Review of Established Materials and Devices

The best elemental or simple compound semiconductor for thermoelectric refrigeration at “ordinary” temperatures is bismuth telluride (Bi2Te3), with space group \( D_{3d}^5(R\mathop 3\limits^ - m) \) [5.1]. Bi2Te3 crystals are remarkable because they can be readily cleaved in planes perpendicular to the trigonal or c axis. As one proceeds in the c direction, one encounters layers of like atoms that follow the sequence: $$ - T{e^{[1]}} - Bi - T{e^{[2]}} - Bi - T{e^{[1]}} - , $$ which is then repeated until a crystal boundary is reached. It has been shown that the tellurium and bismuth layers are held together by strong ionic-covalent bonds, but no bonding electrons remain to connect the adjacent Te[l] layers. The weak van der Waals binding between the layers accounts for the ease of cleavage [5.2].