emitting device having a structure that obliquely intersects an element end face as a semiconductor light emitting device for an external resonator type laser.

  2. Description of the Related Art Conventionally, a window structure type semiconductor light emitting element has been developed as a semiconductor light emitting element for an external cavity type laser from the viewpoint of flatness of wavelength dependency of output characteristics (for example, see Patent Document 1). In the window structure type semiconductor light emitting device disclosed in Patent Document 1, as shown in FIG. 5, the front end interfaces 15a and 15b in the longitudinal direction of the mesa stripe portion 13 are not orthogonal to the longitudinal direction and the substrate surface, but are orthogonal to these. It is not parallel to the direction.

  By making the tip interfaces 15a and 15b of the mesa stripe part 13 in this way, the light emitted from the tip interfaces 15a and 15b of the mesa stripe part 13 is reflected by the element end faces 14a and 14b of the window structure type semiconductor light emitting element. The mesa stripe part 13 is not substantially returned to the mesa stripe part 13 via the tip interfaces 15a and 15b. As a result, it is possible to prevent the light reflected by the element end faces 14a and 14b of the window structure type semiconductor light emitting element and the front end interfaces 15a and 15b of the mesa stripe part 13 from resonating, and output with less wavelength dependence over a wide band. The characteristics can be realized.

  As a reliability test method for such a window structure type semiconductor light emitting device for an external resonator type laser, a method of performing an external resonator type semiconductor laser by incorporating a semiconductor light emitting device (hereinafter referred to as a first reliability test method). And a method (hereinafter referred to as a second reliability test method) performed on a window structure type semiconductor light emitting element without forming an external cavity semiconductor laser. The first reliability test method has an advantage that the reliability can be accurately evaluated because the test can be performed in an actual usage mode of the window structure type semiconductor light emitting device.

  However, when the reliability is evaluated by the first reliability test method, there is a problem that the reliability of the window structure type semiconductor light emitting element cannot be easily evaluated because the system is complicated and the procedure is complicated. . Therefore, normally, the reliability of the window structure type semiconductor light emitting element is evaluated by the second reliability test method. Here, when the reliability is evaluated by the second reliability test method, a predetermined drive current is supplied to the window structure type semiconductor light emitting element to emit light without causing laser oscillation, and the window structure type semiconductor light emitting element has low reflectance. The operation state is detected by monitoring the light emitted from the emission end face.

  Here, in the normal operation in which the window structure type semiconductor light emitting element performs laser oscillation in the external resonator type semiconductor laser, carriers injected into the active layer are recombined by stimulated emission during laser oscillation. Therefore, in the state of laser oscillation in the external resonator type semiconductor laser, the lifetime of carriers in the active layer of the window structure type semiconductor light emitting device is short, and normally, carriers are not accumulated excessively in the active layer. .

Japanese Patent Laid-Open No. 2003-17809

  However, in the first reliability test method for the conventional window structure type semiconductor light emitting device, the reliability evaluation of the window structure type semiconductor light emitting device cannot be easily performed, and the second reliability test is performed. This method has a problem that the reliability of the window structure type semiconductor light emitting device cannot be evaluated with high accuracy. In the second reliability test method, since laser oscillation is not performed, carriers having a long lifetime are excessively accumulated in the active layer without contributing to stimulated emission, and the carriers accumulated in the active layer reduce the lifetime of the device by 1-2. This is because it is reduced by an order of magnitude.

  The present invention has been made to solve such a problem, and does not constitute an external resonator type semiconductor laser by incorporating a semiconductor light emitting element, and has an external resonator type with higher accuracy than a conventional reliability test method. An object of the present invention is to provide a reliability test method for a semiconductor light emitting device for an external resonator type laser capable of evaluating the reliability of the semiconductor light emitting device for laser.

In view of the above points, the invention according to claim 1 is a semiconductor light emitting device that is used for an external cavity laser and has a window region on at least one of element end faces in the optical waveguide direction of an optical waveguide formed inside the laser. a reliability test method for the device, a step of preparing the semiconductor light-emitting device of the same inspected semiconductor light-emitting device, wherein the oscillation threshold at a single inspection semiconductor light emitting element, the semiconductor light emitting element Processed in the threshold value adjusting step for processing the semiconductor light emitting element to be inspected and the threshold value adjusting step so as to be equal to the threshold value assumed in the external resonator type laser constituted by using the flow of test current to be inspected semiconductor light emitting element, by laser oscillation with an oscillation evaluation step of evaluating the reliability of the semiconductor light emitting device, the threshold adjustment step, the of the inspection semiconductor light emitting element Highly reflective to at least one of a window opening step in which a region is opened at a position where the element length of the semiconductor light emitting element to be inspected is shorter than the element length of the semiconductor light emitting element, and an element end face of the semiconductor light emitting element to be inspected It has the structure provided with at least any one process among the highly reflective film formation processes which form a film | membrane .

This configuration, as equal to the threshold value is assumed the oscillation threshold of a single object to be inspected semiconductor light emitting element by the threshold adjustment process by an external cavity laser, the inspected semiconductor light-emitting device is processed Therefore, it is possible to evaluate the reliability of a semiconductor light emitting device for an external resonator type laser with higher accuracy than a conventional reliability test method without incorporating a semiconductor light emitting device to constitute an external resonator type semiconductor laser. It is possible to realize a reliability test method for a semiconductor light emitting device for an external cavity type laser.
In addition, this configuration makes it easy to adjust the oscillation threshold by scratching a part of the semiconductor light emitting element to be inspected or forming a highly reflective film on the end face of the element in the threshold adjustment step. It is possible to realize a reliability test method for a semiconductor light emitting element for an external resonator type laser capable of evaluating the reliability of the semiconductor light emitting element for laser.

The invention according to claim 2 is a reliability of a semiconductor light emitting device used for an external resonator type laser and having a structure in which at least one end face of an optical waveguide formed therein obliquely intersects the end face of the element. A test method comprising: preparing a semiconductor light emitting element to be inspected that is the same as the semiconductor light emitting element; and forming a single oscillation threshold of the semiconductor light emitting element to be inspected using the semiconductor light emitting element. A highly reflective film forming step of forming a highly reflective film on at least one of element end faces of the semiconductor light emitting element to be inspected so as to be equal to a threshold assumed for the external cavity laser; And an oscillation evaluation step of evaluating the reliability of the semiconductor light emitting device by applying a test current to the semiconductor light emitting device to be inspected processed in the reflective film forming step to cause laser oscillation .

With this configuration, for adjusting the oscillation threshold by forming on at least one high-reflection film of the element end face of the inspection semiconductor light-emitting device with a highly reflective film forming step, an external cavity laser in a simple It is possible to realize a reliability testing method for a semiconductor light emitting device for an external resonator type laser that can evaluate the reliability of the window structure type semiconductor light emitting device for use.

  In the present invention, the semiconductor light emitting device is processed so that the oscillation threshold value of the single semiconductor light emitting device is equal to the threshold value assumed for the external cavity laser in the threshold adjustment step. An external resonator capable of evaluating the reliability of a semiconductor light emitting device for an external resonator type laser with higher accuracy than a conventional reliability test method without forming an external resonator type semiconductor laser by incorporating a light emitting device A reliability test method for a semiconductor light emitting device for a type laser can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment)
1 to 4 are diagrams for explaining a reliability test method for an external cavity laser light emitting device according to an embodiment of the present invention. FIG. 1A shows a schematic configuration of a window structure type semiconductor light emitting device as a semiconductor light emitting device for an external resonator type laser. In FIG. 1A, a window region 114 is provided between the emission end of the mesa stripe portion 111 having an active layer and the emission end surface 112 of the window structure type semiconductor light emitting device 100. The reflected light from the emission end face 112 does not resonate with the reflection end face 113 on the opposite side.

  Hereinafter, the distance between the tip interface of the mesa stripe portion 111 and the emission end face 112 of the window structure type semiconductor light emitting device 100 is referred to as a window region length. The value of the window region length is set from the viewpoint of preventing laser resonance. Although depending on the structure of the window structure type semiconductor light emitting device 100, the window region length is usually set to 10 μm or more, and preferably set to about 20 to 40 μm. By setting the window region length in this way, the reflected light from the emission end face 112 is not substantially incident on the mesa stripe portion 111.

  On the emission end face 112, an antireflection film 115 having a predetermined reflectance or less is usually formed so that light emitted from the window structure type semiconductor light emitting device 100 is not reflected. However, as shown in FIG. 1B, the window structure type semiconductor light emitting device 110 in which the non-reflective film 115 is removed from the window structure type semiconductor light emitting device 100 as shown in FIG. Good. Hereinafter, the window structure type semiconductor light emitting device 100 includes the window structure type semiconductor light emitting device 110 unless otherwise specified.

  A method of testing a reliability of a semiconductor light emitting device for an external resonator type laser according to an embodiment of the present invention includes: an external resonator type laser configured by using a semiconductor light emitting device as a single oscillation threshold value of the semiconductor light emitting device. The threshold adjustment step for processing the semiconductor light emitting device and the semiconductor light emitting device processed in the threshold adjustment step are supplied with a test current to cause the laser to oscillate so that it is equivalent to the threshold value assumed in FIG. And an oscillation evaluation step for evaluating the reliability of the light emitting element.

  When the window structure type semiconductor light emitting device 100 is used as a semiconductor light emitting device for an external resonator type laser, the above threshold adjustment step uses the window region 116 of the window structure type semiconductor light emitting device 100 in the external resonator type laser. A high-reflective film that forms a high-reflective film on at least one of the end face of the window structure type semiconductor light-emitting device 100 and a window-peeling step (see FIG. 1C) that is opened at a position that is shorter than that of the window structure type. It is comprised so that at least any one process may be provided among a formation process.

  The mesa stripe portion 111 is usually oriented in the longitudinal direction in a predetermined crystal axis direction such as the <011> axis, for example, so that the emission end face of the window structure type semiconductor light emitting element 100 can be easily formed. Hereinafter, it is assumed that the longitudinal direction of the mesa stripe portion 111 faces the <011> axis direction and the window region length is set to 30 μm. Further, it is assumed that laser oscillation is performed when the window region length is 30 μm or less with respect to the cleavage plane orthogonal to the <011> axis.

  In this case, the screening performed in the window screening process is performed such that a (011) plane orthogonal to the <011> axis is obtained and the window region length is reduced to about 15 μm. In the following, the face obtained in the window making process is referred to as a face end face. By forming the large end face 117 as described above, laser oscillation can be performed in the window structure type semiconductor light emitting device 100.

  In the above description, the window region length (hereinafter referred to as a shortened window region length) of the window region obtained by the cracking is set to about 15 μm. However, an error in the position of the crack end face 117 obtained by the cracking (hereinafter referred to as a cracking error). The shortened window area length may be determined according to the above. Specifically, when the cracking error is 5 μm, for example, the shortened window region length may be set to 10 μm to 25 μm to leave the window region and ensure laser oscillation.

  Further, as shown in FIG. 2 (d), a thin film (hereinafter referred to as a highly reflective film) 121 for increasing the reflectance is formed on the gap end face 117, and the output has a reflectance higher than the reflectance necessary for laser oscillation. The end face may be formed more reliably. Further, when the window structure type semiconductor light emitting element 100 is configured to oscillate when a high reflection film having a predetermined reflectance is provided on the non-reflection film 115, as shown in FIG. In addition, a highly reflective film 122 having a reflectance that enables laser oscillation may be formed on the non-reflective film 115.

  Similarly, when the window structure type semiconductor light emitting device 110 is configured to oscillate when a high reflection film having a predetermined reflectance is provided on the emission end face 112, as shown in FIG. In addition, a highly reflective film 123 having a reflectance that enables laser oscillation may be formed on the emission end face 112. Hereinafter, the process of forming any of the highly reflective films 121 to 123 is referred to as a highly reflective film forming process.

  Next, the oscillation evaluation process will be described. First, a window structure type semiconductor light emitting device (hereinafter referred to as a window structure type semiconductor to be inspected) in which any one of the above-described window grinding process and high reflection film forming process is performed as a threshold adjustment process. A wiring or the like is connected to the light emitting element) so that energization is possible. Next, a laser current is oscillated by supplying a test current to the inspection window structure type semiconductor light emitting element. Here, the laser oscillation is detected by monitoring the output light from the inspection window structure type semiconductor light emitting element.

  It should be noted that the strength of the test current applied to the inspection window structure type semiconductor light emitting element may be changed in accordance with the content of reliability to be evaluated. Specifically, a long-term life test that energizes over a long period of time, an accelerated test that raises the temperature to shorten the time of the life test, a constant-current test that measures fluctuations in light output by energizing a constant current, a constant test It may be changed according to a low output test or the like in which the output is maintained and the current is increased according to the deterioration of the element.

  As described above, in the oscillation evaluation process, the test current is supplied to cause the inspected window structure type semiconductor light emitting element to oscillate and evaluate the reliability, so that the electrons and holes injected into the active layer are oscillated. Recombination by stimulated emission therein does not cause excessive accumulation in the active layer as in the case of no laser oscillation. As a result, the problem of shortening the lifetime of the window structure type semiconductor light emitting element as described in the background art by 1 to 2 digits can be eliminated.

  In the above description, the window structure type semiconductor light emitting element is described as an example of the semiconductor light emitting element for an external cavity laser. However, for example, as shown in FIG. 3, at least one end face of the optical waveguide obliquely intersects the element end face. The present invention can be similarly applied to a diagonally crossed structure semiconductor light emitting device having the above structure. FIGS. 3A1 and 3B1 are explanatory diagrams illustrating an example of a schematic configuration of a diagonally crossed semiconductor light emitting device. The obliquely crossed semiconductor light emitting device 300 shown in FIG. 3A1 has a structure in which the waveguide 311 is inclined at an angle θ in the vicinity of the element end face 312 and the end face of the waveguide intersects with the element end face obliquely. Further, in the oblique cross structure semiconductor light emitting device 500 shown in FIG. 3B1, the waveguide 511 is inclined by an angle φ from a straight line connecting the element end faces 512 and 513, and the end face of the waveguide crosses the element end face obliquely. It has the structure to do.

  In the case where the semiconductor light emitting element for an external resonator type laser is a diagonally crossed semiconductor light emitting element, in the above threshold adjustment step, at least one of the element end faces 312 and 313 of the diagonally crossed semiconductor light emitting element 300 (FIG. 3 ( In a2), a highly reflective film 415 is formed in 312). Similarly, in the case of the obliquely crossed semiconductor light emitting device 500 shown in FIG. 3B1, high reflection is applied to at least one of the element end faces 512 and 513 (512 in FIG. 3B2) of the obliquely crossed semiconductor light emitting device 500. A film 615 is formed. Hereinafter, this process is referred to as a highly reflective film forming process. The oblique cross structure semiconductor light emitting devices (hereinafter referred to as “inspected oblique cross structure semiconductor light emitting devices”) 400 and 600 that can be oscillated by forming the high reflection film in the high reflection film formation step are the above-described in the oscillation evaluation step. Reliability is evaluated in the same way as the method.

  In the above description, the oblique cross structure semiconductor light emitting element having a structure in which at least one end face of the optical waveguide obliquely intersects with the element end face has been described as an example. As shown, the present invention is similarly applied to an obliquely crossed structure semiconductor light emitting device having a configuration in which a window region is provided between the end face of the waveguide and the end face of the element. Since the semiconductor light emitting element shown in FIG. 4 has a window region, the reflectance can be increased by shortening the window region by scratching. Furthermore, since the reflectivity is lowered because the end face of the optical waveguide is inclined with respect to the end face of the element, a further highly reflective film may be formed on the end face of the element.

  As described above, the reliability test method for a semiconductor light-emitting device for an external resonator type laser according to an embodiment of the present invention uses the external resonator to set the oscillation threshold value of a single semiconductor light-emitting device in the threshold adjustment step. Since the semiconductor light emitting device is processed so as to be equivalent to the threshold value assumed for the type laser, it is more reliable than the conventional reliability test method without forming the external resonator type semiconductor laser by incorporating the semiconductor light emitting device. It is possible to evaluate the reliability of the semiconductor light emitting element for external cavity laser with high accuracy.

  In addition, the threshold value adjustment process is used to adjust the oscillation threshold by scratching a part of the window region of the window structure type semiconductor light emitting element or forming a highly reflective film on the end face of the element. The reliability of the window structure type semiconductor light emitting element for laser can be evaluated.

  Furthermore, since the oscillation threshold value is adjusted by forming a highly reflective film on at least one of the element end faces of the obliquely crossed structure semiconductor light emitting element in the threshold value adjusting step, it can be easily used for an external resonator type laser. The reliability of the obliquely crossed semiconductor light emitting device can be reliably evaluated.

  The reliability test method for a semiconductor light emitting device for an external resonator type laser according to the present invention is an external device with a higher accuracy than the conventional reliability test method without incorporating a semiconductor light emitting device to constitute an external resonator type semiconductor laser. The present invention can also be applied to uses such as a reliability test method for an external resonator type semiconductor light emitting device for a laser, which is useful for evaluating the reliability of the semiconductor light emitting device for a resonator type laser.

Sectional drawing of the semiconductor light emitting element for external resonator type lasers (window structure type semiconductor light emitting element) to be tested in the reliability test method of the present invention Sectional drawing which shows the example of a general | schematic structure of the window structure type semiconductor light emitting element made into a test object other than the structure shown in FIG. Top view of a semiconductor light emitting device with an oblique cross structure as a semiconductor light emitting device for an external cavity laser Top view of a semiconductor light emitting device having an oblique cross structure having a window region The figure which shows an example of a rough element structure of a window structure type semiconductor light emitting element

Explanation of symbols

11, 100, 110 Window structure type semiconductor light emitting element 12 Semiconductor substrate 13 Mesa stripe part 14a, 14b, 312, 313, 512, 513 Element end face 15a, 15b End interface of mesa stripe part 28 Emission light 32a, 32b, 114, 116 Window region 33a, 33b, 115 Non-reflective film 200, 210, 220, 230 Inspected window structure type semiconductor light emitting device 111 Mesa stripe part 112 Outgoing end face 113 Reflecting end face 117 Big face (heavy end face)
121, 122, 123, 415, 615 High reflection film 300, 500 Diagonal cross structure semiconductor light emitting device 311 511 Waveguide 400, 600 Diagonal cross structure semiconductor light emitting device to be inspected

Claims (2)

A method for testing a reliability of a semiconductor light-emitting element used in an external resonator type laser and having a window region on at least one of element end faces in an optical waveguide direction of an optical waveguide formed therein ,
Preparing the same semiconductor light emitting device as the semiconductor light emitting device,
The oscillation threshold by itself of the inspection semiconductor light emitting element, so as to equal to the threshold value expected by the external cavity laser is constructed by using the semiconductor light emitting device, the inspection semiconductor A threshold adjustment process for processing the light emitting element;
Wherein said processed by the threshold adjustment step passing a test current to be inspected semiconductor light emitting element, and a oscillation evaluation step of evaluating the reliability of the semiconductor light emitting element by laser oscillation,
The threshold adjustment step is a window opening step in which the window region of the semiconductor light emitting element to be inspected is opened at a position where the element length of the semiconductor light emitting element to be inspected is shorter than the element length of the semiconductor light emitting element; For an external resonator type laser comprising at least one of a high reflection film forming step of forming a high reflection film on at least one of element end faces of the semiconductor light emitting element to be inspected Reliability testing method for semiconductor light emitting devices. A method for testing a reliability of a semiconductor light-emitting element used in an external cavity laser and having a structure in which at least one end face of an optical waveguide formed therein obliquely intersects the end face of the element,
Preparing the same semiconductor light emitting device to be inspected as the semiconductor light emitting device;
The semiconductor light emission to be inspected so that the oscillation threshold value of the single semiconductor light emitting element to be inspected is equivalent to the threshold value assumed for the external cavity laser configured using the semiconductor light emitting element. A highly reflective film forming step of forming a highly reflective film on at least one of the element end faces of the element;
And an oscillation evaluation step for evaluating the reliability of the semiconductor light emitting device by applying a test current to the semiconductor light emitting device to be inspected processed in the highly reflective film forming step to cause laser oscillation. For testing the reliability of semiconductor light emitting devices for lasers.

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