AlGaN/GaN heterostructures with different buffer layers were grown on Si substrates by metal-organic vapor phase epitaxy (MOVPE). The electrical property of the two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface was correlated with both the optical and structural quality of the GaN layer involved. A combination of two sets of hightemperature and low-temperature AlN and an ultrashort exposure to SiH 4 showed the best-grown GaN, followed by a similar buffer layer without the SiH 4 exposure, and a graded AlGaN buffer layer only. The enhancements in both electron mobility and 2DEG density were also accompanied by a reduced donor-acceptor pair (DAP) emission and a reduced dislocation density in the top GaN grown.

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