Solar Blind UV Photodiodes with 100% Internal Quantum Efficiency Based on Silicon Direct Band Gap Raj Korde *a , John Seely b , Eric Gullikson c a IBP USA Group Inc., 1536 West 25 th Street, MS 619, San Pedro CA, USA 90732-4463 b Coastal Physica LLC, 5202 Carolina Beach Road, Wilmington NC, USA 28412 c Lawrence Berkeley National Laboratory. 1 Cyclotron Rd., Bldg. 2R0405, Berkeley, CA, USA 94720-8199 ABSTRACT 5 mm diameter silicon photodiodes having 30-50 nm electrically active thicknesses were fabricated on silicon-on insulator (SOI) wafers to realize solar blind UV photodiodes (UVTN). Their responsivity measurements in the 200-1100 nm range indicated that responsivities drop sharply after 350 nm. Silicon direct bandgap is 3.5 eV which corresponds to 354 nm. Thus, these devices act as wide band gap semiconductor photodiodes like SiC, GaN, AlGaN, diamond etc. UV/VUV/EUV filters can be directly deposited on UVTN detectors to limit their response to specific wavelengths. Four filtered UVTN photometers devoid of chronic red leak and associated electronics will fit in a 1 U CubeSat which can be used to make solar UV/VUV/EUV spectral measurements. Because of their minuscule silicon thickness, UVTN detectors will have low responsivity to x-rays and other space radiation and also will be very hard to space radiation. Thus, these devices are expected to survive in the deep space environment for several decades for applications like water detection (165 nm strong reflection) on small bodies as desired by NASA’s Small Bodies Assessment Group. As the solar blind material is silicon which is high volume manufacturing compatible, this is a disruptive technology development and will have numerous application in space research. For example, one may use UVTN pixels in an imaging array to get a true solar blind (no red leak) UV/VUV/EUV imager with 100% IQE. Keywords: Solar Blind UV Photodiodes, UV Detectors, VUV Photodiodes, Silicon Direct bandgap, EUV Photodiodes, UVTN, VUV Detectors 1. INTRODUCTION Fabrication of stable, 100% internal quantum efficiency (IQE) silicon photodiodes (AXUV) for 5 nm to 400 nm photons have been demonstrated previously [1,2]. Two unique properties are associated with the AXUV photodiodes. The first property is the absence of a surface dead region; i.e. no photogenerated carrier recombination occurs in the doped n-type front region and at the silicon - silicon dioxide interface. Absence of this dead region yields complete collection of photogenerated carriers by an external circuit resulting in 100% internal quantum efficiency. Secondly, diodes with 1 Gigarad (SiO2) hardness were fabricated by nitrogen doping at the Si-SiO2 interface to form an oxynitride window instead of the common silicon dioxide window [3]. AXUV photodiodes typically have 25 μm thick electrically active silicon thickness. Because most of the VUV/UVC photons are absorbed in a 10 nm thickness of silicon, it is important to investigate fabrication of silicon photodiodes with 10s of nm of active silicon thickness. This work describes fabrication of 30-50 nm electrically active silicon thickness photodiodes (UVTN). This is expected to reduce their response to visible light by orders of magnitude because the long wavelength photons are absorbed in several microns of silicon. The UVTN photodiodes do not need external voltages for their operation, are insensitive to magnetic fields, cost less to fabricate, have low mass and have large collection area to size ratio making them extremely attractive for use in small satellites. *ibpusa@cox.net CubeSats, SmallSats, and Hosted Payloads for Remote Sensing VIII, edited by Sachidananda R. Babu, Thomas S. Pagano, Jeffery J. Puschell, Proc. of SPIE Vol. 13146, 131460C © 2024 SPIE · 0277-786X · doi: 10.1117/12.3037964 Proc. of SPIE Vol. 13146 131460C-1