Layer-thickness dependence of Si-nanocrystal (Si-NC) formation induced by furnace annealing in amorphous Si (a-Si)
/SiO2 multilayers is experimentally demonstrated with a radio-frequency-sputtered sample that has a-Si layers with
different thicknesses. Further, a modified model is developed to explain the Si-NC formation based on the Gibbs free
energy variation and it takes into account the whole formation process including nucleation and following growth. The
theoretical results show that there is a lower limit of Si layer thickness below which the crystal formation cannot occur
for a-Si/SiO2 multilayers, and the oxide interfaces cannot constrain the lateral growth of Si-NCs, which may lead to their
touches within the Si layers.
Near-infrared silicon solar cell response enhanced by gold nanoparticles with core-shell structure has been studied
experimentally. The colloidal core-shell gold nanoparticles are synthesized by the standard sodium citrate
reduction method. The enhanced photocurrent response of silicon solar cell is obtained over almost the entire
silicon response spectrum, and the obvious enhancement is observed when λ0 > 800nm. The highest value 12%
near λ0=1160nm is obtained.
The relationship between the reliability of GaN LEDs and their junction temperatures and ideal factors is investigated. 20
groups of both blue and white GaN LEDs are tested. Their ideal factors and junction temperatures under 700mA
operating current are measured. The measurement methods are introduced. After the measurement, 700mA high current
accelerated life test is carried out on the LEDs. Analysis results show that the reliability of the LEDs is strongly
dependent on their junction temperatures and ideal factors. For most of the unreliable LEDs with their 50% ALT life less
than 400 hours, their ideal factors are higher than 10, or the junction temperatures of the blue LEDs under 700mA are
higher than 130°C, and the junction temperatures of the white LEDs under 700mA are higher than 120°C.
High power GaN-based LEDs with nano-structured Ga-doped ZnO (GZO) transparent conductive layer (TCL) were
fabricated by using metal-organic chemical vapor deposition (MOCVD) method. Compared with the conventional LED
with Ni/Au or ITO process, the saturation current in the LEDs with GZO TCL approximately increased up to more than
14 % and 13 %, and the light output intensity up to 57.5 % and 30.1 %, respectively. This improvement was attributed to
the high carrier concentration of GZO TCL and the planar structure at the TCL bottom, which improved the electrical
conductivity, and therefore promoted current spreading. The refractive index of GZO is similar to GaN (n ≈ 2) and
thereby results in the reduction of the reflection loss between GaN and TCL interface. In addition, the nano-structure of
GZO TCL increased the light output critical angle and enhanced surface light emitting while reducing the lateral light
loss and consequently improved light extraction efficiency of LEDs.
The theory of mesopic vision provides an important theoretical foundation for the choice of road lighting sources. Based
upon a number of recent mesopic photometry studies, an equation (Emes = B•EP) to deduce from the Ep (photopic
illumination) to Emes (mesopic equivalent illumination) is proposed, where B is instant for modified coefficient. The
coefficient B can be used easily to calculate the mesopic equivalent illumination by using the measuring results of
photopic illumination for different correlated color temperature (CCT) light sources under mesopic light levels. Using
the equation, we analyze the variation of coefficient B with background lighting level of the different correlated color
temperature lighting sources under mesopic vision levels. By calculating the mesopic equivalent illumination of the
different sources, our results showing that the higher correlated color temperature LED sources have better visual effects.
Moreover, the results provide a basis for further studies on the illuminometer, which might be suitable for mesopic vision.
Gaussian beam is considered to investigate the axial resolution performances with the two-zone and three-zone
amplitude filters. The results show that only special designed three-zone pupils can produce super-resolution
performances in the axial direction. By the two kinds of filters Gaussian beam has the similar performance with Uniform
This paper describes the design and implementation of
a portable, inexpensive and cost effective spectrophotometer. The
device combines the use of compact disc (CD) media as
diffraction grid and 60 watt bulb as a light source. Moreover it
employs a moving slit along with stepper motor for obtaining a
monochromatic light, photocell with spectral sensitivity in visible
region to determine the intensity of light and an amplifier with a
very high gain as well as an advanced virtual RISC (AVR)
microcontroller ATmega32 as a control unit. The device was
successfully applied to determine the absorbance and
transmittance of KMnO4 and the unknown concentration of
KMnO4 with the help of calibration curve. For comparison
purpose a commercial spectrophotometer was used. There are
not significant differences between the absorbance and
transmittance values estimated by the two instruments.
Furthermore, good results are obtained at all visible wavelengths
of light. Therefore, the designed instrument offers an
economically feasible alternative for spectrophotometric sample
analysis in small routine, research and teaching laboratories,
because the components used in the designing of the device are
cheap and of easy acquisition.