The authors report a two-terminal metal-oxide-semiconductor photodetector for which light is absorbed in a capping layer of silicon nanocrystals embedded in a mesoporous silica matrix on p-type silicon substrates. Operated at reverse bias, enhanced photoresponse from 300 to 700 nm was observed. The highest optoelectronic conversion efficiency is as high as 200%. The enhancements were explained by a transistorlike mechanism, in which the inversion layer acts as the emitter and trapped positive charges in the mesoporous dielectric layer assist carrier injection from the inversion layer to the contact, such that the primary photocurrent could be amplified.

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Al 0.15 Ga 0.85 N/GaN high-electron-mobility transistor (HEMT) structures with various δ-doping concentrations and spacer thicknesses grown on sapphire by metalorganic chemical-vapor deposition are investigated. The Hall mobility is as high as 1333 cm2/V s at room temperature and 6330 cm2/V s at 77 K. Two-dimensional electron gas (2DEG) phenomena, which have not been clearly resolved in the literature, are observed by photoluminescence (PL) spectra at low temperature in this study. The PL spectra peaks of the interband transitions from 2DEG subbands to the valence band are in the range from 3.486 to 3.312 eV. The effects of the strain caused by different Al fractions of the top layer, and that of the spacer thickness on the 2DEG phenomena are discussed. Redshifts due to temperature variations for various HEMT structures are observed in 2DEG subbands and in the band-edge emission, which is believed to be evidence of interband transitions from 2DEG subbands to valence bands.