Supplemental material:
Far infrared photoconductivity in a silicon based material: vanadium
supersaturated silicon.
E. García-Hemme1, 2, R. Garcia-Hernansanz1, 2, J. Olea2, 3, D. Pastor1, 2, 3, A. del Prado1, 2
, I. Mártil1, 2 and G. González-Díaz1, 2.
1
Dept. de Física Aplicada III (Electricidad y Electrónica), Univ. Complutense de
Madrid, 28040 Madrid, Spain
2
CEI Campus Moncloa, UCM-UPM, 28040 Madrid, Spain
3
Instituto de Energía Solar, E.T.S.I. de Telecomunicación, Univ. Politécnica de Madrid.
28040 Madrid, Spain
These figures and discussion are provided in support of the main data presented
in the manuscript.
Figure S 1 – ToF-SIMS profiles of V implanted Si samples at 1013 and 1016 cm-2 subsequently
PLM processed at 1 Jcm-2.
Figure S1 shows the concentration depth profile for the V implanted samples at
1013 and 1016 cm-2 doses subsequently PLM processed at 1 Jcm-2. The theoretical Mott
limit is shown as a reference. For the sample implanted with the lowest dose (1013 cm-2),
the Mott limit concentration is not reached. However, for the sample implanted at the
higher dose, a V concentration over the theoretical Mott limit is reached in a layer with
an approximate thickness of 100 nm. Theoretically, the delocalization transition point
could have been surpassed for this sample.
Figure S 2 - High resolution TEM images of V implanted Si sample at 1013 cm-2 dose and
subsequently PLM processed at 1 Jcm-2.
Figure S2 shows the high degree of crystallization obtained in the V implanted
Si sample at 1013 cm-2 and PLM processed at 1 Jcm-2.
Figure S 3 - Sheet conductance as a function of the temperature for the Si implanted Si at 10 16
cm-2, the V implanted Si at 1013 cm-2 and the V implanted at 1016 cm-2. All these samples were
subsequently PLM processed at 1 Jcm-2. Also a reference silicon substrate is shown. Dashed
lines represent the values obtained from the substraction of the V implanted Si at 10 16 cm-2 and
the Si reference substrate.
Figure S3 shows the sheet conductance as a function of the temperature for the
V implanted samples at 1013 and 1016 cm-2 doses and PLM at 1 Jcm-2 and the Si
implanted Si sample at 1016 cm-2 dose and PLM at 1 Jcm-2. Also, a reference silicon
unimplanted substrate is presented.
We can observe the expected behavior for the Si unimplanted substrate, i.e. an
increase of the sheet conductance as the temperature decreases due to the reduction of
the phonon scattering and an abrupt decrease of the sheet conductance at very low
temperatures due to the carrier concentration freeze-out effect. The Si implanted Si
sample and the V implanted sample at the lowest dose 1013 cm-2 show a sheet
conductance behavior almost equal to the Si substrate. These results suggest that, by one
side, the defective layer of the Si implanted Si sample does not significantly affect the
transport properties of the whole sample. By the other side, the implantation of V with a
1013 cm-2 does not affect the transport properties despite the high V concentration.
However, the V implanted sample at the highest dose (1016 cm-2) shows a
different trend. This sample increases its sheet conductance as the temperature
decreases, but at a given temperature of 113 K the sheet conductance decrease as the
temperature decreases, approaching to an almost constant value at very low
temperatures of 0.55 𝑚𝑆 without showing a concentration freeze out effect. We have to
take into account that this sample presents a V concentration over the theoretical
insulator-metal transition and then a band of allowable states could be formed from the
delocalization of the V deep levels states in the implanted and PLM layer, i.e. an
intermediate band (IB). Therefore the absence of the freeze out effect would be coherent
with the proposed Mott transitions since a semi-filled IB could result in a metallic
behavior. Therefore we can assume for this sample a parallel bilayer structure formed
by an IB material in the implanted layer and a silicon substrate.
The total sheet conductance of the two layer associated in parallel is given by
𝐺𝑇 = 𝐺𝐼𝐵 + 𝐺𝑆𝑖 , where 𝐺𝐼𝐵 is the sheet conductance of the IB material and 𝐺𝑆𝑖 is the
sheet conductance of the Si substrate. For temperatures lower than 113K, this sample is
going through an electrical decoupling between the IB material layer and the Si
substrate, otherwise 𝐺𝑇 could not be lower than the sheet conductance of any of the
conduction branches (Si substrate or IB material layer). Therefore, for the lower
temperature range we are measuring only the electrical transport properties of the IB
material (𝐺𝐼𝐵 ).
In the temperature range where the bilayer is coupled (113 K – 300 K), the
dashed line represents the values obtained from the subtraction of the total sheet
conductance and the Si reference substrate sheet conductance, i.e. 𝐺𝐼𝐵 = 𝐺𝑇 − 𝐺𝑆𝑖 . This
magnitude represents the IB material sheet conductance when the two layers are
coupled. We can observe that it shows a very low temperature dependence and that its
value tends to the one measured at low temperatures.
This electrical decoupling effect and metallic behavior has been also observed in
the Ti supersaturated Si1 and Co supersaturated Si.2 This electrical behavior has been
satisfactorily explained and reproduced by means of an analytical model which takes
into account the parallel bilayer structure formed by the IB material and the Si
substrate.3
Moreover, this electrical decoupling effect cannot be associated with the
implantation/PLM induced effects since the Si implanted Si sample shows the same
transport properties than the Si unimplanted reference substrate.
1.
J. Olea, D. Pastor, E. Garcia-Hemme, R. Garcia-Hernansanz, A. del Prado, I.
Martil and G. Gonzalez-Diaz, Thin Solid Films 520, 6614-6618 (2012).
2.
Y. Zhou, F. Liu and X. Song, Journal of Applied Physics 113, 103702 (2013).
3.
J. Olea, G. Gonzalez-Diaz, D. Pastor, I. Martil, A. Marti, E. Antolin and A.
Luque, Journal of Applied Physics 109, 8 (2011).