Stratilat D. Influence of radiation defects on the characteristics of homojunction (GaP; GaAsP) and heterojunction (InGaN/GaN) LEDs

Dissertation for the degree of Doctor of Philosophy in Specialty 104 – Physics and Astronomy – Institute of Nuclear Research of the National Academy of Sciences of Ukraine, Kyiv, 2024. The dissertation work is devoted to establishing the impact of exposure to the electrons with E = 2 MeV, ? - quanta of 137Cs, 60Co, neutrons on characteristics of homojunction GaP, GaAsP LEDs, as well as LEDs with quantum wells InGaN/GaN. The first chapter contains a literary review of the scholarly knowledge related to the dissertation topic. It covers the properties of pristine homojunction LED structures GaP and GaAsP, as well as the heterojunction InGaN with quantum wells. The results of the analysis of the annealing effect on the main parameters and characteristics of irradiated samples are presented. The specifics of the interaction of the ultrasound wave with the initial irregularities and radiation defects of the crystal lattice are described, achievements in the field of scientific research and modern advanced technologies are processed and summarized. Special attention is given to the use of injection luminescence sources and their radiation resistance. The second chapter describes the experimental method – sample preparation for irradiation, the design and operation principle of measuring equipment, devices for irradiation with electrons. The third chapter contains the study of degradation and recovery phenomena inherent in pristine and electron-irradiated GaP LEDs. The influence of radiation defects on the emission spectra of the diodes was studied. The fourth chapter studies the features of the volt-ampere characteristics of LEDs grown based on GaP-GaAs solid solutions. It presents study results of the electron irradiation effect (Е = 2 MeV, Ф = 3 • 10^14 ? 2,6 • 10^16 см^-2) on the main electrophysical parameters of GaAs1-xPx diodes (х = 0,85 – yellow, х = 0,45 – orange). An increase in differential resistance, series resistance of the base, and barrier potential was identified. The recovery processes of the studied samples during isochronous annealing and the mechanisms of degradation-relaxation phenomena were analysed. The fifth chapter contains the results of the optical characteristics of GaAs_1-хP_х pristine LEDs and LEDs irradiated with electrons with E = 2 MeV, Ф = 10^15 ? 10^16 см^-2. The band gap width of the GaAs1-хPх solid solution was estimated for х = 0.45. Lifetime damage coefficients of minority charge carriers for irradiated GaAsP LEDs were calculated, and the effects of radiation on the operating parameter Т1, which determines diode thermal stability, were analysed. The sixth chapter covers studies of the emission spectra of InGaN/GaN white LEDs, the main components of which are the blue LED line with ?_max = 443 nm and a wide bifurcated secondary emission band of the AIT-YAG phosphor (Ce) ? = 500 ? 650 nm. The chapter shows that the non-monotonic dependence of the luminescence intensity on the temperature is caused by the strengthening of the shielding effect of the internal fields by free carriers, as well as by thermal quenching as a result of the increase in the density of the phonon gas. The seventh chapter shows that in InGaN LEDS at T ? 180 K at VAC appear areas with negative diffusion resistance. It is identified that the breakdown areas at VAC are the result of interbarrier carrier tunnelling.