Utilization of synchrotron radiation for in-situ diffusion studies

M. Meduňa¹, O. Caha¹, G. Bauer², G. Mussler³, D. Grützmacher³

¹Institute of Condensed Matter Physics, Masaryk University Brno, Czech Republic

²Institut für Halbleiterphysik, J Kepler Universität, Linz, Austria

³Institute of Bio- and Nanosystems, Forschungszentrum Jülich GmbH, Jülich, Germany

mjme@physics.muni.cz

New devices in electronic and optoelectronic applications, often designed in nanometer scale, are typically subjected to a large thermal load during its production, processing and operation. On the contrary the thermal properties of the new materials used are usually not well known and they result in fast degradation processes at high temperatures. In these cases the in-situ diffraction techniques are very appropriate for detection of temporal structural changes inside the investigated structure.

In on our case, we concentrate on studies of interdiffusion in SiGe electronic devices, which find applications in CMOS technologies, quantum cascade emitters and quantum dot structures. Unfortunately, there are only few experimental data on interdiffusion available in literature. Sufficient set of parameters describing interdiffusion in Ge rich SiGe alloys is still completely missing with reliable precision [1].

We have investigated diffusion properties of strain compensated SiGe multiple quantum well (MQW) structures grown by molecular beam epitaxy. The series of structures with various average Ge contents were studied in-situ by means of reciprocal space mapping of x-ray diffraction or reflectivity using synchrotron radiation (ESRF). Since the temporal evolution of structural changes is usually very fast within the large dynamical range of intensities and close to a detection limit, a high intensity flux was required for in-situ annealing measurements. The annealing at high temperatures requires appropriate ambient conditions, for instance high vacuum, which was realized inside evacuated Be dome chamber allowing proper scattering conditions.

In our experiment, we have found that critical temperatures, where the interdiffusion starts to be evident, is observed in the range from 600 °C to 700 °C for Ge rich SiGe alloys with x_Ge=70 and 90 % and from 700 °C to 800 °C for Si rich alloys with x_Ge=25 and 50 % [2]. The MQW period in different sample series varied in the range from 5 nm to 30 nm. The layer thicknesses and Ge contents obtained from simulations of diffraction patterns allowed us to determine the diffusion coefficients for various temperatures and several average Ge contents in the MQW.

References

1. D.B. Aubertine & P.C. McIntyre, J.Appl. Phys., 97, (2005), 13531.

2. M. Meduňa, J. Novák, G. Bauer, C.V. Falub, & D. Grützmacher, phys. stat. sol. (a), (2008), in print