Electrical observation of non-radiative recombination in Er doped Si nano-crystals during thermal quenching of intra-4f luminescence

Abstract

Thermal quenching of luminescence of Er dopants in Si nano-crystals (Si-nc's) was investigated employing an impedance model for the analysis of photo-injected charges. Relaxation response indicated that Er doping forms not only optical centers but also trapping centers near the Si-nc's. The response time constant of trapped charges was dependent on temperature, with the dependence correlating to thermal quenching. These findings indicate that quenching occurs by trapping followed by consumption of charges. The complex analyses revealed that the response represents nonradiative recombination at the centers rather than release of confined charges from the Si-nc through the centers. We propose a possible energy diagram for the non-radiative recombination.

Time-resolved analysis of charge responses determining luminescence properties

“…6(b) and Ref. 23 it is observed that the lowest value of s 0 5 36 ls in this temperature range in Fig. 8(a) is much higher than the response time constant of Si-nc of ;3.7 ls in a previous study 13 and s E0 ; 9 ns, which provides the maximum intensity from the commercial LED in Fig.…”

“…3(a). 23 The sample temperature T for this experiment was set at 75 K. The inset of this figure shows a reference response spectrum of Si-nc without Er doping. By comparing the spectra of Si-nc with and without Er, it can be understood that the Er doping provides a new response at s 0 5 48 ls (x 0 5 21 krad/s).…”

“…For (ii), a possible loss process, i.e., nonradiative e-h recombination via trapping and interface levels was proposed in a previous paper. 23 The trapping level is higher than the quantum-well level of Si-nc, so only thermally excited charges are trapped in the level. The energy barrier height for the thermal excitation was estimated to be ;55 meV.…”

“…The energy barrier height for the thermal excitation was estimated to be ;55 meV. 23 The trapping level represents a relaxation path for the nonradiative recombination and reduces the luminescence intensity by consuming the confined charges in Si-ncs. Although an additional surface treatment for the Si-nc surface would be useful for (ii), a considerable improvement in the emission intensity can be expected by (i) rather than by (ii).…”

Discrimination between energy transfer and back transfer processes for GaAs host and Er luminescent dopants using electric response analysis

“…7,8,14 We have investigated the luminescence mechanisms by using electric measurements. [15][16][17] In the rare-earth-doped semiconductors, the indirect and bidirectional energy transfers are determined by the dynamics of the charge carriers, such as trapping and recombination of the charges. Therefore, the electric measurements, which are sensitive to the charge carriers, are expected to be able to directly assess the energy F-and B-transfers.…”