Formation of ultra-thin Ge_1−xSn_x/Ge_1−x−ySi_xSn_y quantum heterostructures and their electrical properties for realizing resonant tunneling diode

Huge thermal noise owing to the narrow energy bandgap is one of the critical issues for group IV-based photonics in the mid-infrared regime. With this motivation, we examined to form Ge_1−xSn_x/Ge_1−x−ySi_xSn_y quantum heterostructures (QHs) by molecular beam epitaxy for realizing resonant tunneling diodes composed of group-IV materials. We confirmed the formation of approximately 2 nm-thick Ge_1−xSn_x/Ge_1−x−ySi_xSn_y QHs with atomically flat interfaces by x-ray diffraction and transmission electron microscopy methods. Moreover, by the current density–voltage (J–V) measurement at 10 K, we observed the occurrence of a non-linear distinct hump in the J–V characteristic, which is possibly originated from quantum transport of heavy holes. According to the tunneling transmission spectra simulation result, the hump property would be due to two possible scenarios: a resonant tunneling of heavy holes in the QH and/or a resonance phenomenon that heavy holes pass just above a potential barrier.