Changes in electron and hole traps in GaN-based light emitting diodes from near-UV to green spectral ranges

Abstract

Deep electron and hole traps were studied by admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS) with electrical and optical (ODLTS) injection for GaN-based multi-quantum-well (MQW) light emitting diodes (LEDs) operating in the near-UV (385–390 nm), blue (445 nm), and green (515 nm) spectral regions. AS spectra were dominated by freezing out of Mg acceptors at temperatures around 150 K, by shallow centers in the MQW region, and, for green LEDs, by deeper electron traps with a level near Ec − 0.27 eV located in the MQW region. DLTS spectra showed electron traps with levels Ec − 0.8 eV (NUV), Ec − 0.5 eV (blue), Ec − 0.6 eV (blue and NUV), and Ec − 0.27(green LEDs). In ODLTS, hole traps near Ev + 0.75 eV (NUV), Ev + 0.65 eV (blue), and Ev + 0.45 eV (green LEDs) originating in the quantum well (QW) region were detected (the QW character was confirmed by using excitation light that generated electron-hole pairs only within the QWs). The levels of the electron and hole traps in LED structures differing in the In composition in the QWs were well aligned with respect to the vacuum level.

Electron irradiation of near‐UV GaN/InGaN light emitting diodes

“…(a)) before irradiation showed the presence of electron traps near E c −0.8 eV and hole traps near E v +0.75 eV. These are attributed to defects in the InGaN QWs . The electron traps are similar to the E c −1 eV traps commonly found in n‐GaN and are likely related to nitrogen interstitial acceptors N I .…”

“…The E c −1 eV traps that dominate after irradiation with high doses of electrons have signatures similar to those of the E c −1 eV traps shown to be major lifetime killers in electron irradiated n‐GaN . Since the E c −0.8 eV traps are believed to be due to similar defects (Ni‐) located in InGaN QWs it is logical to also associate them with efficient lifetime killers.…”

“…The density of the E v +0.75 eV hole traps does not change significantly after irradiation. Moreover, if these traps are similar to the major E v +0.9 eV hole traps in n‐GaN , one would not expect them to effectively influence the recombination lifetime and this was demonstrated experimentally . The traps with optical threshold near 1.3 eV whose concentration increased after irradiation are similar to the centers often observed in n‐GaN and attributed to carbon interstitials .…”

“…Figure (b) shows an ODLTS spectrum taken before irradiation with excitation from 3.4 eV LEDs. The spectra are for temperatures higher than 200 K – at lower temperatures the capacitance decreased strongly due to freeze‐out of Mg acceptors in p‐GaN and reliable DLTS measurements were not practicable . The quiescent bias used for DLTS and ODLTS measurements in Fig.…”

“…The degradation of EL efficiency upon electrical stress correlated with the emergence of a broad defect band in electron traps spectra . The deep trap spectra of NUV LEDs are dominated by electron traps with levels near E c −0.8 eV and hole traps in the QWs with levels near E v +0.75 eV . One of the best ways to controllably alter the deep trap concentration and to assess the impact of various centers on performance of semiconductor devices is to study the influence of bombardment with high energy particles on device performance.…”