Lu Shulong

Spatial interference effect of two-photon in femtosecond-pulse pumped spontaneous parametric down-conversion

We have used the transverse correlated properties of the entangled photon pairs generated in the process of spontaneous parametric down-conversion, which is pumped by a femtosecond pulse laser, to perform Youngs interference experiment. Unlike the case of a continuous wave laser pump, a broadband pulse laser pump can submerge an interference pattern. In order to obtain a high visibility interference pattern, we used a lens with a tunable focal length and two interference filters to eliminate the effects of the broadband pump laser. It is proven that the process of two-photon direct interference is a post-selection process.

High quality non-rectifying contact of ITO with both Ni and n-type GaAs*

We report the specific contact resistance for ITO with both metal and a semiconductor. Good quality ITO was deposited by electron beam evaporation with the resistivity of 2.32 × 10-4 Ω ·cm and an averaged transmittance of 92.8% in the visible light region. The circular transmission line model (c-TLM) method was used to evaluate and compare the properties of the ITO/metal and ITO/semiconductor ohmic contacts. The lowest specific contact resistance of the ITO/Ni is 2.81 × 10-6 Ω ·cm2, while that of ITO/n-GaAs is 7 × 10-5 Ω ·cm2. This is the best ohmic contact between ITO and n-GaAs ever reported. These results suggest that good quality ITO has strong potential to be used to realize highly efficient solar cells.

0.6-eV bandgap In0.69Ga0.31As thermophotovoltaic devices with compositionally undulating step-graded InAsyP1−ybuffers

Single-junction, lattice-mismatched In0.69Ga0.31As thermophotovoltaic (TPV) devices each with abandgap of 0.6 eV are grown on InP substrate by metal—organic chemical vapour deposition (MOCVD). Compositionally undulating step-graded InAsyP1−y buffer layers with a lattice mismatch of ~1.2% are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate. With an optimized buffer thickness, the In0.69Ga0.31As active layers grown on the buffer display a high crystal quality with no measurable tetragonal distortion. High-performance single-junction devices are demonstrated, with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm2, which are measured underthe standard solar simulator of air mass 1.5-global (AM 1.5 G).

Temperature-induced switching-over of the luminescence transitions in GaInNAs/GaAs quantum wells

Photoluminescence (PL) spectra of the GaInNAs/GaAs single quantum well (SQW) with different N compositions are carefully studied in a range of temperatures and excitation power densities. The anomalous S-shape temperature dependence of the PL peak is analysed based on the competition and switching-over between the peaks related to N-induced localized states and the peak related to interband excitonic recombination. It is found that with increasing N composition, the localized energy increases and the turning point of the S-shape temperature dependence occurs at higher temperature, where the localized carriers in the bandtail states obtain enough thermal activation energy to be dissociated and delocalized. The rapid thermal annealing (RTA) effectively reduces the localized energy and causes a decrease of the switching-over temperature.