Thermoelectric properties of boron and boron phosphide CVD wafers

The electrical conductivity of amorphous boron wafers obeys Mott´s T^-1/4 rule. BP and B₁₂P₂ show band conduction. The thermoelectric power of polycrystalline B decreases with increasing temperature, while that of amorphous B is almost constant in a wide temperature range. That of BP increases with increasing temperature and becomes constant between 600 and 1100 K, while that of B ₁₂P₂ shows a high value of 800-1000 μ V/K at 400-800 K. The weak temperature dependences of thermal conductivities of BP and B₁₂P₂ polycrystalline wafers reflect phonon scattering by grain boundaries while that of amorphous boron is almost constant in a wide temperature range, showing a characteristic of a glass. The figure of merit for polycrystalline BP is 10^-7/K at high temperatures while that of amorphous B is 10^-5/K, being promising for thermoelectric devices. Low electrical conductivity of B₁₂P₂ produces a lower thermoelectric figure of merit than BP by two orders of magnitude, despite the high thermoelectric power