Imaging of subbands in InAs/GaSb double quantum wells by low-temperature scanning tunneling spectroscopy

The spatial distribution of the electron local density of states (LDOS) in InAs/GaSb double quantum wells (DQWs) was investigated by low-temperature scanning tunneling spectroscopy on cleaved surfaces. For DQW with a thick central barrier, clear standing wave patterns corresponding to subbands confined to each InAs single quantum well appeared in the spatial variation of LDOS spectra. In contrast, for the DQW with a thin central barrier, the standing wave patterns extended over both quantum wells. The deviation of the pattern arising from the asymmetry due to a slight difference of the well thickness appeared clearly. The observed spectra are well explained by the calculated LDOS taken to be the sum of LDOS contributed from all energetically accessible subbands.