Search

The roles of V-shaped pits on the improvement of quantum efficiency in InGaN/GaN multiple quantum well (MQW) light-emitting diodes are investigated by numerical simulation. The simulation results show that V-shaped pits cannot only screen dislocations, but also play an important role on promoting hole injection into the MQWs. It is revealed that the injection of holes into the MQW via the sidewalls of the V-shaped pits is easier than via the flat region, due to the lower polarization charge densities in the sidewall structure with lower In concentration and {10–11}-oriented semi-polar facets.

InGaN/GaN multi-quantum well (MQW) light emitting diodes with heavily Mg doped and unintentionally doped (UID) low-temperature Al0.2Ga0.8N electron blocking layer (EBL) were investigated. Broad short-wavelength electroluminescence peak, which has strong relative intensity to the main emission, was found in the UID-EBL sample at cryogenic temperatures. Study suggests that the broad peak is emitted by the sidewall MQWs. This result indicates that the electroluminescence of sidewall MQWs, in which the carrier density is high enough, can be detected at cryogenic temperatures. The lineshape variation with current density reveals detailed information on the process of carrier injection into the sidewall MQWs.

Little attention was paid to the effect of oxygen vacancy configuration, although it is well known that oxygen vacancy plays a key role in determining the electrical and optical properties of VO2. By means of different heat treatments, the oxygen vacancy configuration in VO1.965 nanometer ceramic is controlled and its behavior is investigated in detail. It is found that VO1.965 ceramic aged at 60°C for a day displays a new first order phase transformation at about 30°C, which is associated with the oxygen vacancy distribution. An explanation based on the symmetry conforming principle is tentatively presented.