Abstract:
An hermetic seal at a smooth interface between a gallium arsenide body and a glass body is effected without organic or inorganic binders by thermally bonding the bodies at the interface while ensuring that the oxygen concentration at the interface is so low that there is no optically detectable variations in color of the gallium arsenide close to the interface.

Description:
TECHNICAL FIELD 
     The present invention relates to the production of an hermetic seal between a gallium arsenide component (GaAs) and a glass body at an interface where irregularities larger than 0.1 μm and smaller than 100 μm have been removed. 
     In the current rapid progress of semiconductor electronics, gallium arsenide has met with a growing interest, primarily because of the following material properties: 
     Its direct band gap permits efficient electrooptical transformation of energy, which is utilized in photodiodes, light-emitting diodes, laser diodes and optical sensors. 
     The high mobility of its charge carriers, which can be utilized in the band widths in analog and digital electronics. 
     It ready alloyability, for example Al x  Ga 1-x  As, which makes it possible to provide &#34;tailored&#34; material parameters such as band gap and etching ability in different processes. 
     DISCUSSION OF PRIOR ART 
     During the manufacture of opto-components based on GaAs, conventional methods for the protective enclosing of the GaAs are usually employed. Typically the body of GaAs is sealed into a metal capsule provided with glass windows for the necessary optical connection to and from the GaAs body. In some cases the capsule is provided, in addition, with lens elements for the more efficient coupling of the GaAs body to an optical fiber (see Swedish patent application No. 8203597-3). These known methods for packaging the GaAs are not fully satisfactory due to the low attainable degree of miniaturization possible using the method and due to the fact that such methods are expensive and usually constitute a predominant part of the total production costs of the opto-component. 
     OBJECTS OF THE INVENTION 
     One object of the invention is to provide an improved method of hermetically bonding gallium arsenide and glassy bodies so that traditional hermetic enclosures can be dispensed with. 
     A further object is to provide a cheaper gallium arsenide opto-component which has an integral optical member such as a lens or an optical fiber. 
     Other objects and advantages of the invention will be apparent from the following. 
     SUMMARY OF THE INVENTION 
     According to the invention a sealing between a gallium arsenide component and a glass body is characterized in that the interface, cleaned from organic and/or inorganic binders, and exhibiting no optically detectable tints or variations in color on the gallium arsenide side, is formed in such a way that the concentration of oxygen on the glass side is considerably lower than the stoichiometric concentration for oxides, formed by gallium and arsenic. Suitably the low oxygen concentration in the glass body extends at least a distance of 10 microns into the glass body from the interface. Variations of color of GaAs indicate oxidation of GaAs and it has been found that oxidation causes problems with the adhesion of the bodies at the interface. Oxidation has been avoided through the method of the invention for example by thermally bonding in a reducing atmosphere, for example a gas mixture of hydrogen gas and nitrogen gas, and by deliberately depleting the oxygen surplus normally occurring in a glass body. A seal according to the invention makes it possible to produce more miniaturized opto-components as well as cheaper opto-components based on gallium arsenide. 
     Basically the invention involves enclosing the GaAs component by directly sealing it to a glass surface. A suitable method for effecting the seal can be that described in U.S. Pat. No. 3,577,629, modified to take account of the special requirements imposed by the use of GaAs material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be exemplified in greater detail in the accompanying drawings, in which: 
     FIGS. 1a and 1b show how a GaAs component can be sealed to one end of an optical fiber, 
     FIG. 2 shows the use of the invention to enclose a GaAs component having electrical leads, 
     FIG. 3 shows an embodiment of opto-component in which a glass lens body is sealed directly to a GaAs component, 
     FIG. 4 shows an optical pressure-measuring device, comprising an optical fiber and a bonded-on piece of gallium arsenide, and 
     FIG. 5 illustrates one method of effecting the hermetic sealing according to the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1a shows how a GaAs body 1 can be hermetically sealed to one end surface 2 of an optical fiber 3. Creation of a good seal requires the intermediate surface or interface 4 between the fiber 3 and the GaAs body 1 to be plane polished to an optical quality finish, i.e., irregularities larger than 0.1 μm are removed. In FIG. 1a the interface 4 is plane, but this is not necessary. The macroscopic surface structure of the interface 4 may deviate somewhat from planeness (irregularities smaller than 100 μm have also been removed). This is illustrated in FIG. 1b, in which the end surface 2 of the fiber 3 has been made somewhat convex and the GaAs body 1 is thereby subjected to a certain flexural stress during its bonding in place. Another important characteristic for a good bond is that the intermediate surface 4 has no optically detectable variations in color. These color variations occur as a result of oxidation of the GaAs surface. Because of the low adhesion of the oxide of the parent (mother) crystal, the presence of oxide at the interface leads to an inferior bond. The concentration of oxygen in the glass body should therefore be considerably lower than the stoichiometric concentration for oxides, formed by gallium and arsenic at least within a volume between the intermediate surface 4 and a distance therefrom which is not smaller than 10 microns. Another feature of a bond according to the invention is that no organic or inorganic binders are used at the intermediate surface 4. However, the GaAs body may in itself contain dopants or alloying additives, such as the previously-mentioned aluminum additive. 
     One embodiment of opto-component in accordance with the invention may involve using the bond of this invention on the GaAs body of the fiber optical temperature sensor described in U.S. patent application Ser. No. 194,397, filed Oct. 6, 1980, now U.S. Pat. No. 4,376,890 having at least one photo-luminescent region. Another opto-component on which the bonding method of this invention can be employed is a so-called photo-luminescence diode as described in U.S. patent application Ser. No. 275,789,  filed June 22, 1981, now U.S. Pat. No. 4,417,140, possibly also containing active electrical circuit elements. 
     FIG. 2 shows the enclosure of a GaAs body 5 with electrical leads 6, 7, by fusing the body 5 to a plane-polished surface 9 of a glass body 8. The active region 10 of the body 5 is fully protected by the glass on one side, the parent crystal on the other side and the hermetic bond in the plane of the interface 11. The interface 11 has the characteristic properties already described above for the intermediate surface 4 in FIG. 1a. Electrical connection surfaces 12, 13 may be provided at the interface 11 by means of thin metallic coatings, for example forming an alloy with the GaAs crystal and the connections 6, 7. 
     FIG. 3 shows an embodiment in which a glassy body 14, hermetically sealed to a GaAs body 15, forms an optical lens element. Light emanating from the body 15 is focused at a point 17 by reason of the convex limit surface 16 in accordance with the normal optical laws for converging lenses. 
     FIG. 4 shows an optical pressure-measuring device, comprising an optical fiber 3 and a gallium arsenide body 1 defining an elastic diaphragm 26. The diaphragm separates an evacuated or gas-filled volume 25 from the region 27 where the pressure to be measured acts. The diaphragm 26, in a preferred embodiment, is arranged to emit photo-luminescence in at least one wavelength interval, and deflections of the diaphragm on pressure changes in the region 27 alter the amount of luminescent light coupled into the fiber 3. 
     FIG. 5 shows one method of implementing a hermetic seal according to the invention. A GaAs body 18 and a glass body 19 have been provided with electrical connections 20, 21 so that a high voltage (e.g. 500 to 1000 volts DC) is applied across them. The bodies 18, 19 have been placed in a container 22, which is purged by a reducing gas, for example, a mixture of hydrogen gas and nitrogen gas. The container 22 is provided with a heating device 23, by means of which the glass body 19 and the GaAs body 18 can be heated to a temperature of 400° C. A temperature regulator 24 is provided for controlling the power supplied to the heating device 23. 
     The method according to FIG. 5 differs from the method described in U.S. Pat. No. 3,577,629 by the use of a reducing atmosphere. To speed up the processing and to facilitate the bonding together of the two bodies, the glass body 19 may be depleted of surplus oxygen prior to putting it in the container 22, by storing the glass body in a reducing atmosphere. It is important to ensure that the oxygen concentration available at the interface, during the bonding operation, is too low to permit any significant oxidation of the GaAs material. 
     Preferably, the coefficient of thermal expansion of the glass body 19 does not deviate significantly from that of GaAs, the expansion of which is 6×10 -6  /°C. A glass quality which satisfies these demands is available on the U.S. market from Corning Glass under their designation number 0211. 
     The invention can be varied in many ways within the scope of the following claims.