I am currently working on DIY buck converter, and I am using IRFZ44N (N- Channel Mosfet) as a switch. I tried to switch it at 37kHz. The problem I had noticed that the mosfet is not producing sqaure wave it's waveform looks like the charging of capacitor. But at low frequency everything works fine. I am giving 12v gate supply. If I am making any mistake please correct it.