Abstract
Indium doped zinc oxide (IZO) thin films were deposited on p-type and n-type porous silicon (PS) substrates, by using IZO aerogel nanopowder with indium content of 0.04 synthesized by sol-gel method used as target source for the rf-magnetron sputtering. The deposited IZO thin films were used to fabricate two heterojunctions, n-IZO/PS/n-Si and n-IZO/PS/p-Si, in order to study the temperature dependence of their electrical junction properties and the effect of the substrate doping type. The IZO thin films have hexagonal wurtzite structure with (002) preferentially orientation. The electrical junction properties were systematically investigated by current-voltage (I-V) characteristics and direct current conductivity (G(dc)-V) measurements in the temperature range 80-300 K. Our study shows that the measurement temperature and the doping type of the Si substrate have significant impact on the electrical properties of the IZO/PS/Si heterostructures. Barrier height and ideality factor obtained from I-V measurement has shown variations of 0.13-0.41 eV and 5.6-1, respectively for the temperature range of 80-300 K. The temperature dependence of series resistance for the two heterojunction diodes has also been studied. Temperature dependent I-V measurement gives mean barrier height of 122 (161) meV and Richardson constant of 3.6 x 10(-4) (1.19 x 10(-3)) A/cm(2)K(2) for the n-IZO/PS/p-Si (n-IZO/PS/n-Si) heterojunction. These values show significant deviation from their standard theoretical values. However, by consideration of Gaussian distribution with a standard deviation of sigma(0) = 0.091 (0.079) gives modified barrier height and Richardson constant of 0.58 (0.527) eV and 39.1 (35.34) A/cm(2)K(2) for the n-IZO/PS/p-Si (n-IZO/PS/n-Si) heterojunction. We note that voltage effect on barrier height is greater in n-IZO/PS/n-Si heterostructure compared to that of n-IZO/PS/p-Si heterojunction. By fitting the experimental I-V data, we have proposed that the current transport mechanism is dominated by the recombination tunneling at lower forward voltages and by the space-charge limited current at higher values for the two heterojunctions. The thermal activation energies are also calculated from conductance measurements and Arrheniusplotof saturation current for the two heterostructures.