Ultrahigh‐Detectivity Photodetectors with Van der Waals Epitaxial CdTe Single‐Crystalline Films

Abstract

Van der Waals epitaxy (vdWE) is crucial for heteroepitaxy of covalence‐bonded semiconductors on 2D layered materials because it is not subject to strict substrate requirements and the epitaxial materials can be transferred onto various substrates. However, planar film growth in covalence‐bonded semiconductors remains a critical challenge of vdWE because of the extremely low surface energy of 2D materials. In this study, direct growth of wafer‐scale single‐crystalline cadmium telluride (CdTe) films is achieved on 2D layered transparent mica through molecular beam epitaxy. The vdWE CdTe films exhibit a flat surface resulting from the 2D growth regime, and high crystal quality as evidenced by a low full width at half maximum of 0.05° for 120 nm thick films. A perfect lattice fringe appears at the interfaces, implying a fully relaxed state of the epitaxial CdTe films correlated closely to the unique nature of vdWE. Moreover, the vdWE CdTe photodetectors demonstrate not only ultrasensitive optoelectronic response with optimal responsivity of 834 A W−1 and ultrahigh detectivity of 2.4 × 1014 Jones but also excellent mechanical flexibility and durability, indicating great potential in flexible and wearable devices.

Recent Advances in 2D Materials for Photodetectors

“…Recently, Lian and his colleagues presented a wafer‐scale CdTe membrane on the mica substrate by a molecular beam epitaxy method. [ 65 ] This ultralarge film has significant potential application in future integrated devices. After characterizing the high crystal quality of this CdTe single‐crystalline membranes, authors reported a high‐performance photodetector with high responsivity (834 A W −1 ), high D * (2.4 × 10 14 Jones) and flexible properties on the basis of CdTe semiconductors.…”

Advances in Self-Powered Ultraviolet Photodetectors Based on P-N Heterojunction Low-Dimensional Nanostructures

“…In a semiconductor with low crystalline quality, there are more defects and grain boundaries, which is not conducive to the separation and transmission of photogenerated carriers. Therefore, improving the crystalline quality of semiconductors is one of the most effective ways to build high-performance self-powered UV detectors [ 78 , 79 , 80 , 81 , 82 ].…”

Two‐Dimensional Metal Telluride Atomic Crystals: Preparation, Physical Properties, and Applications

“…Wang et al. [ 269 ] introduced a vdW epitaxy 2D CdTe photodetector by the PCE, as shown in Figure a. They found that the CdTe photodetector demonstrates ultrasensitive photoresponse of R = 834 A W −1 , high detectivity of D* = 2.4 × 10 14 Jones (Figure 12b), and fast response speed of τ rising /τ decay = 2.6/3.4 ms (Figure 12c).…”

“…Reproduced with permission. [ 269 ] Copyright 2019, Wiley‐VCH. d) Schematic diagram of the PGE MoTe 2 photodetector; e) Schematic of the PGE, where E c , E f , E v , V d are the conduction band, Fermi level, valence band, and bias voltage, respectively.…”