Abstract:
To overcome the dilemma on device design in control of waveguide mode experienced in the conventional weak wave-guide-laser and SCH structure laser, realize higher output and lower dispersion of radiation beam, and improve the waveguide mode, on both sides of an active layer, carrier blocking layers for reducing the waveguide function of the active layer are provided, and waveguide layers are provided on both outer sides of the carrier blocking layers, and cladding layers are provided on both outer sides of the waveguide layers, the active layer is lamination of side barrier layers and a quantum well layer sandwiched therebetween, or side barrier layers, and a quantum well layer and a barrier layer sandwiched therebetween, the composition of the quantum well layer is Ga y  In 1-y  As (0.6&lt;y&lt;1.0), and the carrier blocking layers are made of a material having a wider band gap and a lower refractive index than the material of the waveguide layers.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to industrial fields employing high power semiconductor lasers, including, among others, communications, optical disks and other optical recording, laser printers, laser medical applications, and laser machining. More particularly, it relates to a high power semiconductor laser for exciting solid state laser or exciting a harmonic (generation device) that may require a laser beam with low radiation angle and high power. 
     2. Description of the Related Art 
     Higher outputs of semiconductor lasers have been demanded in various fields. One of the factors that impede higher output per single mode in a semiconductor laser is an end face (facet) melting by laser beam, called catastrophic optical damage (COD). To avoid the COD, with a main purpose of reducing the power density of laser by expanding the waveguide mode (near field pattern), weak waveguide lasers having a thin active layer and separate confinement type lasers called large optical cavity (LOC) structure have been studied. 
     In such structures, however, since there is a close correlation between the band gap and refractive index of each mixed crystal system such as AlGaAs compound, carrier confinement and light confinement into a waveguide cannot be controlled independently. 
     In particular, whether in weak waveguiding laser or in LOC structure laser, in order to get a higher output, a thin active layer is needed for expanding a waveguide mode, whereas a thicker active layer is needed to obtain a high gain for laser oscillation in an expanded waveguide mode, and because of such contradiction, actually, the mode expansion in the epitaxial direction by such technique is limited to about 1 μm at most, and its output is limited at about 100 mW for single mode. 
     In the weak waveguide laser having a thin active layer, since the waveguide mode in the epitaxy direction has an inverted-V profile with exponential tails, the radiation density in the active layer where COD may occur is higher for certain entire beam intensity, and it is not only disadvantageous for higher output, but also growth of a relatively thick cladding layer is needed because the waveguide mode draws a deep tail into the cladding layer. 
     Moreover, in both waveguide mode and radiation pattern (far field pattern), there is a large deviation from the ideal Gaussian beam, and the beam focusing characteristics presents a problem in many applications. 
     Studies have been also made into the so-called window structure for making the vicinity of the exit facet where COD may occur transparent to the laser exit beam, and the laser with the structure for not injecting carrier near the facet. These structures are generally complicated in manufacturing process, and are increased in astigmatism, among other problems. 
     It is also attempted to fabricate a single-mode high-power laser by optical feedback among multiple semiconductor lasers, but the device is complicated and other problems are involved. 
     SUMMARY OF THE INVENTION 
     In the light of the recent background that multiple thin layers can be easily formed by MBE (molecular beam epitaxy) method, MOCVD (metal organic chemical vapor deposition) method, and others, it is hence a primary object of the invention to overcome the dilemma on device design in control of waveguide mode experienced in the conventional weak waveguide laser and LOC structure laser, realize higher output and lower divergence of radiation beam, and improve the waveguide mode. 
     The invention has the following means to achieve the object. 
     That is, in a semiconductor laser device, on both sides of an active layer, carrier blocking layers for reducing the waveguiding function of the active layer are provided, and waveguide layers are provided on both outer sides of the carrier blocking layers, and cladding layers are provided on both outer sides of the waveguide layers. The active layer is a lamination of side barrier layers and a quantum well layer sandwiched therebetween, or a lamination of outermost side barrier layers, and at least two quantum well layers and a barrier layer sandwiched between adjacent quantum well layers, the composition of each quantum well layer is Ga y  In 1-y  As (0.6&lt;y&lt;1.0), and the carrier blocking layer is made of a material having a wider band gap and a lower refractive index than the material for the adjacent waveguide layer. 
     Herein, it is difficult to determine the refractive index by directly measuring in a thin layer state. Accordingly, a bulk value is used for the refractive index of the AlGaAs layers. This value is mentioned, for example, in the publication, Journal of Applied Physics (USA), Vol. 60, No. 2, 15 Jul., 1986, P.754-767. 
     As for GaInAs, there is no detailed data about dependence of the refractive index in bulk on the wavelength and composition, but it can be determined, for example, by one of the following methods. That is, (1) a bulk is prepared and measured, (2) it is estimated from the band gap of GaInAs, and (3) the refractive index is determined so as to be fitted by calculation with the radiation pattern (far field pattern) of output light of the semiconductor laser using the quantum well layer of GaInAs. 
     The invention also provides a semiconductor laser device, in which carrier blocking layers are provided on both outer sides of an active layer formed in a vertical direction from the device surface, the active layer is a lamination of side barrier layers and a quantum well layer sandwiched therebetween, or side barrier layers, and a quantum well layer and a barrier layer sandwiched therebetween, waveguide layers are provided on both outer sides of the carrier blocking layer, cladding layers are provided on both outer sides of the waveguide layers, the composition of the quantum well layer is Al x  Ga 1-x  As (0≦x≦0.2) or Ga z  In 1-z  As (0.6&lt;z&lt;1.0), the composition of the carrier blocking layer is Al x  Ga 1-x  As or (Al y  Ga 1-y ) z  In 1-z  P (0≦y&lt;0.3, 0.20≦z≦0.83), and the waveguide layer and cladding layer are made of GaAs or mixed crystal semiconductor of AlAs and GaAs. 
     In this constitution, carrier blocking layers having a sufficient height for confining the carrier into the active layer are provided on both sides of the active layer of the quantum well laser. The composition of the carrier blocking layer is Al x  Ga 1-x  As or (Al y  Ga 1-y ) z  In 1-z  P, where the range of y is desired to be 0≦y&lt;0.3, and z to be 0.20≦z≦0.83, and x can be restricted by Al content of wave guide layer. 
     By employing (Al y  Ga 1-y ) z  In 1-z  P composition, as compared with Al x  Ga 1-x  As having the same block height, the content of Al is less, and elevation of power level for initiating COD is expected. Further, the band gap of Al x  Ga 1-x  As is 2.2 eV (when x=1.0) at maximum, while that of (Al y  Ga 1-y ) 0 .51 In 0 .49 P is 2.4 eV even in the direct band gap region, so that it can cope with the shortening of oscillation wavelength. (Al y  Ga 1-y ) 0 .51 In 0 .49 P is lattice-matched with GaAs, but lattice-mismatching (Al g  Ga 1-y ) z  In 1-z  P), needless to say, is valid as far as z is in a range of 0.20 to 0.83, i.e., in strained super-lattice scheme not causing lattice relaxation. 
     When the thicknesses of the active layer region and carrier blocking layer is set to be small enough compared with the oscillation wavelength, the waveguiding functions of the active layer region and carrier blocking layer can be canceled out. In such conditions, the waveguide layer and cladding layers having a low refractive index on both sides of waveguide layer or a wide waveguiding layers composed of linear or quadratic graded index structure are formed only for the control of light guide. As a result, designing the waveguide mode completely independent of the active layer design parameter, is possible, so that a waveguide mode close to a Gaussian beam of high output and low divergence angle may be obtained. 
     In the conventional structure, in order to have a higher output of the quantum well semiconductor laser by avoiding COD of the facet or to reduce the beam radiation divergence angle, it is necessary to expand the waveguide mode by setting to so-called weak waveguide. In the optical gain in the active layer, however, there is a certain limit as seen in the gain saturation of the quantum well laser, for example. Accordingly, for maintaining the oscillation in the expanded waveguide mode, as a matter of course, further multilayering of the quantum well is required, and it causes contradiction with the weak waveguide structure, and hence it was a dilemma in the designing the laser diode of high output and low radiation beam angle. 
     Owing to the presence of the carrier blocking layer possessing the anti-waveguide function, the number of quantum wells for giving an optical gain necessary for its oscillation can be set independently of the weak waveguide forming. In particular, after canceling the waveguiding function of the active layer region with the anti-waveguiding function of the carrier blocking layer, it is possible to introduce a waveguide mode control structure having a refractive index distribution of stepped, linear or quadratic curve as shown in FIGS. 1A-1C, separately in the waveguide layer. 
     In this carrier blocking layer, by doping about 10 18  /cm 3  of p-type dopant on p-side and n-type dopant on n-side, the effective carrier blocking and the reduction of electric resistance due to the Schottky barrier at the band discontinuities are achieved. 
     More specifically, the cancellation of the waveguiding functions around the active layer region is considered as follows. 
     The normalized frequency V 0  as an index to the waveguiding function of the active layer is defined as the following formula. 
     
         V.sub.0 =π·d.sub.1 /λ·(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5 
    
     In the case of a multi-quantum well having m quantum well layers, the normalization frequency V 0  is defined as the following formula. 
     
         V.sub.0 =m·π·d.sub.1 /λ·(N.sub.1.sup.2 -N.sub.0.sup.2).sup.0.5 
    
     On the other hand, the index V 1  to the anti-waveguiding function of a carrier blocking layer having a low refractive index is defined as the following formula. 
     
         V.sub.1 =π·d.sub.2 /λ·(N.sub.0.sup.2 -N.sub.2.sup.2).sup.0.5, 
    
     where π is the ratio of the circumference of a circle to its diameter, λ is the oscillation wavelength, N 0  is the refractive index of waveguide layer (the maximum value is employed where there is a refractive index distribution in the waveguide layer), d 1  is the thickness of a quantum well layer, N 1  is the refractive index of quantum well layer, d 2  is the thickness of carrier blocking layer, and N 2  is the refractive index of carrier blocking layer. 
     V 0  =2V 1  is a requirement for the cancellation of the waveguide functions of the active layer and carrier blocking layer, and when |2V 1  -V 0  |&lt;V 1 , that is V 0  /3&lt;V 1  &lt;V 0 , the cancellation is nearly realized. 
     When the waveguiding functions of the active layer and carrier blocking layer are canceled, the waveguide mode can be independently controlled by the surrounding waveguide layer and cladding layer. In any structure as shown in Figs. 1A-1C, the cut-off status for higher mode is desired for the sake of single mode oscillation. Concerning the waveguide structure of step index type in FIG. 1A, this waveguide mode can be described by normalized frequency V 2 , and V 2  can be defined in the following formula. 
     
         V.sub.2 =π·d.sub.3 /λ·(N.sub.0.sup.2 -N.sub.3.sup.2).sup.0.5 
    
     where π is the ratio of the circumference of a circle to its diameter, λ is the oscillation wavelength, d 3  is the thickness between both cladding layers, and N 3  is the refractive index of cladding layer. Incidentally, since the waveguide mode is a sine-functional profile in the waveguide core layer, and exponential tails into the cladding layers, the waveguide mode is brought close to the Gaussian function with the increase of the normalization frequency V 2 . In the symmetric slab waveguide, when the normalization frequency V 2  is less than π/2, it is a single-mode waveguide. In the waveguide structure close to symmetry, the probability of excitation of odd-number order mode is almost nil, and therefore by raising the normalization frequency V further up to about π to bring the mode closer to the Gaussian profile, the same effect is obtained without inducing odd-number order mode oscillation. In all embodiments, V 2  is designed to be close to π. Even in the case of V 2  &gt;π, fundamental mode oscillation will be obtained, since higher order modes have additional coupling loss with the substrate and cap layer (actually, in all embodiments with V 2  =1.17π, we observed fundamental mode oscillation). 
     Therefore, fundamental mode operation with near Gaussian profiles will be realized in the range, π/3&lt;V 2  &lt;2π. 
     By calculating the waveguide mode in the multi-layered structure, a waveguide mode close to the Gaussian profile, nearly realized under the condition of V 1  &lt;V 2  /10. 
     Furthermore, by the use of the graded index structure as shown in FIGS. 1B, 1C, the oscillation mode can be further brought closer to the Gaussian profile. 
     The carrier blocking layer must confine the carrier effectively in the active layer. The inventors repeatedly fabricated trial semiconductor lasers and discovered that, when the composition of the carrier blocking layer is Al z+dz  Ga 1-z-dz  As, and the composition of the waveguide layer is Al z  Ga 1-z  As (when z is changing, the minimum value is employed), and the thickness of the carrier blocking layer is d 2  (angstroms), the carrier can be effectively confined in the active layer on condition that 
     
         dz&gt;2.2×10.sup.3 /d.sub.2.sup.2. 
    
     At the same time, the near Gaussian mode profile condition 
     
         V.sub.1 &lt;V.sub.2 /10 
    
     can be expressed by using dz, d 2  as follows 
     
         dz&lt;5.0×10.sup.4 /d.sub.2.sup.2 
    
     Owing to this effect, as compared with the conventional separated confinement hetero-structure (SCH), a cladding layer with a lower Al content is realized. 
     Furthermore, the inventors repeatedly fabricated trial semiconductor lasers having a carrier blocking layer of (Al y  Ga 1-y ) z  In 1-z  P and as a result found that more generally, when the relationship of the energy gap E gs  (eV) of carrier blocking layer, thickness d 2  (angstroms) of carrier blocking layer, and energy gap E gd  of waveguide layer (eV, the minimum value is employed where there is a distribution in energy gap) is as follows 
     
         E.sub.gs -E.sub.gd &gt;2.5×10.sup.3 /d.sub.2.sup.2, 
    
     the carrier can be sufficiently and effectively confined in the active layer. Besides, the near Gaussian mode profile condition 
     
         V.sub.1 &lt;V.sub.2 /10 
    
     is, by using E gs , E gd , d 2 , expressed as follows: 
     
         E.sub.gs E.sub.gd &lt;6.2×10.sup.4 /d.sub.2.sup.2 
    
     Owing to this effect, as compared with the conventional structure of SCH, a cladding layer of lower Al content is realized. 
     The thickness and composition of carrier blocking layers of p-type and n-type are not always required to be equal to each other. In this case, supposing V 1  of the p-type carrier blocking layer to be V 1p , and V 1  of the n-type carrier blocking layer to be V 1n , and expressing as follows 
     
         V.sub.1 =(V.sub.1p +V.sub.1n)/2.0 
    
     the above discussion can be applied directly. 
     The action of the carrier blocking layer having large band gap, low refractive index and an anti-waveguiding function, provided on both sides of the active layer, serves to reduce or cancel the waveguiding function of active layer. Another function is to block the injected carrier, and confine the electrons and holes into the active layer. By p-doping or n-doping in this layer, it is possible to reduce the electric resistance and enhance the carrier confinement performance. 
     In this invention, meanwhile, since the carrier blocking layer effectively blocks the carrier, the Al composition of the Al X  Ga 1-X  As semiconductor, especially used in the wavequide layer, can be set lower and can be set to 0≦x≦0.20 when the composition of quantum layer is GaInAs and it contributes greatly to reduction of electric resistance and thermal resistance (see FIGS. 15 and 16), and the chemical stability is increased at the same time. The fabrication process is facilitated. 
     The invention hence enables to fabricate a semiconductor laser having a proper beam profile and high efficiency at a low radiation beam angle. Besides, it is possible to fabricate a high power semiconductor laser with a simple structure while avoiding COD on the end face. At the same time, since the electric resistance and thermal resistance are low, it is possible to operate at a high current density. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein: 
     FIGS. 1A-1C are schematic sectional views in the epitaxial direction showing the structure of a semiconductor laser of the invention; 
     FIGS. 2A and 2B is a schematic sectional view showing the structure of examples 1-52 of the invention and comparative example 4; 
     FIG. 3 is a schematic sectional view showing the structure of comparative examples 1-3 of the invention; 
     FIG. 4 shows near field patterns of examples 1-3 and comparative example 1 of the invention; 
     FIG. 5 shows near field patterns of examples 4-8 and comparative example 1 of the invention; 
     FIG. 6 shows near field patterns of examples 9-13 and comparative example 1 of the invention; 
     FIG. 7 shows near field patterns of examples 14-17 and comparative example 1 of the invention; 
     FIG. 8 shows diagram expressing the effective range of the carrier blocking layer, with the width of the carrier blocking layer plotted on the axis of abscissa and the aluminum composition difference between the carrier blocking layer and the waveguide layer on the axis of ordinate; 
     FIG. 9 shows near field patterns of examples 18-20 and comparative example 2 of the invention; 
     FIG. 10 shows near field patterns of examples 21-25 and comparative example 2 of the invention; 
     FIG. 11 shows near field patterns of examples 26-30 and comparative example 2 of the invention; 
     FIG. 12 shows near field patterns of examples 31-34 and comparative example 2 of the invention; 
     FIG. 13 shows diagram expressing the effective range of the carrier blocking layer, with the width of the carrier blocking layer plotted on the axis of abscissa and the energy gap difference on the axis of ordinate; 
     FIG. 14 shows near field patterns of example 35 and comparative example 2 of the invention; 
     FIG. 15 shows graphs of the electric resistivity of Al x  Ga 1-X  As semiconductor; 
     FIG. 16 shows a graph of the thermal resistivity of Al x  Ga 1-X  As semiconductor; and 
     FIG. 17 shows the characteristics of the laser power versus injection current of the typical embodiments (example 33 and 51, and comparative example 4) with the optimized device parameters; the stripe width of 50 μm, the cavity length of 900 μm, and the optical coatings with refrectivities of 4% and 96% are applied on the front and rear facets. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now referring to the drawings, preferred embodiments of the invention are described below. 
     Semiconductor lasers of examples 1 to 52 and comparative examples 1 to 4 manufactured by the MOCVD semiconductor thin layer manufacturing apparatus are structured as follows. 
     First the structure common to examples 1 to 52 is described. As shown in FIG. 2, on an n-type substrate 8 composed of GaAs, an n-type buffer layer 10 of 0.5 μm in thickness was formed, and an n-type cladding layer 1, an n-type waveguide layer 2, an n-type carrier blocking layer 3, an active layer 4, a p-type carrier blocking layer 5, a p-type waveguide layer, a p-type waveguide layer 6, and a p-type cladding layer 7 were sequentially formed thereon, and an n-type cap layer 11 was formed as the top layer. 
     In examples 1 to 17, the specific constitution of each layer is as follows. 
     n-type cap layer 11 Thickness: 0.3 μm Composition: GaAs 
     p-type cladding layer 7 Thickness: 1.0 μm Composition: Al 0 .15 Ga 0 .85 As 
     p-type waveguide layer 6 Thickness: 0.80 μm Composition: Al 0 .05 Ga 0 .95 As 
     n-type waveguide layer 2 Thickness: 0.80 μm Composition: Al 0 .05 Ga 0 .95 As 
     n-type cladding layer 1 Thickness: 1.0 μm Composition: Al 0 .15 Ga 0 .85 As 
     n-type buffer layer 10 Thickness: 0.5 μm Composition: GaAs 
     n-type substrate 8 Composition: (100)GaAs 
     In examples 18 to 34 and comparative example 4, the specific constitution of each layer is as follows. 
     n-type cap layer 11 Thickness: 0.3 μm Composition: GaAs 
     p-type cladding layer 7 Thickness: 1.0 μm Composition: Al 0 .32 Ga 0 .58 As 
     p-type waveguide layer 6 Thickness: 0.40 μm Composition: Al 0 .25 Ga 0 .75 As 
     n-type waveguide layer 2 Thickness: 0.40 μm Composition: Al 0 .25 Ga 0 .75 As 
     n-type cladding layer 1 Thickness: 1.0 μm Composition: Al 0 .32 Ga 0 .68 As 
     n-type buffer layer 10 Thickness: 0.5 μm Composition: GaAs 
     n-type substrate Composition: (100)GaAs 
     In example 35, the specific constitution of each layer is as follows. 
     n-type cap layer 11 Thickness: 0.3 μm Composition: GaAs 
     p-type cladding layer 7 Thickness: 1.0 μm Composition: Al 0 .57 Ga 0 .43 As 
     p-type waveguide layer 6 Thickness: 0.40 μm Composition: Al 0 .50 Ga 0 .50 As 
     n-type waveguide layer 2 Thickness: 0.40 μm Composition: Al 0 .50 Ga 0 .50 As 
     n-type cladding layer 1 Thickness: 1.0 μm Composition: Al 0 .57 Ga 0 .43 As 
     n-type buffer layer 10 Thickness: 0.5 μm Composition: GaAs 
     n-type substrate 8 Composition: (100)GaAs 
     The structure of comparative examples 1 and 2 is shown in FIG. 3. On an n-type substrate 8 composed of GaAs, an n-type buffer layer 10 of 0.5 μm in thickness was formed, and an n-type cladding layer 1, an active layer 4, and a p-type cladding layer 7 were sequentially formed thereon, and an n-type cap layer 11 was formed as the top layer. 
     In comparative example 1, the specific constitution of each layer is as follows. 
     n-type cap layer 11 Thickness: 0.3 μm Composition: GaAs 
     p-type cladding layer 7 Thickness: 1.5 μm Composition: Al 0 .22 Ga 0 .78 As 
     n-type cladding layer 1 Thickness: 1.5 μm Composition: Al 0 .22 Ga 0 .78 As 
     n-type buffer layer 10 Thickness: 0.5 μm Composition: GaAs 
     n-type substrate 8 Composition: (100)GaAs 
     In comparative example 2, the specific constitution of each layer is as follows. 
     n-type cap layer 11 Thickness: 0.3 μm Composition: GaAs 
     p-type cladding layer 7 Thickness: 1.5 μm Composition: Al 0 .65 Ga 0 .35 As 
     n-type cladding layer 1 Thickness: 1.5 μm Composition: Al 0 .65 Ga 0 .35 As 
     n-type buffer layer 10 Thickness: 0.5 μm Composition: GaAs 
     n-type substrate 8 Composition: (100)GaAs 
     In examples 1 to 35, the active layer 4 is formed in a region enclosed by the p-type carrier blocking layer 5 and n-type carrier blocking layer 3, with four quantum well layers 13 isolated by three barrier layers 14, between side barrier layers 12 provided at inner wall side of the carrier blocking layers 5, 3. In the comparative examples, the active layer 4 is formed in a region enclosed by side barriers 12, with four quantum well layers 13 isolated by three barrier layers 14. The specific constitution of the p-type carrier blocking layer 5, n-type carrier blocking layer 3, and active layer 4 differs in each example and comparative example, and is explained by referring to Tables 1-13. 
     
                       TABLE 1______________________________________Layer          Example 1 Example 2 Example 3______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          80        200       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.1   x = 0.1   x = 0.1Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          80        200       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.1   x = 0.1   x = 0.1______________________________________ 
    
     
                       TABLE 2______________________________________Layer          Example 4 Example 5 Example 6______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          80        150       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.2   x = 0.2   x = 0.2Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          80        150       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.2   x = 0.2   x = 0.2______________________________________ 
    
     
                       TABLE 3______________________________________Layer          Example 7 Example 8 Example 9______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          500       750       50Composition: Al.sub.x Ga.sub.1-x As          x = 0.2   x = 0.2   x = 0.3Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          500       750       50Composition: Al.sub.x Ga.sub.1-x As          x = 0.2   x = 0.2   x = 0.3______________________________________ 
    
     
                       TABLE 4______________________________________Layer          Example 10                    Example 11                              Example 12______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          100       200       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.3   x = 0.3   x = 0.3Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          100       200       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.3   x = 0.3   x = 0.3______________________________________ 
    
     
                       TABLE 5______________________________________Layer          Example 13                    Example 14                              Example 15______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          600       50        100Composition: Al.sub.x Ga.sub.1-x As          x = 0.3   x = 0.4   x = 0.4Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          600       50        100Composition: Al.sub.x Ga.sub.1-x As          x = 0.3   x = 0.4   x = 0.4______________________________________ 
    
     
                       TABLE 6______________________________________                              ComparativeLayer          Example 16                    Example 17                              Example 1______________________________________P-type carrier blocking          yes       yes       nolayer 5 (yes/no)Thickness (angstroms)          250       600       --Composition: Al.sub.x Ga.sub.1-x As          x = 0.4   x = 0.4   --Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05N-type carrier blocking          yes       yes       nolayer 3 (yes/no)Thickness (angstroms)          250       600       --Composition: Al.sub.x Ga.sub.1-x As          x = 0.4   x = 0.4   --______________________________________ 
    
     
                       TABLE 7______________________________________Layer          Example 18                    Example 19                              Example 20______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          80        200       500Composition:   y = 0.0   y = 0.0   y = 0.0(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 PSide barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness(angstroms)          80        200       500Composition:   y = 0.0   y = 0.0   y = 0.0(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P______________________________________ 
    
     
                       TABLE 8______________________________________Layer          Example 21                    Example 22                              Example 23______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          80        150       300Composition:   y = 0.04  y = 0.04  y = 0.04(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 PSide barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          80        150       300Composition:   y = 0.04  y = 0.04  y = 0.04(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P______________________________________ 
    
     
                       TABLE 9______________________________________Layer          Example 24                    Example 25                              Example 26______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          500       750       50Composition:   y = 0.04  y = 0.04  y = 0.08(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 PSide barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          500       750       50Composition:   y = 0.04  y = 0.04  y = 0.08(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P______________________________________ 
    
     
                       TABLE 10______________________________________Layer          Example 27                    Example 28                              Example 29______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          100       200       300Composition:   y = 0.08  y = 0.08  y = 0.08(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 PSide barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          100       200       300Composition:   y = 0.08  y = 0.08  y = 0.08(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P______________________________________ 
    
     
                       TABLE 11______________________________________Layer          Example 30                    Example 31                              Example 32______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          600       50        100Composition:   y = 0.08  y = 0.12  y = 0.12(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 PSide barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          600       50        100Composition:   y = 0.08  y = 0.12  y = 0.12(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P______________________________________ 
    
     
                       TABLE 12______________________________________Layer          Example 33                    Example 34                              Example 35______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          250       600       200Composition:   y = 0.12  y = 0.12  y = 0.25(Al.sub.y Ga.sub.1-y).sub.0.51 IN.sub.0.49 PSlide barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.50Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0.20Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.50N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          250       600       200Composition:   y = 0.12  y = 0.12  y = 0.25(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P______________________________________ 
    
     
                       TABLE 13______________________________________             Comperative ComparativeLayer             Example 2   Example 4______________________________________P-type carrier blocking             no          yeslayer 5 (yes/no)Thickness (angstroms)             --          250Composition:      --          Al.sub.0.5 Ga.sub.0.5 As(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P-             --          Al.sub.0.5 Ga.sub.0.5 AsSide barrier layer 12             yes         yesThickness (angstroms)             150         500Composition: Al.sub.x Ga.sub.1-x As             x = 0.25    x = 0.25Quantum well layer 13             yes         yesQuantity of layer 4           4Thickness (angstroms)             50          50Composition: Al.sub.x Ga.sub.1-x As             x = 0       x = 0Barrier layer 14  yes         yesThickness (angstroms)             50          50Composition: Al.sub.x Ga.sub.1-x As             x = 0.25    x = 0.25N-type carrier blocking             no          yeslayer 3 (yes/no)Thickness (angstroms)             --          250Composition:      --          Al.sub.0.5 Ga.sub.0.5 As(Al.sub.y Ga.sub.1-y).sub.0.51 In.sub.0.49 P______________________________________ 
    
     FIG. 2 shows an epitaxial growth profile of examples 1-52 and comparative example 4. FIG. 3 shows an epitaxial growth profile of comparative examples 1-3. FIG. 4 shows near field patterns of examples 1-3 and comparative example 1; FIG. 5 shows near field patterns of examples 4 to 8 and comparative example 1; FIG. 6 shows near field patterns of examples 9-13 and comparative example 1; FIG. 7 shows near field patterns of example 14-17 and comparative example 1, FIG. 9 shows near field patterns of examples 18 to 20 and comparative example 2, FIG. 10 shows near field patterns of examples 21-25 and comparative example 2; FIG. 11 shows near field patterns of example 26-30 and comparative example 2, FIG. 12 shows near field patterns of examples 31 to 34 and comparative example 2; and FIG. 14 shows near field patterns of example 35 and comparative example 2. FIG. 8 expresses the effective range of carrier blocking layer, with the width of the carrier blocking layer plotted on the axis of abscissa, and the aluminum composition difference between the carrier blocking layer and the waveguide layer (the aluminum composition of carrier blocking layer minus the aluminum composition of waveguide layer) on the axis of ordinate in case the carrier blocking layer and the waveguide layer are formed of mixed crystal semiconductor of GaAs and AlAs. FIG. 13 expresses the effective range of carrier blocking layer, with the width of the carrier blocking layer plotted on the axis of abscissa, and the energy gap difference between the carrier blocking layer and the waveguide layer on the axis of ordinate. In FIGS. 8 and 13, circles indicate examples, and numerals refer to example numbers. 
     In the range above the upper right curve in FIG. 8 and FIG. 13, the anti-waveguiding function of the carrier blocking layer is too strong, and it has a bad effect on the waveguide mode. More specifically, a dent is formed in the waveguide mode near the active layer, and the light confinement rate is lowered, while the oscillation threshold current increases. At the same time, the waveguide mode is largely deviated from the Gaussian profile, and an aberration occurs on the radiation pattern. Accordingly, V 1  &lt;V 2  /10 is desired. In the range below the lower left curve, confinement of carriers is insufficient, and the temperature characteristic of the threshold current is worsened. An effective range is between two solid curves. Specifically, the condition 
     
         2.5×10.sup.3 /d.sub.2.sup.2 &lt;Egs-Egd&lt;6.2×10.sup.4 /d.sub.2.sup.2 
    
     is established. 
     And in the range where 
     
         V.sub.0 /3&lt;V.sub.1 &lt;V.sub.0 
    
     is satisfied, the waveguiding function of the active layer is optimally corrected by the carrier blocking layer, and the most preferable waveguide mode is achieved. As clear from FIGS. 4 to 12 and FIG. 14, the weak waveguide semiconductor lasers of comparative examples 1 and 2 show characteristic profiles pointed at the center, having exponential tails on both sides, whereas examples 1 to 35 show profiles close to the bell-shaped Gaussian beam. Accordingly, when using the semiconductor lasers of the examples, even in the same mode expanse as in the prior art, the beam intensity is low in the active layer 4 (mode center) where optical damage may occur, and as a result, as shown in Tables 14 and 15, together with the decrease of Al composition, the optical damage power level could be extremely raised. 
     That is, in examples 18 to 35, as compared with comparative examples 1, 2, decrease of radiation angle and a notable improvement of optical damage level are recognized. In Tables 4-13, the oscillation wavelength of laser is about 810 nm to 690 nm. The optical damage level is an optical output per facet. 
     In examples 1-17, the composition of the quantum well layer is Ga y  In 1-y  As (y=0.8) and the oscillation wavelength are about 980 nm, but the value of y is not limited to this, and even in a range of 0.6&lt;y&lt;1.0, the same effects of the invention as described above are obtained by changing the width of the quantum well layer and the composition of the waveguide layer and cladding layer. In this case, the composition of the waveguide layer and cladding layer is sufficient at x=0.2 at maximum in the case of a mixed crystal semiconductor (Al x  Ga 1-x  As) of GaAs and AlAs, and as judged from FIGS. 15, 16, the electric resistance and thermal resistance can be lowered substantially. 
     As the technology common to the examples, Se was doped at 1×10 18  /cm 3  in density as n-type dopant, and Zn was doped at the same density as p-type dopant. Stripe was formed by Zn diffusion from the surface through a SiO 2  mask, trial diode chips with gain guided structure were fabricated by cleaving, and the oscillation characteristic was measured in pulse mode after die bonding on LD mount. The characteristics of chip having a stripe width of 2.5 μm and a cavity length of 300 μm are shown in Tables 14 and 15, where optical coating is not applied on both facet. 
     In the examples 18-35 with (Al y  Ga 1-y ) z  In 1-z  P carrier block layer (0≦y&lt;0.3 and 0.20≦z≦0.83), the composition of quantum well layer is Al x  Ga 1-x  As (0≦x≦0.2), but this is not limited. The active layer may be the strained quantum well of Ga z  In 1-z  As (0.6&lt;z&lt;1.0). 
     
                       TABLE 14______________________________________                              Optical   Normalized Radiation angle damageLD type frequency V2              (vertical epitaxial direction)                              level (mW)______________________________________Example 1   1.1 π   26°      120Example 2   1.1 π   26°      120Example 3   1.1 π   25°      120Example 4   1.1 π   26°      120Example 5   1.1 π   26°      120Example 6   1.1 π   25°      130Example 7   1.1 π   24°      130Example 8   1.1 π   22°      150Example 9   1.1 π   26°      120Example 10   1.1 π   26°      120Example 11   1.1 π   25°      130Example 12   1.1 π   24°      130Example 13   1.1 π   22°      160Example 14   1.1 π   26°      120Example 15   1.1 π   25°      130Example 16   1.1 π   24°      140Example 17   1.1 π   21°      180Comparative   0.09 π  33°      80Example 1______________________________________ 
    
     
                       TABLE 15______________________________________   Normalized             Radiation angle Optical damageLD type frequency (vertical epitaxial direction)                             level (mW)______________________________________Example 18   1.1 π  29°      150Example 19   1.1 π  27°      160Example 20   1.1 π  24°      180Example 21   1.1 π  29°      150Example 22   1.1 π  28°      160Example 23   1.1 π  25°      170Example 24   1.1 π  23°      170Example 25   1.1 π  21°      170Example 26   1.1 π  29°      150Example 27   1.1 π  28°      160Example 28   1.1 π  26°      170Example 29   1.1 π  25°      180Example 30   1.1 π  21°      180Example 31   1.1 π  29°      130Example 32   1.1 π  28°      150Example 33   1.1 π  25°      180Example 34   1.1 π  21°      180Example 35   1.1 π  28°      100Comparative   0.1 π  35°      90Example 2______________________________________ 
    
     In the following are described embodiments 36-52 in which the Al contents of the waveguide layer, barrier layer, and side barrier layer in the embodiments 1-17 are changed to 0. 
     By the following reasons, the Al content of these layers are changed to 0: 
     1) a burying process which will be necessary for more sophisticated structure, like index guide structure, DFB (distributed-feed back, and so on) is facilitated, because the regrowing interface is made to be Al-free. 
     2) the thermal and electrical resistances are optimum in the Al content x of 0. 
     In examples 36 to 52, the structures thereof are the same as that in FIG. 2 and the specific constitution of each layer is as follows. 
     3) from the practical crystal growth standpoint to obtain better crystal quality. 
     n-type cap layer 11 Thickness: 0.3 μm Composition: GaAs 
     p-type cladding layer 7 Thickness: 1.0 μm Composition: Al 0 .01 Ga 0 .90 As 
     p-type waveguide layer 6 Thickness: 0.80 μm Composition: GaAs 
     n-type waveguide layer 2 Thickness: 0.80 μm Composition: GaAs 
     n-type cladding layer 1 Thickness: 1.0 μm Composition: Al 0 .10 Ga 0 .90 As 
     n-type buffer layer 10 Thickness: 0.5 μm Composition: GaAs 
     n-type substrate 8 Composition: (100)GaAs 
     In the comparative example 3, the structure thereof is the same as that in FIG. 3 and the specific constitution of each layer is as follows. 
     n-type cap layer 11 Thickness: 0.3 μm Composition: GaAs 
     p-type cladding layer 7 Thickness: 1.5 μm Composition: Al 0 .17 Ga 0 .83 As 
     n-type cladding layer 1 Thickness: 1.5 μm Composition: A1 0 .17 Ga 0 .83 As 
     n-type buffer layer 10 Thickness: 0.5 μm Composition: GaAs 
     n-type substrate 8 Composition: (100)GaAs.pa 
     Besides, the embodiment of comparative example 3 does not have enough temperature stability for the continuous operation. 
     
                       TABLE 16______________________________________Layer          Example 36                    Example 37                              Example 38______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          80        200       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Ga.sub.x In.sub.1-x As          x = 0     x = 0     x = 0N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          80        200       500Composition: Al.sub.x Ga.sub.1-x As          x = 0.05  x = 0.05  x = 0.05______________________________________ 
    
     
                       TABLE 17______________________________________Layer          Example 39                    Example 40                              Example 41______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          80        150       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.15  x = 0.15  x = 0.15Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          80        150       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.15  x = 0.15  x = 0.15______________________________________ 
    
     
                       TABLE 18______________________________________Layer          Example 42                    Example 43                              Example 44______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          500       750       50Composition: Al.sub.x Ga.sub.1-x As          x = 0.15  x = 0.15  x = 0.25Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          500       750       50Composition: Al.sub.x Ga.sub.1-x As          x = 0.15  x = 0.15  x = 0.25______________________________________ 
    
     
                       TABLE 19______________________________________Layer          Example 45                    Example 46                              Example 47______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          100       200       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          100       200       300Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.25  x = 0.25______________________________________ 
    
     
                       TABLE 20______________________________________Layer          Example 48                    Example 49                              Example 50______________________________________P-type carrier blocking          yes       yes       yeslayer 5 (yes/no)Thickness (angstroms)          600       50        100Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.35  x = 0.35Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0N-type carrier blocking          yes       yes       yeslayer 3 (yes/no)Thickness (angstroms)          600       50        100Composition: Al.sub.x Ga.sub.1-x As          x = 0.25  x = 0.35  x = 0.35______________________________________ 
    
     
                       TABLE 21______________________________________                              ComparativeLayer          Example 51                    Example 52                              Example 3______________________________________P-type carrier blocking          yes       yes       nolayer 5 (yes/no)Thickness (angstroms)          250       600       --Composition: Al.sub.x Ga.sub.1-x As          x = 0.35  x = 0.35  --Side barrier layer 12          yes       yes       yesThickness (angstroms)          500       500       500Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0Quantum well layer 13          yes       yes       yesQuantity of layer          4         4         4Thickness (angstroms)          80        80        80Composition: Ga.sub.y In.sub.1-y As          y = 0.8   y = 0.8   y = 0.8Barrier layer 14          yes       yes       yesThickness (angstroms)          50        50        50Composition: Al.sub.x Ga.sub.1-x As          x = 0     x = 0     x = 0N-type carrier blocking          yes       yes       nolayer 3 (yes/no)Thickness (angstroms)          250       600       --Composition: Al.sub.x Ga.sub.1-x As          x = 0.35  x = 0.35  --______________________________________ 
    
     
                       TABLE 22______________________________________                              Optical   Normalized Radiation angle damageLD type frequency V2              (vertical epitaxial direction)                              level (mW)______________________________________Example 36   1.1 π   26°      not measuredExample 37   1.1 π   26°      not measuredExample 38   1.1 π   25°      not measuredExample 39   1.1 π   26°      not measuredExample 40   1.1 π   26°      180Example 41   1.1 π   25°      200Example 42   1.1 π   24°      200Example 43   1.1 π   22°      230Example 44   1.1 π   26°      180Example 45   1.1 π   26°      180Example 46   1.1 π   25°      200Example 47   1.1 π   24°      200Example 48   1.1 π   22°      220Example 49   1.1 π   26°      180Example 50   1.1 π   25°      200Example 51   1.1 π   24°      210Example 52   1.1 π   21°      270Comparative   0.09 π  33°      120Example 3Comparative   1.1 π   25°      180Example 4______________________________________ 
    
     Examples 36 to 52 correspond to examples 1 to 17, respectively, and comparative example 3 corresponds to comparative example 1. The deviation of radiation angle between the corresponding ones is less than 1%, and the waveguide mode profiles can be regarded as same. The positioning in FIG. 8 is also same with each corresponding one. The improvement of COD level can be seen in the Tables 14 and 22. 
     FIG. 17 shows the characteristics of the laser power versus injection current of the typical embodiments (example 33 and 51, and comparative example 4) with the device parameters optimized for continuous oscillation mode. For these devices, the stripwidths are 50 μm, the cavity lengths are 900 μm, and the optical coatings with the reflectivities of 4% and 96% were applied on the front and rear facets. 
     Comparative example 4 has the same epitaxy structure with example 33, but the (Al 0 .12 Ga 0 .88) 0 .51 In 0 .49 P carrier block layers are replaced by Al 0 .5 Ga 0 .5 As carrier block layers with the same thickness. 
     The output power levels of the these embodiments are higher than the values reported for the conventional broad-area laser diode with the same stripe width. Also, example 33 (shown in Table 12) and example 51 (shown in Table 21) were proved to be superior to the comparative example 4 with the composition of the AlGaAs to in the carrier block layer and of the GaAs in the quantum well layer (shown in Table 13). 
     In particularly, the maximum laser power is about 2 W for comparative Example 4 as compared to about 2.6 W for Example 33 and about 2.8 W for Example 51. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and the range of equivalency of the claims are therefore intended to be embraced therein.