Wugang Liao

Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. Th...

Structural evolution and photoluminescence of annealed Si-rich nitride with Si quantum dots prepared by plasma enhanced chemical vapor deposition

Silicon-rich nitride films were deposited by plasma enhanced chemical vapor deposition. Silicon quantum dots (Si QDs) were formed by post-thermal annealing processing verified using the High-Resolution Transmission Electron Microscope. The 1100 °C thermal annealing leads to the nucleation of silicon atoms, the growth of Si QDs, and the rearrangement of Si 2p and N 1s elements. The structural evolution of silicon-rich nitride thin film with post annealing promotes the formation of Si QDs and Si3N4 matrix. We also investigated the effect of the NH3-to-SiH4 ratio R on the photoluminescence (PL) of SiNx with Si QDs. We found that the broad blue luminescence originates from both quantum confined effect and radiative defects. The intensity of the PL was changed by adjusting the NH3 flow rate. The increase of R could limit the transformation of Si QDs from amorphous to crystalline status, meanwhile lead to the alteration of distribution of defect states. These can help to understand the annealing-dependent chara...

Microstructure evolution and energy band alignment at the interface of a Si-rich amorphous silicon carbide/c-Si heterostructure

The microstructure evolution of Si-rich amorphous a-SiC:H films obtained under different annealing conditions was investigated by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The influence of its microstructure on the energy band alignment at a Si-rich a-SiC:H/n-type c-Si hetero-interface was analyzed by ultraviolet visible transmission spectroscopy and ultraviolet photoelectron spectroscopy. The results revealed that the as-deposited Si-rich a-SiC:H film was mainly in an amorphous state. After annealing, Si and SiC quantum dots (QDs) formed, and the crystallinity of the QDs and the proportion of SiC QDs increased with increasing the annealing time at the same annealing temperature. It is found that the energy band alignment at the hetero-interface was influenced by the crystallinity of the films, the sizes of the QDs, and the relative proportion of Si to SiC QDs in a-SiC:H films. Moreover, the contact potential at the hetero-interface decreased with the improved crystallinity of the QDs in a-SiC:H film. The determination of energy band alignment at the Si-rich a-SiC:H/c-Si hetero-interface is beneficial to understanding the carrier transport behavior and designing hetero-structure devices.

Charging/discharging behavior and mechanism of silicon quantum dots embedded in amorphous silicon carbide films

The charging/discharging behavior of Si quantum dots (QDs) embedded in amorphous silicon carbide (a-SiCx) was investigated based on the Al/insulating layer/Si QDs embedded in a-SiCx/SiO2/p-Si (metal-insulator-quantum dots-oxide-silicon) multilayer structure by capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Transmission electron microscopy and Raman scattering spectroscopy measurements reveal the microstructure and distribution of Si QDs. The occurrence and shift of conductance peaks indicate the carrier transfer and the charging/discharging behavior of Si QDs. The multilayer structure shows a large memory window of 5.2 eV at ±8 V sweeping voltage. Analysis of the C-V and G-V results allows a quantification of the Coulomb charging energy and the trapped charge density associated with the charging/discharging behavior. It is found that the memory window is related to the size effect, and Si QDs with large size or low Coulomb charging energy can trap two or more electrons by changing t...

The influence of work function of transparent conductive oxide on a-Si/c-Si heterojunction solar cells with different doping types of wafers

The influence of work function of transparent conductive oxide (TCO) on Fermi energy level, energy band and efficiency of different type solar cells was investigated to explore the needs of work function of TCO.

Tunable photoluminescence of Si-rich nitride films with silicon quantum dots by changing the total pressure

Silicon-rich nitride films were prepared by PECVD at low temperature. TEM, Raman and photoluminescence (PL) spectra were characterized to identify the PL mechanisms and the role of total pressure on the distribution of Si QDs.