Localization landscape theory of disorder in semiconductors. II. Urbach tails of disordered quantum well layers
- Ecole Polytechnique, Univ. of Paris-Saclay, Palaiseau (France). Lab. of Condensed Matter Physics; Univ. of California, Santa Barbara, CA (United States). Dept. of Materials
- National Taiwan Univ., Taipei (Taiwan). Graduate Inst. of Photonics and Optoelectronics and Dept. of Electrical Engineering
- Univ. of California, Santa Barbara, CA (United States). Dept. of Materials
- Ecole Polytechnique, Univ. of Paris-Saclay, Palaiseau (France). Lab. of Condensed Matter Physics
Urbach tails in semiconductors are often associated to effects of compositional disorder. The Urbach tail observed in InGaN alloy quantum wells of solar cells and LEDs by biased photocurrent spectroscopy is shown to be characteristic of the ternary alloy disorder. The broadening of the absorption edge observed for quantum wells emitting from violet to green (indium content ranging from 0% to 28%) corresponds to a typical Urbach energy of 20 meV. A three-dimensional absorption model is developed based on a recent theory of disorder-induced localization which provides the effective potential seen by the localized carriers without having to resort to the solution of the Schrödinger equation in a disordered potential. This model incorporating compositional disorder accounts well for the experimental broadening of the Urbach tail of the absorption edge. For energies below the Urbach tail of the InGaN quantum wells, type-II well-to-barrier transitions are observed and modeled. This contribution to the below-band-gap absorption is particularly efficient in near-ultraviolet emitting quantum wells.When reverse biasing the device, the well-to-barrier below-band-gap absorption exhibits a red-shift, while the Urbach tail corresponding to the absorption within the quantum wells is blue-shifted, due to the partial compensation of the internal piezoelectric fields by the external bias. The good agreement between the measured Urbach tail and its modeling by the localization theory thus demonstrates the applicability of the latter to compositional disorder effects in nitride semiconductors.
- Research Organization:
- Univ. of California, Santa Barbara, CA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Building Technologies Office; French National Research Agency (ANR); Ministry of Science and Technology (MOST), Taipei (Taiwan)
- Contributing Organization:
- Ecole Polytechnique Paris National Taiwan University
- Grant/Contract Number:
- EE0007096; ANR-14-CE05-0048-01; MOST-104-2923-E-002-004-MY3; MOST-105-2221-E-002-098-MY3
- OSTI ID:
- 1429092
- Alternate ID(s):
- OSTI ID: 1352104; OSTI ID: 1635239
- Journal Information:
- Physical Review. B, Vol. 95, Issue 14; ISSN 2469-9950
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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