Gallium nitride (GaN) growth via a tri-halide vapor phase epitaxy method using a solid source of GaCl3 and gaseous NH3 was investigated both on Ga-polar and N-polar GaN templates. The relationship between gallium precursor molecule and growth polarity was clarified; it was found that a small amount of GaCl3 could be reduced by H2 originating from the decomposition of NH3 to produce GaCl, and additional Cl2 could suppress the reduction process. Accordingly, GaCl3 was found to be a proper Ga precursor for N-polar GaN growth, whereas GaCl was the proper precursor for Ga-polar GaN growth. The state of the Ga precursor molecule could be predicted by thermodynamic analysis. Furthermore, the decomposition ratio of NH3 could be determined by a combination of the experimental results and the calculated value of the thermodynamic analysis.
The summar:y writing task has been widely used in order to exarnine how well readers comprehend texts (Alderson, 2000). As a scoring criterion of summary protocols, previous studies have considered whether or not a reader can effectively use rnacrorules, which refiect the process of readers' constmction of their mental representation (e.g., Johns & Mayes, 1990; Kim, 2001). In fact, the use of macrorules is assumed to be closely related to the process of how readers construct their menta1 representation of a passage (van Dijk & Kintsch, 1983). However, surnmary task has a methodological problem in that readers' performance in the use of macrorules reflects not only the process of reading comprehension but also their writing ski11s (Cohen, 1993), Therefbre, we haye used another psycholinguistic measure fbr reading comprehension that suppressed the influence of writing skills: the Mleaning ldbntijication 7lechnique (MIT). The present study examined English as a fbreign language (EFL) learners' macrorule use with the MIT as well as in a summary writing task. Focusing on three types of macrorules (i.e., deletion, generalization, and construction rules), Experimental Study 1 showed that EFL students used all three types of macrorules when they did summary writing, In Experimental Study 2 using the MIZ the generalization and constmction rules were more dicacult for learners to use than the deletion rule. These two rules required learners to generate inferences fbr constmcting the implicit main ideas oftexts, whereas the deletion rule simply required learners to select explicit main ideas from texts, Comparison of the two series of experimental studies indicated that surnmary writing encouraged the participants to use the generalization and construction rules by requiring them to integrate pieces of-185-The Japan Language Testing Association NII-Electronic Library Service The JapanLanguageTesting Association infbrmation for making the summary Therefore, macrorule use measured by the summary protocol should be interpreted carefu11M taking the effects of the summary task itselfinto account in terrns ofpromoted strategic macrorule use, Furtherrnore, it was implied that the MIT could be superior to a surnmary writing task as a reading comprehension test, as far as macrorule use under natural reading conditions reflected pure comprehension of a text.
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