arXiv subjects

Paul K. Hurley

Publications and source records attributed to Paul K. Hurley.

5 recordsLinked to original sources

arXiv2025

Defects in the $β$-Ga$_2$O$_3$($\bar201$)/HfO$_2$ MOS system and the effect of thermal treatments

We have investigated the properties of the $β$-Ga$_2$O$_3$($\bar201$)/HfO$_2$/Cr/Au MOS (metal-oxide-semiconductor) system after annealing (450$^\circ$C) in different ambient conditions (forming gas, N$_2$ and O$_2$). Defect properties have been analyzed using an approach combining experimental impedance measurements with physics-based simulations of the capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of $β$-Ga$_2$O$_3$/HfO$_2$ MOS capacitors. This approach enabled us to detect two defect bands in HfO$_2$ characterized by thermal ionization energies of ~1.1eV (acceptor-like) and ~2eV (donor-like) attributed to a polaronic self-trapping state and an oxygen vacancy in HfO$_2$, respectively. This study demonstrates how thermal treatments affect the energy distributions and densities of the observed defects. The adopted methodology also enabled the extraction of the spatial distribution of defects across the HfO$_2$ thickness and Cr/HfO$_2$ interface. The high concentration of oxygen vacancies close to the Cr/HfO$_2$ interface extracted from experimental and simulated electrical data is confirmed by in-situ XPS analysis which shows how Cr is scavenging oxygen from the HfO$_2$ and creating the donor band confined near the Cr/HfO$_2$ interface. This donor band density is observed to be reduced after annealing as per simulation and unchanged for different annealing conditions. We speculate this may be due to the formation of dense films and polyforms of HfO$_2$ under different ambient as revealed by high-resolution TEM images.

cond-mat.mtrl-sci↗

arXiv2021

Coexistence of negative and positive photoconductivity in few-layer PtSe2 field-effect transistors

Platinum diselenide (PtSe_2) field-effect transistors with ultrathin channel regions exhibit p-type electrical conductivity that is sensitive to temperature and environmental pressure. Exposure to a supercontinuum white light source reveals that positive and negative photoconductivity coexists in the same device. The dominance of one type of photoconductivity over the other is controlled by environmental pressure. Indeed, positive photoconductivity observed in high vacuum converts to negative photoconductivity when the pressure is rised. Density functional theory calculations confirm that physisorbed oxygen molecules on the PtSe_2 surface act as acceptors. The desorption of oxygen molecules from the surface, caused by light irradiation, leads to decreased carrier concentration in the channel conductivity. The understanding of the charge transfer occurring between the physisorbed oxygen molecules and the PtSe_2 film provides an effective route for modulating the density of carriers and the optical properties of the material.

cond-mat.mtrl-sci↗

arXiv2020

Isotropic conduction and negative photoconduction in ultrathin PtSe$_2$ films

PtSe$_2$ ultrathin films are used as the channel of back-gated field-effect transistors (FETs) that are investigated at different temperatures and under super-continuous white laser irradiation. The temperature-dependent behavior confirms the semiconducting nature of multilayer PtSe$_2$, with p-type conduction, a hole field-effect mobility up to 40 cm2/(Vs) and significant gate modulation. Electrical conduction measured along different directions shows isotropic transport. A reduction of PtSe$_2$ channel conductance is observed under exposure to light. Such negative photoconductivity is explained by a photogating effect caused by photo-charge accumulation in SiO$_2$ and at the Si/SiO$_2$ interface.

physics.app-ph↗

arXiv2016

First principles modeling of defects in the Al_2O_3/In_0.53Ga_0.47As system

Density functional theory paired with a first order many-body perturbation theory correction is applied to determine formation energies and charge transition energies for point defects in bulk In_0.53Ga_0.47As and for models of the In_0.53Ga_0.47As/Al_2O_3 interface. The results are consistent with previous computational studies that As_Ga antisites are candidates for defects observed in capacitance voltage measurements on metal-oxide-semiconductor capacitors, as the As_Ga antisite introduces energy states near the valence band maximum and near the middle of the energy band gap. However, substantial broadening in the distribution of the Ga_As charge transition levels due to the variation in the local chemical environment resulting from alloying on the cation (In/Ga) sublattice is found, whereas this effect is absent for As_Ga antisites. Also, charge transition energy levels are found to vary based on proximity to the semiconductor/oxide interface. The combined effects of alloy- and proximity-shift on the Ga_As antisite charge transition energies are consistent with the distribution of interface defect levels between the valence band edge and midgap as extracted from electrical characterization data. Hence, kinetic growth conditions leading to a high density of either Ga_As or As_Ga antisites near the In_0.53Ga_0.47As/Al_2O_3 interface are both consistent with defect energy levels at or below midgap.

cond-mat.mes-hall↗

arXiv2010

Low-angle misorientation dependence of the optical properties of InGaAs/InAlAs quantum wells

We investigate the dependence of the low-temperature photoluminescence linewidths from InP-lattice-matched InGaAs/InAlAs quantum wells on the low-angle misorientation from the (100) surface of the host InP substrate. Quantum wells were grown on InP substrates misorientated by 0, 0.2, 0.4 and 0.6 degrees; 0.4 degrees was found to consistently result in the narrowest peaks, with the optimal spectral purity of ~4.25 meV found from a 15nm quantum well. The width of the emission from the 15nm quantum well was used to optimize the growth parameters. Thick layers of Si-doped InGaAs were then grown and found to have bulk, low temperature (77 K), electron mobilities up to μ~ 3.5 x 10^4 cm2/Vs with an electron concentration of ~1 x 10^16.

cond-mat.mtrl-sci↗