2019 Fiscal Year Research-status Report
Searching new operation area for QCL by Gain Mapping using NEGF
| Project/Area Number |
18K04251
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
Yun Joosun 国立研究開発法人理化学研究所, 開拓研究本部, 基礎科学特別研究員 (30817359)
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| Co-Investigator(Kenkyū-buntansha) |
平山 秀樹 国立研究開発法人理化学研究所, 開拓研究本部, 主任研究員 (70270593)
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| Project Period (FY) |
2018-04-01 – 2021-03-31
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| Keywords | Dipole scattering / Self-energy / Random electric field / Interface roughness / Roughness-induced charge / Level broadening |
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| Outline of Annual Research Achievements |
We have investigated the influence of dipole scattering and polarization-induced interface-roughness scattering on the electron scattering in GaN/AlGaN QCLs this fiscal year. The self-energy of dipole scattering was designed to be inserted into the NEGF simulator we developed. Then, various investigations about the effect of dipole scattering had been performed. The results showed that the energy-level broadening owing to the dipole scattering was not so significant. According to our results, the dipole scattering will not significantly prevent the intersubband transition in GaN/AlGaN QCLs. As a next step, we performed an analytical study of a random electric field induced by polarization-induced interface roughness of GaN/AlGaN structures. The generated total root-mean-square of the random electric field induced by the disorder of interface was unexpectedly large. For this project's goal, we should find a way to circumvent the large random electric field. Currently, we have been designing the self-energy of the roughness-induced interface roughness scattering. After the design of self-energy is finished, we can establish several design strategies for suppression or circumvention of the high electric field by NEGF calculation considering the roughness-induced interface roughness charge.
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| Current Status of Research Progress |
Current Status of Research Progress
4: Progress in research has been delayed.
Reason
Fundamental study about why the intersubband transition in GaN/AlGaN is difficult has not been clearly solved. Within our best knowledge, all study of GaN/AlGaN QCLs before this project has not been considering the relatively new scattering mechanisms such as dipole scattering and polarization-induced interface roughness scattering. Even the commercial QCL software has not adopted the description of the polarization-related scattering of GaN/AlGaN structures. Therefore, we would like to say that our delay was inevitable since we should conduct fundamental studies about scattering processes before finding practically worthy GaN/AlGaN QCL structures. For two years, we have performed the development of the NEGF simulator based on a supercomputer system, design of dipole scattering self-energy, and analytical calculation of random electric field generated due to the polarization-induced interface roughness.
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| Strategy for Future Research Activity |
The success of this project promises the great possibility of GaN/AlGaN QCLs. We renew our remained research steps as below.
1. Derivation of the self-energy describing polarization-induced interface roughness scattering, which can trigger severe energy-level broadening in GaN/AlGaN superlattice structures.
2. The invention of a concept and a GaN/AlGaN superlattice structure to suppress or circumvent the polarization-induced interface roughness scattering by utilizing the NEGF simulator adopting the newly designed self-energy.
3. Experiments showing the effect of the newly designed structure by step 2 will be performed.
4. When step 3 is successful, we design a GaN/AlGaN QCL structure by adopting the newly established concept. Gain-mapping should be performed for the structure.
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| Causes of Carryover |
The incurring amount was generated due to the delayed research explained before. The transferred budget will be used to purchase the computational resource of RIKEN's newly developed supercomputer system or to perform the epitaxial growth of GaN/AlGaN superlattice structures based on the research plan.
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