Si Nanocrystal Based Metal-Oxide Semiconductor Memory Devices and Light Emitting Diodes
Date Issued
2009
Date
2009
Author(s)
Lien, Yu-Chung
Abstract
Temperature-dependent μ-PL of self-trapped exciton (STE) based radiation in Si nanocrystals (Si-ncs) with size enlarging from 2.3 to 4.5 nm is demonstrated, while the monotonically decreasing trend of the STE activation energy (from 1.75 to 1.2 meV) with Si-nc size dependent dielectric permittivity is elucidated by Bohr hydrogen-like atom model. Charge accumulation induced capacitance hysteresis accompanied with lengthened retention is observed when Si-nc size exceeds 2.3 nm. A modified flat-band voltage shift model corroborates the proportionality of the charge density with third power of Si-nc size, supporting that the Si-nc volume is more pronounced than Si-nc density for charge retention. The current blocking and charge accumulation effects of an ITO/Si-rich SiOx/p-Si MOS diode with buried Si nano-dots (Si-nds) and SiOx/Si interfacial Si nano-pyramids (Si-nps) are characterized. At the SiOx/p-Si interface, the area density of Si-nps is increasing from 1.3×109 to 1.6×1011 cm-2, which greatly decreases turn-on voltage of the MOS diode from 182 to 52 V, thus enhancing the electro-luminescent power from 17.5 to 50.4 nW. The current blocking phenomenon of such a MOS diode become serious with lengthening step-voltage delay, indicating that a significant charge accumulation associated with a strong screening field is generated within Si-rich SiOx layer. It was observed that the turn-on voltage with Si-nps evidently decreases to 31.6 V under reverse biased conditions for tunneling holes. Counter-clockwise C-V hysteresis analysis reveals a flat-band voltage shift of 8.5 V for electron and -12.9 V for hole, showing nonlinear function with either Si-nd size or Si-nd density. The C–t retention shows higher charge loss rate for electrons (7.6%) than for holes (1.5%) within 0.5 hr due to low SiOx/Si-nd barrier. The multicolor photo-emission of an ITO/Si-rich SiOx/p-Si MOS diode with buried Si-ncs were demonstrated. From PL analysis, the normalized PL intensity monotonically increases and the peak wavelength blue shifts, indicating the increment of Si-nc density and shrinkage of Si-nc size, respectively. This is attributed to cluster growth/ripening at lower composition ratio and nucleation at higher composition ratio by FTIR absorption analysis of Si-O-Si stretching mode. The PL spectra of 40 and 50 W grown sample also shows similar PL spectrum to Si implanted SiO2 (SiO2:Si+), which are mainly contributed by weak oxygen bonding defect, NOV defect. The FTIR also implies the reduction of radiative defect after long-term annealing. With F-N plot, the turn-on electric field from 2.6 to 9.2 MV/cm, and extract the barrier height from 1.02 to 3.62 eV were determined. The band diagram shows the energy band intrinsically bending more serious for larger Si-nc, indicating smaller external electric field to trigger F-N tunneling mechanism. The maximum optical power of 557.2 nW were observed during long-term annealing device. The EL spectra show similar spectra as PL, and the color of EL patterns are in agreement with their EL spectra.
Subjects
Si-ncs
silicon rich silicon oxide
turn-on voltage
charge storage effect
retention time
Type
thesis
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