Connection of photocurrent parameters of LEDs based on GaN heterostructures with a change in their characteristics under heat-current tests
A hardware and software complex for measuring the distribution of the photoelectric response level over the surface of light-emitting heterostructures with quantum wells (QWs) during their local photoexcitation by laser radiation in stationary and dynamic modes is briefly described. The results of measuring the distribution of the photocurrent level over the area of LED GaN-heterostructures in the static mode and the mode of harmonic modulation of the photoexcitation intensity are presented. It is shown that the relative scatter of the photocurrent values at the edges of the structure is higher than in the center, which is confirmed by measuring the limiting frequencies of the photoresponse during harmonic photoexcitation. It has been established that the photocurrent level during photoexcitation of heterostructures with longer wavelength radiation has a larger scatter, which is explained by an increase in the fraction of the photocurrent generated from defect levels. The results of changes in the photocurrent parameters and optical characteristics of LEDs during the heat-current tests are presented. It is shown for the first time that the spectrum of the integrated photocurrent of LEDs based on GaN-heterostructures as a result of tests shifts to the long-wavelength region. In this case, the change in the average level of the photocurrent strongly correlates with the measurement of the level of electroluminescence, that is, it characterizes the rate of degradation of the heterostructures. It is noted that the variation in the level of the integral photocurrent of UV LEDs is markedly higher than the variation observed in blue and green light emitting diodes. Estimates showed that the coefficient of photocurrent decay in the process of testing for all types of LEDs under study correlates markedly with the initial level of the photocurrent. The possibilities of developing on the basis of the obtained results of an industry-oriented methodology for diagnosing the quality of LEDs in terms of the photoelectric response parameters are discussed.