Category Next Generation of Photovoltaics

TEM

The final confirmation of the different crystalline structure among the samples comes from the TEM images and ED measurements. Figure 13.5 shows the cross-sectional TEM images and the ED pattern of samples implanted with 5-1016 down to 1015 cm-2 doses, and annealed at 0.8 J cm-2. For the three first images, Fig. 13.5a-c, we can observe a polycrystalline layer on top of a single crystal silicon substrate. It is clearly appreciable that the grain size increases from Fig. 13.5a-c. The sample implanted with the highest dose (Fig. 13.5a) presents a nanocrystalline structure, with a mean grain size of about 5 nm. When the implanted dose decreases the grain size presents a dimension comparable to the implanted layer thickness. For the sample implanted with a implantation dose of 5-1015 cm-2 (Fig...

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GIXRD

Figure 13.3 shows the X-ray diffractograms at 0.4° glancing angle for the samples PLM annealed at 0.8 J cm-2 and implanted with different doses. For the samples implanted with the highest doses (1016 and 5-1016 cm-2), two diffraction peaks at

47.1 and 55.9° can be observed. For the sample with a dose of 5×1015 cm-2, the peak placed at 47.1° disappears, but the peak at 55.9° is still present. However, both diffraction peaks vanish for the sample implanted with the 1015 cm-2 dose. These peaks are attributed to the (220) and (113) silicon reflections. It is worth highlighting that no peaks associated with Ti-Si phases are present. These results point out the formation of a silicon polycrystalline structure for the samples implanted with the

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highest doses...

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Results

13.3.1 Structural Characterization

13.3.1.1 ToF-SIMS Profiles

Figure 13.2 shows the Ti depth profiles for implanted samples at 1014, 1015, 5-1015, 1016 and 5-1016cm-2 after a PLM process at 0.8 Jcm-2. As comparison we have plotted also the profile for the non-annealed samples with doses of 1015 and 1016 cm-3. As it can be seen, Ti profiles have been pushed to the Si surface, becoming steeper and with a higher and sharp maximum, although this effect is more pronounced for lower doses. The second peak that appears clearly for 1014 and

Depth (nm)

Подпись: Fig. 13.2 ToF-SIMS profiles of Ti-implanted samples with 1014, 1015, 5-1015, 1016 and 5-1016 cm-2 doses after PLM annealing at 0.8 Jcm-2. Also the implanted but non-annealed samples with 1015 and 1016 cm-2 are also shown for reference (Reprinted with permission from [22]. Copyright 2010. American Institute of Physics)

1015 cm-2 doses at 40 nm and 50 nm, respectively, marks the border between melted and non-melted semiconductor zone...

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Experimental

300 |rm silicon (111) n-type samples (|x = 1,450cm2 V-1s-1; n = 2.2-1013 cm-3 at room temperature) were implanted in an Ion Beam Services (IBS) refurbished VARIAN CF3000 Ion Implanter at 30KeV with Ti at high doses (1014,1015, 5-1015, 1016 and 5-1016 cm-2). Then the implanted Si samples were annealed by means of the PLM method to recover the sample crystallinity. The PLM annealing process was performed by J. P. Sercel Associates Inc. (New Hampshire, USA). Samples were annealed with one 20 ns long pulse of a KrF excimer laser (248 nm) at energy densities from 0.2 to 0.8 J cm-2. PLM is a highly non-equilibrium processing technique, which is able to melt and recrystallize the Si surface up to about 100 nm depth in very short times (10-8-10-6 s)...

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Ion Implant Technology for Intermediate Band Solar Cells

Javier Olea, David Pastor, Maria Toledano Luque, Ignacio Martil, and German Gonzalez Diaz

Abstract This chapter describes the creation of an Intermediate Band (IB) on single crystal silicon substrates by means of high-dose Ti implantation and sub­sequent Pulsed Laser Melting (PLM). The Ti concentration over the Mott limit is confirmed by Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) measurements and the recovery of the crystallinity after annealing by means of Glancing Incidence X Ray Diffraction (GIXRD) and Transmission Electron Microscopy (TEM). Rutherford Backscattering Spectroscopy (RBS) measurements show that most of the atoms are located interstitially.

Analysis of the sheet resistance and mobility measured using the van der Pauw geometry shows a temperature-dependent de...

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Summary and Conclusions

In this chapter, we have discussed the possible application of InGaN layers doped with Mn to form the basis for Intermediate Band Solar Cell devices. We have discussed the reasons for choosing to study this promising system; the plasma- assisted molecular beam epitaxy method needed to grow such structures; the specific problems associated with the growth of InGaN and finally the progress made so far in achieving this overall goal. We have also discussed briefly other possible dopants e. g. C which might be used in InGaN for the same application.

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Future Plans and Options

The optimum value for the In content in InGaN has yet to be determined, for the moment we are concentrating on samples with a fixed In content, but we will look in the future at other In/Ga compositions. The InGaN samples have to be grown at relatively low temperature and this may result in less than optimum quality of the resulting material. To further improve the quality of the InGaN, we will look at alternative growth techniques such as migration enhanced epitaxy [25], which is known to improve the properties of films grown at low temperature. One of the key problems with all nitride semiconductor structures is the high density of defects. It is well known that this can be improved significantly by growth on bulk substrates, which are now available commercially...

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Proposed IBSC Structures and Progress So Far

Taking all of the above factors into consideration, two different IBSC structures are proposed as shown in Fig. 12.7. Initial studies have concentrated on the InGaN wurtzite materials. Films of InGaN have been grown on semi-insulating (111) oriented GaAs substrates at temperatures from 400-550°C, with and without Mn fluxes to study the incorporation of Mn into InGaN. The results show that the solubility of Mn increases with decreasing growth temperature as is expected for InGaN, which will have a melting point significantly below that of GaN. In films where Mn is above a temperature-dependent critical value, x-ray studies show that the films phase separate into InN-rich and GaN-rich regions, but below this critical value single phase material is obtained...

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