Ex-situ Thermal Annealing Research Articles

Mitigation of ion-induced desorption for accelerator components by surface treatment and annealing

Ion-induced desorption is a serious limitation for beam intensity and life time in heavy ion accelerator facilities. To investigate how gas desorption is affected by surface conditions and bulk materials, oxygen-free copper, tungsten and aluminum samples were irradiated with 4.8 MeV/u Ca and Au ions. The surfaces were pretreated by various combinations of milling, lapping, polishing and etching, while the bulk is conditioned by thermal annealing. For all tested samples desorption yields of H2, H2O, CO and CO2 are presented. Diamond milling and polishing reduce ion-induced desorption to some extent, but most pronounced effects were achieved by ex-situ thermal annealing at 400 °C for about 4 h under ultra-high vacuum conditions. The decreased desorption persists for at least 9 months of storage in atmosphere. This is a strong indication that for the mitigation of desorption stimulated by high energy ion exposure, not only the surface properties have to be optimized, but also the treatment of the bulk material plays an important role. Storage of annealed samples in argon is favorable compared to storage in atmosphere.

Electronic surface, optical and electrical properties of p – GaN activated via in-situ MOCVD and ex-situ thermal annealing in InGaN/GaN LED

Electronic surface properties, optical and electrical characteristics of p-type Mg-doped Gallium Nitride (p-GaN) activated under different thermal annealing condition were investigated. In this work, p-GaN samples were subjected to in-situ and ex-situ thermal annealing process at 650 °C in Nitrogen (N2) rich condition. In-situ annealing process took place in Metal Oxide Chemical Vapor Deposition (MOCVD) chamber while ex-situ annealing process was carried out in the conventional oven. X-Ray and Ultraviolet Photoemission Spectroscopy (XPS/UPS) were used to observe the energy alignment of the p-GaN surface. From PES spectra, the sample subjected to in-situ thermal annealing shown to exhibit lower surface bend bending of 0.28 eV as compared to ex-situ thermal annealing activation with 0.45 eV band bending. This result is in agreement with specific contact resistance measurement that shows in-situ sample exhibits lower resistance resulted in better carrier injection from metal to p-GaN. Photoluminescence (PL) spectra elucidates that in-situ sample has a good surface quality with less nitrogen related vacancies (VN) formed on the p-GaN surface. All these results are further proved with the higher output power from LED with in-situ annealing. At 20 mA, in-situ sample shown an increment of ~14% light output power compared to ex-situ sample. Results obtained in this work suggest that the thermal activation condition for p-GaN activation process plays an active role on the surface quality as well as the energy alignment of the film surface and shows the potential of in-situ p-GaN activation for tunnel junction structure.

Ge-rich SiGe thin film deposition by co-sputtering in in-situ and ex-situ solid phase crystallization for photovoltaic applications

This study investigates the properties of high Ge content silicon-germanium thin films in the non-hydrogenated state (Ge-rich SiGe) deposited on glass by RF magnetron co-sputtering in both in-situ and ex-situ solid phase crystallization (SPC) at various temperatures, such as RT to 550°C. The structural and optical characteristics of SiGe films have been explored systematically by optimizing growth temperature. Atomic composition of films was determined by EDX, which showed up to 77at% of Ge. Structural properties were characterized by XRD, which revealed all samples to be in amorphous nature. The results from Raman and UV–VIS–IR transmittance measurements showed that the properties of amorphous Si0.23Ge0.77 films improved at 450°C in both in-situ and ex-situ SPC processes. In addition, EDX exposed an advantage of in-situ process over ex-situ due to the incorporation of oxygen during ex-situ thermal annealing. Possible deposition at low substrate temperature as found here suggests that these Si0.23Ge0.77 films have a substantial potential to be used in thin film Si-based solar cells.

Properties of a-SiGe Thin Films on Glass by Co-Sputtering for Photovoltaic Absorber Application.

Non-hydrogenated amorphous Silicon-Germanium (a-SiGe) thin films were deposited at two different base pressures by RF magnetron co-sputtering. Moreover, an ex-situ thermal annealing was carried out to investigate the material properties to be suitable as the bottom cell of multi-junction solar cells. Compositional study of the films using EDX showed Ge-rich thin films with 75 atomic% of Ge. XRD reflection study implied that all samples were entirely amorphous in nature. However, a significant improvement of morphology possibly due to low base pressure was observed while thermal annealing caused peening and reduction of surface inhomogeneity in both as-sputtered films. UV-VIS-IR analysis confirmed the FESEM results. The highest transmittance was observed in the as-deposited sample grown at 4 x 10(-5) Torr, which however reduced after thermal annealing. Tauc's model was implied for band gap determination and band gap energy as low as 1.07 eV was found in the annealed sample grown at lower base pressure (4 x 10(-6) Torr). Electrical properties of films were investigated by Hall effect measurement system and results found the reduction of resistivity with the same trend of optical band gap energy.

Film Texture, Hole Transport and Field-Effect Mobility in Polycrystalline SnO Thin Films on Glass

A p-type oxide semiconductor, tin monoxide (SnO), is expected for high-mobility p-channel oxide thin-film transistors. In this study, we fabricated polycrystalline SnO films by three methods based on pulsed laser deposition, direct deposition at high temperatures, in-situ thermal annealing without exposure to air, and ex-situ thermal annealing after exposure to air. It was found that the crystallite orientation depends largely on the fabrication methods; i.e., the direct deposition enhanced c-axis orientation in particular at higher temperatures, and the in-situ thermal annealing induced homogeneous nucleation of non-oriented crystallites at high temperatures. Further, ex-situ thermal annealing nucleated (101)-oriented crystallites due probably to surface contamination originating from air exposure. In-plane Hall mobility was related to the film texture; i.e., the c-axis oriented films exhibited higher hole mobilities in the a-b plane while the more (101)-oriented films exhibited lower mobilities. This observation was attributed to an intrinsic nature that heavier effective hole mass along the Γ-Z direction ([001] direction) than that of the Γ-M direction ([110] direction), originating from strong anisotropy of the layered crystal structure of SnO. The on-state currents of SnO TFTs fabricated by 300°C deposition or thermal annealing were explained qualitatively by the hole mobilities measured by Hall effect.

Characterization of the post-thermal annealing effect for p-GaAs/i-InGaAsN/n-GaAs hetero-junction solar cells

In this study, we demonstrated the fabrication and characterization of p-GaAs/i-InGaAsN/n-GaAs double hetero-junction solar cells (DHJSCs). The intrinsic InGaAsN absorption layer which is lattice-matched with GaAs substrates was grown by the metal-organic vapor phase epitaxy (MOVPE) system. The metal-organic sources used in the MOVPE growth induced unintentionally-doped carbon adatoms, and this in turn caused some carbon-related defects. This carbon pollution subsequently deteriorated the optical and electrical characteristics of the dilute nitride material. With ex-situ post-annealing being carried out in the furnace, it could not only modify the crystallinity of the InGaAsN material, but the deterioration in the performance of the dilute nitride solar cell due to the nitrogen incorporation could also be mitigated. After conducting the thermal annealing at 550°C for 1h in nitrogen ambience, the conversion efficiency of the DHJSCs was increased from 0.61% to 4.46% under Air Mass 1.5 Global (1000W/m2, AM1.5G) irradiance. The external quantum efficiency (EQE) spectrum further revealed that the efficiency of DHJSCs had been enhanced significantly owing to the crystalline improvement of the intrinsic InGaAsN absorption layer after the ex-situ post-thermal annealing was implemented. This improvement also led to a significant increase in the short-circuit current. The X-ray photoelectron spectroscopy (XPS) measurement result also showed that the ex-situ thermal annealing contributed to the improvement of crystal quality and the reduction of carbon related defects and clusters in the as-grown InGaAsN absorption layer.

Preparation of zinc tin oxide films by reactive magnetron sputtering of Zn on liquid Sn

Zn is sputter-deposited on melted Sn films by radio-frequency magnetron sputtering in oxidizing plasma. The samples present an absorption cut-off wavelength close to the one of ZnO, and an optical transparency higher than 50% in the visible range. Ex-situ thermal annealing improves visible transparency and produces a slight blue-shift in the optical bandgap. X-ray diffraction patterns show typical spectra due to polycrystalline ZnO with evidence of the presence of crystalline SnO, before annealing, and Zn 2SnO 4, after annealing. Rutherford Backscattering studies reveal the existence of a ZnO layer on top of an O-rich (Zn, Sn)O thin film. After optimal thermal treatment, electrical characterization exhibits carrier concentrations of 10 16–10 17 cm − 3 and mobilities of 20–80 cm 2 V − 1 s − 1 for the resulting (Zn, Sn)O n-type films.

分子線エピタキシー法によるＺｎＳ／ＺｎＯヘテロ接合の作製と界面反応

Molecular beam epitaxial growth of a wurtzite ZnS/ZnO heterostructure on a-plane sapphire substrate is reported. X-ray diffraction and cathodoluminescence measurements revealed the formation of a ZnOS alloy layer at the heterointerface. Bandgap bowing parameter for the ZnO-ZnS binary system was roughly estimated to be ∼4.1 eV using an intense visible emission from the interface layer. Such a large bowing is due to the difference in electronegativity between S and O atoms. It is also found that the visible emission peak was pronounced by an ex-situ thermal annealing due to the progress of alloying.