Jamie Phillips

Jamie Phillips
University of Michigan | U-M · Department of Electrical Engineering and Computer Science (EECS)

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150
Publications
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4,486
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Publications

Publications (150)
Article
Intermediate band solar cell provides novel alternative to multi-junction solar cell, but its efficiency is significantly degraded when spectral overlap exists between different absorption bands. Here, a scheme using non-uniform sub-bandgap state filling together with intermediate band transport is proposed to resolve the spectral overlap issue. On...
Conference Paper
In past decade, T2SL detectors with promising performance have been reported by various institutions thanks to the extensive modeling efforts, improvement of T2SL material quality, and development of advanced low-dark-current architectures with unipolar barriers (Xbn, CBIRD, pBiBn, M-structure, etc). One of the most demanding challenges of present...
Article
Multiphoton transitions in GaSb/GaAs quantum-dot intermediate-band solar cells are investigated at variable temperature and excitation intensity. A transition temperature is observed that corresponds to the crossover between quantum-dot intraband transitions dominated by thermal escape due to infrared photogeneration. The transition temperature fol...
Article
The introduction of oxygen in ZnTe provides an isoelectronic radiative defect that can form an intermediate band attractive for optoelectronic applications. ZnTe also exhibits native deep level emission in close spectral proximity to oxygen emission, which can obscure the understanding of these electronic states. The photoluminescence characteristi...
Article
Full-text available
Highly mismatched ZnTeO alloys were grown by molecular beam epitaxy under various oxygen partial pressures (10-7 Torr, 10-6 Torr, and 10-5 Torr). Despite this large variation in oxygen partial pressure, there was almost no change in the concentration of incorporated oxygen. However, increasing the oxygen partial pressure significantly enhanced the...
Article
This paper presents a voltage-controlled, highquality factor (Q) composite thin-film bulk acoustic resonator (FBAR) at 1.28 GHz. The composite FBAR consists of a thin layer of barium strontium titanate (BST) that is sandwiched between two electrodes deposited on a silicon-on-insulator (SOI) wafer. The BST layer, which has a strong electrostrictive...
Article
We experimentally demonstrate a simple narrowband transmission filter using a silicon/air grating, exhibiting broadband high-reflectance between 8 and 14 μm and narrow transmission peaks at slightly off-normal incidence. We explain the response in terms of guided modes in a dielectric slab waveguide, with numerical modal analysis corroborating an i...
Article
This paper presents the design and measurement results of intrinsically switchable interdigitated contour mode resonators based on barium titanate (BTO) thin films. The resonators have lithographically defined interdigitated electrodes that determine their resonance frequencies. The BTO thin film exhibits electrostriction, which allows the resonanc...
Article
Highly mismatched alloys have been predicted to exhibit enhanced thermoelectric properties. Here we report on transport properties of one such system, nitrogen-doped ZnTe epitaxial layers on GaAs (100). Hall effect, electrical resistivity, and Seebeck coefficient measurements were performed between 5 K and 300 K for samples with a room temperature...
Article
The epitaxial growth of high-quality ZnTe on GaSb substrates is demonstrated by molecular beam epitaxy without the use of a group-V beam flux or intermediate GaSb buffer layer. A reduced surface cleaning temperature is achieved using a combination of HCl etching prior to loading into the growth chamber and use of a ZnCl2 flux during the thermal cle...
Article
Atom probe tomography and cross-sectional scanning tunneling microscopy show that GaSb/GaAs quantum dots disintegrate into ring-like clusters of islands upon capping. Band transition energies calculated using an 8-band k.p model of the capped dots with the observed dimensions are consistent with emission energies observed in photoluminescence data....
Article
Intergrowth of two partially miscible phases of BiFeO(3) and BiMnO(3) gives a new class of room-temperature multiferroic phase, Bi(3) Fe(2) Mn(2) O(10+δ) , which has a unique supercell (SC) structure. The SC heterostructures exhibit simultaneously room-temperature ferrimagnetism and remanent polarization. These results open up a new avenue for expl...
Article
A unipolar mercury cadmium telluride (HgCdTe) NBνN infrared (IR) device architecture is analyzed by physics-based numerical device simulations. The device structure is predicted to suppress Shockley–Read–Hall (SRH) and Auger generation–recombination (G–R) processes, while also providing a simplified fabrication process by eliminating p-type doping...
Article
The illumination instabilities of nanocrystalline ZnO thin-film transistors (TFT) with HfO2 gate dielectrics are reported via zero gate bias multiwave length illumination stress method. TFT I D–V G curves exhibit a negative threshold voltage shift together with an increase in I D off current and increase in subthreshold slope with increasing photon...
Conference Paper
HgCdTe-based infrared (IR) detectors remain the front-runner for high performance IR focal plane array (FPA) applications due to their favorable material and optical properties. While state-of-the-art HgCdTe p-n junction technology such as the double layer planar heterostructure (DLPH) devices can achieve near theoretical performance in the mid-wav...
Conference Paper
ZnO thin film electronics have received much attention due to the relatively high electron mobility of ZnO thin films in comparison to amorphous silicon (a-Si) and organic thin films. There is significant interest in using ZnO thin film transistors (TFTs), or similar oxides such as InGaZnO and zinc tin oxide, to replace a-Si TFTs in large area disp...
Article
Full-text available
Strong coupling effects in a dielectric microcavity with a single ZnO nanowire embedded in it have been investigated at room temperature. A large Rabi splitting of ~100 meV is obtained from the polariton dispersion and a non-linearity in the polariton emission characteristics is observed at room temperature with a low threshold of 1.63 μJ/cm(2), wh...
Article
A long-wavelength IR broadband reflector is demonstrated using a high-index-contrast subwavelength grating based on a Si/SiO2 system. The field response has been computationally and experimentally verified to exhibit broadband reflectance in the spectral range of 13-16 μm with Δλ/λ=18.5% for reflectance >70%. The gratings exhibit incident field pol...
Article
The strain-mediated evolution of epitaxial ZnTe/ZnSe quantum structures is studied at the atomic scale using spherical aberration-corrected scanning transmission electron microscopy, coupled with electronic properties characterized by photoluminescence spectroscopy. The growth development of these buried quantum dots clearly demonstrates a homogene...
Article
Positive and negative bias temperature instabilities (PBTI and NBTI) of $ \hbox{ZnO/HfO}_{2}$ thin-film transistors are investigated by the bias-temperature-stress test method. PBTI results show a linear shift in threshold voltage in the positive voltage direction with a magnitude that semilogarithmically increases with time. This is indicative of...
Article
A unipolar, barrier-integrated HgCdTe nBn photodetector with all n-type doping and a type-I band lineup is experimentally demonstrated. Planar mid-wave infrared (MWIR) nBn devices exhibit current-voltage (I-V) characteristics that are consistent with band inversion in reverse bias, indicating a barrier-influenced behavior. Dark current saturation i...
Article
We have investigated the effects of in situ and ex situ post-growth thermal annealing on the organization of InAs/GaAs quantum dot superlattices, which consist of regular arrays of InAs islands embedded in GaAs. Using large-scale and high resolution cross-sectional scanning tunneling microscopy, we have mapped out the spatial distributions of the i...
Article
The electronic structure and thermal carrier capture and escape mechanisms are studied for GaSb/GaAs quantum dots with a type-II band alignment using admittance spectroscopy. Clear signatures are observed corresponding to confined quantum dot states with extracted activation energy of 0.337 eV and the thermal capture cross section in the range from...
Article
We present in this study a theoretical and experimental investigation of the MWIR HgCdTe nBn device concept. Theoretical work has demonstrated that the HgCdTe nBn device is potentially capable of achieving performance equivalent to the ideal double layer planar heterostructure (DLPH) detector. Comparable responsivity, low current denisty Jdark, and...
Article
Jamie Phillips received the BS, MS, and PhD degrees in electrical engineering from the University of Michigan in 1994, 1996, and 1998, respectively. In his graduate studies, he contributed to the epitaxial growth and device applications of self-assembled InGaAs/GaAs quantum-dots, including quantum-dot infrared photodetectors and quantum-dot diode l...
Article
The electronic properties of ZnO/HfO2 interface states are studied by dc current-voltage and ac admittance spec- troscopy on thin-film transistors (TFTs) and metal-insulator- semiconductor capacitor structures. Subthreshold behavior of the transistors indicates an interface state density (Nit )v alue of 7.2 × 10 12 cm −2 . Cole-Cole plots of ac adm...
Article
The performance of leading HgCdTe p-n junction infrared (IR) device technology is limited by thermal generationrecombination (G-R) mechanisms and material processing challenges associated with achieving low, controllable in-situ p-type doping using molecular beam epitaxy (MBE) growth techniques. These aspects are addressed in the proposed hybrid Hg...
Article
ZnO and ZnSe are proposed as n-type layers in ZnTe heterojunction diodes to overcome problems associated with the n-type doping of ZnTe. The structural properties and electrical characteristics of ZnO/ZnTe and ZnO/ZnSe/ZnTe heterojunctions grown by molecular beam epitaxy on (001) GaAs substrates are presented. ZnO shows a strong preference for c-pl...
Article
An n-type mercury cadmium telluride (HgCdTe) unipolar nBn infrared detector structure is proposed as a means of achieving performance limited by intrinsic thermal carrier generation without requirements for p-type doping. Numerical modeling was utilized to calculate the current–voltage and optical response characteristics and detectivity values for...
Article
GaAs alloys with dilute content of Bi and N provide a large reduction in band-gap energy with increasing alloy composition. GaAsBi/GaAsN heterojunctions have a type-II band alignment, where superlattices based on these materials offer a wide range for designing effective band-gap energy by varying superlattice period and alloy composition. The mini...
Article
Infrared detectors require cryogenic operation to suppress dark current, which is typically limited by Auger processes in narrow-band-gap semiconductor materials. Device structures designed to reduce carrier density under nonequilibrium reverse-bias operation provide a means to suppress Auger generation and to reduce dark current and subsequent cry...
Article
This paper describes our recent developments of intermediate-band solar cells, with a focus on the use of dilute alloys and nanostructured materials such as quantum dots (QDs). The concept of “full-spectrum” solar cells and their working mechanism with various material structures are first illustrated. A comprehensive review of ZnTe:O-based interme...
Article
A nearly universal goal for infrared photon detection systems is to increase their operating temperature without sacrificing performance. For high quality HgCdTe photovoltaic infrared detectors at elevated temperatures, the lowdoped absorber layer becomes intrinsic, carrier concentrations are high and Auger processes typically dominate the dark cur...
Article
Self-organized growth of strained semiconductor heterostructures has enabled the realization of ordered arrays of quantum dots that can be incorporated into the active region of electronic and optoelectronic devices. Highly uniform In(Ga)As/Ga(Al)As with greatly reduced photoluminescence linewidths (FWHM=19 meV, T=17K) have been grown and character...
Article
Controllable p-type doping at low concentrations is desired for multilayer HgCdTe samples in a P +/π/N + structure due to the promise of suppressing Auger processes, and ultimately reduced dark current for infrared detectors operating at a given temperature. In this study, a series of arsenic implantation and annealing experiments have been conduct...
Article
In this work, we analyze Auger suppression in HgCdTe alloy-based device structures and determine the operation temperature improvements expected when Auger suppression occurs. We identified critical material (absorber dopant concentration and minority-carrier lifetime) requirements that must be satisfied for optimal performance characteristics. Cal...
Article
High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response across the infrared spectrum (1 to 14 μm and beyond), and are commonly utilized for high performance infrared imaging applications. However, the cooling system required to achieve the desired sensitivity makes them costly, heavy and limits their applicab...
Article
In this letter, we report on the fabrication of ZnO and ZnTe thin-film transistors (TFTs) on SiO<sub>2</sub>/Si substrates in a bottom-gate configuration. The ZnO TFT devices exhibit field effect mobility of mu ~ 4 cm<sup>2</sup>/V middot s and an on/off current ratio exceeding 10<sup>9</sup>. The on/off-current ratio of the ZnTe devices was found...
Article
Full-text available
Carrier generation and recombination processes of ZnTeO thin films are studied by time-resolved photoluminescence, where carrier lifetimes at oxygen states and the conduction band are inferred to be ≫1 μ s and ≪100 ps , respectively. The radiative recombination coefficient for optical transitions from oxygen states to the valence band is extracted...
Article
Full-text available
A 1-D drift-diffusion modeling for impurity photovoltaics is presented. The model is based on the self-consistent solution of Poisson's equation and carrier continuity equations incorporating generation and recombination mechanisms including the intermediate states. The model is applied to a prototypical solar cell device, where strong space charge...
Article
Full-text available
In this work, finite element methods are used to obtain self-consistent, steady-state solutions of Poisson's equation and the carrier continuity equations. Experimental dark current–voltage characteristics between 120 and 300 K of HgCdTe Auger-suppressed photodiodes with cutoff wavelength of λ c = 10 µm at 120 K are fitted using numerical simulatio...
Article
Full-text available
This special cluster of Journal of Physics D: Applied Physics reports proceedings from the Frontiers in Semiconductor-Based Devices Symposium, held in honor of the 60th birthday of Professor Pallab Bhattacharya by his former doctoral students. The symposium took place at the University of Michigan, Ann Arbor on 6-7 December 2009. Pallab Bhattachary...
Article
Oxygen incorporation into ZnTe was studied using pulsed laser deposition and molecular beam epitaxy. Oxygen incorporation at the high partial pressures studied for pulsed laser deposition was found to result in increasing visible transparency with oxygen incorporation, and is attributed to the formation of TeO x based on bonding information obtaine...
Article
Full-text available
Oxygen doping in ZnTe is applied to a junction diode in the aim of utilizing the associated electron states 0.5 eV below the bandedge as an intermediate band for photovoltaic solar cells. The ZnTe:O diodes confirm extended spectral response below the bandedge relative to undoped ZnTe diodes, and demonstrate a 100% increase in short circuit current,...
Article
A switchable thin film bulk acoustic wave resonator (FBAR) filter based on barium titanate (BTO) thin films is reported for the first time. BTO is a ferroelectric material which possesses electrostriction, giving the filter the ability to be placed in either an on state or an off state by changing the applied dc bias voltage. A 1.5 stage ladder typ...
Article
Full-text available
A model for intermediate band solar cells is presented to assess the effect of carrier transport and recombination (CTR) on the efficiency of these devices. The model includes dependencies of physical parameters including optical absorption, carrier lifetime, and carrier transport on the density of intermediate band electronic states. Simulation re...
Article
Full-text available
A 1-D drift-diffusion modeling for impurity photo-voltaics is presented. The model is based on the self-consistent solution of Poisson's equation and carrier continuity equations incorporating generation and recombination mechanisms including the intermediate states. The model is applied to a prototypical solar cell device, where strong space charg...
Article
Optical coupling and light trapping in thin-film solar cells are studied numerically using rigorous solutions of Maxwell's equations. The solar cell investigated consists of a ZnO/a-Si/ZnO/Ag structure, though results may be generalized to any thin-film solar cell technology. Varying diffraction gratings were studied, including periodic rectangular...
Article
The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared photodiodes are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work...
Article
Full-text available
Heterojunction diodes consisting of n-type ZnO and p-type ZnTe were grown by pulsed laser deposition and molecular beam epitaxy, respectively, on GaAs (001) substrates. Strong diode rectifying behavior was observed in the current–voltage characteristics with a current on/off ratio of J on /J off=1 ×105 and a diode ideality factor of n=1.5. A strong...
Conference Paper
A general purpose impedance tuner is proposed for adaptive matching applications to compensate the impedance variations of devices such as antennas or power amplifiers. The impedance tuner, composed of a phase shifter and a variable transformer, is designed based on all-pass networks. Thin-film barium-strontium titanate (BST) parallel-plate capacit...
Article
The growth of wurtzite ZnO on cubic MgO (001) substrates by molecular beam epitaxy is reported. ZnO epilayers exhibit the nonpolar m-plane orientation based on x-ray diffraction and transmission electron microscopy analysis. Comparative studies of ZnO grown by pulsed laser deposition on MgO (001) result in preferred growth in the polar c-plane orie...
Article
The optical properties of ZnO/Mg x Zn1−x O (x=0.17) quantum wells (QWs) grown on c-plane sapphire substrates by pulsed laser deposition are presented. A blueshift in the low-temperature photoluminescence (PL) of the QWs illustrates quantum confinement effects as a function of ZnO well widths in the range from 3nm to 10nm. Enhanced luminescence prop...
Article
The general approach and effects of nonequilibrium operation of Auger suppressed HgCdTe infrared detectors are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work,...
Article
The electrical characteristics of organic (3,4-polyethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) contacts to HgCdTe are studied as a potential alternative to metal/HgCdTe contacts. The use of organic PEDOT:PSS contacts offers the potential for an improved contact technology for HgCdTe IR detector arrays. In this work, PEDOT:PSS contact...
Article
In this effort, significant emphasis was placed on the epitaxial growth and in situ doping of ZnO for optoelectronic devices. The materials research efforts on ZnO have resulted in device-quality material on sapphire substrates for the desired laser diodes, where the eventual material quality improvements necessary for the devices are anticipated f...
Conference Paper
In this paper, a new application of ferroelectric thin film based on electrostrictive and piezoelectric effects is reported. Electrostrictive resonances in the thin film can be controlled with the application of the DC electrical field. A switchable thin film bulk wave acoustic resonator (FBAR) is proposed using barium strontium titanate (BST) thin...
Article
A device architecture for improving the linearity of barium-strontium-titanate (BST) capacitors is proposed, analyzed, and experimentally demonstrated. The basic concept is to reduce the RF swing across the ferroelectric varactors by connecting multiple capacitors in series. With proper biasing networks, the overall device preserves its tunability....
Article
A simple model is developed to explain the hysteretic electric field dependence of the piezoelectric coefficient in ferroelectric thin films. The nonlinear susceptibility and hysteretic electrical polarization behavior can explain the piezoelectric hysteresis characteristics. An empirical model introducing a weighting factor is utilized to represen...
Conference Paper
A device architecture is proposed to improve the linearity of barium strontium titanate (BST) capacitors while maintaining the tunability and the quality factor. Thin-film parallel plate capacitors are fabricated utilizing the proposed architecture. The measurement results successfully demonstrate the effectiveness of this approach. Up to 14 dB of...
Article
Scaling the electrode layout (electrode gap, electrode length) down to microscale dimensions extends the application of electrooptic (EO) modulators to microphotonics. In this paper, design criteria are set up to minimize the switching voltage of microscale EO Mach-Zehnder interferometric modulators. Mach-Zehnder interferometric modulators under di...
Article
Photoconductivity is observed in ZnO epilayers due to photoexcitation in the visible spectral region of 400–700 nm, below the ZnO bandgap energy of 3.4 eV. Photoconductive transients due to visible photoexcitation have time constants in the order of minutes. Treatment of the ZnO surface with SiO2 passivation layers results in a significant reductio...
Article
The electrical characteristics of ZnO thin-film transistors with high-k (Ba,Sr)TiO3 gate dielectrics are presented. The ZnO and (Ba,Sr)TiO3 thin films were deposited on Pt, exhibiting polycrystalline characteristics. The thin-film devices demonstrated transistor behavior over the range of 0–10 V with a stable threshold voltage of approximately 1.2...
Article
The electronic properties of semiconductors are highly dependent on carrier scattering mechanisms determined by crystalline structure, band structure, and defects in the material. Experimental characteristics of lattice vibrational modes and free carrier absorption in single-crystal ZnO samples obtained from different sources are presented in this...
Article
A strong photoconductive response is observed for ZnO epilayers in the presence of both above bandgap and below bandgap photoexcitation. Photoexcitation for energies larger than the bandgap results in a photoconductive response with fast and slow time constants on the order of nanoseconds and larger than milliseconds, respectively. The fast and slo...
Article
Thin films of Pb(Zr0.52Ti0.48)O3 (PZT) were deposited by pulsed laser deposition on ZnO/Al2O3 (0001) layers grown by molecular beam epitaxy, and Pt/SiO2/Si substrates. The ZnO epilayers serve as a crystalline oxide template for PZT deposition, and a conducting material that may be used for electrodes in thin film ferroelectric capacitors. The PZT t...
Article
A model is developed to explain the hysteretic electric field dependence of the electrooptic coefficient in ferroelectric thin films. The reversible electric polarization and the tunable dielectric susceptibility of the ferroelectric thin film are proposed to explain the hysteretic rho-E (electrooptic coefficient- applied electric field) loop. An e...
Conference Paper
A simple two-port measurement technique was developed based on equivalent lumped element circuit model of capacitor using thin film barium strontium titanate (BST) material. This technique allows one to determine the loss contribution due to dielectric BST and conductor separately. The loss tangent of BST obtained is about 0.012 up to 10 GHz for a...
Article
Full-text available
HgCdTe remains the material of choice for high-performance infrared (IR) detectors due to its tunable direct bandgap energy corresponding to the IR spectral region, and the advancement of HgCdTe materials growth and processing technologies. Accurate knowledge of the HgCdTe optical absorption coefficient is important for IR detector design, layer sc...
Article
ZnO thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy (MBE). The crystalline properties of the layers as measured by x-ray diffraction were found to improve with lower growth temperatures, where the full-width at half-maximum (FWHM) of the x-ray rocking curves was shown to be in the range of 100 to 1,100...
Article
Plasma-assisted molecular beam epitaxy was used to grow thin films of ZnO on c-plane sapphire substrates. The crystalline properties of the layers as measured by x-ray diffraction were found to improve with lower growth temperatures, where the full width at half maximum (FWHM) of the (0002) peak x-ray rocking curves was shown to be in the range of...
Article
The electrical properties of several metal contacts to n-type ZnO (0001) were studied. The ZnO samples consisted of bulk single-crystal material, epitaxial layers on sapphire grown by molecular beam epitaxy (MBE), and polycrystalline thin films on sapphire obtained by pulsed laser deposition (PLD). Ohmic and rectifying contacts were observed depend...
Article
The intensity-voltage output characteristics of thin-film linear electro-optic Mach-Zehnder interferometer modulators can be nonperiodic for configurations where the optic axis is perpendicular to the applied electric field. As a result, the electro-optic coefficient for the material can not be determined assuming a periodic half-wave voltage. From...
Article
The growth of ZnO on c-plane sapphire by molecular beam epitaxy is presented for varying ratios of zinc and oxygen flux. Reflection high energy electron diffraction patterns during epitaxial growth suggest clear differences in the evolution of surface morphology for differing Zn flux. Atomic force microscope images indicate sizable hexagonal featur...
Article
Thin films of BaTiO <sub>3</sub> with MgO buffer layers were deposited on patterned GaAs substrates incorporating Al <sub>x</sub> O <sub>y</sub> for optical confinement. The inclusion of Al <sub>x</sub> O <sub>y</sub> layers are used to provide a means for obtaining thick optical confinement layers as a substitute for MgO cladding layers which have...
Article
Thin films of MgO and BaTiO3 were deposited on (001) GaAs substrates using molecular beam epitaxy and pulsed laser deposition, respectively. X-ray diffraction scans indicate crystalline MgO and BaTiO3 thin films with preferential c-axis orientation. Capacitors fabricated from the BaTiO3/MgO/GaAs structures demonstrate ferroelectric hysteresis behav...
Article
Accurate knowledge of the optical-absorption coefficient in HgCdTe is important for infrared (IR) detector design, production process (layer screening), and interpretation of detector performance. Measurements of the optical-absorption coefficient of HgCdTe layers with uniform composition are presented with the goal of developing a revised model in...
Article
A study of optical absorption in HgCdTe layers is presented to provide an improved model for the absorption coefficient. Measurements were performed on samples grown by molecular beam epitaxy using automated compositional control from spectroscopic ellipsometry measurements. Several samples with varying alloy composition and layer thickness were me...