Naiman Liao

Structure and 1/f noise of boron doped polymorphous silicon films

The influence of structure variation on the 1/f noise of nanometric boron doped hydrogenated polymorphous silicon (pm-Si:H) films was investigated. The films were grown by the conventional radio frequency plasma enhanced chemical vapor deposition (PECVD) method. Raman spectroscopy was used to reveal the crystalline volume fraction (X(c)) and crystal size of the pm-Si:H. The measurement of optical and structure properties was carried out with spectroscopic ellipsometry (SE) in the Tauc-Lorentz model. A Fourier transform infrared (FTIR) spectrometer was used to characterize the presence of nanostructure-sized silicon clusters in pm-Si:H film deposited on KBr substrate. The electrical properties of the films were measured using evaporated coplanar nickel as the electrode. A semiconductor system was designed to obtain the 1/f noise of pm-Si:H film as well as that of amorphous and microcrystalline silicon films. The results demonstrate that the 1/f noise of pm-Si:H is nearly as low as that of microcrystalline silicon and much lower than that of amorphous silicon. The disorder to order transition mechanism of crystallization was used to analyze the decrease of noise compared with amorphous silicon.

Growth mechanism of microcrystalline and polymorphous silicon film with pure silane source gas

Microcrystalline, polymorphous and amorphous silicon films were deposited in a standard radio frequency (rf) plasma enhanced chemical vapour deposition system at a high growth rate by using pure silane as source gas. The influence of thermal gradient variation on the growth model of the hydrogenated silicon film was investigated. The structure and optical properties of these silicon samples were characterized by Raman spectroscopy, spectroscopic ellipsometry and Fourier transform infrared spectrometry. The phase state at the boundary of the deposited silicon films was analysed using ion drag and plasma-induced thermophoresis on particles in a rf glow discharge. The results showed that control of the thermal gradient allows a switch from polymorphous to microcrystalline silicon growth. The crystalline volume fraction increases with increasing film thickness, and this demonstrates that there is a crystalline gradient between the surface and the bottom of the microcrystalline silicon film.

Electron irradiation effects on the properties of heavily phosphorus-doped a-Si : H films prepared from undiluted silane

The effects of 1.0 MeV electron irradiation on the dark conductivity and amorphous network of heavily phosphorus-doped a-Si : H films have been studied. The electron irradiation leads to a strong decrease by about two orders of magnitude in the dark conductivity of heavily phosphorus-doped a-Si : H films and the degradation comes to a saturation. The evolutions of the amorphous silicon network of heavily doped a-Si : H films caused by electron irradiation were investigated by Raman spectroscopy. The observed decrease in the amorphous silicon network order in the short and intermediate range suggests that the electron irradiation induces structural defects in the films. This defect creation also tends to saturate after a long irradiation time.

Effects of gas temperature on optical and transport properties of a-Si:H films deposited by PECVD

Effects of silane temperature (T g) before glow-discharge on the optical and transport properties of hydrogenated amorphous silicon (a-Si:H) thin films were investigated. The optical measurements show that the refractive index increases with increasing T g. The transport characterizations show that when T g increases, the dark conductivity increases. However, the temperature coefficient of resistance decreases. In addition, after holding at 130°C for 20 h, the resistance variation, ΔR/R, of the films deposited at T g = room temperature (10.8%) is much larger than those deposited at silane temperatures of 80°C (3%) and 160°C (2%). This can be attributed to different rates of defect creation in a-Si:H films caused by various T g.

Investigation of the microstructure and optical properties of hydrogenated polymorphous silicon films prepared with pure silane

The dependences of microstructure and optical properties of hydrogenated polymorphous silicon (pm-Si:H) films on total gas pressure were studied. Instead of using high diluted silane in H2, pure silane was used as the source gas. The films were grown by the radio-frequency plasma-enhanced chemical vapour deposition method. Fourier-transform infrared spectrometry was used to characterize the presence of Si m H n clusters in pm-Si:H film deposited on KBr substrate. Atomic force microscopy (AFM) analysis characterized the morphology of the pm-Si:H films and X-ray diffraction at grazing incidence angle (XRDGI) microstructure analysis also confirmed the existence of Si m H n nanocrystalline clusters in pm-Si:H. The thickness and optical constants of the films were measured by spectra ellipsometry as well as scanning electron microscopy. Derived using the Tauc relation, the dependence of optical bandgap, Eg , and coefficient, B, on the pressure during deposition process is discussed. The influence of inter-electrode distance on growth rate and surface smooth was analyzed using AFM.

Effects of irradiation with electrons of different energies on the dark conductivity and the network of hydrogenated amorphous silicon films

The effects of irradiation with electrons having energies in the range 0.7–1.7 MeV on the dark conductivity and the network of hydrogenated amorphous silicon (a-Si:H) thin films have been studied. The dark conductivity measurements show that electron irradiation leads to a degradation in the dark conductivity, with the degradation being greater at lower electron energies. The Raman results suggest that the irradiation induces structural defects in the a-Si:H films, with the lower energy electrons producing more disorder in the amorphous network.

Optical Property Analysis of Microbolometer Based on MEMS

The optical constant of TiN and amorphous silicon thin film as well as film thickness of thermal resistive amorphous silicon were measured by ellipsometry apparatus, which were in agreement with the result from SEM section analysis. According to optical admittance matrix theory, relation between sensing film thickness, resonant cavity height of microbolometer and infrared absorptivity was simulated using FEA (Finite Element Analysis) MatLab software. Optimal film thickness and resonant cavity height for high infrared absorptivity ranging from 3–5 to 8–14 μm atmosphere window infrared bands were achieved, which provides reliable evidence to improve the sensitivity of microbolometer.Copyright

Manufacturing and photoelectrical properties of P-doped a-Si:H thin films deposited by PECVD

The effect of gas temperature (Tg) on surface morphology, surface roughness, photoelectrical performances of a-Si:H thin films deposited by PECVD at 250°C substrate temperature has been investigated by atomic force microscopy, spectrometric ellipsometry and semiconductor characterization system, respectively. It is found that the surface morphology and density (ρ) as well as the photoelectrical properties such as refractive index (n), dark conductivity (σ), temperature coefficient of resistance (TCR) and activation energy (Ea) remarkably depend on Tg of SiH4 fed in reaction chamber. The higher the Tg, the larger the clusters of a-Si:H thin films deposited. Also, refractive index of a-Si:H thin films increase as Tg rises and the relationship between Tg enhancement of n and the densification of the films is observed. It is indicated that σ varies by two orders of magnitude but TCR decreases by 1.6 %/°C, and Ea gradually decreases linearly from 289.0 to 138.1 meV with Tg varying from room temperature to 160°C. The results of present study suggest that Tg in PECVD chamber plays an important role in the deposition of a-Si:H thin films and directly affects the surface morphology and photoelectrical properties of films. Control of surface morphology, photoelectrical properties of a-Si:H thin films through changing Tg can be usefully applied to the manufacturing of photoelectrical devices.