The BZT52C20T from Micro Commercial Components is a Zener Diode with Zener Voltage 18.8 to 21.2 V, Zener Current 1 mA, Voltage Forward 0.9 V, Current 5 mA, Current Reverse Reverse Leakage Current:- 0.1 uA. More details for BZT52C20T can be seen below.