| dc.description.abstract | The field of optoelectronics seeks sustainable, abundant, and cost-effective materials that can reliably perform under varying environmental conditions. Bismuth sulfide (Bi2S3), a narrow bandgap (1.3 eV) semiconductor has emerged as a promising candidate, for a range of optoelectronic applications, particularly within the visible to near-infrared (NIR) spectrum. The thesis work investigates the transport characteristics of Bi2S3 devices under the influence of variable temperature and bias voltage conditions for the photodetector application in a wide spectrum of visible to NIR radiations. The research work exploits both the bulk and two-dimensional (2D) forms of Bi2S3 to microfabricate the devices using optical and electron beam lithography. Bulk Bi2S3-based device showed a high voltage responsivity of 3802 V/W at 1064 nm with an incident optical power of 181 μW. It was observed that the bias voltage plays a crucial role in the performance of Bi2S3 photodetector, significantly influencing the separation of photogenerated carriers and overall device performance. Varying the bias voltage from 0.2 to 20 V leads to a remarkable 15971 % enhancement in the photocurrent. Additionally, the Bi2S3 based NIR photodetector exhibits a unique low temperature optical switching phenomenon, critical for applications in the environment with the varying temperature conditions. The photosensitivity is significantly enhanced at lower temperature, with the photocurrent increasing three-fold as temperature lowers from 300 K to 10 K at an illumination of 1064 nm radiation.
In recent years, 2D materials provide the feasibility to miniaturize the devices and generate atomically thin interfaces for enhanced performance. Thus, 2D Bi2S3 based field effect transistor (FET) device is fabricated with the hexagonal boron nitride (hBN). A van der Waals heterostructure of Bi2S3/hBN revealed an interesting insight into the FET characteristics of the device through the charge trapping and de-trapping phenomena at varying localized gate bias and thermal conditions. We investigated the output and transfer characteristics of the device across a temperature range of 10 K to 300 K. The key parameters including threshold voltage (Vth), hysteresis (ΔVth), and subthreshold swing (SS) exhibited a significant temperature dependence. Notably, SS decreased from 7.22 V/dec at 300 K to 0.95 V/dec at 10 K, indicating faster device turn-on. Transient analysis revealed two distinct trap states with time constants of 7.34 s and 71.8 s, attributed to shallow and deep traps, respectively, suggesting the influence of shallow and interface trap states on the device behavior. The trapping and de-trapping were also highly influenced by the localized gate field effect. These findings demonstrated Bi2S3 as a promising material exhibiting unique low-temperature and field-dependent characteristics. Furthermore, 2D Bi2S3 based FET device was studied for the development of a high performance photodetector for visible and NIR radiations at varying temperatures and electric bias conditions. The exceptional performance is demonstrated by the Bi2S3 based FET photodetector with an ultrahigh responsivity of ~106 A/W and a detectivity of ~1014 Jones. An anomalous variation in the transport characteristics of 2D Bi2S3 is observed with the temperature variation. The electrical resistance reduces by 99.26 % at 10 K compared to the response at 300 K. The density functional theory calculations provided a significant insight into the thermodynamic properties of intrinsic defects in Bi2S3. Moreover, the effect of gate bias on the responsivity additionally confirmed its invariance at low temperatures. The noise equivalent power was measured to be 0.2×10-18 W/√Hz at 300 K under a bias of 0.2 V. Such remarkable performance firmly establishes the Bi2S3 photodetector as a leading contender among 2D photodetectors.
These findings offer valuable insights into the intricate relationship between bias, temperature and the performance of Bi2S3 photodetectors, paving the way for further advancements in NIR photodetection technologies and potential applications in various fields. | en_US |
