Room-Temperature Operation of Ge1–xSnx/Ge1–x–ySixSny Resonant Tunneling Diodes Featured with H2 Introduction during Molecular Beam Epitaxy

Abstract

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 Ge_1–xSn_x/Ge_1–x–ySi_xSn_y double-barrier structure (DBS) with group-IV compound materials. Although we observed negative differential resistance (NDR) at 10 K of the Ge_1–xSn_x/Ge_1–x–ySi_xSn_y RTD, we needed to enhance its low operating temperature. This study explored the impact of introducing H₂ during the growth of Ge_1–xSn_x/Ge_1–x–ySi_xSn_y DBS on their crystallinity and homogeneity. Our findings revealed that introducing H₂ during the growth of the Ge_1–x–ySi_xSn_y layer with a high Si composition (approximately 50%) led to island growth, whereas the layer growth was more likely for Ge_1–xSn_x. By introducing H₂ only during the growth of the Ge_1–xSn_x layer, we achieved significantly improved crystallinity and homogeneity in the Ge_1–xSn_x/Ge_1–x–ySi_xSn_y DBS. Consequently, we successfully observed NDR in the Ge_1–xSn_x/Ge_1–x–ySi_xSn_y 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 Ge_1–xSn_x/Ge_1–x–ySi_xSn_y RTDs. Theoretical simulation of the current–voltage characteristics using TCAD indicated that the observed NDR originated from the second quantum level in the Ge_1–xSn_x well. Finally, we examined potential directions for further enhancement of reliability and output performances.