Jingchang Zhong

Grain size effect of nanocrystalline ZnO on characteristics of dye-sensitized solar cells

In this study, we demonstrate a dye-sensitized solar cells (DSSCs) was made by using two different grain sizes of nanocrystalline ZnO (nc-ZnO) as the photoelectrodes of the cells. It can be seen that the efficiency of this new type of solar cells obviously varied as the size and morphology of ZnO nanostructures. The short-circuit photocurrent, fill factor, and power conversion efficiency are enhanced while the smaller nc-ZnO was utilized in such a device.

Fabrication of high-power VCSEL with reticular electrode

We report the fabrication of a novel high-power VCSEL with reticular electrode in this letter. The analysis shows that the reticular electrodes can improve the homogeneity in the injected current and heighten VCSEL optical output power. The high-power reticular electrode VCSELs with 500μm aperture have been made and tested. Testing results show the slope efficiency of 0.75mW/mA, output power of up to 410mW and a peak power conversion efficiency of 35%. Its near-field pattern exhibits a homogeneous distribution. The high-power reticular electrode VCSEL has better optoelectric characteristic.

Vertical-cavity surface-emitting lasers fabricated with efficient packaging method

Vertical cavity surface emitting lasers with large aperture were fabricated by using wet oxidation technique at about 420ºC, and the device chips were packaged with three different packaging methods. The optical output power and wavelength shift of the devices were compared experimentally. The device bonded with diamond spreader shows the best performance, and 200µm-diameter device produces a room temperature continuous wave optical output power of 0.51W. The devices with larger aperture size were also fabricated in experiment.

Distributed Bragg reflector mirror with a double-wavelength reflection: design and calculation

We designed a distributed Bragg reflector mirror with a double-wavelength reflection, which can be used into opticallypumped vertical external cavity surface emitting lasers. This kind of mirror can reflect both the lasing light as a resonance mirror and the pumping light to reflect the pumping light back into absorbing area for increasing the absorption efficiency and improving the thermal characteristics of the laser device. By using GaAs/AlGaAs heterostructure layers and material data, the optical characteristics of the distributed Bragg reflector mirror with a double wavelength reflection at two peaks was calculated. From the calculated results, the two reflection peaks occur at 808nm and 980nm just as the structure design. The reflectivity can be more than 99% for 25-pair DBR. The reflection band width is about 20nm and 25nm for the 808nm and 980nm peaks respectively. This can give a flexibility selection for the double-wavelength distributed Bragg reflector structure design.

VCSEL with reticular electrode and larger emitting aperture and its optoelectronic characteristics

The enlargement of the emitting aperture is usually one of the important methods of increasing verticalcavity surface-emitting laser (VCSEL) optical output power. However, in a VCSEL with a larger aperture, the inhomogeneity in the injected current often causes inhomogeneous or even no emission. To solve this problem and to increase VCSEL output power, as well as to improve its thermal characteristics, we develop a new type of injected VCSEL with a larger aperture and a reticular electrode, where the conventional circular injection electrode of the P side is turned into a reticular one, and the heat sink is on the N side. The tests of the new VCSEL show an improvement in homogeneity in not only the injected current but also the emission intensity. The optical output power is also considerably increased, and the device optoelectronic performance is improved.

Optical coatings optimization of semiconductor laser

The characteristics of GaAs-based semiconductor Laser with antireflective and high reflective coatings are studied. The film designs are optimized with programmed software using the film design program for a double-layer scheme. According to the numerical simulations, the different double-layer with proper parameters is coated onto GaAs-based semiconductor Laser. The thickness of double layers is also calculated using the software taking account of antireflective and high reflective coating in the design of double layer film. With the optimized design of double-layer film, the power properties of GaAs-based semiconductor Laser are improved, and the experimental results satisfy the application requirements as semiconductor Laser.

Numerical simulation and experiment of novel semiconductor/superlattice distributed Bragg reflectors

We introduced a novel semiconductor/superlattice AlAs/(GaAs/AlAs) distributed Bragg reflector (DBR), and the reflection spectrum of the DBR at 980nm wavelength is simulated by employing transfer matrix method. By adjusting the thickness of AlAs layer and the period of superlattice GaAs/AlAs, the DBR with center wavelength at 1500nm is also investigated theoretically. In experiment, this kind of DBR is grown on GaAs (100) substrate. From the measured reflection spectrum, the central wavelength is about 980 nm with high reflectivity.

Temperature characteristics of vertical-cavity surface-emitting lasers

The temperature characteristics of Oxide-confined VCSEL are described, these records of high operating temperature are caused by high characteristic temperature. The VCSEL device temperature is increased by heating from ambient temperature 20°C up to 100°C. The effect of temperature elevation increased from T1 to T2 on the threshold current Ith(T) is often described by a characteristic temperature. We obtain a function T0(T) which decreases from 220K at 20°C temperature to 200K at 100°C. The essential improvements for the oxide-confined VCSEL in this work are focused on the following two points. First, we decrease the series resistance of the VCSEL. Secondly, the oxide-confined technique reduces defects and optical absorption in the active region. The oxide-confined is worthy to be used just because of its better confinements for both beam and current, easier processing, and lower cost. The fact that the device’s threshold current in pulse operation slightly depends on ambient temperature means that the VCSEL’s characteristic temperature (T0) is higher.