Stripe-patterned Si Substrates Research Articles

Simulation of Thermoelectric Generator Composed of Nanopatterned Thermoelement

The conversion efficiency of thermoelectric (TE) devices is determined by the dimensionless figure of merit ZT, which is expressed as ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature, respectively. The key strategy to enhance ZT is through decreasing the thermal conductivity of thermoelectric materials. In this study, finite element analysis was used to investigate the effect of stripe-patterned Si substrates on thermal properties of a thermoelectric thermoelement, which consists of PbSe and PbTe thin film layers grown on the periodic patterned Si substrates. The width and depth of the stripe patterns were varied from 10 µm to 0.5 µm to determine their effects on the heat transport in the thermoelement. The calculated results reveal that the depth and width of the stripe patterns play an important role in decreasing the thermal conductivity of the thermoelectric module. The effect of the dimension of the patterns on the effective thermal conductivity of the TE thermoelement was shown in figure 1. The thermal conductivity is lower with respect to the deeper and narrower stripe patterns. The decreased thermal conductivity results from the enhanced phonon-boundary scattering due to the presence of periodic patterns. The phonons can be scattered more extensively when the dimension of the patterns is comparable to the mean free path of TE materials. Therefore, we modeled a thermoelectric generator (TEG) composed of stripe-patterned TE thermoelements taking advantage of its lower thermal conductivity. The dimension of the patterns was optimized selected to generate to achieve a higher power output of TEG. This work demonstrated the feasibility of using nanopatterned thermoelectric (TE) thermoelements to improve TE generator performance. Figure 1

Good Conformability of Indium-Tin Oxide Thin Films Prepared by Spray Chemical Vapor Deposition

Tin-doped In 2 O 3 (indium-tin oxide, ITO) transparent conducting films were deposited between 200 and 400°C on stripe-patterned Si substrates by spray chemical vapor deposition. ITO films with a homogeneous tin composition and crystallinity were successfully fabricated. The step coverage increased as the deposition temperature decreased and reached 90% at 200°C. Postdeposition annealing lowered the resistivity to 3.3 × 10 -4 Ω cm, which is approximately homogeneous because the measured resistance agreed well with the calculated one assuming the resistivity value of the film deposited on a flat surface and considering the film thickness of various portions. These films should contribute to optoelectric devices.

Deposition of undoped indium oxide thin films on stripe-patterned substrates by spray CVD

Undoped indium oxide (In 2O 3) films were deposited on stripe-patterned Si substrates by an original spray chemical vapor deposition (spray CVD) using ethanol solution of indium (III) chloride. The step coverage of the films increased as the deposition temperature decreased. The grooves with 0.18 μm openings were successfully deposited at 253 °C. The step coverage of undoped indium oxide films were a similar tendency though resistivity of that showed the tendency opposite to the ITO film. Deposition mechanism of the undoped indium oxide films on stripe-patterned Si substrates was similar to that of the ITO films. The lowest resistivity of the films was 4.1×10 −3 Ω cm for the 260 nm-thick film deposited at 280 °C. The resistivity increased at higher temperature.