Electrical and luminescent properties of normal p-side-up and inverted n-side-up light emitting diodes (p-LEDs and n-LEDs) and the effect of Mn incorporation into the upper n-type contact layer structure of GaN-based multiquantum-well MQW LEDs were studied. The latter structure is considered as promising for spintronic applications (spin-LED). It is shown that n-LEDs have more pronounced tunneling compared to p-LEDs and that the active region of the n-LEDs shows domain-like nonuniformities that are absent in p-LEDs. These nonuniformities seem to be related to local segregation of In in the GaN/InGaN MQWs and result in the emergency of double peaked electroluminescence (EL) spectra in n-LEDs. Introduction of Mn leads to strong increase of the resistivity of the GaMnN layer which gives rise to increased threshold voltage for observing the EL and decreased EL intensity.