arXiv subjects

Chennupati Jagadish

Publications and source records attributed to Chennupati Jagadish.

At least 19 recordsLinked to original sources

arXiv2026

Self-powered InAs nanowire detector arrays for extended-SWIR spectrometry at room temperature

Spectral sensing in the extended shortwave infrared (e-SWIR) is important for molecular analysis, infrared imaging, and machine vision, motivating the development of compact spectrometers for broader applications. However, conventional commercial off-the-shelf spectrometers in this wavelength region are expensive and bulky due to their reliance on external dispersive optics/filters and/or cryogenic accessories. Other emerging computational spectrometers are based on Si and InGaAs photodetectors that remain focused on the visible and near-infrared, with few detector platforms operating in the e-SWIR regime that simultaneously provide broadband sensitivity, low-noise room-temperature operation, and diverse spectral signatures for accurate identification and reconstruction. Here, we report a room-temperature e-SWIR computational spectrometer based on InAs/InP core-shell nanowire photodetector arrays with geometry-encoded spectral responses. The detectors exhibit self-powered broadband photoresponse across the 1--3 $μ$m range, with responsivity up to 0.215 A W$^{-1}$, detectivity up to $1.6 \times 10^{9}$ cm Hz$^{1/2}$ W$^{-1}$, and microsecond response times. The excellent detector performance is leveraged to demonstrate filter-free spectral reconstruction using a compact multipixel photodetector array device. This enables high-accuracy molecular absorption spectrum reconstruction and hyperspectral imaging. Our results indicate that InAs nanowire arrays are a promising platform for compact computational spectrometry and imaging in the e-SWIR at room temperature.

physics.optics↗

arXiv2025

Physics-Aware Inverse Design for Nanowire Single-Photon Avalanche Detectors via Deep Learning

Single-photon avalanche detectors (SPADs) have enabled various applications in emerging photonic quantum information technologies in recent years. However, despite many efforts to improve SPAD's performance, the design of SPADs remained largely an iterative and time-consuming process where a designer makes educated guesses of a device structure based on empirical reasoning and solves the semiconductor drift-diffusion model for it. In contrast, the inverse problem, i.e., directly inferring a structure needed to achieve desired performance, which is of ultimate interest to designers, remains an unsolved problem. We propose a novel physics-aware inverse design workflow for SPADs using a deep learning model and demonstrate it with an example of finding the key parameters of semiconductor nanowires constituting the unit cell of an SPAD, given target photon detection efficiency. Our inverse design workflow is not restricted to the case demonstrated and can be applied to design conventional planar structure-based SPADs, photodetectors, and solar cells.

physics.app-ph↗

arXiv2025

Modulation of nanowire emitter arrays using micro-LED technology

A scalable excitation platform for nanophotonic emitters using individually addressable micro-LED-on-CMOS arrays is demonstrated for the first time. Heterogeneous integration by transfer-printing of semiconductor nanowires was used for the deterministic assembly of the infrared emitters embedded in polymer optical waveguides with high yield and positional accuracy. Direct optical pumping of these emitters is demonstrated using micro-LED pixels as source, with optical modulation (on-off keying) measured up to 150 MHz. A micro-LED-on-CMOS array of pump sources were employed to demonstrate individual control of multiple waveguide coupled nanowire emitters in parallel, paving the way for future large scale photonic integrated circuit applications.

physics.optics↗

arXiv2024

Data-driven Discovery for Robust Optimization of Semiconductor Nanowire Lasers

Active wavelength-scale optoelectronic components are widely used in photonic integrated circuitry, however coherent sources of light -- namely optical lasers -- remain the most challenging component to integrate. Semiconductor nanowire lasers represent a flexible class of light source where each nanowire is both gain material and cavity; however, strong coupling between these properties and the performance leads to inhomogeneity across the population. While this has been studied and optimized for individual material systems, no architecture-wide insight is available. Here, nine nanowire laser material systems are studied and compared using 55,516 nanowire lasers to provide statistically robust insight into performance. These results demonstrate that, while it may be important to optimise internal quantum efficiency for certain materials, cavity effects are always critical. Our study provides a roadmap to optimize the performance of nanowire lasers made from any material: this can be achieved by ensuring a narrow spread of lengths and end-facet reflectivities.

physics.optics↗

arXiv2024

Generation of tunable quantum entanglement via nonlinearity symmetry breaking in semiconductor metasurfaces

Tunable biphoton quantum entanglement generated from nonlinear processes is highly desirable for cutting-edge quantum technologies, yet its tunability is substantially constrained by the symmetry of material nonlinear tensors. Here, we overcome this constraint by introducing symmetry-breaking in nonlinear polarization to generate optically tunable biphoton entanglement at picosecond speeds. Asymmetric optical responses have made breakthroughs in classical applications like non-reciprocal light transmission. We now experimentally demonstrate the nonlinear asymmetry response for biphoton entanglement using a semiconductor metasurface incorporating [110] InGaP nano-resonators with structural asymmetry. We realize continuous tuning of polarization entanglement from near-unentangled states to a Bell state. This tunability can also extend to produce tailored hyperentanglement. Furthermore, our nanoscale entanglement source features an ultra-high coincidence-to-accidental ratio of $\approx7\times10^4$, outperforming existing semiconductor flat optics by two orders of magnitude. Introducing asymmetric nonlinear response in quantum metasurfaces opens new directions for tailoring on-demand quantum states and beyond.

physics.optics↗

arXiv2023

Nanowire Array Breath Acetone Sensor for Diabetes Monitoring

Diabetic ketoacidosis (DKA) is a life-threatening acute complication of diabetes in which ketone bodies accumulate in the blood. Breath acetone (a ketone) directly correlates with blood ketones, such that breath acetone monitoring could be used to improve safety in diabetes care. In this work, we report the design and fabrication of a chitosan/Pt/InP nanowire array based chemiresistive acetone sensor. By implementing chitosan as a surface functionalization layer and a Pt Schottky contact for efficient charge transfer processes and photovoltaic effect, self-powered, highly selective acetone sensing has been achieved. This sensor has an ultra-wide detection range from sub-ppb to >100,000 ppm levels at room temperature, incorporating the range from healthy individuals (300-800 ppb) to those at high-risk of DKA (> 75 ppm). The nanowire sensor has been further integrated into a handheld breath testing prototype, the Ketowhistle, which can successfully detect different ranges of acetone concentrations in simulated breath. The Ketowhistle demonstrates immediate potential for non-invasive ketone testing and monitoring for persons living with diabetes, in particular for DKA prevention.

physics.med-ph↗

arXiv2023

An efficient modeling workflow for high-performance nanowire single-photon avalanche detector

Single-photon detector (SPD), an essential building block of the quantum communication system, plays a fundamental role in developing next-generation quantum technologies. In this work, we propose an efficient modeling workflow of nanowire SPDs utilizing avalanche breakdown at reverse-biased conditions. The proposed workflow is explored to maximize computational efficiency and balance time-consuming drift-diffusion simulation with fast script-based post-processing. Without excessive computational effort, we could predict a suite of key device performance metrics, including breakdown voltage, dark/light avalanche built-up time, photon detection efficiency, dark count rate, and the deterministic part of timing jitter due to device structures. Implementing the proposed workflow onto a single InP nanowire and comparing it to the extensively studied planar devices and superconducting nanowire SPDs, we showed the great potential of nanowire avalanche SPD to outperform their planar counterparts and obtain as superior performance as superconducting nanowires, i.e., achieve a high photon detection efficiency of 70% with a dark count rate less than 20 Hz at non-cryogenic temperature. The proposed workflow is not limited to single-nanowire or nanowire-based device modeling and can be readily extended to more complicated two-/three dimensional structures.

physics.app-ph↗

arXiv2023

Decoupling the Roles of Defects/Impurities and Wrinkles in Thermal Conductivity of Wafer-scale hBN Films

We demonstrate a non-monotonic evolution of thermal conductivity of large-area hexagonal boron nitride films with thickness. Wrinkles and defects/impurities are present in these films. Raman spectroscopy, an optothermal non-contact technique, is employed to probe the temperature and laser power dependence property of the Raman active E2ghigh phonon mode, which in turn is used to estimate the rise in the temperature of the films under different laser powers. As the conventional Fourier law of heat diffusion cannot be directly employed analytically to evaluate the thermal conductivity of these films with defects and wrinkles, finite element modeling is used instead. In the model, average heat resistance is used to incorporate an overall defect structure, and Voronoi cells with contact resistance at the cell boundaries are constructed to mimic the wrinkled domains. The effective thermal conductivity is estimated to be 87, 55, and 117 W/m.K for the 2, 10, and 30 nm-thick films, respectively. We also present a quantitative estimation of the thermal resistance by defects and wrinkles individually to the heat flow. Our study reveals that the defects/impurities render a much higher resistance to heat transfer in the films than wrinkles.

cond-mat.mtrl-sci↗

arXiv2023

Pushing limits of photovoltaics and photodetection using radial junction nanowire devices

Nanowire devices have long been proposed as an efficient alternative to their planar counterparts for different optoelectronic applications. Unfortunately, challenges related to the growth and characterization of doping and p-n junction formation in nanowire devices (along axial or radial axis) have significantly impeded their development. The problems are further amplified if a p-n junction has to be implemented radially. Therefore, even though radial junction devices are expected to be on par with their axial junction counterparts, there are minimal reports on high-performance radial junction nanowire optoelectronic devices. This paper summarizes our recent results on the simulation and fabrication of radial junction nanowire solar cells and photodetectors, which have shown unprecedented performance and clearly demonstrate the importance of radial junction for optoelectronic applications. Our simulation results show that the proposed radial junction device is both optically and electrically optimal for solar cell and photodetector applications, especially if the absorber quality is extremely low. The radial junction nanowire solar cells could achieve a 17.2% efficiency, whereas the unbiased radial junction photodetector could show sensitivity down to a single photon level using an absorber with a lifetime of less than 50 ps. In comparison, the axial junction planar device made using same substrate as absorber showed less than 1% solar cell efficiency and almost no photodetection at 0 V. This study is conclusive experimental proof of the superiority of radial junction nanowire devices over their thin film or axial junction counterparts, especially when absorber lifetime is extremely low. The proposed device holds huge promise for III-V based photovoltaics and photodetectors.

cond-mat.mtrl-sci↗

arXiv2021

Self-powered InP Nanowire Photodetector for Single Photon Level Detection at Room Temperature

Highly sensitive photodetectors with single photon level detection is one of the key components to a range of emerging technologies, in particular the ever-growing field of optical communication, remote sensing, and quantum computing. Currently, most of the single-photon detection technologies require external biasing at high voltages and/or cooling to low temperatures, posing great limitations for wider applications. Here, we demonstrate InP nanowire array photodetectors that can achieve single-photon level light detection at room temperature without an external bias. We use top-down etched, heavily doped p-type InP nanowires and n-type AZO/ZnO carrier selective contact to form a radial p-n junction with a built-in electric field exceeding 3x10^5 V/cm at 0 V. The device exhibits broadband light sensitivity and can distinguish a single photon per pulse from the dark noise at 0 V, enabled by its design to realize near-ideal broadband absorption, extremely low dark current, and highly efficient charge carrier separation. Meanwhile, the bandwidth of the device reaches above 600 MHz with a timing jitter of 538 ps. The proposed device design provides a new pathway towards low-cost, high-sensitivity, self-powered photodetectors for numerous future applications.

physics.optics↗

arXiv2021

Ultralow Threshold, Single-Mode InGaAs/GaAs Multi-Quantum Disk Nanowire Lasers

We present single-mode nanowire (NW) lasers with ultralow threshold in the near-infrared spectral range. To ensure the single-mode operation, the NW diameter and length are reduced specifically to minimize the longitudinal and transverse modes of the NW cavity. Increased optical losses and reduced gain volume by the dimension reduction are compensated by excellent NW morphology and InGaAs/GaAs multi-quantum disks. At 5 K, a threshold low as 1.6 μJ/cm2 per pulse is achieved with a resulting quality factor exceeding 6400. By further passivating the NW with an AlGaAs shell to suppress surface non-radiative recombination, single-mode lasing operation is obtained with a threshold of only 48 μJ/cm2 per pulse at room temperature with a high characteristic temperature of 223 K and power output of ~ 0.9 μW. These single-mode, ultralow threshold, high power output NW lasers are promising for the development of near-infrared nanoscale coherent light sources for integrated photonic circuits, sensing, and spectroscopy.

physics.optics↗

arXiv2021

Axial vs. Radial Junction Nanowire Solar Cell

Both axial and radial junction nanowire solar cells have their challenges and advantages. However, so far, there is no review that explicitly provides a detailed comparative analysis of both axial and radial junction solar cells. This article reviews some of the recent results on axial and radial junction nanowire solar cells with an attempt to perform a comparative study between the optical and device behavior of these cells. In particular, we start by reviewing different results on how the absorption can be tuned in axial and radial junction solar cells. We also discuss results on some of the critical device concepts that are required to achieve high efficiency in axial and radial junction solar cells. We include a section on new device concepts that can be realized in nanowire structures. Finally, we conclude this review by discussing a few of the standing challenges of nanowire solar cells.

cond-mat.mes-hall↗

arXiv2021

Infrared up-conversion imaging in nonlinear metasurfaces

Infrared imaging is a crucial technique in a multitude of applications, including night vision, autonomous vehicles navigation, optical tomography, and food quality control. Conventional infrared imaging technologies, however, require the use of materials like narrow-band gap semiconductors which are sensitive to thermal noise and often require cryogenic cooling. Here, we demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas, using a nonlinear wave-mixing process. We experimentally show the up-conversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation. In this process, an infrared image of a target is mixed inside the metasurface with a strong pump beam, translating the image from infrared to the visible in a nanoscale ultra-thin imaging device. Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.

physics.optics↗

arXiv2020

Identifying Carbon as the Source of Visible Single Photon Emission from Hexagonal Boron Nitride

Single photon emitters (SPEs) in hexagonal boron nitride (hBN) have garnered significant attention over the last few years due to their superior optical properties. However, despite the vast range of experimental results and theoretical calculations, the defect structure responsible for the observed emission has remained elusive. Here, by controlling the incorporation of impurities into hBN and by comparing various synthesis methods, we provide direct evidence that the visible SPEs are carbon related. Room temperature optically detected magnetic resonance (ODMR) is demonstrated on ensembles of these defects. We also perform ion implantation experiments and confirm that only carbon implantation creates SPEs in the visible spectral range. Computational analysis of hundreds of potential carbon-based defect transitions suggest that the emission results from the negatively charged VBCN- defect, which experiences long-range out-of-plane deformations and is environmentally sensitive. Our results resolve a long-standing debate about the origin of single emitters at the visible range in hBN and will be key to deterministic engineering of these defects for quantum photonic devices.

physics.app-ph↗

arXiv2020

Exploring the Band Structure of Wurtzite InAs Nanowires Using Photocurrent Spectroscopy

We use polarized photocurrent spectroscopy in a nanowire device to investigate the band structure of hexagonal Wurtzite InAs. Signatures of optical transitions between four valence bands and two conduction bands are observed which are consistent with the symmetries expected from group theory. The ground state transition energy identified from photocurrent spectra is seen to be consistent with photoluminescence emitted from a cluster of nanowires from the same growth substrate. From the energies of the observed bands we determine the spin orbit and crystal field energies in Wurtzite InAs. This information is essential to the development of crystal phase engineering of this important III-V semiconductor.

cond-mat.mes-hall↗

arXiv2020

Characterisation, Selection and Micro-Assembly of Nanowire Laser Systems

Semiconductor nanowire (NW) lasers are a promising technology for the realisation of coherent optical sources with extremely small footprint. To fully realize their potential as building blocks in on-chip photonic systems, scalable methods are required for dealing with large populations of inhomogeneous devices that are typically randomly distributed on host substrates. In this work two complementary, high-throughput techniques are combined: the characterisation of nanowire laser populations using automated optical microscopy, and a high accuracy transfer printing process with automatic device spatial registration and transfer. In this work a population of NW lasers is characterised, binned by threshold energy density and subsequently printed in arrays onto a secondary substrate. Statistical analysis of the transferred and control devices show that the transfer process does not incur measurable laser damage and the threshold binning can be maintained. Analysis is provided on the threshold and mode spectra of the device populations to investigate the potential for using NW lasers for integrated systems fabrication.

physics.app-ph↗

arXiv2019

Strong Hot Carrier Effects Observed in a Single Nanowire Heterostructure

We use Transient Rayleigh Scattering to study the thermalization of hot photoexcited carriers in single GaAsSb/InP nanowire heterostructures. By comparing the energy loss rate in single bare GaAsSb nanowires which do not show substantial hot carrier effects with the core-shell nanowires, we show that the presence of an InP shell substantially suppresses the LO phonon emission rate at low temperatures leading to strong hot carrier effects.

cond-mat.mes-hall↗

arXiv2018

Three-Leaf Dart-Shaped Single-Crystal BN Formation Promoted by Surface Oxygen

Two-dimensional hexagonal boron nitride (h-BN) single crystals with various shapes have been synthesized by chemical vapor deposition over the past several years. Here we report the formation of three-leaf dart (3LD)-shaped single crystals of h-BN on Cu foil by atmospheric-pressure chemical vapor deposition. The leaves of the 3LD-shaped h-BN are as long as 18 μm and their edges are smooth armchair on one side and stepped armchair on the other. Careful analysis revealed that surface oxygen plays an important role in the formation of the 3LD shape. Oxygen suppressed h-BN nucleation by passivating Cu surface active sites and lowered the edge attachment energy, which caused the growth kinetics to change to a diffusion-controlled mode.

cond-mat.mtrl-sci↗