Deionization of Dopants in Silicon Nanofilms Even with Donor Concentration of Greater than 10¹⁹ cm^–3

Abstract

Understanding the dopant properties in heavily doped nanoscale semiconductors is essential to design nanoscale devices. We report the deionization or finite ionization energy of dopants in silicon (Si) nanofilms with dopant concentration (ND) of greater than 10(19) cm(-3), which is in contrast to the zero ionization energy (ED) in bulk Si at the same ND. From the comparison of experimentally observed and theoretically calculated ED, we attribute the deionization to the suppression of metal-insulator transition in highly doped nanoscale semiconductors in addition to the quantum confinement and the dielectric mismatch, which greatly increase ED in low-doped nanoscale semiconductors. Thus, for nanoscale transistors, ND should be higher than that estimated from bulk Si dopant properties in order to reduce their resistivity by the metal-insulator transition.

Absence of free carriers in silicon nanocrystals grown from phosphorus- and boron-doped silicon-rich oxide and oxynitride

“…[ 29 ] and [ 52 ] for details). Following the calculations therein, we can estimate the P-ionization energy of the J -peak (or respectively the beginning of the J -plateau) to ≈200 meV, in accordance with literature values on ionization energies of nano-sized Si [ 54 – 55 ]. For SRO:P the J -plateau indicates a broader distribution of P-ionization energies towards even larger values.…”

Numerical analysis of band tails in nanowires and their effects on the performance of tunneling field-effect transistors

“…In nanostructured semiconductors, the situations around the dopants which cause the band tails are different from bulk semiconductors; the number of neighbor dopants is reduced 13,14) and potentials induced by dopants are greatly affected by surrounding dielectrics because of the large surface-to-volume ratio of nanostructures. [14][15][16][17][18][19] Thus, band tails in nanostructured semiconductors should also be changed from those in bulk semiconductors. In fact, the change of band tails in nanostructured semiconductors can be confirmed in the experimentally derived dopant concentration dependence of ionization energy in silicon-on-insulators with various thicknesses.…”

“…[7][8][9][10][11][12] Exponential decay is defined for bulk semiconductors. In nanostructured semiconductors, the situations around the dopants which cause the band tails are different from bulk semiconductors; the number of neighbor dopants is reduced 13,14) and potentials induced by dopants are greatly affected by surrounding dielectrics because of the large surface-to-volume ratio of nanostructures. [14][15][16][17][18][19] Thus, band tails in nanostructured semiconductors should also be changed from those in bulk semiconductors.…”

“…In fact, the change of band tails in nanostructured semiconductors can be confirmed in the experimentally derived dopant concentration dependence of ionization energy in silicon-on-insulators with various thicknesses. 14) However, the effects of band tails on TFETs in nanostructured semiconductors have not been fully studied yet.…”