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Unintentional annealing of the active layer in the growth of InGaN/GaN quantum well light-emitting diode structures


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The effects of increasing p-type layer thickness on the photoluminescence (PL) of InGaN/GaN quantum well (QW) light-emitting diode (LED) structures are studied using confocal microscopy. Due to composition fluctuations in the QWs, spatially inhomogeneous PL intensity distribution is observed in all the LED structures with different p-type layer thicknesses. Meanwhile, the spectral peak position and the difference in PL intensity between the bright and dark areas exhibit nonmonotonous behavior. Such behavior is attributed to the concurrent effects of thermal annealing during the high-temperature overgrowth of p-type layer, the variation of the quantum-confined Stark effect (QCSE) due to the increase of p-type layer thickness, and carrier delocalization. The PL intensity increases with increasing p-type thickness when the thickness is smaller than a certain value and decreases beyond this thickness.