Relation between Ga vacancies, photoluminescence and growth conditions of MOVPE prepared GaN layers

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated by varia-ble energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties and the concentration of galium vacancies (VGa). Different cor-relations between technological parameters and VGa concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa formation of VGa was significantly influenced by type of reactor atmosphere (N2 or H2), while no similar behaviour was observed for growth from TMGa. Formation of VGa was suppressed with increasing temperature for the growth from TEGa. On the contrary, enhancement of VGa concen-tration was observed for growth from TMGa with cluster formation for the highest temperature of 1100°C. From the correlation of photoluminescence results with VGa concentration determined by VEPAS it can be concluded, that yellow band in GaN is likely not connected with VGa and ad-ditionally, increased VGa concentration enhances excitonic luminescence. Probable explanation is that VGa prevents formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested.