# Design and Analysis of Heavily Doped n+
## 1 Introduction  
Detection of various kinds of diseases and molecules like cancer, antigens, viral diseases, and pathogens has been time-consuming and complicated. Using biosensors based on field-effect transistors (FET) for detecting biomolecules like DNA, enzymes, pathogens, cancer, etc. is cost-effective and less time-consuming, and can be used for early-stage detection of diseases [1]. Different biosensors like piezoelectric, nano-mechanic, optical and electrochemical have been made, but they have expensive manufacturing processes and use costly equipment. MOSFET-based biosensors use a simple method of detection without the use of a transducer [2]. Junctionless transistors for detecting biomolecules can be produced by the fabrication industry cheaply in large quantities [3; 4; 5]. The detection process of biomolecules using FET is based on ISFET (ion-sensitive field effective transistor) which detects charged biomolecules; however, it is unable to detect neutrally charged biomolecules [6; 7]. FET-based biosensors work using the electrical properties of the devices (i.e., ON-state current, threshold voltage and capacitances, etc.). In dielectrically modulated FET (DM FET), a cavity is formed in the gate dielectricmedium to restrict the movement of charged and non-charged biomolecules for the detection of molecules that are label-free. The biomolecules trapped inside the cavity region change the electrical parameters of the FET [8; 9; 10; 11; 12]. Biosensors based on DM FET have some limitations, like Short Channel Effects (SCEs) and problems related to scaling and power supply [13]. To overcome these problems, junctionless MOSFET can be used, which is less prone to SCEs, performs better and has high ON-state current and low OFF-state current. CMOS technology has faced many challenges in the semiconductor industry due to a reduction in the size of the transistor. This has created difficulties in the fabrication of heavily doped ultra-shallow junctions. Further scaling of the device increases the short channel effects (SCEs) [14; 15; 16; 17]. Junction-less transistors were proposed by [PERSON] to overcome these problems. Junction-less transistors do not require doping and are less susceptible to SCEs. Hence, the fabrication process becomes more comfortable and cheaper. [PERSON] et al. proposed a double-gate junctionless MOSFET [15] for detecting molecules using the modulation of dielectric material. A nanocavity was introduced in the gate oxide region of the MOSFET using the process of etching from both sides of the device near the drain and source. The molecules trapped in the cavity region bind to the SiO\({}_{2}\). Furthermore, surface potential in the cavity region is affected [18; 19; 20]. In this paper, the sensitivity of asymmetrical junctionless double-gate MOSFET (AJ DG MOSFET) with a heavily doped n\({}^{+}\) pocket region has been analyzed when subjected to different dielectric oxide materials. Use of different dielectric materials in the cavity created in the gate oxide region has shown significant variation between them, hence making it capable of detecting any small changes in the cavity region. This significant variation in the sensitivity of the device helps detect different biomolecules and can be used for biomedical applications. The proposed transistor, with a dielectrically modulated cavity region, is formed in the gate oxide region to detect the presence of biomolecules in terms of the variation in dielectric constant. To check the sensitivity of the proposed device toward the biomolecule, the length of the cavity and gate oxide region is varied. Different dielectric materials such as air, SiO\({}_{2}\), HfO\({}_{2}\) and Si\({}_{3}\)N\({}_{4}\) are used to analyze the sensitivity of the device. The device was simulated using the TCAD Cogenda tool.