Yuheng Zeng

Oxygen precipitation heterogeneously nucleating on silicon phosphide precipitates in heavily phosphorus-doped Czochralski silicon

Through comparison between the oxygen precipitation (OP) behaviors in heavily and lightly phosphorus (P)-doped Czochralski silicon (CZ-Si) crystals subjected to low-high two-step anneal of 600, 650, or 750 °C/8 h+1050 °C/16 h, we have found that in heavily P-doped CZ-Si, OP is much stronger in the case with the nucleation anneal at 600 or 650 °C while it is to some extent suppressed in the case with the nucleation anneal at 750 °C in contrast to lightly doped CZ-Si where nucleation is enhanced at 750 °C. Transmission electron microscopy investigation reveals that silicon phosphide precipitates of face-centered-cubic SiP form during the nucleation anneal at temperatures 650 °C and below. The SiP precipitates act as the heterogeneous nuclei for OP during the subsequent high temperature anneal while the oxygen precipitate nuclei containing certain amounts of P atoms generate during the nucleation anneal at 750 °C. They are further coarsened to be larger oxygen precipitates during the subsequent high temperat...

Investigation of intrinsic gettering for germanium doped Czochralski silicon wafer

The intrinsic gettering (IG) effects in a germanium-doped Czochralski (GCz) silicon wafer have been investigated through a processing simulation of dynamic random access memory making and an evaluation on IG capability for copper contamination. It has been suggested that both the good quality defect-free denuded zones (DZs) and the high-density bulk microdefect (BMD) regions could be generated in GCz silicon wafer during device fabrication. Meanwhile, it was also indicated that the tiny oxygen precipitates were hardly presented in DZs of silicon wafer with the germanium doping. Furthermore, it was found in GCz silicon wafer that the BMDs were higher in density but smaller in size in contrast to that in conventional Cz silicon wafer. Promoted IG capability for metallic contamination was therefore induced in the germanium-doped Cz silicon wafer. A mechanism of the germanium doping on oxygen precipitation in Cz silicon was discussed, which was based on the hypothesis of germanium-related complexes.

High-pressure behavior of β-Ga2O3 nanocrystals

Freestanding nanocrystalline β-Ga2O3 particles with an average grain size of 14 nm prepared by chemical method was investigated by angle-dispersive synchrotron x-ray diffraction in diamond-anvil cell up to 64.9 GPa at ambient temperature. The evolution of x-ray diffraction patterns indicated that nanocrystalline monoclinic β-Ga2O3 underwent a phase transition to rhombohedral α-Ga2O3. It was found that β- to α-Ga2O3 transition began at about 13.6–16.4 GPa, and extended up to 39.2 GPa. At the highest pressure used, only α-Ga2O3 was present, which remained after pressure release. A Birch–Murnaghan fit to the P-V data yielded a zero-pressure bulk modulus at fixed B0′=4: B0=228(9) GPa and B0=333(19) GPa for β-Ga2O3 and α-Ga2O3 phases, respectively. We compared our results with bulk β-Ga2O3, and concluded that the phase-transition pressure and bulk modulus of nanocrystalline β-Ga2O3 are higher than those of bulk counterpart.

Effects of heavy phosphorus-doping on mechanical properties of Czochralski silicon

The mechanical properties including hardness, Young’s modulus, and fracture toughness of heavily phosphorus (P)-doped Czochralski (Cz) silicon have been investigated by means of nanoindentation and microindentation. In view of the results of nanoindentation characterization, it is derived that the hardness of heavily P-doped Cz silicon is essentially the same as that of lightly P-doped Cz silicon. While, the Young’s modulus of Cz silicon is to a certain extent decreased by the heavy P-doping. With the same microindentation load, the lengths of the radial and lateral cracks in the heavily P-doped silicon are shorter than those in the lightly P-doped silicon, indicating that the heavily P-doped Cz silicon possesses a higher indentation fracture toughness.

Grown-in precipitates in heavily phosphorus-doped Czochralski silicon

Through comparing the oxygen precipitation in the heavily and lightly phosphorus (P)-doped Czochralski silicon (CZ Si) specimens subjected to the simulated cooling processes of silicon ingot, we researched the influences of heavily P doping on grown-in precipitates by preferential etching and transmission electron microscopy (TEM). It was found that grown-in precipitates were more significant in heavily P-doped CZ Si than in lightly one. Most grown-in precipitates in heavily P-doped CZ Si were generated at (800–600) °C. The significant grown-in oxygen precipitates in the heavily P-doped CZ Si would change the density and morphology of oxygen precipitation. TEM examination revealed that the grown-in precipitates in heavily P-doped CZ Si were amorphous oxygen precipitates composed of tiny precipitates in essential. Although more or less phosphorus may be incorporated in the grown-in precipitates, however, phosphorus cannot be detected so far. We further confirmed that extending annealing at 550 °C produced ...

Effect of annealing atmosphere on the recombination activity of copper precipitates formed by rapid thermal process in conventional and nitrogen-doped Czochralski silicon wafers

The effect of annealing atmosphere of Ar, N2, or O2 on the recombination activity of copper (Cu) precipitates, formed by the rapid thermal process (RTP), in conventional Czochralski (CZ) silicon and nitrogen-doped CZ (NCZ) silicon wafers have been investigated. It was revealed that the recombination activity of Cu precipitates formed under N2, Ar, and O2 atmospheres decreased in turn. Moreover, the RTP under O2 atmosphere led to a higher critical temperature for Cu precipitation in comparison with the RTP under Ar or N2 atmosphere. Furthermore, it was found that the Cu precipitates formed under the same conditions possessed stronger recombination activity in CZ silicon than in NCZ silicon. The above results have been tentatively explained.

Oxygen precipitation in heavily phosphorus-doped Czochralski silicon: effect of nitrogen codoping

Oxygen precipitation (OP) in the conventional and nitrogen-codoped heavily phosphorous (P)-doped Czochralski silicon (CZ-Si) wafers subjected to various low- (650–850 °C) and high-temperature (1050 °C) two-step annealing conditions have been comparatively investigated. It was found that the nucleation annealing at 650 °C led to remarkable OP and the resulting bulk micro defect densities were nearly the same in both kinds of silicon wafers. While in the case with the nucleation annealing at 750 or 850 °C, the conventional heavily P-doped CZ-Si featured slight OP, in contrast to the nitrogen-codoped counterpart that put up considerably intense OP. The heavily P doping is believed to exert a significant enhancement effect on oxygen precipitate nucleation at 650 °C but not at 750 and 850 °C, while the nitrogen codoping offers heterogeneous centers for oxygen precipitate nucleation at 750 or 850 °C. It is reasonably believed that nitrogen codoping is also an effective pathway to enhance oxygen precipitation in heavily P-doped CZ-Si.

Oxygen Precipitation in Heavily Phosphorus-doped Czochralski Silicon

Oxygen precipitation in heavily phosphorous (P)-doped Czochralski silicon (CZ-Si) subjected to the ramping or two-step anneals was investigated. It was revealed that the grown-in oxygen precipitates exerted significant effect on oxygen precipitation behaviors and then resulted in distinctive oxygen precipitation for the wafers form various positions of the ingot. Moreover, it was found that both the seed and tang-end wafers processed significantly intense nucleation at 650 oC without the influence of grown-in oxygen precipitates. It was considered that the heavily P-doping introduced phosphorus related precipitation at 650 oC. When the annealing temperature increased, the capability for nucleation of oxygen precipitation by heavily P-doping would be gradually weakened but the one by oxygen clustering became pronounced. In this case, it was understandable that the tang-end wafer processed higher density of oxygen precipitates than the seed-end wafer at around 750 oC, while a lower one at 1000 oC.

Performance enhancement of ultraviolet light emitting diode incorporating an Al nanohole arrays

Enhanced photoluminescence and improved internal quantum efficiency were demonstrated for ultraviolet light emitting diodes (UV-LEDs) with Al nanohole arrays deposited on the top surface. The effects of the thickness and periodicity of the plasmonic structures on the optical properties of UV-LEDs were studied, and an optimized nanohole array parameter was illustrated. Classical electrodynamic simulations showed that the radiated power is mostly concentrated along the edge of the Al nanohole arrays. Even though no obvious dip was observed in the transmission spectra associated with localized surface plasmon resonance, significant improvements in radiatiative recombination and light extraction efficiency were demonstrated, indicating the influence of Al nanohole arrays on the light emission control of UV-LEDs. It is anticipated that the enhanced luminescence can be obtained for various emitting wavelengths by directly adjusting the periodicity and morphology of the Al nanohole arrays and this new technology can alleviate crystal quality requirements of III-nitride thin films in the development of high efficiency UV optoelectronic devices.

Opto-electric investigation for Si/organic heterojunction single-nanowire solar cells

Recently, silicon single nanowire solar cells (SNSCs) serving as the sustainable self-power sources have been integrated into optoelectronic nanodevices under the driver of technology and economy. However, conventional SNSC cannot provide the minimum energy consumption for the operation of nanodevices due to its low power conversion efficiency (PCE). Here, we propose an innovative approach to combine the n-type silicon nanowires (SiNWs) with p-type poly(3,4-ethylthiophene):poly(styrenesulfonate) (PEDOT:PSS) to form the p+n heterojunction, which shows superior opto-electric performances. Besides, PEDOT:PSS also acts as a natural anti-reflection coating (ARC) with an excellent light-trapping capability, especially in the short-wavelength range. Importantly, the photovoltaic performances of Si/PEDOT:PSS SNSC can be well maintained even in large surface recombination velocity, due to the efficient field-effect passivation of PEDOT:PSS. The minority carrier concentration at outer surface of shallow p+n heterojunction is greatly reduced by the electric field, drastically suppressing the surface recombination compared to the conventional p-i-n homojunction SNSC. Furthermore, larger junction area of p+n heterojunction facilitates the separation of photo-generated charge carriers. These results demonstrate that the Si/PEDOT:PSS SNSC is a promising alternative for micro power application.