Current leakage mechanisms related to threading dislocations in Ge-rich SiGe heterostructures grown on Si(001)

Abstract

The present work investigates the role of threading dislocation densities (TDD) in the low density regime on the vertical transport in Si 0.06 Ge 0.94 heterostructures integrated on Si(001). The use of unintentionally doped Si 0.06 Ge 0.94 layers enables the study of the impact of grown-in threading dislocations (TD) without interaction with processing-induced defects originating e.g. from dopant implantation. The studied heterolayers, while equal in composition, the degree of strain relaxation, and the thickness, feature three different values for the TDD: 3×10 6 , 9×10 6 and 2×10 7 cm -2 . Current-voltage measurements reveal that leakage currents do not scale linearly with TDD. The temperature dependence of the leakage currents suggests a strong contribution of field-enhanced carrier generation to the current transport, with the trap-assisted tunneling via TD-induced defect states identified as the dominant transport mechanism at room temperature. At lower temperature and at high electric fields, direct band-to-band tunneling without direct interaction with defect levels becomes the dominating type of transport. Leakage currents related to emission from mid-gap traps by the Shockley-Read-Hall (SRH) generation is observed at higher temperatures (>100 °C). Here, we see a reduced contribution coming from SRH in our material, featuring the minimal TDD (3×10 6 cm -2 ), which we attribute to a reduction in point defect clusters trapped in the TD strain fields.

Subnanometer Control of the Heteroepitaxial Growth of Multimicrometer-Thick Ge / Si - Ge Quantum Cascade Structures

“…This value is in good agreement with the nominal one if taking into account the expected p-type background related to the presence of TDs. In samples with a TDD in the 10 6 cm −2 range, as in our case, a p-type background density of about 5 × 10 15 cm −3 is estimated [21]. With a period length L per approximately 100 nm for the QCL module investigated here, these density values give rise to an effective hole sheet density per period of about 5 × 10 10 cm −2 , a value similar to the difference observed between the effective n 2D value estimated by FTIR and the nominal doping.…”

“…The first step for the deposition of any high-quality Ge/SiGe multilayered structure on Si substrates is the realization of a SiGe VS having an in-plane lattice parameter matching that imposed by the strain compensation condition of the active region, and featuring a low TDD, possibly in the 10 5 -10 6 cm −2 range. As a matter of fact, TDs have the dual effect of worsening the crystalline quality and generating acceptorlike defect states, therefore, inducing an effective p-type doping background [21]. These drawbacks are particularly critical in a QCL due to the large thickness of the multilayered structure and to the fact that the TDD related p-type background is comparable in magnitude to the typical n-type doping used for the active layers of the QCL.…”

Molecular Beam Epitaxy of Si, Ge, and Sn and Their Compounds

“…The electronic effects of vacancies and threading dislocations were investigated with the Hall effect, with capacitance-voltage (C-V) and deeplevel transient spectroscopy (DLTS). Unintentional p-type doping [38] of several 10 15 cm À3 , a mid-gap trap level, and a near valence band level were found. High carrier recombination from band gap levels causes high nonideal dark currents [39,40], reducing the power of lasers and the detectivity of detectors.…”