Thermodynamic analysis of (0001) and $(000\bar{1})$ GaN metalorganic vapor phase epitaxy

Abstract

We performed a thermodynamic analysis of GaN metalorganic vapor phase epitaxy considering the (0001) and surface states. Surface reconstruction, which depends on growth conditions such as temperature and partial pressure, affects growth processes. To discuss the effects of surface states on growth processes, we investigated the driving force of precursor deposition to form the surface phase defined stoichiometrically. In both N2 and H2 carrier gas cases, we showed surface phase diagrams, calculated driving forces, and discussed the difference in growth orientation.

Equilibrium Morphologies of Faceted GaN under the Metalorganic Vapor‐Phase Epitaxy Condition: Wulff Construction Using Absolute Surface Energies

“…In addition, the emergence of the polar (0001) plateau remarkably depends on carrier gas. As the driving force on (0001) surface for H 2 carrier gas is different from that for N 2 carrier gas, the differences in the driving force between the semipolar and (0001) surfaces depending on carrier gas are seen in the growth temperatures of GaN MOVPE. Consequently, the effect of driving force on various surface orientations under H 2 carrier gas condition is more remarkable than that under N 2 carrier gas condition around 800–1100 °C.…”

“…Furthermore, it is well known that the MOVPE condition, such as growth temperature, partial pressure, and carrier gas, is crucial for the equilibrium crystal shape in GaN nanostructures. In this study, these parameters are taken into account by constructing surface phase diagrams among various orientations as functions of growth temperature and partial pressure …”

“…However, these absolute surface energies do not incorporate the experimental conditions such as temperature and partial pressure of molecules supplied during epitaxial growth. To compare the theoretical results with experiments, an improved thermodynamic analysis that incorporates absolute surface energies of polar and semipolar planes on group‐III nitrides under the MOVPE condition has been carried out . According to thermodynamic analysis, it is possible to discuss the orientation dependence of driving force among various surface orientations during MOVPE.…”

CH4 Adsorption Probability on GaN(0001) and (000−1) during Metalorganic Vapor Phase Epitaxy and Its Relationship to Carbon Contamination in the Films

“…In 2001, Kangawa et al proposed a theoretical approach for creating a surface phase diagram using the chemical potentials of molecules as functions of the temperature and partial pressures [7]. To date, reconstructed structures for polar, non-polar, and semi-polar GaN surfaces during the growth process have been studied [8,9,10,11,12,13,14,15,16,17,18,19]. Kusaba et al reported the Ga adatom surface and the 3Ga-H surface for (0001) and the 3N-H surface for (000−1) appear for typical GaN MOVPE conditions [19].…”

“…The growth conditions are set as follows: pGa=2.5×10−4 atm and pcarrier=pN2+pH2=0.7 atm, which means that the V/III ratio, pNH3/pGa, is set at 1200. The details of the structures of candidate reconstructed surfaces are provided in Reference [19]. In the case of GaN(0001) growth, a hydrogen adsorbed surface, 3Ga-H (2 × 2), appears at a H 2 partial pressure greater than about 0.5 atm and around a typical growth temperature of 1050 °C.…”