To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
This work reports the growth of crystalline SrHfxTi1−xO3 (SHTO) films on Ge (001) substrates by atomic layer deposition. Samples were prepared with different Hf content x to explore if strain, from tensile (x = 0) to compressive (x = 1), affected film crystallization temperature and how composition affected properties. Amorphous films grew at 225 °C and crystallized into epitaxial layers at annealing temperatures that varied monotonically with composition from ~530 °C (x = 0) to ~660 °C (x = 1). Transmission electron microscopy revealed abrupt interfaces. Electrical measurements revealed 0.1 A/cm2 leakage current at 1 MV/cm for x = 0.55.
The integration of dissimilar materials is highly desirable for many different types of device applications but often challenging to achieve in practice. The unrivalled imaging capabilities of the aberration-corrected electron microscope enable enhanced insights to be gained into the atomic arrangements across heterostructured interfaces. This paper provides an overview of our recent observations of oxide-semiconductor heterostructures using aberration-corrected high-angle annular-dark-field and large-angle bright-field imaging modes. The perovskite oxides studied include strontium titanate, barium titanate, and strontium hafnate, which were grown on Si(001) and/or Ge(001) substrates using the techniques of molecular-beam epitaxy or atomic-layer deposition. The oxide layers displayed excellent crystallinity and sharp, abrupt interfaces were observed with no sign of any amorphous interfacial layers. The Ge(001) substrate surfaces invariably showed both 1× and 2× periodicity consistent with preservation of the 2 × 1 surface reconstruction following oxide growth. Overall, the results augur well for the future development of functional oxide-based devices integrated on semiconductor substrates.
We report the epitaxial growth of γ-Al2O3 on SrTiO3 (STO) substrates by atomic layer deposition (ALD). The ALD growth of γ-Al2O3 on STO(001) single crystal substrates was performed at a temperature of 345 °C. Trimethylaluminum and water were used as co-reactants. In-situ reflection high-energy electron diffraction and ex-situ x-ray diffraction were used to determine the crystallinity of the Al2O3 films. In-situ x-ray photoelectron spectroscopy was used to characterize the Al2O3/STO heterointerface. The formation of a Ti3+ feature is observed in the Ti 2p spectrum of STO after the first few ALD cycles of Al2O3 and even after exposure of the STO substrate to trimethylaluminum alone at 345 °C. The presence of a Ti3+ feature is a direct indication of oxygen vacancies at the Al2O3/STO heterointerface, which provide the carriers for the quasi-two dimensional electron gas at the interface.
Triruthenium dodecarbonyl and trimethylphosphine or triphenylphosphine, and cis-ruthenium(II)dihydridotetrakis-(trimethylphophine) were used in flowing hydrogen or argon at 575 K to explore the effect of changing the percentage of P on the amorphous character of the films and on the electrical properties of the films. First-principles density-functional calculations are presented that reveal the interaction of Ru with P, and that predict the amorphous structure should be most stable above 20 at.% P and 10 at.% B. The films contained a carbon impurity that depended on the delivery gas and the alkylphoshphine source; film resistivity was highly dependent on the carbon impurity level. The microstructure changed with the percentage P; amorphous films formed provided the percentage of P exceeded 15 at.%. Film resistivity was most sensitive to the carbon impurity and also changed with microstructure. A 15 nm thick, amorphous film containing ∼15 at.% P had a resistivity of 210 μohm-cm.
Germanium nanoparticle nucleation was studied in organized arrays on HfO2 using a SiO2 thin film mask with ~20-24 nm pores and a 6×1010 cm-2 pore density. Poly(styrene-b-methyl methacrylate) diblock copolymer was employed to pattern the SiO2 film. Hot wire chemical vapor deposition produced Ge nanoparticles using 4-19 monolayer Ge exposures. By seeding adatoms on HfO2 at room temperature before growth and varying growth temperatures between 725-800 K, nanoparticle size was demonstrated to be limited by Ge etching of SiO2 pore walls.
Germanium nanoparticles are grown on HfO2 substrates by hot-wire chemical vapor deposition (HWCVD). The oxidation and thermal stability of these unmodified Ge nanoparticles are determined with X-ray photoelectron spectroscopy (XPS). Core-shell nanoparticles were then prepared by growing the Ge cores with HWCVD and selectively growing Si or C shell layers on the Ge cores by conventional CVD. The formation of core-shell nanoparticles was monitored with XPS and low energy ion scattering. Large differences are observed in the thermal stability and oxide formation for unmodified Ge and the different core-shell nanoparticles.
A simple combinatorial approach for studying chemical and physical vapor deposition (CVD and PVD) nanoparticle growth is presented utilizing temperature and precursor flux gradients across sample surfaces. Large temperature gradients (450-700 °C) are induced covering the entire range of interest for most CVD and PVD processes. Precursor flux gradients may also be introduced simultaneously or separately using a tungsten cracking filament mounted on a translation arm. Theory and calibration experiments are explained and results from a study on Ge nanoparticle growth on HfO2 surfaces are presented and analyzed. This method drastically decreases experimental time required to investigate nanoparticle growth and identify optimum deposition conditions. Furthermore, this approach greatly facilitates preparation of library samples containing a wide range (several orders of magnitude) in variation of nanoparticle sizes, density, and composition for subsequent studies.
Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent to seal the pores and prevent penetration of a metallic precursor during barrier deposition. The blanket pMSQ films studied were approximately 220 nm thick and had been etched and ashed. When tantalum pentafluoride (TaF5) is exposed to an unsealed pMSQ sample, X-ray photoelectron spectroscopy (XPS) depth profiling and secondary ion mass spectroscopy (SIMS) depth profiling reveal penetration of Ta into the pores all the way to the pMSQ / Si interface. Boron carbo-nitride films were grown by thermal chemical vapor deposition (CVD) using dimethylamine borane (DMAB) precursor with Ar carrier gas and C2H4 coreactant. These films had a stoichiometry of BC0.9N0.07 and have been shown in a previous study to have a k value as low as 3.8. BC0.9N0.07 films ranging from 1.8 to 40.6 nm were deposited on pMSQ and then exposed to TaF5 gas to determine the extent of Ta penetration into the pMSQ. Ta penetration was determined by XPS depth profiling and sometimes SIMS depth profiling. XPS depth profiling of a TaF5 / 6.3 nm BC0.9N0.07 / pMSQ / Si film stack indicates the attenuation of the Ta signal to < 2 at. % throughout the pMSQ. Backside SIMS of this sample suggests that trace amounts of Ta (< 2 at. %) are due to knock-in by Ar ions used for sputtering. An identical film stack containing 3.9 nm BC0.9N0.07 was also successful at inhibiting Ta penetration even with a 370°C post-TaF5 exposure anneal, suggesting the stability of BC0.9N0.07 to thermal diffusion of Ta. All BC0.9N0.07 films thicker than and including 3.9 nm prevented Ta from penetrating into the pMSQ.
This paper discusses a kinetically-driven patterning scheme to marry top-down and bottom-up assembly of nanoparticle arrays. We explain how Ge atoms interact with different dielectric surfaces to either etch the surface or to accumulate and self assemble into nanocrystals during chemical vapor deposition. By exploiting the different reactivity of these dielectrics, the accumulation of adatoms is controlled and thus subsequent self assembly of nanocrystals is controlled. Scanning electron microscopy and atomic force microscopy are used to determine particle densities. We have achieved dense (>1011 cm-2) arrays of self-assembled Ge nanocrystals within ∼100 µm sized features (defined by optical lithography) with no Ge deposition on the adjacent SiO2 sacrificial mask region. Electron beam lithography was used to pattern smaller (100 µm to 500 nm) features in which to direct the self assembly. As features shrink below 10 µm, nanoparticle nucleation within the feature is sharply affected. Finally, diblock copolymers are used to pattern 20 nm features to template self assembly of nanoparticles at a scale useful for device applications.
Ge is deposited on HfO2 surfaces by chemical vapor deposition (CVD) with GeH4. 0.7-1.0 ML GeHx (x = 0-3) is deposited by thermally cracking GeH4 on a hot tungsten filament. Ge oxidation and bonding are studied at 300-1000 K with X-ray photoelectron spectroscopy (XPS). Ge, GeH, GeO, and GeO2 desorption are measured with temperature programmed desorption (TPD) at 400-1000 K. Ge initially reacts with the dielectric forming an oxide layer followed by Ge deposition and formation of nanocrystals in CVD at 870 K. 0.7-1.0 ML GeHx deposited by cracking rapidly forms a contacting oxide layer on HfO2 that is stable from 300-800 K. Ge is fully removed from the HfO2 surface after annealing to 1000 K. These results help explain the stability of Ge nanocrystals in contact with HfO2.
GeH4 is thermally cracked over a hot filament depositing 0.7–15 ML Ge onto 2–7 nm SiO2/Si(100) at substrate temperatures of 300–970 K. Ge, GeHx, GeO, and GeO2 desorption is monitored through temperature programmed desorption in the temperature range 300–1000 K. Ge bonding changes are analyzed during annealing from 300–1000 K with X-ray photoelectron spectroscopy (XPS). Low temperature desorption features are attributed to GeO and GeH4. No GeO2 desorption is observed, but GeO2 decomposition to Ge through high temperature pathways is seen above 700 K. Germanium oxidization results from Ge etching of the oxide substrate, which is demonstrated through XPS. Ge nanoparticle formation on SiO2 is demonstrated using the agglomeration process. With these results, explanations for the difficulties of conventional chemical vapor deposition to produce Ge nanocrystals on SiO2 surfaces are proposed.
A model is presented that describes silicon nanoparticle deposition in terms of disilane decomposition on silicon dioxide, adatom diffusion, nucleation, nanoparticle growth and coalescence. Total nanoparticle densities are output as a function of time, and segregation of nanoparticles into subsets with common size allows size distributions to be reported for all times during the simulation. Model parameters are fit to low pressure chemical vapor deposition data with disilane pressures ranging from 5×10−4 to 5×10−3 Torr and surface temperatures from 510 to 570 °C. Simulations are used to explain how growth pressure and surface temperature influence incubation time, nanoparticle density and size distribution.
A non-thermal method to facilitate nucleation for subsequent thermal chemical vapor deposition of Si nanoparticles on SiO2/Si(001) with high density and uniform size is demonstrated. Submonolayers of Si adatoms are predeposited on SiO2/Si(001) substrates by hot-wire chemical vapor deposition with disilane in an UHV chamber. The nanoparticles are grown with a disilane pressure of 1×10-4 Torr at 550 °C. The Si nanoparticles density is increased and size distribution is narrowed by predeposition of Si adatoms when compared to thermal growth on bare SiO2/Si(001). The nanoparticles density can be controlled by the amount of Si adatom predeposition. 1.2×1012 cm-2 density and 5.5 nm size are demonstrated on SiO2/Si(001) under UHV-CVD conditions.
Compounds of the type (L2MEL'2)x, where M and E are the group III and V elements, respectively, and L and L' are ligands which may be thermally eliminated are being studied as single source precursors to III-V semiconductors. An array of these compounds have been synthesized with various III-V combinations, and hydride and alkyl ligands. Film growth was studied over the temperature range of 450-600 °C and at 10−4 Torr. Growth rates of 1 μm/hr are typical when the compounds are maintained at 125-140 °C. (Me2Ga(μ-t-Bu2As) [2 led to films which were polygrained with the grains oriented in the (111) direction and retained the 1:1 stoichiometry of the precursor. Films from [Me2Ga(μ-i-Pr2As)]3 did not retain the 1:1 stoichiometry and did not show the preference for (111)- oriented growth.
Email your librarian or administrator to recommend adding this to your organisation's collection.