CdS films are used as window layers in CdS/CdTe solar cells, and an annealing process is required to promote grain growth and recrystallization in them. However, when annealing is performed in an air atmosphere, oxides such as CdO and CdSO₄ form on parts of the layer’s surface, which reduces the shunt resistance and the fill factor and results in poor device performance. In this study, we annealed the CdS film in a CdCl₂ atmosphere instead of air. Then, CdCl₂ annealing and air annealing were compared by investigating the structural and the electrical properties of the CdS window layers. Our results reveal that the CdCl₂ annealing protects the CdS film from oxidation and provides good recrystallization conditions. We also found that this CdCl₂ annealing enhance the device’s performance. In particular, considerably higher shunt resistance and conversion efficiency were obtained for the CdCl₂-annealed device compared with the air-annealed device.

We compared thermal stability, open-circuit voltage, short-circuit current, and fill factor values of single-crystal Cadmium telluride (CdTe) grown using the vertical Bridgman (VB) technique and doped with group V elements (phosphorus and arsenic), and group Ⅰ element (sodium), followed by an annealing process. The sodium-doped CdTe maintained a hole density of 10¹⁶ cm⁻³ or higher; after annealing for a long time, this decreased to 10¹⁵ cm⁻³ or less. The arsenic-doped CdTe maintained a hole density of approximately 10¹⁶ cm⁻³ even after the annealing process; however its bulk minority carrier lifetime decreased by approximately 10%. The phosphorus-doped CdTe maintained its properties after the annealing process, ultimately achieving a hole density of ~10¹⁶ cm⁻³ and a minority carrier lifetime of ~40 ns. The characteristics of a single-crystal solar cell were evaluated using a solar cell device that contained single-crystal CdTe with various dopants. The sodium-doped sample exhibited poor interfacial properties, and its performance decreased rapidly during annealing. The samples doped with group V elements exhibited stable characteristics even during long-term annealing. We concluded, therefore, that group V elements dopants are more suitable for CdTe single-crystal-based solar cell applications involving thermal stress conditions, such as space missions or extreme fabrication temperature environments.

In CdS/CdTe solar cells, Cu is added during the formation of the metallic electrode to enhance the contact properties and achieve an appropriate hole concentration in the cadmium telluride (CdTe) layer. In this study, we added Cu to CdS/CdTe solar cells using two different electrode materials: metallic Cu and Cu₂Te layers. They were deposited on the CdTe surface in the CdS/CdTe solar cells, and subsequent annealing was carried out to form a single-phase copper telluride compound. The devices made by these two materials were comparatively investigated in terms of their contact properties such as barrier height, hole density, and contact resistance. Most of the data indicate that the Cu₂Te-deposited cell is superior to the Cu-deposited cell. Furthermore, we obtained an optimum annealing condition for the Cu₂Te process, at which the cell performance is maximized. These results demonstrate the excellence of the Cu₂Te material and provide practical information about the processing technique of this material.

In the field of spintronics, charge-to-spin conversion without a ferromagnetic material has attracted intense interest from researchers seeking to realize a fully electrical spin device because this design obviates the need for magnetic field control of magnetization. Instead of spin injection from a ferromagnetic source, spin-Hall-induced pure spin current has recently attracted considerable interest for transferring spin information into the semiconductor channel. In the present work, the spin is injected from a platinum electrode via the direct spin Hall effect and is subsequently detected in a strong Rashba channel via the inverse spin Hall effect. Before being detected, the spin state is modulated by a gate voltage; the signal observed with various channel lengths and gate voltages demonstrates this Rashba precessional modulation. The addition of Zeeman precession induced by an external magnetic field provides the signal-elucidating definite spin motion in the channel and clear interplay between the Rashba and Zeeman processions. Our approach opens a fascinating possibility for realizing a ferromagnet-free system for use in low-power and high-temperature spin transistors.

We experimentally investigated the transport properties near metal electrodes installed on a conducting channel in a LaAlO₃/SrTiO₃interface. The local region around the Ti and Al electrodes has a higher electrical conductance than that of other regions, where the upper limits of the temperature and magnetic field can be well defined. Beyond these limits, the conductance abruptly decreases, as in the case of a superconductor. The samples with the Ti- or Al-electrode have an upper-limit temperature of approximately 4 K, which is 10 times higher than the conventional superconducting critical temperature of LaAlO₃/SrTiO₃interfaces and delta-doped SrTiO₃. This phenomenon is explained by the mechanism of electron transfer between the metal electrodes and electronicd-orbitals in the LaAlO₃/SrTiO₃interface. The transferred electrons trigger a phase transition to a superconductor-like state. Our results contribute to the deep understanding of the superconductivity in the LaAlO₃/SrTiO₃interface and will be helpful for the development of high-temperature interface superconductors.