2019年6月20日星期四

Temperature-independent slow carrier emission from deep-level defects in p-type germanium

In the deep-level transient spectroscopy (DLTS) spectra of the 3d-transition metals cobalt and chromium in p-type germanium, evidence is obtained that hole emission from defect levels can occur by two parallel paths. Besides classical thermal emission, we observed a second, slower and temperature-independent emission. We show that this extra emission component allows determining unambiguously whether or not multiple DLTS peaks arise from the same defect. Despite similar characteristics, we demonstrate that the origin of the non-thermal emission is not tunnelling but photoionization related to black-body radiation from an insufficiently shielded part of the cryostat.



Source:IOPscience

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2019年6月14日星期五

Ultralarge transient optical gain from tensile-strained, n-doped germanium on silicon by spin-on dopant diffusion

The direct band gap optical gain of tensile-strained, highly n-doped germanium on silicon is investigated by femtosecond ultrafast transmittance spectroscopy. A germanium film with 0.22% tensile strain is grown on a silicon substrate by using molecular beam epitaxy. An activated doping concentration up to 4 × 1019 cm−3 is achieved by phosphorus diffusion from a spin-on dopant source. The transmittance of the germanium film is clearly increased upon increasing the pump power. A peak optical gain of up to 5300 cm−1 around 1.7 µm and a gain spectrum broader than 300 nm are obtained. These results show a simple yet promising way to realize gain medium for monolithic-integrated germanium lasers.


Source:IOPscience

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2019年6月5日星期三

Vertically oriented epitaxial germanium nanowires on silicon substrates using thin germanium buffer layers

We demonstrate a method to realize vertically oriented Ge nanowires on Si(111) substrates. Ge nanowires were grown by chemical vapor deposition using Au nanoparticles to seed nanowire growth via a vapor–liquid–solid growth mechanism. Rapid oxidation of Si during Au nanoparticle application inhibits the growth of vertically oriented Ge nanowires directly on Si. The present method employs thin Ge buffer layers grown at low temperature less than 600 °C to circumvent the oxidation problem. By using a thin Ge buffer layer with root-mean-square roughness of ~ 2 nm, the yield of vertically oriented Ge nanowires is as high as 96.3%. This yield is comparable to that of homoepitaxial Ge nanowires. Furthermore, branched Ge nanowires could be successfully grown on these vertically oriented Ge nanowires by a secondary seeding technique. Since the buffer layers are grown under moderate conditions without any high temperature processing steps, this method has a wide process window highly suitable for Si-based microelectronics.



Source:IOPscience

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