P.K. Bose

Leakage current characteristics and the energy band diagram of Al/ZrO2/Si0.3Ge0.7 hetero-MIS structures

Zirconium oxide (ZrO2) films have been deposited on Ge-rich SiGe heterolayers at 150 ?C by the microwave plasma enhanced chemical vapour deposition (PECVD) technique using zirconium tetra-tert-butoxide. The possible conduction mechanisms in deposited ZrO2 films have been investigated at both room and high temperature. It is found that the conduction mechanism is dominated by Schottky emission at a low electric field (E 1.2 MV cm?1). The extracted trap energy is about 0.78 eV from the conduction band of ZrO2. It is shown that the current in ZrO2 films exhibits strong temperature dependence at a low electric field. The trapping behaviour of the charge carriers in thin ZrO2 gate dielectric stacks during constant gate voltage stress of metal?oxide?semiconductor capacitors has also been investigated.

Extraction of interface state density of Pt/p-strained-Si Schottky diode

Abstract Interface state density of Pt/p-strained-Si Schottky contacts has been determined using experimental forward bias current–voltage (J–V) and capacitance–voltage (C–V) techniques. The effects of interfacial oxide layers and series resistance present in the structure have been studied using a SEMICAD device simulator. It is shown that the interface state density can be obtained directly from the measure of C–V data and is found to decrease as the energy from the edge of the valence band increases.

Analysis of interface states of Al/TiO2/Si0.3Ge0.7 MIS structures using the conductance technique

TiO2 films have been deposited at a low temperature (~150 ?C) using titanium tetrakis isopropoxide (TTIP) as an organometallic precursor on Si0.3Ge0.7 heterolayers by a microwave plasma-enhanced chemical vapour deposition system. Interfacial properties of the as-deposited films have been characterized using capacitance?voltage and conductance?voltage techniques measured at different frequencies. The energy distribution of interface states and the relaxation time have been determined from Gp/? versus ? analysis. A Dit level of Al/TiO2/SiGe MIS capacitors in the range of 2.87 ? 1011 eV?1 cm?2 (in EC-0.446) eV to 5.04 ? 1011 eV?1 cm?2 (in EC-0.696) eV has been observed from conductance measurements.

Effects of Ti incorporation on the interface properties and band alignment of HfTaOx thin films on sulfur passivated GaAs

Thin HfTaOx and HfTaTiOx gate dielectrics (∼7–8 nm) have been rf sputter-deposited on sulfur passivated GaAs. Our experimental results suggest that the formation of Ga-O at GaAs surface and As diffusion in dielectric may be effectively controlled by Ti incorporation. Possibility of tailoring of band alignment via Ti incorporation is shown. Valence band offsets of 2.6±0.05 and 2.68±0.05 eV and conduction-band offsets of 1.43±0.05 and 1.05±0.05 eV were found for HfTaOx (Eg∼5.45 eV) and HfTaTiOx (Eg∼5.15 eV), respectively.

Effects of annealing on the electrical properties of TiO2 films deposited on Ge-rich SiGe substrates

Titanium oxide (TiO2) high-k dielectric layers were deposited on the Si0.3Ge0.7 substrates by plasma enhanced chemical vapor deposition (PECVD) at low temperature (150°C). To study the effects of annealing on the electrical properties, the TiO2 films were annealed in pure nitrogen ambient in the temperature range of 400–600°C. Good electrical performance for the gate dielectrics was observed for the dielectric films annealed up to 500°C, in terms of interface state density, leakage current, and charge trapping properties. Annealing at 600°C is found to degrade the electrical properties due to Ge segregation and subsequent diffusion into the TiO2 layer. Schottky emission was found to be the dominant leakage current conduction mechanism in PECVD TiO2 films.

Charge trapping and reliability characteristics of sputtered Y2O3 high-k dielectrics on N- and S-passivated germanium

We demonstrate the potential of sulfur passivation to improve the interface characteristics between germanium (Ge) and Y2O3 high-k gate dielectric. Effects of nitrogen (N) and sulfur (S) passivation of the Ge surface on the charge trapping and reliability properties of Y2O3/Ge gate stacks are studied in detail and the results are compared. Sulfur passivation of the Ge surface has been performed using both the wet sulfidation technique with aqueous ammonium sulfide and plasma sulfidation with H2S gas. N-passivation of Ge substrates has been performed in NO plasma for comparison. Ultrathin (~15 nm) Y2O3 films are deposited on both the N- and S-passivated p-Ge (1 0 0) wafers. Y2O3 films on the S-passivated Ge surface show low fixed oxide charge and interface state density than what is achieved with N-passivation. The electrical characterization results of MOS capacitors with Y2O3 films reveal the potential of S-passivation for the fabrication of Y2O3/Ge gate stacks for Ge MOSFETs.

Thermal stability of HfOxNy gate dielectrics on p-GaAs substrates

The structural, electrical and interfacial properties of metal-oxide–semiconductor (MOS) capacitors with hafnium-oxynitride (HfOxNy) gate dielectrics on p-GaAs substrates were investigated with post-deposition annealing (PDA). X-ray photoelectron spectra (XPS) show the presence of nitrogen at the interface and the intensity increases with annealing temperatures. Although the defective Ga-oxide increases with temperatures, the presence of nitrogen stabilizes and modulates the interface trap by reducing the oxygen vacancy. The electrical characteristics of GaAs MOS devices with HfOxNy gate dielectric show low interface state density, frequency dispersion and hysteresis voltage even after annealing at 600 °C. The accumulation capacitance decreases with annealing temperatures due to the formation of a stable thick nitride interfacial layer. The leakage current density of ~2.4 × 10−6 A cm−2 at VG = −1 V was achieved after 600 °C annealing for an EOT of 3.9 nm. The thermal stability and charge trapping behavior of the HfOxNy/p-GaAs gate stack at a constant voltage and current stressing have exhibited good interface quality and high dielectric reliability, making the films suitable for GaAs-based complementary metal-oxide–semiconductor technology

Electrical properties of ultrathin TiO2 films on Si1−yCy heterolayers

Abstract Titanium dioxide (TiO 2 ) based gate insulators are being considered seriously for next generation metal oxide semiconductor field effect transistor applications due to its high permittivity. In this work, ultrathin TiO 2 films have been deposited at 150 °C on carbon implanted solid phase epitaxy grown strained Si 1− y C y layers by microwave plasma enhanced chemical vapor deposition using titanium tetrakis isopropoxide and oxygen. The deposited films have been analyzed by X-ray photoelectron spectroscopy for chemical composition. Using a metal–insulator–semiconductor capacitor structure, the interfacial and electrical properties of the deposited films have been characterized in the temperature range 25–125 °C. The leakage current has been found to be dominated by the Schottky emission at a low electric field, whereas Poole–Frenkel emission takes over at higher fields.

Paramagnetic defects and charge trapping behavior of ZrO2 films deposited on germanium by plasma-enhanced CVD

Internal photoemission and magnetic resonance studies have been performed to investigate the charge trapping behavior and chemical nature of defects in ultrathin (~14 nm) high-k ZrO2 dielectric films deposited on p-Ge (1 0 0) substrates at low temperature (<200 °C) by plasma-enhanced chemical vapor deposition (PECVD) in a microwave (700 W, 2.45 GHz) plasma at a pressure of ~65 Pa. Both the band and defect-related electron states have been characterized using electron paramagnetic resonance, internal photoemission, capacitance–voltage and current–voltage measurements under UV illumination. Capacitance–voltage and photocurrent–voltage measurements were used to determine the centroid of oxide charge within the high-k gate stack. The observed shifts in photocurrent response of the Al/ZrO2/GeO2/p-Ge metal–insulator–semiconductor (MIS) capacitors indicate the location of the centroids to be within the ZrO2 dielectric near to the gate electrode. Moreover, the measured flat band voltage and photocurrent shifts also indicate a large density of traps in the dielectric. The impact of plasma nitridation on the interfacial quality of the oxides has been investigated. Different N sources, such as NO and NH3, have been used for nitrogen engineering. Oxynitride samples show a lower defect density and trapping over the non-nitrided samples. The charge trapping and detrapping properties of MIS capacitors under stressing in constant current and voltage modes have been investigated in detail.

Photoresponse of Si1−xGex heteroepitaxial p–i–n photodiodes

Abstract A simulation study of spectral response, dark current and capacitance of Si 1− x Ge x heteroepitaxial p–i–n photodiodes as a function of thickness of the i -layer and Ge mole fraction has been performed. It has been found that the cut-off wavelength of the diodes increases from 1.12 to 1.50 μm as the Ge mole fraction ( x ) is increased from 0.0 to 0.75 and the photoresponse increases with the thickness of the absorbing i -layer. The simulated photoresponse of p–i–n diodes is in good agreement with reported experimental data. The dark current is found to increase with Ge concentration and remains in the nA range for upto 30% Ge which corresponds to a cut-off wavelength of ≈1.3 μm, extending the possibility of these devices in fiberoptic communication applications.