The Quantum Yield of Heterostructures Based on Gallium Nitride Quantum-Well GaInN
The most important parameter of the LED heterostructures is the value of the external quantum efficiency. However, for the structures used in the manufacture of crystals for blue and white LEDs there is one more requirement: the wavelemgth maximum of the emission spectrum and the variation of its magnitude over the entire area of the structure should be 460±5 nm. Primarily, this is due to the fact that the most applied design of white LEDs the crystals covered with a layer of phosphor of a specific composition, excited by blue radiation, are used. The deviation from the above values of the spectral parameters of heterostructures leads to a sharp deterioration of light and color characteristics of LEDs. In present work the problem of optimizing the design and technology of growing the active region of the radiating structure, consisting of a set of quantum-size Yam Ga1-xInxN and wider bandgap GaN barriers, with a specific wavelength maximum of the emission spectrum, is being solved. The calculation of critical thickness of pseudomorphic layer for a range of Poisson ratio from 0 to 0.2 for GaAlN and from 0 to 0.4 for GaInN. The radiation wavelength is defined by both, by the width of the forbidden zone bulk Ga1-xInxN, that depending on the molar fraction of indium in quantum wells and by the thickness of QW in the quantum-well layers. From the obtained in the work dependences it has been determined that to obtain the desired wavelength at the maximum of the emission spectrum of 460 nm it is necessary to have the Ga1-xInxN layers, containing approximately 10.3% of indium and having pits thickness about 2.5 nm. The influence of the different distribution profile of indium in quantum wells in the external quantum yield, the uniformity of distribution of the radiation wavelength values at the spectrum maximum and the uniformity of distribution of the radiation power on the structure area, have been investigated. In the study of the effect of the number of quantum wells on the properties of heterostructures is shown that to achieve the maximum value of the external quantum yield of radiation, the number of QWS should be from 4 to 5. The best uniformity of the radiation wavelength at the maximum of the spectrum for the square structure is achieved when the number of QW from 5 to 7. Thus, in the present work, the optimum number of quantum wells in the active region of the heterostructure is 5.