What is the fine-grained topic of the following text: Experiments have been carded out at temperatures between 30 K and 300 K. The results indicate that thermal annealing improves the optical quality of GaInNAs, but may cause either a blue shift, as commonly observed by other groups, or a red shift depending on the growth technique. Only return the topic.
The impact of thermal annealing on the optical quality of GaInNAs at varying temperatures.