In situ characterization of crystal growth and heat treatment in semiconductor materials

Abstract

In situ characterization methods are being developed at the Idaho National Laboratory that can be used to characterize the atomic lattice structure of materials used for semiconductor and scintillation detectors during the crystal growth and heat treatment processes, which have been shown to be critical for the development of optimized semiconductor and scintillation radiation detectors. Multiple methods for implanting positrons into the material have been developed and integrated with measurement techniques including Doppler broadening, coincidence Doppler broadening and positron lifetime measurement. The INL developed induced positron technique allows positron measurements to be performed at depth up to 10 cm inside crystal boules. Also, a portable measurement system suitable for field use has been developed that is suitable for assessing heat treatments at depths up to 1 cm inside a material in an industrial environment. Results of measurements that address the effects of composition and heatup/melting/cool down on material lattice structures are discussed along with plans for the in situ crystal studies. INTRODUCTIONPositron-based measurement methods have demonstrated the capability to quantify changes in the atomic lattice structure of materials and to assess the dislocation density and sizes in semiconductor materials. The ability of positrons to quantify changes microstructures, defect concentrations and semiconductor characteristics in materials is well documented 1,2,3,4 . Positron annihilation spectroscopy has the capability to "reveal the nature, concentration and spatial distribution of defects in semiconductors and semiconductor structures with sensitivity unparalleled by other techniques." 5 The primary issue associated with positron semiconductor research has been the ability to only characterize the top 10-50 micron of the material surface, which may be subject to surface treatment and processing effects that can affect quantification of the changes in the lattice structure and defect characteristics of interest. Methods being developed at the INL allow positrons to be implanted in the material to characterize changes in the atomic lattice structure and dislocation density at depths up to 10 cm. This new capability allows the profiling and volumetric characterization of the material lattice structure and defect distributions as a function of depth.Integrated positron implantation and measurement methods are being developed that allow semiconductor and scintillation detector material lattice structures and defect densities to be characterized during both the crystal growth and/or heat treatment processes that have been shown to have a significant effect on the operational characteristics of the fabricated radiation detector. Cadmium-Zinc-Telluride (CZT) detectors are particularly subject to issues related to composition, both surface and volumetric detector characteristics that can affect the ability of the detector to function. 6,7 Positron measurement methods including Doppler broadening, coincid...