Semiconductor betavoltaic batteries with p-n diodes

Description (excerpt)

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT The United States Government has ownership rights in this invention. Licensing inquiries may be directed to Office of Technology Transfer, US Naval Research Laboratory, Code 1004, Washington, D.C. 20375, USA; +1.202.767.7230; nrltechtran@us.navy.mil, referencing Navy Case No. 211618-US1. BACKGROUND OF THE INVENTION Aspects of the present invention relate generally to betavoltaic batteries and, more particularly, to semiconductor betavoltaic batteries incorporating p-n junctions. In general, a betavoltaic power cell or battery is a type of nuclear battery which generates electric current by absorbing beta (β) particles emitted from a radioactive source into a semiconductor absorber. The β-particles generate carriers which are collected at the p-n junction. In general, a β-particle is a high energy, high speed electron (β − ) or positron (β + ) that is ejected from a nucleus by some radionuclides during a form of radioactive decay called B-decay. Advantages of betavoltaic power cells over conventional batteries include a long service life, reliability, and compactness. Various betavoltaic power cells have been explored for supplying low-current power to devices (e.g., microelectronic devices). For example, various betavoltaic cells with Schottky barrier diodes have been evaluated. Such betavoltaic cells include those utilizing a metal β-particle source, such as nickel-63 ( 63 Ni), in conjunction with a semiconductor absorber configured to absorb the β-particles. In general, a Schottky barrier diode (i.e., Schottky diode or hot-carrier diode), is a semiconductor diode formed by the junction of a semiconductor with a metal. In contrast to a Schottky barrier diode, a p-n diode is a type of semiconductor diode based upon a p-n junction. More specifically, a p-n diode is made by forming a metallurgical junction of a p-type semiconducting layer to an n-type semiconducting layer. In general, n-type semiconductors are creating by doping an intrinsic semiconductor with an electron donor element. In n-type semiconductors, electrons are the majority carriers and holes are the minority carriers. In general, p-type semiconductors are created by doping an intrinsic semiconductor with an electron acceptor element. In contrast to n-type semiconductors, in p-type semiconductors, holes are the majority carriers and electrons are the minority carriers. In general, a semiconductor-based heterojunction is the interface that occurs between two layers or regions of dissimilar crystalline semiconductors. The term p-n heterojunction refers to the contact formed by p-type and n-type semiconductors. There remains a need for further development of betavoltaic power devices to improve the compactness and function of such devices. SUMMARY OF THE INVENTION In a first aspect of the invention, there is an electrically inactive betavoltaic battery device comprising: a p-type semiconductor layer including at least one stable isotope that transforms into a beta emitter upon irradiation with thermal neutrons; and an n-type semiconductor beta-absorber layer configured to absorb beta particles; wherein the p-type semiconductor layer and the n-type semiconductor layer form a p-n diode, and wherein the electrically inactive betavoltaic battery device is configured to be transformed into an electrically active betavoltaic battery upon irradiation with thermal neutrons. In implementations, the p-type semiconductor layer comprises nickel oxide including nickel-62 ( 62 Ni), and the n-type semiconductor beta-absorber layer is selected from the group consisting of: gallium oxide (Ga 2 O 3 ), gallium nitride (GaN), silicon carbide (SiC), diamond, and aluminum nitride (AlN). In embodiments, the n-type semiconductor beta-absorber layer is an epitaxial layer or a substrate layer. The betavoltaic battery may include one or more electrodes (e.g., nickel electrodes). In implementations, the betavoltaic battery includes a second n-type semiconductor layer (e.g., Ga 2 O 3 or GaN), between the n-type semiconductor beta-absorber layer and the p-type semiconductor layer, where the p-type semiconductor layer, the n-type semiconductor β-absorber layer, and the second n-type semiconductor layer comprise the p-n diode. In embodiments, the p-type semiconductor layer extends into at least one trench formed in the n-type semiconductor beta-absorber layer. In a second aspect of the invention, there is a method of making an electrically inactive betavoltaic battery device comprising: fabricating a p-n diode comprising a p-type semiconductor layer including at least one stable isotope that transforms into at least one beta-particle emitter upon irradiation with thermal neutrons, and an n-type semiconductor beta-particle absorber layer configured to absorb beta particles. This embodiment enables an electrically inactive betavoltaic battery to be manufactured at a standard