Realization of adjustable electron concentration and its effect on electrical- and Seebeck-property of n-type SnSe crystals

Manipulation of carrier types in SnSe crystals is quite advantageous to fabricate SnSe-based homojunction devices such as thermoelectric modules. However, tuning the n-type charge carrier at an optimal level of SnSe is quite challenging because of its natural p-type without intentional doping. Here, we report the realization of the n-type SnSe through halogens or Ce doping. Importantly, heavily electron doped SnSe single crystals (∼1019 cm−3) can be obtained by Ce-doping through the Bridgeman method. The electrical conductivity of as-grown SnSe crystals evolves from thermally activated behavior to the metallic one when the electron concentrations are increased from 1016 to 1019 cm−3. Remarkably, the power-factor and electronic quality factor of heavily electron Ce-doped SnSe crystals can reach 1.59 and 0.44 μW cm−1 K−2 at 300 K, respectively, which is one of the best thermoelectric n-type SnSe. This work suggests that Ce-doping through the Bridgeman method is an ideal route for further improving the thermoelectric property of n-type SnSe crystals.

在SnSe晶体中对载流子类型的调控对于制造诸如热电模块等基于SnSe的同质结器件是非常有利的。然而，由于在无故意掺杂时SnSe天然为p型，将其n型载流子调节到最佳水平是极具挑战性的。在此，我们报道了通过卤素或铈（Ce）掺杂实现n型SnSe。重要的是，通过布里奇曼（Bridgeman）方法进行Ce掺杂能够获得重电子掺杂的SnSe单晶（约10¹⁹ cm⁻³）。当电子浓度从10¹⁶增加到10¹⁹ cm⁻³时，所生长的SnSe晶体的电导率从热激活行为转变为金属性的行为。值得注意的是，在300 K时，重电子Ce掺杂的SnSe晶体的功率因子和电子品质因数分别能够达到1.59和0.44 μW cm⁻¹ K⁻²，这是热电n型SnSe中性能最好的之一。这项工作表明，通过布里奇曼方法进行Ce掺杂是进一步提高n型SnSe晶体热电性能的理想途径。