Showing papers on "Epitaxy published in 2020"

Wafer-Scale Highly Oriented Monolayer MoS2 with Large Domain Sizes.

Abstract: Two-dimensional molybdenum disulfide (MoS2) is an emergent semiconductor with great potential in next-generation scaled-up electronics, but the production of high-quality monolayer MoS2 wafers still remains a challenge. Here, we report an epitaxy route toward 4 in. monolayer MoS2 wafers with highly oriented and large domains on sapphire. Benefiting from a multisource design for our chemical vapor deposition setup and the optimization of the growth process, we successfully realized material uniformity across the entire 4 in. wafer and greater than 100 μm domain size on average. These monolayers exhibit the best electronic quality ever reported, as evidenced from our spectroscopic and transport characterizations. Our work moves a step closer to practical applications of monolayer MoS2.

The epitaxy of 2D materials growth

Abstract: Two dimensional (2D) materials consist of one to a few atomic layers, where the intra-layer atoms are chemically bonded and the atomic layers are weakly bonded. The high bonding anisotropicity in 2D materials make their growth on a substrate substantially different from the conventional thin film growth. Here, we proposed a general theoretical framework for the epitaxial growth of a 2D material on an arbitrary substrate. Our extensive density functional theory (DFT) calculations show that the propagating edge of a 2D material tends to align along a high symmetry direction of the substrate and, as a conclusion, the interplay between the symmetries of the 2D material and the substrate plays a critical role in the epitaxial growth of the 2D material. Based on our results, we have outlined that orientational uniformity of 2D material islands on a substrate can be realized only if the symmetry group of the substrate is a subgroup of that of the 2D material. Our predictions are in perfect agreement with most experimental observations on 2D materials' growth on various substrates known up to now. We believe that this general guideline will lead to the large-scale synthesis of wafer-scale single crystals of various 2D materials in the near future.

Epitaxial nucleation and lateral growth of high-crystalline black phosphorus films on silicon

Abstract: Black phosphorus (BP) is a promising two-dimensional layered semiconductor material for next-generation electronics and optoelectronics, with a thickness-dependent tunable direct bandgap and high carrier mobility. Though great research advantages have been achieved on BP, lateral synthesis of high quality BP films still remains a great challenge. Here, we report the direct growth of large-scale crystalline BP films on insulating silicon substrates by a gas-phase growth strategy with an epitaxial nucleation design and a further lateral growth control. The optimized lateral size of the achieved BP films can reach up to millimeters, with the ability to modulate thickness from a few to hundreds of nanometers. The as-grown BP films exhibit excellent electrical properties, with a field-effect and Hall mobility of over 1200 cm2V−1s−1 and 1400 cm2V−1s−1 at room temperature, respectively, comparable to those exfoliated from BP bulk crystals. Our work opens the door for broad applications with BP in scalable electronic and optoelectronic devices. Direct synthesis of large area crystalline black phosphorus films is still challenging. Here, the authors report growth of high-quality black phosphorus films on insulating silicon substrates through a gas-phase epitaxial growth strategy with field-effect and Hall mobilities of over 1200 and 1400 cm2 /Vs at room temperature, respectively and a current on/off ratio of up to 106, comparable to the exfoliated flakes.

Systematic investigation of the growth kinetics of β-Ga2O3 epilayer by plasma enhanced chemical vapor deposition

Abstract: β-Ga2O3 has attracted much attention due to its ultrawide-bandgap (∼4.9 eV) with a high breakdown field (8 MV/cm) and good thermal/chemical stability. In order for β-Ga2O3 to be used in electronic and optoelectronic devices, epitaxial growth technology of thin films should be given priority. However, challenges are associated with the trade-off growth rate with crystallization and surface roughness in conventional epitaxy. Herein, plasma enhanced chemical vapor deposition was used to grow the β-Ga2O3 epilayer, and the growth kinetics process has been systematically investigated. A high growth rate of ∼0.58 μm/h and a single 2 ¯ 01 plane orientation with a full width at half maximum value of 0.86° were obtained when grown on the c-plane sapphire substrate at the growth temperature of 820 °C. Then, a proposed model for the mechanism of nucleation and growth of β-Ga2O3 epitaxial films is established to understand the precursor transport and gas phase reaction process. This work provides a cheap, green, and efficient epitaxial growth method, which is indispensable for device applications of β-Ga2O3.

Solid-phase hetero epitaxial growth of α-phase formamidinium perovskite.

Abstract: Conventional epitaxy of semiconductor films requires a compatible single crystalline substrate and precisely controlled growth conditions, which limit the price competitiveness and versatility of the process. We demonstrate substrate-tolerant nano-heteroepitaxy (NHE) of high-quality formamidinium-lead-tri-iodide (FAPbI3) perovskite films. The layered perovskite templates the solid-state phase conversion of FAPbI3 from its hexagonal non-perovskite phase to the cubic perovskite polymorph, where the growth kinetics are controlled by a synergistic effect between strain and entropy. The slow heteroepitaxial crystal growth enlarged the perovskite crystals by 10-fold with a reduced defect density and strong preferred orientation. This NHE is readily applicable to various substrates used for devices. The proof-of-concept solar cell and light-emitting diode devices based on the NHE-FAPbI3 showed efficiencies and stabilities superior to those of devices fabricated without NHE.

Low Temperature Homoepitaxy Of (010) $\beta$-Ga$_2$O$_3$ By Metalorganic Vapor Phase Epitaxy : Expanding The Growth Window

Abstract: In this work, we report on the growth of high-mobility $\beta$-Ga$_2$O$_3$ homoepitaxial thin films grown at a temperature much lower than the conventional growth temperature window for metalorganic vapor phase epitaxy. Low-temperature $\beta$-Ga$_2$O$_3$ thin films grown at 600$^{\circ}$C on Fe-doped (010) bulk substrates exhibits remarkable crystalline quality which is evident from the measured room temperature Hall mobility of 186 cm$^2$/Vs for the unintentionally doped films. N-type doping is achieved by using Si as a dopant and controllable doping in the range of 2$\times$10$^{16}$ - 2$\times$10$^{19}$ cm$^{-3}$ is studied. Si incorporation and activation is studied by comparing silicon concentration from secondary ion mass spectroscopy (SIMS) and electron concentration from temperature-dependent Hall measurements. The films exhibit high purity (low C and H concentrations) with a very low concentration of compensating acceptors (2$\times$10$^{15}$ cm$^{-3}$) even at this growth temperature. Additionally, abrupt doping profile with forward decay of $\sim$ 5nm/dec (10 times improvement compared to what is observed for thin films grown at 810$^{\circ}$C) is demonstrated by growing at a lower temperature.

MOCVD Epitaxy of Ultrawide Bandgap β-(AlxGa1–x)2O3 with High-Al Composition on (100) β-Ga2O3 Substrates

Abstract: Single β-phase (100) (AlxGa1–x)2O3 thin films were successfully grown on (100) oriented β-Ga2O3 substrates via metalorganic chemical vapor deposition (MOCVD). By systematically tuning the precursor...

Growth of bulk GaN crystals

Abstract: Perspectives about growth of bulk gallium nitride crystals, fabricating high structural quality gallium nitride wafers and the market demand for them are presented. Three basic crystal growth technologies, halide vapor phase epitaxy, sodium flux, and ammonothermal, are described. Their advantages and disadvantages, recent development, and possibilities are discussed. The main difficulty with crystallization of thick GaN is determined. Some new solutions for bulk growth are proposed. It is shown that only crystallization on high structural quality native seeds will ensure proper progress. New ideas for fabricating gallium nitride crystals and wafers with a better control of their structural properties and point defect concentration are proposed.

Step flow growth of β-Ga2O3 thin films on vicinal (100) β-Ga2O3 substrates grown by MOVPE

Abstract: Homoepitaxial (100) β-Ga2O3 films were grown on substrates with miscut angles of 2°, 4°, and 6° toward [00 1 ¯] by metal organic vapor phase epitaxy. Step-flow growth mode, resulting in smooth film surfaces and high crystalline quality, could only be achieved if the diffusion length on the film surface corresponds approximately to the width of the terraces. Otherwise, 2D islands or step-bunching is obtained, which results in a deteriorated crystalline quality and reduced Hall mobility of the electrons. By varying the growth parameters such as the O2/Ga ratio, Ar push gas flow, and chamber pressure, the diffusion length could be adjusted so that step-flow growth mode could be achieved at all miscut angles. Furthermore, the growth rate could remarkably be increased from 1.6 nm/min to 4.3 nm/min. For homoepitaxial β-Ga2O3 films grown in step-flow growth mode, TEM measurements revealed a high crystalline quality, which is correlated with a high Hall mobility of 131 cm2/V s at a carrier concentration of 1.6 × 1017cm−3, which is comparable with β-Ga2O3 single crystal bulk values. This study clearly points out the high potential of β-Ga2O3 films for high performance MOSFETs if the influence of the deposition parameters on the structural and electrical properties is well understood.

Improved performance of UVC-LEDs by combination of high-temperature annealing and epitaxially laterally overgrown AlN/sapphire

Abstract: We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) emitting at 265 nm grown on stripe-patterned high-temperature annealed (HTA) epitaxially laterally overgrown (ELO) aluminium nitride (AlN)/sapphire templates. For this purpose, the structural and electro-optical properties of ultraviolet-c light-emitting diodes (UVC-LEDs) on as-grown and on HTA planar AlN/sapphire as well as ELO AlN/sapphire with and without HTA are investigated and compared. Cathodoluminescence measurements reveal dark spot densities of 3.5×109 cm−2, 1.1×109 cm−2, 1.4×109 cm−2, and 0.9×109 cm−2 in multiple quantum well samples on as-grown planar AlN/sapphire, HTA planar AlN/sapphire, ELO AlN/sapphire, and HTA ELO AlN/sapphire, respectively, and are consistent with the threading dislocation densities determined by transmission electron microscopy (TEM) and high-resolution X-ray diffraction rocking curve. The UVC-LED performance improves with the reduction of the threading dislocation densities (TDDs). The output powers (measured on-wafer in cw operation at 20 mA) of the UV-LEDs emitting at 265 nm were 0.03 mW (planar AlN/sapphire), 0.8 mW (planar HTA AlN/sapphire), 0.9 mW (ELO AlN/sapphire), and 1.1 mW (HTA ELO AlN/sapphire), respectively. Furthermore, Monte Carlo ray-tracing simulations showed a 15% increase in light-extraction efficiency due to the voids formed in the ELO process. These results demonstrate that HTA ELO AlN/sapphire templates provide a viable approach to increase the efficiency of UV-LEDs, improving both the internal quantum efficiency and the light-extraction efficiency.

HVPE Growth and Characterization of ε-Ga2O3 Films on Various Substrates

Abstract: In this study we compare the growth of gallium oxide films by halide vapor phase epitaxy (HVPE) on various substrates under the same growth conditions. Gallium oxide films were deposited at 500 °C–600 °C on basal plane (0001) planar and patterned sapphire substrates, (0001) 2H-GaN, 4H-SiC, and bulk β-Ga2O3 substrates. The layers were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and cathodoluminescence (CL) techniques. Most of the films exhibit growth features of hexagonal symmetry. Sn-doped Ga2O3 films exhibit n-type electrical conductivity. Heterojunctions composed of n-type hexagonal Ga2O3:Sn and p-type GaN:Mg demonstrate diode-like I-V characteristics and emit light under forward bias.

Low temperature homoepitaxy of (010) β-Ga2O3 by metalorganic vapor phase epitaxy: Expanding the growth window

Abstract: In this work, we report on the growth of high-mobility β-Ga2O3 homoepitaxial thin films grown at a temperature much lower than the conventional growth temperature window for metalorganic vapor phase epitaxy. Low-temperature β-Ga2O3 thin films grown at 600 °C on Fe-doped (010) bulk substrates exhibit remarkable crystalline quality, which is evident from the measured room temperature Hall mobility of 186 cm2/V s for the unintentionally doped films. N-type doping is achieved by using Si as a dopant, and a controllable doping in the range of 2 × 1016–2 × 1019 cm−3 is studied. Si incorporation and activation is studied by comparing the silicon concentration from secondary ion mass spectroscopy and the electron concentration from temperature-dependent Hall measurements. The films exhibit high purity (low C and H concentrations) with a very low concentration of compensating acceptors (2 × 1015 cm−3) even at this growth temperature. Additionally, an abrupt doping profile with a forward decay of ∼ 5 nm/dec (10 times improvement compared to what is observed for thin films grown at 810 °C) is demonstrated by growing at a lower temperature.

Sn doping of (010) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy

Abstract: Sn doping of (010) β-Ga2O3 grown by conventional plasma-assisted molecular beam epitaxy (PAMBE) and via metal oxide catalyzed epitaxy (MOCATAXY) using a supplied indium flux during molecular beam epitaxy (MBE) growth was investigated. While high Sn concentrations were achievable over a range of growth conditions in conventional PAMBE, Sn doping less than 1019 cm−3 resulted in non-uniform doping profiles for constant Sn cell temperatures, as well as run-to-run variation in doping. Sn doping in MOCATAXY grown β-Ga2O3 allowed for sharp doping profiles and a wide range of donor concentrations from 3.9 × 1016 cm−3 to 2 × 1019 cm−3 and a maximum room temperature Hall mobility of 136 cm2/V s at 3.9 × 1016 cm−3. From temperature-dependent Hall measurements, Sn was found to have a relatively deep donor state at 77 meV below the conduction band edge. The samples showed low electron mobility at cryogenic temperatures, suggesting the existence of high background impurity levels in the MBE grown films and the need for impurity control in the oxide MBE growth environment.

Suppression of dislocation-induced spiral hillocks in MOVPE-grown AlGaN on face-to-face annealed sputter-deposited AlN template

Abstract: AlGaN films were grown on face-to-face annealed sputter-deposited AlN/sapphire (FFA Sp-AlN) templates via metalorganic vapor phase epitaxy (MOVPE), and the growth behavior of the AlGaN films was investigated. The sapphire substrates with small off-cut exhibited poor surface flatness of AlGaN grown on the FFA Sp-AlN templates owing to the formation of large hillock structures. To understand the origin of these hillock structures, the crystallinity and surface morphology of conventional fully MOVPE-grown AlN/sapphire (MOVPE-AlN) templates and the FFA Sp-AlN template were comprehensively studied. The screw- and mixed-type threading dislocation density of the FFA Sp-AlN template was estimated to be approximately 1.8 × 106 cm−2, which was two orders of magnitude lower than that of the MOVPE-AlN template. Consequently, the uniquely observed growth of the hillock structures in the FFA Sp-AlN templates was attributed to their low density of screw- and mixed-type threading dislocations. The large surface off-cut sapphire substrates suppressed the hillock structures on the FFA Sp-AlN templates. The improvement in surface flatness resulted in better optical properties of multiple quantum wells grown on the AlGaN layer. These results demonstrate a promising method for achieving highly efficient and cost effective AlGaN based deep ultraviolet light-emitting diodes.

Delta-doped β-Ga2O3 thin films and β-(Al0.26Ga0.74)2O3/β-Ga2O3 heterostructures grown by metalorganic vapor-phase epitaxy

Abstract: We report on the silicon delta doping of metalorganic vapor-phase epitaxy grown β-Ga2O3 thin films using silane as a precursor. The delta-doped β-Ga2O3 epitaxial films are characterized using capacitance–voltage profiling and secondary-ion mass spectroscopy. The sheet charge density is in the range of 2.9 × 1012 cm−2 to 9 × 1012 cm−2 with an HWHM (towards the substrate) ranging from 3.5 nm to 6.2 nm. We also demonstrate a high-density (n s: 6.4 × 1012 cm−2) degenerate electron sheet charge in a delta-doped β-(Al0.26Ga0.74)2O3/β-Ga2O3 heterostructure. The total charge could also include a contribution from a parallel channel in the β-(Al0.26Ga0.74)2O3 alloy barrier.

Molecular beam epitaxy and characterization of wurtzite ScxAl1−xN

Abstract: We demonstrate the growth of pure wurtzite phase ScxAl1−xN with a Sc composition as high as x = 0.34 on GaN and AlN templates using plasma-assisted molecular beam epitaxy. The wurtzite structure is well maintained even at high growth temperatures up to 900 °C for Sc0.2Al0.8N. Smooth surface morphology (root mean square roughness less than 1 nm) and excellent crystal quality [(002) plane rocking curve full-width at half maximum below 450 arc sec] are achieved over the range of x ≤ 0.34. Optical absorption studies indicate a decreasing bandgap with increasing Sc with a linear relationship of Eg(x) = 6.1 − 3.39x, which is in good agreement with the theoretical prediction. A monotonically tunable refractive index between AlN and GaN is further measured for ScxAl1−xN with various Sc compositions. This work provides a viable path for the epitaxy of wurtzite ScxAl1−xN with high Sc compositions. The distinct effect of substitutional Sc on bandgap and refractive index could be used in designing high-performance optoelectronic, electronic, and piezoelectric devices, and III-nitride integrated photonics and optical cavities.

Oxidized Si terminated diamond and its MOSFET operation with SiO2 gate insulator

Abstract: During selective epitaxial growth of diamond through SiO2 masks, silicon terminations were formed on a diamond surface by replacing oxygen terminations under the masks. The high temperature of selective growth and its reductive atmosphere possibly allowed Si atoms in SiO2 to interact with the diamond surface, resulting in silicon terminated diamond (C–Si diamond) composed of a monolayer or thin multi-layers of carbon and silicon bonds on diamond. Diamond metal oxide semiconductor field effect transistors (MOSFETs), with a C–Si diamond channel and selectively grown undoped or heavily boron-doped (p+) source/drain (S/D) layers, have been fabricated. Both the MOSFETs with undoped and p+ S/D exhibited enhancement mode (normally off) FET characteristics. The drain current (IDS) of the undoped device reached −17 mA/mm with threshold voltage (VT) −19 V; the p+ device attained a high IDS −165 mA/mm with a VT of −6 V being one of the best normally off diamond FETs. Transmission electron microscopy and energy dispersive x-ray spectroscopy confirmed the presence of C–Si diamond under the SiO2 masking area. The field effect mobility and interface state density at the C–Si/SiO2 (220 nm)/Al2O3 (100 nm) MOS capacitor are 102 cm2 V−1 s−1 and 4.6 × 1012 cm−2 eV−1, respectively. The MOSFET operation of C–Si diamond provides an alternative approach for diamond.

Mg acceptor doping in MOCVD (010) β-Ga2O3

Abstract: In this Letter, in situ Mg doping in β-Ga2O3 was demonstrated via metalorganic chemical vapor deposition (MOCVD) epitaxy. The electrical insulating property of the Mg acceptors in β-Ga2O3 was found to be intrinsically activated in the as-grown Mg-doped β-Ga2O3 thin films. Growth conditions for MOCVD β-Ga2O3 were further explored and optimized at a lower growth temperature regime, leading to a better confinement of the Mg-doping profile. Detailed analysis of Mg diffusion characteristics revealed a diffusion barrier energy Ebarrier ∼ 0.9 eV for Mg in MOCVD β-Ga2O3, which is likely related to an interstitial-assisted process. Surface morphologies and electron transport were characterized on samples grown with different growth temperatures and Mg doping levels. The MOCVD growth method demonstrated its feasibility to grow semi-insulating Mg-doped β-Ga2O3 epilayers with controllable Mg incorporation while maintaining good material quality and smooth surface morphology. From capacitance-voltage charge profiling, it is verified that the Mg-doped buffer layer grown at the substrate-epilayer interface could effectively compensate the charge accumulation at the interface. The in situ acceptor doping of Mg in MOCVD β-Ga2O3 will provide versatility for designing β-Ga2O3 power devices.

Homo-epitaxial growth of n-GaN layers free from carbon-induced mobility collapse and off-angle-dependent doping variation by quartz-free hydride vapor phase epitaxy

Abstract: Certain undesired phenomena are observed in n-GaN layers grown by metal–organic chemical vapor deposition (MOCVD) due to the unavoidable C-induced carrier compensation. They are a drastic reduction in carrier mobility, called mobility collapse, and significant non-uniformity in the carrier concentration due to the off-angle dependence of the C-incorporation efficiency of the process. These phenomena are particularly severe for low doping levels between 1015 and 1016/cm3, which are suitable for fabricating drift layers used in vertical-type GaN power devices that operate in the range of a few kilovolts to tens of kilovolts. However, the C-related undesired characteristics are absent in homo-epitaxial n-GaN layers grown by quartz-free hydride vapor phase epitaxy (QF-HVPE), recently developed by us. The utilization of C-free raw materials alongside quartz-free parts enables the growth of highly pure GaN crystals with negligible Si, C, and O incorporations. These crystals exhibited an electron concentration in the low-1015/cm3 range with the highest reported room temperature electron mobility, μ, of 1470 cm2/V s among GaN crystals, whereas n-GaN layers with similar carrier concentrations but containing C-compensation, as in the case of those grown by MOCVD, exhibited a severe mobility collapse (μ = 288 cm2/V s). High uniformity in the carrier concentration with a small standard deviation of 4.0% was observed in a 2-in. n-GaN wafer grown by QF-HVPE on a GaN substrate with an off-angle variation of 0.3°. On the other hand, the standard deviation of the carrier concentration in wafers grown by MOCVD was approximately 17% because of the off-angle-dependent C-incorporation.

Crystalline Interlayers for Reducing the Effective Thermal Boundary Resistance in GaN-on-Diamond.

Abstract: Integrating diamond with GaN high electron mobility transistors (HEMTs) improves thermal management, ultimately increasing the reliability and performance of high-power high-frequency radio frequency amplifiers. Conventionally, an amorphous interlayer is used before growing polycrystalline diamond onto GaN in these devices. This layer contributes significantly to the effective thermal boundary resistance (TBReff) between the GaN HEMT and the diamond, reducing the benefit of the diamond heat spreader. Replacing the amorphous interlayer with a higher thermal conductivity crystalline material would reduce TBReff and help to enable the full potential of GaN-on-diamond devices. In this work, a crystalline Al0.32Ga0.68N interlayer has been integrated into a GaN/AlGaN HEMT device epitaxy. Two samples were studied, one with diamond grown directly on the AlGaN interlayer and another incorporating a thin crystalline SiC layer between AlGaN and diamond. The TBReff, measured using transient thermoreflectance, was improved for the sample with SiC (30 ± 5 m2 K GW–1) compared to the sample without (107 ± 44 m2 K GW–1). The reduced TBReff is thought to arise from improved adhesion between SiC and the diamond compared to the diamond directly on AlGaN because of an increased propensity for carbide bond formation between SiC and the diamond. The stronger carbide bonds aid transmission of phonons across the interface, improving heat transport.

Metal oxide catalyzed epitaxy (MOCATAXY) of β-Ga2O3 films in various orientations grown by plasma-assisted molecular beam epitaxy

Abstract: In this work, the growth of (010), (001), and 2¯01 β-Ga2O3 by plasma assisted molecular beam epitaxy was investigated. The presence of an indium flux during growth markedly expands the growth regime for β-Ga2O3 across all orientations to higher growth temperatures and growth rates. This metal oxide catalyzed growth allows for similar growth rates of around 5 nm/min across all three orientations, more than twice that of conventional (010) growth and seven times that of (001) growth without indium. Smooth surface morphologies for (010) and (001) β-Ga2O3 were demonstrated, while 2¯01 was significantly rougher. Additionally, doping with Sn was achieved across all orientations and Hall measurements demonstrated higher electron mobility (55 cm2/Vs for a carrier concentration of 3.3 × 1018 cm−3) for (001) β-Ga2O3 grown via metal oxide catalyzed epitaxy than conventional growth.

Growth of high-quality one-inch free-standing heteroepitaxial (001) diamond on (11 2 ¯0) sapphire substrate

Abstract: One-inch free-standing (001) diamond layers on a (11 2 ¯0) (a-plane) sapphire substrate with an Ir buffer layer (Kenzan Diamond®) were grown. The full-width at half maximum values of (004) and (311) x-ray rocking curves were 113.4 and 234.0 arc sec, respectively. The dislocation density of the substrates was 1.4 × 107 cm−2, determined by plan-view transmission electron microscopy observation. These values are much lower than the reported values among heteroepitaxial diamonds. Furthermore, x-ray pole figure measurements showed four symmetry of the crystal, showing single crystallinity without any twinning. The curvature radius of diamond was measured to be 90.6 cm, which is much larger than previous values, ca. 20 cm. Surprisingly, a cubic-lattice (001) diamond crystal was epitaxially grown on a trigonal-lattice (11 2 ¯0) sapphire substrate. However, we found that the epitaxial relation is diamond (001) [110]//Ir (001) [110]//sapphire (11 2 ¯0) [0001]. Now, high-quality one-inch diamond wafers will be available as a substrate used for diamond electronic devices.

Stabilization of phase-pure rhombohedral HfZrO4 in pulsed laser deposited thin films

Abstract: Controlling the crystalline structure of hafnium zirconate and its epitaxial relationship to a semiconducting electrode has high technological interest, as ferroelectric materials are key ingredients for emerging electronic devices. Using pulsed laser deposition, a phase-pure, ultrathin film of HfZrO4 is grown epitaxially on a GaN(0001)/Si(111) template. Since standard microscopy techniques do not allow us to determine with certitude the crystalline structure of the film due to the weak scattering of oxygen, differentiated differential phase contrast scanning transmission electron microscopy is used to allow the direct imaging of oxygen columns in the film. Combined with x-ray diffraction analysis, the polar nature and rhombohedral R3 symmetry of the film are demonstrated.

Epitaxial metals for interconnects beyond Cu

Abstract: Experimentally measured resistivity of Co(0001) and Ru(0001) single crystal thin films, grown on c-plane sapphire substrates, as a function of thickness is modeled using the semiclassical model of Fuchs–Sondheimer. The model fits show that the resistivity of Ru would cross below that for Co at a thickness of approximately 20 nm. For Ru films with thicknesses above 20 nm, transmission electron microscopy evidences threading and misfit dislocations, stacking faults, and deformation twins. Exposure of Co films to ambient air and the deposition of oxide layers of SiO2, MgO, Al2O3, and Cr2O3 on Ru degrade the surface specularity of the metallic layer. However, for the Ru films, annealing in a reducing ambient restores the surface specularity. Epitaxial electrochemical deposition of Co on epitaxially deposited Ru layers is used as an example to demonstrate the feasibility of generating epitaxial interconnects for back-end-of-line structures. An electron transport model based on a tight-binding approach is described, with Ru interconnects used as an example. The model allows conductivity to be computed for structures comprising large ensembles of atoms (105–106), scales linearly with system size, and can also incorporate defects.

Review of GaN Thin Film and Nanorod Growth Using Magnetron Sputter Epitaxy

Abstract: Magnetron sputter epitaxy (MSE) offers several advantages compared to alternative GaN epitaxy growth methods, including mature sputtering technology, the possibility for very large area deposition, and low-temperature growth of high-quality electronic-grade GaN. In this article, we review the basics of reactive sputtering for MSE growth of GaN using a liquid Ga target. Various target biasing schemes are discussed, including direct current (DC), radio frequency (RF), pulsed DC, and high-power impulse magnetron sputtering (HiPIMS). Examples are given for MSE-grown GaN thin films with material quality comparable to those grown using alternative methods such as molecular-beam epitaxy (MBE), metal–organic chemical vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE). In addition, successful GaN doping and the fabrication of practical devices have been demonstrated. Beyond the planar thin film form, MSE-grown GaN nanorods have also been demonstrated through self-assembled and selective area growth (SAG) method. With better understanding in process physics and improvements in material quality, MSE is expected to become an important technology for the growth of GaN.