A semiconductor optical device and a fabricating method therefor

Abstract: A semiconductor optical element includes a semiconductor substrate or a semiconductor layer formed on a semiconductor substrate; a plurality of stripe-shaped grooves each having a rectangular cross-section whose width is sufficiently narrow to occur a quantum effect, formed on the semiconductor substrate or the semiconductor layer in parallel with each other at an interval sufficiently narrow to occur a quantum effect or a plurality of rectangular-shaped grooves having a width and a length sufficiently narrow to occur a quantum effect, formed on the semiconductor substrate or the semiconductor layer in a checkered arrangement; and a structure in which a quantum well layer whose thickness is less than the depth of the groove and sufficiently thin to occur a quantum effect and a barrier layer whose thickness is larger than the depth of the groove are alternatively laminated, which structure is provided on the bottom surfaces of the grooves and regions between the adjacent grooves. As a result, an active region comprising a plurality of quantum wires or quantum boxes can be obtained by a simple production process. In addition, this quantum wire or quantum box structure can be employed for an active region of a ridge type semiconductor laser, an inner stripe type semiconductor laser or the like.

Description: FIELD OF THE INVENTION The present invention relates to a semiconductor optical element and a manufacturing method therefor and, more particularly, to a semiconductor optical element including a plurality of quantum wires or quantum boxes in its active region and a method for easily fabricating the same. BACKGROUND OF THE INVENTION Figure 2 is a cross-sectional view showing a structure of a quantum wire semiconductor laser device disclosed in a paper by E.Kapon, Applied Physics Letter 55(26), 25th December 1989, pp.2715 to 2717. The device of figure 2 includes an n⁺ type GaAs substrate 1 patterned with a V-shaped stripe groove An n type Al y Ga 1-y As cladding layer 2, an Al x Ga 1-x AS first SCH (Separate Confinement Heterostructure) layer 3, a GaAs quantum well layer 4, an Al x Ga 1-x AS second SCH layer 5, a p type Al y Ga 1-y As cladding layer 6, and a p⁺ type GaAs contact layer 7 are successively laminated on the substrate 1 keeping the configuration of the V-shaped stripe groove. A p side electrode 8 is disposed on the contact layer 7 and an n side electrode (not shown here) is disposed on the entire rear surface of the substrate 1. A high resistance region 22 is formed in the p type Al y Ga 1-y As cladding layer 6 and the p⁺ type GaAs contact layer 7 by proton implantation A description is given of the operation. When a current equal to the threshold current or more is injected in the forward direction to the pn junction of the quantum wire semiconductor laser shown in figure 2, laser oscillation occurs in the well layer 4 and then a laser light is emitted. While an ordinary semiconductor laser has an active region of approximately 0.05 to 0.2 micron thickness, a quantum well laser generally has a quantum well layer of approximately 300 angstroms thickness or less. In such quite thin layer, a quantum effect occurs so that electrons are localized in the film thickness direction. As a result, a higher gain is obtained in the quantum well laser than in the ordinary semiconductor laser and effects of reductions in the threshold current and the operation current as improvements in laser characteristics are expected. The quantum wire semiconductor laser is obtained by that quantization is also realized in the horizontal direction in addition to the layer thickness direction that is effected in the quantum well laser. This quantum wire semiconductor laser can present more eminent effect of quantization. In the quantum wire semiconductor laser device shown in figure 2, a potential barrier is also formed in the horizontal direction by the epitaxial growth layers on the V-shaped groove. Electrons and holes are confined in the potential barrier and then quantized. In addition, when the length of the quantum wire stripe is approximately 500 angstroms or less, a so-called quantum box in which electrons and holes are confined three-dimensionally is obtained, so that the quantum effect is more eminent. In the device of figure 2, the width W z of the quantum wire in the horizontal direction largely depends on the configuration of the V-shaped groove and the rate of the epitaxial growth of the epitaxial growth layers. This makes it quite difficult to control the width W z at high precision. Further, the maximum output power of a semiconductor laser is generally limited to a level at which a catastrophic optical damage (hereinafter referred to as COD) of the facet occurs. In order to heighten the COD level to enhance the maximum output power, it is required to increase the cross-sectional area of the light emitting region. However, in the structure of figure 2, it is impossible to provide two or more quantum wires in the active region 1, making it impossible to obtain a high output power. Figure 3(a) is a cross-sectional view showing a semiconductor laser device utilizing a two-dimensional multi quantum well structure, disclosed in Japanese Patent Laid-open Application No. 63-29989. The device of figure 3(a) has a p type GaAs substrate 31. A p type Al 0.3 Ga 0.7 As cladding layer 32 is disposed on the substrate 31. A two-dimensional multi-quantum well active layer 37 having stripe configuration, connecting the facets constituting a resonator, is disposed on a center part of the cladding layer 32 in the width direction of the laser device. A silicon dioxide (SiO₂) insulating film 38 is disposed on the cladding layer 32 and the side walls of the active layer 37. An n type Al 0.3 Ga 0.7 As cladding layer 39 is disposed on the insulating film 38 and the active layer 37. An n type GaAs contact layer 40 is disposed on the cladding layer 39. A p side electrode 42 is disposed on the rear surface of the substrate 31 and an n side electrode 41 is disposed on the contact layer 40. A description is given of the structure and production process of the two-dimensional multi-quantum well active layer 37 of this prior art laser device. Figures 3(b) and 3(c) show the production process of the two-dimensional multi-quantum well active layer 37 shown in figure 3(a). First, cladding layer 32 is crystal grown on the substrate 31. Then, an AlGaAs layer 33A of 5 nm thickness and a GaAs layer 33B of 5 nm thickness are alternatively laminated ten times respectively on cladding layer 32 to form a laminated structure. Thereafter, photoresist film 34 is patterned on the laminated structure, and then the laminated structure comprising AlGaAs layers 33A and GaAs layers 33B is etched away using photoresist film 34 as a mask. Then, the side surface of the remaining laminated structure is further etched away by a reactive ion etching to form periodical concave parts 33C each having a depth 1 as shown in figure 3(b). Here, the depth 1 is 5 nm (50 angstroms). Such etching configuration can be realized because it is possible in reactive ion etching to set the etching rate of AlGaAs about 200 times as high as that of GaAs by setting the etching condition appropriately. Next, on the side surface of the laminated structure having periodical concave parts 33C, a GaAs film 37B and an AlGaAs film 37A are alternatively grown by a vapor phase epitaxy. By using the vapor phase epitaxy method, respective films are grown on the side surface of the laminated structure reproducing the concavo-convex configuration thereof precisely, as shown in figure 3(c). The alternative growths of GaAs film 37B and AlGaAs film 37A are repeated until the width of active region 37 becomes approximately 0.8 to 1 µm, resulting in the structure shown in figure 3(c). Thereafter, the laminated structure comprising AlGaAs layer 33A and GaAs layer 33B is etched away by a usual photolithography technique and a dry etching so as to form active region 37 in a stripe configuration. Then, insulating film 38, cladding layer 39 and contact layer 40 are formed thereon and the electrodes 41 and 42 are formed on the contact layer 40 and on the rear surface of substrate 31, respectively. Thus, the laser structure shown in figure 3(a) is completed. A description is given of the operation hereinafter. In the device of figure 3(a), when a voltage is applied across the electrodes 41 and 42 in a forward direction with respect to the pn junction, carriers are injected into active layer 37 and then confined in a region having a small energy band gap in active layer 37, i.e., in GaAs film 37B shown in figure 3(c), and they are recombined thereat, thereby emitting light. The emitted light is reflected and amplified between the cleavage facets provided opposite to each other and perpendicular to the active layer stripe, thereby occurring laser oscillation. Here, since GaAs film 37B has a very fine and slender linear configuration whose cross-section has approximately 5 nm dimensions for one edge, superior laser characteristics that the threshold value is reduced due to the effect of the quantization of injected carriers can be obtained. In addition, in this prior art structure, it is possible to form a plurality of quantum wires in the active layer, so that a laser device having a high output power can be realized. In the prior art quantum wire semiconductor laser device constituted as described above, several etching processes are required for forming the active layer and, therefore, the production process is quite complicated. In addition, it is quite difficult to apply the prior art quantum wire structure to a general laser device such as a ridge type laser device or an inner stripe type laser device. Attention is drawn to Patent Abstracts of Japan, vol. 11, No. 224 (E525) and JP-A-62042481 which describes a device of this kind. SUMMARY OF THE INVENTION It is an object of the present invention, which is defined in the appended claims, to provide a semiconductor optical element including an active region having a plurality of quantum wires or boxes, that can be applied to a ridge type laser device or an inner stripe type laser device and that can be formed by a simple production process. It is another object of the present invention to provide a semiconductor optical element including an active region having a plurality of quantum wires or boxes in which the quantum effect is enhanced. Other object and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic cross-sectional view showing a quantum wire structure of a semiconductor optical element by way of explanation of the present invention; Figure 2 is a cross-sectional view showing a structure of a prior art quantum wire laser device; Figure 3 is a cross-sectional view showing a structure of another prior art quantum wire laser device; Figure 4 is a cross-sectional view showing a quantum wire structure of a semiconductor optical element in accordance with another embodiment of the present invention; Figures 5(a) to 5(d) are cross-sectional views showing process steps for producing the quantum wire or quantum box structure of figure 4; Figure 6(a) is a perspective view showing a semiconductor layer formed in a quantum wire structure; Figure 6(b) is a perspective view showing a semiconductor layer formed in a quantum box structure; Figure 7(a) is a perspective view showing a ridge type semiconductor laser having an active region of quantum wire or quantum box structure; Figure 7(b) is a perspective view showing an inner stripe type semiconductor laser having an active region of quantum wire or quantum box structure; Figures 8(a) to 8(e) are cross-sectional views showing process steps for producing the ridge type semiconductor laser device; and Figures 9(a) and 9(b) are cross-sectional views showing process steps for producing the inner stripe type semiconductor laser device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawing. Figure 1 is a cross-sectional diagram of a quantum wire structure of a semiconductor optical element. Figure 4 is a cross-sectional view showing a quantum wire structure of a semiconductor optical element in accordance with the present invention. Referring first to Figure 1, reference numeral 12 designates an n type GaAs substrate. An n type AlGaAs cladding layer 9 is disposed on the substrate 12. A plurality of stripe-shaped grooves each having a rectangular cross-section of depth d₁ and width x are formed in the cladding layer 9 in parallel with each other at interval y. A well layer 10 of thickness w₁ and a barrier layer 11 of thickness b₁ are alternatively laminated on the bottom surface of the stripe-shaped grooves of the cladding layer 9 and on the regions between the adjacent grooves. Here, well layer 10 comprises, for example, GaAs and barrier layer 11 comprises, for example, AlGaAs having an energy band gap approximately equal to that of cladding layer 9. The n type AlGaAs cladding layer 9 has a higher energy band gap than that of GaAs well layer 10, so that this cladding layer 9 functions as a barrier layer. In figure 1, the depth of groove d₁, the thickness of well layer w₁ and the thickness of barrier layer b₁ have the following relation; d 1 = w 1 = b 1 so that the stripe-shaped groove is completely filled up by first well layers 10 and also newly formed grooves are completely filled up by barrier layers 11. In this structure, each well layer 10 is two-dimensionally surrounded by the barrier layers. That is, the upper, lower and both side surfaces thereof are surrounded by the barrier layers. In addition, since the width of stripe-shaped groove x and the interval y between the adjacent grooves are equal to each other, the well layer formed on the groove has the same dimension as that of the well layer formed on a region between the adjacent grooves. Here, in order to induce the well layer 10 to have an effect as a quantum wire, it is required to set the widths x and y and thickness d₁ to approximately 20 nm or less. In accordance with the embodiment of the present invention shown in figure 4, the width of stripe-shaped groove d₂, the thickness of well layer w₂ and the thickness of barrier layer b₂ have the following relation; w 2 < b 2 , (w 2 + b 2 )/2 ≅ d 2 where the thickness of well layer w₂ is smaller than the thickness of barrier layer b₂ and the half of the sum of w₂ and b₂ is equal to the depth of groove d₂. In this case, well layer 10 is positioned at a center part of the adjacent barrier layers 11 in the layer thickness direction and thus well layer 10 is completely surrounded by barrier layers 11. Therefore, the edges of each well layer 10 are not in contact with any edges of other well layer, as they would be had the arrangement of Figure 1 been adopted, so that the quantum effect is obtained more completely. A description is given of a quantum box structure that further enhances the quantum effect. In the structure shown in figure 4, when not only the thickness w and the widths x and y of the well layer but also the length z thereof are set to approximately 20 nm (200 Å) or less, a quantum box structure in which each well layer 10 is three-dimensionally surrounded by barrier layers 11, that is, the upper and lower surfaces, the both side surfaces and the side surfaces perpendicular to the length direction of well layer 10 are surrounded by barrier layers 11 can be obtained. In this quantum box structure, the quantum effect is further eminent. A description is given of a production process of the quantum wire structure or quantum box structure of the semiconductor optical element in accordance with the above embodiments. Figures 5(a) to 5(d) are cross-sectional views showing process steps for producing the quantum wire or quantum box structure in accordance with the embodiment of figure 4. First, as shown in figure 5(a), a semiconductor layer 9 having an energy band gap corresponding to that of the barrier layer of quantum well structure is epitaxially grown on semiconductor substrate 12. Then, as shown in figure 5(b), portions of semiconductor layer 9 are etched away by a dry etching to form stripe-shaped grooves (13) each having a rectangular cross-section whose dimension is sufficiently small to cause a quantum wire effect or rectangular-shaped grooves arranged in a checkered configuration whose dimension is sufficiently small to cause a quantum box effect. Figures 6(a) and 6(b) are perspective views respectively showing a semiconductor layer processed for the quantum wire and a semiconductor layer processed for the quantum box. In these figures, respective dimensions x, y and z are set to approximately 20 nm or less. Then, as shown in figure 5(c), first well layer 10 is formed on the grooves and, thereafter, as shown in figure 5(d), first barrier layer 11 is formed on the well layer 10. In this way, well layer 10 and the barrier layer 11 are alternatively laminated for several times. The thicknesses of these layers are set such that the thickness of well layer 10 is smaller than that of barrier layer 11 and the sum of the thickness of barrier layer 11 and the thickness of well layer 10 is twice as large as the depth of the groove. In order to form the structure shown in figure 1, the thicknesses of well layer 10 and barrier layer 11 should be equal to the depth of the groove. As the crystal growth method, a growth method that can maintain the configuration of the processed semiconductor layer and can form a thin film of 10 nm thickness at high reproducibility, for example, a vapor phase epitaxial growth such as MBE (Molecular Beam Epitaxy) or MO-CVD (Metal Organic Chemical Vapor Deposition) is preferably employed. In the above-described production method, since the process of laminating well layer 10 and the process of laminating barrier layer 11 are alternatively repeated, a structure including a plurality of quantum wires or quantum boxes can be easily obtained. In addition, since the quantum wire or quantum box structure of this embodiment has grooves directly formed in the semiconductor layer on the semiconductor substrate and the laminated layer structure is formed thereon, this structure can be easily employed for an active region of a semiconductor laser which can be fabricated by a relatively simple process, such as a ridge type semiconductor laser or an inner-stripe type semiconductor laser. As a result, a high performance quantum wire or quantum box laser device is realized. Figures 7(a) and 7(b) are perspective views each showing a semiconductor laser in which the quantum wire structure shown in figure 1 or 4 is employed for an active region thereof, in which figure 7(a) shows a ridge type semiconductor laser and figure 7(b) shows an inner-stripe type semiconductor laser. The device of figure 7(a) has an n type GaAs substrate 12. An n type AlGaAs lower cladding layer 9 is disposed on substrate 12. An active layer 14 including a quantum wire structure is disposed on cladding layer 9. A p type AlGaAs upper cladding layer 19 is disposed on active layer 14. The cladding layer 19 has a stripe-shaped ridge part which connects cleavage facets 30 and 31. A p type GaAs cap layer 20 is disposed on the ridge part of cladding layer 19. An n type GaAs current blocking layer 15 is disposed on cladding layer 19 so as to embed the ridge part. A p type GaAs contact layer 16 is disposed on current blocking layer 15 and cap layer 20. A p side electrode 17 is disposed on contact layer 16 and an n side electrode 18 is disposed on the rear surface of substrate 12. In figure 7(b), like elements are given the same numerals as those shown in figure 7(a). A p type AlGaAs first upper cladding layer 29 is disposed on active layer 14. An n type GaAs current blocking layer 15 is disposed on first cladding layer 29. This current blocking layer 15 has a stripe-shaped groove serving as a current path. A p type AlGaAs second cladding layer 39 is disposed on current blocking layer 15 and first upper cladding layer 29 along the groove configuration of current blocking layer 15. A p type GaAs contact layer 16 is disposed on second upper cladding layer 39. A p side electrode 17 is disposed on contact layer 16 and an n side electrode 18 is disposed on the rear surface of substrate 12, respectively. A description is given of a production method of the ridge structure semiconductor laser shown in figure 7(a) in accordance with figure 8. First, as shown in figure 8(a), n type AlGaAs cladding layer 9 is grown on p type substrate 12 by a first crystal growth. Then, grooves for forming quantum wires or quantum boxes shown in figure 6(a) or 6(b) are formed on n type AlGaAs cladding layer 9. Thereafter, a layer serving as a part of n type AlGaAs cladding layer 9 is grown thereon and then quantum wire or quantum box layer 14 comprising a plurality of well layers and barrier layers is grown thereon as described in the embodiments of figures 1 and 4. P type AlGaAs cladding layer 19 and p type GaAs cap layer 20 are grown thereon. Here, the layer serving as a part of cladding layer 9, quantum wire or quantum box layer 14, p type AlGaAs cladding layer 19 and p type GaAs cap layer 20 are successively grown by a second crystal growth. Figure 8(b) is a cross-sectional view of the wafer in a state after the second crystal growth. Then, as shown in figure 8(c), a SiO₂ film is formed on the surface of the wafer by a sputtering, an electron beam deposition or the like and, thereafter, portions of the SiO₂ film are removed by a photolithography and etching technique to form SiO₂ film 21 in a stripe configuration. The thickness and the stripe width of SiO₂ film 21 are, for example, 0.1 to 1.0 µm and 2 to 10 µm, respectively. Hydrofluoric acid or the like is used as etchant for etching the SiO₂ film. Then, as shown in figure 8(d), portions of p type GaAs cap layer 20 and p type AlGaAs cladding layer 19 are removed by etching to form a ridge configuration. Here, the width of the bottom part of the ridge is desired to be in a range from 2 µm to 10 µm in view of the control of the transverse mode of laser. Then, as shown in figure 8(e), the ridge part is buried by n type GaAs layer 15 by a third crystal growth. After the third crystal growth, SiO₂ film 21 is removed and p type GaAs contact layer 16 is formed on the wafer by a fourth crystal growth. When all crystal growth processes are finished, n side electrode 18 is formed on the rear surface of substrate 12 and p side electrode 17 is formed on p type GaAs contact layer 16. Thereafter, the wafer is divided into chips, thereby completing laser elements. A description is given of a production method of the inner stripe type semiconductor laser shown in figure 7(b) with reference to figure 9. After forming quantum wire or quantum box layer 14 by the same steps as described above, p type AlGaAs first upper cladding layer 29 and n type GaAs current blocking layer 15 are successively crystal grown thereon. Figure 9(a) is a sectional view of the wafer in a state after the crystal growth. Thereafter, a stripe-shaped groove is formed in n type GaAs current blocking layer 15 by a photolithography and etching technique. The surface of p type AlGaAs first upper cladding layer 29 is exposed at the bottom of the groove. N type GaAs current blocking layer 15 can be selectively removed using a mixed solution comprising ammonia and hydrogen peroxide as etchant. The cross-section of the wafer in this state is shown in figure 9(b). After forming the groove, p type AlGaAs second upper cladding layer 39 and p type GaAs contact layer 16 are successively formed on the wafer by a crystal growth. Thereafter, n side electrode 18 is formed on the rear surface of substrate 12 and p side electrode 17 is formed on p type GaAs contact layer 16, respectively. Then, the wafer is divided into chips, thereby completing laser elements. In the above-described two structures, n type GaAs current blocking layer 15 has both functions of concentrating the current into a region directly below the ridge part or directly below the stripe-shaped groove and of absorbing the laser light generated in the active region from both sides of laser light, to stabilize the horizontal transverse mode. When the above-described quantum wire or quantum box structure is adopted for the active region of such laser structures, a semiconductor laser device having high performances such as low threshold value, low operation current and high speed switching can be obtained. While in the above-described embodiments AlGaAs series semiconductor lasers are described, the present invention can be also applied to other material semiconductor lasers. In addition, although the ridge type semiconductor laser and the inner stripe type semiconductor laser are described in the above-illustrated embodiments, the quantum wire or quantum box structure of the present invention can be applied to other semiconductor lasers such as an electrode stripe type laser or a buried hetero type laser. In addition, the quantum wire or quantum box structure of the present invention can be applied not only to semiconductor lasers but also to semiconductor elements such as a light waveguide or an optical switching element. In these cases, a superior device performance can be realized on the basis of the quantum effect. As is evident from the foregoing description, a semiconductor optical element includes a semiconductor substrate or a semiconductor layer formed on a semiconductor substrate; a plurality of stripe-shaped grooves each having a rectangular cross-section whose width is sufficiently narrow to cause a quantum effect, provided on the semiconductor substrate or the semiconductor layer in parallel with each other at interval sufficiently narrow to cause a quantum effect or a plurality of rectangular-shaped grooves having a width and a length sufficiently narrow to cause a quantum effect, provided on the semiconductor substrate or the semiconductor layer in a checkered arrangement; and a structure in which a quantum well layer whose thickness is less than the depth of the groove and sufficiently thin to cause a quantum effect and a barrier layer whose thickness is larger than the depth of the groove are alternatively laminated, which is provided on the bottom surfaces of the grooves formed in the semiconductor substrate or the semiconductor layer and regions between the adjacent grooves. Therefore, an active region comprising a plurality of quantum wires or quantum boxes can be obtained by a simple production process. In addition, this quantum wire or quantum box structure can be employed for an active region of a ridge type semiconductor laser, an inner stripe type semiconductor laser or the like, whereby a semiconductor laser device having a low threshold value and a low operation current can be easily obtained. According to a method for manufacturing a semiconductor optical device, a plurality of stripe-shaped grooves each having a rectangular cross-section whose width is sufficiently narrow to cause a quantum effect are formed on a semiconductor substrate or on a semiconductor layer on the substrate in parallel with each other at interval sufficiently narrow to cause the quantum effect. Or, a plurality of rectangular-shaped grooves each having a width and a length sufficiently narrow to cause a quantum effect are formed on the semiconductor substrate or the semiconductor layer in a checkered arrangement. Then, a quantum well layer having a thickness less than the depth of the groove and sufficiently thin to cause a quantum effect and a barrier layer having a thickness larger than the depth of the groove are alternatively laminated on the wafer having the grooves with maintaining the concavo-convex configuration of the grooves. Therefore, a laser device having a structure comprising a plurality of quantum wires or quantum boxes can be produced without complicated etching processes or the like.

Claims: A semiconductor optical element comprising: a semiconductor layer (9); a plurality of stripe-shaped grooves (13) each having a rectangular cross-section formed in said semiconductor layer in parallel with each other, the groove width and spacing each being 20 nm or less; a quantum well layer (10) and a barrier layer (11) laminated alternately on the bottom surfaces of said grooves and the regions between the adjacent grooves, the thickness of the well layer being less than the groove depth, characterised in that the thickness of the barrier layer is greater than the groove depth. A semiconductor optical element in accordance with claim 1 wherein the thickness of said well layer w, the thickness of said barrier layer b and the depth of said groove d have the following relation; w < b, (w +b)/2 = d A semiconductor optical element in accordance with claim 1 or claim 2, wherein said grooves are rectangular-shaped grooves formed on said semiconductor layer in a checkered arrangement. A semiconductor optical element in accordance with any preceding claim wherein said semiconductor layer is a semiconductor substrate. A semiconductor optical element in accordance with claims 1, 2 or 3, wherein said semiconductor layer (9) is formed on a semiconductor substrate (12). A semiconductor optical element according to claim 5, wherein : said quantum well layer (10) comprises a semiconductor material having an energy band gap smaller than the energy band gap of the semiconductor layer (9) ; and said barrier layer (11) comprises a semiconductor material having an energy band gap larger than that of the quantum well layer; and said well layer and said barrier layer are alternately laminated on the bottom surfaces of said grooves (13) and regions between the adjacent grooves. A semiconductor optical element according to claim 6, wherein said semiconductor layer is a first conductivity type first semiconductor material layer (9) formed on a semiconductor substrate (12) and having an energy band gap larger than that of the quantum well layer; further comprising : a second conductivity type first semiconductor material layer (19) having an energy band gap larger than that of the quantum well layer, formed on the laminated structure (14) of said well layer (10) and said barrier layer (11) and having a stripe-shaped ridge at the center of the element; and a first conductivity type second semiconductor material layer (15) formed on said second conductivity type first semiconductor material layer (19) so as to bury said stripe-shaped ridge. A semiconductor optical element as defined in claim 7 which further comprises a second conductivity type second semiconductor material layer (16) formed on said first conductivity type second semiconductor material layer (15) and said stripe-shaped ridge, an electrode (17) formed on said second conductivity type second semiconductor material layer (16), and an electrode (18) formed on the rear surface of said substrate (12). A semiconductor optical element according to claim 6, wherien said semiconductor layer is a first conductivity type first semiconductor material layer (9) formed on a semiconductor substrate (12) and having an energy band gap larger than that of the quantum well layer (10); further comprising: a second conductivity type first semiconductor material layer (29) having an energy band gap larger than that of the quantum well layer (10), formed on the laminated structure of said well layer (10) and said barrier layer (11) ; a first conductivity type second semiconductor material layer (15) formed on said second conductivity type first semiconductor material layer (29); a stripe-shaped groove formed at the center part of said first conductivity type second semiconductor material layer (15) penetrating through said semiconductor layer; and a second conductivity type second semiconductor material layer (16) formed on said first conductivity type second semiconductor material layer (15) and on said second conductivity type first semiconductor material layer (29) exposed at the bottom part of said stripe-shaped groove. A semiconductor optical element in accordance with claim 9 which further comprises an electrode (17) formed on said second conductivity type second semiconductor material layer (16) and an electrode (18) formed on the rear surface of said substrate (12). A method of manufacturing a semiconductor optical element according to claim 1 comprising steps of: providing a semiconductor substrate (12) or a semiconductor layer (9) formed on a semiconductor substrate; forming a plurality of stripe-shaped grooves (13) each having a rectangular cross-section whose width and spacing are each 20nm or less on said semiconductor substrate or said semiconductor layer in parallel with each other or forming a plurality of such grooves in a checkered arrangement; and alternately laminating a quantum well layer (10) having a thickness less than the depth of said grooves and a barrier layer (11) having a thickness larger than the depth of said grooves, on the wafer. A method of manufacturing a semiconductor optical element in accordance with claim 11 wherein said grooves are formed by dry etching. A method of manufacturing a semiconductor optical element in accordance with claim 11 wherein said well layer and said barrier layer are formed by molecular beam epitaxy or metal-organic chemical vapor deposition.

Inventors: NAGAI YUTAKA, TAKEMOTO AKIRA, WATANABE HITOSHI, NAGAI, YUTAKA, C/O MITSUBISHI DENKI K.K., TAKEMOTO, AKIRA, WATANABE, HITOSHI, Takemoto, Akira, c/o Mitsubishi Denki K.K., WATANABE, HITOSHI, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: H01L33
IPC codes: H01S5, H01L33