Half Bridge convertor - Diode conduction

I'm trying to fathom out when (on a conventional hard switched half bridge convertor) exactly under what situations the MOSFETs inherent diode conducts. I'm sure I've seen some good resources on the web in the past but can't find it now. It was in my head that this could happen during each dead time, but that can't be right can it?

Looking at improving a fairly high frequency, high Vin half bridge power supply design, I'm just wondering if this reverse recovery might be contributing to the losses. The reverse recovery specs of the devices are terrible when you are switching at 100s of kHz.

Has anyone has to resort to using a diode in parallel with the MOSFET inherent diode then a further diode in series with the FET that you see on full bridge designs sometimes?

A MOSFET will conduct in either direction when ON.
When OFF a MOSFET will conduct in the reverse direction through the substrate diode.
In a bridge circuit the substrate diode will conduct when the MOSFET is turned OFF and any inductance in the circuit tries to keep the current flowing.
This current will continue to flow until the inductive energy is dissipated.
If you post a circuit I can be more specific.