Films minces à base de Si nanostructuré pour des cellules ...
Films minces à base de Si nanostructuré pour des cellules ... Films minces à base de Si nanostructuré pour des cellules ...
tel-00916300, version 1 - 10 Dec 2013 Figure 3.18: distribution. Formation of Si-np in SRSO sublayer of CA 50(3/3) ML and their size nm barrier length estimated by [D.Tsoukalas 01]. Thus, a SiO 2 sublayer of 3 nm is at the limit to prevent diusion from two consecutive SRSO sublayers, resulting in 30% of Si-np with sizes between 3-4 nm. However, most of the Si-np have sizes that are restricted to the 3 nm SRSO sublayer thickness and the mean size of the Si-np in our case is 2.7 nm. 3.7.2 Emission properties The emission properties of 50(3/3) ML after CA is investigated (Fig. 3.19). Figure 3.19: PL spectrum of CA 50(3/3) ML. 84
It can be seen that there is a signicant emission from the material in the visible range, contrary to the absence of any emission in SRSO-P15 monolayer. This con- rms that the absence of emission in a monolayered conguration at this annealing is due to the loss of quantum connement of carriers. The agglomeration into big size particles is prevented in the ML leading to this emission. It is interesting to note that the curve is composed of two peaks, peak (1) and peak (2) at 1.41 eV and 1.53 eV respectively indicating there are more than one type of emitters. We can attribute the peak at higher energy (1.53 eV) to Si-np whose sizes range between 2-3 nm, which represent more than 50% of Si-np (ref. Fig. 3.18), since the mean size of our Si-np are only about 2.7 nm and cannot lead to a redshifted emission. Peak (1) at lower energy (1.41 eV) might be attributed to bigger sized particles that are formed due to overgrowth at interfaces as observed in APT. tel-00916300, version 1 - 10 Dec 2013 3.8 Inuence of sublayer thicknesses In order to further explore the emission properties, the inuence of the SRSO and the SiO 2 sublayer thicknesses on the formation of Si-np becomes the next subject of concern. To begin our investigations, ve MLs with dierent thicknesses of SRSO and SiO 2 sublayers were grown as detailed in table 3.8. The total thickness of the samples were xed around 500 nm to ensure uniformity in comparison. Since this part of the study is shared between this thesis and the thesis of M. Roussel 4 , these sublayer thicknesses were chosen to suit the needs of both. Notation Patterns t SRSO (nm) t SiO2 (nm) Total thickness (nm) 28(8/10) 28 8 10 504 52(8/1.5) 52 8 1.5 494 36(4/10) 36 4 10 504 70(4/3) 70 4 3 490 90(4/1.5) 90 4 1.5 504 Table 3.8: SRSO/SiO 2 MLs-Sample details 3.8.1 Fourier transform infrared spectroscopy Typical FTIR spectra of SRSO/SiO 2 ML with annealing is shown in gure 3.20a. The FTIR analyses were made to witness the evolution of phase separation process from 1h-900°C to 1h-1100°C (CA). The as-grown spectrum is also included in 4 Groupe de Physique des Matériaux, Université et INSA de Rouen, UMR CNRS 6634, France. 85
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tel-00916300, version 1 - 10 Dec 2013<br />
Figure 3.18:<br />
distribution.<br />
Formation of <strong>Si</strong>-np in SRSO sublayer of CA 50(3/3) ML and their size<br />
nm barrier length estimated by [D.Tsoukalas 01]. Thus, a <strong>Si</strong>O 2 sublayer of 3 nm is<br />
at the limit to prevent diusion from two consecutive SRSO sublayers, resulting in<br />
30% of <strong>Si</strong>-np with sizes between 3-4 nm. However, most of the <strong>Si</strong>-np have sizes that<br />
are restricted to the 3 nm SRSO sublayer thickness and the mean size of the <strong>Si</strong>-np<br />
in our case is 2.7 nm.<br />
3.7.2 Emission properties<br />
The emission properties of 50(3/3) ML after CA is investigated (Fig. 3.19).<br />
Figure 3.19: PL spectrum of CA 50(3/3) ML.<br />
84