Oxide thin-film transistors (TFTs) were fabricated using a polycrystalline In-Ga-O (IGO) thin film as the n-channel active layer by direct current magnetron sputtering. The 50-nm-thick IGO TFT showed a field-effect mobility of 39.1 cm 2 V À1 s À1 , a threshold voltage of 1.4 V, and a subthreshold gate voltage swing of 0.12 V/decade. The polycrystalline IGO thin film showed the cubic bixbyite structure of In 2 O 3 without an obvious preferred orientation. The average grain size of polycrystalline IGO was approximately 10 m. The high mobility of IGO TFT is related to the In 2 O 3 crystalline phase and large grain size of the IGO film. #

We have studied the chemical potential shift and changes in the electronic density of states near the Fermi level (EF ) as a function of carrier concentration in Pr1−xCaxMnO3 (PCMO, 0.2 ≤ x ≤ 0.65) through the measurements of photoemission spectra. The results showed that the chemical potential shift was suppressed for x 0.3, where the charge exchange (CE)-type antiferromagnetic chargeordered state appears at low temperatures. We consider this observation to be related to charge self-organization such as stripe formation on a microscopic scale in this composition range. Together with the previous observation of monotonous chemical potential shift in La1−xSrxMnO3, we conclude that the tendency toward the charge self-organization increases with decreasing bandwidth. In the valence band, spectral weight of the Mn 3d eg electrons in PCMO was transferred from ∼ 1 eV below EF to the region near EF with hole doping, leading to a finite intensity at EF even in the paramagnetic insulating phase for x 0.3, probably related with the tendency toward charge selforganization. The finite intensity at EF in spite of the insulating transport behavior is consistent with fluctuations involving ferromagnetic metallic states.

We studied hole generation in Mg-doped AlN/Al 0.75 Ga 0.25 N superlattices (SLs) with an average Al content of 0.8. High hole concentrations on the order of 10 18 cm %3 were obtained in the SLs. The temperature dependence of the hole concentration indicated an effective acceptor ionization energy of 40-67 meV, which is much lower than that of Mg-doped Al 0.8 Ga 0.2 N alloy (>400 meV). The hole concentration increased with increasing SL period thickness and became almost constant at about 30 nm. These results indicate that the band bending caused by strong spontaneous and piezoelectric polarization fields enhances the ionization of the Mg acceptors.

We have studied the temperature dependence of the photoemission spectra of Pr1−xCaxMnO3 (PCMO) with x = 0.25, 0.3 and 0.5. For x = 0.3 and 0.5, we observed a gap in the low-temperature CE-type charge-ordered (CO) phase and a pseudogap with a finite intensity at the Fermi level (EF ) in the high-temperature paramagnetic insulating (PI) phase. Within the CO phase, the spectral intensity near EF gradually increased with temperature. These observations are consistent with the results of Monte Carlo simulations on a model including charge ordering and ferromagnetic fluctuations [H. Aliaga et al. Phys. Rev. B 68, 104405 (2003)]. For x = 0.25, on the other hand, little temperature dependence was observed within the low-temperature ferromagnetic insulating (FI) phase and the intensity at EF remained low in the high-temperature PI phase. We attribute the difference in the temperature dependence near EF between the CO and FI phases to the different correlation lengths of orbital order between both phases. Furthermore, we observed a chemical potential shift with temperature due to the opening of the gap in the FI and CO phases. The doping dependent chemical potential shift was recovered at low temperatures, corresponding to the disappearance of the doping dependent change of the modulation wave vector. Spectral weight transfer with hole concentration was clearly observed at high temperatures but was suppressed at low temperatures. We attribute this observation to the fixed periodicity with hole doping in PCMO at low temperatures.

We have developed a high-mobility and high-uniform oxide semiconductor using poly-crystalline semiconductor material composed of indium and zinc (p-IZO). A typical conduction mechanism of p-IZO film was demonstrated by the grain boundary scattering model as in polycrystalline silicon. The grain boundary potential of the 2-h-annealed IZO film was calculated to be 100 meV, which was comparable to that of the polycrystalline silicon. However, the p-IZO thin film transistor (TFT) measurement shows rather uniform characteristics. It denotes that the mobility deterioration around the grain boundaries is lower than the case for low-temperature polycrystalline silicon. This assertion was made based on the difference of the mobility between the polycrystalline and amorphous IZO film being much smaller than is the case for silicon transistors. Therefore, we conclude that the p-IZO is a promising material for a TFT channel, which realizes high drift mobility and uniformity simultaneously.