Metal Oxide Semiconductor Diodes Research Articles

Electrical Performance of Chlorine-Treated AlGaN MOS Diodes with i-ZnO Insulator

The intrinsic zinc oxide (i-ZnO) film deposited by a vapor cooling condensation system was used as the gate dielectric layer of the AlGaN metal-oxide-semiconductor (MOS) diodes. The chlorine surface treatment of AlGaN was utilized to reduce the surface states resided on the AlGaN surface. Comparing with the untreated AlGaN MOS diodes, the chlorine-treated AlGaN MOS diodes revealed a lower leakage current and a lower interface states density. The experimental results indicated that the chlorine surface treatment could effectively improve the quality of the i-ZnO/AlGaN interface and the electrical performance of the AlGaN MOS diodes with i-ZnO insulator layer.

Implementation of the Density Gradient Quantum Corrections for 3-D Simulations of Multigate Nanoscaled Transistors

An efficient implementation of the density-gradient (DG) approach for the finite element and finite difference methods and its application in drift-diffusion (D-D) simulations is described in detail. The new, second-order differential (SOD) scheme is compatible with relatively coarse grids even for large density variations thus applicable to device simulations with complex 3-D geometries. Test simulations of a 1-D metal-oxide semiconductor diode demonstrate that the DG approach discretized using our SOD scheme can be accurately calibrated against Schrodinger-Poisson calculations exhibiting lower discretization error than the previous schemes when using coarse grids and the same results for very fine meshes. 3-D test D-D simulations using the finite element method are performed on two devices: a 10 nm gate length double gate metal-oxide-semiconductor field-effect transistor (MOSFET) and a 40 nm gate length Tri-Gate fin field-effect transistor (FinFET). In 3-D D-D simulations, the SOD scheme is able to converge to physical solutions at high voltages even if the previous schemes fail when using the same mesh and equivalent conditions. The quantum corrected D-D simulations using the SOD scheme also converge with an atomistic mesh used for the 10 nm double gate MOSFET saving computational resources and can be accurately calibrated against the results from non-equilibrium Green's functions approach. Finally, the simulated ID-VG characteristics for the 40 nm gate length Tri-Gate are in an excellent agreement with experimental data.

White light emission and electrical properties of silicon oxycarbide-based metal–oxide–semiconductor diode

White light emission from silicon oxycarbide-based metal–oxide–semiconductor diode has been realized in this work. Emitted light is visible to the naked eyes as the bias voltage is increased higher than 15 V. Electroluminescence intensity increases linearly with current density. According to the analysis of conduction mechanisms in device, electron–hole radiative recombination at twofold coordinated silicon lone-pair centers, neutral oxygen vacancies, and E δ′ defect centers in film is responsible for the light emission.

Structural and electrical properties of HfO 2/Dy 2O 3 gate stacks on Ge substrates

In the present work we report on the structural and electrical properties of metal–oxide–semiconductor (MOS) devices with HfO 2/Dy 2O 3 gate stack dielectrics, deposited by molecular beam deposition on p-type germanium (Ge) substrates. Structural characterization by means of high-resolution Transmission Electron Microscopy (TEM) and X-ray diffraction measurements demonstrate the nanocrystalline nature of the films. Moreover, the interpretation of the X-ray reflectivity measurements reveals the spontaneous growth of an ultrathin germanium oxide interfacial layer which was also confirmed by TEM. Subsequent electrical characterization measurements on Pt/HfO 2/Dy 2O 3/p-Ge MOS diodes show that a combination of a thin Dy 2O 3 buffer layer with a thicker HfO 2 on top can give very good results, such as equivalent oxide thickness values as low as 1.9 nm, low density of interfacial defects (2–5 × 10 12 eV − 1 cm − 2 ) and leakage currents with typical current density values around 15 nA/cm 2 at V g = V FB − 1 V.

Ultrathin SiO2 layer with an extremely low leakage current density formed in high concentration nitric acid

An ultrathin silicon dioxide (SiO2) layer of 1.2–1.4 nm thickness has been formed by immersion of Si wafers in nitric acid (HNO3) aqueous solutions, and its electrical characteristics and physical properties are investigated as a function of the HNO3 concentration. Measurements of transverse optical and longitudinal optical phonons of Si–O–Si asymmetric stretching vibrational mode for SiO2 indicate that the atomic density of the SiO2 layer increases with the HNO3 concentration. X-ray photoelectron spectroscopy measurements show that the valence band discontinuity energy at the SiO2/Si interface also increases and the concentration of suboxide species decreases with the HNO3 concentration. The leakage current density of the ⟨Al/SiO2/Si(100)⟩ metal-oxide-semiconductor (MOS) diodes with the SiO2 layer formed in HNO3 aqueous solutions decreases with the HNO3 concentration and also decreases by postmetallization annealing (PMA) treatment at 250 °C in 5 vol % hydrogen atmosphere. For the MOS diodes with the SiO2 layer formed in 98 wt % HNO3, the leakage current density measured after PMA is much lower than that for thermally grown SiO2 with the same thickness and even lower than that for silicon oxynitride with the same effective oxide thickness. The decrease in the leakage current density by PMA is attributed to (i) elimination of interface states, (ii) elimination of slow states, and (iii) increase in the band discontinuity energy at the SiO2/Si interface.

Study on Stability of Pentacene-Based Metal–Oxide–Semiconductor Diodes in Air Using Capacitance–Voltage Characteristics

The stability of bottom-gate pentacene-based metal–oxide–semiconductor (MOS) diodes in air up to 30 days was investigated. The capacitance–voltage (C–V) characteristics of the pentacene film in air showed a slight hysteresis (36 mV) without any surface treatment for as-fabricated pentacene-based MOS diodes. However, after 30 days, the hysteresis width further increased to 100 mV and flat-band voltages shifted toward positive voltage as well, which indicates that the electron trapping effects become stronger caused by either moisture or oxygen; thus, the stability of pentacene-based MOS diode characteristics degraded gradually.

Depletion of surface accumulation charge in InN by anodic oxidation

Si-doped InN layer by molecular beam epitaxy was subjected to anodic oxidation in 0.1 M potassium hydroxide (KOH) electrolyte and characterized by electrochemical methods to derive carrier profile at the InN surface. The obtained results were compared to the characteristics of a planar resistor structure and vertical metal-oxide-semiconductor (MOS) diodes with Ni-metal contacts on the oxidized InN. Both measurements in electrolyte and in air confirmed the formation of a surface oxide layer after the anodic treatment and depletion of the surface accumulation charge of the as-grown InN. The upward band bending of InN at the oxide interface was also concluded from the analysis of capacitance-voltage characteristics of the MOS diodes. Transmission electron microscopy revealed a nonuniform oxide layer containing porelike structures of a few nanometers in diameter.

Characterization of Tunneling Current through Ultrathin Silicon Dioxide Films by Different-Metal Gates Method

The tunneling currents through ultrathin silicon dioxide films from metal to silicon in the oxide thickness regime between 1.4 and 3.5 nm are characterized using different-metal gates. The energy barrier heights and the effective mass of the silicon dioxide films are determined by the curve fitting of the data calculated by the transfer matrix method with current density–oxide voltage characteristics of metal–oxide–semiconductor (MOS) diodes with aluminum or gold gates. As the oxide thickness decreases, the energy barrier height decreases and the effective mass of the silicon dioxide film increases. The difference in the energy barrier heights between aluminum–oxide and gold–oxide interfaces nearly corresponds to the flatband voltage difference multiplied by the electron charge in the capacitance–voltage curves between MOS diodes with aluminum and gold gates. This makes it possible to precisely characterize tunneling currents by a new different-metal gates method for individually determining the energy barrier heights and the effective mass using the height difference obtained from the flatband voltage difference.

Enhanced 400–600 nm photoresponsivity of metal–oxide–semiconductor diodes withmulti-stack germanium quantum dots

Metal–oxide–semiconductor (MOS) diodes with zero-, one- or three-layer Ge quantum dots(QDs) embedded in the gate oxide are fabricated for visible to near-ultraviolet photodetection.Ge dots are formed by thermally oxidizing one or three stacks of amorphous Si(a-Si)/polycrystalline-Si0.87Ge0.13/a-Si multi-layers that are sandwiched bySiO2 barriers. The current–voltage characteristics of Ge QD MOS diodes exhibit strongrectification in darkness and feature significant current enhancement in the inversion modewhen illuminated. Increasing the number of Ge QD layers from zero through oneto three in the gate oxide improves the responsivity from 4.64 through 482 to812 mA W−1 and enhances the corresponding quantum efficiency from 1.42 through 148 to 245%,respectively. The spectral response reveals a considerable blueshift in peak energies as theGe dot size decreases from 9.1 to 5.1 nm, suggesting that the light absorption originatesfrom the quantum confinement effect of Ge QDs. The temperature and bias dependences ofthe dark current indicate that the carrier transport mechanism involves percolationhopping.

1 nm equivalent oxide thickness in Ga2O3(Gd2O3)∕In0.2Ga0.8As metal-oxide-semiconductor capacitors

An equivalent oxide thickness about 1nm for Ga2O3(Gd2O3) (GGO) on In0.2Ga0.8As has been achieved by employing a thin in situ deposited 3nm thick Al2O3 protection layer. The dual gate oxide stacks of the Al2O3∕GGO (33, 20, 10, 8.5, and 4.5nm)/In0.2Ga0.8As∕GaAs metal-oxide-semiconductor (MOS) capacitors remain amorphous after rapid thermal annealing up to 800–850°C, accompanied with atomically sharp smooth oxide/semiconductor interfaces. Well behaved capacitance-voltage (C-V) curves of the MOS diodes have shown sharp transition from depletion to accumulation with small flatband voltage (1.1V for Au metal gate and 0.1V for Al), and weak frequency dispersion (1.5%–5.4%) between 10 and 500kHz at accumulation capacitance. Low leakage current densities [3.1×10−5 and 2.5×10−9A∕cm2 at V=Vfb+1V for Al2O3(3nm)∕GGO(4.5 and 8.5nm)], a high dielectric constant around 14–16 of GGO for all tested thicknesses, and a low interfacial density of states (Dit) in the low 1011cm−2eV−1 have also been accomplished.

Liquid phase deposited silicon oxide with lower boron impurity grown on gallium nitride by temperature‐difference method

AbstractThis study investigates the growth of silicon oxide film on gallium nitride using hydrosilicofluoric acid and silica gel by the temperature‐difference liquid‐phase deposition. In the conventional liquid phase deposition, the boric acid is used as fluorine scavenger to prompt silicon oxide deposition and it also acts as an impurity in the oxide film. The better metal–oxide–semiconductor diode electrical characteristics can be obtained by the temperature‐difference method with lower boric acid incorporation and higher deposition rate. Compared with the leakage current density of the conventional and temperature‐difference methods, it can be much improved from 9.93 × 10–2 A/cm2 to 5.8 × 10–4 A/cm2 at +2 MV/cm and from 1.35 × 10–2 A/cm2 to 5.15 × 10–4 A/cm2 at –1 MV/cm. The effective oxide charges is improved from 3.88 × 1011 cm–2 to 2.27 × 1011 cm–2. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical Properties of Liquid Phase Deposited SiO[sub 2] on Photochemical Treated GaN

The electrical characteristics of liquid phase deposited SiO 2 on GaN substrate were investigated. More Ga-OH bonds can be formed on GaN surface treated by KOH solution under a mercury arc lamp excitation. The OH bonds will absorb siloxane oligomer and enhance liquid phase deposited SiO 2 . A better quality of SiO 2 /GaN interface can be obtained and the interface state density is 1.24 X 10 12 cm -2 eV -1 at the energy of 0.42 eV below the edge of conduction band. The leakage current density of the metal oxide semiconductor diode can be improved from 6.98 X 10 -5 to 3.28 X 10 -6 A/cm 2 at +1 MV/cm.

Nitric Acid Oxidation of 3C-SiC to Fabricate MOS Diodes with a Low Leakage Current Density

Two-step nitric acid oxidation which involves immersion in followed by immersion in at can form a thick (e.g., ) layer on a surface. Heat-treatment at in pure hydrogen performed after nitric acid oxidation greatly decreases the density of the leakage current flowing through the layer. The hydrogen treatment effectively smoothens the interface. When the hydrogen treatment at is performed before nitric acid oxidation, the surface is greatly flattened and the subsequent nitric acid oxidation results in the interface having an atomic flatness. Without hydrogen treatment, gap states are present up to from the valence-band maximum, and the valence-band discontinuity energy at the interface is . With the hydrogen treatment before nitric acid oxidation, the gap states disappear and the valence-band discontinuity energy increases to . Capacitance-voltage curves of the metal-oxide-semiconductor (MOS) diodes in which hydrogen treatment is performed before nitric acid oxidation show typical accumulation and depletion behavior.

Nitric acid oxidation method to form SiO 2/3C–SiC structure at 120 °C

3C–SiC(0 0 1) surfaces are considerably rough with the roughness root mean square value ( R ms) of 1.3 nm, but the surfaces become considerably smooth (i.e., R ms of 0.5 nm) by heat treatment in pure hydrogen at 400 °C. Two-step nitric acid (HNO 3) oxidation (i.e., immersion in ∼40 wt% HNO 3 followed by that in 68 wt% HNO 3) performed after the hydrogen treatment can oxidize 3C–SiC at extremely low temperature of ∼120 °C, forming thick SiO 2 (e.g., 21 nm) layers. With no hydrogen treatment, the leakage current density of the 〈Al/SiO 2/3C–SiC〉 metal-oxide-semiconductor (MOS) diodes is high, while that for the MOS diodes with the hydrogen treatment is considerably low (e.g., ∼10 −6 A/cm 2 at the forward gate bias of 1 V) due to the formation of uniform thickness SiO 2 layers. The MOS diodes with the hydrogen treatment show capacitance–voltage curves with accumulation, depletion, and deep-depletion characteristics.

Effect of Proton Irradiation on Interface State Density in Sc2O3/GaN and Sc2O3/MgO/GaN Diodes

Proton irradiation of Sc2O3/GaN and Sc2O3/MgO/GaN metal-oxide semiconductor diodes was performed at two energies, 10 MeV and 40 MeV, and total fluences of 5 × 109 cm−2, corresponding to 10 years in low-earth orbit. The proton damage causes a decrease in forward breakdown voltage and a flat-band voltage shift in the capacitance-voltage characteristics, indicating a change in fixed oxide charge and damage to the dielectric. The interface state densities after irradiation increased from 5.9 × 1011 cm−2 to 1.03 × 1012 cm−2 in Sc2O3/GaN diodes and from 2.33 × 1011 to 5.3 × 1011 cm−2 in Sc2O3/MgO/GaN diodes. Postannealing at 400°C in forming gas recovered most of the original characteristics but did increase the interfacial roughness.

Wide Bandgap Semiconductor Nanorod and Thin Film Gas Sensors

In this review we discuss the advances in use of GaN and ZnO-based solid-statesensors for gas sensing applications. AlGaN/GaN high electron mobility transistors(HEMTs) show a strong dependence of source/drain current on the piezoelectricpolarization -induced two dimensional electron gas (2DEG). Furthermore, spontaneous andpiezoelectric polarization induced surface and interface charges can be used to develop verysensitive but robust sensors for the detection of gases. Pt-gated GaN Schottky diodes and Sc2O3/AlGaN/GaN metal-oxide semiconductor diodes also show large change in forwardcurrents upon exposure to H2 containing ambients. Of particular interest are methods fordetecting ethylene (C2H4), which offers problems because of its strong double bonds andhence the difficulty in dissociating it at modest temperatures. ZnO nanorods offer largesurface area, are bio-safe and offer excellent gas sensing characteristics.

Method of observation of low density interface states by means of X-ray photoelectron spectroscopy under bias and passivation by cyanide ions

X-ray photoelectron spectroscopy (XPS) measurements under bias can observe low density interface states for metal-oxide-semiconductor (MOS) diodes with low densities. This method can give energy distribution of interface states for ultrathin insulating layers for which electrical measurements cannot be performed due to a high density leakage current. During the XPS measurements, a bias voltage is applied to the rear semiconductor surface with respect to the ∼3 nm-thick front platinum layer connected to the ground, and the bias voltage changes the occupation of interface states. Charges accumulated in the interface states shift semiconductor core levels at the interface, and thus the analysis of the bias-induced shifts of the semiconductor core levels measured as a function of the bias voltage gives energy distribution of interface states. In the case of Si-based MOS diodes, the energy distribution and density of interface states strongly depend on the atomic density of silicon dioxide (SiO 2) layers and the interfacial roughness, respectively. All the observed interface state spectra possess peaked-structures, indicating that they are due to defect states. An interface state peak near the Si midgap is attributable to isolated Si dangling bonds at the interface, while those above and below the midgap to Si dangling bonds interacting weakly with Si or oxygen atoms in the SiO 2 layers. A method of the elimination of interface states and defect states in Si using cyanide solutions has been developed. The cyanide method simply involves the immersion of Si in KCN solutions. Due to the high Si–CN bond energy of ∼4.5 eV, the bonds are not ruptured at 800 °C and upon irradiation. The cyanide treatment results in the improvement of the electrical characteristics of MOS diodes and solar cells.

Methods of observation and elimination of semiconductor defect states

A method of observation of interface states for ultrathin insulating layer/semiconductor interfaces is developed by use of X-ray photoelectron spectroscopy (XPS) measurements under bias. The analysis of the energy shift of the semiconductor core level as a function of the bias voltage gives energy distribution of interface states. When the atomic density of SiO 2 layers is low (e.g., SiO 2 layers formed at 350 °C), only one interface state peak is observed near the midgap, and it is attributed to isolated Si dangling bonds at the interface. For SiO 2 layers with a high atomic density (e.g., SiO 2 layers formed at 700 °C), on the other hand, two interface state peaks, one above and the other below the midgap, are observed, and they are attributed to Si dangling bonds interacting weakly with a Si or oxygen atom in SiO 2. Interface states can be passivated by cyanide treatment which simply involves the immersion in cyanide solutions such as KCN and HCN solutions. When the cyanide treatment is applied to 〈indium tin oxide/SiO 2/mat-textured single crystalline Si〉 metal-oxide-semiconductor (MOS) solar cells, the photovoltage is greatly increased, leading to a high conversion efficiency of 16.2%. When the cyanide treatment is performed on polycrystalline Si (poly-Si)-based MOS diodes, a greater effect in comparison to that for single crystalline Si-based MOS diodes is observed due to the elimination of defect states in poly-Si as well as Si/SiO 2 interface states. The cyanide treatment can also increase the conversion efficiency of pn-junction single crystalline and poly-Si solar cells.

AlGaN/GaN-based diodes and gateless HEMTs for gas and chemical sensing

The characteristics of Pt/GaN Schottky diodes and Sc/sub 2/O/sub 3//AlGaN/GaN metal-oxide semiconductor (MOS) diodes as hydrogen and ethylene gas sensors and of gateless AlGaN/GaN high-electron mobility transistors (HEMTs) as polar liquid sensors are reported. At 25/spl deg/C, a change in forward current of /spl sim/6 mA at a bias of 2 V was obtained in the MOS diodes in response to a change in ambient from pure N/sub 2/ to 10% H/sub 2// 90% N/sub 2/. This is approximately double the change in forward current obtained in Pt/GaN Schottky diodes measured under the same conditions. The mechanism appears to be formation of a dipole layer at the oxide/GaN interface that screens some of the piezo-induced channel charge. The MOS-diode response time is limited by the mass transport of gas into the test chamber and not by the diffusion of atomic hydrogen through the metal/oxide stack, even at 25/spl deg/C. Gateless AlGaN/GaN HEMT structures exhibit large changes in source-drain current upon exposing the gate region to various polar liquids, including block co-polymer solutions. The polar nature of some of these polymer chains lead to a change of surface charges in gate region on the HEMT, producing a change in surface potential at the semiconductor/liquid interface. The nitride sensors appear to be promising for a wide range of chemicals, combustion gases and liquids.

Field effect detection of biomolecular interactions

We report the detection of biomolecular interactions using field effect devices such as metal-oxide-semiconductor (MOS) capacitor structures and polycrystalline silicon thin film transistors (Poly-Si TFTs). We have developed ion-sensitive field effect transistors with a silicon nitride sensing layer. Near ideal pH sensitivity has been achieved. A penicillin sensor has been fabricated by functionalizing the sensing area with the enzyme penicillinase. Label-free electrical detection of DNA hybridization has been achieved using both MOS capacitors and Poly-Si TFTs. DNA interactions occurring at the metal gate of the devices lead to an increase of negative charges attached to the gate. This change in electrical charges is reflected by significant shifts of the current–voltage or capacitance–voltage characteristics of the TFTs or MOS diodes, respectively. Single base pair DNA mismatches can be detected with the technique. The method can be extended to other chemical or biochemical systems such as proteins and cells.