Low-voltage and high-gain WSe_(2)avalanche phototransistor with an out-of-plane WSe_(2)/WS_(2)heterojunction

The properties of photodetectors based on two-dimensional materials can be significantly enhanced by avalanche effect.However,a high avalanche breakdown voltage is needed to reach impact ionization,which leads to high power consumption.Here,we report the unique features of a low-voltage avalanche phototransistor formed by an in-plane WSe_(2)field effect transistor(FET)with an out-of-plane WSe_(2)/WS_(2)P–N heterojunction(HJ FET).The avalanche breakdown voltage in the device can be decreased from−31 to−8.5 V when compared with that in WSe_(2)FET.The inherent mechanism is mainly related to the redistributed electric field in the WSe_(2)channel after the formation of the out-of-plane P–N heterojunction.When the bias voltage is−16.5 V,the photoresponsivity in the HJ FET is enhanced from 1.5 to 135 A/W,which is significantly higher than that in the WSe_(2)FET because of the obvious reduction of the avalanche breakdown voltage.Moreover,HJ FET shows a higher responsivity than WSe_(2)FET in the range of 400–1,100 nm under low bias voltage.This phenomenon is caused by accelerating electron–hole spatial separation in the heterojunction.These results indicate that the use of an WSe_(2)FET with an out-of-plane WSe_(2)/WS_(2)heterojunction is ideal for high-performance photodetectors with low power consumption.