Voltage waveform at the Emitter of a Buck Converter?
Vge implies IGBT not NPN. THe mid plateau may be gate discharge thus gate current during the threshold of output conductance and the  upper plateau when saturated BJT output.  IGBT's have FET input and BJT output. The time period may be 10us for a half cycle of a 50KHz PWM rate. The input voltage slew rate is limited by (Rg+Rs)*Ciss. The output slew rate is limited by L with a hopefully low Q LPF.