Acceptor-like Interface States Research Articles

Conduction characteristics of n-InAs/n-GaAs heterojunctions with misfit dislocations

We investigated the transport properties of an n-InAs/n-GaAs heterojunction, where misfit dislocations are confined at the hetero-interface by forming a misfit dislocation network. The electric current I across the interface from n-InAs to n-GaAs was measured as a function of applied voltage V a. I is strongly suppressed at up to V a ∼ 1.0 V which is larger than the intrinsic conduction band offset between InAs and GaAs.I increases exponentially at low and high V a (=0.0–0.5 and 1.0–1.2 V), while the increase of I is relatively moderate at intermediate voltage V a (=0.5–1.0 V). We theoretically evaluated the I–V a characteristics of the n-InAs/n-GaAs heterojunction by using the thermionic-field emission model and examined the effects of the interface states due to the misfit dislocations. The comparison of the calculated results with the experimental data indicates the existence of acceptor-like interface states in the band gap of GaAs.

Effect of oxide and interface traps on electrical characteristics of post-deposition annealed HfSiO4/n-Si structures

This study presents detailed results on the modifications in chemical composition, defective bonds, crystal properties based on x-ray photoelectron spectroscopy (XPS) depth profiles and x-ray diffraction of post-deposition annealed HfSiO4/Si structure. It also leads to a link to defect centers and their effect on the electrical characteristics of MOS capacitors. The HfSiO4 films were deposited on n-Si wafers by RF magnetron sputtering and annealed at room temperature (RT), 300 °C, 700 °C, 900 °C, 1100 °C under N2 ambient. That the atomic concentration values of each element in the oxide did not change significantly depending on the annealing temperature showed that the film was deposited with high homogeneity. It was determined that the shift direction of the binding energies of Hf 4f and O 1s XPS spectra were related to the bonding preference of oxygen rather than its concentration. The increase in Hf–M and Hf–Si oxygen defective bonds decreased the binding energy of the XPS spectra. It was determined from the XPS analyses of amorphous films that Hf–Si and Si–Si oxygen defective bonds may cause the positive charge trapping, resulting in the highest negative charge trapping/positive effective oxide charge density () in the 300 °C-MOS capacitor. It was determined that Hf–Hf oxygen defective bonds may be the precursors of negative charge trapping. Interface states only contributed to the dielectric constant (k) in the RT-MOS capacitor. The (barrier height) values showed that the efficiency of acceptor-like and donor-like interface states changes depending on the frequency.

A detailed study on frequency dependent electrical characteristics of MOS capacitors with dysprosium oxide gate dielectrics

Frequency dependent electrical characteristics of Al/Dy2O3/p-Si/Ag MOS capacitors have been systematically investigated incorporating interfacial chemical structures of the capacitors to specify where interface state signals arise from. The results show that capacitance (C) increases with decreasing in the applied voltage frequency due to the response time dependency of the interface states. Conductance (G) curves have a single peak at the relatively high frequencies as expected. Interestingly, the G curves exhibit two distinct peaks at 400 kHz and lower frequencies. These G peaks are associated with acceptor-like interface (Dit,ac) and donor-like interface (Dit,dn) states. Electrochemical analysis has also depicted that non-stoichiometric DySiOx and SiOx bonds are present at the interface between Dy2O3/Si gate stack. Owing to interactions between mobile charge carriers and possible defect sites present at the DySiOx and SiOx, the Dit,ac and Dit,dn signals have been observed at G curves. In addition, the C hysteresis loop widths decrease with decreasing in the voltage frequencies due to opposite polarity and response time dependencies of the Dit,ac and Dit,dn states. The oxide, interface and border trap densities of capacitors exhibit slight frequency variations and their orders are comparable with device used in the state of the art microelectronics technologies. On the other hand, barrier potential varies from 0.97 eV to 1.136 eV depending on the voltage frequencies. Leakage current density was found to be 1.61 × 10−7 Acm−2 at −1 V and Fowler–Nordheim tunneling mechanism dominates the leakage current conduction. Considering to these results, it can be concluded that the Dy2O3 shows promising dielectric and insulating behavior for the application in future microelectronics technology.

Irradiation response of radio-frequency sputtered Al/Gd2O3/p-Si MOS capacitors

The usage of the Gadolinium oxide (Gd2O3) as sensitive region in the MOS (Metal-Oxide-Semiconductor)-based dosimeters was investigated in the presented study. The Gd2O3 films grown on p-type Si (100) by RF magnetron sputtering were annealed at 800°C under N2 ambient. The back and front metal contacts were establishes to produce MOS capacitors. The fabricated Gd2O3 MOS capacitors were irradiated in the dose range 0.5–50Gy by 60Co gamma source. The performed Capacitance-Voltage (C-V) curves of the Gd2O3 MOS capacitors shifted to right side relative to pre-irradiation one. While continuous increments in the oxide trapped charges with increasing in gamma dose were observed, interface trapped charges fluctuated in the studied dose range. However, the variation of the interface trapped charge densities was found in the order of 1011cm−2 and no significant variation was observed with applied dose. These results confirm that a significant deterioration does not occur in the capacitance during the irradiation. The higher oxide trapped charges compared to interface trapped charges showed that these traps were more responsible for the shift of the C-V curves. The sensitivity and percentage fading after 105min of the Gd2O3 MOS capacitor were found as 39.7±1.4mV/Gy and ~14.5%, respectively. The devices sensitivity was found to be higher than that of capacitors composed of Er2O3, Sm2O3, La2O3, Al2O3, and SiO2, but, the high fading values is seen as a major problem for these capacitors. Finally, the barrier height was investigated with gamma exposure and the results showed that its value increased with increasing in radiation dose due to possible presence of the acceptor-like interface states.

Hot-Carrier-Induced Forward and Reverse Saturation Current Degradations for the n-Type Symmetric EDMOS Transistor

In this letter, hot-carrier-induced degradations of forward and reverse saturation current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> ) under the worst stress condition are experimentally investigated for the n-type symmetric extended drain MOS (ns-EDMOS) transistor. It shows that the degradation of the reverse I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> is much larger than that of the forward I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> . Further experiments demonstrate that the phenomenon mainly results from different influences of the substrate current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</sub> ) degradation upon the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> degradation between the forward and the reverse operational conditions. At forward operational condition, the generated acceptor-like interface states will capture the electrons and enhance the Kirk effect. Subsequently, the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> degradation is partially neutralized by the increase of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</sub> . However, for the reverse operational condition, the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</sub> shift aggravates the degradation of the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> . Therefore, instead of forward I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> , reverse I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> should be selected as the critical parameter to evaluate hot-carrier lifetime of the ns-EDMOS device.

Study of Photovoltage Decays in Nanostructured Ge/Si

Motivated by the importance of the oxidized silicon layers, we have studied the surface photovoltage (SPV) transients in nanoislands of GexSi1x on silicon and oxidized Si surfaces. It is shown that the SPV decays can be approximated by the stretched-exponential form, with the β values ranging from 0.3 to 0.6 for the islands grown on oxide-covered Si substrates and from 0.5 to 1 for the ones placed on bare Si. On this basis, a simple qualitative model is proposed that takes into account a donor-and acceptor-like interface states at the GeSi/SiO2 and Si/SiO2 interface, which act as recombination centers with densities dependent on the GeSi coverage. These results can be used to improve the functionality of photoelectric devices based on Ge/Si.

Measurement of interface-state-density distribution near conduction band at interface between atomic-layer-deposited Al2O3 and silicon-doped InAlN

The Al2O3/InAlN interface formed by atomic layer deposition on a sufficiently thick silicon-doped InAlN layer lattice matched to GaN was investigated electrically. A metal-oxide-semiconductor (MOS) diode fabricated through careful interface formation showed a minimized leakage current and a capacitance-voltage (C-V) characteristic with a capacitance change large enough to evaluate the interface-state density, in the range of 1012 eV−1cm−2, near the conduction band. However, the MOS diode with careless interface formation resulted in degraded electrical characteristics, which indicated the process dependence of the interface properties. The effects of the acceptor-like interface states on the C-V curves are discussed.

Interface Properties of Nanocrystalline-${\rm FeSi}_{2}$/Crystalline-Si Near-Infrared Heterojunction Photodiodes

In this paper, we experimentally charactize <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> -type nanocrystalline iron disilicide films (NC- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm FeSi}_{2}$</tex></formula> ), grown on <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$p$</tex></formula> -type single-crystalline Si substrates at room temperature by a facing-target direct-current sputtering method. These <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$p{\hbox{-}}n$</tex></formula> heterojunction devices are promising candidates for near-infrared photodiode applications. However, their current-voltage characteristics show large leakage currents, which limit the device functions. Hence, we have calculated the energy band diagram of the NC- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm FeSi}_{2}/{\rm Si}$</tex></formula> heterojunction, for the first time, to gain insight into the source of this leakage. The conduction and valance band discontinuities are calculated as 0.19 and 0.46 eV, respectively. A built-in potential of 1 V is estimated from the energy band diagram. This estimate is almost twice the value obtained from the measured capacitance-voltage characteristics. This indicates the presence of a large number of defects at the heterojunction interface. From a simulation combined with the experimental results, the defect density is estimated to be at least <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1.3 \times 10^{13}~{\rm cm}^{-2}$</tex> </formula> . The simulation model successfully reproduces the experimental current-voltage characteristics of the device and reveals that acceptor-like interface states centered at approximately 0.35 eV above the valance band are the main sources of the heterojunction leakage. Simulation results predict that passivation of these defects would reduce the leakage current to 10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm A}/{\rm cm}^{2}$</tex></formula> , causing significant improvements in the device's performance.

Anomalous photocurrent observed in an Fe–ZnS:Fe Schottky diode

Anomalous photocurrent was observed in an epitaxial Fe∕Zn0. 96Fe0. 04S Schottky diode grown by molecular beam epitaxy. The temperature dependent decay behavior of the anomalous photocurrent has been studied. A model based on the photoionization of the acceptorlike interface states is proposed to explain this anomalous phenomenon. By fitting the decay curves of the anomalous photocurrent at different temperatures, ionization energy of the interface states is obtained from an Arrhenius plot of the decay time constants. We believe that these interface states are associated with some complex (Fe, S) defects formed at the Fe∕ZnFeS interface.

Illumination induced charge separation at tetraphenyl-porphyrin/metal oxide interfaces

Charge separation processes were studied at tetraphenyl-porphyrin (H2TPP)/metal oxide interfaces by surface photovoltage spectroscopy. The thickness of the depleted Ti and Sn oxide layers was about 2nm. Acceptorlike interface states play a crucial role in the steady-state light-induced negative charging of H2TPP surface layers as well as in tunneling or light-induced discharging. The results indicate that steady-state negative charging of the H2TPP layer is induced by preferential recombination of holes at the (H2TPP)/metal oxide interface and depends only weakly on temperature. The modulated surface photovoltage is dominated by hole transport at low temperatures and by electron transport at higher temperatures. The activation energy of the latter is of the order of 0.4eV.

Photocurrent spectroscopy of an Fe/Zn 0.96Fe 0.04S Schottky diode

Fe/Zn 0.96Fe 0.04S Schottky diode was grown by molecular beam epitaxy. The short-circuit DC photocurrent spectroscopy was measured at temperatures from 10 to 300 K. Anomalous photocurrent was observed at temperatures above 100 K when excitation photon energies were less than the band gap energy of Zn 0.96Fe 0.04S. We have explained this anomalous phenomenon based on the photo-ionization of acceptor-like interface states. We believe that these interface states are associated with some complex (Fe,S) defects formed at the Fe/ZnFeS interface. The transient behavior of photocurrent at various temperatures has also been studied.

Investigation and Localization of the SiGe Source/Drain (S/D) Strain-Induced Defects in PMOSFET With 45-nm CMOS Technology

In this letter, for the first time, the defects that are induced from the SiGe strain source/drain (S/D) in PMOSFET with 45-nm CMOS technology were investigated in detail. With the conventional charge pumping and the improved low gate-leakage gated-diode (L2- GD) measurements, we find that the uniaxial compressive stress from SiGe S/D generates a large number of acceptorlike interface states at the gate oxide/extension of S/D interface, thus enhancing the leakage current. Compared to defects that are caused by the relaxed Si1-x Gex on the conventional graded Si1-xGex buffer layer, the SiGe S/D experienced results that are more serious. The acceptorlike interface states are suspected to be the Si dangling bonds broken by the stress. A schematic model is proposed to illustrate the effect of the stress comprehensively

Electrical Properties of Atomic-Beam Deposited GeO1 − xNx ∕ HfO2 Gate Stacks on Ge

The electrical properties of stack deposited by atomic beam on Ge are reported. The incorporation of N in the layer was found to be quite beneficial in reducing the gate leakage current, improving the uniformity of the device characteristics, and reducing the equivalent oxide thickness of the gate stack down to . On the other hand, N incorporation also led to a large density of fixed positive charges and slow states, which can be reduced by post-deposition anneals in or . These gate stacks were successfully integrated into a simple transistor flow with TiN gates. Both n- and p-channel transistors show promising electrical characteristics, with ratios of about 4–5 orders of magnitude. However, the mobility of the n-channel devices was found to be extremely low, which is most likely related to a large density of acceptor-like interface states in the upper-part of the Ge bandgap.

Characterization of Atomic-Beam Deposited GeO1-xNx/HfO2 Stacks on Ge

The electrical properties of GeO1-xNx/HfO2 stack deposited by atomic beam on Ge are reported. The incorporation of N in the GeOx layer is found to be quite beneficial in reducing the gate leakage current, improving the uniformity of the device characteristics and reducing the equivalent oxide thickness of the gate stack down to about 0.8 nm. On the other hand, N incorporation also leads to a large density of fixed positive charges and slow states, which can be reduced by post- deposition anneals in O2 or N2. These gate stacks were successfully integrated into a simple transistor flow with TiN gates. Both n and p-channel transistors show promising electrical characteristics, with Ion/Ioff ratios of about 4 to 5 orders of magnitude. However, the mobility of the n-channel devices is found to be extremely low, which is most likely due to a large density of acceptor-like interface states in the upper-part of the Ge band-gap.

Thermal Instability of Effective Work Function in Metal/High-&amp;lt;tex&amp;gt;$kappa$&amp;lt;/tex&amp;gt;Stack and Its Material Dependence

Thermal instability of effective work function and its material dependence on metal/high-/spl kappa/ gate stacks is investigated. It is found that thermal instability of the effective work function of metal electrode on a gate dielectric is strongly dependent on the gate electrode and dielectric material. Thermal instability of a metal gate is related to the presence of silicon at the interface, and the Fermi-level pinning position is dependent on the location of silicon at the interface. The silicon-metal or metal-silicon bond formation by thermal anneal at the metal/dielectric interface induces the donor-like or acceptor-like interface states, causing a change of effective work function.

Effects of wet N/sub 2/O oxidation on interface properties of 6H-SiC MOS capacitors

Oxynitrides were grown on n- and p-type 6H-SiC by wet N/sub 2/O oxidation (bubbling N/sub 2/O gas through deionized water at 95/spl deg/C) or dry N/sub 2/O oxidation followed by wet N/sub 2/O oxidation. Their oxide/SiC interfaces were investigated for fresh and stressed devices. It was found that both processes improve p-SiC/oxide but deteriorate n-SiC/oxide interface properties when compared to dry N/sub 2/O oxidation alone. The involved mechanism could be enhanced removal of unwanted carbon compounds near the interface due to the wet ambient, and hence a reduction of donor-like interface states for the p-type devices. As for the n-type devices, incorporation of hydrogen-related species near the interface under the wet ambient increases acceptor-like interface states. In summary, wet N/sub 2/O oxidation can be used for providing comparable reliability for nand p-SiC MOS devices, and especially for obtaining high-quality oxide-SiC interfaces in p-type MOS devices.

Interface state density and channel mobility for 4H-SiC MOSFETs with nitrogen passivation

Interface state density and channel mobility have been characterized for 4H-SiC MOSFETs fabricated with dry thermal oxides and subsequently passivated with nitric oxide. The interface trap density at 0.1 eV below the conduction band edge decreases from approximately 8×10 12 to 1×10 12 eV −1 cm −2 following anneals in nitric oxide (NO) at 1175 °C for 2 h. The room temperature field effect channel mobility increases by an order of magnitude to approximately 35 cm 2/V s following the passivation anneal. The field effect channel mobility of passivated MOSFETs shows almost no change with increasing temperature, while the mobility for unpassivated devices increases with increasing temperature and is thermally activated (∼ T 1.9) due to decreased Coulomb scattering by electrons trapped at the acceptor-like interface states near the conduction band. Over the temperature range 300–473 K, threshold voltage changes of about −0.8 and −3.7 V, respectively, are observed for devices processed with and without NO passivation.

A cause for highly improved channel mobility of 4H-SiC metal–oxide–semiconductor field-effect transistors on the (112̄0) face

4H-silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors fabricated on both (112̄0) and (0001) faces were characterized at various temperatures. From the temperature dependence of channel mobility, carrier transport in the inversion layer at the SiO2/4H-SiC(112̄0) interface was found to be affected by phonon scattering (μ0∼T−2.2), while that at the SiO2/4H-SiC(0001) interface was thermally activated (μ0∼T2.6) due to the decrease of Coulomb scattering by emission of electrons from acceptor-like interface states. From the temperature dependence of threshold voltage, the density of acceptor-like interface states near the conduction band edge seems to be low at the SiO2/4H-SiC(112̄0) interface, but quite high (&amp;gt;1013 cm−2 eV−1) at the SiO2/4H-SiC(0001) interface. The low density of acceptor-like interface states near the conduction band edge on the (112̄0) face should be the primary cause for the high inversion-channel mobility.

Photon emission and related hot-carrier effects in polycrystalline silicon thin-film transistors

The photon emission induced by the drain avalanche in polycrystalline silicon thin-film transistors (polysilicon TFTs) has been studied in wide drain and gate voltage ranges. As the photon emission phenomenon is closely related to hot-carrier effects, the gate and drain bias conditions for maximum device degradation have been determined from measurements of the emitted light intensity. In n-channel polysilicon TFTs, the effects of bias stressing at the maximum light emission are related to hot-hole trapping into the gate oxide near the drain and to formation of acceptor-like interface states consisted of midgap states and band tails.

New observation and improvement in GIDL of n-MOSFETs with various kinds of N 2O-based gate oxides under hot-carrier stress

Degradation in gate-induced drain leakage (GIDL) of n-MOSFETs with various kinds of gate oxides under hot-carrier stress at different gate voltages is investigated. It has been found that the shift of GIDL current is very sensitive to gate voltage and is maximum under a stress with V G = 0.5 V D even for a short stress time. This might result from hot electrons captured by fast acceptor-like interface states. A new technique of N 2O treatment on NH 3-nitrided oxide is also used to prepare the gate oxide and the corresponding MOSFETs show greatly suppressed degradation of GIDL current under hot-carrier stress due to the considerably improved quality of both the gate oxide and Si SiO 2 interface by the N 2O treatment.