Self-powered topological insulator Bi₂Te₃/Ge heterojunction photodetector driven by long-lived excitons transfer

Abstract

Due to the wide spectral absorption and ultrafast electron dynamical response under optical excitation, topological insulator (TI) was proposed to have appealing application in next-generation photonic and optoelectronic devices. Whereas, the bandgap-free speciality of Dirac surface states usually leads to a quick relaxation of photoexcited carriers, making the transient excitons difficult to manipulate in isolated TIs. Growth of TI Bi2Te3/Ge heterostructures can promote the specific lifetime and quantity of long-lived excitons, offering the possibility of designing original near-infrared optoelectronic devices, however, the construction of TI Bi2Te3/Ge heterostructures has yet to be investigated. Herein, the high-quality Bi2Te3/Ge heterojunction with clear interface was prepared by PVD strategy. A significant photoluminescence quenching behaviour was observed by experiments, which was attributed to the spontaneous excitation transfer of electrons at heterointerface via theoretical analysis. Then, a self-powered heterostructure photodetector was fabricated, which demonstrated a maximal detectivity of 1.3×1011 Jones, an optical responsivity of 0.97AW-1, and ultrafast photoresponse speed (12.1 μs) under 1064 nm light illumination. This study offers a fundamental understanding of the spontaneous interfacial exciton transfer of TI-based heterostructures, and the as-fabricated photodetectors with excellent performance provided an important step to meet the increasing demand for novel optoelectronic applications in the future.

Ultrasensitive and Self‐Powered SnSe/Ge Heterojunction Photodetector Driven by Spontaneously Interfacial Excitation Transfer of Carriers

“…Meanwhile, the E c and E v for the single-crystal Ge wafer with n-type conductance locate approximately at 4.13 and 4.79 eV, respectively, as displayed in Figure 3e. [31,36] Therefore, once the layered SnSe film and Ge wafer were physically integrated, their majority carriers may diffuse spontaneously into each other, so that the two Fermi levels from the SnSe and Ge crystals can keep in alignment. Thus, a larger buildin electrostatic-field pointing to SnSe film from Ge wafer may form concurrently inside the broad space charge region near the heterointerface.…”

“…[49,50] The six characteristic parameters of ε n , ε p , N D , N A, V bi , and V a in the above equation, are the permittivity of Ge crystal (≈1.4337 × 10 −12 F cm −1 ), the dielectric constant of SnSe film (≈8.7969 × 10 −13 F cm −1 ), the ionized-donor density inside Ge wafer, the ionized-accepter density inside SnSe film, the built-in potential at heterointerface, and applied external bias, respectively. [29,31] Besides, according to the resistivity of ρ of ≈2.20 × 10 3 Ω cm and the hole mobility of μ of ≈93 cm 2 V −1 S −1 for the as-grown SnSe film, the density of ionized accepters of N A for the SnSe film can be estimated to be ≈5.55 × 10 16 cm −3 by using of the electrical conductivity (σ) equation of 1/…”

“…Whereas, a stronger Coulomb screening effect may usually be induced by continual accumulation of photoexcited carriers in each layers, which may result in an ever-increasing of optical bandgap for the two active absorption layers. [31,42] Therefore, the controllable preparation of suitable Ohmic contact electrodes for the SnSe film and Ge crystal becomes very necessary, so that the photogenerated electrons and holes can be guided out of the heterojunction effectively.…”

“…This ultimately leads to the potential-dependent photoresponse of the heterostructure device. [31,50] In addition, the currentswitching behaviors of the photodetector under −5.0 V were further studied, and the selected optical intensities are fixed as 0.184, 2.105, 2.845, 4.280, and 5.605 W cm −2 , respectively, as shown in Figure 6d. Importantly, the output current can switch reversely without any degradation even under a larger voltage of −5.0 V, which prove that the as-constructed SnSe/Ge heterostructure device possesses a much better reliability.…”

“…It may make the large number of photoexcitons originating from band-gap internal photoemission easy to survive in optoelectronic devices. [22,31] The controlled growth of 2D layered SnSe film with high-quality can minimize the defect density, and facilitate to reduce the grain boundary recombination of photoexcited carriers. However, the photoelectric conversion efficiency from the pure SnSe film in optoelectronic devices is still lower, due to the limited transfer efficiency of carriers.…”