Self-diffusion in intrinsic germanium and effects of doping on self-diffusion in germanium

Self-diffusion in intrinsic germanium single crystals has been investigated over the temperature range 822-1163K using 71Ge as radioisotope and a sputtering technique for serial sectioning. The data can be described by a preexponential factor of (2.48+or-0.6)*10-3 m2 s-1 and an activation enthalpy of (3.14+or-0.92) eV. The present data are discussed together with literature data obtained with conventional sectioning techniques at higher temperatures. The self-diffusion coefficients at 870 and 894K were also measured for Ga-doped (1.7*1018 atoms cm-3) and Sb-doped (1.8*1018 atoms cm-3) samples. The diffusivity is higher in n-type and lower in p-type germanium than in intrinsic material. Since it is known that a vacancy in germanium acts as an acceptor the observed direction and order of magnitude of the doping dependence can be understood in terms of the shift of the Fermi level in doped crystals. This supports the view that self-diffusion in germanium proceeds by a vacancy mechanism.

Source:IOPscience

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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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Infrared and terahertz transmission properties of germanium single crystals

Experimental transmission spectra of samples fabricated of germanium single crystals doped with stibium were registered in the infrared 2.5-25 μm and terahertz 130 μm regions of spectrum. It is shown that doping concentration and treatment of the crystals surface have a noticeable influence on the samples absorption.

Source:IOPscience

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Germanium layers grown by zone thermal crystallization from a discrete liquid source

It is proposed and investigated a method for growing thin uniform germanium layers onto large silicon substrates. The technique uses the hexagonally arranged local sources filled with liquid germanium. Germanium evaporates on very close substrate and in these conditions the residual gases vapor pressure highly reduces. It is shown that to achieve uniformity of the deposited layer better than 97% the critical thickness of the vacuum zone must be equal to l cr = 1.2 mm for a hexagonal arranged system of round local sources with the radius of r = 0.75 mm and the distance between the sources of h = 0.5 mm.

Source:IOPscience

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