The optimizations of the emitter region and the metal grid of a concentrator silicon solar cell are illustrated. The optimizations are done under 1 sun,100 suns and 200 suns using the 2D numerical simulation tool TCAD software.The optimum finger spacing and its range decrease with the increase in sheet resistance and concentration ratio.The processes of the diffusion and oxidization in the manufacture flow of the silicon solar cells were simulated to get a series of typical emitter dopant profiles to optimize.The efficiency of the solar cell under 100 suns and 200 suns increased with the decrease in diffusion temperature and the increase in oxidation temperature and time when the diffusion temperature is lower than or equal to 865℃.The effect of sheet resistance of the emitter on series resistance and the conversion efficiency of the solar cell under concentration was discussed.
Light trapping plays an important role in improving the conversion efficiency of thin-film solar cells.The good wideband light trapping is achieved using our periodically truncated cone Si nanowire(NW) structures,and their inherent mechanism is analyzed and simulated by FDTD solution software.Ordered cylinder Si NW structure with initial size of 80 nm and length of 200 nm is grown by pattern transfer and selective epitaxial growth.Truncated cone Si NW array is then obtained by thermal oxidation treatment.Its mean reflection in the range of300–900 nm is lowered to be 5% using 140 nm long truncated cone Si NW structure,compared with that of 20%using cylinder counterparts.It indicates that periodically truncated Si cone structures trap the light efficiently to enhance the light harvesting in a wide spectral range and have the potential application in highly efficient NW solar cells.
The silicon vertical multi-junction(VMJ)solar cell has a good potential in high concentration,but it requires high quality front and back surface passivation layers to keep its high efficiency.We try to add dopants into the front and back surfaces of the VMJ cell to release this strict requirement in this work.The effects of recombination velocities,doping types and doping profiles of front and back surfaces on the performance of the P-type VMJ cell were calculated under 1 sun and 1000 suns.The 2D numerical simulation tool TCAD software was used.The performance of the VMJ cell without front and back surface dopants was also calculated for comparison.It was found that the requirement of high quality front and back surface passivation layers could be released remarkably by adding either N-type or P+-type front and back surface dopants.For the two types of front surface dopants,the highest efficiencies of the cells were got by light dopant;for the two types of back surface dopants,the doping type and profile affected little on the performance of the cell in our calculation range.It was also found that the series resistance of the VMJ cell with N-type front surface dopant was decreased by the 2D effect of front surface emitter.The VMJ cell with P+-type front surface dopant had the highest efficiency under 1000 suns and the VMJ cell with N-type front surface dopant had the highest efficiency under 1 sun in our calculation range.
We investigate the dark current mechanism for an unpassivated mid wavelength(MW) type II InAs/GaSb superlattice infrared photodetector by doing the variablearea diode tests. The bulk resistance-area product and the resistivity due to the surface current are determined to be17.72 X cm2 and 704.23 X cm at 77 K, respectively. It is found that for all the mesa sizes used, the dark current is dominated or predominated by the surface component, and with scaling back the mesa size, the surface current increases while the bulk component decreases. The activation energy is determined to be 145 meV for the temperature range around 140–280 K, while it is 6 meV when temperature is below 100 K. It is also found that the dark current is dominated by the generation-recombination current for the MW device when temperature is between140 and 280 K.
The effects of ion doses on the properties of boron implanted Si for n-type solar cell application were investigated with doses ranging from 5×1014cm-2to 2×1015cm-2and a subsequent two-step annealing process in a tube furnace.With the help of the TCAD process simulation tool, knowledge on diffusion kinetics of dopants and damage evolution was obtained by fitting SIMS measured boron profiles. Due to insufficient elimination of the residual damage, the implanted emitter was found to have a higher saturation current density(J0e) and a poorer crystallographic quality. Consistent with this observation, V oc, J sc, and the efficiency of the all-implanted p+–n–n+solar cells followed a decreasing trend with an increase of the implantation dose. The obtained maximum efficiency was 19.59% at a low dose of 5×1014cm-2. The main efficiency loss under high doses came not only from increased recombination of carriers in the space charge region revealed by double-diode parameters of dark I–V curves, but also from the degraded minority carrier diffusion length in the emitter and base evidenced by IQE data. These experimental results indicated that clusters and dislocation loops had appeared at high implantation doses, which acted as effective recombination centers for photogenerated carriers.
We report a novel lateral cavity surface emitting laser based on sub-wavelength high-index-contrast grating with in-plane resonance and surface-normal emission. The device is fabricated on a simple commercial wafer without the distributed Bragg reflector and it needs no wafer bonding. It exhibits a side mode suppression ratio of 23.0 d B and a high output power of 5.32 m W at 1552.44 nm. The specific single mode lasing agrees well with the band edge mode calculation of the grating. In 3D simulation, we observe obvious light output from the grating.
A high-speed broadband tunable microwave source utilizing the wavelength tunable characteristics of distributed Bragg reflector(DBR) laser is proposed and demonstrated.The wavelength tuning of the laser is achieved instantaneously by controlling the voltage of the phase section of the DBR laser.By means of optical delay self-heterodyne technology,the microwave signal with the property of frequency broadband tuning is generated.Sweep speeds of 5 and 40 μs of the sweep-frequency source prototype were achieved and the maximum tuning range was up to 38.45 GHz.
The experimental optimization of a 10 GHz optoelectronic oscillator (OEO) based on a 1.55 μm directly modulated distributed feedback (DFB) laser is demonstrated in this paper. The phase noise of the directly modulated laser (DML) based OEO is significantly reduced by proper selection of the laser's bias current and by using a dispersion shifted fiber as a delay line. The phase noise performance of the DML OEO achieved after optimization is close to that of a conventional OEO constructed using a commercial DFB laser and a LiNbO 3 Mach-Zehnder modulator. The DML based OEO is most promising for future realization of a miniature OEO architecture with the components integrated on a semiconductor substrate.
WANG LiXianZHU NingHuaLIU JianGuoLI WeiZHU HongLiangWANG Wei
We propose a polarization-insensitive and broadband subwavelength grating reflector based on a multilayer structure.The reflector has an overlapped high reflectivity(>99.5%) bandwidth of 248 nm between the TE and the TM polarizations,which is much higher than the previously reported results.We believe this subwavelength grating reflector can be applied to unpolarized devices.
