Intrinsic carrier multiplication efficiency in bulk Si crystals evaluated by optical-pump/terahertz-probe spectroscopy

Abstract

We estimated the carrier multiplication efficiency in the most common solar-cell material, Si, by using optical-pump/terahertz-probe spectroscopy. Through close analysis of time-resolved data, we extracted the exact number of photoexcited carriers from the sheet carrier density 10 ps after photoexcitation, excluding the influences of spatial diffusion and surface recombination in the time domain. For incident photon energies greater than 4.0 eV, we observed enhanced internal quantum efficiency due to carrier multiplication. The evaluated value of internal quantum efficiency agrees well with the results of photocurrent measurements. This optical method allows us to estimate the carrier multiplication and surface recombination of carriers quantitatively, which are crucial for the design of the solar cells.

Black-Silicon Ultraviolet Photodiodes Achieve External Quantum Efficiency above 130%

“…Indeed, several examples of internal quantum yield (i.e. number of eh pairs generated by a single photon) exceeding one can be found in the literature for both silicon and germanium [14,15,16,17,18,19,20,21,22,23,24,25].…”

“…However, nowadays it is well known that this limit can be overcome by the carrier multiplication process, i.e., the phenomenon in which the excess energy of hot carriers is utilized to produce further electron-hole pairs by impact ionization [11][12][13]. Indeed, several examples of internal quantum efficiency (IQE) exceeding one have been reported for both silicon and germanium [14][15][16][17][18][19][20][21][22][23][24][25] as well as more recently also for graphene-silicon devices [26][27][28].…”

Ultrafast free-carrier dynamics in Cu2ZnSnS4 single crystals studied using femtosecond time-resolved optical spectroscopy

“…THz-TA measurements were performed using a 1-kHz Ti:sapphire regenerative amplified laser with a pulse duration of 35 fs. 18 The excitation pump with tunable photon energy emitted from an optical parametric amplifier was chopped with a frequency of 250 Hz and focused loosely on the sample attached to a metal plate with a 2-mm-diameter hole. A THz probe pulse with a center frequency of 1 THz generated from two-color pumped air plasma was directed to the excitation spot.…”

Multiple exciton generation in isolated and interacting silicon nanocrystals

“…Far from the ICM th , II is proved to be slightly more efficient in Si NCs than in Si bulk, despite the fact that the differences are not remarkable. As a consequence, II can be relevant also in Si bulk crystals, 12 which means that restrictions arising from momentum conservation do not quench the relevance of this process in k-dispersive materials. This point was firstly discussed by Kane, 161 which proved that the II rate remains almost unchanged if the crystal momentum conservation limit is ignored.…”

“…Due to the restrictions imposed by energy and momentum conservation and by ultrafast interband relaxation, CM was expected to be quite slow in bulk semiconductors. [9][10][11][12] Experimental results pointed out that, in these systems, CM becomes a significant process only for photon energies much greater than E g , while lower CM energy thresholds were initially detected in NCs. At the nanoscale, CM is favored by quantum confinement of the electronic density that enhances the carrier-carrier Coulomb interaction as a consequence of the reduced dielectric screening and augmented wavefunctions overlapping.…”