Claims
- 1. A semiconductor device for producing an electron current, which comprises:
- a cathode having a semiconductor body with a major surface;
- means for increasing the operational stability of said semiconductor device comprising an emission area having at least one group of separate, spaced-apart emission regions at said major surface arranged in a two-dimensional pattern, the area of each said emission region being at most equal to 100 .mu.m.sup.2 ; in combination with
- means for commonly adjusting the operating condition of said group of regions with respect to the emission of electrons, comprising two common electrical connections to at least two corresponding regions of said group.
- 2. A semiconductor device as claimed in claim 1, characterized in that the group of regions is distributed substantially homogeneously over a part of the major surface.
- 3. A semiconductor device as claimed in claim 1 or 2, characterized in that the group of regions is arranged in an annular pattern.
- 4. A semiconductor device as claimed in claim 1 or 2, characterized in that the semiconductor body comprises several groups of regions which are separately adjustable.
- 5. A semiconductor device as claimed in claim 1 or 2, characterized in that the regions each have a surface area of at most 5 .mu.m.sup.2.
- 6. A semiconductor device as claimed in claim 1 or 2, characterized in that the semiconductor body has a pn junction between an n-type region adjoining the major surface and a p-type region, in which, when a voltage is applied in the reverse direction across the pn junction, electrons are generated in the semiconductor body by avalanche multiplication, which emanate from the semiconductor body, the surface being provided with an electrically insulating layer, in which several openings are provided, the pn junction extending at least within the opening substantially parallel to the major surface and locally having a lower breakdown voltage than the remaining part of the pn junction, the part having a lower breakdown voltage being separated from the surface by an n-type conducting layer which has such a thickness and doping that at the breakdown voltage the depletion zone of the pn junction does not extend as far as the surface, but remains separated therefrom by a surface layer which is sufficiently thin to pass the generated electrons.
- 7. A semiconductor device as claimed in claim 6, characterized in that at least one electrode is provided on at least a part of the insulating layer.
- 8. A semiconductor device as claimed in claim 1 or 2, characterized in that the semiconductor body has a pn junction between an n-type region adjoining the major surface and a p-type region, while, when a voltage is applied in the reverse direction across the pn junction, electrons are generated in the semiconductor body by avalanche multiplication, which electrons emanate from the semiconductor body, the pn junction extending at least at the area of the electron-emitting regions mainly parallel to the major surface and locally having a lower breakdown voltage than the remaining part of the pn junction, the part having a lower breakdown voltage being separated from the surface of an n-type conducting layer having such a thickness and doping that at the breakdown voltage the depletion zone of the pn junction does not extend as far as the surface, but remains separated therefrom by a surface layer which is sufficiently thin to allow the generated electrons to pass, and in that the n-type region is coated with a layer of electrically conducting material, which contacts the n-type region and is provided with openings at the area of the electron-emitting regions.
- 9. A semiconductor device as claimed in claim 8, characterized in that the electron-emitting regions are substantially strip-shaped.
- 10. A semiconductor device as claimed in claim 8, characterized in that the electron-emitting regions are distributed over a substantially circular surface region.
- 11. A semiconductor device as claimed in claim 1 or 2, characterized in that the major surface is coated at the area of the electron-emitting regions with a layer of material reducing the electron work function.
- 12. A camera tube provided with means for controlling an electron beam which scans a charge image, characterized in that the electron beam is produced by a semiconductor device as claimed in claim 1 or 2.
- 13. A display arrangement provided with means for controlling an electron beams which produces an image, characterized in that the electron beam is produced by means of a semiconductor device as claimed in claim 1 or 2.
- 14. A display arrangement as claimed in claim 13, characterized in that it has a fluorescent screen which is located in vacuo at a distance of a few millimeters from the semiconductor device and the screen is activated by the electron beam originating from the semiconductor device.
Priority Claims (2)
| Number |
Date |
Country |
Kind |
| 8403538 |
Nov 1984 |
NLX |
|
| 8501490 |
May 1985 |
NLX |
|
BACKGROUND OF THE INVENTION
This is a continuation of application Ser. No. 147,029, filed Jan. 19, 1988, now abandoned, which is a continuation of application Ser. No. 793,886, filed Nov. 1, 1985, now abandoned.
The invention relates to a semiconductor device for producing an electron current comprising a cathode having a semiconductor body provided at a major surface with at least one group of regions which in the operating condition can be given substantially the same operational adjustment on behalf of the emission of electrons.
The invention further relates to a display and a pick-up device provided with such a semiconductor device.
Such arrangements are known from the Netherlands Patent Application No. 7905470 laid open to public inspection on Jan. 15 1981.
In this Application, inter alia a flat display arrangement is shown provided with a fluorescent screen which is activated by electrons originating from a semiconductor device having emission regions which are organized in an xy matrix and in which, depending upon the drive of different groups of emission regions, alternating patterns of electron emission and hence different fluorescent patterns are generated.
In the example concerned, use is made of semiconductor cathodes whose operation is based on avalanche multiplication of electrons when a pn junction is reversebiased. The pn junction has at the area of the emitting surface a reduced breakdown voltage and is separated in situ from the surface by an n-type conducting layer having such a thickness and doping that at the breakdown voltage the depletion zone does not extend as far as the surface, but remains separated therefrom by a surface layer which is sufficiently thin to pass the generated electrons.
The said Patent Application also discloses an application in which such a semiconductor cathode is used in an electron tube, in which the emitting surface is substantially annular. With the use of such a semiconductor cathode in conventional cathode-ray tubes, there is generally not, as in the embodiment shown therein, a virtual source, but the electrons emitted by the semiconductor cathode meet in a so-called "cross-over". The electrons then move mainly along the surface of the generated beam, which, as described in the said Patent Application, may be advantageous from an electro-optical point of view.
In general the desired electron current is fixed, depending upon the type of cathode-ray tube in which the semiconductor cathode is used. Electrode currents (beam currents) higher than 100 .mu.A may be produced, for example, by means of semiconductor cathodes having an annular emitting surface having a diameter exceeding approximately 20 .mu.m. Due to this electron current in connection with the overall emitting surface and the efficiency of the semiconductor cathode, the electron current density is then fixed.
This electron current density can then become so low that in practice stability problems occur. Any residual gases from the vacuum system (for example H.sub.2 O, CO.sub.2, O.sub.2) are adsorbed at the electronemitting surface and can interact in situ with a mono-atomic layer of caesium, which is generally applied in this surface to reduce the work function of the electrons generated in the semiconductor body, and with the surface of the semiconductor crystal. Under the influence of the electrons emanating from the semiconductor body, compounds then formed can be decomposed and adsorbed atoms are drained (desorption). Adsorbed atoms are also drained by diffusion from the emission region under the influence of electric fields (for example the fields produced by the adjustment current). In order to ensure that these mechanisms have sufficient influence, it is often required, however, to increase the electron current density by adjusting the adjustment current to a higher value than is practically possible or desirable.
The present invention has for its object to provide an arrangement of the kind mentioned above which has an increased stability.
An arrangement according to the invention is characterized for this purpose in that the group of regions has for the common operational adjustment electrical connections common to at least two corresponding elements of the regions.
The invention is based on the recognition of the fact that the stability of a semiconductor cathode is increased by means of the measure according to the invention in that a group of small emission regions can be homogeneously distributed over the surface defining the original emission pattern, the overall surface area of the emission regions being considerably smaller than that of the original pattern. In principle this already applies to very small emission patterns having a surface area of approximately 1 .mu.m.sup.2 and also to annular patterns having a diameter from approximately 10 .mu.m with a ring width of approximately 0.5 .mu.m.
The term "common electrical connections" is to be understood herein to mean that such measures are taken that the adjustment is practically equal for all regions belonging to one group, for example, by the use of common metallizations for corresponding semiconductor zones or highly doped buried semiconductor zones, which interconnect all semiconductor zones of the same type belonging to one group. If use is made of the type of semiconductor cathode described in Netherlands Patent Application No. 7905470, in which, for example, the group of electron-emitting regions is annular or is homogeneously distributed over an annular region, all p-type regions of the pn junctions are then interconnected to an electrically conducting manner via the metallization on the lower side of the semiconductor body, while the n-type regions are interconnected via deep n-diffusions outside the actual emitting surfaces. However, the accleration electrode shown therein may in turn be subdivided into several parts, which can be brought to separate potentials. However, this electrode may alternatively be omitted entirely or in part.
A preferred embodiment of an arrangement according to the invention is characterized in that the group of regions is arranged according to an annular pattern. Such an embodiment is particularly suitable, as stated above, for electron-optical considerations. Other arrangements of the emitting regions are also possible, for example, linear arrangements for display apparatus or the activation of laser material, as described in Netherlands Patent Application No. 8300631 and No. 8400632
Due to the said measure, a high local current density is obtained, which leads in principle to the desired stability of the cathode. Nevertheless it is desirable especially for the said cathodes with a reverse-biased pn junction that the effective current density is also as high as possible. This means inter alia that the so-called filling factor (quotient of the sum of the surface areas of the emitting regions and the whole surface area) has to be as high as possible.
In this type of cathode, however, an increasing filling factor gives rise to current supply problems due to the series resistance in the n-type region adjoining the major surface. This in turn leads, with high currents due to potential differences, to inequality of the adjustment of the pn junctions in the various electron-emitting regions. Moreover, due to the resistance in the n-type region, the cathode in practice conveys a comparatively low diode current (about 10 to 20% of the maximum permissible current as determined by the construction of the cathode, especially by the series resistance of the p-type region).
Additionally, any high current densities in the n-type surface regions may give rise to high electric fields, which may lead to caesium migration, as a result of which
instability and inhomigeneity of the emission may occur.
A particular embodiment of a semiconductor device according to the invention, in which these problems are solved at least for the major part, is characterized in that the semiconductor body has a pn junction between an n-type region adjoining the major surface and a p-type region, . When a voltage is applied in the reverse direction across the pn junction, electrons are generated in the semiconductor body by avalanche multiplication, which electrons emanate from the semi-conductor body, the pn junction extending at least at the area of the electron-emitting regions mainly parallel to the major surface and having locally a lower breakdown voltage than the remaining part of the pn junction, the part having a lower breakdown voltage being separated from the surface by an n-type conducting layer having such a thickness and doping that at the breakdown voltage the depletion zone of the pn junction does not extend as far as the surface, but remains separated therefrom by a surface layer which is sufficiently thin to allow the generated electrons to pass, and the n-type region is coated with a layer of electrically conducting material, which contacts the n-type region and is provided with openings at the area of the electron-emitting regions.
Thus, a low-resistance current path parallel to the n-type region is obtained so that such a cathode can be operated at a high effective current density while avoiding the aforementioned problems.
A preferred embodiment of such a semiconductor device, by which a high filling factor can be attained, is characterized in that the electron-emitting regions are substantially strip-shaped.
US Referenced Citations (3)
| Number |
Name |
Date |
Kind |
| 4325084 |
van Gorkom et al. |
Apr 1982 |
|
| 4370797 |
van Gorkom et al. |
Feb 1983 |
|
| 4574216 |
Hoeberechts et al. |
Mar 1986 |
|
Foreign Referenced Citations (2)
| Number |
Date |
Country |
| 1198567 |
May 1966 |
GBX |
| 2117173 |
Mar 1982 |
GBX |
Continuations (2)
|
Number |
Date |
Country |
| Parent |
147029 |
Jan 1988 |
|
| Parent |
793886 |
Nov 1985 |
|
Patent Grant
4890031
