The impact of RF-plasma power in carrier relaxation dynamics of unintentional doped GaN epitaxial layers grown by MBE

•GaN epitaxial layers are prepared by varying RF-plasma power in the MBE system.•Higher plasma power grown sample exhibits a lower defect density with a faster carrier relaxation.•A correlation between carrier relaxation behavior and RF-plasma power has been established.•Plasma power in RF-MBE system led to the formation meta-stable states of GaN epitaxial layers. In this work, unintentionally doped GaN samples were prepared on GaN template by radio frequency (RF)-plasma MBE technique using two different RF-plasma powers. Photoluminescence (PL), steady state photoconductivity (PC) and ultrafast optical pump-probe spectroscopy measurements have been carried out to characterize the samples. The effect of RF-plasma power towards unintentional doping and giving rise to yellow luminescence (YL) is discussed. Our PC measurements show relatively faster decay for sample grown with higher RF-plasma power. In addition, the ultrafast optical pump-probe spectroscopy results show the presence of various defect levels with different relaxation times. A faster ultrafast relaxation time from the conduction band to the closest defect level and conduction band to the next defect level was observed for the sample grown with higher plasma power. A comparatively low defect density and faster carrier relaxation observed in higher RF-plasma power grown samples is caused by lower impurities and gallium vacancies. The results imply that RF-plasma power is very important parameter for the growth of epitaxial GaN films and undesirable impurities and gallium vacancies might get incorporated in the epitaxial GaN films.