Phosphorus-doped Films Research Articles

UV and blue light cut-off filters using phosphorus doped carbon quantum dots extracted from raw egg yolk

Abstract Using raw egg yolk and phosphoric acid, a simple hydrothermal treatment for synthesizing carbon quantum dots (CQDs) has been developed for the manufacture of UV and blue light-blocking filters. Several samples with different doping ratios of phosphoric acid were prepared. Namely: reference (REF.), 25%, 50%, 75% and 100%. The synthesized CQDs were embedded in polyvinyl alcohol (PVA) to produce blocking-light films with desired optical properties. Six films were prepared, one of which was PVA alone, and the other five samples were the prepared CQDs, with different phosphorus doping levels, mixed with PVA in a 1:1 ratio. We aimed to test the ability of these films to block ultraviolet rays and blue light. The experimental results revealed that the prepared films were able to block the blue light, emitted from a 450 nm blue LED, with blocking ratios of 7%, 17.5%, 27%, 30%, 37% and 70% for the films: PVA alone, REF., 25%, 50%, 75% and 100%, respectively. Moreover, it was found that these phosphorus-doped CQDs films can prevent destructive UV light with substantial value reaching 86%. These results suggest that carbon dots, derived from raw egg yolk, can be effectively applied to block harmful UV and blue lights.

Low-thermal-budget electrically active thick polysilicon for CMOS-First MEMS-last integration

Low-thermal-budget, electrically active, and thick polysilicon films are necessary for building a microelectromechanical system (MEMS) on top of a complementary metal oxide semiconductor (CMOS). However, the formation of these polysilicon films is a challenge in this field. Herein, for the first time, the development of in situ phosphorus-doped silicon films deposited under ultrahigh-vacuum conditions (~10−9 Torr) using electron-beam evaporation (UHVEE) is reported. This process results in electrically active, fully crystallized, low-stress, smooth, and thick polysilicon films with low thermal budgets. The crystallographic, mechanical, and electrical properties of phosphorus-doped UHVEE polysilicon films are studied. These films are compared with intrinsic and boron-doped UHVEE silicon films. Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM) are used for crystallographic and surface morphological investigations. Wafer curvature, cantilever deflection profile and resonance frequency measurements are employed to study the mechanical properties of the specimens. Moreover, resistivity measurements are conducted to investigate the electrical properties of the films. Highly vertical, high-aspect-ratio micromachining of UHVEE polysilicon has been developed. A comb-drive structure is designed, simulated, fabricated, and characterized as an actuator and inertial sensor comprising 20-μm-thick in situ phosphorus-doped UHVEE films at a temperature less than 500 °C. The results demonstrate for the first time that UHVEE polysilicon uniquely allows the realization of mechanically and electrically functional MEMS devices with low thermal budgets.

Investigation of phosphorus-doping of MgZnO thin films using efficient spin-on dopant process

Phosphorus doped MgZnO thin films were prepared using the RF sputtering technique on a Si wafer, followed by spin-on doping (SOD) and annealing. The SOD is a cheap and non-destructive process in which the dopant film is spun on a Si wafer and placed in the vicinity of deposited undoped MgZnO thin film at a high temperature to perform doping. After doping, the MgZnO thin films were annealed at temperatures such as 700, 800, and 900 °C, which significantly improved morphological, structural, and optical properties. The atomic force microscopy and scanning electron microscopy measurements revealed that phosphorus-doped MgZnO thin films annealed at 800–900 °C have good morphology and large grains. X-ray diffraction spectra demonstrated the (002) orientation of MgZnO thin films. The photoluminescence spectra measured at 20 K demonstrated the acceptor bound exciton peak at 3.47 eV and acceptor binding energy of around 64.34 meV, indicating the formation of shallow acceptor levels by phosphorus doping of MgZnO thin films using the SOD process. In Raman spectroscopy measurement, the peak of E2high phonons mode of MgZnO wurtzite structure was observed around 436 cm−1. The FWHM value of this peak reduces with augmentation annealing temperature, demonstrating improvement in crystallinity. X-ray photoelectron spectroscopy measurement demonstrated the presence of phosphorus atoms in the SOD processed MgZnO thin films, which is again verified by Fourier-transform infrared spectroscopy measurement showing vibration modes of P–O bonds. It was observed that the different properties of SOD-prepared phosphorus-doped MgZnO films were superior to the film prepared using the alternate costly and destructive ion-implantation technique. These findings have revealed that high-quality phosphorus-doped p-type MgZnO thin films by the SOD process are very suitable for UV optoelectronic device applications.

Evidence of vortices and mixed-state superconductivity in phosphorus-doped graphene. Part I (Nernst)

We have observed phenomena in phosphorus-doped graphene films consistent with mixed-state superconductivity at temperatures as high as 260 K. This evidence includes transport, susceptibility and Nernst/Hall measurements as a function of the thermal gradient. This paper presents evidence of vortices and flux flow in the mixed state of phosphorus-doped graphene samples in the form of well-defined Nernst peaks being measurable up to 260 K.

Sub-nm Near-Surface Activation Profiling for Highly Doped Si and Ge Using Differential Hall Effect Metrology (DHEM)

Contact resistivity at the metal-semiconductor interface is a strong function of the carrier concentration in the near surface. For next generation 2D/3D MOSFET transistors, industry has been investigating very highly doped materials (>1x1021cm-3) approaching alloy concentrations in Silicon and various Silicon-Germanium materials. All the while, contact development in Ge NMOS has favored co-doping approaches. Regardless of the material system, it is very important to accurately measure near-surface dopant activation. In this paper, we use Differential Hall Effect Metrology (DHEM) implemented on the ALPro™ tool to characterize the activation profiles in both materials. The method employs electrochemical means of reducing the electrically active thickness of a semiconductor film and determining the sheet resistance and mobility of the thinned down layer using Van der Pauw/Hall effect type measurements. By repeating this process and using differential equations, depth profiles of mobility and carrier concentration are obtained [1] at sub-nm resolutions.It is difficult to achieve high n-type dopant activation in Ge. Point defects in Ge are known to behave as acceptor sites and reduce the overall free electron density, particularly near the surface. Minimization of these defects is essential to achieving high performance Ge NMOS. Accurate analysis of dopant activation within 5 nm of the surface is critical to understanding effectiveness of various process steps on improving contact resistance. We have previously published a study on the effect of Ge co-doping with Sb and P on near-surface dopant activation. In Ge with only P-doping it was found that only ~5x1018cm-3 or 5% of the total surface dopants (~1x1020cm-3) were electrically active. With Sb as a co-dopant, the active electron concentration increased to ~2x1019cm-3 with a similar P chemical concentration. Prior work has shown similar increases in activation with co-doping but did not capture the significant decrease in electron concentration by 4x within 10 nm of the surface. Here, we further study the effects of the implantation and annealing processes on near-surface dopant activation in n-type Ge. Samples were prepared by growing 3 µm thick epi-Ge layers on Si substrates. Sample 1 was capped with 20 nm SiO2 and Sample 2 was capped with 20 nm Al2O3 to minimize implant damage and control implant depth. Both samples were implanted first with Sb (dose: 6x1014cm-2, energy: 65 keV) followed by P (dose: 6x1014cm-2, energy: 90 keV). Post-implant anneal was done at 500°C for 10 s in N2 to activate the dopants. ALProTM and SIMS measurements were done to characterize active dopant concentration and total chemical dopant concentration, respectively. The Al2O3 capped sample (Sample 2) showed significantly lower carrier concentration than the SiO2 capped sample (Sample 1) throughout the depth of the profile (Figure 1). Carrier concentration at the surface was lower by nearly an order of magnitude, decreasing from ~2x1019cm-3 to ~2x1018cm-3. Additionally, the peak concentration decreased from 1x1020cm-3 to 5x1019cm-3 at a depth of ~30 nm in both cases. The variations in the carrier profile for the Al2O3 capped sample also indicate greater process variation. SIMS profiles show that there is significant diffusion of Al into the Ge matrix after implant and anneal. Al chemical concentration is 1x1020cm-3 at the Ge surface and steadily decays up to a depth of more than 300 nm. This indicates that there is significant damage caused during the implantation process and the activation anneal is not enough to remove these defects. Al atoms then diffuse from the Al2O3 capping layer into the highly defective Ge substrate. Al is a p-type dopant in Ge and counter-dopes the Sb and P implants to reduce overall electron concentration in Sample 2. It is important to note the high resolution DHEM technique was able to resolve this important phenomenon right near the surface of the material.Additionally, we present early data on very highly phosphorus-doped (~1x1021cm-3) epitaxial silicon thin films grown on Si substrates. In very highly doped Silicon materials, the effect of near-alloy levels of dopant in the matrix on dopant deactivation is not well-known. Samples were obtained with different levels of dopant concentration above ~1x1021cm-3and different anneal temperatures. It was found that near-surface activation in these un-capped samples led to a lowering of activation in the <20nm region from the surface. Extensive post-DHEM metrology (using TEM and SIMS analysis) will also be presented demonstrating control and precision of DHEM data.

Microstructure analysis of silicon nanocrystals formed from silicon rich oxide with high excess silicon: Annealing and doping effects

Thin films consisting of silicon nanocrystals fabricated by high silicon content in silicon rich oxide show unique properties of decreasing resistivity and increasing light absorption while maintaining quantum confinement effects. With that said, the effect of the annealing temperature and doping element on the microscopic structure of silicon nanocrystals (Si NCs) and the film are still under research. In this study, individual intrinsic, boron-, and phosphorus-doped films are annealed at various temperatures, and their structural properties are analyzed via atom probe tomography together with glancing incidence x-ray diffraction, Raman spectroscopy (Raman), transmission electron microscopy (TEM), and energy filtered TEM. In addition, photoluminescence (PL) is performed and linked with their microstructural properties. The Si NC growth is confirmed at annealing temperatures of 1000 °C and 1100 °C. The microstructure of the Si NCs in the whole film is dramatically changed by increasing the annealing temperature from 1000 °C to 1100 °C. In addition, doping changes the arrangement of the Si NCs by assisting their penetration across the SiO2 barrier layers. This study helps to understand the relationship between the microscopic and macroscopic properties of the Si NC film, showing that the size and distribution of the Si NCs are correlated with the obtained PL profiles.

(p+)Nanocrystalline/(n−)crystalline/(n+)nanocrystalline Si fast recovery diode with (p+)nanocrystalline SiC inserted in cathode junction

Surge suppressed by (p+)nanocrystalline SiC islands buried in cathode junction of operating (p+)nanocrystalline/(n−)crystalline/(n+)nanocrystalline Si fast recovery diode was studied in this paper. The proposed diode was prepared by plasma enhanced chemical vapor deposition (PECVD) technique. Firstly, heavily boron doped Si film was prepared with PECVD on one end of the lightly doped n−-type cubic Si (c-Si) substrate to form an anode. Hereafter, heavily boron doped SiC layer was deposited in the lithography mask etched pits in another side of c-Si, heavily phosphorus doped Si film was subsequently grown on the end inserted SiC to form a cathode. For a comparison, a traditional p+-n−-n+ type device without SiC was fabricated by the PECVD growing heavily boron and heavily phosphorus doped films on two sides of the c-Si respectively. Nanocrystallization was demonstrated by X-ray diffraction and high resolution transmission electron microscopy in the fabricated films. Capacitance vs. voltage relation, current vs. voltage feature and reverse recovery waveform were measured to reveal the performance of the studied components. The important roles of (p+)nanocrystalline SiC in the static and dynamic conduction processes in operating device were probed, which indicates that the reverse recovery behaviors were improved.

Elevated temperature dependent transport properties of phosphorus and arsenic doped zinc oxide thin films

Elevated temperature dependent Hall effect measurements were performed in a wide temperature range from 80 to 800 K to study transport properties of zinc oxide (ZnO) thin films heavily doped with phosphorus (P) and arsenic (As), and grown on sapphire substrates by RF magnetron sputtering. Double thermal activation processes in both P- and As-doped ZnO thin films with small activation energy of ∼0.04 eV and large activation energy of ∼0.8 eV were observed from variable temperature Hall effect measurements. The samples exhibited n-type conductivities throughout the temperature range. Based on photoluminescence measurements at 11 K and theoretical results, the large activation energy observed in the temperature dependent Hall effect measurement has been assigned to a deep donor level, which could be related to oxygen vacancy (VO) in the doped ZnO thin films.

Phosphorus-doped bismuth telluride films by electrodeposition

Phosphorus-doped Bi2Te3 films were synthesized on a stainless-steel electrode by electrochemical deposition. X-ray diffraction, scanning electron microscopy and transmission electron microscopy confirmed that the films are single-phased Bi2Te3 solid solutions with a rhombohedral structure. The as-prepared films exhibit n-type characteristics with the Hall coefficient −1.76E−2 m3 C−1 and the electrical conductivity 280 S cm−1. The thermal conductivity is 0.47 W m−1 K−1, which is as low as one-third of the value observed in the bulk material. The doped P atoms occupy the interstitial positions between the two adjacent Te(1) layers connected by Van der Waals interaction in Bi2Te3.

Electrochemical Properties of P-Doped Silicon Thin Film Anodes of Lithium Ion Batteries

Silicon would seem to be a possible candidate to replace graphite or carbon as anode materials for lithium ion batteries based on its potential high capacity of 4200 mAhg-1. The main problem that must be solved for commercial application of silicon as anode material was the poor cyclic performance due to severe volume expansion during repeated charged-discharged cycles and its low electrical conductivity. In this work, we proposed Phosphorus doped (P-doped) Si films as anodes in lithium ion batteries. The electrochemical properties of the silicon based electrodes were examined by means of charge-discharge and impedance test. In comparison with the bare silicon electrode, the P type silicon electrode exhibited higher specific capacity of 2585 mAhg-1 until the 50th cycle. It was attributed to the improved electrical conductivity of Si film and reduced charge transfer resistance

Thermal and fire stability of cotton fabrics coated with hybrid phosphorus-doped silica films

Hybrid phosphorus-doped silica films have been prepared through sol–gel processes to enhance the thermal and fire stability of cotton. To this aim, 3-aminopropyltriethoxysilane and N,N,N′,N′,N″,N″-hexakis-methoxymethyl-[1,3,5]triazine-2,4,6-triamine have been reacted with diethylphosphatoethyltriethoxysilane. FT-IR spectroscopy was exploited for assessing the formation of the silica skeleton on the cotton surface and for evaluating the interactions between the cellulosic fibres and the doped film. The effect of the concurrent presence of Si, P and N on cotton has been investigated by thermogravimetric analyses and the flammability behaviour has been assessed by vertical flammability tests, as well. The sol–gel treatments in the presence of phosphorus and nitrogen turned out to play a protective role on the degradation of the cotton fibres, hindering the formation of volatile species that fuel the further degradation and favouring the formation of a carbonaceous structure.

Mechanical properties of thin films of hydrogenated silicon and their relationship with microstructure

Thin films of hydrogenated silicon were deposited on glass and single-crystalline silicon substrates using a capacitively coupled radio-frequency plasma-enhanced vapor-deposition system with the help of direct-current bias stimulation. Micro-Raman scattering was applied to investigate the microstructure of the thin films obtained. The crystalline volume fraction, X c, was obtained from the Raman spectra. Microscopic mechanical characterization of the thin films was carried out by nanoindentation based on the conventional depth-sensing indentation method. An analytical relation between X c and the elastic modulus was thereby established. The elastic modulus of the film on a glass substrate was found to be lower than that of the film on a monocrystalline silicon substrate with the same X c. The grain size of a phosphorus-doped thin film was smaller than that of the intrinsic one, with greater ordering of the grains and X c was found to be usually above 40%. A film with boron doping was on the opposite side, with X c usually below 40%. In the phosphorus-doped, intrinsic, and boron-doped films, the elastic moduli were lower when the X c values were 45%, 30%, and 15%, respectively.

Structure differences between TiO 2 and phosphorus implanted TiO 2 films caused by thermal treatment

The titanium oxide film has been deposited on Si wafers (110) by unbalance reactive magnetron sputtering and modified by phosphorus ion implantation and succeeding vacuum annealing. The structural, states of surface chemistry and surface morphology of the films have been investigated by X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), atomic force microscope (AFM) and Scanning Electron Microscope (SEM), respectively. The results of XRD show rutile structure of as-deposited film, which is not changed by phosphorus implantation and vacuum annealing. However, a slightly shift of the peaks position to higher degree and the half width increases after ion implanted and vacuum annealing represent that the variety of the structure film caused by these treatments. The surface roughness is inclined to increase with the rising of annealing temperature for both undoped and P doped titanium oxide films. The surface chemistry presents significant difference between undoped and phosphorus doped films after a vacuum annealing, it may be attributed to the different evolvement of the surface defects existing in the film, which may be considered as an important influencing factor in the blood compatibility of the titanium oxide film.

Effect of VI/II ratio upon photoluminescence and electrical properties of phosphorus-doped ZnTe films grown by metalorganic vapor phase epitaxy

We have investigated photoluminescence and electrical properties of P−doped ZnTe layers grown by metalorganic vapor phase epitaxy as a function of VI/II ratio. Near band-edge emissions are strongly influenced by VI/II ratio. The low VI/II ratio corresponding to Zn-rich condition brings about heavy p-type doping with P as compared to Te-rich condition. The best VI/II ratio for obtaining high quality layer is one. A maximum carrier concentration of 5.4 × 10 18 cm −3 is attained even for as-grown ZnTe layer. In this sample, the carrier concentration is almost independent of the measurement temperature, indicating conduction in an impurity band formed by shallow acceptor.

A study of metal contact properties on thermal annealed PECVD SiC thin films for MEMS applications

AbstractThe investigation of metal contact properties of thermal annealed PECVD n‐type SiC thin films for micro‐electromechanical system (MEMS) is reported. The PECVD SiC films were annealed at 1200 °C during 2 hours to obtain poly 3C‐SiC, which is evidenced by the presence of (111) plane of 3C–SiC crystalline phase in the X‐ray diffraction (XRD) pattern and by strong and narrow Lorentzian SiC stretching peak in the FTIR spectra. Hall Effect measurements at room temperature demonstrate that these annealed phosphorus doped films are n‐type semiconductor with donor concentration of 6 × 1019 cm–3. The studied metals were titanium, aluminum and nickel. The metal to poly‐SiC contact were studied using the TLM technique. The three metals exhibited excellent I‐V linearly and showed ohmic characteristics at room temperature. In the best case, a specific resistance of 6 × 10–4 Ωcm2 was obtained for nickel contacts. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Defect Reduction in Polycrystalline Silicon Thin Films at 150 °C

We report defect reduction in 50-nm-thick laser-crystallized polycrystalline silicon (poly-Si) films by a combination of hydrogen plasma at 100 W for 5 s at room temperature with 4.7×105 Pa H2O vapor heat treatment at 150 °C for 6 h. The present treatment increased the photoconductivity to 1×10-3 S/cm for undoped poly-Si films under the illumination of 532 nm light at 100 mW/cm2. It also increased the electrical conductivity to 30 S/cm for 2×1019 cm-3 phosphorus-doped poly-Si films. Those values were comparable to those for samples treated with 1.3×106 Pa H2O vapor heat treatment for 3 h at 260 °C. Hydrogen concentration increased from 1.6 to 5.4 at. % as hydrogen plasma duration increased from 5 to 120 s. It was decreased by subsequent H2O vapor heat treatment at 150 °C, and ultimately ranged from 1.1 to 4.5 at. %. Hydrogen atoms play a catalytic role in the dissociation of H2O molecules at 150 °C.

Phosphorus-doped silicon quantum dots for all-silicon quantum dot tandem solar cells

Doping of Si quantum dots is important in the field of Si quantum dots-based solar cells. Structural, optical and electrical properties of Si QDs formed as multilayers in a SiO 2 matrix with various phosphorus (P) concentrations introduced during the sputtering process were investigated for its potential application in all-silicon quantum dot tandem solar cells. The formation of Si quantum dots was confirmed by transmission electron microscopy. The addition of phosphorus was observed to modify Si crystallization, though the phosphorus concentration was found to have little effect on quantum dot size. Secondary ion mass spectroscopy results indicate minimal phosphorus diffusion from Si QDs layers to adjacent SiO 2 layers during high-temperature annealing. Resistivity is significantly decreased by phosphorus doping. Resistivity of slightly phosphorus-doped (0.1 at% P) films is seven orders of magnitude lower than that of intrinsic films. Dark resistivity and activation energy measurements indicate the existence of an optimal phosphorus concentration. The photoluminescence intensity increases with the phosphorus concentration, indicating a tendency towards radiative recombination in the doped films. These results can provide optimal condition for future Si quantum dots-based solar cells.

Field emission properties of DLC and phosphorus-doped DLC films prepared by electrochemical deposition process

Field emission behavior of diamond-like carbon (DLC) and phosphorus-doped DLC (p-DLC) films prepared by electrochemical deposition process was comparatively investigated. It was shown phosphorus incorporation in the DLC film could lower the turn on field from 12 to 9.5V/μm and increase the current density from 12.6 to 45.7μA/mm2 under high electric field. And better field emission performance of p-DLC films would be mainly attributed to the influence of the surface morphology and the changes of microstructure due to the phosphorus incorporation.

Formation of Low-Defect-Concentration Polycrystalline Silicon Films by Thermal Plasma Jet Crystallization Technique

Defect concentration in polycrystalline silicon (poly-Si) films formed by thermal plasma jet (TPJ) annealing and excimer laser annealing (ELA) has been investigated on basis of the electrical property and spin density (Ns). Phosphorus-doped Si films with an average concentration of 4.3 ×1017 cm-3 and crystallized by TPJ annealing showed electrical conductivity (σ) values of 2.0 ×10-3–7.8 ×10-2 S/cm, whereas ELA Si films show much lower σ values of (1.6–4.5) ×10-6 S/cm regardless of irradiated laser energy density. Ns values in TPJ annealed Si films were (2.3–4.5) ×1017 cm-3, which are roughly one order of magnitude lower than those of ELA films. These results indicate that dangling bonds in crystallized films are the predominant traps and they strongly govern the electrical property. TPJ crystallization offers the possibility of fabricating poly-Si films with a low defect concentration presumably owing to the much lower cooling rate (∼105 K/s) during crystalline growth than that of ELA (∼1010 K/s). By treating TPJ annealed films with hydrogen plasma for 10 min at 250 °C, a defect density as low as 5.0 ×1016 cm-3 is achieved.

Temperature dependent photoluminescence study on phosphorus doped ZnO nanowires

We report temperature dependent photoluminescence studies on phosphorus doped ZnO nanowires. The shape of the spectra is very similar to those of phosphorus doped ZnO films. The photoluminescence spectrum at 10K is dominated by neutral acceptor bound exciton (AX0) emissions. The acceptor binding energy determined also agrees with the corresponding value in phosphorus doped films. Studies on the AX0 intensity show two quenching channels, associated with the thermal dissociations of AX0 to a free exciton and of shallow residual donors. The residual donors revealed provide a clue for the difficulty in p doping of ZnO.