Beyond Quantum Efficiency Limitations Originating from the Piezoelectric Polarization in Light-Emitting Devices

• Published in: ACS photonics Vol. 6; no. 8; pp. 1963 - 1971
• Main Authors: Muziol, Grzegorz, Turski, Henryk, Siekacz, Marcin, Szkudlarek, Krzesimir, Janicki, Lukasz, Baranowski, Michal, Zolud, Sebastian, Kudrawiec, Robert, Suski, Tadeusz, Skierbiszewski, Czeslaw
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.08.2019
• Subjects: piezoelectric polarization; green gap; light-emitting diodes; photonic devices; III-nitrides; quantum wells
• ISSN: 2330-4022; 2330-4022
• DOI: 10.1021/acsphotonics.9b00327

Blue and violet light-emitting devices based on III-nitrides caused an ongoing revolution in general lighting. One of the highly deliberated discussions in this field is devoted to the problem called the “green gap”, which is a lack of efficient emitters in this spectral regime. One of the reasons behind the insufficient internal quantum efficiency (IQE) of green III-nitride devices is related to the quantum confined Stark effect. In this paper we present a counterintuitive feature of quantum well systems with a large built-in electric field that leads to a huge enhancement in IQE. We show, by means of numerical simulations, that an increase in the InGaN quantum well thickness initially leads to a decrease in the oscillator strength; however, after a certain critical thickness is reached, a highly efficient recombination path appears via excited states. A peculiar quantum well system with a zero-probability transition between the ground states and an extremely high one through the excited states is demonstrated. Remarkably, the oscillator strength in a wide QW is higher than in conventionally used QWs with thicknesses lower than 5 nm. Experimental evidence is provided showing a change in the nature of the optical transition with increasing thickness of the QW. Furthermore, we show that, counterintuitively, the devices with higher In content exhibit a higher enhancement in IQE, which might solve some problems related to the “green gap”. The predictions shown in this paper are valid for all semiconductor systems exhibiting large piezoelectric polarization such as III-nitrides, II-oxides, and II-sulfides.