Degradation behavior of an InGaAs/AlGaAs Multi Quantum Well (MQW) light emitting diode (LED) was investigated. The LED has a current confinement structure that results in a pinpoint light source. The low degradation behavior was confirmed compared with a conventional current confinement structure LED with a bulk GaAs active layer. The failure rate of the MQW LED is lower than 20 Fit, which is much lower than the bulk GaAs LED.
The characteristics of the degraded LEDs with the respective structures were different. Dark areas, such as dark line defects, or dark spot defects were observed in the emitting areas of both the LEDs after extended life test. It is well documented that such defects act as non-radiative recombination centers for injected carriers and cause large degradation in light output. There is a correlation between the degradation of the emitting light and the increasing dark area for both types of LEDs. However, linear regression analysis for both LED types revealed that the MQW LEDs exhibit a 50 % reduction in the degradation of light output. This would indicate that the dark area in a MQW LED is less effective against the degradation when compared to a bulk LED. A transmission electron microscope revealed crystal defects in the active layer of the dark area of the MQW LED, and further test using a scanning sheet resistance microscope confirmed that the electrical resistivity of the active layer of the dark area is higher in the MQW LED. Therefore, the flow of electric current would be restricted in this region. The high resistivity may be due to the existence of the defects and further investigation is now in progress.