Room-Temperature Operation of Ge_1–<i>x</i>Sn_<i>x</i>/Ge_{1–<i>x</i>–<i>y</i>}Si_<i>x</i>Sn_<i>y</i> Resonant Tunneling Diodes Featured with H₂ Introduction during Molecular Beam Epitaxy

As oscillators used for terahertz communication, a resonant tunneling diode (RTD) composed of group-IV semiconductors is desirable. From the perspective of energy band engineering, we focus on the Ge1–xSnx/Ge1–x–ySixSny double-barrier structure (DBS) with group-IV compound materials. Although we observed negative differential resistance (NDR) at 10 K of the Ge1–xSnx/Ge1–x–ySixSny RTD, we needed to enhance its low operating temperature. This study explored the impact of introducing H2 during the growth of Ge1–xSnx/Ge1–x–ySixSny DBS on their crystallinity and homogeneity. Our findings revealed that introducing H2 during the growth of the Ge1–x–ySixSny layer with a high Si composition (approximately 50%) led to island growth, whereas the layer growth was more likely for Ge1–xSnx. By introducing H2 only during the growth of the Ge1–xSnx layer, we achieved significantly improved crystallinity and homogeneity in the Ge1–xSnx/Ge1–x–ySixSny DBS. Consequently, we successfully observed NDR in the Ge1–xSnx/Ge1–x–ySixSny RTD over a wide temperature range of 10–300 K. Moreover, the improved crystallinity and homogeneity allowed for NDR to appear in both sweep directions of the bias voltage at 200 K. The peak current density and peak-to-valley current ratio were approximately 9.65 kA/cm2 and 1.31, respectively, surpassing previous Ge1–xSnx/Ge1–x–ySixSny RTDs. Theoretical simulation of the current–voltage characteristics using TCAD indicated that the observed NDR originated from the second quantum level in the Ge1–xSnx well. Finally, we examined potential directions for further enhancement of reliability and output performances.