GermaniumGe70/74

Abstract

We demonstrate a technique to study self-diffusion in germanium, using isotope heterostructures ( Ge/ Ge). After interdiffusing the nominally undoped layers of Ge and Ge at temperatures between 543 and 690'C, the diffusion profiles are measured with secondary-ion-mass spectroscopy. The analysis of the experimental data allows an accurate determination of the self-diffusion enthalpy and the self-diffusion entropy. The isotope heterostructures are especially well suited for self-diffusion studies because the diffusion takes place at the interfaces inside the crystal. Thus, no surface effects or limited amounts of tracers complicate the measurements. We compare our results with those obtained with the standard techniques where the tracer self-diffusion coefficients are determined based on studying the redistribution of radioactive tracers, initially deposited on the specimen surface. Utilizing the stable isotopes in our experiment avoids complications due to decay of the radioactive tracers encountered in the traditional measurements.

Self-diffusion in germanium isotope multilayers at low temperatures

“…At temperatures between 525 and 600°C our data are in excellent agreement with literature data measured by ion beam sputtering techniques. 24,28 The data point for 500°C measured by Raman scattering 20 is also in agreement with our experimental results. Our diffusion study expands the range of experimental data by three orders of magnitude compared to results obtained with the sputtering techniques.…”

“…Arrhenius plots of Ge self-diffusivities obtained by NR ͑filled circles and filled squares͒ in comparison to literature data from secondaryion-mass spectroscopy ͑SIMS͒, 28 Raman spectroscopy, 20 and radiotracer sputter sectioning. 24 The continuous line represents a fit to the Arrhenius equation of all diffusivities displayed.…”

“…14͒ were obtained. The isotope heterostructures are chemically homogeneous solids, which are composed of a stack of isotope enriched layers ͑e.g., 28 Si / 30 Si͒ grown by suitable deposition techniques. The interdiffusion of stable isotopes during diffusion annealing takes place at the isotope interface͑s͒ inside the crystal, unaffected by possible surface effects.…”

Germanium: From its discovery to SiGe devices

“…The 70 Ge isotope concentration profile in Fig. 13 (b) follows a complementary error function for 4.5 orders of magnitude [50]! Phonons were studied with Raman spectroscopy in isotope bulk and superlattices [51,52].…”

Isotopically Controlled Semiconductors

“…The observation that donor doping enhances Ga self-diffusion, while acceptor doping retards it, is direct evidence for a negatively charged native defect, presumably the Ga vacancy, promoting self-diffusion (25) . Detailed self-diffusion studies have been conducted with isotope multilayer structures of silicon (26) , germanium (27,28) , gallium phosphide (29) and most recently with gallium antimonide (30) . The last study was conducted with isotope control of both sublattices and yielded the surprising result that Ga diffuses ~10 3 times faster than Sb under intrinsic conditions.…”