Quantum Confinement Effect of Thermoelectric Properties

제구철,Chang-Ho Cho 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.1

Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems. Using the quantum confinement effect based on the conduction band model, we theoretically determine the optimal concentration for the best figure-of-merit in n-type Bi2Te3 quantum well structures. The Bi2Te3 system has polycrystalline structures that can be prepared by using powders of hot-pressed alloys. The enhanced figure-of-merit due to the quantum confinement is almost caused by the enhanced Seebeck coefficient and by improved resistivity. It results from competition between the strong intrinsic characteristic and the enhancement of the volume ratio of the concentration in the quantum-confined system. The optimum concentration for the best figure-of-merit in the system amounts to 2.1 × 10^11 cm^-2 at room temperature. Control of the carrier concentration, as well as the quantum confinement effect, is also a very important effect to optimize the figure-of-merit in low-dimensional systems.

N-형 전하밀도를 갖는 저차원의 Bi₂Te₃의 열전특성

제구출 한국물리학회 2008 새물리 Vol.57 No.2

We investigate the quantum-confined thermoelectric properties of Bi$_2$Te$_3$ quantum well structures as a function of temperature. The Seebeck coefficient is strongly improved by quantum confinement effects, and the thermal conductivity is improved by grain effects due to the well size. As a result, the figure of merit is enhanced. In contrast to the single-crystal system, the figure of merit for quantum-well structures increases with increasing temperature, and quantum confinement effects allow for more degrees of freedom for optimizing the figure of merit. \end{abstract} 본 연구에서는 Bi$_2$Te$_3$ 양자우물구조에서 열전성능을 결정하는 Seebeck 계수와 전기전도도들에 대한 양자감금효과와 grain 효과로 작용하는 우물폭 크기에 대한 열전도도를 온도변화에 따라 살펴본다. 고정된 밀도에서 양자감금효과로 인하여 Seebeck 계수는 커지나 전기 전도도는 양자감금 효과에 크게 영향을 받지 않는다. 따라서 저차원 구조의 성능지수 증가는 양자감금효과로 인한 Seebeck 계수와 grain 효과로 인한 열전도도의 개선으로 이루어지며, 단결정과는 다르게 온도가 증가할수록 커지는 현상을 보여 준다.

Enhanced quantum confinement in tensile-strained silicon nanocrystals embedded in silicon nitride

조창희,강장원,박일규,박성주 한국물리학회 2017 Current Applied Physics Vol.17 No.12

Here, we report that the tensile strain in silicon nanocrystals embedded in silicon nitride significantly changes the size-dependent evolution of the conduction and valence energy levels, compared with strain-free silicon nanocrystals. Using capacitance spectroscopy, the quantum-confined energy shifts in the conduction and valence levels were identified as DEC(eV) ¼ 11.7/d2, and DEV(eV)¼『4.5/d2, where d is the mean diameter of the silicon nanocrystals in nanometers. These findings indicated that the tensile strain in the silicon nanocrystals significantly increased the quantum confinement, by a factor of 3.3 in the conduction levels, and by a factor of 1.8 in the valence levels.

Interband Transition and Confinement of Charge Carriers in CdS and CdS/CdSe Quantum Dots

Minh Tan Man,Hong Seok Lee 한국진공학회 2015 Applied Science and Convergence Technology Vol.24 No.5

Quantum-confined nanostructures open up additional perspectives in engineering materials with different electronic and optical properties. We have fabricated unique cation-exchanged CdS and CdS/CdSe quantum dots and measured their first four exciton transitions. We demonstrate that the relationship between electronic transitions and charge-carrier distributions is generalized for a broad range of core-shell nanostructures. These nanostructures can be used to further improve the performance in the fields of bio-imaging, light-emitting devices, photovoltaics, and quantum computing.

Enhanced quantum confinement in tensile-strained silicon nanocrystals embedded in silicon nitride

Cho, C.H.,Kang, J.W.,Park, I.K.,Park, S.J. Elsevier 2017 CURRENT APPLIED PHYSICS Vol.17 No.12

<P>Here, we report that the tensile strain in silicon nanocrystals embedded in silicon nitride significantly changes the size-dependent evolution of the conduction and valence energy levels, compared with strain-free silicon nanocrystals. Using capacitance spectroscopy, the quantum-confined energy shifts in the conduction and valence levels were identified as Delta E-C(eV) = 11.7/d(2), and Delta E-V(eV) = -4.5/d(2), where d is the mean diameter of the silicon nanocrystals in nanometers. These findings indicated that the tensile strain in the silicon nanocrystals significantly increased the quantum confinement, by a factor of 3.3 in the conduction levels, and by a factor of 1.8 in the valence levels. (C) 2017 Elsevier B.V. All rights reserved.</P>

Interband Transition and Confinement of Charge Carriers in CdS and CdS/CdSe Quantum Dots

Man, Minh Tan,Lee, Hong Seok The Korean Vacuum Society 2015 Applied Science and Convergence Technology Vol.24 No.5

Quantum-confined nanostructures open up additional perspectives in engineering materials with different electronic and optical properties. We have fabricated unique cation-exchanged CdS and CdS/CdSe quantum dots and measured their first four exciton transitions. We demonstrate that the relationship between electronic transitions and charge-carrier distributions is generalized for a broad range of core-shell nanostructures. These nanostructures can be used to further improve the performance in the fields of bio-imaging, light-emitting devices, photovoltaics, and quantum computing.

Influence of ZnTe separation layer thickness on optical properties in CdTe/ZnTe double quantum dots on Si substrates

Lim, Kee Hong,Man, Minh Tan,Le, Anh Thi,Choi, Jin Chul,Lee, Hong Seok Elsevier 2020 THIN SOLID FILMS - Vol.699 No.-

<P><B>Abstract</B></P> <P>We investigate the influence of the ZnTe separation layer thickness on the photoluminescence (PL) dynamics of CdTe/ZnTe double quantum dots (DQDs) on Si substrates. The results clarify that the DQD's structure effectively improves the limit of the carrier collection and the thermal stability of the corresponding single-layer QDs. The unusual temperature-dependent PL is explained using the single model for thermal redistribution of carrier states. This model indicates that the main nonradiative process at high temperatures is caused by scattering via multiphonons with longitudinal optical phonon energy of about 19–21.3 meV. The confinement-induced mixing and electron-carrier coupling effects cause blue-shift and enhanced PL intensity. We propose that the separation layer controls carrier dynamics in optoelectronic devices by modulating the thermal escape and e-h pairs in the intermixing layers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Influence of ZnTe separation layer thickness in double quantum dots were investigated. </LI> <LI> Photoluminescence dynamic probed the electric field screening effects. </LI> <LI> Separation layer thickness plays a key role in the intermixing and thermal escape effects. </LI> <LI> Carrier dynamics of double quantum dots are evaluated by different models. </LI> <LI> Thermal escape is assisted by multiple phonons with energy of 19.1–21.3 meV. </LI> </UL> </P>

Review of Low-Dimensional Nanomaterials for Blue-Light Emission

최원국 한국센서학회 2023 센서학회지 Vol.32 No.6

Low-dimensional (zero-dimensional (0-dim), 2-dimensional (2-dim)) nanoparticles, such as chalcogenide compound semiconductors,III-V semiconductors, transition metal dichalcogenides (TMDs), II-VI semiconductors, nanocarbons, hybrid quantum dots (QDs), andperovskite QDs (PQDs), for which blue light emission has been observed, are reviewed. Current synthesis and device fabrication technologiesas well as their prospective applications on next-generation quantum-dot-based light-emitting diodes are discussed.

The Impact of Carrier Transport Confinement on the Energy Transfer Between InGaN/GaN Quantum‐Well Nanorods and Colloidal Nanocrystals

Jiang, Bin,Zhang, Chunfeng,Wang, Xiaoyong,Park, Min Joo,Kwak, Joon Seop,Xu, Jian,Zhang, Huichao,Zhang, Jiayu,Xue, Fei,Xiao, Min WILEY‐VCH Verlag 2012 Advanced Functional Materials Vol.22 No.15

<P><B>Abstract</B></P><P>The energy transfer (ET) between InGaN/GaN multiple‐quantum‐well (MQW) nanorods (NRs) and semiconductor nanocrystals (NCs) for efficient color conversion is studied. An exceptional contribution of carrier transport confinement to the ET mechanisms is observed in the proximal side‐wall coupling system, which consists of InGaN/GaN NRs and CdSe NCs. Under relatively low or high excitation, the ET rate shows different carrier‐density dependence, resulting from different electron‐hole configurations, i.e., bound excitons and free carriers. In the localized exciton regime, the ET rate decreases when increasing temperature from 20 K to 200 K. However, in the free‐carrier regime, the ET rate varies insignificantly in the same temperature range. The temperature dependence in this NR‐NC coupling system is different from that in the previously studied planar MQW‐NC coupling system. It is suggested that the carrier transport confinement in NRs is a major factor for these divergences. The highly efficient ET with efficiency up to 80% shows a promising potential of using such NR‐NC coupled structures for ET‐pumped, NC‐based, light‐emitting devices.</P>

Synthesis of homogeneous and bright deep blue CsPbBr 3 perovskite nanoplatelets with solidified surface for optoelectronic material

Kim Taeyun,Suh Yo‐Han,Kim Kangyong,Kim Hyeonjung,Park Jongnam 대한화학회 2022 Bulletin of the Korean Chemical Society Vol.43 No.8

Halide perovskite nanocrystals have easily tunable emissions throughout the visible spectrum, making them an extremely promising material for lightemitting applications. Whereas high quantum yield and long-term colloidal stability have already been achieved for nanocrystals emitting in the red and green spectral range, the blue region currently lags behind with low quantum yields and insufficient colloidal stability. In this study, we present a facile synthetic and postsynthetic approach for obtaining two-dimensional CsPbBr3 nanoplatelets (NPLs) with homogeneous-thickness control of their solidified surface, resulting in sharp photoluminescence and electroluminescence peaks with a deep-blue emission at 465-nm wavelength owing to quantum confinement. The subsequent addition of a solidifying ligand solution seals the surface defects likely stemming from vacancies within a subensemble of weakly emissive NPLs. The overall photoluminescence quantum yield of the blue-emissive colloidal dispersions is consequently enhanced by 65% 2%.