Empirical correlation for minority carrier lifetime to defect density profile in germanium on silicon grown by nanoscale interfacial engineering

Abstract

High-quality Ge-on-Si heterostructures have been explored for many applications, including near infrared photodetectors and integration with III–V films for multijunction photovoltaics. However, the lattice mismatch between Ge and Si often leads to a high density of defects. Introducing annealing steps prior to and after full Ge island coalescence is found to reduce the defect density. The defect density in Ge is also found to decrease with increasing dopant density in Si substrates, likely due to the defect pinning near the Ge-Si interface by dopants. The authors establish an empirical correlation between the minority carrier lifetime (τG) and the defect density in the Ge film (ρD) as a function of distance from the Ge-Si interface: τGe = C/ρD, where C is a proportionality constant and a fitting parameter which is determined to be 0.17 and 0.22 s/cm2 for Ge films grown on low-doped, high-resistivity Si substrates and high-doped, low-resistivity Si substrates, respectively. The effective minority carrier lifetime measured as a function of Ge film thickness is then related to the recombination velocity on Ge film surface, average minority carrier lifetime within Ge film, and recombination velocity at the Ge-Si interface. Using this relation, the authors estimate the Ge-Si interface recombination velocity for Ge films grown on low-doped, high-resistivity and high-doped, low-resistivity Si substrates to be 220 and 100 cm/s, respectively.

Disentangling nonradiative recombination processes in Ge micro-crystals on Si substrates

“…2(b)]. This exceeds the literature data reported for Ge on Si heterostructures, 14,[27][28][29] and provides the first direct proof put forward in any recent work, 20 that band-gap engineered SiGe/Ge architectures are effective in mitigating the optical activity of buried dislocations.…”

Effect of threading dislocation density and dielectric layer on temperature-dependent electrical characteristics of high-hole-mobility metal semiconductor field effect transistors fabricated from wafer-scale epitaxially grown p-type germanium on silicon substrates

“…This c correlates very well with the characteristic length over which the TDD decreases ($1 lm) from the Ge-Si interface. 31 Our previous work 31 shows that the minority carrier lifetime in the Ge epilayer also rises to its maximum value approximately 1 lm from the Ge-Si interface.…”

Impact of minority carrier lifetime on the performance of strained germanium light sources

“…On the other hand, if SRH can be greater than 10 ns, the IQE can be greater than 50% for large strain values. Given that epitaxiallygrown Ge films tend to have SRH of approximately 1 ns [14], [15], considerably less than the bulk lifetime values of >100 ns for the similar level of n-type doping [26], there is an acute need for research efforts such as those of Refs [14]- [16], [27] which explore innovative ways of improving the material quality and thereby improving SRH. Without such efforts, an efficient CMOS-compatible LED is not possible no matter how much research efforts would be put into strain engineering and other techniques.…”

“…The importance of material quality, however, has been generally overlooked. This is a serious gap in the literature: epitaxial Ge typically suffers from high defect densities and poor carrier lifetimes [14]- [16], a problem which is well known to inhibit efficient light emission. Moreover, it is important for experimentalists to know whether or not this low carrier lifetime will present a performance bottleneck as Ge light sources mature and, if so, how severe this bottleneck will be.…”