Application note from STMicroelectronics on the performance of each diode in a parallel diode connection and how the forward voltage dispersion can have a great impact over thermal effect on the current imbalance. Link here (PDF)
The use of diodes in parallel is commonly found in power electronic design. An important consideration for this practice is the current sharing between diodes due to the difference of electrical characteristics. This application note highlights the cause of the behavior of several diodes are connected in parallel. Some recommendations will be given to help the designer to produce a safe design. An electro-thermal model is described which simulates the current and junction temperature of each diode for given application conditions. This tool is illustrated using an example.