Deep trap analysis in green light emitting diodes: Problems and solutions

Abstract

Some green light emitting diodes (LEDs) based on GaN/InGaN multiquantum-well (MQW) structures exhibit strong frequency and temperature dependence of capacitance and prominent changes in capacitance-voltage profiles with temperature that make it difficult to obtain reliable deep level transient spectroscopy (DLTS) measurements. DLTS performed at low probing signal frequency and with constant capacitance between the measurements by controlling applied bias mitigates these issues. This allows measurement of deep electron and hole traps in specific quantum wells (QWs) in the MQW structure. The dominant electron and hole traps detected have levels near E-c(-) (0.45-0.5) eV and E-v(+) (0.6-0.63) eV. Their density increases significantly after aging for a long period (2120h) at high driving current and elevated temperature. The reason for the observed anomalies in DLTS spectra of these green LEDs is the high density of states in the QWs with activation energies near 0.08, 0.12-0.14, and 0.3eV, detected in admittance spectra, and, for the 0.08eV and 0.3eV, these states are likely related to defects.