I. A. Prokhorov

Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry

Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likely due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.

X-ray diffraction diagnostics methods as applied to highly doped semiconductor single crystals

Si(As, P, B) and GaSb(Si) single crystals are used as examples to demonstrate the possibilities of methods of X-ray diffraction for the diagnostics (examination of a real structure) of highly doped semiconductor crystals. Prominence is given to characterizing the state of impurity: whether it is in a solid solution or at a certain stage of its decomposition. An optimum combination of X-ray diffraction methods is found to obtain the most complete information on the microsegregation and structural heterogeneity in crystals with low and high X-ray absorption. This combination is based on X-ray diffraction topography and X-ray diffractometry methods having an increased sensitivity to lattice strains.

X-ray diffraction topography for materials science

In this paper, which is dedicated to the 100th anniversary of the discovery of X-ray diffraction (which occurs in 2012), the role and significance of X-ray diffraction topography for materials science are described. The basic principles, methods, and history of the development of X-ray topography (XRT) are briefly stated. A wide experience of practical application of XRT to study the mechanisms of formation of real structure in bulk single crystals and thin films is summarized. Examples of the application of topography methods for investigating and optimizing the production technology of a variety of practically important materials and microelectronic devices are presented.

Concentration and structural inhomogeneities in highly doped GaSb(Si) single crystals

Concentration and structural inhomogeneities in highly doped GaSb(Si) single crystals grown under various conditions of heat and mass transfer are studied by methods of X-ray topography, high-resolution X-ray diffractometry, and digital image processing. It is established that the inhomogeneity of crystals is determined by specific features of impurity microsegregation during growth under conditions of nonstationary convection in a melt and by peculiarities of the dislocation structure of crystals. The processes related to the initial stage of the decay of the Si supersaturated solid solution in GaSb contribute considerably to the inhomogeneity of crystals on the micro- and macrolevels.

Some results of the growth of semiconductor crystals in microgravity conditions (to the 50th anniversary of Yuri Gagarin’s flight into space)

The history of the growth of semiconductor crystals aboard space vehicles and their subsequent investigation has been described shortly. It has been shown using Ge(Ga), GaSb(Si), and GaSb(Te) crystals as an example that the formation of segregation growth striations can be avoided during their recrystallization by the vertical Bridgman method in conditions of physical simulation of microgravity on the Earth, mainly due to the essential weakening of the thermal gravitation convection. By their structure and impurity distribution, they approach the crystals grown in space. The investigation of recrystallization of Te has made it possible to determine the role of the detachment effect characteristic of the microgravity conditions and the features of the microstructure of the samples that crystallize with a free surface. The analysis of the results obtained from experiments in space allows us to better understand the processes occurring during the crystallization of the melts and to improve the crystal growth in terrestrial conditions.

Growth of high-homogeneity GaSb:Te crystals for thermophotovoltaic energy converters

Problems concerning the technology of growing highly homogeneous semiconductor crystals are discussed. The dependence between the inhomogeneity of GaSb:Te substrates and the efficiency of thermophotovoltaic converters (TPVCs) fabricated on their base via the diffusion technique is examined. The macro- and microhomogeneities of grown crystals can be substantially increased on account of the theoretically substantiated and experimentally implemented approximation to diffusive mass transfer conditions in the melt. The characteristics of TPVCs on substrates made of crystals with the most homogeneous properties exceed the analogous characteristics of other samples.

Comparative studies of the features of the formation of impurity heterogeneity in GaSb:Te crystals in the case of directed crystallization under space and ground conditions

The results of comparative studies concerned with the formation of impurity heterogeneity in GaSb:Te crystals grown at the POLIZON facility by the Bridgman method under space and ground conditions are presented. Crystallization is carried out in the same temperature-time modes of the heaters: on board the Foton-M 3 spacecraft in space and by the vertical Bridgman method under conditions of weakened thermogravitational convection on Earth. In both cases, Marangoni convection is eliminated, and the effect of vibration microaccelerations on the ampoule that contains the melt is minimized. The microuniformity of the dopant distribution in the crystal areas that are recrystallized by the Bridgman method is higher than that in the seed grown by the Czochralski method. Microuniformity is higher under space conditions than under ground conditions with weakened thermogravitational convection. Spectral Fourier analysis of the spreading resistance distribution Rs reveals the characteristic periods of heat and mass transfer processes in the melts under ground and space conditions.

Possibilities for achieving steady-state growth conditions during oriented crystallization of gallium antimonide by the vertical Bridgman method using the “Polizon” setup

The possibility of controlling the heat-and-mass transfer processes to achieve steady-state conditions of gallium antimonide crystallization by the vertical Bridgman method with a upper heat supply was studied using the “Polizon” setup. Steady-state conditions near the crystallization front are achieved due to elimination of the Marangoni convection, growth axis orientation along the gravity vector, minimization and optimization of the radial and axial temperature gradients, respectively, and crystallization during steady motion of the temperature field along a cell with a sample without its mechanical motion with respect to heaters. The experimental results were compared with numerical calculations of the heat-and-mass transfer processes and crystallization parameters, including those for microgravity conditions.

X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions

Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a)relax ∼ (1.1–1.2) × 10–4 is recorded in isotopically modified 13С (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.

Development of the Growth Technology of Highly Homogeneous Semiconductor Crystals

Different technological solutions for growing GaSb(Te) and Ge(Ga) single crystals, making it possible to optimize the growth of highly homogeneous (at the microlevel) semiconductor crystals by the Bridgman method, are described. The possibility of implementing steady-state growth conditions (providing uniform dopant distribution over the crystal) has been experimentally confirmed.