Seminarium Fizyki Ciała Stałego

The growth modes of heteroepitaxial layers of nitrides such as Stranski-Krastonow (SK) and Volmer-Weber (VW) in relation with dislocation generation are discussed. The MOCVD growth of BGaN/GaN layers is described and X-Ray Diffraction (XRD), Secondary Ion Mass Spectrometry (SIMS) and Scanning Electron Microscopy (SEM) measurements are presented. The unexpected change of growth mode of BGaN/GaN from SK to VW one at high growth temperature is observed in SEM images. This change of growth mode is first connected with formation of micro-voids at the BGaN/GaN interface. It is shown that micro-voids are responsible for blocking threading dislocations within the overgrown BGaN layer. This leads to lateral growth of the BGaN layer along the a-direction and a drastic reduction in the defects concentration shown by High-Resolution Photoinduced Transient Spectroscopy (HRPITS) and optical measurements.In addition, a change in the growth mode from Stranski–Krastonow, characteristic for MOCVD grown GaN, to laterally grown BGaN in the Volmer-Weber growth mode is observed. The mechanism responsible for such a dramatic growth mode change appears to be related to defect reactions leading to the formation a BN atomic layer at the BGaN growth front.Finally, it is suggested that the main role of BGaN layers in nitride technology may be connected with efficient way of dislocations elimination from grown GaN.