To clarify the origin of the major donor states in indium gallium zinc oxide (IGZO), we report measurement results and an analysis of several physical properties of IGZO thin films. Specifically, the concentration of H atoms and O vacancies (V O ), carrier concentration, and conductivity are investigated by hard X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, thermal desorption spectroscopy, and Hall effect measurements. The results of these experiments suggest that the origin of major donor states is H occupancy of V O sites. Furthermore, we use first-principles calculations to investigate the influence of the coexistence of V O and H in crystalline InGaO 3 (ZnO) m (m ¼ 1). The results indicate that when H is trapped in V O , a stable complex is created that serves as a shallow-level donor. V C 2014 AIP Publishing LLC.

This study examines the crystallinities of indium-gallium-zinc oxide (IGZO) films deposited by sputtering at room temperature under varying conditions and a difference in composition among the films, then we assess the effect of these differences on the FET characteristics. Each sample is found to be nanocrystalline IGZO. The crystallinity and the degree of the c-axis alignment are improved with the increase of the O 2 gas flow ratio in the IGZO deposition. The composition analysis results demonstrate that the ratio of In to Ga and Zn is uneven, and the elements exist separately in all the samples with different conditions. Moreover, every sample is in a composite-like (composite-compound-like) state. An FET, including IGZO deposited with an O 2 gas flow ratio of 50%, which is the condition that improves crystallinity, exhibits a favorable reliability.

We found out that in an indium gallium zinc oxide (IGZO) transistor, the energy barrier in the channel region, i.e., the conduction band energy relative to the Fermi energy is lowered by electrons flowing from n + regions under source and drain electrodes. We have named this phenomenon "conduction band lowering (CBL) effect". Owing to this effect, even when the Fermi energy of an IGZO film gets closer to the mid-gap, a transistor formed using the film in the channel region is always turned on around a gate voltage of 0 V. In other words, by sufficiently reducing the donor concentration of the channel region, such IGZO transistors are turned on at a certain low gate voltage determined by the CBL effect and their characteristics variation can be suppressed.

For realizing a red‐colour emission using SrGa2S4 compounds, Mn and rare‐earth‐element (REE) co‐doping is tried. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra are measured using samples so prepared. As a result, enhancement of the Mn red emission is observed. Considering the 4f and 5d levels of REE in the host material, it is expected that the energy transfer from REE to Mn is caused by the weak coupling between the d levels of REE and Mn. Moreover, in the Ce co‐doping case, another process is expected as a resonant energy transfer between the 4f–5d transition of Ce3+ and a certain transition of Mn2+. To specify the Mn2+ levels related to the resonant transfer, PL spectra of a Mn only doped CaGa2S4 single crystal and an undoped one are measured at low temperatures, though we could not find emission expected to be related to the resonant transfer. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In–Ga–Zn oxide (IGZO) is a next-generation semiconductor material seen as an alternative to silicon. Despite the importance of the controllability of characteristics and the reliability of devices, defects in IGZO have not been fully understood. We investigated defects in IGZO thin films using electron spin resonance (ESR) spectroscopy. In as-sputtered IGZO thin films, we observed an ESR signal which had a g-value of g = 2.010, and the signal was found to disappear under thermal treatment. Annealing in a reductive atmosphere, such as N2 atmosphere, generated an ESR signal with g = 1.932 in IGZO thin films. The temperature dependence of the latter signal suggests that the signal is induced by delocalized unpaired electrons (i.e., conduction electrons). In fact, a comparison between the conductivity and ESR signal intensity revealed that the signal's intensity is related to the number of conduction electrons in the IGZO thin film. The signal's intensity did not increase with oxygen vacancy alone but also with increases in both oxygen vacancy and hydrogen concentration. In addition, first-principle calculation suggests that the conduction electrons in IGZO may be generated by defects that occur when hydrogen atoms are inserted into oxygen vacancies.