Insulators can be defined as those materials where thermal conduction drived by phonons is the main physical process, and any kind of electronic processes can be neglected.
Other researchers use a model elaborated using the framework of bands, which is a useful theoretical model, i.e., the existence of a gap between the conduction and valence bands with a width > 3.0 eV defines an insulator.
For students, insulators can be defined using the interactive PhET simulation "Conductivity" as plastics where an applied voltage or a light shined on them, does not move the electronic degrees of freedom.
More elaborated models where proposed in the 60s by Profs. Mott and Ziman among others.
I am wonder if any physicist that have worked using ab initio calculations can enlighten us about insulators?
Thanks to all readers and researchers willing to participate ad to follow this RG thread.
References:
1. N. F. Mott, Electrons in disordered structures, Advances in Physics, Vol 16(41,49), 1967.
2. J. M. Ziman, Phil. Mag. Vol 6, 1961.
3. PhET Interactive Simulations, University of Colorado Boulder, licensed under CC-BY-4.0 (https://phet.colorado.edu).
4. https://phet.colorado.edu/en/simulations/conductivity
Dear Doctor
Go To
Electrical conduction mechanism in bulk ceramic insulators at high voltages until dielectric breakdown
- April 2015
- Journal of Applied Physics 117(15):154902
- DOI:10.1063/1.4917208
- Claudia Neusel, Hans Jelitto, Gerold A. Schneider
[In order to develop and verify a dielectric breakdown model for bulk insulators thicker than 100 μm, the knowledge of the dominating conduction mechanism at high electric fields, or respectively voltages, is necessary. The dielectric breakdown is the electrical failure of an insulator. In some existing breakdown models, ohmic conduction is assumed as dominating conduction mechanism. For verification, the dominating dc conduction mechanism of bulk insulators at room temperature was investigated by applying high voltages up to 70 kV to the insulator until dielectric breakdown occurs. Four conduction models, namely, ohmic, space charge limited, Schottky, and Poole-Frenkel conduction, were employed to identify the dominating conduction mechanism. Comparing the calculated permittivities from the Schottky and Poole-Frenkel coefficients with experimentally measured permittivity, Schottky and Poole-Frenkel conduction can be excluded as dominating conduction mechanism. Based on the current density voltage characteristics (J-V-curve) and the thickness-dependence of the current density, space charge limited conduction (SCLC) was identified to be the dominating conduction mechanism at high voltages leading to dielectric breakdown. As a consequence, breakdown models based on ohmic conduction are not appropriate to explain the breakdown of the investigated bulk insulators. Furthermore, the electrical failure of the examined bulk insulators can only be described correctly by a breakdown model which includes SCLC as conduction mechanism.]
Quite interesting answer from a physical perspective, Dear Prof. Sundus F Hantoosh
I appreciate it, thank you for taking your time & effort,
Best Regards.
Dear Doctor
Go To
Yin, J., Hwang, D., Siboni, H.Z. et al. Efficiency improvement by using metal–insulator-semiconductor structure in InGaN/GaN micro-light-emitting diodes. Front. Optoelectron. 17, 8 (2024). https://doi.org/10.1007/s12200-024-00111-9
[Abstract
InGaN/GaN micro-light-emitting diodes (micro-LEDs) with a metal–insulator-semiconductor (MIS) structure on the sidewall are proposed to improve efficiency. In this MIS structure, a sidewall electrode is deposited on the insulating layer-coated sidewall of the device mesa between a cathode on the bottom and an anode on the top. Electroluminescence (EL) measurements of fabricated devices with a mesa diameter of 10 μm show that the application of negative biases on the sidewall electrode can increase the device external quantum efficiency (EQE). In contrast, the application of positive biases can decrease the EQE. The band structure analysis reveals that the EQE is impacted because the application of sidewall electric fields manipulates the local surface electron density along the mesa sidewall and thus controls surface Shockley–Read–Hall (SRH) recombination. Two suggested strategies, reducing insulator layer thickness and exploring alternative materials, can be implemented to further improve the EQE of MIS micro-LEDs in future fabrication.
Conclusions
In summary, InGaN/GaN micro-LEDs with MIS structures are proposed to improve efficiency by depositing metal on the sidewall as a sidewall electrode. The measured EQE values of the device with a 10 μm diameter mesa indicate that applying negative or positive biases on the sidewall electrode increase or decrease the EQE, respectively. The underlying mechanisms of micro-LEDs with MIS structures on the sidewall are investigated by analyzing the band structures of MIS structures. Negative (positive) biases on the sidewall electrode can repel (attract) the electrons and thus increase (decrease) the surface SRH recombination on the sidewall, which explains the sidewall bias-dependent efficiency performance of MIS micro-LEDs. The variation in I–V characteristics under different sidewall biases can be attributed to the reduction in carrier mobility due to the applied electric field on the sidewall. The band structure analysis also indicates that high sidewall electric fields can suppress most surface SRH recombination and significantly improve the efficiency. The simulated SRH recombination distribution along the quantum wells region under different sidewall biases further corroborates the theory from band structure analysis. Therefore, a thinner sidewall insulator layer with high-κ dielectric can be adopted to further improve the device performance of InGaN/GaN micro-LEDs with MIS structures.]
Thank you so much for the post in this thread, Dear Prof. Sundus F Hantoosh
Indeed metal insulator transitions has been a superb research topic for quite a long time.
I apologize for the late reply.
Kind Regards.