Post-growth Annealing Temperature Research Articles

Post-growth tuning of detachable Ge membranes adhesion strength via porous Ge transformation

Post-growth tuning of detachable Ge membranes adhesion strength via porous Ge transformation

Engineering polar distortions in multiferroic Sr1−xBaxMnO3−δ thin films

The physical properties of perovskite oxide thin films are governed by the subtle interplay between chemical composition and crystal symmetry variations, which can be altered by epitaxial growth. In the case of perovskite-type multiferroic thin films, precise control of stoichiometry and epitaxial strain allows for gaining control over the ferroic properties through selective crystal distortions. Here, we demonstrate the chemical tailoring of the polar atomic displacements by tuning the stoichiometry of multiferroic Sr1−xBaxMnO3−δ (0 ≤ x ≤ 0.5) epitaxial thin films. A combination of x-ray diffraction and aberration-corrected scanning transmission electron microscopy enables unraveling the local polarization orientation at the nanoscale as a function of the film’s composition and induced crystalline structure. We demonstrate experimentally that the orientation of polarization is intimately linked to the Ba doping and O stoichiometry of the films and, with the biaxial strain induced by the substrate, it can be tuned either in-plane or out-of-plane with respect to the substrate by the appropriate choice of the post-growth annealing temperature and O2 atmosphere. This chemistry-mediated engineering of the polarization orientation of oxide thin films opens new venues for the design of functional multiferroic architectures and the exploration of novel physics and applications of ferroelectric textures with exotic topological properties.

A Novel 19$\sqrt {19} $ × 19$\sqrt {19} $ Superstructure in Epitaxially Grown 1T‐TaTe2

The spontaneous formation of electronic orders is a crucial element for understanding complex quantum states and engineering heterostructures in 2D materials. A novel × charge order in few-layer-thick 1T-TaTe2 transition metal dichalcogenide films grown by molecular beam epitaxy, which has not been realized, is report. The photoemission and scanning probe measurements demonstrate that monolayer 1T-TaTe2 exhibits a variety of metastable charge density wave orders, including the × superstructure, which can be selectively stabilized by controlling the post-growth annealing temperature. Moreover, it is found that only the × order persists in 1T-TaTe2 films thicker than a monolayer, up to 8 layers. The findings identify the previously unrealized novel electronic order in a much-studied transition metal dichalcogenide and provide a viable route to control it within the epitaxial growth process.

Magnetic domain structure of epitaxial Gd films grown on W(110)

We present a detailed real-space spin-polarized scanning tunneling microscopy (SP-STM) study of the magnetic domain structure of Gd(0001) films epitaxially grown on W(110). To find optimal preparation conditions, the influence of the substrate temperature during deposition and of the postgrowth annealing temperature was investigated. Our results show that the lowest density of surface defects, such as step edges as well as screw and edge dislocations, is obtained for room-temperature deposition and subsequent annealing at 900 K. SP-STM data reveal small-size magnetic domains at lower annealing temperatures, evidently caused by pinning at grain boundaries and other crystalline defects. The coverage-dependent magnetic domain structure of optimally prepared Gd films was systematically investigated. For low coverage up to about 80 atomic layers (AL), we observe $\ensuremath{\mu}\mathrm{m}$-size domains separated by domain walls which are oriented approximately along the $[1\overline{1}0]$ direction of the underlying W substrate. Above a critical film thickness ${\mathrm{\ensuremath{\Theta}}}_{\text{crit}}\ensuremath{\approx}(100\ifmmode\pm\else\textpm\fi{}20)$ AL, we identify stripe domains, indicative of a spin reorientation transition from in plane to out of plane. In agreement with existing models, the periodicity of the stripe domains increases the further the coverage exceeds ${\mathrm{\ensuremath{\Theta}}}_{\text{crit}}$. While the orientation of the stripe domains is homogeneous over large distances just above ${\mathrm{\ensuremath{\Theta}}}_{\text{crit}}$, we find a characteristic zigzag pattern at $\mathrm{\ensuremath{\Theta}}\ensuremath{\gtrsim}200$ AL and irregular stripe domains beyond 500 AL. Intermediate minima and maxima of the magnetic signal indicate the nucleation of branching domains. The results are discussed in terms of various contributions to the total magnetic energy, such as the magnetocrystalline, magnetostatic, and magnetoelastic energy density.

Effects of annealing temperature on a ZnO thin film-based ultraviolet photodetector

In this paper, the effects of annealing temperature on the performance of a ZnO thin film-based Metal-Semiconductor-Metal (MSM) type ultraviolet (UV) photodetector is reported. ZnO thin films were grown on a glass substrate using the Pulsed Filtered Cathodic Vacuum Arc Deposition (PFCVAD) technique at room temperature and after the deposition process the samples were annealed at 400, 450 and 550 °C in air condition to investigate the annealing effect on the structural, electrical, and optical properties of the photodetector. ZnO thin films which have grains in nanometer range has an increasing in the diameter of grains from 10.5 to 18.3 nm as a function of annealing temperature results in a red shift in the cut-off wavelength of the photodetector from 3.25 eV (381 nm) to 3.23 eV (383 nm). It is demonstrated that the sensitivity and the speed (rise/fall times) of the ZnO thin film based MSM photodetectors enhances with increasing post growth annealing temperature of ZnO thin film due to the increase in the absorption coefficient and the decrease of the total area of the grain boundaries due to the larger grain sizes formation in ZnO thin films with increasing thermal annealing temperature.

Successful growth of Zinc Nitride thin films by vacuum tube furnace using nitrogen as source gas

Abstract We have successfully grown Zn3N2 thin films using a simple and cost effective approach. Growth was achieved in a vacuum tube furnace by evaporating Zinc powder at 850 OC and flowing nitrogen gas into the tube at the rate of 150 sccm. After achieving evaporation temperature of 850 OC in the tube, nitrogen gas was filled in the vacuum tube having working pressure of 5 atm and then system was kept in the nitrogen environment for 1 h at a constant flow rate of 150 sccm. In order to grow quality thin films, a bunch of samples were grown by varying the various growth parameters during the growth process. The first batch of samples was grown using different source to substrate distances (21–25 cm with a step of 2 cm) and pieces of a representative sample were post growth annealed in a nitrogen environment in the temperature range 350–600 °C. The obtained Zn3N2 thin films were characterized by X-Ray Diffraction, UV/Vis spectroscopy and Scanning Electron Microscope (SEM). XRD data showed a strong peak at 36.60° which is related to the (400) plan of pure Zn3N2 for all samples along with some additional peaks due to Zn structure. The optimum values of source to substrate distance and post growth annealing temperature are found to be 23 cm and 600 °C respectively.

Comparison of Thermoelectric Properties of ZnO and ZnSnO Thin Films Grown on Si Substrate by Thermal Evaporation

In this manuscript, we compared the thermoelectric properties of ZnO and ZnSnO thin films grown on silicon (100) substrate. We have evaporated Zn and Sn+Zn metal powders were evaporated in vacuum tube furnace alternatively, under same experimental conditions for the growth of ZnO and ZTO respectively. After the deposition, these grown films were cut into pieces and post growth annealed at different annealing temperatures from 600oC to 800oC in the air using programmable muffle furnace. Seebeck and Hall data suggested that ZTO sample shows highest value of Seebeck coefficient, electrical conductivity and power factor as compared to the ZnO samples. It is also observed that the value of Seebeck coefficient showing an increasing trend for both of the samples as we increase the post growth annealing temperature. The higher thermoelectric properties for ZTO are due the presence of Sn atoms in ZnO structure. Tin dopants may generate secondary phases and/or enhanced the carrier mobility which might be the reason that ZTO has improved thermo-electric properties as compared to ZnO. XRD and Raman measurements were used to confirm the formation of ZTO. XRD data verified the hexagonal structure of ZnO but a slight red shift is observed for the case of ZTO samples. To further justify our argument, we have also performed Raman spectroscopy measurements which confirmed the presence of Sn elements in ZTO.

Low‐temperature‐grown gallium arsenide photoconductors with subpicosecond carrier lifetime and photoresponse reaching 25 mA/W under 1550 nm CW excitation

The authors show in this Letter that photoconductors based on GaAs grown at low temperatures can exhibit photoresponses as high as 25 mA/W under continuous-wave 1550-nm-wavelength illumination. It is achieved by using an optical Fabry–Perot cavity in order to improve the external quantum efficiency and by decreasing the post-growth annealing temperature down-to 450°C.

Properties of N-Type GaN Thin Film with Si-Ti Codoping on a Glass Substrate

In this study, n-type gallium nitride (GaN) films were fabricated by a silicon–titanium (Si-Ti) codoping sputtering technique with a zinc oxide (ZnO) buffer layer on amorphous glass substrates with different post-growth annealing temperatures for optimizing the GaN crystal quality. Si-Ti-codoped n-type GaN films that were thermally annealed at 400 °C had a low thin-film resistivity of 2.6 × 10−1 Ω-cm and a high electron concentration of 6.65 × 1019 cm−3, as determined through Hall measurement. X-ray diffraction (XRD) results revealed a high (002) XRD intensity with a narrow spectral line and a full width at half maximum (FWHM) value that indicated the superior crystal growth of a hexagonal structure of the GaN thin films. In addition, photoluminescence measurement results demonstrated a near-band-edge emission at 365 nm, indicating the crystal growth of GaN thin films on glass substrates. The Burstein–Moss effect was observed in the Tauc plot results, indicating that the Fermi level inside the conduction band moves upward and thus improves the n-type properties of the GaN thin film. X-ray photoelectron spectroscopy measurement results revealed that all atoms doped into the GaN film are present and that both Si and Ti atoms bond with N atoms.

Influence of α- and β-W phases on performance of SMR devices

Abstract Solidly mounted resonators (SMRs) rely on high-quality Bragg reflectors, for which tungsten has been used as the high acoustic impedance layer. It is unclear about the effects of tungsten phases on the acoustic performance of SMRs. In this study, high-quality flat layers of different phase structures of W (α-W and β-W) are obtained by changing the post-growth annealing temperature and magnetron sputtering parameters. Our results show that the α-W has higher Young's modulus and acoustic impedance (205 GPa and 63 kg/m2s) than β-W (170 GPa and 57 kg/m2s). These small differences result in amplified difference in acoustic performance of Bragg reflectors using tungsten (W) as their high-impedance layer. Our tests show that the SMR of α-W Bragg reflector has a higher return loss (18.4 dB) at around 2.75 GHz and higher quality factor (687) than that of β-W Bragg reflector (9.2 dB and 228, respectively).

Effect of thermal oxidation on the optical, electrical, and chemical properties of zinc nitride films grown by reactive magnetron sputtering

Abstract We have studied the effect of post growth annealing in oxygen ambient on the optical, chemical and electronic properties of zinc nitride thin films. The films were prepared by reactive radio frequency magnetron sputtering of zinc target in the presence of argon and nitrogen gasses at a substrate temperature of 300 °C. Post growth annealing was performed at annealing temperatures of 300, 400, 500, 600, and 700 °C in the oxygen environment to transform the zinc nitride films into p-type zinc oxide. Atomic force microscopy of the films reveal that surface roughness and grain size of the films are directly proportional to the post-growth annealing temperature. X-ray photoelectron spectroscopy of the films revealed that as-grown film has the highest intensity of nitrogen in the film whereas little nitrogen remains in the films that were annealed at 500 °C and higher temperatures. Films annealed at higher temperatures have lower carrier concentration but higher Hall mobility compared to the as-grown film and the films annealed at lower temperature. Moreover, as-grown film and the films annealed at lower temperature have n-type conductivity whereas films annealed at temperatures above 500 °C exhibit p-type conductivity. Films annealed at lower temperature have bandgap values closer to the zinc oxynitride but bandgap of the films annealed at higher temperatures have values close to the bandgap of zinc oxide. This indicates that post growth annealing of zinc nitride films at 500 °C in oxygen ambient transforms it into p-type zinc oxide.

Optimizing the electrical transport properties of ZnSnO thin films by post growth annealing in air

Abstract In this manuscript, we have successfully enhanced the thermoelectric properties of ZnSnO thin films by post growth annealing method. Thin films of ZnSnO were grown on Si substrate by evaporating the Zinc and Tin metal powders in the tube furnace. After growth, post growth annealing was performed in open environment using a temperature range of 600−800 °C. The XRD results confirmed the formation of hexagonal closed packed structure of ZnSnO and the crystanality was found to be improved with post growth annealing temperature. The vibrational mode of ZTO at 435 cm−1 was verified by Raman spectroscopy measurements along with other Raman active modes related to single crystal Si and SnO2 as well. Seebeck data demonstrated that the values of Seebeck coefficient were increased from 204 to 1032 μV/°C as the annealing temperature increased from 600 to 800 °C. This increasing behavior of Seebeck coefficient was related with the mobility enhancement of the charge carriers by post growth annealing process. The Hall data supported our argument that mobility of carrier increased with annealing temperature due to high thermal energy. The giant enhancement of Seebeck coefficient and power factor values makes this material a potential candidate for thermoelectric power generation applications in near future.

Control of the Urbach band tail and interband dephasing time with post-growth annealing in low-temperature-grown GaAs

Femtosecond four-wave mixing experiments on low-temperature-grown (LT-) GaAs for a range of post-growth annealing temperatures indicate that the Urbach band tail abruptly diminishes above 550°C due to the conversion of As-related point defects to As clusters and that the interband dephasing time is limited by scattering with As point defects for annealing temperatures below 550°C. In addition, we observe a complex interplay of polarization source terms associated with the exciton and Urbach band tail for annealing temperatures below 550°C. These experiments shed light on the carrier dynamics and ultrafast nonlinear optical properties of LT-GaAs.

Complimentary effects of annealing temperature on optimal tuning of functionalized carbon-V2O5 hybrid nanobelts for targeted dual applications in electrochromic and supercapacitor devices.

Herein, carbon nanosphere-decorated vanadium pentoxide (C@V2O5) hybrid nanobelts were grown via a single step hydrothermal route with improved electronic conductivity as compared to that of pristine oxide. This hybrid nanomaterial exhibits different complimentary ranges of optimum post-growth annealing temperatures, which are suitable for dual applications either in electro-chromic smart windows or in supercapacitors. C@V2O5 nanobelts annealed at 350 °C appear to favor electro-chromic applications. They exhibit maximum dynamic optical transmission modulation as they switch from yellow to dark green, fast switching response, and high visible transmittance. In contrast, C@V2O5nanobelts annealed at 250 °C have been found to be most suitable for supercapacitor applications. They display a high specific capacity and an enhanced diffusion coefficient. Moreover, they exhibit long lifetimes with a capacity retention of ∼94% even after 5000 cycles of operation. Therefore, the obtained results clearly indicate that optimization of the post-growth annealing temperatures is very important and rather complementary in nature in terms of determining the most favorable device functionalities. It enables us to optimally tune these hybrid nanomaterials for targeted, device-specific, energy applications in either electrochromic or supercapacitor technologies simply based on the annealing temperature alone.

Optical absorption and thermal conductivity of GaAsPN absorbers grown on GaP in view of their use in multijunction solar cells

The optical absorption and thermal conductivity of GaAsPN absorbers are investigated by means of optical absorption spectroscopy and photo-thermal deflection spectroscopy (PDS) for different 100 nm-thick GaAsNP/GaP samples under different growth conditions and various post-growth annealing temperatures. It is first shown that the As content strongly modifies the optical absorption spectrum of the GaAsPN: with a maximum absorption coefficient of 38,000 cm A 1 below the GaP bandgap energy. The optical absorption and thermal conductivities of the samples are then evaluated for various growth and annealing conditions using PDS: the results showing overall agreement with optical absorption spec-troscopy measurements. A significant improvement in optical absorption and thermal conductivity after annealing is demonstrated. The best thermal conductivity measured is equal to 4 W/m K. These results are promising for the development of absorbers in multijunction solar-cell architecture.

Strain relaxation of thin Ge films on Si(001) grown by carbon-mediated epitaxy

Strain relaxation of thin Ge layers grown by carbon-mediated epitaxy at 50 °C on Si(001) was investigated for a multi-step growth procedure. Additionally, the impact of the post-growth annealing temperature on the strain relaxation obtained for a single carbon-mediated growth step was analyzed. The degree of relaxation was monitored in situ by reflection high energy electron diffraction and ex situ by high-resolution x-ray diffraction and transmission electron microscopy. For multi-step growth, relaxation occurs mainly during the first cycle (growth and annealing). Full relaxation is already achieved after 3–4 cycles. The relaxation process during a single growth cycle can be divided into three sections: annealing up to 200 °C is sufficient to trigger most of the strain relaxation. After annealing up to 450 °C, the film lattice parameter already equals the Ge bulk value, though the layer shows a rough surface. Only an annealing step up to 650 °C results in a smooth surface and interface. Smooth and fully relaxed Ge films of only 26 nm thicknesses were obtained by carbon-mediated growth.

Effects of annealing and deposition temperature on the structural and optical properties of AZO thin films

Al-doped ZnO (AZO) thin films were deposited on p- type Si(100) substrate by r.f magnetron sputtering at 200, 300 and 400 °C substrate temperatures. The deposited films were annealed in air atmosphere for 1 h at temperatures of 700, 800 and 900 °C. The deposition temperature and post-deposition annealing effects on structural and optical properties of the AZO samples were analyzed using X-ray diffraction, atomic force microscope and photoluminescence (PL). After annealing, the value of full width half maximum of the diffraction peaks was decreased as well as, the intensity of visible and strong UV PL emission peaks were increased with temperature. However, the deep-level emission related with zinc point defects was removed by annealing of the samples. Results revealed that all of the as-deposited and annealed AZO films have hexagonal structure along (002) direction and their crystallinity were improved with the increased deposition and post-growth annealing temperatures. In addition, the surface roughness and the particle size of the films were increased with increased deposition and annealing temperatures.

Characterization of low temperature InGaAs-InAlAs semiconductor photo mixers at 1.55 μm wavelength illumination for terahertz generation and detection

The structural, optical, and electrical properties of undoped and Be doped lattice matched InGaAs–InAlAs multiple quantum well structures, grown by molecular beam epitaxy (MBE) at low (∼250 °C) and normal (∼450 °C) growth temperatures, have been investigated in detail. Double crystal x-ray diffraction studies showed that the thickness of the low temperature (LT) grown quantum well (QW) layers decrease with post growth annealing, while the normal temperature grown QW layers retain their initial thickness. This behaviour is associated with the As precipitation and is the first evidence and report of a direct observation of this phenomenon in LT InGaAs–InAlAs QWs. Room temperature photoluminescence (PL) measurements revealed signs of optical activities in the LT undoped and lower doped structures suggesting that the native defects in LT InGaAs–InAlAs are not sufficient to completely inhibit band to band recombination. Optimal combination of doping, including a modulation doped structure, and post growth annealing temperature results in materials with sub-picoseconds lifetimes (<200 fs) and a resistivity of ∼107 Ω/sq, which is a high value for this material. The results imply the possibility of fabricating efficient photo-mixers operating at the telecom wavelength of 1.55 μm for THz imaging or other optoelectronic applications.

Tensile strained Ge quantum wells on Si substrate: Post-growth annealing versus low temperature re-growth

Abstract We investigate tensile strained Ge/Si 1 − x Ge x ( x = 0.87) multiple quantum wells (MQW) on a Ge virtual substrate abruptly grown on Si for integration in CMOS technology. Two schemes are discussed – Scheme A in situ growth of the MQW stack combined with post-growth rapid thermal annealing (RTA) and Scheme B re-growth of the MQW stack on an RTA strain optimized Ge-VS. Samples are characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning transmission electron microscopy, Brewster transmission and photo-reflectance spectroscopy. The strain in the as-grown virtual substrate of Scheme A , measured with Raman spectroscopy and XRD, increases from 0.17% to 0.24% after RTA to 850 °C. XRD reveals an activated inter-diffusion of the MQWs and, at the highest temperatures ( T RTA > 750 °C), a structural relaxation. The MQWs of Scheme B appear to be of inferior quality. The inter-band transitions in this material are comparatively blue shifted and broad, which is attributed to relaxation induced dislocations at the interface between the virtual substrate and the multiple quantum wells.

Morphology and Magneto-optical Properties of Amorphous AlN Films Doped with Nickel

ABSTRACTStructural and magneto-optical properties of Ni-doped amorphous AlN layers (a-AlN) deposited by radio frequency (rf) sputtering on Silicon (001) substrates were investigated. The as-grown material exhibits weak ferromagnetic behavior as evidenced by the magneto-optic Kerr effect (MOKE) measurement with Kerr rotation less than 100 μrad at room temperature regardless of the Ni fraction. The samples with a Ni concentration below 10 at.% show a weak but monotonically increasing MOKE signal with post-growth annealing temperature. A hundred-fold increase in the Kerr rotation value was observed for samples with Ni content exceeding 20 at.% after thermal annealing at 450°C in nitrogen; and the Kerr rotation value abruptly decreases above that temperature. The morphology of as-grown and annealed a-AlN:Ni films were characterized by small angle x-ray scattering and transmission electron microscopy. It was found that the as-deposited film contains nano-particles of different sizes with average diameters less than 30 nm. The size distribution of nano-particles in the thermally annealed a-AlN:Ni was studied as a function of annealing time and temperature. The results correlate well with those obtained from the MOKE measurements.