Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

Abstract

Heterostructures of wurtzite based devices have attracted great research interests since the tremendous success of GaN in light emitting diodes (LED) industry. Among the possible heterostructure material candidates, high quality GaN thin films on inexpensive and lattice matched ZnO substrate are both commercially and technologically desirable. However, the energy of ZnO polar surfaces is much lower than that of GaN polar surfaces. Therefore, the intrinsic wetting condition forbids such heterostructures.As a result, poor crystal quality and 3D growth mode were obtained. To dramatically change the growth mode of the heterostructure, we propose to use hydrogen as a surfactant, confirmed by our first principles calculations. Stable H involved surface configurations and interfaces are investigated, with the help of newly developed algorithms. By applying the experimental Gibbs free energy of H2, we also predict the temperature and chemical potential of H, which is critical in experimental realizations of our strategy. This novel approach will for the first time make the growth of high quality GaN thin films on ZnO substrates possible. We believe that our new strategy may reduce the manufactory cost and improve the crystal quality and the efficiency of GaN based devices.

Missing links towards understanding the equilibrium shapes of hexagonal boron nitride: algorithm, hydrogen passivation, and temperature effects

“…Theoretically, this energy term should include the contributions of the translational, rotational, and vibrational states, 36,37,49,50 where the vibrational states of H2 are dominant at high growth temperatures. 36,37 Here, to estimate this energy term, following the method in our previous works, 27 we used the following expression for the quantity Δ𝜇 𝐻 : 27, 50…”

“…In previous wurtzite or zinc blende polar surface studies, 27,39,40,42 a slab model with two conjugated polar surfaces was always applied, where one of the two surfaces (bottom surface) is passivated by correspondingly fractionally-charged pseudo-H atoms to satisfy ECM, avoiding unphysical charge transfers simultaneously. Later, by constructing pseudo-molecules or a set of tetrahedral clusters, the pseudo-chemical potentials of the pseudo-H atoms can be properly estimated, and the absolute formation energy can be obtained, to an accuracy of within several meV/Å 2 .…”

“…Passivation on surfaces or edges usually satisfy the electron counting model (ECM), 24 lowering the total energy. [25][26][27] One of the possible unavoidable impurities that passivate the edge is hydrogen (H). In the growth chamber, H2 is usually a part of the carrier gas.…”

“…This term is especially significant at high growth temperatures. Therefore, it is also necessary to consider such effects, which have been observed in compound semiconductors, such as GaN, ZnO, and the growth of their heterostructures, 27,37,38 in the thermodynamic analysis. Whether such effects can be exploited in h-BN growth is still an open question.…”

Stability of wurtzite semipolar surfaces: Algorithms and practices

“…Absolute surface energy is one of the key quantities in surface studies. [9, [29][30][31][32] A complete set of knowledge of absolute formation energies of GaN surfaces with all possible orientations is necessary for the related thermodynamic stability analyses, for example, determining the equilibrium crystal shape (ECS) by Wulff's theorem [33]. Such thermodynamic property is one of the key factors in understanding and controlling the growth of GaN nanostructures, which are considered as the major candidates for realizing broadband and multi-color emission [34][35][36][37][38][39][40][41].…”