Electronic charge trapping in chemical vapor-deposited thin films of Al2O3 on silicon

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Abstract
Electronic charge trapping in 200‐nm thick films of Al2O3 has been investigated by photoinjection‐photodepopulation and capacitance‐voltage measurements. The Al2O3films were chemically vapor deposited on (100) silicon substrates by hydrolysis of AlCl3 at 900 °C in the presence of H2 and CO2. Released charge during monochromatic depopulation at 480 nm was measured as a function of applied voltage. Analysis of these results gave (a) optically releasable charges (1.5×1017 cm−3) and (b) fixed charges introduced during photoinjection (4.90×1017 cm−3). The centroid of these charges was determined to be 140 nm from the metal‐Al2O3 interface. The charge densities calculated from these measurements and the C‐Vmeasurements showed excellent internal consistency. The photodepopulation current measurements as a function of wavelength were carried out in the range 700–350 nm. These results indicated that the trapping states are continuously distributed in this spectral energy range in a nonuniform manner. These results combined with optical bleaching measurements indicated dynamical broadening of the individual trapping states. A phenomenological model of electron traps in Al2O3 is proposed which is consistent with the results obtained in this research. According to this model, one distribution of trapping states describes both the optically releasable and the fixed charges.