Diamond Wafer as A Semiconductor Material in Nuclear battery

Today we will introduce a nuclear battery as a technology similar to radiation detectors. Nuclear battery is a device that converts energy from radiation into electricity. The cells consist of radioisotopes and the diodes. It has similar operating principle as a solar cell and uses a semiconductor junction for the energy conversion. The longevity of the battery depends on the half-life of the radioisotope and radiation tolerance of the cell (diode). For long operation, low energy beta emitting radioisotopes are suitable to mitigate irradiation induced damage for diodes.

Using 3H (T1/2 = 12yrs), 63Ni (T1/2 = 100yrs) as the beta-source, a long operating time from several years to decades can be realized. X-ray voltaic batteries are also used for this purpose. Alphavoltaic batteries offer higher energy density than these two types of batteries, however irradiation by heavy ion induces damage for diodes, and it degrades energy conversion efficiency. Nuclear batteries are expected to be applied to supply power to the devices in remote environments such as space and underground. The power density of a nuclear battery is the order of several nW/cm2 to µW/cm2, which limits the application to powering ultra-low power sensors and electronics. Since there is a trade-off between lifetime of the device and output power density, it is necessary to select a proper isotope according to the application. Recently, the use of wide bandgap materials has been intensively studied to improve the energy conversion efficiency of nuclear batteries.

The reason for this is that the built-in potential of the diode increases with the increase in the band gap of the semiconductor material. As a result, the open-circuit voltage and energy conversion efficiency of the cell are improved. By using diamond pn junction, which is an ultra-wide gap material, a conversion efficiency is expected to be approaching 30%. For diamond, several characterizations using Schottky diodes (SBDs) have been reported. A Russian research group has reported a prototype of a diamond nuclear battery.   By combining of 130 single cells based on diamond Schottky barrier diodes, the total active area of about 15 cm2 was obtained . They reported open circuit voltage (Voc) of 1-1.85 V, and output power of 45 nW to 36 μW using several radioisotopes. Although it is a tiny device, characteristics of the nuclear battery using a diamond pn junction have also been reported. Since the diamond pn junction has an built-in potential of about 4.5 V, which can further improve the energy conversion efficiency of the cell. Here, we will introduce the improvement of energy conversion efficiency using diamond pn junctions.  

Instead of beta emitting radioisotopes, the electron beam of SEM is used for characterization. The diameter of the diode is 240 μm. The open-circuit voltage Voc was 4.26 V. The short-circuit current Isc (V = 0 V) was 10.7 nA, and the maximum value of P (V × I) , PMP, was 38.6 nW. Using the equation, the fill factor (FF) and the conversion efficiency ηs are calculated from the current-voltage characteristics of the semiconductor: FF = 0.85 and ηs = 28%. Here, the average electron-hole pair formation energy ε was set to 13 eV. For ηs obtained from the I-V and P-V characteristics of semiconductors, the reported value for diamond SBDs using electron beam irradiation is 11%. Diamond pn junctions have achieved a conversion efficiency that is more than twice that of diamond SBDs and the highest for a nuclear battery.

CSMH, a wide bandgap Semiconductor Material and Device company manufacturing with unique technology with investments from Korea, China, and Singapore. we are equipped with advanced semiconductor production equipment to produce high-quality Diamond wafers and AlN templates on a variety of substrates, including Si, sapphire, and polished diamond.

The company has built an intelligent manufacturing plant, started mass production of diamond wafers, diamond heat sinks, and has a substantial intellectual property (IP) portfolio. Our product's performance has improved to a level that is among the best in the world after more than 10 years of technological development.