Post-growth Annealing Process Research Articles

Growth of droplet-free InSbBi on GaAs substrate

Indium antimonide bismide (InSbBi) has emerged as a highly promising material for long-wavelength infrared photodetection devices due to its unique small energy bandgap (<0.17 eV) compared to existing III–V compound semiconductors. Despite its potential, experimental studies on InSbBi are still incomplete and scarce. Furthermore, the challenges associated with incorporating Bi and producing high-quality, defect-free samples are yet to be adequately addressed. To tackle these issues, we systematically investigated the growth of InSbBi on a GaAs substrate in this study. We incorporated up to 3.4% of Bi into InSbBi material. Our research contributes significantly to the field by demonstrating a technique for growing high-quality InSbBi material with Bi content of up to 2.3%, which is free of droplets and features a smooth surface. We achieved this goal by dynamically adjusting the Sb flux, carefully controlling the interplay between the Bi flux and the growth temperature, and implementing a post-growth annealing process. Our work is crucial for developing InSbBi technology as it contributes to the understanding of the growth process and surface morphology of InSbBi. Moreover, our results provide a path toward producing high-quality InSbBi samples.

Energy Storage Properties of Sol-Gel-Processed SrTiO3 Films.

Dielectric films with a high energy storage density and a large breakdown strength are promising material candidates for pulsed power electrical and electronic applications. Perovskite-type dielectric SrTiO3 (STO) has demonstrated interesting properties desirable for capacitive energy storage, including a high dielectric constant, a wide bandgap and a size-induced paraelectric-to-ferroelectric transition. To pave a way toward large-scale production, STO film capacitors were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the sol-gel method in this paper, and their electrical properties including the energy storage performance were studied as a function of the annealing temperature in the postgrowth rapid thermal annealing (RTA) process. The appearance of a ferroelectric phase at a high annealing temperature of 750 °C was revealed by X-ray diffraction and electrical characterizations (ferroelectric P-E loop). However, this high dielectric constant phase came at the cost of a low breakdown strength and a large hysteresis loss, which are not desirable for the energy storage application. On the other hand, when the RTA process was performed at a low temperature of 550 °C, a poorly crystallized perovskite phase together with a substantial amount of impurity phases appeared, resulting in a low breakdown strength as well as a very low dielectric constant. It is revealed that the best energy storage performance, which corresponds to a large breakdown strength and a medium dielectric constant, is achieved in STO films annealed at 650 °C, which showed a large energy density of 55 J/cm3 and an outstanding energy efficiency of 94.7% (@ 6.5 MV/cm). These findings lay out the foundation for processing high-quality STO film capacitors via the manufacturing-friendly sol-gel method.

Performance Study of Virtual Frisch Grid CdZnTeSe Detectors

Nuclear detectors for x-ray and gamma-ray spectroscopy and imaging are a vital tool in many homeland security, medical imaging, astrophysics and other applications. Most of these applications require room-temperature operation due to the operational constraints imposed by a cryogenic cooling system. CdZnTe (CZT) has been the main material with the desired detection properties, and CZT crystals have been used commercially for three decades. However, CdZnTe still suffers from long-standing issues of high densities of performance-limiting intrinsic defects such as Te inclusions and networks of dislocation walls (sub-grain boundaries). A recently invented new quaternary material CdZnTeSe showed excellent material properties for radiation detection. The material was found to be free from dislocation networks, possess reduced Te inclusions, and have better compositional homogeneity. Virtual Frisch grid detectors were fabricated from crystals taken from a CdZnTeSe ingot that was grown by the traveling heater method. The detectors were fabricated from an as-grown ingot, bypassing the post-growth annealing process commonly practiced for industrial-grade CZT. The performances of the detectors were studied with different Frisch grid lengths using an amplifier shaping time ranging from 1–6 µs. The detectors showed high-quality spectroscopic performance with an as-measured energy resolution of ~1.1% at 662 keV for an optimum Frisch grid length of 3 mm. The charge collection was observed to enhance for longer Frisch grids.

Investigating the potential of AgZnO thin film composites for waste heat recovery using Seebeck data

In this paper, we have demonstrated the thermoelectric properties of Silver Zinc oxide (AgZnO) composite grown by thermal evaporation method. A mixture of Silver and Zinc powders with 1:4 ratio was evaporated on silicon substrate using a vacuum tube furnace. The grown composites were subjected to post growth annealing process at various temperatures ranging from 500 to 800 °C in a programmable muffle furnace. XRD data proved that the crystallinity of the annealed samples was improved because more and more oxygen atoms were able to fill the oxygen vacancy type defects in the host crystal of AgZnO. The observed structural behavior was also verified by Raman spectroscopy measurements. Seebeck measurements revealed a remarkable enhancement in the values of Seebeck coefficient (303–711 μV/°C) and electrical conductivity (17–176 S/cm) with annealing temperature. The high annealing temperature may cause an enhancement in the mobility of Ag atoms which resulted in the increase of Seebeck coefficient and electrical conductivity simultaneously.

Optimizing the thermoelectric properties of thermally evaporated AgSnO2 thin films by post growth annealing process

In this manuscript, we have studied the thermoelectric properties of Silver Tin Oxide thin films deposited by thermal evaporation method. Tube furnace was used to deposit thin films on silicon (100) substrate by evaporating a mixture of Silver (Ag) and Tin (Sn) having (1:1) ratio. The experimental conditions were set as: distance from source to substrate (5 cm), Evaporation temperature inside the tube furnace (1000 °C), flow rate of oxygen gas (120sccm) and evaporation time for deposition was set as 40 min. Furthermore, diffusion of oxygen and mobility of charge carriers was controlled by annealing the samples at various temperatures after successful growth. We have observed that the value of Seebeck coefficient was increased from 242 to 630 µV/oC by increasing the annealing temperature from 600 to 900 ° C. This behavior is due the fact that increasing annealing temperature causes the mobility of charge carriers increased due to which simultaneous enhancement in Seebeck coefficient and electrical conductivity is observed. The enhancement in the carrier mobility was demonstrated by the fact that extra oxygen atoms resulted in the generation of grain boundaries defects which block the slow moving carriers and only fast moving electrons are able to reach cold end of sample. XRD and Raman spectroscopy results confirmed the hexagonal structure of AgSnO2. XRD data further confirmed the degradation of crystal quality due to increase in annealing temperature. The morphology of as grown and annealed samples was observed with the help of SEM.

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

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.

Impact of In Situ Annealing Time on CdTe Polycrystalline Film and Device Performance

We studied the impact of in situ post-growth annealing process on cadmium telluride (CdTe) polycrystalline thin film in this work. Samples of different annealing times have been characterized by x-ray diffraction (XRD) and a scanning electron microscope (SEM). The optoelectronic properties of CdTe film were deeply studied with light I–V testing, external quantum efficiency (EQE) and photoluminescence (PL)/time-resolved photoluminescence (TRPL) measurements. It is found that the in situ post-growth annealing treatment has a great effect on cadmium sulfide (CdS)/CdTe intermixing as well as interface pinholes. Elementary correlations between annealing time, film and junction morphology, carrier lifetime and device performance were investigated, and the annealing time turns out to be crucial to CdTe device performance. Solar cells with CdTe polycrystalline thin film annealed in situ at 550°C/550°C for 10 min show the best performance. With the help of precisely controlled annealing time, better CdTe film microstructure and morphology can be realized after in situ post-growth annealing.

A novel blanket annealing process to achieve highly transparent and conducting Al doped ZnO thin films: Its mechanism and application in perovskite solar cells

Achievement of high conductivity by doping an oxide thin film while maintaining its high visible transparency remains a challenge in the field of materials science and technology. Here, we demonstrate a simple and novel technique to control compensating defects in Al doped ZnO (AZO) thin films involving a post-growth annealing process with Zn blanket. We also provide an in-depth understanding of the mechanism of achieving high conductivity. As low as 8.8 Ω/sq sheet resistance (resistivity 3.1 × 10−4 Ω cm) with 90% visible transmission value and wherefrom a figure of merit (FOM) value of 6.5 × 10−2 Ω−1 for a RF sputtered 350 nm AZO thin film can be achieved. Such very low sheet resistance has been attributed to a decrease in the number of compensating defects and lesser out diffusion of Zn in AZO. Application of the developed AZO film as conducting substrate has successfully been tested by fabricating perovskite solar cells on flexible Corning® Willow® Glass substrate. The present findings open up the possibility of enough high quality industrial-scale production of transparent conducting oxides (TCOs) bearing crucial significance from the perspective of transparent electrodes for solar cells.

Charge Density Wave States in 2H-MoTe2 Revealed by Scanning Tunneling Microscopy**Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0301003 and 2016YFA0300403, and the National Natural Science Foundation of China under Grant Nos 11521404, 11634009, U1632102, 11504230, 11674222, 11574202, 11674226, 11574201 and U1632272.

2H- and -phase monolayer MoTe2 films on highly oriented pyrolytic graphite are studied using scanning tunneling microscopy and spectroscopy (STM/STS). The phase transition of MoTe2 can be controlled by a post-growth annealing process, and the intermediate state during the phase transition is directly observed by STM. For 2H-MoTe2, inversion domain boundaries are presented as bright lines at high sample bias, but as dark lines at lower sample bias. The dI/dV mappings reveal the distinct distributions of electronic states between domain boundaries and interiors of domains. It should be noted that a 2 × 2 periodic structure is clearly discernable inside the domains, where the STS measurement shows a small dip of size ∼150 meV at the vicinity of the Fermi level, indicating that the 2 × 2 periodic structure may be an incommensurate charge density wave. Moreover, a 4 × 4 periodic structure appears in 2H-MoTe2 grown at a higher substrate temperature.

Effect of surface passivation by a low pressure and temperature environment-grown thermal oxide layer for multi-crystalline silicon solar cells

In this study, we show that the efficiency and carrier life time of multi-crystalline silicon solar cells were significantly improved by using a low pressure (20,000 Pa) and temperature (650 °C~750 °C) environment grown thermal oxide (TO) as the surface passivation layer. In this experiment, during the first stage, the oxidation process was done at 650 °C and a lower pressure of 20,000 Pa for 2 mins under the flow a gas mixture of N2/O2 in ratio of 2:1. In the second stage, a temperature of 750 °C was used at the same pressure for the post-growth annealing process under a pure N2 ambient for 25 mins. Consequently, conversion efficiency was significantly increased by 0.55% with the surface passivation layer grown by low pressure and temperature TO process. The sheet resistance, carrier lifetime, internal quantum efficiency (IQE), increased by 6.32 Ω/sq., 22.18 μs, 4.33%, respectively, and the average reflection was reduced of 0.62%. Thus, the low pressure and temperature thermal oxidation process was an efficient way to increase the efficiency of the multi-crystalline silicon solar cells.

Correlation between defect-related photoluminescence emission and anomalous Raman peaks in N-Al co-doped ZnO thin films

The origins of defect-related photoluminescence (PL) and anomalous Raman peaks in N-doped ZnO are poorly understood. These features may be related to defects that control p-type conduction in N-doped and N-Al co-doped ZnO (AZO) films. In this study, we investigate the effects of introducing N2 gas during film deposition or a post-growth annealing process on crystallinity and defects in AZO films. A clear correlation between interstitial Zn (Zni)-related PL emissions and Raman features is found. X-ray diffraction and Hall results revealed that N was incorporated into AZO films deposited in the presence of N2 (N-doped AZO), whereas films annealed in N2 gas (N2-annealed AZO) had improved crystallinity with no substitution of N2 at O sites [(N2)O] or N at O sites (NO). The Raman scattering and PL spectra results indicated that Zni-related vibration and emission were dominant in the N-doped AZO films. X-ray photoelectron spectroscopy showed increases and decreases in the binding energies of Zn 2p and O 1s states in N2-annealed and N-doped AZO films, respectively. Together, these results demonstrate that the presence of Zni donor defects may be stabilized by the formation of small clusters and/or caused by the presence of NO acceptor defects, preventing p-type conduction in N-doped AZO films.

Optical fingerprints of donors and acceptors in high-quality NH_3-doped ZnO films

In this article, the authors have studied the optical properties of the donor-like and acceptor-like defects in a batch of NH3-doped ZnO films with high crystalline quality. The donors and acceptors responsible for the low-temperature photoluminescence lines have been clearly revealed. The main form of the shallow donors has been determined as the Zni-NO complex. A few possibilities have been proposed for the shallow acceptors, including the (NH4)Zn, (N2)Zn, and VZn small clusters. The transition within the Frenkel pair (Zni-VZn) should be the origin for the green deep-level emission. The post-growth annealing process could change the amounts of the donors and acceptors. The shallow and deep acceptors tend to form at higher annealing temperatures while the shallow donors could be suppressed simultaneously. Possible mechanisms of how the annealing process affecting the defects formation have been also discussed.

Fabrication of particular structures of hexagonal boron nitride and boron–carbon–nitrogen layers by anisotropic etching

Anisotropic etching of hexagonal boron nitride (h-BN) and boron–carbon–nitrogen (BCN) basal plane can be an exciting platform to develop well-defined structures with interesting properties. Here, we developed an etching process of atomically thin h-BN and BCN layers to fabricate nanoribbons (NRs) and other distinct structures by annealing in H2 and Ar gas mixture. BCN and h-BN films are grown on Cu foil by chemical vapor deposition (CVD) using solid camphor and ammonia borane as carbon, nitrogen and boron source, respectively. Formation of micron size well-defined etched holes and NRs are obtained in both h-BN and BCN layers by the post growth annealing process. The etching process of h-BN and BCN basal plane to fabricate NRs and other structures with pronounced edges can open up new possibilities in 2D hybrid materials.

CoMn<sub>2</sub>O<sub>4</sub> 스피넬 박막의 합성과 후열처리가 박막의 물리적 특성에 미치는 영향

C), crystal structure became cleared accompanying achange of surface structure. In the temperature dependences of magnetization, phase transitions were observed at ~100 K for bothbefore and after post-growth treated samples which were not observed for the bulk. For both samples, ferromagnetic behaviors wereobserved above 100 K while it turned to ferrimagnetism at low temperature below 100 K. In particular, the ferrimagnetic behaviorbecame strong after the post-growth treatment. These results indicate that the post-growth annealing process plays an important role indetermining the physical properties of spinel CoMn

Effects of post-growth annealing in a CoFeB/MgO/CoFeB trilayer structure

CoFeB/MgO/CoFeB tri-layer thin-film stacks have been widely used in the design of STT-RAM devices as functional magnetic-tunnel-junction (MTJ) structures. The materials properties of the CoFeB and MgO layers, including composition and lattice quality, have been extensively researched from the stand point of optimizing for the best MTJ performance. On the other hand, post-growth annealing is required for the MTJ structure to acquire its functional property, i.e. its TMR performance. In this work, we have studied the various possible effects resulting from the post-growth annealing process. Specifically, we show that the post-growth annealing causes boron in the top and bottom CoFeB layers to migrate into the adjacent Ta layers as well as deterioration in lattice quality of the MgO layer. Furthermore, we evaluate other effects that could be possibly induced during the annealing process, including Ta diffusion and layer intermixing in the CoFeB/MgO/CoFeB tri-layer structure. The post-growth annealing causes little change in the Ta diffusion and the layer intermixing. These annealing effects were also evaluated with respect to variations in the MgO growth process; more specifically, an additional natural oxidation treatment during the MgO layer deposition and the insertion of a Fe layer before the MgO layer. Our results indicate that the addition of a natural oxidation process during the MgO deposition process and the insertion of a thin-layer of Fe before the MgO layer both lead to a reduction in the layer intermixing between the MgO and the CoFeB layer and to an improvement in MgO lattice quality. We also show that the post-growth annealing does not alter the beneficial effect of these MgO growth process modifications.

Post-Growth Laser Annealing for High-Performance Ge Photodiodes on Si

Near-infrared (NIR) laser light is used to irradiate Ge epitaxial layers on Si as a post-growth annealing process with a low thermal budget for high-performance photonic device applications. In contrast to ordinary furnace/lamp annealing, where both of Ge and Si are heated, NIR laser irradiation enables a preferential annealing of Ge layers due to the optical absorption selectively in Ge. Ge pin photodiodes on Si, fabricated applying a preferential annealing of Ge with an NIR laser (1.07 µm in wavelength), show a significant reduction of dark leakage current with keeping high photodetection efficiencies, resulting from the reduction of threading dislocation density in Ge. The results indicate that the NIR laser annealing is promising to incorporate the fabrication of Ge devices at the back end of line in the Si process.

In situ Raman characterization of CeO2 thin films sputtered on (1 1 1) Si in order to optimize the post growth annealing parameters

The purpose of this paper is to show the possibility for optimizing the post growth annealing process of CeO2 thin films sputtered on (111) Si by using in situ Raman characterization. In fact, the post growth annealing is an important step in the microelectronic process and consequently the studies, which permit to find the good annealing conditions, are time consuming because many annealing temperatures, many annealing times and many annealing atmospheres should be tested and characterized for each test. For these reasons, we propose to characterize the crystallinity of CeO2 thin films by in situ Raman spectroscopy during the post growth annealing. This original method permits to observe, in operando, the evolution of CeO2 thin film crystallinity versus the annealing temperature and/or the annealing time changes. In fact, the lowest Raman line broadening, which is related to an improvement in crystallinity of the CeO2 layer, has been obtained with an annealing performed at 900°C for 3h. So, the determination of the best annealing parameters is much faster with this method than with classical methods. To our knowledge, it is the first time that the optimization of post-annealing parameters by using in situ Raman characterization has been reported for thin films.

Annealing effect on the electrical and optical properties of Au/n-ZnO NWs Schottky diodes white LEDs

We report the post-growth heat treatment effect on the electrical and the optical properties of hydrothermally grown zinc oxide (ZnO) nanowires (NWs) Schottky white light emitting diodes (LEDs). It was found that there is a changed in the electroluminescence (EL) spectrum when post growth annealing process was performed at 600°C under nitrogen, oxygen and argon ambients. The EL spectrum for LEDs based on the as grown NWs show three bands red, green and blue centered at 724, 518 and 450nm respectively. All devices based on ZnO NWs annealed in oxygen (O2), nitrogen (N2) and argon (Ar) ambient show blue shift in the violet and the red emissions whereas a red shift is observed in the green emission compared to the as grown NWs based device. The color rendering index (CRI) and the correlated color temperature (CCT) of all LEDs were calculated to be in the range 78–91 and 2753–5122K, respectively. These results indicate that light from the LEDs can be tuned from cold white light to warm white light by post growth annealing.

Hg based II–VI compounds on non‐standard substrates

AbstractThe Army Research Laboratory (ARL) is pursuing scalable infrared (IR) material technologies to meet the growing need for large format arrays. A two pronged approach is being undertaken at ARL using II–VI semiconductor materials. The first encompasses the well developed IR material system HgCdTe but grown on large area, extremely lattice mismatched Si(112) substrates. To overcome the high dislocation density associated with the large mismatch within the as‐grown material, ARL has successfully pursued a postgrowth thermal cycle annealing (TCA) process to reduce the dislocation density by an order of magnitude. Current results show HgCdTe/Si material can consistently be achieved with dislocation density values on the order of 1 × 106 cm−2. The second approach involves developing HgCdSe material using lattice matched, large area, and commercially available III–V substrates, specifically GaSb. Preliminary results indicate that quality HgCdSe growth by molecular beam epitaxy (MBE) can be achieved and that the bandgap of the material can be controlled through the Cd/Se ratio of fluxes used during growth.

Power and gas pressure effects on properties of amorphous In–Ga–ZnO films by magnetron sputtering

Amorphous In–Ga–ZnO thin films were deposited on quartz glass substrate at room temperature utilizing radio frequency magnetron sputtering technique. Sputtering power and oxygen flow rate effects on the physical properties of the In–Ga–ZnO films were systematically investigated. It is shown the film deposition rate and the conductivity of the In–Ga–ZnO films increased with the sputtering power. The as-grown In–Ga–ZnO films deposited at 500 W exhibited the Hall mobility of 17.7 cm2/Vs. Average optical transmittance of the In–Ga–ZnO films is greater than 80% in the visible wavelength. The extracted optical band gap of the In–Ga–ZnO films increased from 3.06 to 3.46 eV with increasing the sputtering power. The electrical properties of the In–Ga–ZnO films are greatly dependent on the O2/Ar gas flow ratio and post-growth annealing process. Increasing oxygen flow rate converted the In–Ga–ZnO films from semiconducting to semi-insulating, but the resistivity of the films was significantly reduced after being annealed in vacuum. Both the as-grown and annealed In–Ga–ZnO films show n-type electrical conductivity.