Abstract Although InGaN layers or InGaN/GaN superlattices are commonly used as efficiency improving buffers for LED structure production, there is still a controversy and active discussion about the mechanisms improving the luminescence properties of InGaN QWs grown above such buffers. In this manuscript it is shown that presence of In in the buffer layer is not the primary reason for photoluminescence improvement which can be also achieved by introduction of GaN buffer layer grown at lower temperature under nitrogen atmosphere. SIMS analysis suggests that low temperature buffer layer does not influence the impurity incorporation and hence the PL improvement is caused by suppressed contamination of MQW region grown above the low temperature buffer. AFM images for two samples that differ mostly in morphology however supports another explanation in which formation of larger V-pits is the main reason for the luminescence improvement.