United States Patent (19)
`Watanabe
`
`54 SEMICONDUCTOR LIGHT EMITTER
`(75) Inventor: Masanori Watanabe, Nara, Japan
`(73) Assignee: Sharp Kabushiki Kaisha, Osaka, Japan
`
`(21) Appl. No.: 278,178
`(22 Filed:
`Jul. 21, 1994
`(30)
`Foreign Application Priority Data
`Jul. 22, 1993
`JP
`Japan .................................... 5-181039
`Jun. 10, 1994 (JP)
`Japan .
`... 6-128767
`Jun. 28, 1994 (JP
`Japan ..
`... 6-146487
`(51) Int. Cl. ...
`HOS 3/18; HOIL 33/00
`52 U.S. Cl. ................
`... 372/45; 372/43; 257/98
`58) Field of Search .................................. 372/45, 43, 44;
`257/98
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`1/1986 Kuroda et al. ............................ 372/45
`4,563,764
`5/1986 Scholl ....................................... 257/94
`4,590,501
`4,766,470 8/1988 Scholl et al. .............................. 372/45
`4,779,280 10/1988 Sermage et al. .......................... 372/45
`4,990,970 2/1991 Fuller ..............
`257/98
`5,319,219 6/1994 Cheng et al. ............................. 372/45
`5,363,395 11/1994 Gaines et al. ............................. 372/45
`FOREIGN PATENT DOCUMENTS
`0247267 12/1987 European Pat. Off..
`57-49284 3/1982 Japan.
`60-77473 5/1985 Japan.
`2-125670 5/1990 Japan.
`
`US005537433A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,537,433
`Jul. 16, 1996
`
`2-170486 7/1990 Japan.
`3-114277 5/1991 Japan.
`3-163882 7/1991 Japan.
`4-290275 10/1992 Japan.
`85/03809 8/1985 WIPO
`OTHER PUBLICATIONS
`DialogTM English Patent Abstract of Japanese Laid-Open
`Patent Publication No. 57-49284 (Mar. 23, 1982) (2 pages
`total).
`Primary Examiner-Rodney B. Bovernick
`Assistant Examiner-Robert McNutt
`Attorney, Agent, or Firm-Morrison & Foerster
`(57)
`ABSTRACT
`A semiconductor light emitter, such as the light-emitting
`diode or the semiconductor laser, having a structure in which
`a light emitting area or an active layer, a transparent layer
`which is pervious to light radiated from the light emitting
`area or the active layer; and an opaque layer or an opaque
`substrate which is impervious to the radiated light are
`arranged in order or in the inverse order. The semiconductor
`light emitter includes (a) total reflection layer(s) arranged
`between the transparent layer(s) and the opaque layer(s) so
`as to come into contact with the transparent layer. The
`refractive index of the total reflection layer is smaller than
`that of the transparent layer. Therefore, at least one part of
`light, which has been radiated from the light emitting area or
`the active layer and which has been reflected by the total
`reflection layer thereafter, is either radiated outward from
`side surfaces of the transparent layer or returned to the active
`layer.
`
`1 Claim, 10 Drawing Sheets
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`U.S. Patent
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`Jul. 16, 1996
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`Sheet 1 of 10
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`5,537,433
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`Fig. 1 PRIOR ART
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`U.S. Patent
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`Jul. 16, 1996
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`Sheet 2 of 10
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`U.S. Patent
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`Jul. 16, 1996
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`U.S. Patent
`
`Jul. 16, 1996
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`Sheet 4 of 10
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`U.S. Patent
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`U.S. Patent
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`Jul. 16, 1996
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`U.S. Patent
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`Jul. 16, 1996
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`U.S. Patent
`
`Jul. 16, 1996
`
`Sheet 10 of 10
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`5,537,433
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`

`

`1.
`SEMICONDUCTOR LIGHT EMITTER
`
`5,537,433
`
`2
`layers 732 are plated on both electrodes, respectively. On the
`other hand, as a printed board to mount the LED chip
`thereon, there is prepared a printed board as shown FIG. 2B
`where wirings 728 (over two areas) for the respective
`electrodes are printed on an insulator substrate 729 to form
`a solder resist film 733 and an adhesive agent 731 is painted
`thereon. Then, seating the above LED chip on the substrate
`and heating the solder layers 732 for at first melting and
`subsequently resolidifying, solders 730 connecting the elec
`trode wirings 728, 728 to the LED electrodes 721 and 722
`can be completed, respectively. In this way, by arranging the
`chip laterally on the board and then fixing it thereon, the
`light can be radiated from the side surfaces of the chip.
`The above-mentioned mounting method presupposes a
`extracting up of a great deal of light from the side surfaces
`of the chip. Therefore, it is not practical to apply the above
`mounting method for a conventional LED using a multi
`layer reflection film on a light absorbing substrate.
`On the other hand, it is very important to reduce a
`threshold current in the semiconductor laser to obtain a high
`efficiency of converting current to light. In the prior art,
`Japanese Patent Application Laid-Open Hei 2 No. 170486
`discloses a semiconductor laser intended to reduce the
`threshold current, or to improve the current/light converting
`efficiency by returning spontaneous emission, which emits
`in an active layer and does not contribute to an oscillation of
`the laser, to the active layer (photon recycle). FIG. 3 shows
`a cross-sectional view of this semiconductor laser.
`The semiconductor laser is manufactured as follows: at
`first, by Superimposing an n-type AloGaAs layer of a
`thickness W4n(n: refractive index of medium) on an n-type
`AlAs layer of a thickness W4n by turns with 10 cycles by
`means of MOCVD (metal organic chemical vapor deposi
`tion) method, an n-type multi-layer reflection film 902 is
`fabricated on a n-type GaAs substrate 901. Then, after
`forming a n-type AloGaAs cladding layer 903, a GaAs
`active layer 904 and a p-type AlGaAs cladding layer
`905 in order, p-type AloGaos.As layers and p-type AlAs
`layers are mutually laminated to have W4n in thickness,
`respectively, with 10 cycles, whereby a p-type multi-layer
`reflection film 906 is formed and then a p-type GaAs cap
`layer 907 is overlaid thereon. Next, after forming a mesa
`stripe by etching, ap-type AlGaAs buried layer 908 and
`a n-type AlGaAs buried layer 909 are provided by LPE
`method (Liquid Phase Epitaxy). Then, a Zn diffusion area
`910 is formed by selective diffusion and a p-electrode 911
`and a n-electrode 912 are provided. Then the semiconductor
`laser is completed to be of 100 um in oscillator length by
`cleavage.
`In the above semiconductor laser, however, since the
`multi-layer reflection film affords high reflectivity for lim
`ited light in a specific incident direction (a vertical incident
`light in case of W4n in layer thickness), there is risen a
`problem that, although a beam traveling from the active
`layer 904 to the multi-layer reflection film 902 or 906 is
`reflected by the multi-layer reflection film to contribute to
`the photon recycle, an incident beam oblique to the multi
`layer reflection film is so absorbed that it does not contribute
`to the outward radiation.
`Furthermore, since the semiconductor laser needs high
`accuracy in thickness of each layer of the multi-layer film,
`it is difficult to manufacture. Again, because of many bound
`aries between different kinds of semiconductors, the semi
`conductor laser is apt to have an increased resistance.
`SUMMARY OF THE INVENTION
`Bearing the above-mentioned problems in mind, the first
`object of the present invention is to provide a semiconductor
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to a reflection layer of a semicon
`ductor light emitter, and more particularly, to a high effective
`total reflection layer of a semiconductor light emitter which
`is utilized for a light-emitting diode, a semiconductor laser
`and so on.
`2. Description of the Prior Art
`In the semiconductor light emitter, such as the light
`emitting diode (LED), the semiconductor laser etc., it is very
`important to extract light from inside effectively, in other
`words, to improve an outer radiative efficiency, from a point
`of obtaining a semiconductor light-emitter of high power
`and efficiency.
`Particularly, in case of using a substrate absorbing a
`radiative wavelength, it has been devised a countermeasure
`to prevent the substrate from absorbing the light by a
`provision of a reflecting layer between the substrate and a
`light-emitting section, since the light absorption in the
`substrate may be one of factors to reduce the outer radiative
`efficiency of the semiconductor light emitter.
`As an example of the prior art, FIG. 1, shows a cross
`sectional view of an LED having a multi-layer reflection
`film arranged on an opaque substrate, thereby emitting the
`light from an upper surface of the LED. This emitter is
`produced as follows; on the whole surface of an n-type GaAs
`substrate 510, n-type AlInP/AlGalnP multi-layer reflection
`layers 511 (layer thickness: 0.041 um(AlInP); 0.040 um(Al
`GalinP), 20 pairs), an n-type AlGalnP cladding layer 512, an
`undoped AlGalnP emitting layer 513, a p-type AlGalnP
`cladding layer 514 and a p-type GaAs contact layer 515 are
`fabricated in order.
`Thereafter, a surface electrode 516 is deposited on a
`surface of the LED and then the electrode 516 and the p-type
`GaAs contact layer 515 are etched except a central portion
`of the LED. Further, a back surface electrode 517 is also
`deposited on a back surface of the LED.
`In the above LED, however, since the multi-layer reflec
`tion film affords high reflectivity for only light in a specific
`incident direction, i.e., a vertical incident light in this case,
`there is caused a problem that, although a beam p traveling
`straight downward is reflected by the multi-layer reflection
`film to radiate upward, a beam q traveling downward
`obliquely is absorbed by the multi-layer reflection film so
`that it does not contribute to the outward radiation.
`Further, since the multi-layer reflection film reflects
`mainly the light traveling straight downward, the light is
`radiated through the upper surface of the LED chip, so that
`the amount of light radiated through the side surfaces of the
`chip is remarkably small. Such a fact is inconvenient for
`applying a simple mounting method of the chip described
`hereinafter.
`We now describe a method disclosed in Japanese Patent
`Application Laid-Open Sho 57 No. 49284 as a simple
`method to mount the LED on a printed board directly
`without wire-bonding. As shown in FIG.2A, in the above
`method, a p-type semiconductor layer 718 is fabricated on
`an n-type semiconductor substrate 719 to form an electrode
`721 on an upper surface of the LED chip, which radiates the
`light in the vicinity of a pn junction surface 720, and an
`electrode 723 on a lower surface thereof. Thereafter, solder
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`5,537,433
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`light emitter intended to increase the outside radiative effi
`ciency or the current utilization efficiency by employing a
`reflection layer with a simple construction to reflect the
`incident light oblique to the reflection layer.
`The second object of the present invention is to provide
`either a light-emitting diode (LED), which is capable of
`extracting the light from side surfaces of the chip.
`In order to solve the above-mentioned objects, according
`to the first object of the present invention, there is provided
`a semiconductor light emitter having a structure in which a
`light-emitting area or an active layer; a transparent layer
`which is pervious to light radiated from the light emitting
`area or the active layer, and an opaque layer or an opaque
`substrate which is impervious to the radiated light are
`arranged in order or in the inverse order, comprising:
`a total reflection layer arranged between the transparent
`layer and the opaque layer so as to come into contact with
`the transparent layer, a refractive index of the total reflection
`layer being smaller than that of the transparent layer;
`wherein at least one part of light which has been radiated
`from the light-emitting area or the active layer and which has
`been reflected by the total reflection layer thereafter, is either
`radiated outward from side surface of the transparent layer
`or returned to the active layer.
`Furthermore, according to the second object of the present
`invention, there is also provided a semiconductor light
`emitter having a structure including a light-emitting area or
`an active layer; a first transparent light-pervious layer which
`is pervious to light radiated from the light-emitting area or
`the active layer, and a first opaque layer or an opaque
`substrate which is impervious to the radiated light, are
`arranged in order; under the light-emitting area or the active
`layer, a second transparent layer which is pervious to light
`radiated from the light-emitting area or the active layer; and
`a second opaque layer or an opaque substrate which is
`impervious to the radiated light, are arranged in order, over
`the light-emitting area or the active layer, the semiconductor
`light emitter comprising:
`a first total reflection layer arranged between the first
`40
`transparent layer and the first opaque layer so as to
`come into contact with the first transparent layer, a
`refractive index of the first total reflection layer being
`smaller than that of the transparent layer; and
`a second total reflection layer arranged between the
`second transparent layer and the second opaque layer
`so as to come into contact with the second transparent
`layer, a refractive index of the second total reflection
`layer being smaller than that of the transparent layer;
`wherein at least one part of light which has been radiated
`from the light-emitting area or the active layer and
`which has been reflected by the first or second total
`reflection layer thereafter, is either radiated outward
`from side surfaces of the first or second transparent
`layer or returned to the active layer.
`In the first object of the present invention, any of the
`following features is preferable: the product of the layer
`thickness and the refractive index of the total reflection layer
`is more than 1.41 times as much as a center light-emitting
`wavelength of the semiconductor light emitter; the transpar
`ent layer consists of AlGaAs or AlGanP and the total
`reflection layer consists of any one of AlAs, AlGaAs, AllnP
`and AlGalnP, of which refractive indexes are lower than that
`of the transparent layer, respectively; the transparent layer
`consists of any one of ZnSe, ZnSSe and ZnMgSSe and the
`total reflection layer consists of any one of ZnCdS, ZnCdSSe
`and ZnMgSSe, of which refractive indexes are lower than
`
`55
`
`45
`
`50
`
`65
`
`4
`that of the transparent layer, respectively; the semiconductor
`light emitter is a light-emitting diode; and the semiconductor
`light emitter is a semiconductor laser,
`Further, in case that the semiconductor light emitter is the
`light-emitting diode, any of the following features is pref
`erable: i.e., the transparent layer consists of GaAsP and the
`total reflection layer consists of any one of GalP, GaAsP and
`AlGaAs, of which refractive indexes are lower than that of
`the transparent layer, respectively; the transparent layer
`consists of either GaN or AlGanN and the total reflection
`layer consists of AlGanN of which refractive index is lower
`than that of the transparent layer; a protection film is formed
`on side surfaces of the transparent layer; and a first and a
`second electrodes are formed on the top and bottom surfaces
`of the substrate and the light-emitting diode is arranged so
`that the respective surfaces of the first and the second
`electrodes are roughly perpendicular to surfaces of a first
`and a second electrodes formed on atop and bottom surfaces
`of the light-emitting diode, respectively, and the first elec
`trode of the printed board is electrically connected with the
`first electrode of the light emitting diode and the second
`electrode of the printed board is electrically connected with
`the second electrode of the light-emitting diode.
`Next, the operation of the invention with reference to
`drawings is described. FIG. 4 is a schematic cross-sectional
`view of the semiconductor light emitter, showing the prin
`ciple of the invention. In the figure, it is presumed that a
`refractive index of a medium 1 in the light-incident side is
`3.527; the refraction index of the total reflection layer 2 is
`3.189, lower than the refractive index of the medium 1; a
`refractive index of a medium 3 is a value in a range of
`4.066-0.276i, where i is the imaginary unit, and that the
`incident angle of the light from the medium 1 through the
`medium 2 is expressed to the angle A. FIG. 5 shows a
`variation of a reflectivity R calculated in response to the
`changes of thickness d of the reflection layer 2 under the
`conditions of 50° and 66 on the above angle A. Note that,
`the wavelength of the light is 0.564 um.
`In the structure shown in FIG. 4, a critical angle Ac at
`which the incident angle A exhibits the total reflection is
`64.7. Under the condition that the incident angle A is 50
`which is below the critical angle, as the layer thickness d is
`increased, the reflectivity R periodically repeats its rise and
`fall. Under the condition that the incident angle A is 66
`which is over the critical angle, a requirement for total
`reflection can be satisfied, so that, if the layer thickness dis
`large enough in comparison with the wavelength , the
`reflectivity R can be 100%. On the contrary, when the layer
`thickness d is small in comparison with the wavelength ,
`the reflectivity Ris so small that it cannot exceed 50% unless
`the layer thickness d is about 0.25 um and that the reflec
`tivity R of nearly 100% cannot be attained unless the layer
`thickness d is more than about 1 um.
`This means that even though the incident angle A satisfies
`the condition of A>Ac, there exists a flow-out of the light
`called "evanescent wave' in the total reflection layer, so that
`the layer thickness d thereof has to be larger than the
`distance of the flow-out in order to obtain the sufficient
`reflectivity.
`Now, we define the medium 2 as the total reflection layer
`by the reflectivity of more than 50%. As described above,
`although a lower limit in the layer thickness of the total
`reflection layer is 0.25 um, it varies in response to the
`wavelength. Converting the above thickness to a light path
`length (i.e. the product of refractive index and layer thick
`ness), the length corresponds to 1.41 times (=3.189x0.25
`um/0.564 um) the wavelength, whereby such a value is
`applicable independent of the wavelength.
`
`

`

`5
`This lower limit in the layer thickness of the total reflec
`tion layer is considerably large in comparison with the layer
`thickness of low refractive index in the conventional multi
`layer reflection film. The layer thickness of W4n (n: refrac
`tive index) is given as that of the low refractive index layer
`in the conventional multi-layer reflection film, which cor
`responds to 0.25 times the wavelength in the above light
`path length. Comparing with this value, the light path length
`of the total reflection layer exceeds 1.41 times the wave
`length, so that the ratio therebetween is more than 5.6 times
`at least. Consequently, it is understood that the multi-layer
`reflection film is quite different from the total reflection layer
`in terms of the operational principle, since the former
`employs the Bragg reflection while the latter employs the
`total reflection.
`Now, a case of radiating the light from side surface 4 of
`the semiconductor light emitter by utilizing the total reflec
`tion layer is studied, with reference to FIG. 4. Note that,
`through this study, it is assumed that the side surface 4 is
`perpendicular to the total reflection layer 2. An incident
`angle C to the side surface 4 that the light radiated therefrom
`has to satisfy, is in a range of 0 <C<Cmax, where the total
`reflection critical angle Cmax of the light radiating from the
`medium 1 to the material 5 (refraction index: 1.5 by assum
`ing a resin) is 25.16 =arc sin(1.5/3.527). By the way, the
`relationship between the angles C and A is expressed by the
`equation of A=90°-C. Therefore, in order to attain a high
`reflectivity of the total reflection layer 2 for the light
`radiating from the side surface, a high reflectivity should be
`obtained in the angle A of the range of AminkA<90, where
`Amin=90°-Cmax=64.84°. This angle is approximately equal
`to the total reflection critical angle Ac (=64.7) of the total
`reflection layer 2 mentioned above.
`Therefore, it is understood that there is no need to use the
`multi-layer reflection film which has been employed con
`ventionally, since the total reflection layer 2 can reflect most
`of the light radiating from the side surface 4. Of course,
`since the angle depends on the difference in the refractivity
`between the medium 1 and the total reflection layer 2
`greatly, the multi-layer reflection film can be used together
`in connection with the utilized combination of the medium
`1 and the total reflection layers 2. It is expected that the
`suitable multi-layer reflection film to be combined is ones
`which exhibits a high reflectivity against the vertical inci
`dent light radiating toward the top surface, besides the layers
`which exhibits a high reflectivity against the oblique inci
`dent light so as to secure the reflectivity against the light
`radiating toward the side surface. For the material used for
`the total reflection layer, it is desirable that not only the
`refractive index thereof is less than that of the medium on
`the incident side but also a lattice match can be attained
`therein. Bearing these points into mind, when the medium
`on the incident side is AlGalnP, any one of AlGalnP (where,
`the alloy composition ratio of Al thereof is larger than that
`of the medium on the incident side), AilnP, AlGaAs and
`AlAs is appropriate for the material, particularly.
`Similarly in case that the medium on the incident side is
`AlGaAs, any one of AlGanP, AlInP, AlGaAs (where, the
`alloy composition ratio of Al thereof is larger than that of the
`medium on the incident side) and AlAs is appropriate for the
`material, particularly. Further, in case that the medium on the
`incident side is ZnSe or ZnSSe, either ZnCdS or ZnMgSSe
`is appropriate for the material. In case that the medium on
`the incident side is ZnMgSSe, ZnMgSSe where the alloy
`composition ratio of Mg or S thereof is larger than that of the
`medium on the incident side is appropriate for the material.
`Also, in case that the medium on the incident side is GaAsP,
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`any one of GaP, GaAsP where the alloy composition raio of
`P thereof is larger than that of the medium on the incident
`side, and AlGaAs is appropriate for the material, particu
`larly. Again, in case of the medium on the incident side of
`AlGainN, AlGalnN where the alloy compound ratio of Al
`thereof is larger than that of the medium on the incident side
`or the alloy composition ratio of Inis smaller than that of the
`medium is appropriate.
`Note, although the accurate refractive indexes have not
`been known for all of the above materials, a material of a
`large bandgap generally has a lower refractive index. Par
`ticularly, in the III group elements of the III-V group
`semiconductors, the larger the material has a composition
`ratio of the element Ga rather than the element. In and
`furthermore, a composition ratio of the element Al rather
`than the element Ga, the smaller the refractive index thereof
`exhibits. Also, in the V group elements, the larger the
`material has a composition ratio of the element Prather than
`the element. As and furthermore, a composition ratio of the
`element N rather than the element P, the smaller the refrac
`tive index thereof exhibits. Similarly, also in the II group
`elements of the II-VI group semiconductors, the larger the
`material has a composition ratio of the element Zn rather
`than the element Cd and furthermore, a composition ratio of
`the element Mg rather than the element Cd, the smaller the
`refractive index thereof exhibits. Alternatively, in the VI
`group elements, the larger the material has a composition
`ratio of the element Se rather than the element Te and
`furthermore, a composition ratio of the element S rather than
`the element Se, the smaller the refractive index thereof
`exhibits. Similarly, also in the VI group semiconductors,
`such as SiC, SiGe etc., the larger the material has a com
`position ratio of the element Si rather than the element Ge
`and furthermore, a composition ratio of the element Crather
`than the element Si, the smaller the refractive index thereof
`exhibits.
`The above-mentioned total reflection layers are suitable
`for the light-emitter radiating the light from side surfaces
`thereof. FIG. 6A shows a schematic view in case of radiating
`the light from the top surface, while FIG. 6B shows a
`schematic view in case of radiating the light from the side
`surfaces. Among light radiating from a point P in FIG. 6A,
`a component of light radiating from the top surface is
`restricted by the total reflection at the top surface to thereby
`occupy only a circular area 6. The ratio of the solid angle of
`the radiative light to the whole solid angle is 5.1%.
`On the other hand, as shown in FIG. 6B, the light emitting
`from a point Q on a central axis of a cylindrical body radiates
`from an area 7 of a side surface of the cylindrical body taken
`along two parallel surfaces in the cylindrical body. The ratio
`of the solid angle of the radiative light to the whole solid
`angle is 44.1%. In this way, it is understood that the solid
`angle of the light radiating from the side surface is over
`whelmingly larger than that of the light radiating from the
`top surface.
`In order to radiate from the side surface, however, it is
`necessary to either thicken a transparent area sufficiently or
`reflect the light incident obliquely on a substrate so that the
`light beam emitting at a center of the body can reach the side
`surface without being absorbed by the substrate.
`If the above-mentioned total reflection layer is used, it is
`possible to guide the light beam emitting at a center of the
`body up to the side surface, without excessively thickening
`the transparent area. Further, if the above total reflection
`layer is provided on not only the lower part of the emitting
`layer but the upper part thereof, it is possible to guide the
`light, which would travel toward the upper part and which
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`would be absorbed in the vicinity of the electrode, to the side
`surface.
`There is a case that the light reflected by the total
`reflection layer is absorbed into the light emitting layer
`again. Different from a case that the light is absorbed into the
`substrate etc., such a phenomenon can contribute to emitting
`again. As mentioned before, such an effect is called the
`photon recycle effect. The photon recycle effect exists in
`both the light-emitting diode and the semiconductor laser.
`Particularly, in the semiconductor laser, the threshold cur
`rent for oscillation can be reduced.
`Since the light can be extracted from the side surfaces
`mainly in this way, the semiconductor light emitter accord
`ing to the present invention is especially suitable for such an
`application that the LED chips of the invention are mounted
`laterally on the printed board. According to this mounting
`form, since the chips are electrically connected to the printed
`board without wire-bonding, the process of connecting
`becomes simple and the reliability of electrical connection
`can be improved.
`On the other hand, since the semiconductor light emitter
`of the present invention is so constructed as mentioned
`above, it is also suitable for an application as the semicon
`ductor laser. FIG. 7 shows a schematic diagram of an
`arrangement of the light radiated from the top surface or the
`side surface of the semiconductor light emitter employed in
`the present invention. With reference to FIG. 7, it shall now
`be described of a fact that the stereographic angle which the
`oblique light occupies is overwhelmingly larger in compari
`son with that of the vertical light. The stereographic angle of
`0 to 0, which is shown with G close to the vertical
`direction, is expressed by the equation:
`
`2.
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`9
`
`sinödö= 2 (1 - cose) as 2E 0/2
`O
`
`where, the above approximate equation is effected when the
`angle 0 is sufficiently smaller than 1.
`On the other hand, the stereographic angle of TL/2-0 to TE/2,
`which is shown with H close to the horizontal direction, is
`expressed by the equation:
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`laser guides the light by the total reflection at the boundary
`surface between the active layer and the cladding layers to
`thereby attain the laser oscillation. On the contrary, the total
`reflection layer of the present invention is arranged outside
`the cladding layer to operate to return the light the active
`layer to the active layer again. Since the total reflection layer
`is arranged in the area where the waveguide light does not
`reach, it is easy to distinguish the total reflection layer from
`the cladding layer.
`BRIEF DESCRIPTION OF THE DRAWING
`FIG. 1 is a cross-sectional view showing a conventional
`LED;
`FIG. 2A is a perspective view showing an example of a
`LED chip used in a conventional lateral mounting method;
`FIG. 2B is a front cross-sectional view of the LED chip
`of FIG. 2A, to which the lateral mounting method is applied;
`FIG. 3 is a cross-sectional view showing a conventional
`semiconductor laser;
`FIG. 4 is a schematic cross-sectional view showing a
`relationship among a light beam, a side surface and a
`reflection layer, in order to describe an operation of the
`present invention;
`FIG. 5 is a diagram showing a relationship between a
`reflectivity R and the thickness d of the reflective layer, in
`order to describe the operation of the present invention;
`FIG. 6A is a schematic view showing a stereographic
`angle of a light radiated from an upper surface of an emitter,
`in order to describe the operation of the present invention;
`FIG. 6B is a schematic view showing a stereographic
`angle of a light radiated from a side surface of the emitter,
`in order to describe the operation of the present invention;
`FIG. 7 is a schematic view showing the light radiated
`from the upper surface or the side surface of the emitter, in
`order to describe the operation of the present invention;
`FIG. 8 is a cross-sectional view of a AlGalnP type LED
`in accordance with the first embodiment of the present
`invention;
`FIG. 9 is a top view in which the LED chips of FIG. 8 are
`laterally mounted in a matrix pattern;
`FIG. 10 is a top view of a AlGalnP type of LED in
`accordance with the second embodiment of the present
`invention;
`FIG. 11 is a cross-sectional view of the LED of FIG. 10;
`FIG. 12 is a cross-se