Properties of Defects in GeSn and III-V Based Heterostructures

New materials and devices, which promise improved performance are being vigorously explored for sub -10 nm technology nodes. In order to enable monolithic integration of the materials, heterogeneous epitaxial growth is being considered. Due to a higher hole mobility, a large lattice constant (in comparison to Si and Ge) and a tunable bandgap, GeSn is gaining importance as an alternative material for pFETs (in both FinFETs and tunnel FETs configuration). On the other hand, for nFETs, the higher electron mobilities, tunable band alignment and direct bandgap of the III-V material systems, favor them as the optimal choice. Nonetheless, due to hetero-epitaxy of these materials, a plethora of extended defects (EDs) are introduced, which can undesirably thread the active device region. Unfortunately, due to the novelty of GeSn and III-V materials (in the scope of tunneling devices), a knowledge gap exists regarding the defect's signature and their structural identification. Due to this lack of information, several assumptions have been made, which remain to be verified or refuted. In this research work, deep level transient spectroscopy (DLTS) was adopted as the primary characterization technique. The methodology of the DLTS technique is developed. The importance of DLTS when measuring oxide/semiconductor interface states in small bandgap semiconductors is discussed. A model representing an original approach for the description of extended defect properties is presented. The peculiar features in the DLTS spectra due to tunneling in the tunnel diodes are explained, and an original method for the correct interpretation of the spectra is proposed. An important observation of tunneling emission of holes from the trap, in a tunnel diode, is made for the first time. Electrically active defects, which lead to sub-threshold leakage current in heterojunction and homo-junction III-V tunnel diodes are identified. It is shown that the band-like distribution of electronic states, associated with an ED can create a transition path in addition to the band to band tunneling path. The results which are presented in this work, have practical implications for improving the performance of the diodes. Since advancement of the GeSn technology relies on fast detection, monitoring and evolution of the EDs, a low-cost defect selective wet etchant is proposed. It is shown that the etchant not only reveals dislocations but also crystal originated particles (COPs), both of which lead to device performance degradation. The GeSn gate-stack is studied and compared with that of Ge using DLTS. A signature of GeSn oxide traps, with special attention to the capture cross-section, which was previously unavailable, is provided. Importantly, the signature of electrically active clean dislocations, originating from the lattice mismatch between a GeSn layer (with 7.8% Sn) and the underlying Ge substrate, and leading to Shockley-Read-Hall leakage current is presented. An important result is that these dislocation-states are not the source of un-intentional p-type doping, in contrary to the common assumption. This work enables improved understanding of defects in novel material systems, and provides a fresh outlook for understanding EDs characteristics using DLTS.status: publishe