Papers by Kunal Bhatnagar
Bulletin of the American Physical Society, 2017
Physical Review B, 2017
The electronic properties of epitaxial oxide thin films grown on compound semiconductors are larg... more The electronic properties of epitaxial oxide thin films grown on compound semiconductors are largely determined by the interfacial atomic structure, as well as the thermodynamic conditions during synthesis. Ferroelectric polarization and Fermi-level pinning in SrTiO 3 films have been attributed to the presence of oxygen vacancies at the oxide/semiconductor interface. Here, we present scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) analysis of GaAs films grown on SrTiO 3 combined with first-principles calculations to determine the atomic and electronic structures of the SrTiO 3 /GaAs interfaces. An atomically abrupt SrO/As interface is observed and the interfacial SrO layer is found to be O-deficient. Firstprinciples density functional theory (DFT) calculations show SrO/Ga and Sr/As interfaces are favorable under O-rich and O-poor conditions, respectively. SrO/Ga interface is reconstructed via the formation of Ga-Ga dimers while Sr/As interface is abrupt and consistent with the experiment. DFT calculations further reveal that intrinsic two-dimensional electron gas (2DEG) forms in both SrO/Ga and Sr/As interfaces and the Fermi level is pinned to the localized 2DEG states. Interfacial O vacancies can enhance the 2DEG density while it is possible for Ga/As vacancies to unpin the Fermi level from the 2DEG states.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2015
This study entails a comparison of the broken-gap InAs/GaSb heterojunction system on two differen... more This study entails a comparison of the broken-gap InAs/GaSb heterojunction system on two different substrates, including Si and native GaSb as a control. Through the use of different integration schemes such as AlSb and SrTiO 3 buffer layers, GaSb was grown on miscut Si substrates using solid-source molecular beam epitaxy. The InAs/GaSb p þ-in þ heterostructures were grown on the GaSb/Si virtual substrates and compared in terms of their surface morphology and crystalline quality. Esaki tunnel diodes were fabricated, and their performance compared across the different integration platforms. The control sample shows the best peak current density of 336 kA/cm 2 and a conductance slope of 274 mV/decade compared to the broken-gap junction on SrTiO 3 /Si and AlSb/ Si virtual substrates. These results show the possibility of integrating the InAs/GaSb system in ultralow power tunnel field-effect transistors logic applications with the cost-effectiveness and maturity of the silicon technology. V
Performance evaluation of broken gap Esaki tunnel diodes on Si and GaSb substrates
Electronics Letters, 2016
n-InAs/p-GaSb Esaki diodes with 3 nm GaSb i-layers are fabricated on Si and GaSb substrates. The ... more n-InAs/p-GaSb Esaki diodes with 3 nm GaSb i-layers are fabricated on Si and GaSb substrates. The on Si sample devices exhibit lower peak to valley ratios and peak current density than their on GaSb counterparts at 3.27 against 4.45 and 119 against 336 kA/cm2, respectively. The findings are similar to other reports of integrating III-V Esaki diodes onto Si.
Aps Texas Sections Fall Meeting Abstracts, Oct 1, 2007
IEEE Transactions on Electron Devices, 2015
In0.53Ga0.47As Esaki tunnel diodes grown by Molecular Beam Epitaxy (MBE) on a Si substrate via a ... more In0.53Ga0.47As Esaki tunnel diodes grown by Molecular Beam Epitaxy (MBE) on a Si substrate via a graded buffer and control In0.53Ga0.47As Esaki tunnel diodes grown on an InP substrate are compared in this work. Statistics are used as tool to show peak to valley ratio for the III-V on Si sample and the control perform similarly below 8.6×10 −10 cm 2. Existence of a critical device area suggests the potential to utilize III-V on Si for other deeply scaled tunnel devices.
Surface treatments to reduce leakage current in In0.53Ga0.47As p-i-n diodes
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2015
In-situ monitoring during MBE growth of InAs based heterostructures
Journal of Crystal Growth, 2015
The use of reflectance anisotropy spectroscopy (RAS) for the real time monitoring of the growth o... more The use of reflectance anisotropy spectroscopy (RAS) for the real time monitoring of the growth of InAs based heterostructures by molecular beam epitaxy within the photon energy range 1.5–5.0 eV is reported. The complete desorption of the native oxide for InAs substrates was monitored using a single wavelength and epitaxial growth of InAs was also monitored under both the As- and In-rich surface reconstructions. Further the changes in the RAS and reflectance data for ternary and quaternary layers demonstrated the usefulness of this system as an in-situ tool for monitoring the composition of layers for this important class of narrow gap semiconductors. In addition, emissivity corrected pryometry temperature was measured using the RAS system. Growth rates for the individual layers in a heterostructure were also determined from an analysis of the reflectance data.
Nano-gap grating devices with enhanced optical properties and methods of fabrication
ABSTRACT A method of producing a grating structure comprises the steps of forming a stamp from fl... more ABSTRACT A method of producing a grating structure comprises the steps of forming a stamp from flexible plastic material, the stamp including a negative of a periodic grating pattern on a first surface; forming an ink by applying a polymer film to the stamp, the ink including a first surface and an opposing second surface, wherein the first surface of the ink contacts the first surface of the stamp such that the ink retains a positive of the periodic grating pattern; placing the ink and the stamp on a substrate such that the second surface of the ink contacts an upper surface of the substrate; and removing the stamp from the ink by applying a tensional force to one edge of the stamp.
Heterointegration of III-V on Silicon using a Crystalline Oxide Buffer Layer
Journal of Crystal Growth, 2015
Abstract The integration of III–V compound semiconductors with Si can combine the cost advantage ... more Abstract The integration of III–V compound semiconductors with Si can combine the cost advantage and maturity of Si technology with the superior performance of III–V materials. We have achieved the heteroepitaxial growth of III–V compound semiconductors on a crystalline SrTiO 3 buffer layer grown on Si(0 0 1) substrates. A two-step growth process utilizing a high temperature nucleation layer of GaAs, followed by a low-temperature GaAs layer at a higher growth rate was employed to achieve highly crystalline thick GaAs layers on the SrTiO 3 /Si substrates with low surface roughness as seen by AFM. The effect of the GaAs nucleation layer on different surface terminations for the SrTiO 3 layer was studied for both on axis and miscut wafers, which led to the conclusion that the Sr terminated surface on miscut substrates provides the best GaAs films. Using GaAs/STO/Si as virtual substrates, we have optimized the growth of high quality GaSb using the interfacial misfit (IMF) dislocation array technique. This work can lead to the possibility of realizing infrared detectors and next-generation high mobility III–V CMOS within the existing Si substrate infrastructure.
AlxIn1−xAsySb1−y alloys lattice matched to InAs(100) grown by molecular beam epitaxy
Journal of Crystal Growth, 2015
Abstract Al x In 1− x As y Sb 1− y quaternary alloys lattice-matched to InAs were successfully gr... more Abstract Al x In 1− x As y Sb 1− y quaternary alloys lattice-matched to InAs were successfully grown by molecular beam epitaxy (MBE) for use as buffer layers for substrate isolation in InAs channel devices. The use of In-containing quaternary buffer layers with 5% In was found to dramatically improve the heterointerface between the buffer and a surface InAs channel layer. The composition of these alloys and the extent of lattice matching were accurately determined by double crystal X-ray measurements. A simple model was used to estimate the variation of critical thickness with lattice mismatch for AlInAsSb epitaxially grown on an InAs substrate. Layers with high Al content and low As mole fraction were grown by modulated MBE technique which was found to significantly improve the surface morphology and the composition control of the alloys. In contrast, quaternary alloys with low Al content were grown by conventional MBE and had an rms roughness of less than 0.2 nm.
Fluorescence enhancement from nano-gap embedded plasmonic gratings by a novel fabrication technique with HD-DVD
Nanotechnology, 2012
Investigation of Gadolinium Gallium Oxide using spectroscopic ellipsometry
Spectroscopic Ellipsometry (SE) is a non-destructive characterization technique used for determin... more Spectroscopic Ellipsometry (SE) is a non-destructive characterization technique used for determining film thickness, interfacial roughness and optical properties of single and multilayered materials. SE measures the change in the polarization state of the incident light upon reflection from these layers providing insight into the properties and composition of topmost and underlying materials. The Horiba Jobin Yvon - UVISEL located in the Angelo State Materials Characterization Lab is based on the principle of phase modulated spectroscopic ellipsometry. This tool has been used to successfully characterize a variety of semiconductor samples. We will detail results from semiconductor heterostructures containing Gadolinium Gallium Oxide (GdGaO3), a novel material with promise for application as a high-k dielectric in the design of compound semiconductor MOSFETs. Models for this unusual material have been developed and used to characterize various structures with success. We have obtaine...
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Papers by Kunal Bhatnagar