One of the most exciting aspects of this work is the nature (electrons or holes) of the carriers at the IB. The bilayer decoupling is independent on its nature and it is only dependent on the barrier current limitation for the electrons. The impossibility of the IB carriers to go to the substrate is irrespective whether they are electrons or holes. The only difference we can find between electrons or holes is its mobility sign. According to the model, at low temperatures F!0, layers are decoupled and we are measuring only the mobility at the TIL, which is:
—n1an12t1 + p1Mp12t1
Meff = 1 p1 . (13.10)
n1Mn1fi C p1^p1^1
According to our model, holes mobility and its concentration at IB do not depend on the temperature while electrons terms do. Samples with low electron mobility should change the polarity at higher temperatures, while for samples with higher electron mobility, the polarity change should be observed at lower temperatures. Samples presented in the Fig. 13.7b do not change the mobility sign
Fig. 13.13 (a) Sheet resistance and (b) mobility as a function of measured temperature for an-Si substrate (—) and for double sheet TIL/n-Si substrate for different implantation doses:
1015 
cm-2 (square experimental; filled square analytical model);
5-1015 cm-2 (circle experimental; bullet analytical model) and
1016 cm-2 (triangle experimental; filled triangle analytical model) (Reprinted with permission from [21]. Copyright 2009. Institute of Physics)
(at less at temperatures higher than 90 K), although it value decreases very quickly. Figure 13.14 shows the sheet resistance and Hall mobility of a sample implanted with a dose of 5×1015 cm-2 and annealed at 0.6 J cm-2. This sample has presumably low electron mobility because it is annealed at low energy. The polarity change at T = 190K is clearly shown in the inset. In the Fig. 13.15, we plot the Hall mobility of a sample implanted with 1016 cm-2 dose and annealed at a energy of 0.8 J cm-2. In this sample, the electron mobility should be higher than the sample of the Fig. 13.14 because the higher annealing energy. Hall measurements were conducted down to a temperature of 7 K being the polarity change clearly evidenced at T = 40 K. Results of Figs. 13.14 and 13.15 are in fully agreement with the prediction of (13.10). Also, the value of the mobility at low temperatures is in good accordance with the values showed in Table 13.3, which were obtained through the fitting of the sheet resistance and mobility at higher temperatures instead of direct measurements.
