Photoluminescence lifetime distributions of chalcogenide glasses obtained by wide-band frequency resolved spectroscopy

Radiative recombination of excitons in amorphous semiconductors

“…(8), with i ¼ 1; one gets R spt1 ¼ 1:03 Â 10 7 s 21 ðt r1 ¼ 0:97 Â 10 À7 sÞ at 15 K, R spt1 ¼ 1:84 Â 10 7 s 21 ðt r1 ¼ 0:55 Â 10 À7 sÞ at 20 K and R spt1 ¼ 1:08 Â 10 6 s À1 ðt r1 ¼ 0:92 msÞ at 4.4 K. For i ¼ 2; we get R spt2 ¼ 1:18 Â 10 7 s À1 ðt r2 ¼ 0:85 Â 10 À7 sÞ at 15 K, 2.14 Â 10 7 s À1 ðt r2 ¼ 0:47 Â 10 À7 sÞ at 20 K and 0.74 Â 10 6 s À1 ðt r2 ¼ 1:34 msÞ at 4.4 K. Thus, this radiative lifetime is found to be in the ms time range and agrees very well with the radiative lifetime of the fast component in the QFRS measurement by Aoki et al [5].…”

“…The theory is applied to calculate the rate of spontaneous emission for three samples of a-Si:H for which the PL spectra have been measured at 4.4 K [5], 15 K [2], 20 K [7]. The rate is independent of the excitation density but it increases and hence the radiative lifetime becomes shorter as the PL energy, increases, which is quite consistent with the observed results [5]. Eq.…”

“…(6) and (7). The PL intensity as a function of _o has been measured in a-Si:H [2,5]. From these measurements the photon energy corresponding to the PL peak maximum can be determined.…”

“…For finding E 01 and E 02 from Eq. (9), we need to know the value of E mx and the carrier (exciton) temperature T. Wilson et al [2] have measured the PL intensity as a function of the emission energy for three different samples of a-Si:H at 15 K. Stearns [7] and Aoki [5] have also measured it at 20 and 4. For calculating the maximum rate for possibility (i), the excitonic reduced mass is obtained as m ex ¼ 0:17m e : Using this in Eq.…”

“…Using the time-resolved spectroscopy (TRS), Wilson et al [2] have observed PL peaks in the nanosecond (ns), microsecond (ms) and millisecond (ms) time ranges in a-Si:H at a temperature of 15 K. In contrast to this, using the quadrature frequency-resolved spectroscopy (QFRS), only a double-peak structure PL has been observed in aSi:H at the liquid helium temperature. One peak appears for a short time in the ms range and the other in the ms range [3][4][5]. Using the effective mass approach, a theory for the excitonic states in amorphous semiconductors has been developed by Singh et al [6] and the occurrence of the double-peak structure has successfully been explained.…”