We report an experimental evidence that some hydrogens passivate electron traps in an amorphous oxide semiconductor, a-In-Ga-Zn-O (a-IGZO). The a-IGZO thin-film transistors (TFTs) annealed at 300 °C exhibit good operation characteristics; while those annealed at ≥400 °C show deteriorated ones. Thermal desorption spectra (TDS) of H2O indicate that this threshold annealing temperature corresponds to depletion of H2O desorption from the a-IGZO layer. Hydrogen re-doping by wet oxygen annealing recovers the good TFT characteristic. The hydrogens responsible for this passivation have specific binding energies corresponding to the desorption temperatures of 300–430 °C. A plausible structural model is suggested.

Epitaxial growth of nitride compounds by the metalorganic vapor phase epitaxy (MOVPE) technique is demonstrated for the first time on β-Ga2O3 single crystal substrates, which are near-UV transparent and n-type conductive. High-quality (0 0 0 1) GaN epi-layer with a narrow bandedge luminescence was obtained using a low temperature conductive buffer layer. InGaN multi-quantum well (MQW) structure was also successfully grown. The first blue light-emitting diode (LED) on β-Ga2O3 with vertical current injection is demonstrated.

The polarization of photoluminescence (PL) was investigated on (11̄00) GaN grown by metalorganic vapor phase epitaxy. We found that the PL intensity and wavelength have polarization dependence parallel and perpendicular to the c axis. We quantitatively analyzed the dependence and found that, since the crystal field of wurtzite GaN along the c axis is strong enough to fix the |z〉 axis of p functions at the c axis, the difference in symmetry between three valence bands appears as the polarization anisotropy in radiative emission, even in bulk GaN.

We investigated roles of hydrogen on physical properties of a-IGZO films and thin-film transistors (TFTs) by comparing standard and ultra-high vacuum (UHV) sputtering systems. It was confirmed that the impurity hydrogens come mainly from the residual gas in the deposition chamber and the molecules adsorbed to the surface of the sputtering target. It was found impurity hydrogen has unfavorable effects as follows; (i) enhances selective Zn desorption during film deposition, and (ii) weakens chemical bonds of the resulting film, causing temperature instability. On the other hand, the UHV a-IGZO films with less hydrogen had low density and exhibited structural instability, suggesting that some hydrogens would have a favorable effect to enhance structural relaxation rate and to form denser and more stable structures during film deposition at room temperature. The revealed hydrogen effects are discussed in relation to those in amorphous silicon and silicon dioxide.Amorphous oxide semiconductors represented by amorphous InGa-Zn-O (a-IGZO) have superior properties for thin-film transistors (TFTs) such as large electron mobilities > 10 cm 2 /(Vs), good uniformity, stability, and low-temperature fabrication process; 1 therefore, a-IGZO TFTs are used in large-area, high-resolution and/or highframe rate liquid-crystal displays (LCDs) and organic light-emitting diode displays (OLEDs). Although the high mobility is obtained for a-IGZO TFTs even fabricated at room temperature (RT) without thermal treatments, post-deposition thermal annealing e.g. at 300-400 • C is required to obtain satisfactory good uniformity and stability. [2][3][4][5] In particular, addition of appropriate amount of water in the annealing atmosphere produces further improved TFTs (wet O 2 annealing). 6 It is reported that the wet O 2 annealing reduced donor states and weak oxygen-metal chemical bonds, 6,7 the latter of which was confirmed by suppressed desorption of H 2 O and metal-related species in a lowtemperature region 100-300 • C. Unexpectedly, it also revealed that the wet O 2 annealing suppressed desorption of hydrogen although the wet O 2 annealing uses H 2 O in the annealing atmosphere. It has also been reported that a-IGZO films contain high-density impurity hydrogens at 10 20 -10 21 cm −3 , which exist mainly as -OH groups. 8,9 On the other hand, it has also been reported that post-deposition hydrogen treatments (e.g., thermal annealing in a hydrogen-containing atmosphere, 10 hydrogen plasma, 11-13 and proton implantation) 14 generate shallow donor states and increase free electrons and electronic conductivity, which is supported also by theoretical calculations; 15 therefore, hydrogen treatments e.g. by subsequent deposition of aSiN x :H have been proposed to fabricate co-planar and self-alignment structure TFTs. 11 To explain these results, we proposed a model that the impurity hydrogens in unannealed a-IGZO would work as shallow donors, but the generated free electrons are trapped and compensated by excess oxygens introduced during film depos...

We grew GaN crystals by metalorganic vapor phase epitaxy on (111) and (100) MgAl2O4 substrates. We obtained a single-crystal GaN layer with a specular surface on the (111) substrate. The full width of half-maximum of the x-ray rocking curve for a 3.6 μm thick GaN layer was 310 s, comparable to the reported values for GaN on Al2O3 substrates. In the room-temperature photoluminescence, a band-edge emission at around 360 nm was dominant. A smooth cleaved (11̄00) facet of the GaN epitaxial layer was obtained, assisted by the inclined (100) cleavage of the (111) MgAl2O4 substrate. We intend this cleaved facet, which is normal to the surface, to be used as a cavity mirror in a laser diode.