X Wu

Effect of rapid thermal annealing on InP1-xBix grown by molecular beam epitaxy

The effect of post-growth rapid thermal annealing on structural and optical properties of InP1-xBix thin films was investigated. InPBi shows good thermal stability up to 500 °C and a modest improvement in photoluminescence (PL) intensity with an unchanged PL spectral feature. Bismuth outdiffusion from InPBi and strain relaxation are observed at about 600 °C. The InPBi sample annealed at 800 °C shows an unexpected PL spectrum with different energy transitions.

Growth of semiconductor alloy InGaPBi on InP by molecular beam epitaxy

We report the first successful growth of InGaPBi single crystals on InP substrate with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InGaPBi thin films reveal excellent surface and structural qualities, making it a promising new III-V compound family member for heterostructures. The strain can be tuned between tensile and compressive by adjusting Ga and Bi compositions. The maximum achieved Bi concentration is 2.2 ± 0.4% confirmed by Rutherford backscattering spectroscopy. Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the InP bandgap.

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

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=240u2009u2009nm, T=750u2009u2009nm and H=500u2009u2009nm, T=300u2009u2009nm, respectively. Furthermore, antireflection behavior in the SiN CNs decorated Si sample with H=500u2009u2009nm, T=300u2009u2009nm 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.