Effect of electron blocking layer on inter-QW transport in III-nitride multi-QW LEDs

Strong disparity in electron and hole transport characteristics and excessive depth of optically active quantum wells (QWs) in III-nitride materials are the main causes of inhomogeneous carrier distribution and uneven QW injection in multi-QW light emitters of visible range. Both polar and nonpolar LED structures suffer from inhomogeneous injection. Undoped wide-bandgap electron blocking layer (EBL) located on the P-side of the active region can only make the situation worse by further reducing already insufficient hole injection. On the other hand, P-doped EBL facilitates the hole injection, improves the overall active region injection uniformity, and reduces the carrier leakage. We show, however, that EBLs act very differently in polar and nonpolar III-nitride multi-QW structures. While in nonpolar LED the p-doped EBL ultimately promotes the inter-QW carrier exchange, the injection efficiency in polar structure remains limited by strong electron leakage from the marginal p-side QW.