CA1088193A - Method of fabrication of optoelectric devices by ion implantation - Google Patents
Method of fabrication of optoelectric devices by ion implantationInfo
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- CA1088193A CA1088193A CA257,941A CA257941A CA1088193A CA 1088193 A CA1088193 A CA 1088193A CA 257941 A CA257941 A CA 257941A CA 1088193 A CA1088193 A CA 1088193A
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Abstract
A METHOD OF FABRICATION OF OPTOELECTRONIC DEVICES BY ION IMPLANTATION At least a binary semiconductor substrate is selected from the group comprising the alloys of the elements of columns II and VI and the alloys of the elements of columns III and V of the Periodic Table of Elements and having a first type of conductivity. One face of the substrate is subjected to ion implantation with impurities which are capable of endowing the substrate with a second type of conductivity to a given depth. A surface layer is removed from the implanted face of the substrate to a depth which has the effect of eliminating the greater part of the defects produced by the implantation but not of eliminating the greater part of the implanted impurities.
Description
This invention relates to a method of fabrication of optoelectronic devices by ion im,plantation.
Optoelectronic devices such as ligh-t emitters or detectors, for example, are usually fabricated from binary or ternary semi~conductor alloys. The operating principle of these devices is based on mechanisms for converting photons to charge carriers in the case of optoelectronic devices which operate as light detectors or on mechanisms for converting charge carriers to photons in the case of optoelectronic devices which operate as light emitters.
The charge carriers in a semiconductor are electrons and holes having properties which are directly related to the nature and the quality of the semiconductor. In particular, in the case of optoelectronic devices, carrier lifetime is a very important parameter which governs the quality of electrical energy to light energy conversion or light energy to electrical energy conversion. As the case may be, said lifetime is dirPctly related to the treatments (ion implanta-tion, annealiny) applied to the semiconductor throughout all stages of manufacture. During the process of preparation of the device, it will therefore be sought to ensure that the lifetime of the charge carriers is not modified to an excessive degree in order to maintain the intrinsic properties of the starting material. ~ ~
One of the most important optoelectronic devices is ,,, the electroluminescent diode in which a light emission is obtained by means of an injection of charge carriers.
At the present time, practically all existing electroluminescent diodes have a base of Type III-V semi-conductors. These are binary or ternary alloys having a base of gallium. Among the alloys which can be mentioned by way .. , , ~ ~
of example are Ga P, Ga As P, Ga ~l As and so forth~
Diodes or diode matrices made from alloys are p-_ junctions in which the substrate is usually of type n and in which an acceptor impurity such as zinc is either diffused or implanted. Another solution makes use of liquid or gaseous epitaxial growth of the p-type layer on the -type substrate.
In point of fact, although III-V semiconductors have reached a very advanced stage of development and fabrication at the present time, they are nevertheless attended by a number of disadvantages, viz:
-they have a base of gallium which is a very costly material, -the theoretical quantum yields are fairly limited, -they are well suited to emission in the red or infrared region but cannot readily be employed for radiative emissions of shorter wavelengths such as green or blue.
On the other hand, there does exist another class of alloys having a base of II-VI elements such as the alloys Zn Te, Zn Se, Cd Te, Mg Zn Te and so forth. Apart from the fact that their cost price is lower than that of the gallium compounds, these alloys result in emissions ranging from the infrared region to the ultraviolet region of the spectrum with very high theoretical ~uantum yields. However, although it is relatively easy to fabricate electroluminescent _-n junctions from the III-V alloys by means of conventional thermal techniques (diffusion, alloying), the intrinsic properties of II-VI semiconductors usually make it essential to have recourse to a method of doping without thermodynamic equilibrium such as ion implantation.
A number of attempts have been made up to the present time with a view to doping semiconductors of the II-VI type or .
.
9~
III-V type by ion implantation in order to produce electro-luminescent devices. As a general rule, the ~uantum yields obtained with the devices thus formed are of a low order. This result is due to the fact that, during ion implantation, a large quantity of defects is created within the semiconductor by the penetrating ion beam. These defects produce non-radiative recombination centers. In consequence, they are liable on the one hand to inhibit the desired doping action and, on the other hand, they reduce the quantum yield of the material. The conventional method of removing these defects consists in annealing the crystal at a temperature which is usually lower than the temperature required for gaseous diffusion. However, in spite of this annealing process, the result produced by the defects is not wholly eliminated and the quantum yield of these diodes remains of low value.
The present invention is precisely directed to a method of fabrication of optoelectronic devices which overcomes the disadvantages mentioned in the foregoing by making it possible in particular to fabricate devices of this type from compounds of the II-VI type while endowing these devices with -substantially higher yields than those obtained by simple ion implantation and annealing.
In a first alternative embodiment, the method of fabrication of optoelectronic devices in accordance with the invention essentially consists in starting from an at least binary semiconductor substrate selected from the group comprising the alloys of the elements of columns II and VI
and the alloys of the elements of columns III and V of the Periodic Table of El~ments and having a first type of conduct-ivity and in carrying out on one of the faces of said substrate an ion implantation with :impurities which are capable of "
endowing said substrate with a second type of conductivity to a given depth, in removiny a surface layer from -the implanted face of said substrate to a dep-th which ls sufficient to permit removal of the greater part of the defects caused by said implantation hut not to permit removal of the greater part of the implanted impurities.
In accordance with a first alternative procedure, thermal annealing of the substrate is carried out prior to removal of the surface layer.
In accordance with a second alternative procedure, thermal annealing is carried out after removal of the surface layer.
In a first mode of execution, the surface layer is removed by ionic abrasion or by chemical attack.
In a second mode of e~ecution, the ion implantation is carried out through a surface layer having a thickness corresponding to the zone of creation of the greater part of the defects and said deposited layer is removed by chemical attack.
In a second alternative embodiment, the method of fabrication of optoelectronic devices in accordance with the invention essentially consists in starting from at least a binary semiconductor substrate selected from the group comprising the alloys of elements of columns II and VI and alloys of elements of columns III and V of the Periodic Table of Elements and having a first type of conductivity, in depositing a layer of material on one of the faces of said substrate, in carrying out an ion implantation wi-th impurities which are capable of endowing said substrate with a second type of conductivity to a predetermined depth, the thickness of said layer of material being such that the greater part of the defects is concentrated in sai.d layer at the time of ion implantation.
Thus in accordance with this second alternative embodiment, the layer in which the defects are concentrated is not removed as in the first alternative embodiment. This layer can be either of metal (aluminum, for example) or of semiconductor material (tin-doped indium oxide In203, for example which is both conductive and -transparent) or of insulating material.
A more complete understanding of the invention will in any case be gained from the following description of a number of embodiments of the invention which are given by way of example and not in any limiting sense, reference being made to the accompanying drawings, wherein:
Figure 1 provides schematic illustrations of the different stages of a first embodiment of the method;
Figure 2 provides schematic illustrations of the different stages of a second embodiment of the method;
Figure 3 is a graph which glves the impurity profile, the defect profile and the quantum yield as a function o~ the depth within the substrate in the case of an implanted layer of Zn Te;
Figure 4 is a graph giving the quantum yield as a function of the abrasion depth.
In the following description, consideration will be given to the case of fabrication of electroluminescent diodes in a substrate of Zn Te. It is readily apparent that the steps of the method would be the same if use were made of substances other than those which have been described in the foregoing.
Fig. 3 shows the curve I which gives the defect, i - 6 -. : ~, - , , .. : , .
. : . . . .
: . . : ' : . :
: . ~: , profile at the time of ion imp:Lantation and the curve II which gives the impurity profile as a function of the depth within the substrate which is plotted as abscissae. An arbitrary unlt is adopted for the axis of ordinates. These curves have been plotted in the case of boron implantation into a Zn Te crystal with an energy of 140 (KeV). It will be noted that the curve which gives the profile of doping with impurities is displaced towards the right, that is to say towards the greater depths with respect to the curve I which gives the concentra-tion of defects.
Fig. 1 shows the different stages of a first alter- -native mode of execution of the method. The starting material consists of a crystal 2 of Zn Te which is polished mechanically and then chemically on its top face 4. This substrate 2 is p-type. Boron ions are introduced by ion implantation so as to form an n-type surface layer 6. In this zone 6, there is found the defeet profile and the impurity concentration proEile which is represented on curves I and II of Fig. 3. In the following stage shown in Fig. lb, the surface layer ~
represented by a ehain-dotted line, is abraded by means of a well-known ionic machining process.
An annealing operation is then carried out, for example at a temperature of 550C for a period of 30 minutes.
As mentioned earlier, this annealing operation is not necessary and can also be performed prior to the abrasion stage.
In order to complete the fabrication of the electro-lumineseent diode, a metal is deposited on the implanted faee in order to form the electrical contacts. By wa~ of example, this deposit eonsists of indium which results in the formation of the contact pads 10, 10', 10" after etehing.
, . .
-A deposit of gold 12 is then formed on the rear face of the substrate in order to form the second electrical contact.
Fig. 2 shows a second alternative mode of e~ecution of the method. In this alternative form, a layer 14 of a substance which will subse~uently be relatively easy to remove is deposited on the front face 4 of the substrate before carrying out the ion implantation in order to form the doped zone 6. The thickness e' of this deposlt is such that, at the time of ion implantation, the greater part of the defects caused by this implantation is localized within the surface layer 14. In a second stage, said layer 14 is then removed and this can preferably be carried out by chemical attack.
There are then formed the deposits which are intended to give rise to the electrical contact as described in connection with Fig. lc.
There can be mentioned by way of explanation the study which is carried out by cathodoluminescence and photo-luminescence on a layer of Zn Te implanted with boron donor ions. To this end, the starting material consists of a ~-type substrate having a concentration of acceptors of the order of 1016/cm3 (various experiments have been made with concentra-tions ranging from 10 to 10 atoms/cm ~. A boron implanta-tion is carried out with an energy of 140 KeV and a dose of 5 x 1014 atoms/cm2. Abrasions of the top layer of the substrate are carried out by ionic machining down to various depths. Analogous results have been obtained by chemical attack with cerium sulphate, for example.
There are shown in Fig. 3 the curves III and IV
which serve to show the results obtained in the luminescence of the implanted layer described earlier and fabricated by means of the method according to the invention~ Curve IV
' ' ~ . . . ~ . ' , :
relates to the alternative procedure in which an additional annealing opera-tion has been performed prior -to abrasion whilst curve III relates to the procedure in which no annealiny has taken place. These curves give the quantity Q of light emitted by the implanted material as a function of the abrasion depth d.
It is apparent that curve III has a well-marked minimum in the regions of small depth. It is found that, if sufficient abrasion is performed, the quan-tity of light emitted by the layer is multiplied by a substantial factor which is greater than 10. The gain obtained with respect to a layer annealed without abrasion (zero abrasion point of curve IV) is of smaller value but still very substantial.
The influence of annealing prior to abrasion appears on curve IV (as shown in Fig. 3).
~ lthough it is possible to revert to a crystal which is sound from a macroscopic viewpoint as a result of thermal annealing after ion implantation, complete rearrangement of the crystal lattice in the presence of impurities nevertheless appears to be difficult at the atomic level. This mechanism is characteristic of semiconductor compounds by reason of the fact that, while in the case of a monoatomic semiconductor such as silicon, for example, the silicon atom displaced by ion bombardment can return only to a silicon site, the annealing mechanism is much more complex in the case of a binary or ternary compound and is liable to give rise to associations of defects which are either inherent or induced by implantation and which, from a macroscopic point of view, distort the lattice and result in very low quantum yields -since this latter is directly related to the quality of the crystal.
..
, : ''' .' ' , ' ~:
There will now be described a series of experiments concerned with the fabrication of an electroluminescent diode in the green region of the spectrum (wavelenyth of 5480 A) by implantation of boron donor ions into a Zn Te Crystal. To this end, the starting material consists of a p-type substrate having a concentration of holes of 3 x 1016 atoms/cm3; boron ions having an energy of 140 KeV are implanted in respect of a dose of 5 x 1014 atoms/cm2. There is -then carried out an ionic or chemical abrasion so as to remove a surface layer of variable thickness and the metal contacts are deposited, namely indium or aluminium on the implanted layer and gold on the rear face of the crystal. There will thus be obtained the curve shown in Fig. 4 which represents the quantum yield R of the diode as a function of the abrasion depth d. A very well-defined maximum appears in the case of an abrasion depth of o 4000 A.
~n electroluminescent diode for the applica-tion of the invention will be obtained by abrasion to a depth of 4000 A.
This value is clearly valid under the experimental conditions described abo~e but would be different under other conditions of fabrication. ;
Two methods of collective fabrication of electro-luminescent diodes for the practical application of the present invention will now be described.
The first of these methods is based on the principle of the so-called planar technology. A layer of Zn, Te, for example, is employed as starting material and a uniform insulating deposit is formed on this layer followed by select-ive etching of the insulator; implantation is carried out with suitable ions until junctions are obtained in the holes - 10 - ,, .
: . . . .
:: . , . ~ , , . -- . . . : : . .
formed in the insulator; in accordance with the method of the present invention/ a surface abrasion to a precise depth is carried out in the holes; a metal coat:incJ is deposited, then etched so as to define the contacts on the top faces of the diodes and the external connections. It then remains necessary to cut-out the entire layer in order to mount the individual electroluminescent diodes if so desired. -The second of these two methods is even more straightforward. A layer of Zn Te/ for example, is employed as starting material; a uniform implantation with suitable ions is carried out over the entire surface; masking is effected by means of an ordinary photosensitive resin and this is followed by etching so as to define the electroluminescent zones; in accordance wi-th the method of the present invention, surface abrasion is performed in the unmasked zones to a pre-determined depth, whereupon the resin is removed; a metal coating is then deposited and etched so as to define the contacts on the top faces of the diodes and the external connections.
It will be noted that the disturbed surface zone is employed in this case for the purpose of ensuring electrical insulation between diodes. Selective abrasion defines the location of the diodes and at the same time increases their quantum efficiency.
.
, . ~ . .
.
Optoelectronic devices such as ligh-t emitters or detectors, for example, are usually fabricated from binary or ternary semi~conductor alloys. The operating principle of these devices is based on mechanisms for converting photons to charge carriers in the case of optoelectronic devices which operate as light detectors or on mechanisms for converting charge carriers to photons in the case of optoelectronic devices which operate as light emitters.
The charge carriers in a semiconductor are electrons and holes having properties which are directly related to the nature and the quality of the semiconductor. In particular, in the case of optoelectronic devices, carrier lifetime is a very important parameter which governs the quality of electrical energy to light energy conversion or light energy to electrical energy conversion. As the case may be, said lifetime is dirPctly related to the treatments (ion implanta-tion, annealiny) applied to the semiconductor throughout all stages of manufacture. During the process of preparation of the device, it will therefore be sought to ensure that the lifetime of the charge carriers is not modified to an excessive degree in order to maintain the intrinsic properties of the starting material. ~ ~
One of the most important optoelectronic devices is ,,, the electroluminescent diode in which a light emission is obtained by means of an injection of charge carriers.
At the present time, practically all existing electroluminescent diodes have a base of Type III-V semi-conductors. These are binary or ternary alloys having a base of gallium. Among the alloys which can be mentioned by way .. , , ~ ~
of example are Ga P, Ga As P, Ga ~l As and so forth~
Diodes or diode matrices made from alloys are p-_ junctions in which the substrate is usually of type n and in which an acceptor impurity such as zinc is either diffused or implanted. Another solution makes use of liquid or gaseous epitaxial growth of the p-type layer on the -type substrate.
In point of fact, although III-V semiconductors have reached a very advanced stage of development and fabrication at the present time, they are nevertheless attended by a number of disadvantages, viz:
-they have a base of gallium which is a very costly material, -the theoretical quantum yields are fairly limited, -they are well suited to emission in the red or infrared region but cannot readily be employed for radiative emissions of shorter wavelengths such as green or blue.
On the other hand, there does exist another class of alloys having a base of II-VI elements such as the alloys Zn Te, Zn Se, Cd Te, Mg Zn Te and so forth. Apart from the fact that their cost price is lower than that of the gallium compounds, these alloys result in emissions ranging from the infrared region to the ultraviolet region of the spectrum with very high theoretical ~uantum yields. However, although it is relatively easy to fabricate electroluminescent _-n junctions from the III-V alloys by means of conventional thermal techniques (diffusion, alloying), the intrinsic properties of II-VI semiconductors usually make it essential to have recourse to a method of doping without thermodynamic equilibrium such as ion implantation.
A number of attempts have been made up to the present time with a view to doping semiconductors of the II-VI type or .
.
9~
III-V type by ion implantation in order to produce electro-luminescent devices. As a general rule, the ~uantum yields obtained with the devices thus formed are of a low order. This result is due to the fact that, during ion implantation, a large quantity of defects is created within the semiconductor by the penetrating ion beam. These defects produce non-radiative recombination centers. In consequence, they are liable on the one hand to inhibit the desired doping action and, on the other hand, they reduce the quantum yield of the material. The conventional method of removing these defects consists in annealing the crystal at a temperature which is usually lower than the temperature required for gaseous diffusion. However, in spite of this annealing process, the result produced by the defects is not wholly eliminated and the quantum yield of these diodes remains of low value.
The present invention is precisely directed to a method of fabrication of optoelectronic devices which overcomes the disadvantages mentioned in the foregoing by making it possible in particular to fabricate devices of this type from compounds of the II-VI type while endowing these devices with -substantially higher yields than those obtained by simple ion implantation and annealing.
In a first alternative embodiment, the method of fabrication of optoelectronic devices in accordance with the invention essentially consists in starting from an at least binary semiconductor substrate selected from the group comprising the alloys of the elements of columns II and VI
and the alloys of the elements of columns III and V of the Periodic Table of El~ments and having a first type of conduct-ivity and in carrying out on one of the faces of said substrate an ion implantation with :impurities which are capable of "
endowing said substrate with a second type of conductivity to a given depth, in removiny a surface layer from -the implanted face of said substrate to a dep-th which ls sufficient to permit removal of the greater part of the defects caused by said implantation hut not to permit removal of the greater part of the implanted impurities.
In accordance with a first alternative procedure, thermal annealing of the substrate is carried out prior to removal of the surface layer.
In accordance with a second alternative procedure, thermal annealing is carried out after removal of the surface layer.
In a first mode of execution, the surface layer is removed by ionic abrasion or by chemical attack.
In a second mode of e~ecution, the ion implantation is carried out through a surface layer having a thickness corresponding to the zone of creation of the greater part of the defects and said deposited layer is removed by chemical attack.
In a second alternative embodiment, the method of fabrication of optoelectronic devices in accordance with the invention essentially consists in starting from at least a binary semiconductor substrate selected from the group comprising the alloys of elements of columns II and VI and alloys of elements of columns III and V of the Periodic Table of Elements and having a first type of conductivity, in depositing a layer of material on one of the faces of said substrate, in carrying out an ion implantation wi-th impurities which are capable of endowing said substrate with a second type of conductivity to a predetermined depth, the thickness of said layer of material being such that the greater part of the defects is concentrated in sai.d layer at the time of ion implantation.
Thus in accordance with this second alternative embodiment, the layer in which the defects are concentrated is not removed as in the first alternative embodiment. This layer can be either of metal (aluminum, for example) or of semiconductor material (tin-doped indium oxide In203, for example which is both conductive and -transparent) or of insulating material.
A more complete understanding of the invention will in any case be gained from the following description of a number of embodiments of the invention which are given by way of example and not in any limiting sense, reference being made to the accompanying drawings, wherein:
Figure 1 provides schematic illustrations of the different stages of a first embodiment of the method;
Figure 2 provides schematic illustrations of the different stages of a second embodiment of the method;
Figure 3 is a graph which glves the impurity profile, the defect profile and the quantum yield as a function o~ the depth within the substrate in the case of an implanted layer of Zn Te;
Figure 4 is a graph giving the quantum yield as a function of the abrasion depth.
In the following description, consideration will be given to the case of fabrication of electroluminescent diodes in a substrate of Zn Te. It is readily apparent that the steps of the method would be the same if use were made of substances other than those which have been described in the foregoing.
Fig. 3 shows the curve I which gives the defect, i - 6 -. : ~, - , , .. : , .
. : . . . .
: . . : ' : . :
: . ~: , profile at the time of ion imp:Lantation and the curve II which gives the impurity profile as a function of the depth within the substrate which is plotted as abscissae. An arbitrary unlt is adopted for the axis of ordinates. These curves have been plotted in the case of boron implantation into a Zn Te crystal with an energy of 140 (KeV). It will be noted that the curve which gives the profile of doping with impurities is displaced towards the right, that is to say towards the greater depths with respect to the curve I which gives the concentra-tion of defects.
Fig. 1 shows the different stages of a first alter- -native mode of execution of the method. The starting material consists of a crystal 2 of Zn Te which is polished mechanically and then chemically on its top face 4. This substrate 2 is p-type. Boron ions are introduced by ion implantation so as to form an n-type surface layer 6. In this zone 6, there is found the defeet profile and the impurity concentration proEile which is represented on curves I and II of Fig. 3. In the following stage shown in Fig. lb, the surface layer ~
represented by a ehain-dotted line, is abraded by means of a well-known ionic machining process.
An annealing operation is then carried out, for example at a temperature of 550C for a period of 30 minutes.
As mentioned earlier, this annealing operation is not necessary and can also be performed prior to the abrasion stage.
In order to complete the fabrication of the electro-lumineseent diode, a metal is deposited on the implanted faee in order to form the electrical contacts. By wa~ of example, this deposit eonsists of indium which results in the formation of the contact pads 10, 10', 10" after etehing.
, . .
-A deposit of gold 12 is then formed on the rear face of the substrate in order to form the second electrical contact.
Fig. 2 shows a second alternative mode of e~ecution of the method. In this alternative form, a layer 14 of a substance which will subse~uently be relatively easy to remove is deposited on the front face 4 of the substrate before carrying out the ion implantation in order to form the doped zone 6. The thickness e' of this deposlt is such that, at the time of ion implantation, the greater part of the defects caused by this implantation is localized within the surface layer 14. In a second stage, said layer 14 is then removed and this can preferably be carried out by chemical attack.
There are then formed the deposits which are intended to give rise to the electrical contact as described in connection with Fig. lc.
There can be mentioned by way of explanation the study which is carried out by cathodoluminescence and photo-luminescence on a layer of Zn Te implanted with boron donor ions. To this end, the starting material consists of a ~-type substrate having a concentration of acceptors of the order of 1016/cm3 (various experiments have been made with concentra-tions ranging from 10 to 10 atoms/cm ~. A boron implanta-tion is carried out with an energy of 140 KeV and a dose of 5 x 1014 atoms/cm2. Abrasions of the top layer of the substrate are carried out by ionic machining down to various depths. Analogous results have been obtained by chemical attack with cerium sulphate, for example.
There are shown in Fig. 3 the curves III and IV
which serve to show the results obtained in the luminescence of the implanted layer described earlier and fabricated by means of the method according to the invention~ Curve IV
' ' ~ . . . ~ . ' , :
relates to the alternative procedure in which an additional annealing opera-tion has been performed prior -to abrasion whilst curve III relates to the procedure in which no annealiny has taken place. These curves give the quantity Q of light emitted by the implanted material as a function of the abrasion depth d.
It is apparent that curve III has a well-marked minimum in the regions of small depth. It is found that, if sufficient abrasion is performed, the quan-tity of light emitted by the layer is multiplied by a substantial factor which is greater than 10. The gain obtained with respect to a layer annealed without abrasion (zero abrasion point of curve IV) is of smaller value but still very substantial.
The influence of annealing prior to abrasion appears on curve IV (as shown in Fig. 3).
~ lthough it is possible to revert to a crystal which is sound from a macroscopic viewpoint as a result of thermal annealing after ion implantation, complete rearrangement of the crystal lattice in the presence of impurities nevertheless appears to be difficult at the atomic level. This mechanism is characteristic of semiconductor compounds by reason of the fact that, while in the case of a monoatomic semiconductor such as silicon, for example, the silicon atom displaced by ion bombardment can return only to a silicon site, the annealing mechanism is much more complex in the case of a binary or ternary compound and is liable to give rise to associations of defects which are either inherent or induced by implantation and which, from a macroscopic point of view, distort the lattice and result in very low quantum yields -since this latter is directly related to the quality of the crystal.
..
, : ''' .' ' , ' ~:
There will now be described a series of experiments concerned with the fabrication of an electroluminescent diode in the green region of the spectrum (wavelenyth of 5480 A) by implantation of boron donor ions into a Zn Te Crystal. To this end, the starting material consists of a p-type substrate having a concentration of holes of 3 x 1016 atoms/cm3; boron ions having an energy of 140 KeV are implanted in respect of a dose of 5 x 1014 atoms/cm2. There is -then carried out an ionic or chemical abrasion so as to remove a surface layer of variable thickness and the metal contacts are deposited, namely indium or aluminium on the implanted layer and gold on the rear face of the crystal. There will thus be obtained the curve shown in Fig. 4 which represents the quantum yield R of the diode as a function of the abrasion depth d. A very well-defined maximum appears in the case of an abrasion depth of o 4000 A.
~n electroluminescent diode for the applica-tion of the invention will be obtained by abrasion to a depth of 4000 A.
This value is clearly valid under the experimental conditions described abo~e but would be different under other conditions of fabrication. ;
Two methods of collective fabrication of electro-luminescent diodes for the practical application of the present invention will now be described.
The first of these methods is based on the principle of the so-called planar technology. A layer of Zn, Te, for example, is employed as starting material and a uniform insulating deposit is formed on this layer followed by select-ive etching of the insulator; implantation is carried out with suitable ions until junctions are obtained in the holes - 10 - ,, .
: . . . .
:: . , . ~ , , . -- . . . : : . .
formed in the insulator; in accordance with the method of the present invention/ a surface abrasion to a precise depth is carried out in the holes; a metal coat:incJ is deposited, then etched so as to define the contacts on the top faces of the diodes and the external connections. It then remains necessary to cut-out the entire layer in order to mount the individual electroluminescent diodes if so desired. -The second of these two methods is even more straightforward. A layer of Zn Te/ for example, is employed as starting material; a uniform implantation with suitable ions is carried out over the entire surface; masking is effected by means of an ordinary photosensitive resin and this is followed by etching so as to define the electroluminescent zones; in accordance wi-th the method of the present invention, surface abrasion is performed in the unmasked zones to a pre-determined depth, whereupon the resin is removed; a metal coating is then deposited and etched so as to define the contacts on the top faces of the diodes and the external connections.
It will be noted that the disturbed surface zone is employed in this case for the purpose of ensuring electrical insulation between diodes. Selective abrasion defines the location of the diodes and at the same time increases their quantum efficiency.
.
, . ~ . .
.
Claims (5)
1. A method of fabrication of optoelectronic devices starting with a binary semiconductor substrate selected from the group comprising the alloys of the elements of columns II and VI and the alloys of the elements of columns III and V of the Periodic Table of Elements and having a first type of which is of intrinsic character and comprising the steps of:
depositing a layer of a different material on one of the faces of said substrate having a layer thickness determined to be just sufficient to be able to contain the greater part of the defects to be produced in the following ion implantation step, and thereafter carrying out an ion implantation with dopant ions of an element of a column of said Periodic Table other than those of the elements of the substrate alloy which ions are capable of endowing said substrate, to a predetermined depth, with a second type of conductivity which is of extrinsic character.
depositing a layer of a different material on one of the faces of said substrate having a layer thickness determined to be just sufficient to be able to contain the greater part of the defects to be produced in the following ion implantation step, and thereafter carrying out an ion implantation with dopant ions of an element of a column of said Periodic Table other than those of the elements of the substrate alloy which ions are capable of endowing said substrate, to a predetermined depth, with a second type of conductivity which is of extrinsic character.
2. A method according to Claim 1, wherein the material of said deposited layer is a material more readily removable by at least one kind of chemical attack than the underlying portion of said substrate and wherein said deposited layer is removed by chemical attack after said ion implantation.
3. A method according to Claim 1, wherein thermal annealing is carried out.
4. A method of fabrication of optoelectronic devices as defined in Claim 1, in which said ion implantation is carried out with an implantation dose of the order of magnitude of 1014 at/cm2.
5. A method of fabrication of optoelectronic devices as defined in Claim 1, in which said first type of conductivity is p-type conductivity, so that said substrate in its starting state has p-type intrinsic conductivity, and in which said dopant ions are donor ions and are implanted in a dose of the magnitude of about 5 x 1014 at/cm2.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA257,941A CA1088193A (en) | 1976-07-28 | 1976-07-28 | Method of fabrication of optoelectric devices by ion implantation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA257,941A CA1088193A (en) | 1976-07-28 | 1976-07-28 | Method of fabrication of optoelectric devices by ion implantation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088193A true CA1088193A (en) | 1980-10-21 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA257,941A Expired CA1088193A (en) | 1976-07-28 | 1976-07-28 | Method of fabrication of optoelectric devices by ion implantation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088193A (en) |
-
1976
- 1976-07-28 CA CA257,941A patent/CA1088193A/en not_active Expired
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