US006043509A United States Patent [19] [11] Patent Number: 6,043,509 Kurihara et al. [45] Date of Patent: Mar. 28, 2000 [54] LIGHT-EMITTING DIODE HAVING 5,061,643 10/1991 Yagi ............ .. 438/46 MOISTURE-PROOF CHARACTERISTICS 5,093,696 3/1992 Kinoshita .... .. 372/46 AND HIGH OUTPUT POWER 5,491,350 2/1996 Unno et al. ............................. .. 257/99 [75] Inventors: T00ru Kurihara; Toshiya Toyoshima; FOREIGN PATENT DOCUMENTS Seiji Mizuniwa; Masahiro Noguchi, 5-63235 3/1993 Japan . all of Ibaraki-ken, Japan 5-243611 9/1993 Japan . 6-252444 9/1994 Japan . [73] Assignee: Hitachi Cable, Ltd., Tokyo, Japan 7-30150 1/1995 Japan . 7-38150 2/1995 Japan . [21] Appl. No.: 09/201,835 Primary Examiner—Minh Loan Tran [22] Filed: Dec. 1, 1998 Attorney, Agent, or Firm—McDermott, Will & Emery Related US. Application Data [57] ABSTRACT ALight-emitting diode having improved moisture resistance Division of application No. 08/766,867, Dec. 13, 1996, Pat. characteristics comprises a p-type gallium arsenide substrate No. 5,888,843. and four epitaxial layers of AlxGa1_xAs (22, 23, 24 and 25). Int. Cl.7 ................................................... .. H01L 29/06 These epitaxial layers comprises an intervening layer (22) of US. Cl. ............................... .. 257/13; 257/94; 257/96; p-type Alx1Ga1_x1As, a cladding layer (23) of p-type 257/103 Alx2Ga1_x2As, an active layer (24) of Alx3Ga1_x3As, and a Field of Search ................................ .. 257/12, 13, 94, Window layer (25) of Alx4Ga1_x4As so as to form a double 257/96, 103, 79 hetero structure, Where X1, X2, X3 and X4 represent miXed crystal ratios of aluminum to arsenic of the layers, References Cited respectively, and meet the condition that: U.S. PATENT DOCUMENTS 4,592,791 6/1986 Nakajima et al. 448/171 4,944,811 7/1990 Sukegawa et al. ..................... .. 438/46 4 Claims, 3 Drawing Sheets 25 WINDOW LAYER (II-TYPE Alx4 Got-X4 AS) 24 ACTIVE LAYER , (p-TYPE Am (am-X3 As) \. \ 23 CLADDING LAYER (p-TYPE Alxz (Eda-x2 AS) 22 lNTERVENlNG LAYER (p-TYPE Alx1 (Sm-x1 As) 21 SUBSTRATE (p-TYPE 60 As) U.S. Patent Mar. 28,2000 Sheet 1 of3 6,043,509 FIG. I PRIOR ART 14 wmnow LAYER "J (n-TYPE Aim 00-03 As) ~“W'YEELLYERG P‘ m (Ix-x22 A)s \ l2 CLADDING LAYER (p-TYPE Alxn Gm-xu AS) 11 SUBSTRATE (p-TYPE 60 A5) FIG.2 25 WINDOW LAYER (fl-TYPE Alx4 GG1-X4 AS) 24 ACTIVE LAYER (D-TYPE Alxa Goa-x3 AS) \ 23 CLADDING LAYER (p-TYPE Alxz G?a-xz AS) 22 INTERVENING LAYER (p-TYPE Alx1 Sch-x1 As) 21 SUBSTRATE (p-TYPE 60 As) U.S. Patent Mar. 28,2000 Sheet 2 of3 6,043,509 F / G . 3 23 CLADDING CONDUCTION BAND LAYER m.VIA.D. EVMD. mmxn 2 2 V m 6 V1,||||| FNE1|llll 4TIVI ml.TA EY RH C MIll: N D 2 4 E NH 2 5 WLINIA DY 0H w F/6.5 vm.vM O.0. 4206 z552325DEE F_L w“A.- L. 2 I0 w- 5l o 6I O DISTANCE FROM SURFACE (11m) U.S. Patent Mar. 28,2000 Sheet 3 of3 6,043,509 F [6‘ - 4A 34 ADDITIONAL 52 FIRST ,SOURCE RECEPTACLE 33 sEOOND ; 3O ADDITIONAL RECEPTACLE H 1 gm SOURCE H [ HOLDER 1 , \ hr‘ i ' j ,‘ \\ F \35 SUBSTRATE 3? SECOND 31 SUBSTRATE 36 FIRST GROWTH HOLDER GROWTH MELT MELT 37 35 31 36 6,043,509 1 2 LIGHT-EMITTING DIODE HAVING acteristics thereof are improved While high output poWer MOISTURE-PROOF CHARACTERISTICS thereof is maintained. AND HIGH OUTPUT POWER It is a further object of the invention to provide a method of manufacturing a light-emitting diode in Which the process This application is a divisional of application Ser. No. becomes easier and more cost-effective. 08/766,867 ?led Dec. 13, 1996 now US. Pat. No. 5,888,843. According to the ?rst feature of the invention, a light emitting diode having a plurality of hetero-junctions of BACKGROUND OF THE INVENTION aluminum gallium arsenide, compromise: a substrate of p-type gallium arsenide; This invention relates to a light-emitting diode and a an intervening layer of p-type Alx1Ga1_x1As formed on method of manufacturing the same, and more particularly to, the substrate; a light-emitting diode having a hetero-junction of aluminum a cladding layer of p-type Alx2Ga1_x2As formed on the gallium arsenide structure and a method of manufacturing intervening layer; the same. an active layer of p-type Alx3Ga1_x3As formed an the Compound semiconductor materials, such as gallium ars 15 cladding layer; and enide and aluminum gallium arsenide (AlxGa1_xAs), have a WindoW layer of n-type Alx4Ga1_x4As formed on the been Widely used as a semiconductor light source, e.g., a active layer; light-emitting diode, etc. by utiliZing their light-emitting Wherein x1, x2, x3 and x4 represent mixed crystal ratios function. For example, light-emitting diodes are made from of aluminum to arsenic of the layers, respectively, and meet the condition that: a Wafer Which comprises a p-n junction formed by a plurality 20 of epitaxial layers groWn on a single crystal substrate by Liquid Phase Epitaxy (LPE), Metal Organic Vapor Phase Epitaxy (MOVPE), etc. According to the second feature of the invention, a A conventional light-emitting diode having a double method of manufacturing a light-emitting diode having a plurality of hetero-junctions of aluminum gallium arsenide hetero structure of AlxGa1_xAs (Oéxé 1) layers comprises a 25 p-type gallium arsenide substrate, and three epitaxial layers layers, comprises the steps of: of AlxGa1_xAs, Which are a cladding layer of p-type epitaxially groWing an intervening layer on a substrate of gallium arsenide from a ?rst groWth melt doped With at Alx11Ga1_x11As, an active layer of Alx22Ga1_x22As, and a least one p-type dopant; WindoW layer of Alx33Ga1_x33As. These epitaxial layers are epitaxially groWing a cladding layer on the intervening formed on the substrate, in order, by groWing from three 30 layer from a second groWth melt doped With less than different groWth malts. In this case, the mixed crystal ratios a predetermined amount of dopant; of aluminum to arsenic x11, x22, x33 of the layers meet the epitaxially groWing an active layer on the cladding layer condition that: from the ?rst groWth melt; and epitaxially groWing a WindoW layer on the active layer 35 from the second groWth melt, the second groWth melt being subsequently doped With at least one n-type While the ratio x22 may be determined depending on a dopant after the groWth of the intervening layer, the desired Wavelength, the ratios x11 and x33 are preferably dopant being suf?cient to turn the type of conductivity determined so that the differences betWeen x11 and x22, and of the second groWth melt into n-type; 40 betWeen x33 and x22, i.e. x11-x22 and x33-x22 are as large Wherein the at least one p-type dopant in the cladding as possible, in vieW of making injection of minority carriers layer is thermally diffused from the intervening layer more efficient by the hetero junction structure, and facili by subsequent epitaxial groWths of the active layer and tating recombination of injected carriers caused by the the WindoW layer so as to invert the initial type of con?nement of the carriers. conductivity of the cladding layer to p-type. For particular light-emitting diodes, such as a light BRIEF DESCRIPTION OF THE DRAWINGS emitting diode lamp, the output poWer of such light-emitting The invention Will be explained in more detail in con diodes is preferably higher than that of other types of diodes. junction With the appended draWings, Wherein: To obtain these characteristics, the aforementioned mixed FIG. 1 is a cross-sectional vieW shoWing a conventional crystal ratios of aluminum to arsenic x11 and x33 are epitaxial Wafer used for a light-emitting diode, necessarily higher. In the conventional light-emitting diode, FIG. 2 is a cross-sectional vieW shoWing an epitaxial hoWever, there is a disadvantage in that such light-emitting Wafer used for a light-emitting diode in a preferred embodi diodes having higher mixed crystal ratios of aluminum to ment according to the invention, arsenic are more likely to be deteriorated under a highly FIG. 3 is a diagram shoWing a band structure for the moist environment. Because the higher the mixed crystal preferred embodiment according to the invention, ratios of the epitaxial layers are, the more likely the epitaxial FIGS. 4A, 4B, 4C, 4D and 4E are How diagrams shoWing layers are to be oxidiZed under the environment. To solve a method of manufacturing the epitaxial Wafer in a preferred this problem, for example, the light-emitting diode chip may embodiment according to the invention, and be molded by a particular resin material having loW moisture FIG. 5 is a graph shoWing a pro?le of mixed crystal ratio absorption characteristics. HoWever, such a measure is still of aluminum to arsenic in the epitaxial Wafer manufactured insuf?cient, because since a thinner layer of molding resin is by the method according to the invention. required for a thin light-emitting diode lump, the more DESCRIPTION OF THE PREFERRED limited environments it can be applied to. EMBODIMENTS SUMMARY OF THE INVENTION Before explaining a light-emitting diode according to the 65 ?rst preferred embodiment, the aforementioned conven Accordingly, it is an object of the invention to provide a tional light-emitting diode Will be explained With reference light-emitting diode in Which the moisture-resistance char to FIG. 1. 6,043,509 3 4 FIG. 1 shows the conventional epitaxial Wafer used for a that of cladding layer 23 As a result, oXidation under conventional light-emitting diode.