Design of p‐WSe₂/n‐Ge Heterojunctions for High‐Speed Broadband Photodetectors

Abstract

Van der Waals (vdW) 2D/3D heterostructures are extensively studied for high-performance photodetector applications. Until now, the type of 2D materials has been the primary area of interest rather than the design of 3D semiconductors. In this study, high-speed broadband photodiodes (PDs) based on vdW p-WSe 2 /n-Ge heterojunctions are reported, and the performance compared with different n-Ge regions formed via the ion-implantation process. The fabricated PD with a typical long n-Ge region and low doping concentration responds to a broad spectral range from visible to infrared near 1550 nm with a response time of ≈3 µs and responsivity of 1.3 A W −1 . The inferior responsivity of PDs with short n-Ge regions can be improved as demonstrated by experimental results and process simulation. Density functional theory calculations are performed to estimate the variation of the energy band structures with the doping concentration of n-Ge. Fast photoresponse and efficient carrier separation across the heterojunction can be expected regardless of the n-Ge doping concentration. Based on the experimental results together with theoretical band structure and process simulation, it is shown that the heterojunction with an optimized n-Ge design is a promising high-speed broadband photodetector that can be implemented with complementary metal-oxidesemiconductor design and fabrication processes.

High‐Speed Photodetectors on Silicon Photonics Platform for Optical Interconnect

“…Therefore, high-speed PDs with ultrawide wavelength operation are highly desired. In recent years, some results have been demonstrated toward this direction, such as GeSn PDs, [11,260] all Si PDs, [13] 2D material-based PDs [224,261] as well as Ge PDs in combination with perovskite material. [254] However, device performance in these reports is typically far from that of PDs working in the usual O/C bands.…”

Vertically Stacked vdW Double Heterojunction Photodiode with Ultrawide Bandgap Gallium Oxide Electron Reservoir

“…where ε 1 and ε 2 are the dielectric constants of WSe 2 and Ge (Ga 2 O 3 ), respectively; N d is the doping concentration of Ge (Ga 2 O 3 ); and N a is the doping concentration of WSe 2 . [19] The depletion widths of the x n under zero bias were calculated as 377 nm for Ge and 40 nm for Ga 2 O 3 , and the corresponding depletion widths of WSe 2 (x p ) were 10 and 67 nm, respectively. The calculation results showed that WSe 2 was fully depleted by the DHJ.…”

“…Moreover, optimized Ge design via the ion-implantation process shows great potential for high-speed broadband photodetectors that can be integrated with CMOS designs and processes. [15][16][17][18][19] A vdW 2D/Ge heterostructure with enhanced responsivity in the SWIR range (>1550 nm), while maintaining a relatively simple two-terminal diode configuration, can be pivotal for photodetectors. To achieve improvement, photogenerated carriers can be multiplied via an additional layer on top of the 2D/Ge junction (i.e., double heterojunction, DHJ), resulting in a complicated device configuration with dual bias polarity operations.…”

Broad-Spectrum Germanium Photodetector Based on the Ytterbium-Doped Perovskite Nanocrystal Downshifting Effect

“…To fabricate PDs with broad spectral responses, several methods have been proposed. Through material integration and surface texturing, broad-spectrum PDs have been obtained. ,, In addition, applying the downshifting effect by adding a layer of fluorescent materials to fabricate integrated devices is one of the most common and effective means of solving technical difficulties in UV–vis band detection. In recent years, due to their excellent optoelectronic properties and huge material family system, perovskites have been rapidly developed in many optoelectronic fields, such as photovoltaics, − light emission, − photodetection, , etc .…”