Surface supersaturation during crystal growth can be obtained by measuring inter-step distance of spiral steps and with an equation given by Cabrera and Levine. Surface supersaturations thus measured for YBCO (YBa2Cu3O7), InP, SiC and GaN are presented. Surface supersaturation in the growth of YBCO depends strongly on growth temperature and decreases with the temperature irrespective of growth methods. Liquid phase epitaxy (LPE) of InP gives very low supersaturation which depends on the growth and saturation temperatures. Clear double spiral steps were found on vapor grown surface of SiC and it turned out that the surface supersaturation was considerably low as low as 0.02 for example. This is due to the high growth temperature. Experimentally obtained growth rate of GaN by metal organic vapor phase epitaxy (MOVPE) as a function of surface supersaturation showed a good agreement with BCF theory in low supersaturation limit as demonstrated by Akasaka et al..
We review the studies on the scaling of the minimal step-step distance lmin in the bunch with the bunch size N, lmin ∝N-γ. We build our retrospective around the different values of the exponent γ obtained from models and experiments. It was mainly studied in the context of the electromigration driven instability on Si(111) vicinal surfaces. In this context, the full scaling relation is given in general form as lmin ~ (A/lcFN2)1/(n+1), where A is the magnitude of the step-step repulsions with range n, F is the electromigration force acting on the charged surface atoms and lc is a length-scale, characteristic for the regime of step bunching, diffusion-limited (DL) or attachment-detachment limited (KL).
Elementary explanations of physical bases of epitaxial growth such as elasticity, surface diffusion are given. The elastic interaction of “defects” and the lattice misfit alter the growth mode of thin films. Step dynamis based on the Burton-Cabrera-Frank type model is discussed briefly. The existence of the diffusion barrier at the step edge, as well as other asymmetries at the step, brings about various morphological instabilities of steps.
The III/V alloy semiconductors have become of commercial importance for light emitting diode, solar cell, high speed electronics, and many other applications. These materials can be grown by several epitaxial processes; however, commercial production is most often done using organometallic vapor phase epitaxy (OMVPE or equivalently MOVPE or MOCVD). Even after decades of effort to understand the fundamental aspects of both the growth processes and the materials properties, our understanding of both is still incomplete. However, thermodynamics gives underlying, vital information that leads to an understanding of both the growth processes and the materials properties. In particular, thermodynamics is decisive in determining the optimal growth process. Only so called “non-equilibrium” processes such as OMVPE and molecular beam epitaxy (MBE) can be used for the growth of alloys containing both Al and In, such as AlGaInP and AlGaInN, two materials from which the highest performance LEDs and solar cells are fabricated. The thermodynamics of mixing of these materials can be understood using the delta-lattice-parameter (DLP) model. It allows the prediction of the parameters necessary for the growth of specific alloys for particular device applications. It also gives the key information allowing us to understand the microstructures of the resultant materials. When constituent lattice constants differ widely, the alloys exhibit miscibility gaps. This means that many materials cannot be grown using equilibrium growth techniques. Nevertheless, metastable materials can be grown by OMVPE and MBE using kinetic factors to prevent the establishment of thermodynamic equilibrium during epitaxial growth. However, these materials often exhibit compositional fluctuations driven by thermodynamic forces. The resulting microstructures have enormous consequences for the materials properties and device performance. This review will focus on some of these materials, notably the metastable alloys AlGaInN, GaAsN, and GaAsBi.
It is known that the growth process of semiconductors depends on the growth conditions such as temperature, partial pressures of gaseous sources, and growth orientation. However, there has been little study of the relation between the growth process and the growth conditions. In 2001, we developed an ab initio based-approach that incorporates gas-phase free energy. Using the theoretical approach, we can discuss the influence of the growth conditions on the stability of surface reconstruction. In this research, we propose a newly improved thermodynamic analysis that incorporates surface energies obtained by ab initio calculations. The theoretical approach was applied to study the growth processes of InN(0001), (000-1), (10-10) and (11-20) by MOVPE. Calculation results reproduced the difference in optimum growth temperature.
Suppression techniques of the GaN crystal nucleation in the Na flux method has become an important technique for establishing a high-quality GaN single crystal growth technology. By technologies capable of promoting GaN crystal nucleation is developed, Na flux method allows application to fabrication of GaN polycrystals as well as bulk GaN single crystal.
We report on the high-density aggregation of GaN polycrystals, fabricated using the Na flux method under continuous propeller stirring. It is seen from the XRD profile that the aggregation of GaN polycrystals was randomly directed when grown under continuous stirring conditions using propeller at 100 rpm. The relative bulk density and real density of the aggregation of polycrystals content to the density of the bulk GaN crystal were 92.1% and 98.4%, respectively. It is noted that the use of a propeller for continuous stirring in the Na flux method has the possibility of fabricating a high-quality raw materials for various methods of GaN-based materials.