  GaN and ZnO microcavities have been grown on patterned silicon substrate.
Thanks to a common platform these microcavities share similar photonic
properties with large quality factors and low photonic disorder which gives the
possibility to determine the optimal spot diameter and to realize a complete
comparative phase diagram study. Both systems have been investigated under the
same experimental condition. Experimental results are well reproduced by
simulation using Boltzmann equations. Lower polariton lasing threshold has been
measured at low temperature in the ZnO microcavity as expected due to a larger
Rabi splitting. However the threshold is strongly impacted by LO phonons
through phonon-assisted polariton relaxation. We observe and discuss this
effect as a function of temperature and detuning. Finally the polariton lasing
threshold at room temperature is quite similar in both microcavities. This
study highlights polariton relaxation mechanism and their importance for
threshold optimization.
