Thermoelectric properties of materials are essentially based on the thermoelectrical figure of merit (Z=S^{2} \sigma / K), where (S) is the thermoelectrical power, (\sigma) the electrical conductivity and (K) the thermal conductivity. Narrow-bandgap semiconductors (\mathrm{Bi}{2} \mathrm{Te}{3}(\mathrm{n}), \mathrm{Sb}{2} \mathrm{Te}{3}(\mathrm{p})) layered onto amorphous substrates using the molecular beam technique are investigated. These materials present the highest values of (Z). Following the previous work on these materials, the variations in mobility (\mu) and carrier density (n) as a function of film thickness are performed. It is found that (\mu) and (n) tend to constant values when the film thickness is higher than (6000 \AA). We also undertook the study of the thermoelectric properties of (\mathrm{Bi}{x} \mathrm{Sb}{2-x} \mathrm{Te}{3}) alloys as a function of the bismuth concentration (x). The optimal value of (S) was obtained at (x=0.1). The improvement of (S) in comparison with that of (\mathrm{Sb}{2} \mathrm{Te}{3}) results in the reduction in antisite defects or the carrier compensation. Thermopile and pressure sensors based on (\left[\mathrm{Bi}{0.1} \mathrm{Sb}{1.9} \mathrm{Te}{3}(\mathrm{p})-\mathrm{Bi}{2} \mathrm{Te}{3}(\mathrm{n})\right]) are constructed. These ([\mathrm{p}-\mathrm{n}]) active junctions constitute the sensitive elements of both the thermopiles and the vacuum gauges. In comparison with the [Bi-Sb] couple, an improvement in the sensitivity by a factor (2.8 \pm 0.2) was achieved. Thermal simulation based on COSMOS/M software confirmed the experimental findings.