In this paper, the hydrophobic plasma-activated bonding of GaAs/Si was studied. We systematically analyzed the effect of different power, gas flow rate and activation time of plasma to the roughness of GaAs and Si wafers. The roughness of GaAs wafers decreased with increasing of power and activation time of plasma. The roughness of Si wafers did not change significantly with increasing of power of plasma, and decreased first and then increased with increasing of gas flow rate of Ar in our experiment. The number of dangling bonds in the surface of GaAs and Si wafers was increasing with the activation time. When the activation time was 3 minutes, the GaAs/Si wafers were successfully bonded under different power of plasma. By scanning acoustic microscope (SAM) testing, it was found that when the power was 200W, the bonded GaAs/Si wafer had the best bonding interface. Furthermore, the GaAs/Si bonding internal mechanism by plasma-activated bonding method was analyzed by testing the chemical composition of the bonding interface.
Femtosecond lasers have been found suitable for maskless photolithography with submicron resolution, which is very attractive for solving the problem of high photomask cost. Direct femtosecond laser writing of lithographic patterns is reported with submicron feature width on thin positive photoresist film. We use a scanning electron microscope to investigate the feature sizes of femtosecond laser lithography, which are determined by the incident laser power, the number of scan times and the substrate materials. Submicron T-shaped gates have been fabricated using a two-step process of femtosecond laser lithography where the gate foot and head can be separately defined on positive AZ4620 photoresist film. This work has led to the stable fabrication of sub-300 nm T-gates on the samples of GaN on sapphire substrate and AlGaN/GaN on Si substrate.
In this paper we studied the influence of N electrode on the extraction efficiency of high power light-emitting diodes
(LEDs). Simulation and experimental results show that comparing with traditional metal N electrodes the extraction
efficiency of LEDs with transparent N electrode is increased by 15%, and it is easier in process than the other techniques.
So we proposed a new kind of strip LEDs with transparent electrodes on both P-GaN and N-GaN. The design of
transparent electrodes was trade-off between transmittance and resistance. At the same time, the strip structure has some
advantages over the traditional square LEDs, which can increase the extraction efficiency and reduce the thermal
resistance. Antireflective and high reflective optical coatings were also used in this design. The fabrication of LEDs with
transparent electrodes on both P-GaN and N-GaN has been demonstrated. The output power of blue LEDs is 240mW at
350mA, forward voltage is below 3.5V. The luminous flux of white LEDs reached 65lm at 350mA.
Different types of dielectric optical coatings for GaN based high bright LEDs were designed and discussed. The optical
coatings included the anti-reflection (AR) coating, high-reflection (HR) coating, and omni-directional high reflection
coating. Main materials for the optical coatings were dielectric materials such as SiO2, Ta2O5 and Al2O3, which were
different from the metallic reflector such as Ag usually used now. For the application of anti-reflection coating in GaN
LEDs, it was introduced into the design of transparent electrodes with transparent materials such as ITO to form
combined transparent electrodes. With the design of P, N transparent electrodes using the AR coating and ITO for GaN
LEDs, the extraction efficiency was improved by about 15% experimentally. For the dielectric high-reflection coating, it
has higher reflectivity and lower absorption than the metal reflector, and it was supposed to improve the extraction
efficiency obviously. While the dielectric omni-directional reflection coating using dielectric materials was also designed
and discussed in this article, since which was anticipated to improve the extraction efficiency furthermore. Using SiO2
and Ta2O5, the average reflectivity of a design of all dielectric omni-directional high reflection coating on the sapphire
surface was over 94%.
The effects of plasma induced damage in different conditions of ICP and PECVD processes on LEDs were presented.
For ICP mesa etch, in an effort to confirm the effects of dry etch damage on the optical properties of p-type GaN, a
photoluminescence (PL) measurement was investigated with different rf chuck power. It was founded the PL intensity of
the peak decreased with increasing DC bias and the intensity of sample etched at a higher DC bias of -400V is less by
two orders of magnitude than that of the as-grown sample. Meanwhile, In the I-V curve for the etched samples with
different DC biases, the reverse leakage current of higher DC bias sample was obviously degraded than the lower one. In
addition, plasma induced damage was also inevitable during the deposition of etch masks and surface passivation films
by PECVD. The PL intensity of samples deposited with different powers sharply decreased when the power was
excessive. The PL spectra of samples deposited under the fixed condition with the different processing time were
measured, indicating the intensity of sample deposited with a lower power did not obviously vary after a long time
deposition. A two-layer film was made in order to improve the compactness of sparse dielectric film deposited with a