Improving green LEDs: A meta study into the causes and remedies of the green gap
Abstract: This literature review investigates and evaluates different strategies to improve InGaN-based light emitting diodes (LED) by analyzing published theoretical and experimental studies. The issues of non-uniform carrier distribution, piezoelectric polarization fields and poor wave function overlap can be mitigated by the use of InGaN barriers and substrates as well as staircase designs for quantum wells (QW). It is found that QWs made for long emission wavelengths suffer from Auger recombination due to high carrier concentrations in the QWs. Lower barriers will enhance the injection of holes and thus increase the radiative recombination rate in all QWs. Piezoelectric polarization fields due to lattice mismatch can be suppressed by using InGaN barriers and substrates with decreased lattice mismatch. The radiative recombination rate is found to increase as the barriers and substrates contain higher Indium content. A large overlap design called “staggered QW” is evaluated and shown to increase wave function overlap and thus the recombination rate for InGaN LEDs. The concept of nanowire LEDs is presented as a possible solution to grow QWs with reduced quantum confined stark effect (QCSE).
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