Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon

Abstract

We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing.

Crystallinity and Sub-Band Gap Absorption of Femtosecond-Laser Hyperdoped Silicon Formed in Different N-Containing Gas Mixtures

“…As reported, nitrogen can be doped in silicon lattices in different configurations, such as single nitrogen atoms, paired nitrogen atoms, and nitrogen molecules [ 26 , 31 , 32 , 33 ]. With the irradiation of fs-laser pulses, nitrogen atoms were dissociated from NF 3 and then doped in silicon lattices at a substitutional or interstitial site (single atoms and paired atoms).…”

“…With the irradiation of fs-laser pulses, nitrogen atoms were dissociated from NF 3 and then doped in silicon lattices at a substitutional or interstitial site (single atoms and paired atoms). The super-statured nitrogen atoms in the doped layer combine with vacancies to form various nitrogen vacancies complexes [ 26 , 32 , 33 ]. These complexes effectively improved the crystallinity of the hyperdoped silicon by locking dislocations and suppressing the formation of large defects [ 25 , 26 , 29 , 30 ].…”

Fluorescent nucleobases as tools for studying DNA and RNA

“…Although both nucleobases emit at similar wavelengths, their excitation maxima differ substantially. 8-AzaG absorbs at 256 nm in buffer, whereas 4-thieno-R absorbs at 294 nm, with the sulfur-substituted nucleobase requiring less energy to excite 43 .…”

Sub-bandgap photo-response of non-doped black-silicon fabricated by nanosecond laser irradiation

“…In the hyper-doped Si samples, supersaturated impurities (such as S, Se, Te, N, and P) can be doped into the Si surface layer via pulsed laser irradiation or ion implantation [4][5][6][7]. The supersaturated impurities can introduce energy levels and even intermediate bands in the Si bandgap, which can contribute to a broad sub-bandgap absorption [4,8]. Photodiodes based on these materials exhibit very high photo-response around the band-edge region [9][10][11].…”