Xincai Wang

Optical absorption enhancement in nanopore textured-silicon thin film for photovoltaic application

Silicon thin film with a nanopore textured surface is systematically studied via simulation for photovoltaic application, where the optical characteristics are closely correlated with the nanopore structural parameters. It is found that the solar energy absorption could be optimized when the nanopore array structure dimensions are set as follows: periodicity of 700 nm, depth of 2000 nm, and pore diameter versus periodicity ratio of 87.5%. The result provides an additional guideline for the nanostructure surface texturing-process design for photovoltaic applications.

Design guideline of high efficiency crystalline Si thin film solar cell with nanohole array textured surface

Silicon thin film with a nanohole (NH) array textured surface is systematically studied via simulation for solar energy harvesting and compared with a nanopillar (NP) array textured one. It is found that for the same thickness and optimized structure parameters, the NH array shows superior light trapping capability and thus, higher power conversion efficiency than its NP counterpart. The requirement for efficient cells at the optically optimized NH and NP geometries are studied in terms of minority carrier diffusion length, emitter doping level, and the emitter junction depth after considering the impact of surface recombination velocity. The results provide a practical guideline to design and fabricate high efficiency and cost effective NH textured Si thin film solar cells.

Pulsed Laser Annealing of Silicon-Carbon Source/Drain in MuGFETs for Enhanced Dopant Activation and High Substitutional Carbon Concentration

We report for the first time, the use of pulsed laser annealing (PLA) on multiple-gate field-effect transistors (MuGFETs) with silicon-carbon (Si_1-xC_x) source and drain (S/D) for enhanced dopant activation and improved strain effects. Si_1-xC_x. S/D exposed to consecutive laser irradiations demonstrated superior dopant activation with a ~60% reduction in resistivity compared to rapid thermal annealed S/D. In addition, with the application of PLA on epitaxially grown Si_0.99C_0.01 substitutional carbon concentration C_sub increased from 1.0% (as grown) to 1.21%. This is also significantly higher than the C_sub of 0.71% for rapid thermal annealed Si_0.99C_0.01 S/D. With a higher strain and enhanced dopant activation, MuGFETs with laser annealed Si_0.99C_0.01 S/D show a ~53% drain-current improvement compared to MuGFETs with rapid thermal annealed Si_0.99C_0.01 S/D.

High efficiency silicon nanohole/organic heterojunction hybrid solar cell

High efficiency hybrid solar cells are fabricated based on silicon with a nanohole (SiNH) structure and poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The SiNH structure is fabricated using electroless chemical etching with silver catalyst, and the heterojunction is formed by spin coating of PEDOT on the SiNH. The hybrid cells are optimized by varying the hole depth, and a maximum power conversion efficiency of 8.3% is achieved with a hole depth of 1 μm. The SiNH hybrid solar cell exhibits a strong antireflection and light trapping property attributed to the sub-wavelength dimension of the SiNH structure.

Strained SiGeSn formed by Sn implant into SiGe and pulsed laser annealing

Incorporation of tin (Sn) in substitutional sites in strained Si0.75Ge0.25 was demonstrated by Sn implant and pulsed laser annealing. The surface of Si0.75Ge0.25 was amorphized by Sn implant but was recrystallized after pulsed laser annealing. The crystalline Si1−x−yGexSny layer formed was studied by Rutherford backscattering spectrometry and Raman spectroscopy. A substitutionality up to 62% Sn and 80% Ge was obtained at an optimal laser power of 400mJcm−2 for five laser pulses. A compressive strain of −1.15% was also obtained due to Sn incorporation. The presence of Sn also increased the active B dopant concentration in activating Si1−x−yGexSny to give low sheet resistance. The implantation of Sn and B followed by pulsed laser annealing could be useful for application in strain engineering of high mobility metal-oxide-semiconductor field-effect transistors.

Design guidelines for slanting silicon nanowire arrays for solar cell application

The reflectance and absorption characteristics of slanting silicon nanowires (SiNWs) structure have been simulated using finite element method to provide a design guideline for its application in solar cell. The slanting angle for the nanowire structure is set at 40° on Si (111) wafer. The impact of the structural periodicity (P) and wire diameter/periodicity (D/P) ratio on the optical characteristics of the slanting SiNW has been systematically analyzed. It has been found that due to the much suppressed light reflection and stronger light trapping ability, the light absorption is significantly enhanced for the slanting SiNW structure compared with vertical SiNW structure. The optimal absorption condition is achieved when P = 800 nm and D/P = 0.7, yielding the highest ultimate efficiency of 33.45%. The result is better than the 28.36% that can be achieved for optimum vertical SiNWs. A comparison of the absorption characteristics of optimum slanting and vertical SiNWs structures is presented and analyzed i...

Maskless fabrication of large scale Si nanohole array via laser annealed metal nanoparticles catalytic etching for photovoltaic application

In this paper, laser annealing is used to produce metal (Ag) nanoparticles as etching catalyst on a silicon surface, which enables controllable fabrication of large-scale nanohole array surface texturing without using a mask. Semispherical Ag nanoparticles with variable size and distribution are achievable by manipulating the laser annealing parameters and metal film thickness, and the underlying physics is clarified. The nanoholes array in silicon can then be realized by selective etching of silicon under Ag pattern. The optical characteristics suggest that the surface reflection can be significantly suppressed owing to the nanohole texturing, which is promising for thin film photovoltaic applications.

N-Channel MOSFETs With Embedded Silicon–Carbon Source/Drain Stressors Formed Using Cluster-Carbon Implant and Excimer-Laser-Induced Solid Phase Epitaxy

In this letter, we report the use of a novel cluster-carbon (C₇ H₇ ⁺) implant and pulsed-excimer-laser-induced solid-phase-epitaxy technique to form embedded silicon-carbon (Si:C) source/drain (S/D) stressors. A substitutional carbon concentration C_sub of ~ 1.1% was obtained in this letter. N-channel MOSFETs (n-FETs) integrated with embedded silicon-carbon (Si:C) S/D stressors formed using the novel cluster-carbon implant and pulsed-laser-anneal technique demonstrate improvement in current drive of 14% over control n-FETs formed with Si preamorphization implant. I_OFFI_DSAT comparison shows a 15% I_DSAT enhancement for n-FETs with embedded Si:C S/D at an I_OFF = 1 nA/mum despite a slightly higher series resistance.

Route to Low Parasitic Resistance in MuGFETs with Silicon-Carbon Source/Drain: Integration of Novel Low Barrier Ni(M)Si:C Metal Silicides and Pulsed Laser Annealing

We report the demonstration of two distinct approaches to reduce parasitic resistances in MuGFETs with silicon-carbon (Si:C) S/D. First, the addition of dysprosium (Dy) in NiSi:C contacts reduces the electron barrier height by 38% on SiC. Device integration of the Ni(Dy)Si:C contacts provides a 30% reduction in series resistance leading to improved IDsat performance. Second, we also report the first demonstration of pulsed laser annealing (PLA) for MuGFETs with Si:C S/D for enhanced dopant activation, leading to ~50% lower series resistance. High carbon substitutional concentration (above 1.0%) in Si:C can be achieved with PLA for enhanced strain effects.

Design principles for plasmonic thin film GaAs solar cells with high absorption enhancement

In this paper, a systematic design and analysis of gallium arsenide thin film solar cells incorporated with a periodic silver nanoparticles (NPs) structure to enhance light absorption is presented using the finite element method. The influence of the silver nanoparticles diameter and structure periodicity on light absorption has been examined. It is found that the absorption is significantly enhanced due to the surface plasmon induced by the silver nanoparticles. The optimal structural parameters are achieved when the diameter of the nanoparticles is 200 nm and the periodicity is 444 nm. This gives rise to a maximum ultimate photocurrent of 26.32 mA/cm2 under AM1.5G solar irradiation. In addition, the underlying physics that accounts for the enhancement is discussed.In this paper, a systematic design and analysis of gallium arsenide thin film solar cells incorporated with a periodic silver nanoparticles (NPs) structure to enhance light absorption is presented using the finite element method. The influence of the silver nanoparticles diameter and structure periodicity on light absorption has been examined. It is found that the absorption is significantly enhanced due to the surface plasmon induced by the silver nanoparticles. The optimal structural parameters are achieved when the diameter of the nanoparticles is 200 nm and the periodicity is 444 nm. This gives rise to a maximum ultimate photocurrent of 26.32 mA/cm2 under AM1.5G solar irradiation. In addition, the underlying physics that accounts for the enhancement is discussed.