Description
Of great interest are studies of light-emitting crystals, LEDs and devices based on them according to the methods of in-house development, ranging from installation methods to methods of measuring parameters using the study of degradation characteristics (changes in parameter values over time). The results of such studies make it possible with a high degree of confidence to judge the quality of LED manufacturing, the applied crystal, the influence of various factors on the durability of lighting devices, and a simultaneous prediction of changes in their characteristics over time.
In order to study the parameters of emitting structures and LEDs based on them, a special complex was created in the process of development to provide continuous operation modes for samples for a long time (currently about 8 years).
The applied measurement tools and the corresponding conditions allowed us to develop a number of proprietary methods for studying the radiative properties and processes in heterostructures, methods for assessing the potential degree of degradation of LEDs and devices based on them. The most important of these is the method of studying the redistribution of the luminous flux (radiation power) according to the spatial radiation pattern of the luminous intensity (radiant power) during the first 1000-2000 hours of life.
It can not only draw conclusions about changes in the structure itself, the reasons for which can be explained at the level of the physics of its work, but also suggest that such a redistribution of the luminous flux, proportional to the redistribution of radiative recombination centers with an operating time, also exists inside the radiating crystal in its active area. The proposed method has revealed great prospects for its use in studying the potential degree of degradation of LED parameters in production, the definition of epitaxy defects, or the installation of chips in cases.
Based on studies of complete sets of characteristics, gradually measured over a long period of time between LEDs and emitting crystals (up to 50,000 hours), methods have been developed for determining the potential degree of change in the quantum efficiency of structures, luminous flux (radiation power), spectral parameters of radiation, and electrical characteristics resorting to testing of samples during the period of stabilization of parameters (1000-2000 hours). The results of long-term real observation of changes in the parameters of heterostructures (up to 50,000 hours) in conjunction with the study of the redistribution of the luminous flux (radiation power), the relationship of the studied changes, formed the basis for the creation of a production method for sorting radiating crystals and LEDs according to the principle operation. Initially, all the characteristics inherent in serviceable crystals or LEDs will be present at the time of sorting, and such devices will be recognized as suitable for production. However, the degree of change in their parameters during production can vary significantly. Identification of this fact was possible only when a large number of LEDs were examined by the proposed method, which allowed to detect a very important drawback in the world-wide system of sorting ready-made LEDs, and thus explain the reason for the appearance of potentially defective devices in the total mass that were considered suitable. As a result of the application of the technique, it is justified that the proposed sorting option allows you to make a reliable prediction of the quality of the LEDs produced (to identify more than 95% of potentially unusable devices) and to adjust the necessary technological operations to eliminate possible defects at the output. It is also shown that the proposed methods of sorting in production do not incur any additional time, equipment, energy, or staff labor.
It should be noted that in this capacity, the ARCHILAYT laboratory can be an important link in the production chain for studying and testing the entire line of lighting equipment. From the results of laboratory studies may depend on the choice of a manufacturer of LEDs, the definition of parameters and durability of future products.
