Sputter Epitaxy Research Articles

Single-crystal p–i–n-Si thin-film solar cells grown on Si substrate by sputter epitaxy

An intrinsic sputter-epitaxial (SE) Si film with a thickness of 1000 nm and a 50-nm-thick n+ SE-Si film were successfully grown as the light-absorbing layer and emitter layer, respectively, on a heavily doped p-Si(100) wafer to form the p–i–n junction of a solar cell (SC). Heavily doped n+ SE-Si with an electron concentration n of 3 × 1020 cm−3 was grown by cosputtering of Sb with Si. The characteristics of SE-Si grown at 310 °C was investigated in relation to annealing temperature. The oxygen concentration in SE-Si was ∼1018 cm−3, which was found to originate from the gas released in the chamber. Oxygen-induced thermal donors then became the source of n in the film, and n was reduced to 1 × 1016 cm−3 after forming-gas annealing at 700 °C because the thermal donors were neutralized by hydrogen. The SC exhibited a maximum internal quantum efficiency of 73.7%.

Sputter epitaxy of heavily doped p+/n+ Ge film on Si(100) by cosputtering with Al/Sb for solar cell application

Heavily doped p+ or n+ Ge films were grown on Si substrates by sputter epitaxy. Ge was cosputtered with Al or Sb to add dopant impurities. The maximum carrier densities were 1.0 × 1021 for p-type films and 8.4 × 1019 cm−3 for n-type films. The activation ratio of Sb was 56%. A pn junction diode was fabricated on a Si(100) substrate; it exhibited a good rectifying property with an on/off ratio of 529.

Liquid-target reactive magnetron sputter epitaxy of High quality GaN(0001̄) nanorods on Si(111)

Direct current magnetron sputter epitaxy with a liquid Ga sputtering target has been used to grow single-crystal GaN(0001̄) nanorods directly on Si(111) substrates at different working pressures ranging from 5 to 20mTorr of pure N2. The as-grown GaN nanorods exhibit very good crystal quality from bottom to top without stacking faults, as determined by transmission electron microscopy. The crystal quality is found to increase with increasing working pressure. X-ray diffraction results show that the rods are highly (0001)-oriented. The nanorods exhibit an N-polarity, as determined by convergent beam electron diffraction methods. Sharp and well-resolved 4K photoluminescence peaks at ~3.474eV with a FWHM ranging from 1.7meV to 35meV are attributed to the intrinsic GaN band edge emission and corroborate the superior structural properties of the material. Texture measurements reveal that the rods have random in-plane orientation when grown on Si(111) with native oxide, while they have an in-plane epitaxial relationship of GaN[112̅0]//Si[11̄0] when grown on substrates without surface oxide.

Low-temperature fabrication technologies of Si solar cell by sputter epitaxy method

We applied an epitaxial n+-type Si emitter layer grown on a p-type Si substrate by our environmentally-light-load sputter epitaxy method using RF magnetron sputtering without dopant activation annealing for a Si solar cell. We also applied low-temperature cleaning of the substrate with a hydrogen-fluoride treatment at room temperature prior to the emitter layer growth instead of the conventionally used high-temperature thermal cleaning under vacuum condition. In addition, by our sputter epitaxy method, we determined the optimum temperature for the emitter growth. An emitter layer with good crystallinity is obtained, and the solar cell, formed with an emitter layer grown at the optimum growth temperature of 410 °C, exhibits an energy conversion efficiency of 12.3% in 100% aperture ratio equivalent without a texture or an antireflection coat. By the above low-temperature processes, a solar cell can be fabricated with process temperatures below 410 °C, which exhibits low temperature processes.

Stabilization of wurtzite Sc0.4Al0.6N in pseudomorphic epitaxial ScxAl1−xN/InyAl1−yN superlattices

Pseudomorphic stabilization in wurtzite ScxAl1−xN/AlN and ScxAl1−xN/InyAl1−yN superlattices (x=0.2, 0.3, and 0.4; y=0.2–0.72), grown by reactive magnetron sputter epitaxy was investigated. X-ray diffraction and transmission electron microscopy show that in ScxAl1−xN/AlN superlattices the compressive biaxial stresses due to positive lattice mismatch in Sc0.3Al0.7N and Sc0.4Al0.6N lead to the loss of epitaxy, although the structure remains layered. For the negative lattice mismatched In-rich ScxAl1−xN/InyAl1−yN superlattices, a tensile biaxial stress promotes the stabilization of wurtzite ScxAl1−xN even for the highest investigated concentration x=0.4. Ab initio calculations with fixed in-plane lattice parameters show a reduction in mixing energy for wurtzite ScxAl1−xN under tensile stress when x⩾0.375 and corroborate the experimental results.

Fabrication of Interdigitated Electrodes using Molecular Beam Epitaxy and Optical Lithography

ABSTRACTThis study reports the fabrication of interdigitated electrodes using molecular beam epitaxy and photolithography techniques. Sandwich-based 10 nm silver and 50 nm gold films were deposited on glass substrates using magnetron sputtering and molecular beam epitaxy deposition. The thickness and roughness were determined by use of a suitable mathematical model and ellipsometric measurements. The gold film (111) orientation was determined by X-ray diffraction. Optical microscopy measurements were made for the lateral resolution determination of the fabricated electrodes and the quality was similar to that of the photomask. Atomic force microscopy measurements offered information regarding the topography of the sample and the possible application of the fabricated system for molecular detection.

Structural and compositional evolutions of InxAl1−xN core–shell nanorods grown on Si(111) substrates by reactive magnetron sputter epitaxy

Catalystless growth of InxAl1−xN core–shell nanorods have been realized by reactive magnetron sputter epitaxy onto Si(111) substrates. The samples were characterized by scanning electron microscopy, x-ray diffraction, scanning transmission electron microscopy, and energy dispersive x-ray spectroscopy. The composition and morphology of InxAl1−xN nanorods are found to be strongly influenced by the growth temperature. At lower temperatures, the grown materials form well-separated and uniform core–shell nanorods with high In-content cores, while a deposition at higher temperature leads to the formation of an Al-rich InxAl1−xN film with vertical domains of low In-content as a result of merging Al-rich shells. The thickness and In content of the cores (domains) increase with decreasing growth temperature. The growth of the InxAl1−xN is traced to the initial stage, showing that the formation of the core–shell nanostructures starts very close to the interface. Phase separation due to spinodal decomposition is suggested as the origin of the resultant structures. Moreover, the in-plane crystallographic relationship of the nanorods and substrate was modified from a fiber textured to an epitaxial growth with an epitaxial relationship of InxAl1−xN[0001]//Si[111] and InxAl1−xN[11]//Si[1 by removing the native SiOx layer from the substrate.

Formation of GeSn layers on Si (001) substrates at high growth temperature and high deposition rate by sputter epitaxy method

GeSn layers are formed on Si substrates by the sputter epitaxy method. Flat GeSn layers with 11.5 % Sn content are obtained. In the X-ray diffraction spectra of the GeSn layers with 11.5 % Sn content grown at 523 K, a sharp Ge (004) peak appears at about 64.5306° and the full width at half maximum is about 0.0984°. However, the surface segregation of Sn is observed in the GeSn layers with 11.5 % Sn content at growth temperatures of 548 K and above in this study, which increases the surface roughness. The crystallinity of the GeSn layers formed on Si substrates strongly depends on the growth temperature, but the primary factor degrading the crystallinity is the large lattice mismatch between Si and GeSn. According to a transmission electron microscope image, some dislocations appear at the interface of the GeSn layer grown at 523 K and Si owing to the large lattice mismatch, but there is no Sn surface segregation and a highly ordered atomic arrangement is observed in the upper region. It is considered that a high deposition rate limits Sn surface segregation and enables the growth of GeSn layers at relatively high temperatures, resulting in improved crystallinity. The band gap of the GeSn layers with 8.4 % Sn content is determined by Fourier transform infrared spectroscopy measurement and is about 0.52 eV, which indicates that band gap narrowing occurs.

Формирование нанопленок Cu, Ag, Au под воздействием атомов водорода

Due to their electrical properties, thin metallic films are widely used in modern micro- and nanoelectronics. These properties allow solving fundamental problems of surface and solid state physics. Up-to-date methods of producing thin films involve high vacuum or multi-stage processes, which calls for complicated equipment. The authors propose an alternative method of producing thin metallic films using atomic hydrogen. Exothermal reaction of atoms recombination in a molecule (about 4.5 eV / recombination act) initiated on the solid surface by atomic hydrogen may stimulate local heating, spraying and surface atoms transfer. We investigated the process of atomic hydrogen treatment of Cu, Ag and Au metal films, obtained by thermal vacuum evaporation. There are two methods of obtaining nanofilms using atomic hydrogen treatment: sputtering and vapor-phase epitaxy. In the first method, a film is formed by reducing the thickness of the starting film. This method allows obtaining a film as thick as the monolayer. In the second method, a nanofilm is formed by deposition of metal atoms from the vapor phase. This method allows obtaining a film thickness from monolayer to ~10 nm. These methods allow creating nanofilms with controlled parameters and metal thickness. Such films would be technologically pure and have good adhesion.

Hetero-epitaxial Γ-Al2O3 on Si (100) substrate by sputtering

In this paper, the hetero-epitaxy of γ-Al2O3 films on Si (100) substrates by RF magnetron sputtering has been systematically studied. Crystal quality improves with growth temperature from 400°C to 700°C. The films sputtered with 4.5% extra O2 or on a Si substrate with a thin oxide show better crystal qualities. Low sputtering power such as 60W is essential to maintain good interfaces. Direct evidence of sputtering epitaxy of γ-Al2O3 on Si (100) is demonstrated for the first time. These results are very useful for low-cost growth of epitaxial γ-Al2O3 which has been used as buffer layers for epitaxial III–V materials on Si and barrier layers for electronic devices.

Homoepitaxial growth of ZnO films with reduced impurity concentrations by helicon-wave-excited-plasma sputtering epitaxy using a crystalline ZnO target prepared by hydrothermal technique

Homoepitaxial growth of reduced donor concentration ZnO films exhibiting atomically smooth surface is demonstrated by helicon-wave-excited-plasma sputtering epitaxy. Using a crystalline ZnO target prepared by hydrothermal method, concentrations of B, C, Cr, Li, and Si in the films underran the detection limits of secondary-ion-mass spectrometry. Consequently, low temperature photoluminescence spectra were dominated by sharp emission peaks originating from the recombination of excitons bound to a neutral Al donor, of which concentration was 2 × 1016 cm−3. Nonradiative lifetime dominated the recombination process above 50 K, which is most likely due to the presence of lifetime killers such as Ni and Fe.

Electrical spin injection into InGaAs/GaAs quantum wells: A comparison between MgO tunnel barriers grown by sputtering and molecular beam epitaxy methods

An efficient electrical spin injection into an InGaAs/GaAs quantum well light emitting diode is demonstrated thanks to a CoFeB/MgO spin injector. The textured MgO tunnel barrier is fabricated by two different techniques: sputtering and molecular beam epitaxy. The maximal spin injection efficiency is comparable for both methods. Additionally, the effect of annealing is also investigated for the two types of samples. Both samples show the same trend: an increase of the electroluminescence circular polarization (Pc) with the increase of annealing temperature, followed by a saturation of Pc beyond 350 °C annealing. Since the increase of Pc starts well below the crystallization temperature of the full CoFeB bulk layer, this trend could be mainly due to an improvement of chemical structure at the top CoFeB/MgO interface. This study reveals that the control of CoFeB/MgO interface is essential for an optimal spin injection into semiconductor.

Stress evolution during growth of GaN (0001)/Al2O3(0001) by reactive dc magnetron sputter epitaxy

We study the real time stress evolution, by in situ curvature measurements, during magnetron sputter epitaxy of GaN (0 0 0 1) epilayers at different growth temperatures, directly on Al2O3(0 0 0 1) substrates. The epilayers are grown by sputtering from a liquid Ga target in a mixed N2/Ar discharge. For 600 °C, a tensile biaxial stress evolution is observed, while for 700 °C and 800 °C, compressive stress evolutions are observed. Structural characterization by cross-sectional transmission electron microscopy, and atomic force microscopy, revealed that films grew at 700 °C and 800 °C in a layer-by-layer mode while a growth temperature of 600 °C led to an island growth mode. High resolution x-ray diffraction data showed that edge and screw threading dislocation densities decreased with increasing growth temperature, with a total density of 5.5 × 1010 cm−2 at 800 °C. The observed stress evolution and growth modes are explained by a high surface mobility during magnetron sputter epitaxy at 700–800 °C. Other possible reasons for the different stress evolutions are also discussed.

Direct-current sputter epitaxy of Si and its application to fabricate n+-emitters for crystalline-Si solar cells

Direct-current sputter epitaxy of Si on a Si(001) substrate was realized at 175 °C at a growth rate of 3.3 nm·s−1 and was applied to form n+-emitters of crystalline-Si solar cells. A solar cell with a 50-nm-thick n+-emitter exhibited a short current density of 23.8 mA·cm−2 owing to an increased internal quantum efficiency at wavelengths between 400 and 600 nm. The improved efficiency was due to the step junction characteristics of the epitaxially grown n+-emitter exhibiting a better response at short wavelengths, a performance better than that of the graded junction formed by thermal diffusion.

Effects of boron dopants of Si (001) substrates on formation of Ge layers by sputter epitaxy method

The formation of Ge layers on boron-doped Si (001) substrates by our sputter epitaxy method has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the substrate resistance, and flat Ge layers are obtained on Si substrates with 0.015 Ω cm resistivity. Highly boron-doped Si substrates cause a transition in the dislocation structure from complex dislocations with 60° dislocation glide planes to 90° pure-edge dislocations, resulting in the formation of flat Ge layers. Furthermore, we have found that the surface morphology of the Ge layers improves with increasing Ge layer thickness. Ge atoms migrating on the deposited Ge layers tend to position themselves at the reactive sites, where the reactivity is related to the number of bonding contacts between the Ge atom and the surface. This modifies the surface morphology, resulting in a flatter surface. Boron dopants together with the sputter epitaxy method effectively suppress the growth of Ge islands and result in the formation of flat Ge layers.

Thin Film of Giant Magnetoresistance (GMR) Material Prepared by Sputtering Method

In recent decades, a new magnetic sensor based on magnetoresistance effect is highly researched and developed intensively. GMR material has great potential as next generation magnetic field sensing devices. It has also good magnetic and electric properties, and high potential to be developed into various applications of electronic devices such as: magnetic field sensor, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory. GMR material can be developed to be solid state magnetic sensors that are widely used in low field magnetic sensing applications. A solid state magnetic sensor can directly convert magnetic field into resistance, which can be easily detected by applying a sense current or voltage. Generally, there are many sensors for measuring the low magnetic field, such as: fluxgate sensor, Hall sensor, induction coil, GMR sensor, and SQUID sensor. Compared to other low magnetic field sensing techniques, solid state sensors have demonstrated many advantages, such as: small size (<0.1mm2), low power, high sensitivity (~0.1Oe) and good compatibility with CMOS technology. The thin film of GMR is usually prepared using: sputtering, electro deposition or molecular beam epitaxy (MBE) techniques. But so far, not many researchers reported the manufacture of thin film of GMR by dc-Opposed Target Magnetron Sputtering (dc-OTMS). In this paper, we inform the development of GMR thin film with sandwich and spin valve structures using dc-OTMS method. We have also developed organic GMR with Alq3 as a spacer layer.

Electronic transport properties in aluminum indium nitride nanorods grown by magnetron sputter epitaxy

The electronic transport properties of the wide-bandgap aluminum indium nitride (AlInN) nanorods (NRs) grown by ultrahigh-vacuum magnetron sputter epitaxy (MSE) have been studied. The conductivities of the ternary compound nanostructure locates at the value of 15Ω−1cm−1, which is respectively one and two orders of magnitude lower than the binary GaN and InN counterparts grown by chemical vapor deposition (CVD). The very shallow donor level/band with the activation energy at 11±2meV was obtained by the temperature-dependent measurement. In addition, the photoconductivity has also been investigated. The photoconductive (PC) gain of the NRs device can reach near 2400 under a low bias at 0.1V and the light intensity at 100Wm−2 for ultraviolet response in vacuum. The power-insensitive gain and ambience-dependent photocurrent are also observed, which is attributed to the probable surface-controlled PC mechanism in this ternary nitride nanostructure.

Epitaxial growth of superlattice YbGaO3(ZnO)5 and InGaO3(ZnO)5 films by the combination of sputtering and reactive solid phase epitaxy

This article describes the epitaxial growth of superlattice YbGaO3(ZnO)5 (YGZO) and InGaO3(ZnO)5 (IGZO) thin films, which feature nanoscale multilayered structures, on (111) plane yttria-stabilized zirconia (YSZ) substrates through a combination of sputtering and reactive solid phase epitaxy processes. Our fabrication process involved thin ZnO epilayers deposited through sputtering onto the YSZ substrates, and then YbGaO3(ZnO)5 or InGaO3(ZnO)5 thin films deposited at room temperature on ZnO epi-layers, followed by high-temperature annealing (1200°C) of the bilayer structures. To suppress vaporization of ZnO from the films, high-temperature annealing was performed in a box made of ceramic ZnO. We used X-ray diffraction and transmission electron microscopy (TEM) to analyze the thin films annealed under various conditions. The microstructural evolution in the film formed during reactive solid phase epitaxy process was explored by TEM observations. Single-crystalline YGZO and IGZO thin films without varying composition could be synthesized through a suitable annealing process in the ceramic ZnO box.

Bandgap Engineering and Optical Constants of YxAl1-xN Alloys

We study wurtzite YxAl1-xN (0≤x ≤0.22) films with (0001) orientation deposited by magnetron sputtering epitaxy on Si(100) substrates and we determine the alloys band gap energies and optical constants. Room temperature spectroscopic ellipsometry (SE) is employed in the energy range from 1 to 6.3 eV, and data modeling based on the standard dielectric function model is used. As a result of the SE data analysis the YxAl1-xN refractive index and extinction coefficient are determined. The band gap of YxAl1-xN is found to decrease linearly from 6.2 eV (x = 0) down to 4.5 eV (x = 0.22). We further observe an increase of the refractive index with increasing Y content; from 1.93 to 2.20 (at 2 eV) for x = 0 and 0.22, respectively, reflecting the increase in material density.

SiGe Doped-Channel FET Formed by Sputter Epitaxy Method

We report on a Si/Si0.7Ge0.3 p-type doped channel field effect transistor (p-DCFET) with a Si0.7Ge0.3 compressively strained channel fabricated by our previously proposed sputter epitaxy method. We have found that a postanneal is effective to increase the strain of the Si0.7Ge0.3 channel sandwiched by i-Si layers and that a 575 ˚C anneal for 10 min is most effective to obtain the largest strain. By comparison to the results of model simulation, the experimetally obtained I-V curves indicate that the hole mobility is enhanced by strain, the value of which is comparable to the theoretical prediction.