Development of quantum well thermoelectric device

The electronic and thermal properties of bulk materials are altered when they are incorporated into quantum wells. Two-dimensional quantum wells have been synthesized by alternating layers of B/sub 4/C and B/sub 9/C in one system and alternating layers of Si and Si/sub 0.8/G/sub 0.2/ in another system. Such nanostructures are being investigated as candidate thermoelectric materials for high figures of merit (Z). The predicted enhancement is attributed to the confined motion of charge carriers and phonons in the two dimensions and separating them from the ion scattering centers. Molecular beam epitaxy (MBE) and sputtering techniques have been used to prepare these multilayer films. Films have been deposited on single-crystal silicon substrates. The /spl alpha/ and /spl rho/ properties of these films have been determined over a broad range of temperatures from 4.2 K to 1200 K and were previously reported. The /spl alpha//sup 2///spl rho/ values for these P type B-C and N type SiGe films were more than a factor of 10 to 30 times higher than bulk P type B-C and N type SiGe. Several one and two couple devices were fabricated with P-type B/sub 4/C/B/sub 9/C QW films and N-type bulk Bi/sub 2/Te/sub 3/. One of these couples produced 0.182 milliwatt at a /spl Delta/T of a 50/spl deg/C. This device produced ten times more power than the bulk Bi/sub 2/Te/sub 3/ commercial material of the same dimensions and /spl Delta/T. Hi-Z is also producing thicker B/sub 4/C/B/sub 9/C films (>10 /spl mu/m) on thinner Si substrates (<1 /spl mu/m) to minimize thermal bypass heat losses. Successful scale up of these films for the P-leg is expected to yield a 1 cm square device that will produce /spl sim/5 Watts at a /spl Delta/T of 200/spl deg/C. With a minimum assumption for thermal losses the device efficiency should approach 20%.