Understanding the Mechanism of Electronic Defect Suppression Enabled by Nonidealities in Atomic Layer Deposition.

Silicon germanium (SiGe) is a multifunctional material considered for quantum computing, neuromorphic devices, and CMOS transistors. However, implementation of SiGe in nanoscale electronic devices necessitates suppression of surface states dominating the electronic properties. The absence of a stable and passive surface oxide for SiGe results in the formation of charge traps at the SiGe-oxide interface induced by GeOx. In an ideal ALD process in which oxide is grown layer by layer, the GeOx formation should be prevented with selective surface oxidation (i.e., formation of an SiOx interface) by controlling the oxidant dose in the first few ALD cycles of the oxide deposition on SiGe. However, in a real ALD process, the interface evolves during the entire ALD oxide deposition due to diffusion of reactant species through the gate oxide. In this work, this diffusion process in nonideal ALD is investigated and exploited: the diffusion through the oxide during ALD is utilized to passivate the interfacial defects by employing ozone as a secondary oxidant. Periodic ozone exposure during gate oxide ALD on SiGe is shown to reduce the integrated trap density (Dit) across the band gap by nearly 1 order of magnitude in Al2O3 (<6 × 1010 cm-2) and in HfO2 (<3.9 × 1011 cm-2) by forming a SiOx-rich interface on SiGe. Depletion of Ge from the interfacial layer (IL) by enhancement of volatile GeOx formation and consequent desorption from the SiGe with ozone insertion during the ALD growth process is confirmed by electron energy loss spectroscopy (STEM-EELS) and hypothesized to be the mechanism for reduction of the interfacial defects. In this work, the nanoscale mechanism for defect suppression at the SiGe-oxide interface is demonstrated, which is engineering of diffusion species in the ALD process due to facile diffusion of reactant species in nonideal ALD

Control of InGaAs facets using metal modulation epitaxy (MME)

Control of faceting during epitaxy is critical for nanoscale devices. This work identifies the origins of gaps and different facets during regrowth of InGaAs adjacent to patterned features. Molecular beam epitaxy (MBE) near SiO2 or SiNx led to gaps, roughness, or polycrystalline growth, but metal modulated epitaxy (MME) produced smooth and gap-free "rising tide" (001) growth filling up to the mask. The resulting self-aligned FETs were dominated by FET channel resistance rather than source-drain access resistance. Higher As fluxes led first to conformal growth, then pronounced {111} facets sloping up away from the mask.Comment: 18 pages, 7 figure

Origin and implications of the observed rhombohedral phase in nominally tetragonal Pb(Zr\u3csub\u3e0.35\u3c/sub\u3eTi\u3csub\u3e0.65\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e thin films

The structural and electrical properties of Pb(Zr0.35Ti0.65)O3 (PZT) thin films ranging in thickness from 700 to 4000 Å have been investigated. These (001)/(100)-textured films were grown by metalorganic chemical vapor deposition on (111)-textured Ir bottom electrodes. It was observed that, in the as-deposited state, the thinnest PZT films are rhombohedral even though bulk PZT of this composition should be tetragonal. Thicker films have a layered structure with tetragonal PZT at the surface and rhombohedral PZT at the bottom electrode interface. In this article we investigate the origin of this structure and its effect of the ferroelectric and dielectric properties of PZT capacitors. It has been suggested that thin films stresses can affect the phase stability regions of single domain PZT. This possibility has been investigated by piezoresponse microscopy and thin film stress measurements. In the as-deposited state the majority of PZT grains contain a single ferroelastic domain, whereas after a high temperature anneal, a large fraction of the grains contain several ferroelastic domains. Wafer curvature measurements in combination with x-ray diffraction stress measurements in the Ir bottom electrode showed that the as-deposited PZT films are, within experimental error, stress free at room temperature. Landau–Ginbzurg–Devonshire formalism was used to explain the origin of the rhombohedral phase as a result of substrate constraint on single domain PZT grains. Annealing was found to affect the relative volume fractions of the rhombohedral and tetragonal phases and the electrical properties of PZT films. Intermediate temperature anneals increased the volume fraction of the rhombohedral phase and the coercive field extracted from the polarization-electric field hysteresis loops. After a high temperature anneal (650 °C) the majority of the grains transformed into a polydomain state, decreasing the volume fraction of the rhombohedral phase and the coercive field. If the high temperature anneal was performed after deposition of the top electrode, the coercive field became independent of the PZT thickness

Isolating the photovoltaic junction: atomic layer deposited TiO2-RuO2 alloy Schottky contacts for silicon photoanodes

We synthesized nanoscale TiO2-RuO2 alloys by atomic layer deposition (ALD) that possess a high work function and are highly conductive. As such, they function as good Schottky contacts to extract photogenerated holes from n-type silicon while simultaneously interfacing with water oxidation catalysts. The ratio of TiO2 to RuO2 can be precisely controlled by the number of ALD cycles for each precursor. Increasing the composition above 16% Ru sets the electronic conductivity and the metal work function. No significant Ohmic loss for hole transport is measured as film thickness increases from 3 to 45 nm for alloy compositions >= 16% Ru. Silicon photoanodes with a 2 nm SiO2 layer that are coated by these alloy Schottky contacts having compositions in the range of 13-46% Ru exhibit average photovoltages of 525 mV, with a maximum photovoltage of 570 mV achieved. Depositing TiO2-RuO2 alloys on nSi sets a high effective work function for the Schottky junction with the semiconductor substrate, thus generating a large photovoltage that is isolated from the properties of an overlying oxygen evolution catalyst or protection layer

Origin and passivation of fixed charge in atomic layer deposited aluminum oxide gate insulators on chemically treated InGaAs substrates

We report experimental and theoretical studies of defects producing fixed charge within Al(2)O(3) layers grown by atomic layer deposition (ALD) on In(0.53)Ga(0.47)As(001) substrates and the effects of hydrogen passivation of these defects. Capacitance-voltage measurements of Pt/ALD-Al(2)O(3)/n-In(0.53)Ga(0.47)As suggested the presence of positive bulk fixed charge and negative interfacial fixed charge within ALD-Al(2)O(3). We identified oxygen and aluminum dangling bonds (DBs) as the origin of the fixed charge. First-principles calculations predicted possible passivation of both O and Al DBs, which would neutralize fixed charge, and this prediction was confirmed experimentally; postmetallization forming gas anneal removed most of the fixed charge in ALD-Al(2)O(3). (C) 2010 American Institute of Physics. (doi:10.1063/1.3399776

Selective Passivation of GeO2/Ge Interface Defects in Atomic Layer Deposited High-k MOS Structures.

Effective passivation of interface defects in high-k metal oxide/Ge gate stacks is a longstanding goal of research on germanium metal-oxide-semiconductor devices. In this paper, we use photoelectron spectroscopy to probe the formation of a GeO2 interface layer between an atomic layer deposited Al2O3 gate dielectric and a Ge(100) substrate during forming gas anneal (FGA). Capacitance- and conductance-voltage data were used to extract the interface trap density energy distribution. These results show selective passivation of interface traps with energies in the top half of the Ge band gap under annealing conditions that produce GeO2 interface layer growth. First-principles modeling of Ge/GeO2 and Ge/GeO/GeO2 structures and calculations of the resulting partial density of states (PDOS) are in good agreement with the experiment results.This work was supported in part by the Stanford Initiative for Nanoscale Materials and Processes (INMP). This work was performed at the National Synchrotron Light Source and the Stanford Synchrotron Radiation Laboratory, which are supported by the US Department of Energy. Additional support was provided by the National Institute of Standards and Technology.This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/acsami.5b06087