Emergence of Negative Differential Resistance Through Hole Resonant Tunneling in GeSn/GeSiSn Double Barrier Structure

We examined the fabrication and the operation of GeSn/GeSiSn resonant tunneling diode (RTD) and demonstrated the observation of negative differential resistance (NDR) at a low temperature through the hole resonant tunneling. First, we revealed the possible designed contents of GeSiSn to Si and Sn of 40–60% and ∼10%, respectively to achieve the valence band offset over 0.3 eV with sustaining the biaxial strain value less than 1.0%, which is an important factor for the pseudomorphic growth of GeSn/GeSiSn heterostructure on Ge. Then, we successfully fabricated GeSn/GeSiSn RTD with a double barrier structure composed of ultra-thin GeSiSn barriers and GeSn well, which has the steep heterointerface. The current-density–voltage (J–V) characteristics at 10 K of the fabricated GeSn/GeSiSn RTD showed NDRs at applied voltages of approximately −1.5 and −1.8 V with peak to valley current ratio of 1.06 and 1.14, respectively, and peak current density of ∼3 and ∼5 kA/cm2, respectively. We also demonstrated that the observed NDR is reproducible. The quantum level and J–V simulations suggests that these two NDRs would originate from the hole resonant tunneling current through the first and second quantum levels formed in the GeSn well layer. Furthermore, we also discussed issues newly found in this study and future remarks of GeSn/GeSiSn heterostructures as RTD applications for the terahertz oscillator and the nonvolatile RAM.