JP4185716B2 - Semiconductor laser device and optical disk device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a semiconductor laser device having an oscillation wavelength band of 780 nm (greater than 760 nm and smaller than 800 nm) that does not contain Al in an active region, and an optical disk device using the semiconductor laser device.
[0002]
[Prior art]
  A semiconductor laser device of 780 nm band is widely used as a semiconductor laser device for reproducing a disc such as a CD (compact disc) or an MD (mini disc). Among them, as a semiconductor laser device for CD-R (CD recordable) capable of high-speed writing, a highly reliable semiconductor laser device with high output of 120 mW or more is strongly desired.
[0003]
  By the way, in the case of the conventional AlGaAs quantum well structure in which Al is contained in the well layer / barrier layer, there is a problem that reliability is lowered particularly at high temperature and high output. This is considered to be because Al is an active substance and thus reacts with a small amount of impurities such as oxygen, thereby amplifying deterioration of the material. One way to counter this is to realize high output and high reliability by adopting a structure in which Al is not contained in the well layer / barrier layer. However, actually, a semiconductor laser device having a high output of 120 mW or more and sufficient reliability in the 780 nm band has not yet appeared.
[0004]
  As a semiconductor laser device having an oscillation wavelength of 810 nm having a structure in which Al is not contained in the well layer / barrier layer, Japanese Patent Application Laid-Open No. 11-220244 and Japanese Journal of Applied Physics Vol. The one disclosed in L387-L389 has been proposed. Therefore, based on this conventional technique, an attempt was made to create a semiconductor laser device that oscillates at 780 nm.
[0005]
  FIG. 13 is a structural diagram showing a semiconductor laser device having an InGaAsP quantum well structure in which Al is not contained in the well layer / barrier layer. FIG. 14 shows a diagram of the energy band gap (Eg) in the vicinity of the active region in the semiconductor laser device shown in FIG.
[0006]
  In FIG. 13, 1 is an n-type GaAs substrate, and 2 is an n-type Al._0.63Ga_0.37As lower cladding layer, 3 is In_0.484Ga_0.516P lower guide layer 4 is an active region. Here, the active region 4 has a single quantum well (SQW) structure including a barrier layer 5 and a well layer 6. 7 is In._{0 .484}Ga_0.516P upper guide layer, 8 is p-type Al_0.63Ga_0.37As upper cladding layer, 9 is p-type GaAs protective layer, 10 is SiO₂A current blocking layer, 11 is an n-side electrode, and 12 is a p-side electrode. The barrier layer 5 is made of In._0.4Ga_0.6It is composed of P, the strain is -0.62% in tensile strain, and the layer thickness is 5 nm for both 5a and 5b. In_0.4Ga_0.6The Eg of P is calculated to be about 2.02 eV when strain is not taken into consideration, but is considered to be about 1.93 eV to 1.96 eV due to the influence of tensile strain. Well layer 6 is made of In._0.162Ga_0.838As_0.671P_0.329Eg is 1.57 eV, lattice-matched with the substrate, and the layer thickness is 5 nm.
[0007]
  In a semiconductor laser device in which Al is not contained in a conventional well layer / barrier layer, In_0.484Ga_0.516In between the P guide layer (Eg = 1.89 eV) and the InGaAsAs well layer_0.4Ga_0.6Inserting P barrier layer, Eg difference “ΔEg” from the layer adjacent to the well layer (ie, guide layers 3, 7) is 0.37 eV to 0.40 eV, and Al enters the well layer / barrier layer It is larger than the semiconductor laser device. For example, in the quantum well structure of an AlGaAs semiconductor laser, ΔEg is usually about 0.25 eV. As described above, in the conventional semiconductor laser device in which Al is not contained in the well layer / barrier layer, a material capable of taking ΔEg as large as possible is selected as the Al-free material used for the barrier layer 5 to ensure the confinement of carriers. It is.
[0008]
[Problems to be solved by the invention]
  However, the conventional semiconductor laser device having an InGaAsP quantum well structure in which Al is not contained in the well layer / barrier layer has the following problems. That is, when the characteristics of the semiconductor laser device were measured, the threshold current was as high as 100 mA, and the differential efficiency was 0.6 W / A, so that good characteristics could not be obtained. Also, the temperature characteristics are very poor, and oscillation does not occur at 80 ° C. or higher. In the case of an AlGaAs-based 780 nm band semiconductor laser device in which Al is contained in the well layer / barrier layer, the threshold current is 35 mA, the differential efficiency is 0.9 W / A, and the temperature characteristic is about 110K. Therefore, when compared with the AlGaAs semiconductor laser device, the characteristics are deteriorated.
[0009]
  Accordingly, an object of the present invention is to provide an Al-free semiconductor laser device capable of remarkably improving the characteristics regardless of the magnitude of ΔEg, and an optical disk device using the semiconductor laser device.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the first invention provides:
  An active region including a quantum well formed by laminating at least a lower cladding layer, one or a plurality of well layers, and a barrier layer on a GaAs substrate, and an oscillation wavelength in which the upper cladding layer is formed is greater than 760 nm and In a semiconductor laser device smaller than 800 nm,
  The barrier layer has a larger band gap energy than the well layer._1-xGa_xAs_1-yP_yAnd consisting of
  When the lattice constant of the well layer is a1, while the lattice constant of the barrier layer is a2, the following relationship is established.
            0 <x <1
            0.2 <y <0.75
            | (A2−a1) / a1 | × 100> 0.65
[0011]
  As will be described in detail later, in the conventional case where an InGaP barrier layer is used in a 780 nm band semiconductor laser device,
    1) Reduction of hole injection efficiency due to the spread of Ev in the barrier layer
    2) | ΔEc |
This causes a characteristic defect.
[0012]
  By the way, when the composition of InGaAsP is changed, the values of the energy (Ec) of the conduction band and the energy (Ev) of the valence band change even if the same Eg. When InGaAsP is used for the barrier layer, at the same Eg, when approaching the InGaP composition, Eg spreads to the valence band side, and | ΔEv | between the well layer and the barrier layer increases, but | ΔEc | decreases. On the other hand, when approaching the GaAsP composition, Eg spreads toward the conduction band, and | ΔEv | between the well layer and the barrier layer decreases, while | ΔEc | increases. The change in Ev is particularly related to the composition of the P element in InGaAsP, and the change in Ec is particularly related to the difference in strain from the well layer.
[0013]
  According to the above configuration, the barrier layerISince nGaAsP is used, and the composition ratio of the P element is larger than 0.2 and smaller than 0.75, the difference | ΔEv0 | of the Ev relative to the GaAs substrate can be set smaller than the conventional InGaP barrier layer. . Therefore, the efficiency of hole injection from the guide layer to the well layer is greatly improved.
[0014]
  Further, the strain amount of the barrier layer with respect to the well layer is 0.65%.Biggeris doing. Therefore, ΔEc between the barrier layer and the well layer is set to about 0.12 eV or more. This about 0.12 eV corresponds to ΔEc between the barrier layer and the well layer when AlGaAs having a group III Al composition of about 0.27 is used as the barrier layer in the quantum well structure of the AlGaAs semiconductor laser. . Therefore, the overflow of electrons from the well layer is suppressed.
[0015]
  In this way, the cause of the characteristic defect in the conventional semiconductor laser device using the InGaP barrier layer is eliminated, and 780 nm band using InGaAsP having a composition close to GaAsP or GaAsP, which has been considered to be ineffective due to a small Eg. The characteristics of this semiconductor laser device are remarkably improved.
[0016]
  In addition, I n G a A s I of P barrier layer n The growth of dislocations is suppressed by the element, and higher reliability can be obtained.
[0017]
  In one embodiment, in the semiconductor laser device of the first invention, when the lattice constant of the GaAs substrate is a0, the value of (a1-a0) / a0 is a positive value.
[0018]
  According to this embodiment, the strain of the well layer with respect to the GaAs substrate is a compressive strain. Therefore, for example, even when the lattice constant a2 of the barrier layer is set to a tensile strain smaller than the lattice constant a0 of the GaAs substrate, the average strain amount of the entire active region can be suppressed. Therefore, the amount of defects in the crystal can be reduced to improve the reliability, and the critical film thickness of the entire active region is increased, so that the thickness of the barrier layer can be increased. Moreover, since the well layer is compressive strained, a semiconductor laser device having a polarization mode of TE mode can be obtained.
[0019]
  In one embodiment, in the semiconductor laser device of the first invention, the well layer contains no Al element.
[0020]
  According to this embodiment, the well layer and the barrier layer do not contain an Al element that reacts with a small amount of impurities such as oxygen because it is an active substance. Therefore, high reliability can be obtained even at high temperature and high output.
[0021]
  In one embodiment, in the semiconductor laser device of the first invention, the well layer is made of InGaAsP.
[0022]
  According to this embodiment, in the InGaAsAsP well layer, Eg spreads to the valence band side as compared with the GaAs substrate, so that | ΔEc0 | <| ΔEv0 |. Conversely, when AlGaAs is used as the well layer, Eg of the well layer spreads toward the conduction band and becomes | ΔEc0 |> | ΔEv0 |. Therefore, when the InGaAsP well layer and the barrier layer are combined, | ΔEc | between the well layer and the barrier layer is larger and | ΔEv | is smaller than when AlGaAs is used as the well layer. Therefore, | ΔEc | between the well layer and the barrier layer is increased, and the overflow of electrons is suppressed, and further, a low threshold current, a high differential efficiency, and a high temperature characteristic are achieved.
[0023]
  In one embodiment, in the semiconductor laser device of the first invention, any or all of the barrier layers are in contact with the AlGaAs layer on the surface opposite to the well layer side.
[0024]
  According to this embodiment, when the barrier layer is in contact with the AlGaAs layer, a large barrier is formed between the barrier layer and the AlGaAs layer on the conduction band side. Accordingly, by positioning the AlGaAs layer on the side opposite to the well layer side, it is possible to suppress a part of the electrons overflowing from the well layer to the barrier layer from overflowing further to the AlGaAs layer. Thus, the effect of confining electrons in the well layer is further increased, and the characteristics are further improved.
[0025]
  In one embodiment, in the semiconductor laser device of the first invention, the barrier layer in contact with the AlGaAs layer is located on the outermost side in the active region.
[0026]
  According to this embodiment, the AlGaAs layer in contact with the barrier layer is located at the outermost position in the active region. Therefore, some electrons are prevented from overflowing outside the active region, and the electron confinement effect is further increased.
[0027]
  In one embodiment, in the semiconductor laser device of the first invention, the thickness of the barrier layer in contact with the AlGaAs layer is greater than 4 nm.
[0028]
  According to this embodiment, since the thickness of the barrier layer in contact with the AlGaAs layer is larger than 4 nm, the influence of Al in the AlGaAs layer is greatly suppressed, and the reliability is high even at high temperature and high output. Sex is obtained.
[0029]
  MaIn one embodiment, in the semiconductor laser device of the first invention, a guide layer made of AlGaAs is provided between the active region and the cladding layer.
[0030]
  According to this embodiment, a large barrier is formed between the active region and the AlGaAs guide layer on the conduction band side. Therefore, the overflow of electrons to the guide layer outside the active region is suppressed, and InGa PCompared with the case where the guide layer is used, the threshold current and the characteristic temperature are significantly improved. Furthermore, lattice matching with the GaAs substrate is also achieved.
[0031]
  In one embodiment, in the semiconductor laser device of the first invention, the cladding layer is made of AlGaAs.
[0032]
  According to this embodiment, the overflow of electrons from the barrier layer or the guide layer can be further suppressed. In addition, AlGaAs maintains lattice matching with the GaAs substrate even if group III composition fluctuations occur, so that the entire cladding layer having a thickness of 1 μm or more reliably achieves lattice matching with the GaAs substrate. It can be done.
[0033]
  In one embodiment, in the semiconductor laser device of the first invention, a guide layer made of InGaP or InGaAsP is provided between the active region and the cladding layer, and the cladding layer is made of AlGaInP or InGaP. It is configured.
[0034]
  According to this embodiment, the guide layer is InGaP or InGaAsP, but on the conduction band side, the InGaAsAsP barrier layer in the first invention functions as a barrier between the well layer and the guide layer. become. Therefore, by appropriately selecting the thickness of the barrier layer, electrons are sufficiently retained in the well layer, and good device characteristics can be obtained.
[0035]
  Further, the cladding layer is made of AlGaInP or InGaP. Thus, by using AlGaInP or InGaP, which has a difference Ev with respect to the GaAs substrate, which is larger than the guide layer InGaP or InGaAsP, as the clad layer, the clad layer | ΔEv0 | A large band structure is obtained. Therefore, holes are injected into the well layer without any problem.
[0036]
  Further, Al is not contained in the guide layer outside the active region as well as the well layer and the barrier layer. Therefore, higher reliability can be obtained even at high temperature and high power operation.
[0037]
  In one embodiment, in the semiconductor laser device of the first invention, the value of y representing the composition ratio of P in the group V element of the barrier layer is greater than 0.25.
[0038]
  According to this embodiment, by making | ΔEv0 | of the barrier layer larger than | ΔEv0 | of the well layer, the injected holes are surely confined by the well layer.
[0039]
  In one embodiment, in the semiconductor laser device of the first invention, the value of y representing the composition ratio of P in the group V element of the barrier layer is smaller than 0.6.
[0040]
  According to this embodiment, | ΔEv0 | of the barrier layer can be more reliably reduced. Therefore, holes are more reliably injected from the guide layer into the barrier layer.
[0041]
  In addition, the second invention,
  G a A s On the substrate, at least a lower cladding layer, an active region including a quantum well in which one or more well layers and a barrier layer are stacked, and an upper cladding layer having an oscillation wavelength of 760 are formed. nm Larger and 800 nm In smaller semiconductor laser devices,
  The barrier layer has a larger band gap energy than the well layer. n _1-x G a _x A s _1-y P _y And consisting of
  The lattice constant of the well layer is a 1 On the other hand, the lattice constant of the barrier layer is a 2 If
            0 <x ≦ 1
            0 . 2 <y <0 . 75
            ｜ ( a 2 -A 1) / a 1 | × 100> 0 . 65
  Is established,
  Between the active region and the cladding layer, A l G a A s With a guide layer composed of
It is characterized by that.
[0042]
  According to the above configuration, the barrier layer is made of G. a A s P or I n G a A s P and the composition ratio of the P element is 0 . Greater than 2 and 0 . Since it is smaller than 75, I in the conventional case n G a G compared to P barrier layer a A s E to substrate v Difference | ΔE v0 | Can be set small. Therefore, the efficiency of hole injection from the guide layer to the well layer is greatly improved.
[0043]
  Further, the strain amount of the barrier layer with respect to the well layer is reduced to 0. . It is larger than 65%. But ΔE between the barrier layer and the well layer c Is 0 . 12 e It is set to about V or higher. This 0 . 12 e About V means A l G a A s As a barrier layer in the quantum well structure of semiconductor lasers III Family A l Composition is 0 . 27 A l G a A s ΔE between the barrier layer and the well layer c It corresponds to. Therefore, the overflow of electrons from the well layer is suppressed.
[0044]
  Further, on the conduction band side, the active region and A l G a A s A large barrier is formed between the guide layer. Therefore, the overflow of electrons to the guide layer outside the active region is suppressed, and I n G a Compared with the case where the P guide layer is used, the threshold current and the characteristic temperature are significantly improved. Furthermore, the above G a A s Lattice matching to the substrate is also achieved.
[0045]
  Also,ThirdThe optical disc apparatus according to the present invention is the above first.Or secondThe semiconductor laser device according to the invention is used as a light emitting device.
[0046]
  According to the above configuration, a semiconductor laser device that operates stably with a higher light output than the conventional one is used as a light emitting device of an optical disc device for CD / MD. Therefore, it is possible to read and write data even if the rotational speed of the optical disk is higher than before, and the access time to the optical disk, which has been a problem when writing to CD-R, CD-RW (CDrewritable), etc. Shorter.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0048]
  <First embodiment>
  FIG. 1 is a diagram showing a configuration of the semiconductor laser device of the present embodiment. This embodiment relates to a semiconductor laser device having a quantum well active region of InGaAsP well layer / GaAsP barrier layer and an oscillation wavelength of 780 nm.
[0049]
  In FIG. 1, 21 is an n-type GaAs substrate, 22 is an n-type GaAs buffer layer (layer thickness 0.5 μm), and 23 is an n-type Al._0.5Ga_0.5As lower cladding layer (layer thickness 1.7 μm), 24 is Al_0.35Ga_0.65As lower guide layer (layer thickness 45 nm), 25 is an active region. Here, the active region 25 has a double quantum well (DQW) structure including a barrier layer 26 and a well layer 27. 28 is Al_0.35Ga_0.65As upper guide layer (layer thickness 45nm), 29a is p-type Al_0.5Ga_0.5As upper first cladding layer (layer thickness 0.2 μm), 30 is a p-type GaAs etching stop layer (layer thickness 3 nm), 29b is a ridge stripe-shaped p-type Al_0.5Ga_0.5As upper second cladding layer (layer thickness 1.28 μm), 31 is p-type GaAs protective layer (layer thickness 0.7 μm), 32 is n-type Al_0.7Ga_0.3As first current blocking layer (layer thickness 0.6 μm), 33 is n-type GaAs second current blocking layer (layer thickness 0.7 μm), 34 is p-type GaAs buried protective layer (layer thickness 0.6 μm), 35 is A p-type GaAs cap layer (layer thickness 2 μm), 36 is an n-side electrode, and 37 is a p-side electrode.
[0050]
  The barrier layer 26 is made of GaAs._0.72P_0.28The strain is tensile strain-1%, the layer thicknesses are 26 nm and 26 c are 8 nm, and 26 b is 7 nm. GaAs_0.72P_0.28Eg is calculated to be about 1.77 eV when distortion is not taken into consideration. The effect of tensile strain on Eg is not clear in the vicinity of the composition of the material, and is not considered here. Well layer 27 is made of In._0.162Ga_0.838As_0.671P_0.329Eg is 1.57 eV, lattice-matched with the substrate, and the layer thicknesses of both 27a and 27b are 5 nm. Note that ΔEg between the well layer 27 and the barrier layer 26 is 0.20 eV.
[0051]
  By the way, in a conventional AlGaAs-based semiconductor laser device having a quantum well structure, ΔEg is usually about 0.25 eV, and when ΔEg is about 0.20 eV as in this embodiment, the carrier overflows and the characteristics deteriorate. Be able to.
[0052]
  The InGaAsAs well layer / GaAsP barrier layer semiconductor laser device having the above structure can be manufactured as follows. That is, first, on a GaAs substrate 21 having a (100) plane, a GaAs buffer layer 22, an AlGaAs lower cladding layer 23, an AlGaAs lower guide layer 24, three barrier layers 26 and two well layers 27 are alternately arranged. The active region 25 having the DQW structure, the AlGaAs upper guide layer 28, the AlGaAs first upper cladding layer 29a, the GaAs etching stop layer 30, the AlGaAs upper second cladding layer 29b, and the GaAs protective layer 31 are formed by metal organic vapor phase epitaxy. To grow crystals sequentially. Further, a resist mask whose stripe direction is the (011) direction is formed by a photographic process at a portion where the ridge stripe portion is formed on the GaAs protective layer 31.
[0053]
  Next, only the GaAs protective layer 31 and the AlGaAs upper second cladding layer 29b in portions other than the resist mask are removed by etching to form a ridge stripe portion. Then, the AlGaAs first current blocking layer 32, the GaAs second current blocking layer 33, and the GaAs buried protective layer 34 are sequentially grown on the entire surface including the upper side and both sides of the ridge stripe portion by the metal organic chemical vapor deposition method. At this time, the current blocking layers 32 and 33 and the buried protective layer 34 are formed in a convex shape on the ridge stripe portion, reflecting the shape of the ridge stripe portion.
[0054]
  Next, a resist mask is formed in a region on the GaAs buried protective layer 34 excluding the convex portion. Then, the buried protective layer 34, the second current blocking layer 33, and the first current blocking layer 32 in the convex shape are sequentially removed by etching to expose the top of the ridge stripe portion. Thereafter, a GaAs cap layer 35 is grown on the entire surface by metal organic vapor phase epitaxy. Finally, the n-side electrode 36 is formed on the surface of the substrate 21, and the p-side electrode 37 is formed on the surface of the cap layer 35. As described above, a semiconductor laser device of an InGaAsP well layer / GaAsP barrier layer having a buried ridge structure with a stripe width of 2.5 μm is formed.
[0055]
  For comparison, only the barrier layer 26 in FIG. 1 is replaced with the same In as the barrier layer 5 in the semiconductor laser device of the InGaAsP quantum well structure shown in FIG._0.4Ga_0.6A semiconductor laser device of InGaAsP well layer / InGaP barrier layer with P was formed in the same manner, and the device characteristics were compared by the difference between the GaAsP barrier layer and the InGaP barrier layer. In the case of a comparative semiconductor laser device using an InGaP barrier layer, ΔEg between the well layer and the barrier layer is 0.36 eV to 0.39 eV.
[0056]
  Both semiconductor laser devices were opened with a cavity length of 800 μm, coated with an end face reflection coating, mounted on a stem, and then measured for element characteristics. As a result, the semiconductor laser device of the present embodiment using the GaAsP barrier layer exhibited a threshold current Ith = 25 mA, a differential efficiency ηd = 1.0 W / A, and a temperature characteristic T0 = 140K. In contrast, the comparative semiconductor laser device using the InGaP barrier layer exhibited a threshold current Ith = 38 mA, a differential efficiency ηd = 0.52 W / A, and a temperature characteristic T0 = 108K. As described above, the comparative semiconductor laser device using the InGaP barrier layer cannot obtain good characteristics even though ΔEg between the well layer and the barrier layer is large as described above. On the other hand, in the semiconductor laser device of the present embodiment using the GaAsP barrier layer, although the ΔEg is as small as 0.20 eV, the device characteristics can be remarkably improved as compared with the InGaP barrier layer. Below, we will examine the reason.
[0057]
  (Desk on Ec and Ev)
  The Eg of the semiconductor is the difference between the energy (Ec) of the conduction band and the energy (Ev) of the valence band. However, even if the Eg is the same, Ec and Ev are different depending on the material system and composition. In general, the AlGaAs system has a high Ec and Ev, whereas the InGaAsP system has a low Ec and Ev. At heterointerfaces between different semiconductor layers, the difference between Ec and the difference between Ev (ΔEc, ΔEv) between the two layers affect the behavior of electrons and carriers. Therefore, attention is paid to Ec and Ev with respect to InGaAsP used in the well layer and the barrier layer in the semiconductor laser device of this embodiment and the semiconductor laser device for comparison, and the relationship is examined.
[0058]
  In the following, the magnitudes of Eg, Ec, and Ev of the semiconductor are defined as difference values | ΔEg0 |, | ΔEc0 |, with respect to Eg, Ec, and Ev of GaAs used for the substrate in both semiconductor laser devices. It is expressed by | ΔEv0 |. | ΔEg0 | is | ΔEcO | + | ΔEvO |. Here, the ratio of | ΔEc0 | in | ΔEg0 | is expressed as | ΔEc0 | / | ΔEg0 |.
[0059]
  Then, for InGaP | ΔEc0 | / | ΔEg0 |
      | ΔEc0 | / | ΔEg0 | = 0.18
The numerical value is disclosed in Appl. Phys. Lett. 66, p1785 (1995), and this is used for the examination. On the other hand, it is generally known that | ΔEc0 | / | ΔEg0 | of GaAsP corresponding to the present embodiment is larger than the above InGaP, but the specific numerical value is unknown. Therefore, several values are set as | ΔEc0 | / | ΔEg0 | of GaAsP. Further, for InGaAsP, which is a composition between InGaP and GaAsP, the value between InGaP and GaAsP depends on the composition. Assuming that it changes, let us consider how | ΔEg0 |, | ΔEc0 |, | ΔEv0 | Here, as an example most suitable for the actual GaAsP characteristic, a case where | ΔEc0 | / | ΔEg0 | of GaAsP is 0.60 is shown. For InGaAsP-based Eg itself, the relationship with the composition was estimated based on the experimental results. This is because although several relational expressions with the composition of InGaAsP-based Eg are presented, they are different from each other and are not clear.
[0060]
  In FIG. 4, an equal Eg curve is drawn by connecting (x, y) with the same Eg on a plane having the horizontal axis x as the group III Ga composition and the vertical axis y as the group V P composition. FIG. FIG. 5 depicts an equal Ec curve connecting (x, y) with the same Ec on a plane having the horizontal axis x as the group III Ga composition and the vertical axis y as the group V P composition. FIG. Note that | ΔEc0 | is drawn at equal intervals of 50 meV. Similarly, FIG. 6 shows a case where the horizontal axis x is a group III Ga composition, while the vertical axis y is a group V P composition with the same Ev (x, y) connected. It is the figure which drew the Ev curve. Note that | ΔEv0 | is drawn at equal intervals of 50 meV. In FIG. 7, the horizontal axis x is a group III Ga composition, while the vertical axis y is a group V P composition, and the amount of strain with respect to GaAs is the same (x, y). It is the figure which drew the iso-strain curve (iso-lattice constant curve).
[0061]
  Comparing the equal Eg line, the equal Ec line, and the equal Ev line, when the composition is close to InGaP along the equal Eg line, | ΔEv0 | increases, but | ΔEc0 | slightly decreases, and Eg is the valence band. It can be seen that it spreads to the side. Conversely, when the composition approaches GaAsP, | ΔEv0 | decreases, but | ΔEc0 | increases, and Eg spreads toward the conduction band.
[0062]
  (Comparison between the desktop study diagram and this embodiment, the effects seen from FIGS. 4 to 7)
  4 to 7, the composition (x, y) points of the InGaAsAs well layer 27 and the GaAsP barrier layer 26 in the semiconductor laser device of the present embodiment are indicated by ○ and ●, respectively. When | ΔEc0 | is read from FIG. 5 and | ΔEv0 | is read from FIG. 6, the relationship between the energy bands of the GaAs substrate 21, the InGaAsAs well layer 27 and the GaAsP barrier layer 26 is shown in FIG. Further, an energy band in the vicinity of the active region of the element structure is drawn as shown in FIG. FIG. 2B shows the case of a comparative semiconductor laser device using an InGaP barrier layer.
[0063]
  In FIG. 2, when the semiconductor laser device of the present embodiment is compared with the semiconductor laser device for comparison, first, it is clearly understood that the semiconductor laser of the InGaP barrier layer as shown in FIG. In the apparatus, a very large barrier is formed on the Ev side against holes flowing from the guide layer. It is presumed that the influence of this barrier makes it difficult for holes to be injected into the well layer, causing an increase in threshold current and a decrease in differential efficiency. On the other hand, in the case of a semiconductor laser device having a GaAsP barrier layer, as shown in FIG. 2 (a), there is no barrier on the Ev side, and carriers and electrons are efficiently injected for both electrons and holes. It is estimated that this led to a decrease in threshold current and an increase in differential efficiency.
[0064]
  Secondly, the semiconductor laser device with the GaAsP barrier layer has a smaller Eg than the semiconductor laser device with the InGaAs barrier layer, but | ΔEc |, which is the difference between the Ec of the well layer and the barrier layer, becomes larger. I know that. In this way, by setting the barrier layer to GaAsP, | ΔEc | becomes larger, and therefore, the overflow of electrons is further suppressed, leading to further reduction of threshold current, increase of differential efficiency, and improvement of temperature characteristics. Presumed.
[0065]
  (Determination of effective range of composition and strain)
  FIG. 5 and FIG. 6 are the cases where | ΔEc0 | / | ΔEg0 | of GaAsP is assumed to be 0.60 as described above, and the true curve is unknown. However, since the element characteristics obtained from the semiconductor laser device of this embodiment and the semiconductor laser device for comparison are not significantly different from the estimations shown in FIGS. 5 and 6 as described above, FIG. ~ The tendency of the curve shown in Fig. 7 is judged to roughly represent the actual situation.
[0066]
  Based on this determination, the upper and lower limits of | ΔEc0 | and | ΔEv0 | in which the InGaAsP composition functions effectively as a barrier layer will be described below.
[0067]
  Regarding carrier injection into the well layer, holes are considered to be dominant, and | ΔEv0 | is set not to be unnecessarily large. In addition, regarding the overflow of carriers from the well layer, electrons are considered to be dominant, and | ΔEc0 | is set not to be unnecessarily small. In the InGaAsAs well layer in the semiconductor laser device having an oscillation wavelength of 780 nm, it is estimated that | ΔEc0 | = about 0.03 eV and | ΔEv0 | = about 0.12 eV. However, this value is not exact because it varies depending on the strain amount of the well layer.
[0068]
  First, regarding the minimum value of | ΔEv0 |, ΔEv between the barrier layer and the well layer needs to be at least a positive value. Therefore, | ΔEv0 |> about 0.12 eV, and it can be said from FIG. 6 that a boundary of | ΔEv0 | exists in the vicinity of the P composition of 0.15 to 0.30.
[0069]
  Next, it is necessary to suppress the maximum value of | ΔEv0 | to such an extent that hole injection from the guide layer is not excluded. As the guide layer and the cladding layer, various materials and compositions such as InGaP and AlGaAs that are lattice-matched with the GaAs substrate are used, but at least | ΔEv0 | needs to be smaller than when InGaP having the largest | ΔEv0 | is used. And | ΔEv0 | <about 0.38 eV (the value of | ΔEv0 | at the intersection of the broken line with zero GaAs and the InGaP line in FIG. 6). Therefore, it can be said from FIG. 6 that a boundary of | ΔEv0 | exists in the vicinity where the P composition is 0.60 to 0.80.
[0070]
  Also, the minimum value of | ΔEc0 | needs to be set so that ΔEc between the barrier layer and the well layer is about 0.12 eV or more in order to prevent the overflow of electrons from the well layer. This 0.12 eV corresponds to the case where AlGaAs having a group III Al composition of about 0.27 is used for the barrier layer in the AlGaAs semiconductor laser device. Therefore, | ΔEc0 | of the barrier layer is | ΔEc0 |> about 0.15 eV (about 0.03 eV + 0.12 eV) because | ΔEc0 | of the well layer is about 0.03 eV. As can be seen from FIG. 5 and FIG. 7, the iso-Ec line is almost parallel to the equi-lattice constant line, so that | ΔEc0 | Can do. That is, it can be said that there is a boundary of | ΔEc0 | in the vicinity of the difference in strain amount from the well layer strain amount of −0.65% to −0.85%.
[0071]
  Next, regarding the maximum value of | ΔEc0 |, it is considered that electron injection has little influence unless it is a considerably large barrier, and is not particularly considered.
[0072]
  As described above, according to the result of actually producing several types of barrier layer semiconductor laser devices based on the roughly estimated boundary between the P composition and the strain amount and measuring the characteristics, the P composition is 0.2 or less and 0. If it is set to .75 or more, the device characteristics are greatly deteriorated. Therefore, for the P composition, a range larger than 0.2 and smaller than 0.75 is effective. Furthermore, extremely effective device characteristics can be obtained within a range larger than 0.25 and smaller than 0.6. Further, when the difference in strain amount from the strain amount of the well layer is set to −0.65% or less, the device characteristics are deteriorated. Therefore, a range larger than −0.65% is effective for the difference in strain amount from the well layer strain amount.
[0073]
  Note that the estimated values of | ΔEg0 |, | ΔEc0 |, | ΔEv0 | are not considered because there is no clear data regarding the change in the band structure due to strain, and indicate the true value. Not exclusively. However, the range obtained in the present embodiment is obtained based on the result of actually making a semiconductor laser device with reference to these estimations and studying the characteristics. Therefore, the range is not affected by the truth of the estimated value.
[0074]
  (Advantages of AlGaAs guide layer against electronic overflow)
  On the conduction band side, a large barrier is formed between the GaAsP barrier layers 26a and 26c and the AlGaAs guide layers 24 and 28 by using AlGaAs as a guide layer. Therefore, even if some of the electrons overflow into the barrier layers 26a and 26c, overflow to the guide layers 24 and 28 can be suppressed, and the effect of confining electrons in the well layer 27 is further increased. It is very effective in improving the characteristics. This remarkably appears when the conventional InGaAsP-based semiconductor laser device shown in FIG. 13 is compared with the semiconductor laser device having the comparative InGaP barrier layer. In both cases, the well layer is InGaAsP and the barrier layer is InGaP, which is substantially the same material, whereas the guide layer has the difference that the former is InGaP and the latter is AlGaAs. However, the device characteristics are such that the threshold current is 100 mA for the former and 38 mA for the latter, and the temperature characteristics are so bad that the former cannot oscillate at 80 ° C. and cannot be evaluated. Appears. From the above, the effect of using AlGaAs as the guide layer can be seen.
[0075]
  (High reliability by Al free)
  In the present embodiment, since Al is not included in the well layer 27 and the barrier layer 26 in contact with the well layer 27, high reliability can be obtained even at high temperature and high output. Further, by adding In to the barrier layer 26 to form an InGaAsP barrier layer, higher reliability can be obtained. This is probably because In suppresses the growth of dislocations.
[0076]
  Further, in the present embodiment, the outer sides of the outermost barrier layers 26a and 26c in the active region are the AlGaAs guide layers 24 and 28. Therefore, when the thickness of the GaAsP barrier layer 26 is 4 nm or less, the reliability at high temperature and high output is lowered. This is considered to be an influence of Al of the guide layers 24 and 28. Therefore, by making the layer thickness of the GaAsP barrier layer 26 larger than 4 nm, the influence of Al on the guide layers 24 and 28 can be greatly suppressed, and high reliability can be obtained even at high temperatures and high outputs. .
[0077]
  (Advantages of Ec and Ev due to InGaAsP well layer)
  As can be seen from FIG. 3, in the InGaAsP well layer 27, Eg spreads to the valence band side and becomes | ΔEc0 | <| ΔEv0 | as compared with the GaAs substrate 21. On the contrary, in the GaAsP barrier layer 26, Eg spreads toward the conduction band and becomes | ΔEc0 |> | ΔEv0 |. Therefore, the combination of the InGaAsP well layer 27 and the GaAsP barrier layer 26 is more than | ΔEc | when considering ΔEc and ΔEv between the well layer 27 and the barrier layer 26 as compared with, for example, the case where AlGaAs is used as the well layer. Larger and | ΔEv | can be smaller. That is, according to the present embodiment, it is possible to increase | ΔEc | while keeping | ΔEv | small with a barrier layer having a small Eg. As a result, | ΔEc | between the well layer 27 and the barrier layer 26 is increased to suppress the overflow of electrons, thereby enabling lower threshold current, higher differential efficiency, and higher temperature characteristics.
[0078]
  (Effect of tensile strain barrier layer on unstrained well layer)
  In this embodiment, InGaAsP lattice-matched to the GaAs substrate 21 is used as the well layer 27, but the well layer 27 is also affected by the strain due to the tensile strain of the barrier layers 26 on both sides. Therefore, strain is usually introduced into the well layer. However, in this embodiment, the strain effect can be obtained without introducing strain into the well layer 27, and a low threshold current and high output can be obtained. Is possible.
[0079]
  In addition, the semiconductor laser device in the present embodiment performs TM mode oscillation. It is known that the light emission from the tensile strained layer becomes TM mode with the light hole band contributing to the light emission. Although the lattice constant of the InGaAsAs well layer 27 in the present embodiment is the same as that of the GaAs substrate 21, the tensile strain energy is applied under the influence of the tensile strain of the GaAsP barrier layer 26, and the TM mode is applied. It becomes. Usually, when tensile strain is added to the well layer to form the TM mode, if the barrier layer is also tensile strain, the amount of strain in the entire active region becomes very large and reliability is lowered. However, in the case of the present embodiment, since an unstrained well layer is used, the strain amount of the entire active region can be suppressed, and TM mode capable of achieving both high element characteristics and high reliability. Thus, the semiconductor laser device can be obtained.
[0080]
  As described above, the TM mode is selected in the present embodiment. However, the TE mode may be selected by lowering the tensile strain amount of the barrier layer or compressing the well layer. Is possible.
[0081]
  As described above, in the present embodiment, the active region 25 in the semiconductor laser device has a DQW structure including the barrier layer 26 and the well layer 27, and the barrier layer 26 has a strain of −1% GaAs._0.72P_0.28In, in which the well layer 27 is lattice-matched with the GaAs substrate 21_0.162Ga_0.838As_0.671P_0.329It consists of. Thus, the barrier layer 26 has a P composition larger than 0.2 and smaller than 0.75, and a well layer strain amount (= substrate strain amount) larger than −0.65%. By using GaAsP having a difference in strain amount and combining it with the InGaAsAs well layer 27, | ΔEv0 | of the barrier layer 26, well layer 27, and guide layers 24, 28 can be changed to | ΔEv0 | <of the barrier layer 26. | ΔEv0 | <the magnitude relationship of | ΔEv0 | of the guide layers 24 and 28 can be established, so that holes can be efficiently injected from the guide layers 24 and 28. Furthermore, ΔEc between the barrier layer 26 and the well layer 27 can be set to 0.12 eV or more, and an overflow of electrons from the well layer 27 can be suppressed.
[0082]
  Therefore, although ΔEg between the well layer 27 and the barrier layer 26 is as small as 0.20 eV, the threshold current Ith = 25 mA, the differential efficiency ηd = 1.0 W / A, the temperature characteristic T0 = 140 K, and the InGaP barrier layer In comparison, the device characteristics can be remarkably improved.
[0083]
  At this time, since the thickness of the GaAsP barrier layer 26 is larger than 4 nm, the influence of Al of the AlGaAs guide layers 24 and 28 can be greatly suppressed, and high reliability can be obtained at high temperature and high output. be able to.
[0084]
  Further, by adding In to the GaAsP barrier layer 26 to form an InGaAsP barrier layer, it is possible to suppress the growth of dislocations and to obtain higher reliability.
[0085]
  (Freedom of various configurations)
  In the present embodiment, the InGaAsAs well layer 27 has the same lattice constant as that of the GaAs substrate 21. However, even if the InGaAsAs well layer 27 is strained, the GaAsAs barrier layer 26 is effective and leads to improvement in device characteristics. Further, the number of wells in this embodiment is two, but the number of wells is not limited to this, and the same effect can be obtained with an arbitrary number of wells. In this embodiment, the buried ridge structure is used. However, the present invention is not limited to this, and the same effect can be obtained for all structures such as a ridge structure, an internal stripe structure, and a buried hetero structure. .
[0086]
  In the present embodiment, an n-type substrate is used as the substrate. However, a similar effect can be obtained by using a p-type substrate and replacing the n-type and p-type of each layer. Further, although the wavelength is 780 nm, the present invention is not limited to this, and a similar effect can be obtained if it is a so-called 780 nm band larger than 760 nm and smaller than 800 nm.
[0087]
  <Second Embodiment>
  FIG. 8 is a diagram showing the configuration of the semiconductor laser device according to the present embodiment. The present embodiment relates to a semiconductor laser device having a wavelength of 780 nm having a quantum well active region of an InGaAsAsP compressive strain well layer / InGaAsAs barrier layer.
[0088]
  In FIG. 8, 41 is an n-type GaAs substrate, 42 is an n-type GaAs buffer layer (layer thickness 0.5 .mu.m), 43a is an n-type Al._0.4Ga_0.6As lower second cladding layer (layer thickness: 3.0 μm), 43b is n-type Al_0.5Ga_0.5As lower first cladding layer (layer thickness 0.2 μm), 44 is Al_0.42Ga_0.58As lower guide layer (layer thickness 0.1 μm), 45 is an active region. Here, the active region 45 has a DQW structure including a barrier layer 46 and a well layer 47. 48 is Al._0.42Ga_0.58As upper guide layer (layer thickness 0.1 μm), 49a is p-type Al_0.5Ga_0.5As upper first cladding layer (layer thickness 0.2 μm), 50 is a p-type GaAs etching stop layer (layer thickness 3 nm), 49b is a ridge stripe-shaped p-type Al_0.5Ga_0.5As upper second cladding layer (layer thickness 1.28 μm), 51 is p-type GaAs protective layer (layer thickness 0.7 μm), 52 is n-type Al_0.7Ga_0.3As first current blocking layer (layer thickness 0.6 μm), 53 is n-type GaAs second current blocking layer (layer thickness 0.7 μm), 54 is p-type GaAs buried protective layer (layer thickness 0.6 μm), 55 is A p-type GaAs cap layer (layer thickness 2 μm), 56 is an n-side electrode, and 57 is a p-side electrode.
[0089]
  The barrier layer 46 is made of In._0.09Ga_0.91As_0.41P_0.59Eg is 2.02 eV, strain is tensile strain -1.45%, layer thickness is 10 nm for 46a and 46c, and 5 nm for 46b. The well layer 47 is made of In._0.27Ga_0.73As_0.55P_0.45Eg is 1.55 eV, the strain is 0.35% compressive strain, and the layer thicknesses of both 47a and 47b are 8 nm. Note that ΔEg between the well layer 47 and the barrier layer 46 is 0.47 eV.
[0090]
  Note that the effect of strain on the Eg of the barrier layer 46 and the well layer 47 is not clear even in the vicinity of the composition of the material, and is not considered in this embodiment.
[0091]
  The InGaAsP compression strained well layer / InGaAsAsP barrier layer semiconductor laser device having the above-described structure is formed by forming a buried ridge structure having a stripe width of 2 μm by the same growth and process method as in the first embodiment. Can do. Then, the obtained semiconductor laser device was opened with a cavity length of 800 μm, end face reflection coating was applied, and the device characteristics were measured after mounting on the stem. As a result, the threshold current Ith = 29 mA, the differential efficiency ηd = 0.95 W / A, and the temperature characteristic T0 = 150K. As described above, even in a semiconductor laser device in which compressive strain is introduced into a well layer and an InGaAsP barrier layer is used, good element characteristics can be obtained.
[0092]
  FIG. 9 shows an energy band near the active region in the semiconductor laser device of the present embodiment. Also in the case of this semiconductor laser device, as in the case of the semiconductor laser device in the first embodiment, since the barrier layer 46 is made of InGaAsP having a P composition smaller than 0.6, the barrier layer is made of InGaP. | ΔEv | between the well layer 47 and the barrier layer 46 can be increased while | ΔEc |
[0093]
  As can be seen from FIGS. 5 and 6, the manner of change in the composition of the equal Ec line and the equal Ev line is greatly different in the vicinity of the composition of the barrier layer 46 in this semiconductor laser device, and the barrier can be selected by selecting an appropriate composition. It is possible to independently control | ΔEc0 | and | ΔEv0 | of the layer 46 to some extent. For example, since the equal Ec line is substantially parallel to the equal lattice constant line, it is also possible to change Ev with almost no change in the Ec and strain amount of the barrier layer 46. In the present embodiment, the In composition and the P composition are adjusted so that | ΔEv | between the well layer 47 and the barrier layer 46 is larger than that of the semiconductor laser device of the first embodiment. As a result, the confinement of holes in the well layer 47 can also be improved.
[0094]
  In this embodiment, as can be seen from a comparison between FIG. 9 and FIG. 2B, the barrier of the valence band is set smaller than that of the conventional semiconductor laser using InGaP for the barrier layer. . Therefore, also in this embodiment, the efficiency of carrier injection for both electrons and holes is greatly improved, and the device characteristics are improved. Further, since Al is not contained in the well layer 47 and the barrier layer 46 in contact with the well layer 47, high reliability can be obtained even at high temperature and high output.
[0095]
  In the present embodiment, the InGaAsP barrier layer 46 has a tensile strain of −1.45% because the lattice constant is deviated from the GaAs substrate 41. However, by introducing compressive strain into the well layer 47, the average strain amount of the active region as a whole can be suppressed, and the amount of defects in the crystal compared to the case where the well layer is lattice-matched to the substrate. The reliability can be further improved. Further, by reducing the average strain amount, the critical film thickness of the entire active region is also increased, and the layer thicknesses of the barrier layers 46a and 46b can be set to 10 nm. Also in the present embodiment, the outermost barrier layers 46a and 46c in the active region are the guide layers 44 and 48 made of AlGaAs, but the distance from the well layer 47 to the AlGaAs guide layers 44 and 48 is 10 nm. Therefore, the influence of Al from the guide layers 44 and 48 to the active region can be further reduced, and high reliability can be obtained even at high temperature and high output. In this embodiment, since In is added to the barrier layer 46 to form an InGaAsP layer, higher reliability can be obtained by suppressing the growth of dislocations with In.
[0096]
  In the present embodiment, InGaAsP having a compressive strain of 0.35% is used as the well layer 47, and the effect of strain can be obtained. Therefore, a low threshold current and high output can be achieved. It is known that the polarization mode becomes the TE mode because the heavy hole band contributes to the light emission of the compression strain layer. The polarization mode of the semiconductor laser device in the present embodiment is also the TE mode, and the TE mode semiconductor laser device can be formed by making the well layer 47 compressive strain.
[0097]
  In this embodiment, the active region is an InGaAsAs compressive strain well layer / InGaAsP tensile strain barrier layer. However, the present invention is not limited to this combination. A combination of InGaAsAsP unstrained well layer / InGaAsAsP tensile strain barrier layer or InGaAsAs compressive strain well layer / GaAsP barrier layer is also possible. Further, although the number of wells in this embodiment is two, it is not limited to this, and the same effect can be obtained with an arbitrary number of wells. In this embodiment, the buried ridge structure is used. However, the present invention is not limited to this, and the same effect can be obtained for all structures such as a ridge structure, an internal stripe structure, and a buried hetero structure. it can.
[0098]
  In the present embodiment, an n-type substrate is used as the substrate. However, a similar effect can be obtained by using a p-type substrate and replacing the n-type and p-type of each layer. Further, although the wavelength is 780 nm, the present invention is not limited to this, and a similar effect can be obtained if it is a so-called 780 nm band larger than 760 nm and smaller than 800 nm.
[0099]
  <Third Embodiment>
  FIG. 10 is a diagram showing a configuration in the semiconductor laser device of the present embodiment. The present embodiment relates to a semiconductor laser device having a wavelength of 780 nm having an InGaAsP well layer / GaAsP barrier layer quantum well active region.
[0100]
  In FIG. 10, 61 is an n-type GaAs substrate, 62 is an n-type GaAs buffer layer (layer thickness is 0.5 μm), and 63 is an n-type (Al_0.5Ga_0.5)_0.516In_0.484P lower cladding layer (layer thickness 1.7 μm), 64 is Ga_0.516In_0.484P lower guide layer (layer thickness 50 nm), 65 is an active region. Here, the active region 65 has an SQW structure including a barrier layer 66 and a well layer 67. 68 is Ga._0.516In_0.484P upper guide layer (layer thickness 50 nm), 69a is p-type (Al_0.5Ga_0.5)_0.516In_0.484P upper first cladding layer (layer thickness 0.2 μm), 70 is a p-type GaAs etching stop layer (layer thickness 3 nm), 69b is a ridge stripe p-type (Al)_0.5Ga_0.5)_0.516In_0.484P upper second cladding layer (layer thickness 1.28 μm), 71 is a p-type GaAs protective layer (layer thickness 1.0 μm), 72 is SiN_xA current blocking layer, 73 is an n-side electrode, and 74 is a p-side electrode.
[0101]
  The barrier layer 66 is made of GaAs._0.75P_0.25Eg is 1.73 eV, strain is tensile strain -0.89%, and layer thicknesses of 66a and 66b are both 5 nm. The well layer 67 is made of In._0.27Ga_0.73As_0.55P_0.45Eg is 1.55 eV, the strain is 0.35% compressive strain, and the layer thickness is 8 nm. Note that ΔEg between the well layer 67 and the barrier layer 66 is 0.18 eV. Note that the effect of strain on the Eg of the barrier layer 66 and the well layer 67 is not clear even in the vicinity of the composition of the material, and is not considered in this embodiment.
[0102]
  The InGaAsP well layer / GaAsP barrier layer semiconductor laser device having the above-described configuration is fabricated as follows. That is, first, a ridge stripe portion is formed by the same growth and process technique as in the first embodiment. Then, the entire surface including the upper side and both sides of the ridge stripe portion is covered with SiN._xThe current blocking layer 72 is grown by plasma vapor deposition. At this time, the current blocking layer 72 is formed in a convex shape on the ridge stripe portion, reflecting the shape of the ridge stripe portion.
[0103]
  Next, a resist mask is formed on the current blocking layer 72 in a region excluding the protective layer 71 of the convex portion. Then, the current blocking layer 72 around the protective layer 71 in the convex portion is removed by etching to expose the top of the ridge stripe portion. Finally, the n-side electrode 73 is formed on the surface of the substrate 61, and the p-side electrode 74 is formed on the surfaces of the current blocking layer 72 and the protective layer 71. As described above, an InGaAsP well layer / GaAsP barrier layer semiconductor laser device having a ridge waveguide structure with a stripe width of 3 μm is formed.
[0104]
  Then, the obtained semiconductor laser element was opened with a cavity length of 800 μm, end face reflection coating was applied, and mounted on the stem, and then element characteristics were measured. As a result, the threshold current Ith = 30 mA, the differential efficiency ηd = 0.9 W / A, and the temperature characteristic T0 = 130K. As described above, in a semiconductor laser device using a GaAsP barrier layer having a ridge waveguide structure, although ΔEg is as small as 0.18 eV, good element characteristics can be obtained.
[0105]
  FIG. 11 shows an energy band near the active layer in the semiconductor laser device of the present embodiment. Also in the case of this semiconductor laser device, as in the case of the semiconductor laser device in the first embodiment, the barrier layer 66 is made of GaAsP having a P composition smaller than 0.60. | ΔEv | between the well layer 67 and the barrier layer 66 can be made large while | ΔEc | Therefore, in particular, it is possible to suppress the overflow of electrons, and to obtain good element characteristics such as low threshold current, high differential efficiency, and high temperature characteristics. Even if InGaAsP with In added to the barrier layer is used, if the P composition is smaller than 0.75, | ΔEv | between the well layer and the barrier layer is small as can be seen from FIGS. It is possible to increase | ΔEc | as it is, and good device characteristics can be obtained. In the present embodiment, the In composition and the P composition of the InGaAsAs well layer 67 are increased as compared with the first embodiment, and the increase in | ΔEc | between the well layer 67 and the barrier layer 66 is increased. I am trying.
[0106]
  In the present embodiment, the guide layers 64 and 68 are InGaP, and as can be seen from FIG._0.75P_0.25The barrier layer 66 is a barrier between the well layer 67 and the guide layers 64 and 68. Where GaAs_0.75P_0.25When the thickness of the barrier layer 66 is reduced to 4 nm or less, the threshold current increases, the differential efficiency decreases, and the temperature characteristics decrease. This is because the number of electrons tunneling through the barrier layer 66 increases and the electrons overflow into the guide layers 64 and 68 so that the electrons are not sufficiently accumulated in the well layer 67. Further, when the thickness of the GaAsP barrier layer 66 is increased to 20 nm or more, the electron injection efficiency is lowered, so that the threshold current is increased and the differential efficiency is lowered. From the above, by making the thickness of the barrier layer 66 larger than 4 nm and smaller than 20 nm, electrons can be sufficiently stored in the well layer 67 and good device characteristics can be obtained. It becomes possible.
[0107]
  Further, in the present embodiment, InGaP is used for the guide layers 64 and 68, and AlGaInP is used for the cladding layers 63 and 69. When the cladding layer is AlGaAs, as shown in FIG. 2 (b) in the comparative example in the first embodiment, | ΔEv0 | of the barrier layer of InGaP is larger than that of the cladding layer. Injection into the well layer is hindered. However, in the case of the present embodiment, AlGaInP having a larger | ΔEv0 | than InGaP is used for the cladding layers 63 and 69, so that | ΔEv0 | of the cladding layers 63 and 69 is as shown in FIG. The band structure is larger than that of the guide layers 64 and 68 of InGaP, and holes are injected into the well layer 67 without any problem. Further, in the case of this band structure, Al is not included in the InGaP guide layers 64 and 68 outside the barrier layers 66a and 66b as well as the well layer 67 and the barrier layers 66a and 66b in contact therewith. . Therefore, high reliability can be obtained even at high temperature and high output operation.
[0108]
  The effect of hole injection into the well layer 67 and the effect of high reliability at high temperature and high output can be similarly obtained by using InGaAsP as the guide layer and InGaP as the cladding layer. .
[0109]
  In the present embodiment, since the InGaAsAs well layer 67 has a 0.35% compressive strain, a semiconductor laser device having a polarization mode of TE mode can be obtained.
[0110]
  In the present embodiment, the active region is an InGaAsP compressive strain well layer / GaAsP tensile strain barrier layer, but is not limited to this combination. A combination of InGaAsP unstrained well layer / GaAsP barrier layer, InGaAsAsP unstrained well layer / InGaAsP tensile strain barrier layer, or InGaAsP compressive strain well layer / InGaAsP tensile strain barrier layer is also possible. Further, although the number of wells in this embodiment is one, it is not limited to this and the same effect can be obtained with an arbitrary number of wells. In this embodiment, the ridge waveguide structure is used. However, the present invention is not limited to this, and the same effect can be obtained for all structures such as a buried ridge structure, an internal stripe structure, and a buried hetero structure. be able to.
[0111]
  In the present embodiment, an n-type substrate is used as the substrate. However, a similar effect can be obtained by using a p-type substrate and replacing the n-type and p-type of each layer. Although the wavelength is 780 nm, the present invention is not limited to this, and the same effect can be obtained in a so-called 780 nm band larger than 760 nm and smaller than 800 nm.
[0112]
  <Fourth embodiment>
  The present embodiment relates to an optical disk device using the semiconductor laser device in each of the above embodiments. FIG. 12 is a configuration diagram of the optical disc apparatus according to the present embodiment. This optical disc apparatus writes data on the optical disc 81 and reproduces data written on the optical disc 81. As a light emitting device used at that time, the semiconductor laser according to any one of the above embodiments is used. A device 82 is provided.
[0113]
  Hereinafter, the configuration and operation of the optical disc apparatus will be described. In the present optical disc apparatus, when writing, the signal light emitted from the semiconductor laser device 82 (laser light on which the data signal is superimposed) passes through the collimator lens 83 to become parallel light and passes through the beam splitter 84. Then, after the polarization state is adjusted by the λ / 4 polarizing plate 85, the light is condensed by the laser light irradiation objective lens 86 to irradiate the optical disk 81. In this way, data is written on the optical disc 81 by the laser beam on which the data signal is superimposed.
[0114]
  On the other hand, at the time of reading, the laser beam with which the data signal emitted from the semiconductor laser device 82 is not superimposed follows the same path as in the case of the writing and irradiates the optical disc 81. Then, the laser beam reflected by the surface of the optical disk 81 on which the data is recorded passes through the objective lens 86 for irradiating the laser beam and the λ / 4 polarizing plate 85 and then is reflected by the beam splitter 84 to change the traveling direction by 90 °. Is done. Thereafter, the light is condensed by a reproduction light objective lens 87 and is incident on a signal detection light receiving element 88. In this way, the data signal read from the optical disk 81 is converted into an electric signal in accordance with the intensity of the incident laser beam in the signal detecting light receiving element 88, and is reproduced into the original information signal by the signal light reproducing circuit 89. It is.
[0115]
  In the optical disk device according to the present embodiment, as described above, the semiconductor laser device 82 that operates at a higher light output than before is used. Therefore, data can be read and written even if the rotational speed of the optical disk 81 is increased as compared with the conventional technique. Accordingly, it is possible to provide an optical disc apparatus that can significantly shorten the access time to the optical disc, which has been a problem at the time of writing to CD-R, CD-RW, etc., and realizes a more comfortable operation. It becomes possible.
[0116]
  In the present embodiment, the example in which the semiconductor laser device in each of the above embodiments is applied to a recording / reproducing optical disk device has been described. However, the present invention is not limited to this, and it goes without saying that the present invention can also be applied to an optical disk recording apparatus and an optical disk reproducing apparatus that use a semiconductor laser device having a wavelength of 780 nm band as a light emitting device.
[0117]
  In the first and second embodiments, the active region formed by sandwiching the well layer with the barrier layer is further sandwiched with the AlGaAs guide layer. However, the present invention is limited to this. It is not a thing. For example, it may be an active region including a structure in which a thin AlGaAs layer is provided inside the barrier layer itself.
[0118]
【The invention's effect】
  As apparent from the above, the semiconductor laser device having the oscillation wavelength of 780 nm band according to the first aspect of the invention has a larger band gap energy than the well layer._1-xGa_xAs_1-yP_yConstitutes the barrier layer and 0 <x <1, 0.2 <y <0.75, the Ev difference | ΔEv0 | relative to the GaAs substrate can be set smaller than in the conventional InGaP barrier layer. Therefore, the efficiency of hole injection from the guide layer to the well layer is greatly improved.
[0119]
  Further, when the lattice constant of the well layer is a1, while the lattice constant of the barrier layer is a2, the relationship | (a2−a1) / a1 | × 100> 0.65 is established. The difference ΔEc between the conduction band energy of the barrier layer and the well layer can be set to about 0.12 eV or more. This about 0.12 eV corresponds to ΔEc between the barrier layer and the well layer when AlGaAs having a group III Al composition of about 0.27 is used as the barrier layer in the quantum well structure of the AlGaAs semiconductor laser. . Therefore, it is possible to suppress the overflow of electrons from the well layer.
[0120]
  That is, according to the present invention, the cause of the characteristic failure in the semiconductor laser device using the InGaP barrier layer can be eliminated. Conventionally, GaAsP or InGaAsP, which has been considered to be ineffective due to the small Eg, can be obtained. With regard to the 780 nm band semiconductor laser device used, it is possible to achieve significant improvements in characteristics such as a reduction in threshold current, an improvement in differential efficiency, and an improvement in temperature characteristics.
[0121]
  Further, the barrier layer III G in group elements a The value of x representing the composition ratio of n G a A s I of P barrier layer n Higher reliability can be obtained by suppressing the growth of dislocations by the element.
[0122]
  In the semiconductor laser device of one embodiment, since the strain of the well layer with respect to the GaAs substrate is a compressive strain, even when the lattice constant of the barrier layer is set to a tensile strain smaller than the lattice constant of the GaAs substrate, the semiconductor laser device is active. It is possible to suppress the average distortion amount as the entire region. Therefore, it is possible to improve the reliability by reducing the amount of defects in the crystal, and the critical film thickness of the entire active region is increased, so that the thickness of the barrier layer can be increased. Further, since the well layer has a compressive strain, the polarization mode can be changed to the TE mode.
[0123]
  In addition, the semiconductor laser device of one embodiment is high even at high temperatures and high power because the well layer and the barrier layer do not contain Al elements that react with trace amounts of impurities such as oxygen because they are active substances. Reliability can be obtained.
[0124]
  In the semiconductor laser device of one embodiment, since the well layer is made of InGaAsP, | ΔEc | between the well layer and the barrier layer is made larger than that in the case where AlGaAs is used as the well layer, and | ΔEv | Can be smaller. Therefore, | ΔEc | between the well layer and the barrier layer can be increased to suppress the overflow of electrons, and further lower threshold current, higher differential efficiency, and higher temperature characteristics can be achieved.
[0125]
  Also, in the semiconductor laser device of one embodiment, any or all of the barrier layers are in contact with the AlGaAs layer on the surface opposite to the well layer side, so that the conduction band side is A large barrier can be formed between the AlGaAs layer and the AlGaAs layer. Accordingly, by positioning the AlGaAs layer on the side opposite to the well layer side, it is possible to suppress a part of electrons from overflowing to the AlGaAs layer. That is, the effect of confining electrons in the well layer can be further increased, and the characteristics can be further improved.
[0126]
  Further, in the semiconductor laser device of one embodiment, since the barrier layer in contact with the AlGaAs layer is positioned at the outermost position in the active region, it is possible to prevent a part of electrons from overflowing to the outside of the active region. The electron confinement effect can be increased more effectively.
[0127]
  Further, in the semiconductor laser device of one embodiment, since the thickness of the barrier layer in contact with the AlGaAs layer is larger than 4 nm, the influence of Al in the AlGaAs layer is greatly suppressed, and high temperature and high output are achieved. High reliability can be obtained even at times.
[0128]
  MaIn addition, since the semiconductor laser device according to one embodiment includes the guide layer made of AlGaAs between the active region and the cladding layer, the active region and the AlGaAs guide layer are disposed on the conduction band side. A large barrier can be formed between them. Therefore, it is possible to suppress the electrons from overflowing to the guide layer outside the active region. As a result, the threshold current and the characteristic temperature can be significantly improved as compared with the case where the InGaAsAs guide layer is used. Furthermore, lattice matching with respect to the GaAs substrate can be achieved.
[0129]
  In the semiconductor laser device of one embodiment, since the cladding layer is made of AlGaAs, the overflow of electrons from the barrier layer or the guide layer can be further suppressed. In addition, AlGaAs maintains lattice matching to the GaAs substrate even if group III composition fluctuations occur, so that the entire cladding layer having a thickness of 1 μm or more reliably achieves lattice matching to the GaAs substrate. I can.
[0130]
  The semiconductor laser device of one embodiment has a guide layer made of InGaP or InGaAsP between the active region and the cladding layer. On the conduction band side, the first semiconductor laser device has the first layer. The InGaAsP barrier layer in the invention functions as a barrier between the well layer and the barrier layer. Therefore, by optimally selecting the thickness of the barrier layer, electrons can be sufficiently accumulated in the well layer, and good device characteristics can be obtained.
[0131]
  Further, since AlGaInP or InGaP having a larger | ΔEv0 | than the guide layer InGaP or InGaAsP is used as the clad layer, | ΔEv0 | of the clad layer is made larger than the guide layer so that holes to the well layer are formed. Can be injected without problems.
[0132]
  Further, the well layer and the barrier layer can be made to contain Al even in the guide layer outside the active region, and higher reliability can be obtained at high temperature and high output operation.
[0133]
  In the semiconductor laser device of one embodiment, since the value of y is larger than 0.25, the implantation of the barrier layer by making | ΔEv0 | larger than | ΔEv0 | The formed holes can be surely confined by the well layer.
[0134]
  In the semiconductor laser device of one embodiment, since the value of y is smaller than 0.6, | ΔEv0 | of the barrier layer is more reliably reduced, and holes from the guide layer to the barrier layer are obtained. Can be injected more reliably.
[0135]
  The oscillation wavelength of the second invention is 780. nm The band semiconductor laser device has a larger band gap energy than the well layer. n _1-x G a _x A s _1-y P _y And a barrier layer, and 0 <x ≦ 1,0 . 2 <y <0 . Since the relationship of 75 is established, I in the conventional case n G a G compared to P barrier layer a A s E to substrate v Difference | ΔE v0 | Can be set small. Therefore, the efficiency of hole injection from the guide layer to the well layer is greatly improved.
[0136]
  Further, the lattice constant of the well layer is defined as a 1 On the other hand, the lattice constant of the barrier layer is a 2 Was If ( a 2 -A 1) / a 1 | × 100> 0 . Since the relationship of 65 is established, the difference ΔE in the conduction band energy between the barrier layer and the well layer c To 0 . 12 e It can be set to about V or higher. This 0 . 12 e About V means A l G a A s As a barrier layer in the quantum well structure of semiconductor lasers III Family A l Composition is 0 . 27 A l G a A s ΔE between the barrier layer and the well layer c It corresponds to. Therefore, it is possible to suppress the overflow of electrons from the well layer.
[0137]
  Furthermore, between the active region and the cladding layer, A l G a A s In the conduction band side, the active region and A are provided. l G a A s A large barrier can be formed between the guide layer. Therefore, it is possible to suppress the electrons from overflowing to the guide layer outside the active region. As a result, I n G a Compared with the case where the P guide layer is used, the threshold current and the characteristic temperature can be significantly improved. In addition, G a A s It is also possible to achieve lattice matching with the substrate.
[0138]
  Also,ThirdThe optical disc apparatus according to the first aspect of the present invention operates stably at a higher light output than the prior art.Or secondSince the semiconductor laser device of the invention is used as a light emitting device, data can be read and written even if the rotational speed of the optical disk is higher than that of the conventional one. In particular, the access time to the optical disk, which has been a problem when writing to CD-R, CD-RW, etc., can be remarkably shortened.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a semiconductor laser device according to the present invention.
FIG. 2 is a diagram showing energy bands in the vicinity of an active region in the semiconductor laser device shown in FIG. 1 and a comparative semiconductor laser device.
3 is a diagram showing the relationship of energy bands of a GaAs substrate, an InGaAsP well layer, and a GaAsP barrier layer in FIG. 1. FIG.
FIG. 4 is an iso-Eg diagram of InGaAsP.
FIG. 5 is an isoc diagram of InGaAsP.
FIG. 6 is an iso-Ev diagram of InGaAsP.
FIG. 7 is an isolattic diagram of InGaAsP.
FIG. 8 is a diagram showing a configuration in a semiconductor laser device different from that in FIG. 1;
9 is a diagram showing an energy band in the vicinity of an active region in the semiconductor laser device shown in FIG.
10 is a diagram showing a configuration of a semiconductor laser device different from those in FIGS. 1 and 8. FIG.
11 is a diagram showing an energy band near an active region in the semiconductor laser device shown in FIG.
FIG. 12 is a configuration diagram of an optical disc apparatus according to the present invention.
FIG. 13 is a diagram showing the structure of a conventional InGaAsAsP quantum well semiconductor laser device in which Al is not contained in a well layer / barrier layer.
14 is a diagram showing an energy band gap (Eg) in the vicinity of an active region in the semiconductor laser device shown in FIG.
[Explanation of symbols]
21, 41, 61 ... GaAs substrate,
22, 42, 62 ... GaAs buffer layer,
23 ... AlGaAs lower clad layer,
24, 44 ... AlGaAs lower guide layer,
25, 45, 65 ... active region,
26, 66 ... GaAsP barrier layer,
27, 47, 67 ... InGaAsP well layer, 28, 48 ... AlGaAs upper guide layer,
29a, 49a ... AlGaAs upper first cladding layer,
29b, 49b ... AlGaAs upper second cladding layer,
30, 50, 70 ... GaAs etching stop layer,
31, 51, 71 ... GaAs protective layer,
32, 52 ... AlGaAs first current blocking layer,
33, 53 ... GaAs second current blocking layer,
34, 54 ... GaAs buried protective layer,
35,55 ... GaAs cap layer,
36, 56, 73 ... n-side electrode,
37, 57, 74 ... p-side electrode,
43a ... AlGaAs lower second cladding layer,
43b ... AlGaAs lower first cladding layer,
46: InGaAsP barrier layer,
63 ... AlGaInP lower clad layer,
64 ... GaInP lower guide layer,
68 ... GaInP upper guide layer,
69a ... AlGaInP upper first cladding layer,
69b ... AlGaInP upper second cladding layer,
72 ... SiN_xCurrent blocking layer,
81 ... optical disc,
82 ... Semiconductor laser device,
83 ... collimating lens,
84: Beam splitter,
85 ... λ / 4 polarizing plate,
86 ... Objective lens for laser light irradiation,
87 ... Objective lens for reproduction light,
88. Light receiving element for signal detection,
89 ... Signal light regeneration circuit.

Claims (14)

An active region including a quantum well formed by laminating at least a lower cladding layer, one or a plurality of well layers, and a barrier layer on a GaAs substrate, and an oscillation wavelength in which the upper cladding layer is formed is greater than 760 nm and In a semiconductor laser device smaller than 800 nm,
The barrier layer is made of In _1-x Ga _x As _1-y P _y having a larger band gap energy than the well layer,
When the lattice constant of the well layer is a1, while the lattice constant of the barrier layer is a2,
0 < x <1
0.2 <y <0.75
| (A2−a1) / a1 | × 100> 0.65
A semiconductor laser device characterized in that the relationship is established. The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein the value of (a1-a0) / a0 is a positive value when the lattice constant of the GaAs substrate is a0. In the semiconductor laser device according to claim 1 or 2,
A semiconductor laser device, wherein the well layer does not contain an Al element. The semiconductor laser device according to claim 3,
A semiconductor laser device, wherein the well layer is made of InGaAsP. In the semiconductor laser device according to any one of claims 1 to 4,
Any or all of the barrier layers are in contact with the AlGaAs layer on the surface opposite to the well layer side. The semiconductor laser device according to claim 5,
The semiconductor laser device, wherein the barrier layer in contact with the AlGaAs layer is located at the outermost position in the active region. In the semiconductor laser device according to claim 5 or 6,
A semiconductor laser device, wherein the thickness of the barrier layer in contact with the AlGaAs layer is greater than 4 nm. The semiconductor laser device according to any one of claims 1 to 7,
Between the active region and the cladding layer, a semiconductor laser device characterized by comprising a guide layer formed of A l G a A s. The semiconductor laser device according to any one of claims 1 to 8,
Upper hear Rudd layer semiconductor laser device, characterized in that it consists of AlGaAs. The semiconductor laser device according to any one of claims 1 to 7 ,
Provided with a guide layer formed of I n G a P or I n G a A s P between the active region and the cladding layer,
It said cladding layer is a semiconductor laser device characterized in that it consists of A l G a I n P or I n G a P. In the semiconductor laser device according to any one of claims 1 to 10 ,
The value of the y representing the composition ratio of P in the group V elements in said barrier layer is 0. The semiconductor laser device and greater than 25. In the semiconductor laser device according to any one of claims 1 to 11,
The value of the y representing the composition ratio of P in the group V elements in said barrier layer 0. Sixth semiconductor laser device according to claim smaller Ikoto than. In G a A s substrate, at least a lower cladding layer, an active region comprising one or more well layers and the quantum well barrier layer and is formed by laminating, oscillation wavelength upper cladding layer is formed is 760 In a semiconductor laser device larger than nm and smaller than 800 nm ,
The barrier layer, together constituting a band gap energy than the well layer is greater _{I n 1-x G a x} A s 1-y P y,
When the lattice constant of the well layer is a 1 and the lattice constant of the barrier layer is a 2 ,
0 <x ≦ 1
0. 2 <y <0. 75
| (A 2 -a 1) / a 1 |. × 100> 0 65
Is established,
Between the active region and the cladding layer, a semiconductor laser device according to claim <br/> further comprising a guide layer formed of A l G a A s.   14. An optical disk device, wherein the semiconductor laser device according to claim 1 is used as a light emitting device.

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