Si/SiGe Multiple-Quantum-well Resonant Tunneling Device

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Resonant tunneling devices. Have been categorized into one of the highest speed devices which surpass 2D devices, such as HEMT and MODFET, and JJ devices, and have been expected to meet the demand for high speed operations from GHz to THz. So far, the tunneling devices have been applied to III-V material systems with which high tunneling barriers are obtained. If Si/SiGe tunneling devices are realized, we can expand a new Si-based ultra-high speed integration device system. However, the peak-to-valley current ratio (PVCR), in the negative differential resistance (NDR) region of, the I-V curve, as a figure of merit, has been low and 1.2 at RT since the first report of a Si/SiGe RTD in 1988. On the basis of the theoretical analysis, we have applied for the first time a combination of electron tunneling and a multiple quantum well to a Si/SiGe RTD and have succeeded in enhancing the PVCR value of a Si/SiGe RTD and obtaining a PVCR value of more than 7.6 in 1998. In this work, we have further investigated the RTD device structure and process to enhance the NDR effect. As a result, we have found that the surface crystalline quality of a strain-relief buffer largely affects the NDR performance, and have proposed an annealed thin two-layer buffer and an annealed thin multi-layer buffer, which has a thin SiGe layer with a high concentration of Ge. The proposed buffers exhibit surfaces with high crystallin quality. By introducing the high crystalline quality buffer to a electrontunneling multiple-well RTD, we have succeeded in realizing a PVCR value of more than 180 at RT which is comparable to or more than those of III-V RTDs. This result indicates the important device physics of very low inelastic scattering in SiGe RTDs. Through this research, it has' been demonstrated that the PVCR performance comparable to those of III-V RTDs has been obtained by the use of SiGe materials, which gives a great motive force to further extend Si/SiGe tunneling devices.