United States Patent 19 (11) 3,925,121 Touchy (45) Dec. 9, 1975

54 PRODUCTION OF SEMCONDUCTIVE 3,255,056 6/1966 Flatley et al...... 148/9 X MONOCRYSTALS OF GROUP -V 3,298,879 lf 1967 Scott et al...... 148? 87 3,408,238 10, 1968 Sanders...... 148/190 X SEMCONDUCTOR COMPOUNDS 3,422,322 171969 Haisty...... 48/190 X 75) Inventor: Wolfgang Touchy, Munich, 3,502,518 3/970 Antell...... 148/190 X Germany 3,537,921 1 / 1970 Boland...... 48/89 X 1. y 3,660, 156 5? 1972 Schmidt...... 48/89 X (73) Assignee: Siemens Aktiengesellschaft, Berlin & 3,660, 78 5, 1972 Takahashi et al...... 148,189 Munich, Germany 22) Filed: Mar. 8, 1973 Primary Examiner-G. Ozaki Attorney, Agent, or Firm-Hill, Gross, Simpson, Van (21) Appl. No.: 339,218 Santen, Steadman, Chiara & Simpson (44. Published under the Trial Voluntary Protest Program on January 28, 1975 as document no. 57 ABSTRACT B 339,218. Semiconductor monocrystals composed of Group (30) Foreign Application Priority Data III-V compounds such as GaAs having a p-conductive layer therein are produced by masking a surface of a Mar. 23, 1972 Germany...... 224224. Group III-V monocrystal with a protective layer com posed of a material, such as silicon dioxide which al (52) U.S. Cl...... 148/189; 1481 i 87; 148719 l; lows Group III elements to diffuse through the layer 252/62.3 GA; 357/30 while preventing diffusion of Group V elements, sub 5 Int. Cl’...... HOL 7/44 jecting the masked monocrystal to a heat treatment in (58) Field of Search ...... 148,189, 87, 190, 191, a gaseous atmosphere so as to remove some of the 148/188; 252/62.3 GA Group III atoms from the monocrystal and then dop ing the treated monocrystal with an element of Group 56 References Cited II, such as Zn. UNITED STATES PATENTS 3.245,847 4f 1966 Pizzarello...... 48/89 X 8 Claims, No Drawings 3,925, 121 1 2 hydrogen, at a temperature sufficient for Group III ele PRODUCTION OF SEMCONDUCTIVE ments to diffuse from the monocrystal and through the MONOCRYSTALS OF GROUP III-V protective layer, such as in the range of about 500 to SEMICONDUCTOR COMPOUNDS 1,000°C for about 1 to 5 hours and then doping the so treated monocrystal with a Group II element, such as BACKGROUND OF THE INVENTION ZC. 1. Field of the Invention The invention relates to monocrystal semiconductors DESCRIPTION OF THE PREFERRED and more particularly to production of Group III-V EMBODIMENTS semiconductor monocrystals having a p-conductive O The invention provides an economic process for pro layer therein for use as electro-luminescent semicon ducing Group III-V semiconductor compound mono ductor components. crystals having a p-conductive layer therein whereby 2. Prior Art some of the Group III element atoms within a Group Electro-luminescent semiconductor components, III-V compound monocrystal are replaced with Group such as LEDs (light emitting diodes), coupling ele 15 II element atoms. ments and the like require a p-n junction in the crystal In accordance with the principles of the invention, of the semiconductor material. the process generally comprises covering or masking It is known to produce p-n junctions for luminescent the surface of a Group III-V semiconductor compound diodes in semiconductor crystals which have been monocrystal with a protective layer such that the ele doped with elements having donor properties, such as 20 ments of the third group of the Periodic System within sulphur, selenium or tellurium by the subsequent diffu the semiconductor compound are able to diffuse sion of zinc and/or cadmium atoms into the crystal. through the protective layer upon heating of the mono However, diodes produced in this manner are unsuited crystal, heating the monocrystal in a gaseous atmo for prolonged operations, since they have been operat sphere under time-temperature conditions enabling a ing for a period of several thousand hours, a drop in 25 portion of the Group III element to diffuse from the power of more than half of the original value of the monocrystal through the protective layer and then dop emitting radiation may take place. ing the so-treated monocrystal with an element of the It is known that acceptor atoms located at interstitial second group of the Periodic System. positions in a crystal travel under the influence of their The semiconductor material that are processed in ac own radiation and cause a non-radiating recombination 30 cordance with the principles of the invention to pro so that the electrical properties of semiconductor com duce electro-luminescent components are selected ponents containing such atoms vary constantly. This from monocrystals of binary Group III-V semiconduc disadvantage can be overcome, as disclosed by me in tor compounds, such as gallium arsenide (GaAs), gal German Offenlegungsschrift 2,010,745, by pulling an lium nitride (GaN), and boron phosphide (BP) and n-conductive gallium arsenide monocrystal under an 35 from monocrystals of tertiary or quaternary semicon increased arsenic vapor pressure. The resultant gallium arsenide monocrystal has a higher arsenic content than ductor compounds, such as gallium aluminum arsenide the stoichiometric composition and has gallium vacan (GaAl)As), gallium arsenide phosphide Ga(AsP)), cies in the crystalline structure. A subsequent diffusion indium gallium phosphide (InGa)P), indium alumi of acceptor atoms thus takes place primarily via the 40 num phosphide (InAl)P, aluminum gallium phos gallium vacancies and not via the interstitial positions. phide (AlGa)P), gallium indium arsenide (Galin)As), However, the known process for producing gallium ar indium aluminum arsenide (InAl)As), gallium alumi senide monocrystals having an excess of arsenic are ex num arsenide phosphide (GaAl)(AsP)), and/or gal tremly economical, particularly when monocrystals of lium aluminum nitride phosphide (GaAl)(NP). 45 The protective layer utilized in the practice of the in large diameter are desired. vention may be of any of the conventional masking lay SUMMARY OF THE INVENTION ers utilized in semiconductor technology. However, the The invention provides a method of treating Group protective layer selected must allow Group IIl elements III-V semiconductor monocrystals so as to render them to diffuse through it while stopping Group V elements. useful as electro-luminescent semiconductor compo 50 In an exemplary embodiment, a protective layer nents whereby the semiconductor material is doped composed of silicon dioxide and having a thickness in with a Group II element so that the atoms thereof are the range of about 500 to 1500A has been found to be incorporated at gallium vacancies of the monocrystal. particularly effective. However, a protective layer may It is a novel feature of the invention to produce a also be formed of aluminum oxide, silicon nitride, Group III-V semiconductor compound monocrystal 55 phosphorus pentoxide or a mixture thereof, such as of having a p-conductive layer therein by masking the sur silicon dioxide and phosphorus pentoxide, in a thick face of a semiconductor compound monocrystal, such ness adapted to the permeability of the individual ele as composed of binary, tertiary or quarternary Group ments. For a given layer thickness, protective layers III-V compounds, for example GaAs, (GaAl)As, or composed of silicon dioxide diffusion doped with zinc (GaAl)(AsP) with a protective layer composed of a 60 atoms are most permeable; next in permeability are material that allows elements of Group III to diffuse protective layers composed of silicon dioxide, then therethrough upon heating the monocrystal, while pre those composed of phosphorus pentoxide, aluminum venting elements of Group V from diffusing from the oxide and silicon nitride. monocrystal, such as a material selected from the The time-temperature for heat treatment conditions group consisting of silicon dioxide, aluminum oxide 65 for out-diffusion of Group Ill element atoms from the and mixtures thereof; heat-treating the masked semi masked monocrystals include temperatures in the conductor monocrystal in a suitable gaseous atmo range of about 500 to 1,000°C and time periods rang sphere, such as composed of a mixture of nitrogen and ing from about 1 to 5 hours. 3,925,121 3 4 The Group II element utilized to dope the heat source and a gaseous atmosphere composed of treated semiconductor crystal is preferably selected about 80% by volume of hydrogen and about 20% from the group consisting of cadmium, magnesium, by volume nitrogen; and zinc and mixtures thereof. subjecting the coated semiconductor monocrystal to An exemplary embodiment of the invention will now time-temperature conditions comprising heating be described in somewhat more detail to illustrate fur the coated monocrystal at a temperature in the ther the principles of the invention. range of about 500 to 1,000 C. for a period of A gallium arsenide wafer is prepared, such as by time ranging from about 1 to 5 hours whereby the treatment with a suitable polishing agent and a protec Group III element of the Group III-V compound tive layer of silicon dioxide is applied over the entire diffuses out of the monocrystal through the protec surface thereof. The protective layer may be applied in tive layer and the Group II element diffuses into the various ways, sputtering processes, both reactive sput monocrystal through the protective layer. tering and high frequency sputtering are particularly 2. A method as defined in claim 1 wherein the semi useful, also pyrolysis processes involving the decompo conductor monocrystal is composed of a Group III-V sition of, for example, silicon hydrides or organic sili 15 compound selected from the group consisting of con compounds are also useful. The coated semicon (GaAs), (GaN), (BP), (GaAl)As), Ga(AsP)), (In ductor wafer is then heated at a temperature of about Ga)P), (InAl)P), (AlGa)P), (Gain)As), (InAl 700 to 900C in a gas atmosphere, such as one consist )As), (GaAl)(AsP) and (GaA)(NP). ing of 80 percent by volume hydrogen and 20 percent 3. A method as defined in claim 1 wherein the Group by nitrogen. During the heat treatment, which prefera II element utilized to dope the treated monocrystal is bly lasts for about two hours, gallium atoms diffuse out selected from the group consisting of cadmium, magne of the crystal and through the silicon dioxide layer. sium, zinc and mixtures thereof. However, arsenic atoms are stopped from leaving the 4. A method as defined in claim 1 wherein the treated crystal by the protective layer. monocrystal is doped with zinc. The so-treated semiconductor wafer is then doped 25 5. A method as defined in claim 4 wherein the zinc is with a Group II element, for example zinc in accor dance with various doping techniques. A diffusion obtained from a diffusion source selected from the source utilized in an in-diffusion process may be ele group consisting of elemental zinc in an atmosphere mental zinc in an atmosphere containing arsenic or be containing arsenic, zinc arsenide in an atmosphere con zinc arsenide, again in an atmosphere containing ar 30 taining arsenic, a liquid alloy of zinc, and a mixture of senic, or be a liquid alloy of zinc. Further, it is also pos organic zinc compounds and organic silicon com sible to utilize a paint-on or spin-on process, with a mix pounds. ture of organic zinc and organic silicon compounds as 6. A method as defined in claim 1 wherein the semi the diffusion source. conductor monocrystal is composed of gallium arse The out-diffusion of, for example gallium atoms and 35 mide, the protective layer is composed of silicon dioxide the in-diffusion of, for example zinc atoms can be ef and the time-temperature conditions comprise heating fected simultaneously, if desired. With simultaneously said monocrystal at a temperature in the range of about in and out diffusion of this type, a semiconductor wafer 700 to 900°C for a period of time ranging from about is coated with a protective layer and placed in an am l to 2 hours. pule containing vaporized zinc arsenide and subjected 40 7. A method of producing a semiconductor mono to the heat treatment outlined above. crystal composed of gallium arsenide having a p-n con As is apparent from the foregoing specification, the ductive layer therein, comprising the steps of present invention is suceptible of being embodied with covering the surface of a gallium arsenide wafer with various alterations and modifications which may differ a layer of silicon dioxide having a thickness of particularly from those that have been described in the 45 about 500 to 1,500 A; preceeding specification and description. For this rea placing a zinc diffusion source adjacent to the coated son, it is to be fully understood that all of the foregoing wafer and sealing the space about said diffusion is intended to be merely illustrative and is not to be source and coated wafer, and construed or interpreted as being restrictive or other subjecting the sealed space to a heat treatment in wise limiting of the present invention, excepting as set 50 cluding temperatures in the range of about 700 C. forth and defined in the hereto-appendant claims. to 900 C. for a period of time ranging from about I claim: 1 to 5 hours; 1. A method of producing a semiconductor mono whereby at least some of the gallium of the wafer dif crystal composed of Group III-V compounds and hav fuses out of said wafer through the silicon dioxide ing a p-conductive layer therein, comprising the steps 55 layer and at least some of the zinc diffuses into said of, wafer through the silicon dioxide layer. covering the surface of a monocrystal composed of a 8. A method as defined in claim 7 wherein the coated Group III-V compound with a protective layer wafer is placed in an ampule containing vaporized zinc composed of a material that allows Group III ele and arsenic prior to being subjected to the heat-treat ments to diffuse therethrough and selected from 60 ment and then subjecting the coated wafer to said heat the group consisting of silicon dioxide, aluminum treatment for substantially simultaneous out-diffusion oxide and mixtures thereof; of gallium from said wafer and in-diffusion of zinc into sealing the coated semiconductor monocrystal in an said wafer. ampule containing a Group II element diffusion k 65