Al<sub>x</sub>Ga<sub>1-x</sub>N layer was grown on sapphire substrate with GaN template by Metal Organic Chemical Vapor Deposition
system (MOCVD). High temperature AlN (HT-AlN) interlayer was inserted between Al<sub>x</sub>Ga<sub>1-x</sub>N layer and GaN template
to solve the cracking problem that often appears on Al<sub>x</sub>Ga<sub>1-x</sub>N surface when directly grown on high temperature GaN
template. Optical microscope, scanning electron microscopy (SEM), atomic force microscope (AFM), high resolution x-ray
diffraction (HRXRD) and cathodoluminescence (CL) were used for characterization. It was found that the cracking
was successfully eliminated. Furthermore, the crystalline quality of Al<sub>x</sub>Ga<sub>1-x</sub>N layer with HT-AlN interlayer was much
improved. Interference fringes were found in the HRXRD images. CL test showed that yellow emission was much
reduced for AlGaN layer with HT-AlN interlayer.
The photodynamic therapy of cerebral gliomas is one kind of adjunctive therapy after operative tumor removal. But it is not widely accepted until now. We report two cases of failure treatment in our totally consecutive ten patients treated with this method and analyse the cause of the poor outcome. Unlike the uninary system and digest system, the difficult of necrotic tumor or brain tissue exclusion in the brain is marked and resulted in poor result. Our view is that the problem of massive necrotic tumor tissue exclusion which is the wish of therapist and the key of achieving good result might limit the further application of photodynamic therapy on cerebral gliomas.