Yuri N. Makarov

Dislocation effect on light emission efficiency in gallium nitride

We modify the model of nonradiative carrier recombination on threading dislocation cores [Z. Z. Bandic, P. M. Bridger, E. C. Piquette, and T. C. McGill, Solid-State Electron. 44, 221 (2000)] to estimate quantitatively the light emission efficiency in GaN as a function of the dislocation density and nonequilibrium carrier concentration. The model predictions are in good agreement with available data on the minority carrier diffusion length in GaN. The dislocation density must be reduced, at least, down to ∼107 cm−2 in order to provide a light emission efficiency close to unity. The n-type background doping is found to be favorable for the further efficiency improvement.

On the sublimation growth of SiC bulk crystals: development of a numerical process model

Abstract The development of a numerical process model to simulate the sublimation growth of SiC bulk crystals is discussed. Radiation, conduction and convection are considered as heat transfer mechanisms. Mass transport by diffusion and convection is taken into account. First results on the simulation of heat and mass transfer in a 2 inch SiC growth set-up show a negligible effect of convection on process conditions. Chemical reactions in the SiC-graphite system have also been implemented into our model. Preliminary analysis on the dependence of concentration fields and growth velocity on possible chemical reaction mechanisms, e.g. graphitization, reveal that the incorporation of chemical processes into modelling is very important for an accurate description of SiC sublimation growth.

SiC-bulk growth by physical-vapor transport and its global modelling

4H- and 6H-SiC bulk crystals have been prepared by physical vapor transport (PVT) both in resistively and inductively heated growth reactors. Epitaxial SiC layers were grown on the wafers by chemical vapor deposition. Structural and electrical material properties of the 1–1.4 inch boules and epitaxial layers were investigated by defect etching and optical microscopy, stress birefringence and Hall effect. Single crystalline material exhibits a low micropipe density MPD ≈ 70 cm−2 and stress level. Blocking characteristics of the epitaxial layers have been determined electrically revealing high breakdown fields of 1.8–1.9 MV/cm. Finally simulation results applying a process model of SiC PVT crystallization including heat and mass transfer and chemical reactions are presented.

Growth of Low-Defect SiC and AlN Crystals in Refractory Metal Crucibles

Recently the wide bandgap semiconductors, silicon carbide (SiC) and aluminum nitride (AlN), have acquired increased importance due to the unique properties that make them applicable to a variety of rapidly-emerging, diverse technologies. In order to meet the challenges posed by these applications the materials need to be manufactured with the highest possible quality, both structural and chemical, at increasingly lower cost. This requirement places rather extreme constraints on the crystal growth as the simultaneous goals of high quality and low cost are generally incompatible. Refractory metal carbide technology, particularly, tantalum carbide (TaC), was originally developed for application in highly corrosive and reactive environments. The SiC group of Prof Yuri A Vodakov (for example, [1]) at Karmon Ltd in St Petersburg, Russia was the first to study and utilize the properties of refractory metal carbides, first for the growth of SiC and later for the growth of AlN. We discuss how the refractory metal carbides can answer many of the problems of growing SiC and AlN in a relatively simple and low cost manner.

Analysis of Graphitization during Physical Vapor Transport Growth of Silicon Carbide

We have analyzed the graphitization process of the source material during physical vapor transport growth of SiC by comparison of experimental monitoring (digital x-ray imaging, and 13 C-labeling) and 2D numerical modeling of the sublimation and recrystallization process. Growth runs under different conditions (temperature and inert gas pressure) were used for verification of the calculated source evolution. Effects like formation of a condensed disk on top of the source material, consumption of SiC powder close to the hot graphite walls, mass transport through the core part and along the side walls could be confirmed. The rate of the sublimation and recrystallization effect, however, was overestimated by the model in the range of the experimental parameters in this study. Regardless of the latter, the crystal growth rate was described very well (modeling: 280µm/h, experiment: 310µm/h and 300µm/h).

Analysis of Threading Dislocations in Wide-Bandgap Hexagonal Semiconductors by Energetic Approach

Using the anisotropic elasticity theory, we analyze preferential orientations and stability of threading dislocations in hexagonal AlN and SiC. The effect of growth surface on the orientation of low-mobility dislocations is considered. The theoretical predictions are compared with recent observations on CVD-grown 4H-SiC.

Experimental and Theoretical Analysis of Sublimation Growth of Bulk AlN Crystals

Sublimation seeded growth of bulk AlN single crystals in a resistance-heated furnace has been studied experimentally and theoretically. The growth temperature, the temperature drop between the AlN powder source and single-crystal seed, and the ambient nitrogen pressure are varied to find the optimal growth conditions. Ambiguous effect of the process parameters on the crystal growth rate is revealed; it is found, in particular, that the growth sharply slows down and even fails at a higher temperature and a lower source-seed temperature drop. Simulation of the process suggests that the effect is associated with certain evaporation of the seed under unfavorable growth conditions. The optimal growth conditions providing a stable growth of single-crystal AlN boules of about 10 mm diameter and 10 mm long at a rate of 0.3-0.5 mm/hr are found. The crystals grown at a near-atmospheric pressure have pronounced hexagonal facet shape, decrease of the pressure favors growth of more rounded crystals with a distinct stepwise surface and few growth centers.

Bulk SiC Crystal Growth at Constant Growth Rate Utilizing a New Design of Resistive Furnace

In this work the problem of growth rate decaying during growth is considered. A new design and growth profiles are suggested in order to reduce deviations of growth parameters during the process of growth.

Inverse-Computation Design of a SiC Bulk Crystal Growth System

Inverse modeling was applied to the optimization of a crucible design for SiC sublimation growth. We found a crucible shape providing the optimal temperature distribution in terms of the powder source stability during long-term operation and of the convex crystal shape. Considerable improvement of temperature uniformity throughout the powder charge was achieved. The results obtained show selective sensitivity of the thermal field inside the crucible to modification of the crucible design. The inverse problem approach is easy-to-adapt to various optimization criteria and seems to be especially effective in the case of multi-factor optimization.

Computational Analysis of SiC HTCVD from Silicon Tetrachloride and Propane

This work focuses on computational analysis of SiC High Temperature Chemical Vapor Deposition (HTCVD) from silicon tetrachloride (SiCl4) and propane (C3H8) precursors supplied separately and diluted by argon and hydrogen, respectively. It is aimed at verification of the technological parameters providing complete precursor decomposition in the growth chamber, the optimal gas composition for SiC growth, and the required silicon-to-carbon ratio in the wafer region, as well as suppression of parasitic deposits at the reactor walls and inlet unit via the optimization of the reactor geometry and temperature distributions. As a result, a high growth rate and maximal yield are expected to be achieved due to minimal precursor losses.