High Band-to-Band Tunneling Current in InAs/GaSb Heterojunction Esaki Diodes by the Enhancement of Electric Fields Close to the Mesa Sidewalls

InAs/GaSb heterojunction Esaki diodes with a high peak current density of 9 MA/cm 2 are demonstrated. Negative differential resistance (NDR) is achieved from 300 to 4 K, showing that band-to-band tunneling (BTBT) is the dominant transport mechanism. By increasing the doping concentrations, the peak current increases because of more carriers available for tunneling. NDR is also clearly observed for the devices with nondegenerate doping concentrations, which could be attributed to the induced quantum wells at the InAs/GaSb heterojunction. To calibrate the BTBT current, devices of different mesa areas were characterized. The peak current density increases as the device is scaled down. A model of tunneling enhancement close to the mesa sidewalls by the surface defects is proposed. TCAD simulations show that the electric fields close to the sidewalls are enhanced because of the induced surface defects by dry etching in InAs and GaSb. Careful processing steps to reduce those surface defects during etching steps are required to avoid an overestimation of the BTBT current.