JP4821390B2 - Self-oscillation type semiconductor laser - Google Patents

Description

  The present invention relates to a nitride-based light emitting device such as a self-excited oscillation type semiconductor laser.

  DVD (Digital Versatile Disk), a typical optical disc in recent years, has spread in a very wide range of fields, from playback systems such as movies, music, games, and car navigation systems to recording systems such as TV recorders and personal computer drives. Yes. The recording capacity is about seven times that of a CD, which is sufficient for recording a current TV picture with a standard image quality. However, when recording a high-definition digital high-definition video that is expected to spread in the future, the amount of information is overwhelmingly larger than in the past, so the current DVD can only record about 20-30 minutes. Thus, there is an increasing expectation for a next-generation optical disk system capable of recording a large capacity about five times as much as a conventional DVD.

  A nitride blue-violet semiconductor laser having a wavelength of 405 nm band is used as a light source for the next generation optical disk system. This is because the light can be narrowed down smaller than the AlGaInP red semiconductor laser having a wavelength of 650 nm band used in the conventional DVD, and is suitable for high-density signal recording.

  In the conventional optical disk system, when reading the signal of the optical disk, in order to prevent excessive noise from being induced in the semiconductor laser due to the reflected light from the optical disk, the optical output of the semiconductor laser is a pulse of about 100 MHz to several GHz. The device is used in the form of a shape. As means for this, there are a method of superimposing modulation by adding a high-frequency superposition module to a drive circuit of the semiconductor laser, and a method of using a so-called self-excited oscillation type semiconductor laser that can obtain a pulsed light output even by direct current drive. Particularly in the latter case, the high-frequency superposition module and its unnecessary radiation countermeasure are not required, which is extremely effective for reducing the cost and size of the optical disc system. Therefore, the realization of a self-excited oscillation type is strongly desired also for nitride blue-violet semiconductor lasers used as light sources for next-generation optical disk systems.

  The self-excited oscillation operation is realized by providing a region having a so-called saturable absorption characteristic in the vicinity of the active layer, in which light absorption is saturated and weakened when the light intensity is increased. As a specific means, for example, a structure in which a saturable absorption layer is provided independently of the active layer is well known.

  FIG. 7 is a sectional view showing a conventional self-oscillation type semiconductor laser. n-type substrate 701, n-type buffer layer 702, n-type cladding layer 703, n-type optical confinement layer 704, active layer 705, p-type cap layer 706, p-type optical confinement layer 707, saturable absorption layer 708, p-type cladding A layer 709, a p-type contact layer 710, an insulating layer 711, a p-electrode 712, and an n-electrode 713. In this structure, in order to maintain stable self-excited oscillation, it is important to quickly extinguish carriers excited by absorption in the saturable absorber layer, that is, to shorten the carrier life of the saturable absorber layer. It becomes. In a conventional self-pulsation type semiconductor laser, a method of doping a saturable absorption layer with a high concentration of impurities is generally used as the means.

In addition, patent documents 1-5 are mentioned as a prior art document relevant to this invention.
JP-A-10-93199 JP-A-10-163666 JP 2002-246686 A JP 2002-319733 A JP 2005-19835 A

  However, the conventional self-oscillation type semiconductor laser has a problem that the element lifetime is short. The reason is that high-concentration impurity doping into the saturable absorber layer causes impurity diffusion into the active layer or diffusion of defects due to the impurity, thereby reducing the crystal quality of the active layer. In particular, since high-concentration impurity doping is performed in the current injection path, diffusion of impurities and defects is promoted even during operation of the semiconductor laser, and the deterioration of the active layer quality with time is remarkable.

A self-pulsation type semiconductor laser according to the present invention includes an active layer made of a group III nitride semiconductor, a functional layer provided above the active layer and having a function of current confinement or light distribution control, and the functional layer. And a saturable absorption layer that absorbs light generated in the active layer, and the functional layer and the saturable absorption layer have a stripe-shaped opening, and the active layer When the dislocation density of the region facing the functional layer is Na, the dislocation density of the region facing the opening of the active layer is Nb, and the dislocation density of the region facing the functional layer of the saturable absorber layer is Nc , Na <Nc, and Nb <Nc.

The self-pulsation type semiconductor laser according to the present invention includes an active layer made of a group III nitride semiconductor, a functional layer having a function of current confinement or light distribution control, and a saturable state that absorbs light generated in the active layer. An absorption layer, wherein the functional layer has a stripe-shaped opening, the dislocation density of the region facing the functional layer of the active layer is Na ′, and the region facing the opening of the active layer Nb ′, the dislocation density of the region of the saturable absorption layer facing the functional layer is Nc ′, and the dislocation density of the region of the saturable absorption layer facing the opening is Nd ′. It may be characterized in that Na ′ <Nc ′, Nb ′ <Nc ′, and Nc ′> Nd ′.

  These nitride-based light emitting devices have stripe-shaped openings and have a layer that functions as current confinement or light distribution control, and has a saturable absorption layer in the vicinity of or in the layer. This layer contains many dislocations. For example, when an element is fabricated on a GaN substrate, if AlN is used as a layer that functions as current confinement or light distribution control, a large number of dislocations occur in the AlN layer due to a large degree of lattice mismatch, resulting in lattice relaxation. . Here, due to the nature of the nitride-based material, the influence of dislocations generated in the AlN layer is reflected in a direction perpendicular to the AlN layer, so that the saturable absorption layer provided in the vicinity of the AlN layer or in the AlN layer. Crystallinity deteriorates and non-radiative recombination time is shortened. As a result, the carrier life of the saturable absorbing layer can be shortened.

  At this time, since a layer containing many dislocations does not exist in the stripe-shaped opening, good crystallinity is maintained in the main current injection region or the main light emitting region. Furthermore, since the good crystallinity of the active layer is kept uniform in the horizontal direction, carriers are wasted in the active layer region with poor crystallinity when the injection current spreads horizontally in the active layer. There is no. That is, the luminous efficiency in the active layer is kept high, and heat generation can be suppressed to a small level. As described above, self-excitation having a good device lifetime can be achieved by providing a saturable absorption layer in a self-aligned manner without devising high concentration doping or the like, and by deteriorating crystallinity only in a necessary region. An oscillation type semiconductor laser is realized.

  According to the present invention, a nitride-based light emitting device having a good device lifetime is realized.

  Hereinafter, preferred embodiments of a nitride-based light emitting device according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

(First embodiment)
FIG. 1 is a sectional view showing a first embodiment of a nitride-based light emitting device according to the present invention. On an n-type substrate 101, an n-type buffer layer 102, an n-type cladding layer 103, an n-type optical confinement layer 104, an active layer 105, a p-type cap layer 106, a p-type optical confinement layer 107, a lower current confinement layer 108, an absorption The layer 109 and the upper current confinement layer 110 are stacked in this order. The lower current confinement layer 108, the absorption layer 109, and the upper current confinement layer 110 are provided with stripe-shaped openings 111. A p-type cladding layer 112 and a p-type contact layer 113 are further stacked in this order on the upper current confinement layer 110. A p-electrode 114 is provided on the upper surface of the p-type contact layer 113, and an n-electrode 115 is provided on the lower surface of the n-type substrate 101.

  The n-type substrate 101 is made of, for example, a GaN substrate. The n-type buffer layer 102 is made of, for example, GaN having a thickness of 1 μm. The n-type cladding layer 103 is made of, for example, AlGaN having a thickness of 2 μm. The n-type optical confinement layer 104 is made of, for example, GaN having a thickness of 0.1 μm. The active layer 105 has a multiple quantum well structure including, for example, an InGaN well layer having a thickness of 3 nm and an InGaN barrier layer having a thickness of 4 nm. The p-type cap layer 106 is made of, for example, AlGaN having a thickness of 10 nm. The p-type optical confinement layer 107 is made of, for example, GaN having a thickness of 0.1 μm.

  The lower current confinement layer 108 and the upper current confinement layer 110 are made of AlN having a thickness of 0.05 μm, for example, and also have a function as a light distribution control layer due to a difference in refractive index in the horizontal direction. The absorption layer 109 has a composition and a layer thickness set so as to absorb the oscillation light generated in the active layer 105, and is made of, for example, InGaN having a thickness of 3 nm. The p-type cladding layer 112 has a superlattice structure with a 130 period composed of, for example, GaN with a thickness of 2.5 nm and AlGaN with a thickness of 2.5 nm. The p-type contact layer 113 is made of, for example, GaN having a thickness of 0.1 μm. The n-type impurity is, for example, Si, and the p-type impurity is, for example, Mg.

  In this embodiment, at least the lower current confinement layer 108 includes many dislocations and is lattice-relaxed, and absorbs light generated in the active layer 105 between the lower current confinement layer 108 and the upper current confinement layer 110. An absorption layer 109 is provided. The absorption layer 109 deteriorates in crystallinity at least reflecting the influence of dislocations in the lower current confinement layer 108, and the non-radiative recombination time is shortened. As a result, the carrier lifetime of the absorption layer 109 is shortened, and the absorption layer 109 functions as a saturable absorption layer. At this time, since there is no region containing many dislocations in the stripe-shaped opening 111, the main current injection region or the main light emitting region maintains good crystallinity.

  Furthermore, since the good crystallinity of the active layer 105 is kept uniform in the horizontal direction, when the injection current spreads in the horizontal direction in the active layer 105, carriers are wasted in the active layer region having poor crystallinity. There is nothing to do. That is, the luminous efficiency in the active layer is kept high, and heat generation can be suppressed to a small level. As described above, self-excitation having a good device lifetime can be achieved by providing a saturable absorption layer in a self-aligned manner without devising high concentration doping or the like, and by deteriorating crystallinity only in a necessary region. An oscillation type semiconductor laser is realized.

  Here, the dislocation density of the active layer 105 is only required to be substantially uniform in the horizontal direction, and there may be a difference in the in-plane distribution of the wafer or the variation between the wafers. That is, when the dislocation density of the region facing the lower current confinement layer 108 of the active layer 105 is Na, the dislocation density of the region facing the opening 111 of the active layer 105 is Nb, and the dislocation density of the absorption layer 109 is Nc, Na ≈Nb <Nc. Alternatively, Na <Nc and Nb <Nc. Preferably, for example, 0.1 × Na <Nb <10 × Na, more preferably 0.5 × Na ≦ Nb ≦ 2 × Na, and (Nc / Na)> 10, and (Nc / Nb)> 10, More preferably, if (Nc / Nb)> 100, the effect of the present embodiment becomes remarkable.

  Note that the lower current confinement layer 108 and the upper current confinement layer 110 do not need to be made of the same material, and may be AlGaN having different Al compositions, for example. Further, the lower current confinement layer 108 and the upper current confinement layer 110 do not have to have the same layer thickness. If at least the lower current confinement layer 108 includes many dislocations and is lattice-relaxed, the layer thickness is not limited. good.

  Next, an example of the manufacturing method of 1st Embodiment is demonstrated. A 300 hPa reduced pressure MOVPE apparatus is used to fabricate the element structure. A mixed gas of hydrogen and nitrogen is used as a carrier gas, and trimethylgallium and trimethylaluminum trimethylindium are used as Ga, Al, and In sources, respectively. Silane is used as the n-type impurity, and biscyclopentadienyl magnesium is used as the p-type impurity.

  After the n-type GaN substrate 101 is put into the growth apparatus, the substrate is heated while supplying ammonia, and the growth is started when the growth temperature is reached. In the first growth, an n-type GaN buffer layer 102, an n-type AlGaN cladding layer 103, an n-type GaN optical confinement layer 104, an active layer 105 having a multiple quantum well structure composed of an InGaN well layer and an InGaN barrier layer, p-type AlGaN A cap layer 106, a p-type GaN optical confinement layer 107, an AlN lower current confinement layer 108, an InGaN absorption layer 109, and an AlN upper current confinement layer 110 are formed. The growth temperature is, for example, 200 to 800 ° C. for the AlN lower current confinement layer 108, InGaN absorption layer 109, and AlN upper current confinement layer 110, 800 ° C. for the active layer 105, and 1100 ° C. otherwise. Since the AlN lower current confinement layer 108 and the AlN upper current confinement layer 110 are grown at a low temperature, they are amorphous at the end of the first growth. A SiO2 film is deposited thereon, and a SiO2 mask having a stripe-shaped opening is formed using a normal photolithography technique.

  Next, a mixed solution of phosphoric acid and sulfuric acid is maintained at 50 to 200 ° C. to form an etching solution, and stripe-shaped openings 111 are formed in the AlN lower current confinement layer 108, the InGaN absorption layer 109, and the AlN upper current confinement layer 110. . At this time, amorphous AlN and InGaN are easily etched, and single crystal GaN is difficult to etch. Therefore, etching with high selectivity and good controllability is performed.

  Next, after supplying again to the growth apparatus, the temperature of the substrate is raised while supplying ammonia, and the second growth is started when the temperature reaches the growth temperature. At this time, the AlN lower current confinement layer 108 and the AlN upper current confinement layer 110 are single-crystallized in the process of raising the temperature of the substrate. However, since the lattice constant difference with GaN is large, a large number of dislocations are generated and Relaxation occurs. The influence of the dislocation is reflected in a direction perpendicular to the AlN lower current confinement layer 108 and the AlN upper current confinement layer 110, and thus the crystallinity of the InGaN absorption layer 109 is deteriorated. Next, a p-type AlGaN / GaN superlattice cladding layer 112 and a p-type GaN contact layer 113 are formed. Thereafter, a p-electrode 114 is formed on the upper surface and an n-electrode 115 is formed on the lower surface.

  The semiconductor laser fabricated in this way maintains the crystallinity of the stripe-shaped opening 111 well, and the InGaN absorption layer 109 functions as a saturable absorption layer because of its short carrier lifetime. Therefore, a self-excited oscillation type semiconductor laser having good reliability is realized.

(Second Embodiment)
FIG. 2 is a cross-sectional view showing a second embodiment of the nitride-based light emitting device according to the present invention. The difference from the first embodiment is that the upper current confinement layer 110 is omitted. Thus, the absorption layer 109 does not necessarily need to be located between the current confinement layers, and may be located above the current confinement layer.

  Even in this case, the carrier life of the absorption layer 109 can be shortened by the influence of dislocations in the lower current confinement layer 108. At this time, a cap layer 201 for protecting the absorption layer 109 may be provided as shown in FIG. The cap layer 201 is made of, for example, AlGaN. Note that the cap layer 201 may not be adjacent to the absorption layer 109 as long as it is located above the absorption layer 109. Further, the cap layer 201 is not necessarily required depending on the manufacturing method, and the cap layer 201 may be omitted, for example, when a manufacturing method that can sufficiently protect the absorption layer 109 is used.

  An example of the manufacturing method of the second embodiment is that, in the manufacturing method of the first embodiment, instead of forming the AlN upper current confinement layer 110, the AlGaN cap layer 201 is formed at, for example, 200 to 800 ° C. This is the same as in the first embodiment.

(Third embodiment)
FIG. 3 is a cross-sectional view showing a third embodiment of the nitride-based light emitting device according to the present invention. The difference from the first embodiment is that, for example, a first light distribution control layer 301 is provided between the lower current confinement layer 108 and the absorption layer 109, and the first current distribution control layer 301 is provided between the absorption layer 109 and the upper current confinement layer 110, for example. This is that a second light distribution control layer 302 is provided. Thus, the absorption layer 109 does not necessarily have to be adjacent to the current confinement layer, and may be located in the vicinity of the current confinement layer.

  The first light distribution control layer 301 is made of, for example, AlGaN, and the second light distribution control layer 302 is made of, for example, AlGaN. At this time, the upper current confinement layer 110 may be omitted as in the second embodiment of the present invention. For example, when the upper current confinement layer 110 is omitted, a cap layer for protecting the absorption layer 109 may be provided on the absorption layer 109 or above the absorption layer 109. Note that the compositions and layer thicknesses of the first light distribution control layer 301 and the second light distribution control layer 302 may not be the same, and can be set appropriately and independently. Further, either the first light distribution control layer 301 or the second light distribution control layer 302 may be omitted.

  An example of the manufacturing method of the third embodiment is that in the manufacturing method of the first embodiment, after the formation of the AlN lower current confinement layer 108, the AlGaN first light distribution control layer 301, the InGaN absorption layer 109, the AlGaN second light. The second embodiment is the same as the first embodiment except that the distribution control layer 302 and the AlN upper current confinement layer 110 are formed at 200 to 800 ° C., for example.

(Fourth embodiment)
FIG. 4A is a bird's eye view showing a fourth embodiment of the nitride-based light emitting device according to the present invention. FIG. 4B and FIG. 4C are cross-sectional views along the AA ′ plane and the BB ′ plane in FIG. 4A, respectively. Thus, the stripe-shaped openings 111 may be interrupted in the resonator direction. Specifically, the stripe-shaped opening 111 is not necessarily provided in the vicinity of the end face, and the absorption layer 109 may be left in the vicinity of the end face.

At this time, when the equivalent refractive index _{n a} of the buried region 111a of the stripe-shaped opening 111, the equivalent refractive index of the striped region 111b of aperture 111 is interrupted and _{n b,} generally _{n a} ≠ _{n b} Therefore, the effect of greatly improving the device life is added. For example, when n _a > n _b , the light distribution in the vicinity of the end face shifts downward. Conversely, when n _a <n _b , the light distribution in the vicinity of the end face shifts upward. Even in this case, optical confinement of the active layer 105 in the vicinity of the end face can be reduced. Thus, since the optical confinement of the active layer 105 can be reduced only in the vicinity of the end face, the light density at the end face can be reduced, the end face deterioration can be suppressed, and the device life can be greatly improved.

  An example of the manufacturing method of the fourth embodiment is the same as that of the first embodiment except that the manufacturing method of the first embodiment uses a SiO2 mask having a pattern in which stripe-shaped openings are interrupted in the resonator direction. .

  4A to 4C show an example in which the stripe-shaped opening 111 is interrupted in the direction of the resonator in the first embodiment of the present invention, the second embodiment of the present invention. Similarly, in the embodiment and the third embodiment of the present invention, the stripe-shaped opening 111 may be interrupted in the resonator direction.

It should be noted that the above first to fourth embodiments are merely examples, and various modifications can be made, and those skilled in the art can understand that such modifications are also within the scope of the present invention. For example, the absorption layer 109 may consist of a bulk layer, a quantum well layer, or a multiple quantum well structure. Further, the absorption layer 109 may be doped with impurities within a range that does not deteriorate the crystallinity, for example, in order to control the conductivity type. The material constituting the absorption layer 109 can be variously selected depending on the wavelength of light generated in the active layer 105. For example, Al _x In _y Ga _1-xy N (0 ≦ z ≦ 1, 0 ≦ It may be composed of a single layer or a plurality of layers including w ≦ 1, 0 ≦ z + w ≦ 1). The lower current confinement layer 108 or the upper current confinement layer 110 may be made of a material other than AlN as long as lattice relaxation is achieved including dislocations. For example, Al _x In _y Ga _1-xy N (0.4 ≦ x ≦ 1, 0 ≦ y ≦ 0.6, 0 ≦ x + y ≦ 1).

  Moreover, the manufacturing method of each said embodiment is an illustration, and it can be understood by those skilled in the art that various modifications are possible.

(Fifth embodiment)
FIG. 5 is a cross-sectional view showing a fifth embodiment of the nitride-based light emitting device according to the present invention. On the n-type substrate 501, an n-type buffer layer 502, an n-type cladding layer 503, an n-type optical confinement layer 504, an active layer 505, a p-type cap layer 506, a p-type optical confinement layer 507, and a current confinement layer 508 are provided. They are stacked in this order. The current confinement layer 508 is provided with a stripe-shaped opening 509. On the current confinement layer 508, an absorption layer 510, a p-type cladding layer 511, and a p-type contact layer 512 are further stacked in this order. A p-electrode 513 is provided on the upper surface of the p-type contact layer 512, and an n-electrode 514 is provided on the lower surface of the n-type substrate 501.

  The n-type substrate 501 is made of, for example, a GaN substrate. The n-type buffer layer 502 is made of, for example, GaN having a thickness of 1 μm. The n-type cladding layer 503 is made of, for example, AlGaN having a thickness of 2 μm. The n-type optical confinement layer 504 is made of, for example, GaN having a thickness of 0.1 μm. The active layer 505 has a multiple quantum well structure including, for example, an InGaN well layer having a thickness of 3 nm and an InGaN barrier layer having a thickness of 4 nm. The p-type cap layer 506 is made of, for example, AlGaN having a thickness of 10 nm. The p-type optical confinement layer 507 is made of, for example, GaN having a thickness of 0.1 μm.

  The current confinement layer 508 is made of, for example, AlN having a thickness of 0.1 μm, and also has a function as a light distribution control layer due to a difference in refractive index in the horizontal direction. The absorption layer 510 has a composition and a layer thickness set to absorb light generated in the active layer 505, and is made of, for example, InGaN having a thickness of 3 nm. The p-type cladding layer 511 has a 130-period superlattice structure made of, for example, GaN having a thickness of 2.5 nm and AlGaN having a thickness of 2.5 nm. The p-type contact layer 512 is made of GaN having a thickness of 0.1 μm, for example. The n-type impurity is, for example, Si, and the p-type impurity is, for example, Mg.

  In this embodiment, at least the current confinement layer 508 includes many dislocations and is lattice-relaxed, and an absorption layer 510 that absorbs oscillation light generated in the active layer 505 is provided in the vicinity thereof. Here, in the absorption layer 510, the region 510a located outside the stripe reflects the influence of the dislocation of the current confinement layer 508, so that the crystallinity is deteriorated and the non-radiative recombination time is shortened. As a result, the region 510a located outside the stripe in the absorption layer has a short carrier life and functions as a saturable absorption layer. On the other hand, in the absorption layer 510, the region 510b located in the stripe is not affected by the dislocation of the current confinement layer 508, and thus good crystallinity is maintained. As a result, the stripe-shaped opening 509 does not have a region containing many dislocations, and the main current injection region or the main light emitting region maintains good crystallinity.

  Furthermore, since the good crystallinity of the active layer 505 is kept uniform in the horizontal direction, when the injection current spreads in the horizontal direction in the active layer 505, carriers are wasted in the active layer region having poor crystallinity. There is nothing to do. That is, the luminous efficiency in the active layer is kept high, and heat generation can be suppressed to a small level. As described above, self-excitation having a good device lifetime can be achieved by providing a saturable absorption layer in a self-aligned manner without devising high concentration doping or the like, and by deteriorating crystallinity only in a necessary region. An oscillation type semiconductor laser is realized.

  Here, the dislocation density of the active layer 505 is only required to be substantially uniform in the horizontal direction, and there may be a difference in the in-plane distribution of the wafer and the variation between the wafers. That is, the dislocation density of the region facing the current confinement layer 508 of the active layer 505 is Na ′, the dislocation density of the region facing the opening 509 of the active layer 505 is Nb ′, and the dislocation density of the absorption layer 510 is opposed to the current confinement layer 508. Assuming that the dislocation density of the region 510a is Nc ′, and the dislocation density of the region 510b facing the opening 509 of the absorption layer 510 is Nd ′, Na′≈Nb ′ <Nc ′ and Nc ′> Nd ′. Alternatively, Na ′ <Nc ′, Nb ′ <Nc ′, and Nc ′> Nd ′. Preferably, for example, 0.1 × Na ′ <Nb ′ <10 × Na ′, more preferably 0.5 × Na ′ ≦ Nb ′ ≦ 2 × Na ′, and (Nc ′ / Na ′)> 10 And (Nc ′ / Nb ′)> 10 and (Nc ′ / Nd ′)> 10, more preferably (Nc ′ / Nb ′)> 100 and (Nc ′ / Nd ′)> 100 If so, the effect of the present embodiment becomes remarkable.

  Next, an example of the manufacturing method of 5th Embodiment is demonstrated. A 300 hPa reduced pressure MOVPE apparatus is used to fabricate the element structure. A mixed gas of hydrogen and nitrogen is used as a carrier gas, and trimethylgallium and trimethylaluminum trimethylindium are used as Ga, Al, and In sources, respectively. Silane is used as the n-type impurity, and biscyclopentadienyl magnesium is used as the p-type impurity.

  After the n-type GaN substrate 501 is put into the growth apparatus, the substrate is heated while supplying ammonia, and the growth is started when the growth temperature is reached. In the first growth, an n-type GaN buffer layer 502, an n-type AlGaN cladding layer 503, an n-type GaN optical confinement layer 504, an active layer 505 having a multiple quantum well structure comprising an InGaN well layer and an InGaN barrier layer, p-type AlGaN A cap layer 506, a p-type GaN optical confinement layer 507, and an AlN current confinement layer 508 are formed. The growth temperature is, for example, 200 to 800 ° C. for the AlN current confinement layer 508, 800 ° C. for the active layer 505, and 1100 ° C. otherwise. Since the AlN current confinement layer 508 grows at a low temperature, it is amorphous at the end of the first growth. A SiO2 film is deposited thereon, and a SiO2 mask having a stripe-shaped opening is formed using a normal photolithography technique.

  Next, a mixed solution of phosphoric acid and sulfuric acid is maintained at 50 to 200 ° C. to obtain an etching solution, and a stripe-shaped opening 509 is formed in the AlN current confinement layer 508. At this time, amorphous AlN is easily etched, and single crystal GaN is difficult to etch. Therefore, etching with high selectivity and good controllability is performed. Next, after supplying again to the growth apparatus, the temperature of the substrate is raised while supplying ammonia, and the second growth is started when the temperature reaches the growth temperature. At this time, the AlN current confinement layer 508 is single-crystallized in the process of raising the temperature of the substrate. However, since the lattice constant difference with GaN is large, dislocation occurs and lattice relaxation occurs.

  Next, after forming an InGaN absorption layer 510, a p-type AlGaN / GaN superlattice cladding layer 511, and a p-type GaN contact layer 512, a p-electrode 513 is formed on the upper surface and an n-electrode 514 is formed on the lower surface. Here, the influence of dislocations generated in the AlN current confinement layer 508 is reflected in the direction perpendicular to the AlN current confinement layer 508. For this reason, in the InGaN absorption layer 510, the region 510a located outside the stripe deteriorates crystallinity, shortens the carrier life, and functions as a saturable absorption layer. On the other hand, in the InGaN absorption layer 510, the region 510b located in the stripe is not affected by the dislocations of the AlN current confinement layer 508, and thus good crystallinity is maintained.

  In the semiconductor laser fabricated in this manner, the crystallinity within the stripe is maintained well, and the InGaN absorption layer located outside the stripe functions as a saturable absorption layer. Therefore, a self-excited oscillation type semiconductor laser having good reliability is realized.

(Sixth embodiment)
FIG. 6 is a cross-sectional view showing a sixth embodiment of the nitride-based light emitting device according to the present invention. The difference from the fifth embodiment is that a light distribution control layer 601 is provided between the current confinement layer 508 and the absorption layer 510. Thus, the absorption layer 510 does not necessarily have to be adjacent to the current confinement layer, and may be located in the vicinity of the current confinement layer. The light distribution control layer 601 is made of, for example, AlGaN. Further, a cap layer for protecting the absorption layer 510 may be provided above the absorption layer 510.

  An example of the manufacturing method of the sixth embodiment is the same as that of the fifth embodiment except that the AlGaN light distribution control layer 601 is formed under the InGaN absorption layer 510 in the second growth of the manufacturing method of the fifth embodiment. It is the same.

  In the fourth embodiment of the present invention, the stripe-shaped opening 111 in the first embodiment of the present invention is interrupted in the resonator direction. However, the fifth embodiment of the present invention and the present invention are described. Similarly, in the sixth embodiment, the stripe-shaped opening 509 may be interrupted in the resonator direction.

It should be noted that the fifth and sixth embodiments are examples, and various modifications can be made, and those skilled in the art can understand that such modifications are also within the scope of the present invention. For example, the absorption layer 510 may consist of a bulk layer, a quantum well layer, or a multiple quantum well structure. Further, the absorption layer 510 may be doped with impurities within a range that does not deteriorate crystallinity, for example, for the purpose of controlling the conductivity type. The material constituting the absorption layer 510 can be variously selected depending on the wavelength of light generated in the active layer 505. For example, Al _z In _w Ga _1-zw N (0 ≦ z ≦ 1, 0 ≦ It may be composed of a single layer or a plurality of layers including w ≦ 1, 0 ≦ z + w ≦ 1). The current confinement layer 508 may be made of a material other than AlN as long as lattice relaxation is achieved including dislocations. For example, Al _x In _y Ga _1-xy N (0.4 ≦ x ≦ 1, 0 ≦ y ≦ 0. 6, 0 ≦ x + y ≦ 1).

  Moreover, the manufacturing method of each said embodiment is an illustration, and it can be understood by those skilled in the art that various modifications are possible.

  The effects of the above embodiments will be described. The first effect is that a good self-oscillation operation can be realized in a nitride-based light emitting device, particularly a semiconductor laser. The reason is that it has a functional layer having a function of current confinement or light distribution control, an absorption layer in the vicinity of the functional layer or in the functional layer, and the dislocation density in the region facing the functional layer of the absorption layer is active. This is because the absorption layer functions as a saturable absorption layer because it is higher than the dislocation density of the layer.

  The second effect is that good reliability can be obtained in the nitride-based self-pulsation semiconductor laser. The reason is that, among the absorption layers, the absorption layer located outside the stripe functions as a saturable absorption layer, while the inside of the stripe maintains good crystallinity, and the active layer is uniform in the horizontal direction. This is because good crystallinity is maintained.

  The third effect is that a further improvement effect of the element lifetime can be added in the nitride-based self-oscillation semiconductor laser. The reason is that leaving the absorbing layer in the vicinity of the end face reduces the light density of the active layer in the vicinity of the end face and suppresses end face deterioration.

  Further, in the manufacturing method of each embodiment of the present invention, at least a layer functioning as current confinement or light distribution control is formed at a low temperature, and a saturable absorbing layer is provided in the vicinity of or in the layer. For example, when AlN is used as a layer that functions as current confinement or light distribution control and is formed at a low temperature of about 200 to 800 ° C., it becomes amorphous. Next, after forming a stripe-shaped opening in the AlN layer and passing through a temperature raising process for regrowth, the amorphous AlN layer introduces a lot of dislocations and undergoes single crystal crystallization while causing lattice relaxation. Therefore, the crystallinity of the saturable absorbing layer provided in the vicinity of the AlN layer or in the AlN layer is deteriorated, and the carrier life of the saturable absorbing layer can be shortened. At this time, since a layer containing many dislocations does not exist in the stripe-shaped opening, good crystallinity is maintained in the main current injection region or the main light emitting region.

  Furthermore, since the good crystallinity of the active layer is kept uniform in the horizontal direction, carriers are wasted in the active layer region with poor crystallinity when the injection current spreads horizontally in the active layer. There is no. That is, the luminous efficiency in the active layer is kept high, and heat generation can be suppressed to a small level. As described above, self-excitation having a good device lifetime can be achieved by providing a saturable absorption layer in a self-aligned manner without devising high concentration doping or the like, and by deteriorating crystallinity only in a necessary region. An oscillation type semiconductor laser is realized.

  As an application example of the present invention, there is a self-excited oscillation type semiconductor laser.

It is sectional drawing which shows 1st Embodiment of the nitride-type light emitting element by this invention. It is sectional drawing which shows 2nd Embodiment of the nitride-type light emitting element by this invention. It is sectional drawing which shows 3rd Embodiment of the nitride-type light emitting element by this invention. (A) is a bird's-eye view which shows 4th Embodiment of the nitride type light emitting element by this invention. (B) And (c) is sectional drawing in the AA 'surface and BB' surface in (a), respectively. It is sectional drawing which shows 5th Embodiment of the nitride-type light emitting element by this invention. It is sectional drawing which shows 6th Embodiment of the nitride-type light emitting element by this invention. It is sectional drawing which shows the conventional self-excited oscillation type semiconductor laser.

Explanation of symbols

101 n-type substrate 102 n-type buffer layer 103 n-type cladding layer 104 n-type optical confinement layer 105 active layer 106 p-type cap layer 107 p-type optical confinement layer 108 lower current confinement layer 109 absorption layer 110 upper current confinement layer 111 opening 111a Embedded region 111b in the opening 111 Region in which the opening 111 is interrupted 112 p-type cladding layer 113 p-type contact layer 114 p-electrode 115 n-electrode 201 cap layer 301 first light distribution control layer 302 second light distribution control layer 501 n-type substrate 502 n-type buffer layer 503 n-type cladding layer 504 n-type optical confinement layer 505 active layer 506 p-type cap layer 507 p-type optical confinement layer 508 current confinement layer 509 opening 510 absorption layer 510a located outside the stripe Absorbing layer 510b Absorbing layer 511 located within stripe p-type Lad layer 512 p-type contact layer 513 p-electrode 514 n-electrode 601 light distribution control layer 701 n-type substrate 702 n-type buffer layer 703 n-type cladding layer 704 n-type optical confinement layer 705 active layer 706 p-type cap layer 707 p-type light Confinement layer 708 Saturable absorption layer 709 p-type cladding layer 710 p-type contact layer 711 insulating layer 712 p-electrode 713 n-electrode

Claims (11)

An active layer made of a group III nitride semiconductor;
A functional layer provided above the active layer and having a function of current confinement or light distribution control;
A saturable absorption layer provided above the functional layer and absorbing light generated in the active layer; and
The functional layer and the saturable absorption layer have a stripe-shaped opening,
The dislocation density of the region of the active layer facing the functional layer is Na, the dislocation density of the region of the active layer facing the opening is Nb, and the dislocation density of the region of the saturable absorbing layer facing the functional layer Is a self-pulsation type semiconductor laser , wherein Na <Nc and Nb <Nc. The self-pulsation type semiconductor laser according to claim 1,
The self-pulsation type semiconductor laser in which Na and Nb are substantially equal to each other. The self-pulsation type semiconductor laser according to claim 1 or 2,
A self-pulsation type semiconductor laser in which the dislocation density of the active layer is substantially uniform. An active layer made of a group III nitride semiconductor;
A functional layer having a function of current confinement or light distribution control;
A saturable absorption layer that absorbs light generated in the active layer, and
The functional layer has a stripe-shaped opening,
The dislocation density of the region of the active layer facing the functional layer is Na ′, the dislocation density of the region of the active layer facing the opening is Nb ′, and the dislocation density of the region of the saturable absorber layer facing the functional layer is Assuming that the dislocation density is Nc ′ and the dislocation density of the region facing the opening of the saturable absorber layer is Nd ′, Na ′ <Nc ′, Nb ′ <Nc ′, and Nc ′> Nd ′. A self-excited oscillation type semiconductor laser . In the self-pulsation type semiconductor laser according to claim 4,
The Na ′ and the Nb ′ are self-pulsation type semiconductor lasers that are substantially equal to each other. The self-pulsation type semiconductor laser according to claim 4 or 5,
A self-pulsation type semiconductor laser in which the dislocation density of the active layer is substantially uniform. The self-pulsation type semiconductor laser according to any one of claims 1 to 6,
The saturable absorption layer is a self-pulsation type semiconductor laser provided in the functional layer. The self-pulsation type semiconductor laser according to any one of claims 1 to 6,
The saturable absorption layer is a self-pulsation type semiconductor laser provided adjacent to the functional layer. The self-pulsation type semiconductor laser according to any one of claims 1 to 6,
The saturable absorption layer is a self-pulsation type semiconductor laser provided in the vicinity of the functional layer. The self-pulsation type semiconductor laser according to any one of claims 1 to 9,
The functional layer has a stripe-shaped opening inside the resonator, self-pulsation type semiconductor laser having no opening in the resonator end. The self-pulsation type semiconductor laser according to any one of claims 1 to 10,
The saturable absorbing layer is made of Al _z In _w Ga _1-zw N (0 ≦ z ≦ 1, 0 ≦ w ≦ 1, 0 ≦ z + w ≦ 1),
The functional layer is a self-pulsation type semiconductor laser made of Al _x In _y Ga _1-xy N (0.4 ≦ x ≦ 1, 0 ≦ y ≦ 0.6, 0 ≦ x + y ≦ 1).

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