Search

The possibility of bandgap engineering in binary systems of oxide insulators is explored by studying the photoconductivity of nanometer-thin Hf oxide layers containing different concentrations of cations of different sorts (Si, Al, Sr, or Ce) deposited on (100)Si. Photoconductivity is shown as a feasible method to trace phase separation in nanometer-thin layers of binary systems of metal oxides.

The effects of postdeposition anneals on the electrical and interfacial properties of amorphous LaSc[O.sub.3] films on Si deposited by molecular beam deposition (MBD) are investigated. The results have shown an increase of the [kappa] value after thermal treatment of the LaSc[O.sub.3] films and the chemical composition of the interface has depended on the annealing conditions.

The structural and optical properties of type-II InP/GaAs quantum dots were investigated using reflection high energy electron diffraction, transmission electron microscopy and other techniques. The results revealed a bimodal dispersion of the dot size distribution giving rise to two distinct emission bands.

Ge nanoclusters in SiO2 layers 180 nm thick implanted with 120 keV Ge(super +1) ions were investigated for cluster coarsening and luminescence emission intensity. Results indicated that crystalline clusters were already formed at an annealing of 400 degrees C.

Abstract: Sn nanoclusters are synthesized in 180nm SiO2 layer after ion implantation and heat treatments in the 400–1100°C temperature range. The distribution and coarsening of nanoclusters is characterized by Rutherford backscattering spectrometry and transmission electron microscopy and the results are correlated with photoluminescence (PL) measurements. After annealing in N2 in the 400–600°C range, a monomodal array of Sn nanoclusters with diameters varying from 2 to 3.5nm is observed in the region around the maximum of the implanted profile. With increasing temperature, this array evolves to different regions of the SiO2 layer. For T ⩾700°C, a cluster band with small particles is observed near to the SiO2 layer surface, whereas the deeper region undergoes a coarsening resulting in large Sn particles of different sizes in metallic and in oxidized phases. The blue–violet (≈3.2eV) PL of the SiO2 layers shows to be dependent of the structural evolution above mentioned. For the N2 annealed samples, the blue–violet PL intensity increases up to 600°C and then decreases for higher temperatures. On the other hand, for heat treatments in vacuum, the PL intensity is increased by a factor of ≈5 and the TEM data show a homogeneous size distribution of Sn nanoclusters. The low intensity of PL for the N2 annealed samples is associated with Sn oxidation. [Copyright &y& Elsevier]

180 nm thick SiO2 layers thermally grown on crystalline Si were irradiated with He+, Si+, Kr++ and Au+ ions transferring different amounts of electronic (Se) and nuclear (Sn) energy to the film. After the irradiation, the SiO2 layers were implanted with 120 keV Ge+ ions at a fluence of 1.2 × 1016 cm−2. Thermal annealings in the 400–800 °C temperature range were performed to allow the formation of Ge-nanoclusters, characterized by transmission electron microscopy. The photoluminescence (PL) properties of the pre-irradiated Ge-implanted layers were investigated and compared with those from non-pre-irradiated samples. The results showed that, in both situations, PL emissions are observed in the blue-violet and ultra-violet spectral regions. At 800 °C the blue-violet PL intensity of the Ge-implanted layer pre-irradiated with Si+ ions is about 65% higher than in the non-pre-irradiated Ge-implanted layer while for the Au-irradiated layer a decrease by a factor of ≈6 was observed. Furthermore, we also observe that the mean cluster sizes are affected by the pre-irradiation. These data indicate a pre-irradiation memory effect on the PL intensity and on the cluster growth. The results are discussed in terms of a new model correlating the formation of PL luminescence centers with the cluster coarsening behavior. [Copyright &y& Elsevier]

Abstract: The chemical reactions at the higher-κ LaLuO3/Ti1N X /poly-Si gate stack interfaces are in detail investigated. Electrical and structural characterization methods are employed to explore the thermal stability of the gate stack. A Ti-rich TiN metal layer degrades the gate stack performance after high temperature annealing while the gate stack with a near stoichiometric TiN layer is stable during 1000°C, 5s anneals. Based on these results an integration process of TiN/LaLuO3 in a gate-first MOSFET process on SOI is shown. [Copyright &y& Elsevier]

Abstract: Short channel p-type metal-oxide-semiconductor field effect transistors (MOSFETs) with GdScO3 gate dielectric were fabricated on a quantum well strained Si/strained Si0.5Ge0.5/strained Si heterostructure on insulator. Amorphous GdScO3 layers with a dielectric constant of 24 show small hysteresis and low density of interface states. All devices show good performance with a threshold voltage of 0.585V, commonly used for the present technology nodes, and high Ion/Ioff current ratios. We confirm experimentally the theoretical predictions that the drive current and the transconductance of the biaxially strained (100) devices are weakly dependent on the channel orientation. The transistor’s hole mobility, extracted using split C–V method on long channel devices, indicates an enhancement of 90% (compared to SiO2/SOI transistors) at low effective field, with a peak value of 265cm2/Vs. The enhancement is however, only 40% at high electrical fields. We demonstrate that the combination of GdScO3 dielectric and strained SiGe layer is a promising solution for gate-first high mobility short channel p-MOSFETs. [Copyright &y& Elsevier]

Abstract: TiN/LaLuO3 (LLO) gate stacks formed by molecular beam deposition have been investigated by X-ray photoelectron spectroscopy, medium energy ion scattering, spectroscopic ellipsometry, scanning transmission electron microscopy, electron energy loss spectroscopy and atomic force microscopy. The results indicate an amorphous structure for deposited LLO films. The band offset between the Fermi level of TiN and valence band of LLO is estimated to be 2.65±0.05eV. A weaker La–O–Lu bond and a prominent Ti2p sub-peak which relates to Ti bond to interstitial oxygen have been identified for an ultra-thin 1.7nm TiN/3nm LLO gate stack. The angle-dependent XPS analysis of Si2s spectra as well as shifts of La4d, La3d and Lu4d core levels suggests a silicate-type with Si-rich SiO x LLO/Si interface. Symmetrical valence and conduction band offsets for LLO to Si of 2.2eV and the bandgap of 5.5±0.1eV have been derived from the measurements. The band alignment for ultra-thin TiN/LLO gate stack is affected by structural changes. [Copyright &y& Elsevier]

Abstract: Spectroscopy of internal photoemission, photoconductivity, and optical absorption is used to characterize the differences in the electronic structure of interfaces of silicon with several oxides (Sc2O3, Lu2O3, LaLuO3) grown as epitaxial layers or as amorphous films. As compared to their crystalline counterparts, the amorphous oxides exhibit significant band-tail states predominantly associated with the smearing-out of the conduction band edge. In Sc2O3 a difference in bandgap width between the crystalline and amorphous phases, caused by variation of the energy of the oxide valence band top, is also observed. No structure-sensitive interface dipoles are found to affect the band alignment at the Si/oxide interfaces. [Copyright &y& Elsevier]

Abstract: The electrical properties of MOS capacitors with LaScO3 thin films grown by molecular beam deposition (MBD) have been studied with and without post deposition annealing (PDA) in O2 environment followed by forming gas. An EOT of 0.65nm could be achieved for samples without PDA. However, the films suffer from large hysteresis and interface trap density. Applying PDA reduces the hysteresis, the D it (down to the mid of 1011 (eVcm2)−1) and the leakage current by two orders of magnitude (down to the range of 10−4A/cm2) for an EOT of 1.1nm. Furthermore we have successfully integrated LaScO3 into FD MOSFETs on SOI substrates. The p-FETs with LaScO3 show excellent characteristics with a steep subthreshold slope down to 65mV/dec and hole mobilities comparable to HfO2 and HfSiON. [Copyright &y& Elsevier]