scholarly journals Indirect to direct band gap crossover in two-dimensional WS2(1−x)Se2x alloys

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Cyrine Ernandes ◽  
Lama Khalil ◽  
Hela Almabrouk ◽  
Debora Pierucci ◽  
Biyuan Zheng ◽  
...  
Keyword(s):  
Band Gap ◽  
Structure Evolution ◽  
Transition Metal Dichalcogenide ◽  
Light Emitting ◽  
Light Emitting Devices ◽  
Direct Band Gap ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Direct Band ◽  
Pl Intensity ◽  
Fast Increase

AbstractIn atomically thin transition metal dichalcogenide semiconductors, there is a crossover from indirect to direct band gap as the thickness drops to one monolayer, which comes with a fast increase of the photoluminescence signal. Here, we show that for different alloy compositions of WS2(1−x)Se2x this trend may be significantly affected by the alloy content and we demonstrate that the sample with the highest Se ratio presents a strongly reduced effect. The highest micro-PL intensity is found for bilayer WS2(1−x)Se2x (x = 0.8) with a decrease of its maximum value by only a factor of 2 when passing from mono-layer to bi-layer. To better understand this factor and explore the layer-dependent band structure evolution of WS2(1−x)Se2x, we performed a nano-angle-resolved photoemission spectroscopy study coupled with first-principles calculations. We find that the high micro-PL value for bilayer WS2(1−x)Se2x (x = 0.8) is due to the overlay of direct and indirect optical transitions. This peculiar high PL intensity in WS2(1−x)Se2x opens the way for spectrally tunable light-emitting devices.

Reabsorption effects on direct band gap emission from germanium light emitting diodes

2014 ◽  
Author(s):  
Yen-Yu Chen ◽  
Chia-Chun Yen ◽  
Yi-Hsin Nien ◽  
Wen-Wei Hsu ◽  
Qing-Qi Chen ◽  
...  
Keyword(s):  
Band Gap ◽  
Light Emitting Diodes ◽  
Light Emitting ◽  
Direct Band Gap ◽  
Direct Band

Room-temperature direct band-gap electroluminescence from germanium (111)-fin light-emitting diodes

2017 ◽  
Vol 56 (3) ◽  
pp. 032102 ◽  
Author(s):  
Kazuki Tani ◽  
Shin-ichi Saito ◽  
Katsuya Oda ◽  
Makoto Miura ◽  
Yuki Wakayama ◽  
...  
Keyword(s):  
Band Gap ◽  
Room Temperature ◽  
Light Emitting Diodes ◽  
Light Emitting ◽  
Direct Band Gap ◽  
Direct Band

scholarly journals Strong Photoluminescence Enhancement from Bilayer Molybdenum Disulfide via the Combination of UV Irradiation and Superacid Molecular Treatment

2021 ◽  
Vol 11 (8) ◽  
pp. 3530
Author(s):  
Yuki Yamada ◽  
Takeshi Yoshimura ◽  
Atsushi Ashida ◽  
Norifumi Fujimura ◽  
Daisuke Kiriya
Keyword(s):  
Band Gap ◽  
Uv Irradiation ◽  
High Performance ◽  
Transition Metal Dichalcogenides ◽  
Direct Band Gap ◽  
Metal Dichalcogenides ◽  
Direct Band ◽  
Pl Intensity ◽  
Optical Applications ◽  
Indirect Band Gap

A direct band gap nature in semiconducting materials makes them useful for optical devices due to the strong absorption of photons and their luminescence properties. Monolayer transition metal dichalcogenides (TMDCs) have received significant attention as direct band gap semiconductors and a platform for optical applications and physics. However, bilayer or thicker layered samples exhibit an indirect band gap. Here, we propose a method that converts the indirect band gap nature of bilayer MoS2, one of the representative TMDCs, to a direct band gap nature and enhances the photoluminescence (PL) intensity of bilayer MoS2 dramatically. The procedure combines UV irradiation with superacid molecular treatment on bilayer MoS2. UV irradiation induces the conversion of the PL property with an indirect band gap to a direct band gap situation in bilayer MoS2 when the interaction between the top and bottom layers is weakened by a sort of misalignment between them. Furthermore, the additional post-superacid treatment dramatically enhances the PL intensity of bilayer MoS2 by a factor of 700×. However, this procedure is not effective for a conventional bilayer sample, which shows no PL enhancement. From these results, the separated top layer would show a strong PL from the superacid treatment. The monolayer-like top layer is physically separated from the substrate by the intermediate bottom MoS2 layer, and this situation would be preferable for achieving a strong PL intensity. This finding will be useful for controlling the optoelectronic properties of thick TMDCs and the demonstration of high-performance optoelectronic devices.

Direct Band-gap Electroluminescence from Strained n-Ge Light Emitting Diodes

2013 ◽  
Vol 50 (9) ◽  
pp. 305-308 ◽  
Author(s):  
P. Velha ◽  
K. F. Gallacher ◽  
D. C. Dumas ◽  
D. J. Paul ◽  
M. Myronov ◽  
...  
Keyword(s):  
Band Gap ◽  
Light Emitting Diodes ◽  
Light Emitting ◽  
Direct Band Gap ◽  
Direct Band

Optical Studies of Poly (N-Carbazole) (PVK) Blending with Polyvinylpyrrolidone (PVP) Using Tauc/Davis-Mott Model

2013 ◽  
Vol 652-654 ◽  
pp. 527-531 ◽  
Author(s):  
A.N. Alias ◽  
T.I. Tunku Kudin ◽  
Z.M. Zabidi ◽  
M.K. Harun ◽  
Ab Malik Marwan Ali ◽  
...  
Keyword(s):  
Band Gap ◽  
Urbach Energy ◽  
Quartz Substrate ◽  
Optical Studies ◽  
Direct Band Gap ◽  
Mott Model ◽  
Blended Polymer ◽  
Electronic Parameters ◽  
Direct Band ◽  
Indirect Band Gap

The optical absorption spectra of blended poly (N-carbazole) (PVK) with polyvinylpyrrolidone (PVP) in various compositions are investigated. A doctor blade technique was used to coat the blended polymer on a quartz substrate. The electronic parameters such as absorption edge (Ee), allowed direct band gap (Ed), allowed indirect band gap (Ei), Urbach edge (Eu) and steepness parameter (γ) were calculated using Tauc/Davis-Mott Model. The results reveal that the Ee, Ed and Ei increase with increasing of PVP ratio. There also have variation changing in Urbach energy and steepness parameter.

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