Electron and Hole Photoemission Detection for Band Offset Determination of Tunnel Field-Effect Transistor Heterojunctions
Wei Li, Qin Zhang, R. Bijesh, Oleg A. Kirillov, Yiran Liang, Igor Levin, Lianmao Peng, Xuelei Liang, S. Datta, David J. Gundlach, Nhan V. Nguyen
The electrical performance of a tunnel field-effect transistor depends critically on the band offset at their semiconductor heterojunction interface. Historically, it has been difficult to experimentally determine how the electronic bands align at the heterojunction interface. We report here on experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as optically and electrically transparent electrode in a traditional internal photoemission measurement, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. Specifically for Al2O3/InAs/GaSb layer structure, the barrier height from the top of InAs and GaSb valence band to the bottom of Al2O3 conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of Al2O3 valence band to the bottom of InAs and GaSb conduction band. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to assess electron quantum tunneling efficiency of the transistor performance.