BetAvolTaic energy converters based on GAllium Nitride semiconductors – BATGAN

Betavoltaics are promising electrical power sources for micro-electromechanical systems (MEMS), low accessibility environmental sensors, pacemakers and biomedical implants, space applications and any small load electronic devices where size, weight and/or accessibility is an issue. Betavoltaics are very power dense (400 mW/cm3 or 3.80 mW/kg for 63Ni), can withstand extreme environments, and have long half-lives (100 years for 63Ni). They potentially produce a power per unit volume similar to that of current alkaline batteries, continuously, over a whole century, in stable and safe packages without recharging. Betavoltaics have the structure of a p-n junction like a solar cell, but use beta radiation, i.e. energetic electrons resulting from neutron decay into an electron and proton. These electrons cause multiple impact ionization events resulting in the generation and collection of many electron-hole pairs, which are then collected. Because beta radiation penetrates only several microns in solid materials, beta radiation can be easily shielded and sealed packaging can assure safety. Several isotopes produce pure beta radiation without producing gamma radiation, which is difficult to shield, or without producing alpha radiation, which is even easier to shield but is damaging to semiconductor p-n junctions.
France, due to its world leading nuclear power program, is uniquely positioned to lead the development of these batteries, as irradiation currently wasted by nuclear reactors could produce betavoltaic isotopes on an industrial scale. France, to the best of our knowledge, is not conducting any betavoltaic research, and recent advances and programs come mostly from the United States.
The project BATGAN brings together leading researchers in the French community in order to provide a clear path to industrial production of superior betavoltaic devices. The project will demonstrate power output on the order of several microwatts, enough to power MEMs devices and various sensors. The project will also demonstrate technologies that will lead to the creation of commercializable multi-layer devices. The partners have complementary expertise in growth of wide-bandgap materials (UMI GT-CNRS), processing of advanced semiconductor materials (LPN), deposition of nuclear beta emitters for use in devices (CEA-LIST), and a French startup possessing world-class experience on innovative uses of ZnO. This project BATGAN, is to construct different betavoltaic battery devices out of p-i-n diodes made of gallium nitride (GaN) and a 63Ni power source. GaN and related compounds are extremely radiation resistant and the wide bandgap of 3.4 eV increases energy efficiency. 63Ni is an isotope with a 100 years half-life. It emits 17 keV beta radiation which penetrates up to 1.5 microns in GaN. BATGAN will make a front-contacted two-cell battery and also make the first study of radiation related degradation of devices made of GaN and the ternary alloys AlGaN, InGaN, and BGaN. Next generation devices will demonstrate the technological building blocks for a stackable multi-layer design. It will make use of a lift-off process uniquely developed by the UMI and Nanovation to prove potential for commercial construction of three- dimensional batteries. Such a lift-off procedure does not exist for SiC, another leading contender for betavoltaic p-i-n devices. Thus only GaN leads to radiation-resistant, stackable thin film devices. As the project is based on proven physical principles and mature building blocks, it has a high probability of success. At the same time, scientific knowledge will result from studies of material damage vs. time, from studies of specialized non-contaminating packaging of 63Ni, and from studies of heteroepitaxy on sacrificial ZnO layers. The project has the capability of enabling many MEMS, remote sensing, and space applications that were until now not possible.