JP2005223110A - Semiconductor laser device, application system, crystal growth method, and compound semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser wherein optical confinement in an active layer is sufficiently large. <P>SOLUTION: The semiconductor laser device 100 includes a first layer 107 consisting of a group III-V compound semiconductor layer which contains at least one kind of group-V element other than nitrogen and nitrogen as a group-V composition. A second layer 106 consisting of a group III-V compound semiconductor layer expressed by a composition formula GaAs<SB>1-h-k</SB>Sb<SB>h</SB>N<SB>k</SB>(0<k≤0.015, 0<h<1) is adjacent to the first layer 107, and a third layer 105 consisting of an alloy GaAs group III-V compound semiconductor layer is adjacent to the second layer 106. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention generally relates to a semiconductor laser device, and more particularly to a semiconductor laser device improved so that light confinement in an active layer is sufficiently large. The present invention also relates to an application system using such a semiconductor laser element. The present invention further relates to a crystal growth method improved to obtain such a semiconductor laser device. The present invention also relates to a compound semiconductor device improved so as to obtain excellent characteristics.

  In recent years, the spread of broadband Internet has been remarkable in homes, and in particular, optical fiber communication using light having a wavelength of 1.31 μm is rapidly spreading. Semiconductor laser elements (LDs) used as light sources in optical fiber communications can be said to be key devices that support the modern information society.

  Conventionally, a semiconductor laser in this wavelength region has been constructed by a material system called InGaAsP on an InP substrate.

On the other hand, a semiconductor laser as shown in FIG. 10 has been proposed (see, for example, Patent Document 1). Referring to FIG. 10, in the active layer region 4 of this device, Ga _0.75 In _0.25 N _0.01 As _0.99 is used for the well layer 6, and the light guide (barrier) layer 5 is formed with Ga _{0.005 . It} is a single quantum well structure having ₉₄ In _0.06 N _0.02 As _0.98 . The substrate is an n-type GaAs substrate 2. A lower clad layer 3 made of N-type GaAs is provided on a GaAs substrate 2, and an active layer region 4 is provided thereon.
The active layer region 4 has a non-doped Ga _0.94 In _0.06 N _0.02 As _0.98 light guide (barrier) layer 5 grown on the lower cladding layer 3, and then non-doped Ga _0.75 In _0. Forming a _.25 N _0.01 As _0.99 well layer 6, followed by growing a non-doped Ga _0.94 In _0.06 N _0.02 As _0.98 light guide (barrier) layer 5; The upper cladding layer 7 made of p-type GaAs and the p-type GaAs contact layer 8 are grown in this order, and mesa etching is performed to the lower part of the active layer. Then, the first p-type GaAs buried layer 11 and the second n-type GaAs buried layer 12 are grown in order to form an electrode pattern opening by the SiO ₂ mask 10, and the p-type electrode 9 is formed thereon. After the substrate polishing step, the n-type electrode 1 is formed on the back surface, and further through a cleavage step, a BH (Buried Heterostructure) type laser device is completed.

  When such an active layer is used, carriers such as electrons and holes can be efficiently confined in the active layer, and a semiconductor laser that is resistant to changes in environmental temperature relative to the LD on the InP substrate can be obtained.

As described above, Patent Document 1 discloses a configuration of a semiconductor laser having a buried heterostructure using GaAs as a buried layer. As an example, GaAs is used as upper and lower cladding layers, and aluminum (Al) is not included. A semiconductor element composed of a semiconductor material is disclosed. Thereby, the problem of oxidation occurring in the semiconductor material containing Al is avoided, and the structure is extremely advantageous for extending the life of the semiconductor laser element.
JP 2001-223437 A

  However, the semiconductor laser disclosed in Patent Document 1 uses a cladding layer and a buried layer made of GaAs and constitutes a BH structure made of a semiconductor material that does not contain Al. It has been found that a semiconductor laser with good characteristics cannot always be obtained with the technology alone.

The semiconductor laser disclosed in Patent Document 1 describes a single quantum well structure using Ga _0.9 In _0.1 As or Ga _0.94 In _0.06 N _0.02 As _0.98 as the light guide layer 5. Studies have shown that these materials cannot be used as light guide layers.

  The light guide layer 5 has a role of concentrating the light distribution inside the laser in the vicinity of the active layer, and therefore requires a sufficiently large refractive index and an appropriate thickness. However, since GaInAs has a large lattice mismatch with respect to GaAs, the In composition ratio can be increased only to a certain extent. Therefore, the refractive index cannot be sufficiently increased as compared with GaAs. Also, because of the lattice mismatch, the layer thickness can only be increased to a certain extent. For this reason, it has been found that a refractive index and a layer thickness suitable for use as a light guide layer cannot be obtained.

  On the other hand, when GaInNAs is used as the light guide layer, it is active because it can be lattice-matched with GaAs due to the effect of mixed crystal of N, and a refractive index sufficiently higher than that of GaAs can be obtained. It was found that optical confinement in the layer can be sufficiently performed. However, when this mixed crystal material is lattice-matched with GaAs, the heterojunction with GaAs becomes Type-II, and the hole injection efficiency is greatly reduced, and the laser oscillation It has been found that there is a drawback that the threshold current increases significantly.

  Thus, it can be said that there has been no knowledge about a semiconductor material optimal as a light guide layer for a GaInNAs well layer. In particular, when an attempt is made to construct a BH structure made of a semiconductor material not containing Al using a cladding layer and a buried layer made of GaAs, lattice matching with GaAs is possible, and the refractive index difference from GaAs is sufficiently large. Although it is essential that the heterojunction between the layers be a type I heterojunction, no study has been made regarding the selection of materials from such a viewpoint.

  In view of such circumstances, the present invention provides a semiconductor material that is optimal as a light guide layer for a GaInNAs well layer when GaAs is selected as a cladding layer.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an improved semiconductor laser device in which an optimum semiconductor material is selected as the light guide layer and the light confinement in the active layer is sufficiently increased.

  Another object of the present invention is to provide an application system using such a semiconductor laser device.

  Still another object of the present invention is to provide an improved crystal growth method so that such a semiconductor laser device can be obtained.

  Still another object of the present invention is to provide a compound semiconductor device improved so as to obtain excellent characteristics.

The semiconductor laser device according to the first aspect of the present invention has a first layer composed of a group III-V compound semiconductor layer containing at least one kind of group V element other than nitrogen and nitrogen as a group V composition. The first layer is a second layer composed of a III-V group compound semiconductor layer having a composition of GaAs _1-hk Sb _h N _k (where 0 <k ≦ 0.015, 0 <h <1). Are adjacent. Adjacent to the second layer is a third layer made of a III-V compound semiconductor layer composed of GaAs.
With this configuration, when the first layer functions as a well layer in the quantum well structure, the second layer functions as a light guide layer, and the third layer functions as a cladding layer, the cladding layer and the light guide layer Since the difference in refractive index can be made sufficiently large and the guide layer can be lattice-matched with GaAs, a layer structure of a semiconductor laser with sufficiently large light confinement in the active layer can be obtained.

  The first layer preferably contains antimony as a composition.

  Preferably, the first layer includes a structure sandwiched from above and below by the second layer and further sandwiched from above and below by the third layer.

  It is preferable that the composition ratios h and k of the second layer substantially satisfy h = 2.6 × k.

  Of the second layer, the vicinity of the interface adjacent to the first layer preferably has tensile strain, and the vicinity of the interface adjacent to the third layer is preferably lattice-matched to GaAs.

  Further, the third layer is provided vertically so as to sandwich the layer including the first layer and the second layer, and the first layer and the second layer are doped with impurities. Instead, it may be configured such that any one of the third layers provided above and below is doped with an impurity so that one of them is p-type and the other is n-type.

  The first layer may function as a well layer in the quantum well structure, the second layer as a light guide layer, and the third layer as a cladding layer.

  Preferably, the first layer and the second layer, and the second layer and the third layer are formed by a type I heterojunction. By making the heterojunction band lineup between each layer an ideal type I type, carriers can be sufficiently injected and confined, and a good semiconductor laser device with a very small oscillation threshold current can be obtained. Become.

  Preferably, the semiconductor laser element has a mesa structure and includes a current confinement layer made of GaAs provided on both sides of the light generating region intersecting the light traveling direction.

  The semiconductor laser element preferably has a buried hetero structure. By using a buried heterostructure, it is possible to achieve a significant reduction in device drive current and a significant increase in efficiency during laser oscillation.

  Preferably, the first layer has a plurality of layers of two or more layers, and the plurality of layers are separated by a fourth layer made of a III-V group compound semiconductor composed of GaAsSbN. In this case, it is preferable that the plurality of first layers have compressive strain, and the fourth layer separating them has tensile strain. The plurality of first layers may function as well layers in a multiple quantum well structure, and the fourth layer may function as a barrier layer.

  The first layer is preferably any one of GaInNAs, GaInAsSb, and GaInNAsSb.

  A second aspect of the present invention relates to an application system in which any one of the semiconductor lasers according to claims 1 to 14 is used. Since a good semiconductor laser element having sufficiently large light confinement in the active layer and a very small oscillation threshold current is used, the characteristics of the entire system can be improved.

  According to a third aspect of the present invention, a layer A composed of a group III-V compound semiconductor layer containing at least one group V element other than nitrogen and nitrogen as a group V composition is used as a layer III-V composed of GaAsSbN. According to a crystal growth method, crystal growth is performed on a layer B made of a group compound semiconductor layer. According to this crystal growth method, the light emission characteristics of the light emitting layer such as GaInNAs, GaInNAsSb, and GaInAsSb are remarkably improved, and a flat crystal film can be obtained.

  The layer A preferably contains antimony as a composition.

The compound semiconductor device according to the fourth aspect of the present invention has a layer α composed of a III-V group compound semiconductor layer containing at least one group V element other than nitrogen and nitrogen as a group V composition. Adjacent to one layer is a layer β made of a III-V group compound semiconductor layer having a composition of GaAs _1-hk Sb _h N _k (where 0 <k ≦ 0.015, 0 <h <1). Includes layer structure. With this configuration, the characteristics of an element having a crystal layer such as GaInNAs, GaInNAsSb, and GaInAsSb are remarkably improved.

  The layer α preferably contains antimony as a composition.

  According to the semiconductor laser device of the present invention, the difference in refractive index between the cladding layer and the light guide layer can be made sufficiently large, and the guide layer can be lattice-matched with GaAs, so that light confinement in the active layer can be achieved. However, a sufficiently large layer structure of a semiconductor laser can be obtained. Also, since the band lineup of heterojunctions between each layer can be an ideal type I type, carrier injection and confinement can be sufficiently performed, and a good semiconductor laser device with a very small oscillation threshold current can be obtained. It will be obtained.

  The optical guide layer can be freely set by setting the mixed crystal composition to a predetermined value from the tensile strain to the compressive strain even when a strained crystal is required due to the demand from the quantum well design. It is also possible to set.

  Furthermore, since GaAs containing no Al can be used for the cladding layer, a good buried heterostructure can be realized, and the drive current of the device can be greatly reduced and the efficiency at the time of laser oscillation can be improved. It will be possible to achieve a significant rise.

  Further, by using the semiconductor element of the present application in an application system, the characteristics of the entire system can be improved.

  Further, according to the crystal growth method of the present application, the light emission characteristics of the light emitting layer such as GaInNAs, GaInNAsSb, and GaInAsSb are remarkably improved, and a flat crystal film can be obtained.

  In addition, the compound semiconductor element of the present application significantly improves the characteristics of an element having a crystal layer such as GaInNAs, GaInNAsSb, and GaInAsSb.

  Embodiments of the present invention will be described below with reference to the drawings.

  In Example 1, a structure of a semiconductor laser element constructed on a substrate made of GaAs and having a double quantum well structure in which an optical guide layer and a barrier layer are GaAsSbN and a well layer is GaInNAs as an active layer will be described. The present embodiment is characterized in that GaAsSbN that substantially lattice matches with GaAs is used as the light guide layer and the barrier layer.

  FIG. 1 is a perspective view of the structure of the semiconductor laser device 100 according to the first embodiment.

Referring to FIG. 1, a semiconductor laser device 100 includes a substrate 111 made of n-type GaAs. A lower cladding layer 110 of 1 μm thickness made of n-type GaAs, a lower light guide layer 109 of 0.12 μm thickness made of i (intrinsic) -GaAs _0.978 Sb _0.016 N _0.006 , and i-Ga _0.64 In 7 nm thick well layer 107 made of _0.36 N _0.006 As _0.994, 0.05 μm thick barrier layer 108 made of i-GaAs _0.978 Sb _0.016 N _0.006, and 7 nm thick made of i-Ga _0.64 In _0.36 N _0.006 As _0.994 the well layer 107, the i-GaAs _0.978 Sb _0.016 N upper light guide layer 106 of 0.12μm thickness consisting of _0.006, an upper cladding layer 105 of 1μm thickness made of p-type GaAs, consists p ⁺ -type GaAs 0. A contact layer 104 having a thickness of 5 μm is laminated.

  The contact layer 104, the upper cladding layer 105, the upper light guide layer 106, the well layer 107, the barrier layer 108, the lower light guide layer 109, the lower cladding layer 110, and the substrate 111 are mesa-etched up to the surface of the substrate 111. . Then, a second current confinement layer 103 made of p-type GaAs and a first current confinement layer 102 made of n-type GaAs are grown in order. A p-type side electrode metal 101 made of Ti / Pt / Au is formed so as to be in contact with the contact layer 104, and an n-type side electrode metal 112 made of AuGe / Ni is provided on the back surface of the substrate 111.

When a resonator length of 1000 μm is cleaved and a current is passed through the upper and lower electrodes 101 and 112, a laser is emitted at a wavelength of 1.31 μm at an oscillation threshold current density of 400 [A / cm ² / well] per quantum well. Oscillated.

In the case of Ga _0.9 In _0.1 As used as a light guide (barrier) layer in the semiconductor laser disclosed in Patent Document 1, the critical film thickness of this material is as thin as about 0.033 μm and is a cladding layer. Since the difference in refractive index from GaAs is extremely small (n (GaInAs) -n (GaAs) = 0.04), it is possible to design a light guide structure that concentrates the light distribution in the semiconductor laser near the well layer. I can't.

By the way, when N is mixed into GaAs or GaInAs, the refractive index is remarkably higher than when other elements are mixed, Japan Journal of Applied Physics, vol. 37, 1998, No. .3A, p.753. Therefore, by mixing N in the light guide layer, the refractive index difference between the cladding layer and the guide layer can be remarkably increased, and the light confinement in the active layer can be sufficiently increased. It is expected to be able to make. That is, it is considered that a material in which N is mixed is a preferable material for the light guide layer. Also in the semiconductor laser disclosed in Patent Document 1 shown as the background art, a material of Ga _0.94 In _0.06 N _0.02 As _0.98 is disclosed as a light guide (barrier) layer, and in this case, N is mixed crystal It was found that the effect was such that a sufficiently higher refractive index than that of GaAs could be obtained. Further, since the composition is substantially lattice-matched with GaAs, a thick film can be obtained, and light confinement in the active layer can be performed more sufficiently.

  On the other hand, when this mixed crystal material is used as a guide layer and lattice-matched with a cladding layer made of GaAs, the band lineup of the heterojunction between the guide layer and the cladding layer is type II as shown in FIG. Type heterojunction. In this case, when the clad layer is p-type, the hole injection efficiency from the clad layer to the light guide layer is reduced, and when the clad layer is n-type, holes leak to the clad layer. There was found. In particular, the heterobarrier in the valence band is a major factor that lowers the injection efficiency for holes that have a large effective mass and are difficult to overcome. The problem that the band lineup at the heterojunction with GaAs becomes the type II type due to the mixed crystallization of N is due to the decrease in the band edge energy level of the valence band accompanying the mixed crystallization of N. . Therefore, the same applies when a GaAsN mixed crystal is used as the light guide layer.

  On the other hand, in the configuration using GaAsSbN of the present invention, since the refractive index is remarkably increased because N is mixed, the difference in refractive index between the cladding layer and the light guide layer can be remarkably increased (n (GaAsSbN) -n (GaAs) = 0.17), the point that a structure capable of sufficiently increasing the light confinement in the active layer can be made is the same as the latter case of the background art described above. In addition, the band edge energy level of the valence band can be increased by mixing Sb. At this time, if this material is used as a guide layer and GaAs is used as a clad layer, the heterojunction between the guide layer and the clad layer can obtain a type I band lineup as shown in FIG. I found it.

This point will be described with reference to FIG. FIG. 3 shows a band discontinuity (ΔE _v) between the GaAs cladding layer and the light guide layer when the Sb mixed crystal ratio is changed in the GaAsSbN layer used as the light guide layer in this example. ) Shows the state of change. When Sb is not mixed, ΔE _v is a negative value, that is, a type II type heterojunction (FIG. 2A), whereas by mixing Sb, the energy of the valence band is obtained. The edge rises and ΔE _v changes to a positive value, ie, a type I heterojunction (FIG. 2B). In this case, the hole injection efficiency from the p-type cladding layer is greatly improved and the leakage of holes to the n-type cladding layer is greatly reduced as compared with the case where conventional GaInNAs is used as the light guide layer. In particular, in the case of the GaAsSbN mixed crystal, which is a feature of the present application, the energy edge of the valence band can be controlled independently only by the Sb mixed crystal ratio, while the energy edge of the conduction band is controlled independently only by the N mixed crystal ratio. Due to the unique properties of this mixed crystal material, the flexibility of setting the band lineup and the controllability are extremely high.

  Further, the reduction of the lattice constant accompanying the mixed crystallization of N can be compensated for by the mixed crystallization of Sb, and the lattice matching with the GaAs of the substrate can be achieved.

This point will be described with reference to FIG. FIG. 4 shows a change in the lattice constant of the light guide layer when the Sb mixed crystal ratio is changed in the GaAsSbN layer used as the light guide layer in this example. When Sb is not mixed, the lattice constant is smaller than that of GaAs and the lattice is distorted. In this case, when the critical film thickness is about 250 nm or more, crystal defects are caused by lattice relaxation. On the other hand, when Sb is mixed into the light guide layer as in the present application, the lattice constant is increased and can be completely matched with GaAs. In order to make the lattice constant of the GaAs _1-hk Sb _h N _k mixed crystal coincide with that of GaAs, the expansion of the lattice constant due to the mixed crystallization of Sb and the reduction of the lattice constant due to the mixed crystallization of N may be balanced. . For this purpose, it has been found that the composition ratios h and k generally satisfy h = 2.6 × k in consideration of the respective atomic radii of Sb and N.

  In addition, even when a strained crystal is required due to the demand from the design of the quantum well, it can be freely set by setting the mixed crystal composition to a predetermined value from the tensile strain to the compressive strain. is there.

  As described above, in the configuration of the present application, particularly when GaAs containing no Al is used for the cladding layer, an ideal refractive index distribution, lattice constant, and band lineup can be realized. It became clear that there was an effect.

  Here, since the refractive index of the light guide layer is sufficiently larger than that of GaAs, an advantage that GaAs containing no Al can be used as the cladding layer material will be described. When a layer containing Al as a mixed crystal composition is used as a clad layer and etched into a mesa shape, the etching side surface is oxidized and a non-light-emitting center is generated. However, as in the present application, Al is not included as a composition. When GaAs is used for the cladding layer, there is no such problem, and a good buried heterostructure can be realized. By adopting a buried heterostructure, it has become possible to achieve a significant reduction in device drive current and a significant increase in laser oscillation efficiency.

  Furthermore, when GaAsSbN is used as a light guide layer / barrier layer and a light emitting layer (well layer) made of GaInNAs is grown on the crystal as shown in the present application, the crystal is grown on GaInAs, GaInNAs, GaAsN or the like. It was found that a flat crystal film having significantly excellent light emission characteristics than that of the case can be obtained. This is because the well layer growth mode is a layer-growth mode in the combination of the surface energy of the GaInNAs layer that is the well layer and the underlying GaAsSbN layer and the interfacial energy of the heterointerface. It is considered that this progresses more flatly and the flatness and crystallinity of the interface are improved. Further, when a barrier layer made of GaAsSbN is sandwiched between a plurality of GaInNAs well layers, the flatness of the outermost surface during crystal growth while the barrier layer made of GaAsSbN is grown on the lower GaInNAs well layer. Therefore, even when a GaInNAs well layer is further laminated thereon to form a multi-quantum well, there is no difference in crystallinity between the well layers, and light emission with a narrow spectral line width occurs. It was. Thus, it has been found that using a GaAsSbN crystal as a base layer for a GaInNAs well layer or a barrier layer provided between a plurality of well layers is effective from the viewpoint of crystal growth.

As a result of examination by the inventors of the present application, it has been found that the crystallinity of GaInNAs, which is a well layer, is improved and the light emission characteristics are improved when the underlayer contains Sb as a composition. It was also found that when GaInNAs, which is a well layer, contains a small amount of Sb, the light emitting characteristics are particularly excellent when the underlayer contains Sb as a composition. In the GaAs _1-hk Sb _h N _{k used} as the underlayer, the crystallinity of the GaAs _1-hk Sb _h N _k is greatly deteriorated when the N mixed crystal ratio k is larger than 0.015. As can be seen, the present invention could not be implemented unless k ≦ 0.015.

The semiconductor laser of FIG. 1 was manufactured as follows. First, each layer from the lower cladding layer 110 to the contact layer 104 on an n-type GaAs substrate is crystallized by molecular beam epitaxy (MBE) using N ₂ plasma as the nitrogen source and a solid source as the other material. It is grown and processed into a mesa shape having a width of 3 μm using photolithography and wet etching technology, and the second current confinement layer 103 and the first current confinement layer 102 are formed on both sides of the mesa by metal organic chemical vapor deposition (MO−). After re-growth by the CVD method, the substrate 111 was thinned to a thickness of 100 μm, electrodes 101 and 112 were deposited on the upper and lower sides, and divided into a predetermined size by cleaving to complete the device.

  The structure of the semiconductor laser device having the triple quantum well structure in which the well layer is replaced with GaInNAsSb and the number of wells is three as the active layer in the configuration of the first embodiment will be described. The present embodiment is characterized in that GaAsSbN that substantially lattice matches with GaAs is used as the light guide layer and the barrier layer.

  FIG. 5 shows the structure of the semiconductor laser device 200 of the second embodiment.

Referring to FIG. 5, the semiconductor laser element 200 includes a substrate 211 made of n-type GaAs. A lower cladding layer 210 made of n-type GaAs and having a thickness of 0.12 μm made of i (intrinsic) -GaAs _0.978 Sb _0.016 N _0.006 are sequentially provided on the substrate 211. On the lower light guide layer 209, a 7 nm thick well layer 207 made of i-Ga _0.72 In _0.28 N _0.004 As _0.926 Sb _0.07 and a 20 nm thick barrier layer 208 made of i-GaAs _0.989 Sb _0.005 N _0.0066 are formed. The layers 207 are alternately formed so as to be three layers. Further, an upper light guide layer 206 made of i (intrinsic) -GaAs _0.978 Sb _0.016 N _0.006 and having a thickness of 0.1 μm, an upper cladding layer 205 made of p-type GaAs having a thickness of 1 μm, and p ^{+ having a} thickness of 0.5 μm. A contact layer 204 made of type GaAs is laminated.

  The contact layer 204, the upper cladding layer 205, the upper light guide layer 206, the well layer 207, the barrier layer 208, the lower light guide layer 209, the lower cladding layer 210, and the substrate 211 are mesa-etched up to the surface of the substrate 111. . A second current confinement layer 203 made of p-type GaAs and a first current confinement layer 202 made of n-type GaAs are grown in this order on the mesa-etched portion. A p-type side electrode metal 201 made of Ti / Pt / Au is formed so as to be in contact with the contact layer 104, and an n-type side electrode metal 212 made of AuGe / Ni is provided on the back surface of the substrate 211.

When the resonator length is 500 μm and a current is passed through the upper and lower electrodes 201, 212, the wavelength is 1.31 μm at a low oscillation threshold current density of 300 [A / cm ² / well] per quantum well. Caused laser oscillation.

  In this example, the number of wells, the composition of the well layers, and the composition ratio are different from those of Example 1, but the heterojunction band lineup between the layers realizes the type I type as in Example 1. In addition, a semiconductor laser with good characteristics can be obtained while using GaAs for the cladding layer, and since it is made of a material that does not contain Al, it can be manufactured without problems such as oxidation of the layer containing Al. I can do it. As for the crystallinity of the GaInNAsSb mixed crystal, which is a well layer, the well layer can be grown more flat and with good crystallinity by crystal growth on the GaAsSbN layer, as in Example 1. As a result, the characteristics of the semiconductor laser are improved.

  In particular, in this embodiment, a GaAsSbN layer having a tensile strain composition is used for the barrier layer 208 between the well layers, and the influence of the strain of the well layer having a compressive strain can be reduced. Thus, when the GaAsSbN layer is arranged adjacent to the well layer, the composition thereof can be arbitrarily set as compression strain, lattice matching, and tensile strain, and the feature is that the degree of freedom of control is extremely high.

  In this example, the structure of a semiconductor laser device having a single quantum well structure in which the well layer is GaInNAs (Sb) containing a small amount of Sb and the number of wells is one is shown. This embodiment is characterized in that GaAsSbN, which is generally lattice-matched to GaAs, is used as the light guide layer, and GaAsSbN having tensile strain is used as the barrier layer adjacent to the well layer.

  FIG. 6 is a perspective view of the structure of the semiconductor laser device 300 according to the third embodiment.

A second current confinement layer 303 made of p-type GaAs and a first current confinement layer 302 made of n-type GaAs are provided on a substrate 311 made of n-type GaAs. The first current confinement layer 302 and the second current confinement layer 303 have a groove penetrating to the surface of the substrate 311. In the groove, a lower cladding layer 310 made of n-type GaAs having a thickness of 1 μm, a lower light guide layer 309 made of i-GaAs _0.978 Sb _0.016 N _0.006 and having a thickness of 0.13 μm, i-Ga _0.64 In _0.36 N _0.006 As _0.989 Sb A well layer 307 having a thickness of 6 nm made of _0.005 , a light guide layer 306 having a thickness of 0.13 μm made of i-GaAs _0.978 Sb _0.016 N _0.006 and an upper cladding layer 305 having a thickness of 1 μm made of p-type GaAs are provided. A barrier layer 308 having a thickness of 220 nm made of i-GaAs _0.989 Sb _0.005 N _0.006 is provided only in a portion adjacent to the well layer 307 in each of the lower light guide layer 309 and the upper light guide layer 306. A contact layer 304 of 0.5 μm thickness made of p ⁺ -type GaAs is provided so as to contact the upper cladding layer 305, and a p-type electrode metal 301 made of Ti / Pt / Au is provided thereon. An n-type electrode metal 312 made of AuGe / Ni is provided on the back surface of the substrate 311.

When the resonator length was cleaved to 250 μm and current was passed through the upper and lower electrodes 301 and 312, laser oscillation was generated at a wavelength of 1.29 μm at an oscillation threshold current density of 350 [A / cm ² / well].

  In this example, the number of wells, the composition and composition ratio of the well layer, and the shape of the buried heterostructure are different from those of Examples 1 and 2, but each layer has a type I heterojunction. As in Examples 1 and 2, a semiconductor laser with good characteristics can be obtained while using GaAs for the cladding layer, and since it is made of a material not containing Al, the layer containing Al is oxidized. Semiconductor lasers can be manufactured without any problems.

  Further, in this embodiment, GaAsSbN having a lattice matching composition is used for the light guide layers 306 and 309, and a GaAsSbN layer 308 having a thin film tensile strain is disposed only in a portion adjacent to the well layer 307. Thereby, the strain of the well layer 307 having a compressive strain is offset, and the amount of strain contained is reduced.

  The semiconductor laser of FIG. 6 is manufactured as follows. First, the second current confinement layer 303 and the first current confinement layer 302 are crystal-grown on the n-type GaAs substrate 311 by a chemical molecular beam epitaxial growth (CBE) method, and have a width of 2 μm using photolithography and wet etching techniques. Grooves are formed. Each layer from the lower cladding layer 310 to the upper cladding layer 305 is regrown in the groove by the second CBE method, and the contact layer 304 is regrown on the entire surface by the third CBE method, After thinning 311 to a thickness of 100 μm, electrodes 301 and 312 were deposited on the upper and lower sides, and divided into predetermined sizes by cleaving to complete the device. Example 3 differs from Examples 1 and 2 in the manufacturing process and shape of the buried heterostructure, but the same effect is obtained.

  In this example, the structure of a buried hetero semiconductor laser element having a GRIN-SCH (Graded Index-Separate Confinement Heterostructure) structure by changing the N composition and the Sb composition little by little will be described. This embodiment is characterized in that GaAsSbN whose composition gradually changes is used as the light guide layer.

  FIG. 7 shows the structure of the semiconductor laser device 400 of the fourth embodiment.

Referring to FIG. 7, a 1 μm-thick lower cladding layer 410 made of n-type GaAs, a 0.15 μm-thick lower light guide layer 409 made of i-GaAsSbN, and i-Ga on a substrate 411 made of n-type GaAs. _0.72 In _0.28 As _0.93 Sb _0.07 8 nm thick well layer 407, i-GaAsSbN 0.15 μm thick upper light guide layer 406, p-type GaAs 1 μm thick upper cladding layer 405, p ⁺ -type GaAs A contact layer 404 having a thickness of 0.5 μm is provided. The lower cladding layer 410, the lower light guide layer 409, the well layer 407, the upper light guide layer 406, the upper cladding layer 405, and the contact layer 404 are mesa-etched up to the surface of the substrate 411. A first current confinement layer 402 made of n-type GaAs and a second current confinement layer 403 made of p-type GaAs are provided in the mesa-etched portion. A p-type side electrode metal 401 made of Ti / Pt / Au is provided so as to be in contact with the contact layer 404. An n-type side electrode metal 412 made of AuGe / Ni is provided on the back surface of the substrate 411.

When the resonator length was cleaved to 800 μm and current was passed through the upper and lower electrodes 401 and 412, laser oscillation was generated at a wavelength of 1.2 μm at an oscillation threshold current density of 250 [A / cm ² / well].

In this embodiment, the N mixed crystal ratio and the Sb mixed crystal ratio of the upper and lower light guide layers are adjusted, and the light guide layer from the cladding layer to the end of the well layer is forbidden as shown in FIG. 8A. The composition ratios h and k substantially satisfy h = 2.6 × k so that the band width gradually changes in a parabolic manner and the GaAs _1-hk Sb _h N _k mixed crystal always always lattice matches with GaAs. Was set as follows. By doing so, optical confinement in the well layer is more efficiently performed, and laser oscillation with a lower threshold current occurs. In particular, it is particularly advantageous from the viewpoint of controlling the light distribution inside the laser element to create such a refractive index distribution by setting an N composition that can change the refractive index of the material significantly. Note that the band lineup of the light guide layer does not necessarily have the parabolic shape shown in this embodiment, but the linear shape shown in FIG. 8 (b) or the step shape shown in FIG. 8 (c). Also good.

  Also in this embodiment, the type I type heterojunction between the layers is realized as in the other embodiments. In addition, a semiconductor laser with good characteristics can be obtained while using GaAs for the cladding layer, and since it is made of a material that does not contain Al, it can be manufactured without problems such as oxidation of the layer containing Al. I can do it.

  Also, a GaInAsSb mixed crystal, which is a well layer, is grown on the GaAsSbN optical guide layer, and the well layer can be grown more flat and with good crystallinity as in the other embodiments. This has improved the characteristics of semiconductor lasers.

  In this embodiment, an example of a laser that oscillates at a shorter wavelength than other embodiments is shown. The configuration of the semiconductor laser of the present application can be applied to any wavelength (wavelength of about 900 nm or more) at which no light absorption occurs in GaAsSbN that is a guide layer.

  FIG. 9 is an example of an application system using the semiconductor laser device of the present application, and constitutes an optical transmission unit 500 in an optical fiber communication system using a semiconductor laser as a transmission light source.

  The semiconductor laser 501 is the semiconductor laser described in detail in the first embodiment, and is driven by an electric circuit 502 for controlling the semiconductor laser according to an input electric signal. The input electric signal to this system is an optical signal. It is emitted from. The optical signal from the semiconductor laser 501 is condensed on the optical fiber 504 through the condensing lens 503, and the optical signal is output from the optical fiber. The semiconductor laser 501 is fixed to a submount 505 for heat dissipation. Reference numeral 506 denotes an electric terminal, and 507 denotes a substrate.

Since an element having a lower threshold current than that of the conventional example shown in Example 1 was used as the semiconductor laser 501, a transmission speed of 2.5 Gb / s was obtained, and excellent characteristics were exhibited.
As described above, the semiconductor laser of the present invention can be improved not only when the semiconductor laser is used alone but also as a part of the system as in this embodiment, so that the characteristics of the entire system can be improved. Needless to say, the semiconductor laser can be used not only in the above-described optical fiber communication system but also in various systems such as a spatial light transmission system and a sensor system such as distance measurement.

  The semiconductor element is not necessarily limited to a semiconductor laser, and can be applied to any optical device such as a light emitting diode, a light receiving element, an optical waveguide element, an optical amplifier, or a solar cell manufactured in a similar structure. Needless to say, a device having excellent characteristics can be manufactured with the basic structure shown in the embodiment of the present invention.

  Moreover, about the III-V compound semiconductor mixed crystal used as each layer in each Example shown to this application, group III elements (boron etc.) and group V element (Bi) other than having demonstrated the details in embodiment are included. A mixed crystal may be appropriately formed, or an impurity element (Zn, Be, Mg, Te, S, Se, Si, or the like) may be appropriately included. Further, the substrate is not limited to that shown in the embodiment, and the same effect can be obtained even when another substrate is used. For example, a II-VI compound semiconductor substrate such as a ZnSe substrate having a lattice constant relatively close to that of GaAs, or a IV group semiconductor substrate such as a Ge substrate can be used. In addition, a crystal produced on an arbitrary substrate such as glass, plastic, or ceramic can be used.

In addition, the raw materials of the respective constituent elements used for crystal growth are not limited to the specific raw materials described in the embodiment or specific combinations of the respective raw materials, and any raw materials may be used in any combination. Needless to say, you can.
Moreover, although all have shown about the case where the mixed crystal of this application is applied to the well layer in a quantum well structure, there is no restriction | limiting regarding the number of wells, distortion amount, and well layer thickness in that case. Further, a compressive or tensile strain may be introduced into the barrier layer.

  In the description so far, the direction indicated as “up” indicates a direction away from the substrate, and “down” indicates a direction approaching the substrate. Crystal growth proceeds from “down” to “up”.

  In the p-type semiconductor portion and the n-type semiconductor portion shown in each embodiment, p and n may be reversed.

  Since the semiconductor laser device according to the present invention has sufficiently large light confinement in the active layer, it can be effectively used in an optical communication system.

1 is a perspective view of a semiconductor laser device according to Example 1. FIG. It is a figure which shows the band lineup of a heterojunction. It is a figure which shows the mode of the change by Sb composition of the valence band discontinuity of a GaAsSbN layer and GaAs. It is a figure which shows the mode of the change by the Sb composition of the lattice constant of a GaAsSbN layer. 6 is a perspective view of a semiconductor laser device according to Example 2. FIG. 7 is a perspective view of a semiconductor laser device according to Example 3. FIG. 7 is a perspective view of a semiconductor laser device according to Example 4. FIG. It is a figure which shows the band lineup of a heterojunction. It is a figure which shows the application system using a semiconductor laser element. It is sectional drawing of the conventional semiconductor element.

Explanation of symbols

101 p-type side electrode metal 102 first current confinement layer 103 second current confinement layer 104 contact layer 105 upper clad layer 106 upper light guide layer 107 well layer 108 barrier layer 109 lower light guide layer 110 lower clad layer 111 substrate 112 n-type Side electrode metal

Claims (19)

A first layer comprising a group III-V compound semiconductor layer containing at least one group V element other than nitrogen and nitrogen as a group V composition;
A second layer composed of a III-V compound semiconductor layer having a composition of GaAs _1-hk Sb _h N _k (where 0 <k ≦ 0.015, 0 <h <1) is adjacent to the _first layer. Having a layer of
A semiconductor laser device comprising a layer structure having a third layer made of a III-V compound semiconductor layer having a composition of GaAs adjacent to the second layer.   2. The semiconductor laser device according to claim 1, wherein the first layer contains antimony as a composition.   The semiconductor laser device according to claim 1, wherein the first layer includes a structure sandwiched from above and below by the second layer and further sandwiched from above and below by the third layer.   2. The semiconductor laser device according to claim 1, wherein the composition ratios h and k of the second layer substantially satisfy h = 2.6 × k.   The vicinity of the interface adjacent to the first layer of the second layer has tensile strain, and the vicinity of the interface adjacent to the third layer is lattice-matched to GaAs. 2. The semiconductor laser device according to 1. The third layer is provided up and down so as to sandwich the layer including the first layer and the second layer,
Impurities are doped in the first layer and the second layer so that one of the third layers provided above and below is p-type and the other is n-type. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is formed.   2. The semiconductor laser device according to claim 1, wherein the first layer functions as a well layer in the quantum well structure, the second layer functions as a light guide layer, and the third layer functions as a cladding layer.   2. The semiconductor laser device according to claim 1, wherein the first layer and the second layer, and the second layer and the third layer form a type I heterojunction.   2. The semiconductor according to claim 1, wherein the semiconductor laser element has a mesa structure, and includes a current confinement layer made of GaAs provided on both sides of the light generating region intersecting the light traveling direction. Laser element.   The semiconductor laser device according to claim 1, wherein the semiconductor laser device has a buried hetero structure.   The first layer has a plurality of layers of two or more layers, and the plurality of layers are separated by a fourth layer made of a III-V group compound semiconductor having a composition of GaAsSbN. The semiconductor laser device according to claim 1.   12. The semiconductor laser device according to claim 11, wherein the plurality of first layers have compressive strain, and the fourth layer separating the first layers has tensile strain.   12. The semiconductor laser device according to claim 11, wherein the plurality of first layers function as well layers in a multiple quantum well structure, and the fourth layer functions as a barrier layer.   2. The semiconductor laser device according to claim 1, wherein the first layer is one of GaInNAs, GaInAsSb, and GaInNAsSb.   An application system using the semiconductor laser according to claim 1. A layer A composed of a III-V group compound semiconductor layer containing at least one group V element other than nitrogen and nitrogen as a group V composition,
A crystal growth method comprising growing a crystal on a layer B made of a III-V compound semiconductor layer having a composition of GaAsSbN.   The crystal growth method according to claim 16, wherein the layer A contains antimony as a composition. A layer α composed of a group III-V compound semiconductor layer containing at least one kind of group V element other than nitrogen and nitrogen as a group V composition;
A layer β made of a III-V group compound semiconductor layer having a composition of GaAs _1-hk Sb _h N _k (where 0 <k ≦ 0.015, 0 <h <1) adjacent to the _first layer. The compound semiconductor element containing the layer structure which has this.   The compound semiconductor device according to claim 18, wherein the layer α contains antimony as a composition.

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