Properties of Defective Regions Observed by Photoluminescence Imaging for GaN-Based Light-Emitting Diode Epi-Wafers

Abstract

A photoluminescence (PL) imaging method using a vision camera was employed to inspect InGaN/GaN quantum-well light-emitting diode (LED) epi-wafers. The PL image revealed dark spot defective regions (DSDRs) as well as a spatial map of integrated PL intensity of the epi-wafer. The Shockley-Read-Hall (SRH) nonradiative recombination coefficient increased with the size of the DSDRs. The high nonradiative recombination rates of the DSDRs resulted in degradation of the optical properties of the LED chips fabricated at the defective regions. Abnormal current-voltage characteristics with large forward leakages were also observed for LED chips with DSDRs, which could be due to parallel resistances bypassing the junction and/or tunneling through defects in the active region. It was found that the SRH nonradiative recombination process was dominant in the voltage range where the forward leakage by tunneling was observed. The results indicated that the DSDRs observed by PL imaging of LED epi-wafers were high density SRH nonradiative recombination centers which could affect the optical and electrical properties of the LED chips, and PL imaging can be an inspection method for evaluation of the epi-wafers and estimation of properties of the LED chips before fabrication.

BAlGaN light‐emitting diode emitting at 350 nm

“…Inset is the IV on a semi-log scale, in which the BAlGaN LED demonstrates an apparent parasitic diode behaviour between 4 and 5 V. The increase in operating voltage could be explained by the voids in the active region enforcing a more restricted path to carriers, thereby increasing the resistance. Meanwhile, leakage current or tunnelling through surface states in the voids could act as parallel diodes with lower barrier heights than the main diode, resulting in the characteristic behaviour seen in Figure 3b [10,11].…”