Evaluation of the influence of thermal annealing on the performance of vertical topological insulator p-n heterojunction broadband photodetector

Abstract

The rapid progress and continuum search for new broadband photodetectors generation with ultrafast response synchronizes with the conductive surface electronic structure and the strong broadband absorption properties of 3D topological insulators. Here, we introduce the fabrication of a vertical p-n heterojunction based on thermally evaporated thin films of Sb2Te3/Bi2Te3 on Si substrate for broadband photodetection. The realization of these characteristics dictated us to study the structural, optical absorption, and morphological properties of each layer in the fabricated device as a function of annealing temperature using XRD, spectrophotometric measurements, and FE-SEM techniques, respectively. The annealing process up to T = 423 K enhanced the film’s crystallinity, and grain growth process besides improving the film quality and surface roughness. Furthermore, the optoelectronic characterizations showed that all fabricated photodetectors exhibit a good response to halogen light illumination in the wavelength range (310–1100) nm with different intensities (10–50) mW/cm2. Whilst the 423 K annealed photodetector showed the highest photosensitivity with a conspicuous stable and fast response. The main device parameters, including spectral responsivity, specific detectivity, and response times were determined in addition to explaining the forward and reverse bias conduction mechanisms. The estimated spectral responsivity of the fabricated devices was about 0.247, 0.397, and 0.148 A/W for the as fabricated and 423 K and 573 K, respectively. This significant improvement of the device’s performance rather than other topological insulator devices may be due to the strong built-in field at the topological insulators’ interfaces. Moreover, the fabricated photodetectors showed improved and repeatable ON/OFF transient switching behavior with 85.23 ms and 84.66 ms as a rise and fall time, respectively. According to the prominent results in addition to the simple architecture of the fabricated photodetectors, this topological insulator photosensor can be considered a potential candidate in prospective high-performance optoelectronics.