Impact of carrier gas on the GaN layers properties grown on (001) and (11$n$) GaAs substrates by AP-MOVPE: comparative study

The impact of carrier gas on the GaN layers properties grown by atmospheric pressure metal-organic vapor-phase epitaxy (AP-MOVPE) on (001) and (11$n$) GaAs substrates were investigated. The Arrhenius plots of growth rate deduced from laser reflectometry measurements give an activation energy of $E_{\mathrm{a}1}$ = 0.045 eV when the H$_2$ was used as the carrier gas. In the case of using N$_2$ as the carrier gas, the results give $E_{\mathrm{a}2}$ = 0.081 eV as a value of activation energy, which is approximately 2 times greater than $E_{\mathrm{a}1}$. Scanning electron microscopy results show that when N$_2$ is used, the resulting material quality is low, but the use of H$_2$ is successful to prevent the cracking of GaN layers and results in improvement of crystalline properties. From the $X$-ray diffraction result, we conclude that both (001) and (113) GaAs substrate orientations as well as the use of H$_2$ as the carrier gas favors the GaN growth with cubic structure, whereas the GaN hexagonal structure is favored for growth on (112) and (111) GaAs substrates orientations with N$_2$. Cathodoluminescence measurements show that a mechanism of phase transformation occurs when the growth temperature rise from 800 to 900$^\circ$C.