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In this paper we review the recent studies on wide InGaN quantum wells (QWs). InGaN QWs are known to suffer from an extremely high built-in piezoelectric polarization, which separates the electron and hole wavefunctions and causes the quantum-confined Stark effect. We show both by means of modeling and experimentally, that wide InGaN QWs can have quantum efficiency superior to commonly used thin QWs. The high efficiency is explained by initial screening of the piezoelectric field and subsequent emergence of optical transitions involving the excited states of electrons and holes, which have a high oscillator strength. A high pressure spectroscopy and photocurrent measurements are used to verify the mechanism of recombination through excited states. Furthermore, the influence of QW width on the properties of optoelectronic devices is studied. In particular, it is shown how the optical gain forms in laser diodes with wide InGaN QWs. [ABSTRACT FROM AUTHOR]