(oral talk) Nanostructured Silicon Hyperdoped with Se by Ion Implantation and Flash Lamp Annealing

Hyperdoping of silicon involves the introduction of extremely high concentrations of dopants to create intermediate bands within its bandgap, allowing it to absorb photons with lower energy than the Si bandgap. This enables silicon to efficiently capture infrared light, making hyperdoped Si a promising option for solar cells and photodetectors.
Hyperdoping can be made using two methods: ultrafast laser or ion implantation. The laser hyperdoping is advantageous for simultaneously creating random surface textures with lower reflectance and forming the hyperdoped layer absorbing sub-bandgap photons, thus enabling nearly complete absorption across a wide spectrum. Nevertheless, the practical application of laser hyperdoping is limited due to the presence of severe laser-induced damage that extends considerably deeper than the hyperdoped layer resulting in carrier recombination, which compromises the performance of the fabricated devices. In contrast, hyperdoping through ion implantation offers several distinct advantages, including a controllable doping profile and the ability to achieve a relatively shallow doping depth. However, ion implantation alone does not create surface structures, thus the planar surface will suffer from reflectance losses. To overcome the reflection losses, nanostructured Si can be utilized which can achieve >99% absorption in above-bandgap absorption. We aim to extend the high absorption into sub-bandgap wavelengths by combining the nanostructured Si and ion implantation hyperdoping.
In our study, we fabricate inductively coupled plasma-reactive ion etching (ICP-RIE) nanostructured Si samples that do not have crystal damage. The nanostructures are subsequently ion implanted with Selenium (Se) with high dosages to create a hyperdoped layer. In the meantime, we evaluate any morphological damage to the nanostructures after implantation since the ICP-RIE does not introduce any crystal damage. Then, we apply flash lamp annealing that is necessary to activate the dopants without too much compromising dopants concentration. However, it is also known to involve the melting and resolidification of the surface layer which is potentially damaging to the nanostructures. We thus characterize the impact of the annealing on the morphological, optical, and electrical properties of the Se-hyperdoped and nanostructured silicon. We expect to obtain high sub-bandgap absorption combined with reduced carrier recombination by flash lamp annealing.