Rohit Pant

Bio: Rohit Pant is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: Heterojunction & Responsivity. The author has an hindex of 9, co-authored 18 publications receiving 168 citations.

Self-Powered, Broad Band, and Ultrafast InGaN-Based Photodetector.

Abstract: A self-powered, broad band and ultrafast photodetector based on n + -InGaN/AlN/n-Si(111) heterostructure is demonstrated. Si-doped (n + type) InGaN epilayer was grown by plasma-assisted molecular beam epitaxy on a 100 nm thick AlN template on an n-type Si(111) substrate. The n + -InGaN/AlN/n-Si(111) devices exhibit excellent self-powered photoresponse under UV-visible (300-800 nm) light illumination. The maximum response of this self-powered photodetector is observed at 580 nm for low-intensity irradiance (0.1 mW/cm 2 ), owing to the deep donor states present near the InGaN/AlN interface. It shows a responsivity of 9.64 A/W with rise and fall times of 19.9 and 21.4 I¼s, respectively. A relation between the open circuit voltage and the responsivity has been realized.

Defect-Mediated Transport in Self-Powered, Broadband, and Ultrafast Photoresponse of a MoS2/AlN/Si-Based Photodetector

Abstract: By combining unique properties of ultrathin 2D materials with conventional 3D semiconductors, devices with enhanced functionalities can be realized. Here, we report a self-powered and ultrafast pho...

In-Plane Anisotropic Photoconduction in Nonpolar Epitaxial a-Plane GaN

Abstract: Nonpolar a-plane GaN epitaxial films were grown on an r-plane sapphire using the plasma-assisted molecular beam epitaxy system, with various nitrogen plasma power conditions. The crystallinity of the films was characterized by high-resolution X-ray diffraction and reciprocal space mapping. Using the X-ray “rocking curve—phi scan”, [0002], [1–100], and [1–102] azimuth angles were identified, and interdigitated electrodes along these directions were fabricated to evaluate the direction-dependent UV photoresponses. UV responsivity (R) and internal gain (G) were found to be dependent on the azimuth angle and in the order of [0002] > [1–102] > [1–100], which has been attributed to the enhanced crystallinity and lowest defect density along [0002] azimuth. The temporal response was very stable irrespective of growth conditions and azimuth angles. Importantly, response time, responsivity, and internal gain were 210 ms, 1.88 A W–1, and 648.9%, respectively, even at a bias as low as 1 V. The results were validated ...

Highly Responsive, Self-Powered a-GaN Based UV-A Photodetectors Driven by Unintentional Asymmetrical Electrodes

Abstract: Optoelectronic properties of nonpolar a-plane GaN are superior along the [0002] azimuth direction compared to other azimuth directions. We have grown a-GaN on r-sapphire, and interdigitated electro...

Next-generation self-powered and ultrafast photodetectors based on III-nitride hybrid structures

Abstract: Energy consumption is one of the most important aspects of any electronic device which needs further improvements in order to achieve a better sustainable future. This is equally true for commercially available photodetectors, which consume a lot of energy by using huge external bias voltage. So far, thin films have been widely used for photodetection of various bands of electromagnetic radiation. The only property which holds them back is the slower performance and lower responsivity compared to nanostructure-based devices. However, the disadvantage associated with nanostructure-based photodetectors is that they lack scalability for mass production or commercialization, due to the complex and expensive device fabrication steps. One of the plausible solutions for this limitation could be the use of hybrid structures, which are the combination of high-quality crystal materials such as ZnO, (Al, Ga, In)N, and GaAs with 2D materials consisting of MoS2, graphene, WSe2, and SnS2. This would provide extensive control over bandgap engineering, which could be used for scalable modular device fabrication. These approaches promise the development of photodetectors with relatively higher responsivities as well as self-powered photodetection. The current perspective focuses on the advancements in III-nitride-based photodetectors and their promising potentials for self-powered, broadband, and ultrafast photodetectors using hybrid III-nitride/2D interfaces.

Random circuit breaker network model for unipolar resistance switching (Advanced Materials (2008) 20 (1154))

Abstract: The existence of reversible resistance switching (RS) behaviors induced by electric stimulus has been known for some time, and these intriguing physical phenomena have been observed in numerous materials, including oxides. As conventional charge-based random access memory is expected to face a size limit in the near future, a surge of renewed interest has been developed in RS phenomena for possible applications in small nonvolatile memory devices called resistance random access memory (RRAM). Of particular interest is unipolar RS, which shows the RS at two values of applied voltage of the same polarity. The unipolar RS exhibits a much larger resistance change than other RS phenomena, and this greatly simplifies the process of reading the memory state. When fabricated with oxide p-n diodes, memory cells using unipolar RS can be stacked vertically, which has the potential for dramatically increasing memory density. Therefore, unipolar RRAM may be a good candidate for multi-stacked, high density, nonvolatile memory. The most important scientific and technical issues concerning unipolar RS are how it works and the identification of its controlling parameters. Some studies have reported that unipolar RS comes from a homogeneous/inhomogeneous transition of current distribution, while others maintain that it comes from the formation and rupture of conducting filaments. Even with recent extensive studies on unipolar RS, its basic origin is still far from being understood. In addition, no model exists that actually explains how the reversible switching can occur at two values of applied voltage. This lack of a quantitative model poses a major barrier for unipolar RRAM applications. In this study, we describe RS behavior in polycrystalline TiO2 film. To explain the basic mechanism of unipolar RS behavior, we propose a new percolation model based on a network of ‘‘circuit breakers’’ with two switchable metastable states. The random circuit breaker (RCB) network model can explain the long-standing material issue of how unipolar RS occurs. This simple percolation model is different from the conventional percolation models, which have dealt only with static or irreversible dynamic processes. In addition, the RCB network model provides an indication of how to overcome the substantial distribution of switching voltages, which is currently considered the most serious obstacle to practical unipolar RRAM applications. The unipolar RS phenomenon can be explained by the current (I)-voltage (V) curves in Figure 1a, which are derived from measurements of our polycrystalline TiO2 thin capacitors. At the pristine state (green dot), they are in an insulating state. As the external voltage Vext increases from zero and reaches a threshold voltage Vforming, a sudden increase occurs in the current. If the current is not limited to a certain value, here called the compliance current Icomp, the TiO2 capacitor would experience a dielectric breakdown and be destroyed. However, [*] Prof. T. W. Noh, S. C. Chae, S. B. Lee, S. H Chang, Dr. C. Liu ReCOE & FPRD, Department of Physics and Astronomy Seoul National University Seoul 151-747 (Korea) E-mail: twnoh@snu.ac.kr

An Efficient Way to Assemble ZnS Nanobelts as Ultraviolet-Light Sensors with Enhanced Photocurrent and Stability

Abstract: Although there has been significant progress in the fabrication and performance optimization of one-dimensional nanostructure-based photodetectors, it is still a challenge to develop an effective and low-cost device with high performance characteristics, such as a high photocurrent/ dark-current ratio, photocurrent stability, and fast time response. Herein an efficient and low-cost method to achieve high-performance 'visible-blind' microscale ZnS nanobelt-based ultraviolet (UV)-light sensors without using a lithography technique, by increasing the nanobelt surface areas exposed to light, is reported. The devices exhibit about 750 times enhancement of a photocurrent compared with individual nanobelt-based sensors and an ultrafast time response. The photocurrent stability and time response to UV-light do not change significantly when a channel distance is altered from 2 to 100 μm or the sensor environment changes from air to vacuum and different measurement temperatures (60 and 150°C). The photoelectrical behaviors can be recovered well after returning the measurement conditions to air and room temperature again. The low cost and high performance of the resultant ZnS nanobelt photodetectors guarantee their highest potential for visible-blind UV-light sensors working in the UV-A band.

A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

Abstract: Two-dimensional transition metal dichalcogenides (2D TMDs) have attracted much attention in the field of optoelectronics due to their tunable bandgaps, strong interaction with light and tremendous capability for developing diverse van der Waals heterostructures (vdWHs) with other materials. Molybdenum disulfide (MoS2) atomic layers which exhibit high carrier mobility and optical transparency are very suitable for developing ultra-broadband photodetectors to be used from surveillance and healthcare to optical communication. This review provides a brief introduction to TMD-based photodetectors, exclusively focused on MoS2-based photodetectors. The current research advances show that the photoresponse of atomic layered MoS2 can be significantly improved by boosting its charge carrier mobility and incident light absorption via forming MoS2 based plasmonic nanostructures, halide perovskites–MoS2 heterostructures, 2D–0D MoS2/quantum dots (QDs) and 2D–2D MoS2 hybrid vdWHs, chemical doping, and surface functionalization of MoS2 atomic layers. By utilizing these different integration strategies, MoS2 hybrid heterostructure-based photodetectors exhibited remarkably high photoresponsivity raging from mA W−1 up to 1010 A W−1, detectivity from 107 to 1015 Jones and a photoresponse time from seconds (s) to nanoseconds (10−9 s), varying by several orders of magnitude from deep-ultraviolet (DUV) to the long-wavelength infrared (LWIR) region. The flexible photodetectors developed from MoS2-based hybrid heterostructures with graphene, carbon nanotubes (CNTs), TMDs, and ZnO are also discussed. In addition, strain-induced and self-powered MoS2 based photodetectors have also been summarized. The factors affecting the figure of merit of a very wide range of MoS2-based photodetectors have been analyzed in terms of their photoresponsivity, detectivity, response speed, and quantum efficiency along with their measurement wavelengths and incident laser power densities. Conclusions and the future direction are also outlined on the development of MoS2 and other 2D TMD-based photodetectors.

Self-Powered, Broad Band, and Ultrafast InGaN-Based Photodetector.

Abstract: A self-powered, broad band and ultrafast photodetector based on n + -InGaN/AlN/n-Si(111) heterostructure is demonstrated. Si-doped (n + type) InGaN epilayer was grown by plasma-assisted molecular beam epitaxy on a 100 nm thick AlN template on an n-type Si(111) substrate. The n + -InGaN/AlN/n-Si(111) devices exhibit excellent self-powered photoresponse under UV-visible (300-800 nm) light illumination. The maximum response of this self-powered photodetector is observed at 580 nm for low-intensity irradiance (0.1 mW/cm 2 ), owing to the deep donor states present near the InGaN/AlN interface. It shows a responsivity of 9.64 A/W with rise and fall times of 19.9 and 21.4 I¼s, respectively. A relation between the open circuit voltage and the responsivity has been realized.

A highly efficient bilayer graphene/ZnO/silicon nanowire based heterojunction photodetector with broadband spectral response.

Abstract: This paper presents three self-powered photodetectors namely, p+-bilayer graphene (BLG)/n+-ZnO nanowires (NWs), p+-BLG/n+-Si NWs/p--Si and p+-BLG/n+-ZnO NWs/p--Si The Silvaco Atlas TCAD software is utilized to characterize the optoelectronic properties of all the devices and is validated by analytical modeling The proposed dual-junction photodetectors cover broadband spectral response varying from ultraviolet to near-infrared wavelengths The dual-heterojunction broadband photodetector exhibits photocurrent switching with the rise and fall time of 148 and 127 ns, respectively At -05 V bias, the highest external quantum efficiency, photocurrent responsivity, specific detectivity, and the lowest noise equivalent power of 71%, 028 A W-1, 42 × 1012 cmHz1/2 W-1, and 259 × 10-17 W, respectively, are found for the dual-heterojunction device with a wavelength of 480 nm at 300 K The proposed nanowires based photodetectors offer great potential to be utilized as next-generation optoelectronic devices