Origin of p-type characteristics in a SnSe single crystal

Abstract

SnSe single crystals have recently been found to exhibit excellent thermoelectric performance with an extremely high figure of merit (ZT) value of 2.6. Although this high ZT value has attracted considerable attention, the microscopic origin of the p-type characteristics of SnSe is not yet clearly understood. Here, we directly observed and identified intrinsic point defects existing on SnSe via scanning tunneling microscopy (STM) and investigated the effect of defects on the electronic properties using density functional theory (DFT) calculations. Our results demonstrate that the most dominant Sn vacancies move the Fermi energy inside the dispersive valence band and produce extra holes throughout the system. On the other hand, Se vacancies create a nondispersive donor level and generate immobile electrons localized near the vacancy site. Our combined STM/DFT studies show that the p-type characteristics of SnSe originate from extra holes in the dispersive Bloch-like band created by Sn vacancies. We expect that our results provide important information for the development of highly efficient SnSe-based thermoelectric devices.

A plausible method of preparing the ideal p-n junction interface of a thermoelectric material by surface doping

“…Here, n-type doping of the surface of a p-type semiconducting SnSe single crystal has been examined by direct measurement of the electron band structure using angle-resolved photoemission spectroscopy (ARPES) in conjunction with first principles calculations. While bulk SnSe exhibits p-type charge carriers due to Sn vacancies [19], Ta adsorption leads to the shift of the whole band structure towards higher binding energy that is as much as 0.2 eV only with 0.025 monolayer (ML) of Ta, converting the type of charge carriers from p-type that of the bulk to n-type, consistent with the theoretical results. Based on the comparison to the previous theoretical study [24], highly efficient and surface localized n-type doping has been realized by Ta adsorption, while the bulk remains as a p-type semiconductor.…”

“…When considering electron affinity, Ta exhibits the lowest electron affinity among Sn, Se, and Ta. In addition, although SnSe is an insulator with an energy gap of 0.9 eV [32,33], it is supposed to exhibit impurity states in the gap region especially when the investigated sample is p-type semiconductor due to Sn vacancies [19]. As a result, electrons are expected to be transferred from Ta to SnSe.…”

“…The type of charge carriers of SnSe can be controlled by introducing impurities. The formation of Sn vacancies [19] and the substitution of Sn with Na [20,21] result in hole doping, while Br or Bi substitution [16,22] brings about electron doping, all of which are determined in the process of sample growth. Alternatively, it can also be achieved after the sample growth, for example, by the adsorption of foreign atoms such as K [23].…”

Lateral Heterostructures Formed by Thermally Converting n-Type SnSe2to p-Type SnSe

“…2 and a previous report. 31 In Fig. 5b For the DOS curves of SnSe 2 and SnSe, the Fermi levels are set to be 0 eV.…”

High-performance SnSe thermoelectric materials: Progress and future challenge

“…Point defects (include atom vacancies and substitutions) belong to atomic scale, dislocations and precipitates belong to nano scale, and grain boundaries belong to submicro scale [125]. Figure 9(a) shows a Sn vacancy in SnSe structure characterized by STM [52], which illustrates that there are Sn vacancies exist in the SnSe structure, making the whole system presenting p-type [126].…”