CA1072423A - Method of producing homogeneously doped semiconductor material of p-conductivity - Google Patents
Method of producing homogeneously doped semiconductor material of p-conductivityInfo
- Publication number
- CA1072423A CA1072423A CA320,602A CA320602A CA1072423A CA 1072423 A CA1072423 A CA 1072423A CA 320602 A CA320602 A CA 320602A CA 1072423 A CA1072423 A CA 1072423A
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- Canada
- Prior art keywords
- semiconductor material
- irradiation
- gamma
- atoms
- photons
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT
A process for the production of substantially homogeneously doped p-conductive semiconductor material is described, which comprises subjecting the semiconductor material to be doped to irradiation with .gamma.-photons wherein the semiconductor material is gallium and wherein zinc atoms are produced as doping atoms on irradiation of the gallium with .gamma.-photons.
A process for the production of substantially homogeneously doped p-conductive semiconductor material is described, which comprises subjecting the semiconductor material to be doped to irradiation with .gamma.-photons wherein the semiconductor material is gallium and wherein zinc atoms are produced as doping atoms on irradiation of the gallium with .gamma.-photons.
Description
~ ~f The present invention relates to a process for the production of hornogeneously doped p-conductive semiconductor material, and is a divisional application of Canadian Application Seri&l No. 233,055 filed on August 7 The doping of semiconductor material is frequently carried out (~orexample, in the case of silicon) during deposition of the semiconductor mate-rial from the gas phase by the thermal decomposition of a gaseous silicon compound of silicon on a heated carrier body of the same material. During this process, doping is effected by mixing a gaseous compound of a dopant with the gaseous silicon compound, so that this also decomposes on the car-rier body. Silicon rods produced in this way are polycrystalline and must be converted into the monocrystalline state by a subsequent zone melting treatment. In this subsequent treatment, the dopant concentration often thereby changes uncontrollably and very much higher dopant concentrations must be used to ensure that the desired concentration of dopant still exists in the final product.
Germanium is frequently produced by the Czochralski crucible draw-:ing method, in which a seed crystal is submerged into a germanium melt con--taining a suitable dopant and which is located in a crucible, and a mono-crystalline rod is drawn from the melt by movement of the seed crystal. Hereagain, the dopant is found to evaporate uncontrollably during the crystal growth process.
In the case of A B compounds, e.g. in the case of gallium arsenide or gallium phosphide, doping is frequently likewise effected from a melt contained in a crucible or boat.
These known doping processes are time-consuming and inaccurate.
Consequently, the components produced from this semiconductor material do not possess optimal values for their electrical properties.
~,,, ... . ..
, It is an ob~ect of the present invention to provide a process ~or the production of p-conductive material by means o~ which it is possible to obtain a p dopiIIg o~ a semiconductor crystal which is homogeneous throughout l;he crystal (e.g. in the case of a rod over the rod length and rod cross-section independent of the diameter of the rod) in a simple and economical rashion, and by means o~ which, in particular, very high ohmic semiconductor material can be produced. Previously this could be effected only with di~-riculty using the convention processes with narrow radial and axial resis-tance tolerances.
As an example, where the semiconductor material is silicon, aluminium atoms are produced as doping atoms on irradiation of the silicon with y-photons, in accordance with the nuclear reaction:-Si (y, p) ~ ~ 7Al.
From the natural isotope Si contained in the silicon, the stable isotope 7A1 is formed in accordance with the nuclear reaction, during which process protons are emitted.
As another example, f`or the production of p-doped germanium, gal-lium is i`ormed as the dopant by irradiation with y-photons in accordance with the nuclear reaction:-70Ge (Y' n) Ge -~ 9Ga.
From the natural isotope 7 Ge present in the germanium, the unstable isotope 9Ge is formed, neutrons being emitted. The 9Ge is spontaneously converted into the stable isotope 9Ga um, nuclear reaction (K) being emitted. ~o ex-ternal irradiation is required ~or this second stage.
As another example, for the production of p-doped gallium arsenide, gallium phosphide, or gallium arsenide phosphide, zinc is used as a p-dopant and is formed from the gallium by irradiating the material with y-photons, in ~"~
,. . .
Germanium is frequently produced by the Czochralski crucible draw-:ing method, in which a seed crystal is submerged into a germanium melt con--taining a suitable dopant and which is located in a crucible, and a mono-crystalline rod is drawn from the melt by movement of the seed crystal. Hereagain, the dopant is found to evaporate uncontrollably during the crystal growth process.
In the case of A B compounds, e.g. in the case of gallium arsenide or gallium phosphide, doping is frequently likewise effected from a melt contained in a crucible or boat.
These known doping processes are time-consuming and inaccurate.
Consequently, the components produced from this semiconductor material do not possess optimal values for their electrical properties.
~,,, ... . ..
, It is an ob~ect of the present invention to provide a process ~or the production of p-conductive material by means o~ which it is possible to obtain a p dopiIIg o~ a semiconductor crystal which is homogeneous throughout l;he crystal (e.g. in the case of a rod over the rod length and rod cross-section independent of the diameter of the rod) in a simple and economical rashion, and by means o~ which, in particular, very high ohmic semiconductor material can be produced. Previously this could be effected only with di~-riculty using the convention processes with narrow radial and axial resis-tance tolerances.
As an example, where the semiconductor material is silicon, aluminium atoms are produced as doping atoms on irradiation of the silicon with y-photons, in accordance with the nuclear reaction:-Si (y, p) ~ ~ 7Al.
From the natural isotope Si contained in the silicon, the stable isotope 7A1 is formed in accordance with the nuclear reaction, during which process protons are emitted.
As another example, f`or the production of p-doped germanium, gal-lium is i`ormed as the dopant by irradiation with y-photons in accordance with the nuclear reaction:-70Ge (Y' n) Ge -~ 9Ga.
From the natural isotope 7 Ge present in the germanium, the unstable isotope 9Ge is formed, neutrons being emitted. The 9Ge is spontaneously converted into the stable isotope 9Ga um, nuclear reaction (K) being emitted. ~o ex-ternal irradiation is required ~or this second stage.
As another example, for the production of p-doped gallium arsenide, gallium phosphide, or gallium arsenide phosphide, zinc is used as a p-dopant and is formed from the gallium by irradiating the material with y-photons, in ~"~
,. . .
2~
accordance with the nuclear react;on:-69Ga (Y' n) 3Ga ~+ 68z From the stable isotope 9Ga, the unstable isotope Ga is formed duringwhich process neutrons are emitted. Ga is a ~ radiator with a half-life period of 1.14 hours, and is converted into the stable isotope Zn. Here again, no external measures need to be ta~en to effect this transformation.
In accordance with this invention there is provided a process for the production of substantially homogeneously doped p-conductive semi-conductor material comprising the step of subjecting semiconductor material to be doped to irradiation with ~-photons, whereby p-doping atoms are pro-duced in said material by a nuclear reaction or reactions initiated by the ~-photons, wherein said semiconductor material is gallium arsenide, or gal-lium phosphide, and wherein zinc atoms are formed as doping atoms from gal-lium atoms on irradiation of the gallium with ~-photons, in accordance with the nuclear reaction:
69Ga ( ~ ' n) 68Ga ~ > Zn.
The doping concentration is dependent upon the duration of the y-radiation and the strength of the photon stream per unit of area (photon stream density). The product of the two values is referred to as the "fluence".
Thus, for example, starting with a germanium rod having a specific resistance of 47 Q cm (i.e. the intrinsic conductivity at 300 K), a desired resistance of 8.75 Q cm p-type can be produced as follows:-A 35 MeV electron bearn of 100 ~A current density is arranged tostrike a o.6 cm thick tungsten target. The radiation produced by the retar-clation of the electrons is used to irradiate the germanium and acts to ini-tiate the following nuclear reactions therein:-.1 " ' ~ , :
~(~7;~42~
1 76Ge (y n) 75Ge ~~ 75As (stable) T = o2 min 2 70G (y, n) 69Ge ~ ~ 69Ga (stable) T / = 38 h.
When the irradiation is set to last for 10 mins., and after thecomplete disintegration of the radioactive isotopes produced, the following dopant concentrations in the germanium beneath the irradiated surface are obtained :-1. 1.14 x 10 atoms As/cm3 2. 2.11 x 10 atoms Ga/cm3.Since As leads to n-doping and Ga leads to p~doping, after allowing for com 10 pensation 9.7 x 10 atoms Ga/cm3 remain for p-doping.
In the above example the following dopant production is required :-Starting value : 2.4 x 10 3 cm 3 ~ 47 ~ cm Target value : 2.75 x 10 4 cm 3 ~ 3.75 ~ cm To be produced : 2.56 x 10 cm 3.
The required duration of irradiation is thus about 44 hours.
Various devices for carrying out the irradiation are known. For example, can de Graaff-generators, cyclotrons, linear accelerators or nuclear reactors can be used for this purpose.
In order to heal any damage to the crystal lattice caused by ex-posure to the ~-radiation, the irradiated semiconductor crystals may advan-tageously be annealed for at least one hour at a temperature above 500 C.
When the semiconductor material is silicon, the annealing can expediently be carried out in a silicon tube. The annealing step can be dispensed with, however, if the semiconductor material is to be further processed to form components and at least one high-temperature process is to be carried out during the further processing.
,i ; _ '' : ' ,. ' ' ".
: :
:~7~3 In a particularl~ advantageous embodiment of the invention, the semiconductor material is in the form of a semiconductor rod, ~Ihich is caused to rotate about its longitudinal axis during the irradiation. A polycrystal-line silicon rod having a length of 900 mm and a diameter of 35 mm may, for example, be used as the starting material. This rod is ~one-melted in vacuum and subsequently or simultaneously a seed crystal having (111)-orientation is fused onto it.
In accordance with another embodiment of the invention, the semi-conductor material is in the form of a crystalline wafer and an x-y scanning of the wafer with a y-photon beam is effected during irradiation.
The process of the invention makes it possible to provide silicon, germanium and gallium arsenide or gallium arsenide phosphide crystals with a homogeneous p-doping. Such crystals are particularly useful for the produc-1;ion of electronic semiconductor components.
The advantages of the process of the invention in comparison with the known doping processes are clearly shown by the greater homogeneity o-f t;he concentration of dopant in the crystal and by the avoidance of the need for high-temperature processes and their unfavourable consequences.
:,
accordance with the nuclear react;on:-69Ga (Y' n) 3Ga ~+ 68z From the stable isotope 9Ga, the unstable isotope Ga is formed duringwhich process neutrons are emitted. Ga is a ~ radiator with a half-life period of 1.14 hours, and is converted into the stable isotope Zn. Here again, no external measures need to be ta~en to effect this transformation.
In accordance with this invention there is provided a process for the production of substantially homogeneously doped p-conductive semi-conductor material comprising the step of subjecting semiconductor material to be doped to irradiation with ~-photons, whereby p-doping atoms are pro-duced in said material by a nuclear reaction or reactions initiated by the ~-photons, wherein said semiconductor material is gallium arsenide, or gal-lium phosphide, and wherein zinc atoms are formed as doping atoms from gal-lium atoms on irradiation of the gallium with ~-photons, in accordance with the nuclear reaction:
69Ga ( ~ ' n) 68Ga ~ > Zn.
The doping concentration is dependent upon the duration of the y-radiation and the strength of the photon stream per unit of area (photon stream density). The product of the two values is referred to as the "fluence".
Thus, for example, starting with a germanium rod having a specific resistance of 47 Q cm (i.e. the intrinsic conductivity at 300 K), a desired resistance of 8.75 Q cm p-type can be produced as follows:-A 35 MeV electron bearn of 100 ~A current density is arranged tostrike a o.6 cm thick tungsten target. The radiation produced by the retar-clation of the electrons is used to irradiate the germanium and acts to ini-tiate the following nuclear reactions therein:-.1 " ' ~ , :
~(~7;~42~
1 76Ge (y n) 75Ge ~~ 75As (stable) T = o2 min 2 70G (y, n) 69Ge ~ ~ 69Ga (stable) T / = 38 h.
When the irradiation is set to last for 10 mins., and after thecomplete disintegration of the radioactive isotopes produced, the following dopant concentrations in the germanium beneath the irradiated surface are obtained :-1. 1.14 x 10 atoms As/cm3 2. 2.11 x 10 atoms Ga/cm3.Since As leads to n-doping and Ga leads to p~doping, after allowing for com 10 pensation 9.7 x 10 atoms Ga/cm3 remain for p-doping.
In the above example the following dopant production is required :-Starting value : 2.4 x 10 3 cm 3 ~ 47 ~ cm Target value : 2.75 x 10 4 cm 3 ~ 3.75 ~ cm To be produced : 2.56 x 10 cm 3.
The required duration of irradiation is thus about 44 hours.
Various devices for carrying out the irradiation are known. For example, can de Graaff-generators, cyclotrons, linear accelerators or nuclear reactors can be used for this purpose.
In order to heal any damage to the crystal lattice caused by ex-posure to the ~-radiation, the irradiated semiconductor crystals may advan-tageously be annealed for at least one hour at a temperature above 500 C.
When the semiconductor material is silicon, the annealing can expediently be carried out in a silicon tube. The annealing step can be dispensed with, however, if the semiconductor material is to be further processed to form components and at least one high-temperature process is to be carried out during the further processing.
,i ; _ '' : ' ,. ' ' ".
: :
:~7~3 In a particularl~ advantageous embodiment of the invention, the semiconductor material is in the form of a semiconductor rod, ~Ihich is caused to rotate about its longitudinal axis during the irradiation. A polycrystal-line silicon rod having a length of 900 mm and a diameter of 35 mm may, for example, be used as the starting material. This rod is ~one-melted in vacuum and subsequently or simultaneously a seed crystal having (111)-orientation is fused onto it.
In accordance with another embodiment of the invention, the semi-conductor material is in the form of a crystalline wafer and an x-y scanning of the wafer with a y-photon beam is effected during irradiation.
The process of the invention makes it possible to provide silicon, germanium and gallium arsenide or gallium arsenide phosphide crystals with a homogeneous p-doping. Such crystals are particularly useful for the produc-1;ion of electronic semiconductor components.
The advantages of the process of the invention in comparison with the known doping processes are clearly shown by the greater homogeneity o-f t;he concentration of dopant in the crystal and by the avoidance of the need for high-temperature processes and their unfavourable consequences.
:,
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the production of substantially homogeneously doped p-conductive semiconductor material comprising the step of subjecting semiconductor material to be doped to irradiation with .gamma.-photons, whereby p-doping atoms are produced in said material by a nuclear reaction or reac-tions initiated by the .gamma.-photons, wherein said semiconductor material is gal-lium arsenide, or gallium phosphide, and wherein zinc atoms are formed as doping atoms from gallium atoms on irradiation of the gallium with .gamma.-photons, in accordance with the nuclear reaction:
.
.
2. A process as claimed in claim 1, wherein the doping concentration produced is determined by selection of the duration of irradiation and the density of the .gamma.-photon stream per unit area.
3. A process as claimed in claim 1, wherein, in order to heal any damage to the crystal lattice caused by irradiation, the irradiated semi-conductor material is annealed for at least one hour at a temperature above 500 C.
4. A process as claimed in claim 1, wherein said semiconductor material is in the form of a rod, which is caused to rotate about its longi-tudinal axis during the irradiation step.
5. A process as claimed in claim 1, wherein said semiconductor material is in the form of a crystalline wafer, and wherein an x-y scanning of the wafer with a.gamma.-photon beam is effected during irradiation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320,602A CA1072423A (en) | 1974-08-16 | 1979-01-31 | Method of producing homogeneously doped semiconductor material of p-conductivity |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2439430A DE2439430C2 (en) | 1974-08-16 | 1974-08-16 | Process for the production of homogeneously doped semiconductor material with p-conductivity |
| CA233,055A CA1068583A (en) | 1974-08-16 | 1975-08-07 | Method of producing homogeneously doped semiconductor material of p-conductivity |
| CA320,602A CA1072423A (en) | 1974-08-16 | 1979-01-31 | Method of producing homogeneously doped semiconductor material of p-conductivity |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072423A true CA1072423A (en) | 1980-02-26 |
Family
ID=27164068
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA320,602A Expired CA1072423A (en) | 1974-08-16 | 1979-01-31 | Method of producing homogeneously doped semiconductor material of p-conductivity |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1072423A (en) |
-
1979
- 1979-01-31 CA CA320,602A patent/CA1072423A/en not_active Expired
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