Relation between photocurrent parameters of LEDs based on GaN heterostructures
and a change in their characteristics under heat-current tests
V. A. Sergeev1,2 ,
I. V. Frolov1, O. A. Radaev1,2
1 Ulyanovsk
Branch of Kotelnikov Institute of Radioóngineering
and Electronics of Russian Academy of Sciences, Goncharov st. 48/2, Ulyanovsk
432071, Russia
2 Ulyanovsk
State Technical University, Severnyy Venec 32, Ulyanovsk 432027, Russia
The paper is received
on February 22, 2019
Abstract. 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.
Keywords:
light emitting heterostructures, photoexcitation,
photocurrent, distribution, electroluminescence, testing, degradation.
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