Charge Carrier Lifetime and Trap States in Novel Pure-Boron-Based Ultrashallow p – n Junctions

Abstract

Trap states and carrier transport parameters are critical to the performance of p–n-junction-based photodetectors. This study investigates ultrashallow p–n junctions for ultraviolet and low-energy particle detection fabricated using chemical vapor deposition-based pure-boron deposition (CVD-PB) with a junction depth only tens of nanometers, in comparison, also using ion implantation (IMP), epitaxy (EPI), and vacuum evaporation (VEP). Deep-level photothermal spectroscopy (DLPTS) and homodyne photocarrier radiometry (HoPCR) were used to analyze charge carrier dynamics, including charge carrier lifetime and trap states. A phenomenological theoretical model for HoPCR signals was developed to explain trap-state-modulated carrier transport dynamics. CVD-PB junctions demonstrated long recombination lifetimes in the doping layer ( $7.09~\pm ~0.01~\mu $ s) and bulk ( $35.80~\mu $ s), comparable to high-energy ion-implanted (HE-IMP) junctions ( $5.68~\pm ~0.58$ and $36.10~\mu $ s). EPI and VEP junctions have short carrier bulk recombination lifetimes ( $1.95~\pm ~0.17$ and $0.63~\pm ~0.03~\mu $ s, respectively). DLPTS revealed an electron trap in the EPI junction with an activation energy of 0.09 eV and a capture cross section of $7.52\times 10^{-{20}}~\pm ~6.82\times 10^{-{21}}$ cm2; no detectable traps were observed in CVD-PB or HE-IMP junctions. Simulations showed that EPI junctions had twice the dark current of CVD-PB and HE-IMP at 10 V, with a 15% reduction in photocurrent. When reversely biased at 5 V and without typical guarding ring designs generally used in optoelectronics, CVD-PB exhibited the lowest dark current ( $0.95~\mu $ A/cm ${}^{{2}}$ ) when compared to HE-IMP ( $3.25~\mu $ A/cm ${}^{{2}}$ ) and EPI ( $51.77~\mu $ A/cm ${}^{{2}}$ ).