Beats me...
With power devices, I think the basic progression is:
- Research; materials science improvements; first offering of small devices (e.g., 3N136?), targeted for small signal and RF amplifier applications
- Which were lateral devices (actually built the same way the cartoon diagrams show). Scaled up, larger devices were used for audio and RF power amplification. "Freedom from 2nd breakdown" (due to low power density -- an engineering bug rephrased as a marketing feature!).
- HexFETs (IR?), introduction of the first practical power switching devices (80s-90s?)
- Vertical technologies (V and Trench MOS, ca. 90s-00s)
- Advanced VDMOS, Superjunction (00s-10s), elimination of Rds(on)-Vdss^2 tradeoff