Ruiying Zhang

Absorption enhancement analysis of crystalline Si thin film solar cells based on broadband antireflection nanocone grating

1 mu m thick Si solar cells based on nanocone grating (NCG) with height of 100-800 nm and period of 100, 500, and 800 nm are numerically investigated through reflectivities, absorption enhancement factors, absorption spectra, optical generation rates, ultimate efficiencies, and diffraction angles. Compared with the planar Si solar cell, absorption enhancement are observed in any solar cells with NCG surface. Their absorption enhancement mechanism varies with the incident wavelength range. When incident wavelength lambda lambda > 500 nm, even though the absorption enhancement is still dominated by antireflection of the front surface, cavity-resonance effect and guided-mode excitation induced by high order diffraction start to make contribution. When lambda > 600 nm, the contribution of guided-mode excitation induced by lower-order diffraction becomes larger and larger once the diffraction angle is larger than its critical angle. For the structure with P = 100 nm, high-order diffraction cut-off at the longer wavelength range is the main reason of its lower absorption enhancement and ultimate conversion efficiency. For P = 800 nm, the lower absorption enhancement and ultimate efficiency is also observed due to the high reflection loss and mode leakage induced by 1(st) order diffraction where its diffraction angle is lower than its critical angle. Higher absorption and ultimate conversion efficiencies are achieved in P = 500 nm due to the good balance between antireflection performance and guide-mode excitation induced by the high order diffraction is achieved. Moreover, such absorption enhancement is closely related with its height of NCG gratings. Reflection loss reduction, the interaction volume reduction between the incident light and Si material, and higher photon density in NCG structure coexists with H increasing, which results in absorption enhancement in P = 500 nm and P = 800 nm, but absorption reduction in P = 100 nm where high order diffraction cut-off. Based on these analysis, we do believe that high absorption and ultimate conversion efficiency should be achieved in NCG-based solar cells where both the lower reflection in short wavelength domain and guide-mode excitation induced by 1(st) and 2(nd) diffraction in longer wavelength domain can be achieved. According to this rule, the optimized structure is NCG with P = 559 nm and H = 500 nm, by which, the highest optical generation rate of 536.57 x 10(4) W/cm(3) and ultimate efficiency of 28.132% are achieved. Such analysis should benefit the design of the thin film solar cells with nano-structured diffraction gratings.

Broadband quasi-omnidirectional antireflection AlGaInP window for III-V multi-junction solar cells through thermally dewetted Au nanotemplate

Al(Ga)InP subwavelength structures (SWS) were fabricated and optimized through thermally dewetted Au nanotemplate and ICP pattern-transfer. When λ< 900 nm, most AlGaInP nanostructures exhibit the reflectivity of less than 2% and insensitive to the incident angle up to 45°. When λ extends to 1800 nm, the reflectivity of less than 5% over 0°-45° is achieved in the optimized nanostructure, which benefits III-V multi-junction solar cells to improve their efficiency. Moreover, not only is such cost-effective nano-fabrication process completely compatible with the other processing of III-V solar cells, but their defined disordered SWS benefit the antireflection performance over broadband and wide view according to the comparison between the measurement and simulation results from AlGaInP SWS.

Fabrication of InGaAsP Double Shallow Ridge Rectangular Ring Laser With Total Internal Reflection Mirror by Cascade Etching Technique

InGaAsP double shallow ridge rectangular ring laser photonics integration circuits have been successfully fabricated by cascade etching technique. Varied thresholds with coupling current I_c and coupling length L_c are observed. The lowest threshold current of 75 mA, including I_c and I_d, at I_c = 30 mA in the device of L_c = 300 mum is obtained. The device of L_c = 200 mum exhibits single-mode operation with sidemode suppression ratio = 15 dB and Q = 6513 just beyond the threshold. The cascade etching technique is of interest for fabrication of other multilayer monolithic photonic integration circuits.

Efficiency improvement in Si thin film solar cells by employing composite nanocone-shaped grating structure

The improvement in both the light absorption and energy conversion efficiency for thin film silicon solar cells by employing Al2O3/Si or SiN/Si composite nanocone-shaped gratings (CNCG) is theoretically studied. Our results show that the enhancement of the absorption and efficiency for Si thin film solar cells decorated by CNCG is mainly dominated by the nanocone-shaped gratings, but slightly fluctuated with the dielectric cladding layer and its thickness. The performance improvement is more significant using SiN/Si CNCG than using Al2O3/Si CNCG. The highest conversion efficiency of 6.60 and 9.53% are achieved in 1-mu m-thick solar cells with SiN (120 nm)/Si CNCG and 2-mu m-thick Si solar cells with SiN (90 nm)/Si CNCG respectively, which are compared to the conversion efficiencies of 3.23 and 3.96% for their planar counterparts. When the surface passivation effect is considered, the conversion efficiency should be enhanced more

A short carrier lifetime semiconductor optical amplifier with n-type modulation-doped multiple quantum well structure

Semiconductor optical amplifiers (SOAs) with n-type modulation-doped multiple quantum well structure have been investigated. The shortened carrier lifetime is derived from the PL spectrum and electrical modulation frequency response measurement. The carrier lifetime in semiconductor optical amplifiers with any n-type-2-modulated doping multiple quantum well structure is less than 60% of that in the undoped partner. The shortest measured carrier lifetime of 236 ps in the MD-MQW SOA with sheet carrier density of 3 x 10(12) cm(-2) was only 38% of that in the undoped MQW SOA, which can increase the wavelength conversion efficiency via four wave mixing by a factor of about 7 and switching speed via XGM and XPM applications by a factor of 2.63.

Flexible Coupling Ratio in Single Ring Resonator Through Active Vertical Coupler

A flexibly coupled semiconductor rectangular ring resonator based on a two-section active vertical coupler is demonstrated. The measured and calculated results show consistently varied thresholds and coupling ratio dependent on coupling length and internal loss. For the same configuration devices, the adjustable range of the coupling ratio widens with the reflectivity of the total internal reflection mirrors; for the same reflectivity, such range widens with the coupling length. The widest range of 0.0076-0.4707 is achieved in the device with m. Flexible coupling should increase the tolerance of device design and fabrication and bring a benefit to very large scale integration.

Broadband and omnidirectional antireflection of SiN composite nanostructures–decorated Si surface for highly efficient Si solar cells

Abstract. SiN composite nanostructures (CNs), composed of SiN nanorods and the underlying SiN film, are formed on Si substrate through SiN deposition, nanosphere lithography, and dry etching. The antireflection performance of Si samples decorated by the SiN CNs with different morphology is experimentally investigated. All the SiN CNs decorated Si samples exhibit antireflection over 300 to 1000 nm and a wide view. Their antireflection performance varies with the height of the nanorods (H) and the thickness of the underneath film (T). A reflectivity of less than 10% over 300 to 1000 nm and an incident angle of 8 deg and 65 deg are achieved in the optimal antireflection structures with H=240  nm, T=750  nm and H=500  nm, T=300  nm, respectively. Furthermore, antireflection behavior in the SiN CNs decorated Si sample with H=500  nm, T=300  nm is compared with that in Si samples decorated by 565- and 60-nm thick SiN film. A weighted reflectance of about 5% is achieved in an SiN CNs decorated Si sample in any incident angle, which is much lower than that in any SiN film coated Si sample. Moreover, such a performance is beyond the limitation of interface reflectivity of Si and SiN materials, and should benefit Si solar cells to simultaneously enhance the absorption and surface passivation.

A 1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well DFB laser by MOCVD

1.5 mu m n-type InGaAsP/InGaAsP modulation-doped multiple quantum well (MD-MQW) DFB lasers have been fabricated successfully by low pressure metal organic chemical vapour deposition (LP-MOCVD) technology. The experimental results indicate that n-type MD-MQWs can effectively reduce the threshold Current compared with conventional multiple quantum well DFB lasers. Theoretical analysis indicates that such an effect is due to the much smaller absorption loss and lower Auger recombination, compared with that in an undoped MQW structure. Moreover, the introduction of n-type dopant of suitable levels of concentration in the barrier layers enhances the dynamic characteristics of DFB lasers, due to a coupling between the adjacent quantum well layers and tunnelling-assisted injection, which can reduce the relatively long capture time and increase the effective differential gain 1/X dG/dn .

A Novel Extremely Broadband Superluminescent Diode Based on Symmetric Graded Tensile-strained Bulk InGaAs

A novel broadband superluminescent diode (SLD), which has a symmetric graded tensile-strained bulk InGaAs active region, is developed. The symmetric-graded tensile-strained bulk InGaAs is achieved by changing the group III TMGa source flow only during its growth process by low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE), in which the much different tensile strain is introduced simultaneously. At 200mA injection current, the full width at half maximum (FWHM) of the emission spectrum of the SLID can be up to 122nm, covering the range of 1508-1630nm, and the output power is 11.5mW.

Design of High-

A compact InP/InGaAsP passive ring resonator (PRR), in which a loss-compensation section is vertically integrated, for angular velocity sensing is theoretically studied in this paper. The loss compensation is realized by current injection into the optical gain section, which is optically coupled with the PRR. Based on the proposed loss-compensation scheme, the propagation loss in the PRR can be reduced down to 0.01 dB/cm. Consequently, the quality factor of up to 1.5 × 107 and resonance depth of more than 7 dB are theoretically obtained in such resonators with a radius of larger than 5 mm. Furthermore, when these compact PRRs are used as angular velocity sensors, the resolution of better than 10°/h and the angle random walk of less than 0.075° / √h are theoretically predicted. These characteristics indicate that our proposed compact PRRs are capable of acting as an angular velocity sensor in high efficient monolithically integration of resonant optical gyroscope applications in proof of principle.