RU2461915C1 - Nuclear battery - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention can be used as a battery in different electronic devices which consume low current but are forced to operate without replacement of power sources for a decade. The essence of the invention lies in that the nuclear battery has a housing filled with isotope material, in which there is at least one semiconductor detector in whose volume wells are formed, wherein all dimensions of the wells are smaller than the free path of particles emitted by the gaseous isotope. The detector is in form of alternating n⁺, i (either ν or π) and p⁺-type layers in the sequence n⁺-i-p⁺-i-…-n⁺-i-p⁺, wherein these layers lie in planes which are perpendicular to walls of the wells; ohmic contacts are formed on n⁺-type layers, said ohmic contacts being electrically connected to each other. The same contacts are also formed to p⁺-type layers which are also connected to each other.

EFFECT: simple technology making a semiconductor detector which converts energy of beta-particles to electric current.

1 dwg

Description

The invention relates to devices that convert the energy of particles emitted by isotopes into electric current, and can be used as a battery in various electronic devices that consume a small current, but are forced to work without replacing power sources for a decade, for example, in pacemakers, or in deep-sea sensors, or in devices launched into space, or in devices installed in hard-to-reach places.

Nuclear batteries are known whose operating principle is based on the conversion of the energy of particles arising from the radioactive decay of isotopes into an electric current when passing through a semiconductor detector operating in beta or photovoltaic mode. Known batteries use gaseous, liquid, and solid-state isotopes that emit alpha, beta particles, as well as gamma quanta [1, 2, 3].

A device [1] is known, which comprises a housing in which an amorphous silicon semiconductor detector is placed, representing a pin structure, and the inside of the housing is filled with tritium ( ³ H), which emits electrons. The half-life of tritium is approximately 12 years. In the operating mode, each beta particle that reaches the surface of the detector flies into the detector and creates more than one thousand electron-hole pairs in it. The resulting holes and electrons are separated by the internal field of the pin structure, which leads to the formation of voltage at the detector contacts and the appearance of an electric current when the load is connected. The disadvantage of such a battery is the small current values proportional to the area of only one surface of a flat detector.

The closest analogue of the invention is the isotope battery proposed in the American patent (Patent US 6774531) [3]. In the prototype, the efficiency of the detector is significantly increased due to the special design of the 3D-silicon detector.

The known battery contains a housing filled with gaseous tritium, where a beta-volt detector of n-type silicon is placed. Wells for tritium are created in the detector volume, on the walls of which a p ⁺ -type conductivity layer is formed, and all the well sizes do not exceed the mean free path of electrons in tritium.

A disadvantage of the known device is that the implementation of a detector containing deep wells in the semiconductor volume, on the walls of which a p-n junction is formed, is a very difficult technical problem, which has been solved so far only for silicon. For other semiconductors having a higher density than silicon, the known detector design is generally ineffective. Indeed, at an average electron energy E = 6 keV emitted by tritium, an electron can penetrate into the detector only to a depth of 0.1-0.2 μm, and in the presence of a p-type layer on the walls of the wells, a significant part of the charge generated by electrons recombines in it without reaching pn junction.

The technical result, which is aimed at the claimed solution, is to eliminate these disadvantages.

This result is achieved by the fact that a nuclear battery with radioactive isotopes containing a housing filled with isotope material, where at least one semiconductor detector is located, in which wells are created in volume, all well sizes being less than the mean free path of particles emitted by a gaseous isotope , differs in that alternating layers of n ⁺ , i (either ν, or π) and p ⁺ types of conductivities are created in the detector volume in the following sequence: n ⁺ -ip ⁺ -i- ... -n ⁺ -i-p ⁺ , moreover, these layers lie in planes, perpendicular On the walls of the wells, on the n + -type layers, ohmic contacts are created that are electrically interconnected, the same contacts are created on the p ⁺ -type layers and are also connected.

In the proposed device, the detector design eliminates the need to form p-n junctions on the walls of the wells. Therefore, the detector can be made not only of silicon, but also of other semiconductors, for example, gallium arsenide.

Figure 1 schematically shows a section of one of the possible designs of the proposed battery. The battery contains a housing 1 with electrodes 2 and 3. The housing is filled with the material of the radioactive isotope 4. Two detectors 5 and 6 of gallium arsenide are placed in the housing. The detectors are made of epitaxial material containing a sequence of layers n ⁺ 7, i 8, p ⁺ 9, ohmic contacts 10 and 11, respectively, are connected to wires with electrodes 2 and 3 of the housing by high-doped layers n ⁺ 7, p ⁺ 9. Wells 12 are formed perpendicular to the planes in which the n ⁺ , i, p ⁺ layers are grown in the detector volume.

An example of practical implementation. Two identical detectors 5 and 6 were installed in a sealed metal case 1 having electrodes 2 and 3 electrically isolated from the case due to dielectric inserts. The inside of the case was filled with radioactive tritium emitting beta particles. The detectors were made from gallium arsenide grown by gas phase epitaxy. The following layers were successively grown on the n ⁺ type conductive substrate: n ⁺ layer 7 10 μm thick, i-layer 8 compensated by chromium during epitaxy, 30 μm thick, p ⁺ layer 9 10 μm thick, then i-layer 8 30 microns thick, n ⁺ layer 7 10 microns thick and then again i-layer 8 30 microns thick, p ⁺ layer 9 10 microns thick. Using standard methods of photolithography, chemical etching, and vacuum deposition, ohmic contacts 10 and 11 to highly doped layers were formed. Using reactive-ion etching and short-term chemical etching, wells 12 were formed in the detectors with a top hole diameter of 80 μm and a pitch of 100 μm. The result was a new design nuclear battery.

In operating mode, with detector sizes of 5 × 5 cm ^{2, the} total volume of wells filled with tritium is 0.25 cm ³ . Moreover, the radioactivity of the indicated volume with tritium is 10 ¹⁰ Bq. Since 70% of the electrons emitted as a result of the radioactive decay of tritium fall into the active regions of the detector i.e. in the semi-insulating region 8 (part falls into highly doped layers) and each electron generates approximately 1700 electron-hole pairs, the maximum current from this battery will be 2.5 μA.

Thus, a nuclear battery with a new design of the betavoltaic detector is proposed. The implementation of the detector does not require the creation of p-n junctions on the walls of wells formed in the volume of the detector; therefore, not only silicon structures can be used to create a semiconductor detector.

Information sources

1. Kherani N.P., Shmayda W.T., Zukotynski S. / Nuclear batteries / Patent US 5606213, 1997.

2. Chu F.Y., Mannik L., Peralta S.B., Ruda H.E. / Radioisotope-powered semiconductor battery / Patent US 5859484, 1999.

3. Gadeken L. / Apparatus and method for generating electrical current from the nuclear decay process of radioactive material / Patent US 6774531, 2004.

Claims (1)

A nuclear battery containing a housing filled with isotope material, where at least one semiconductor detector is placed, in which wells are created in the volume, all well sizes being smaller than the mean free path of particles emitted by the gaseous isotope, characterized in that the detector is made in the form alternating layers of n ⁺ , i (either ν or π) and p ⁺ -types of conductivity in this sequence n ⁺ -ip ⁺ -i- ... -n ⁺ -ip ⁺ , and these layers lie in planes perpendicular to the walls of the wells; to n ⁺ -type layers, ohmic contacts are created that are electrically connected to each other, the same contacts are created to p ⁺ -type layers, which are also connected.