Research on two-dimensional (2D) materials and related van der Waals heterostructures (vdWHs) is intense and remains one of the leading topics in condensed matter physics. Lattice vibrations or phonons of a vdWH provide rich information, such as lattice structure, phonon dispersion, electronic band structure and electron–phonon coupling. Here, we provide a mini review on the lattice vibrations in vdWHs probed by Raman spectroscopy. First, we introduced different kinds of vdWHs, including their structures, properties and potential applications. Second, we discussed interlayer and intralayer phonon in twist multilayer graphene and MoS2. The frequencies of interlayer and intralayer modes can be reproduced by linear chain model (LCM) and phonon folding induced by periodical moiré potentials, respectively. Then, we extended LCM to vdWHs formed by distinct 2D materials, such as MoS2/graphene and hBN/WS2 heterostructures. We further demonstrated how to calculate Raman intensity of interlayer modes in vdWHs by interlayer polarizability model.
J. Semicond. 2019, 40 (9): 091001
doi: 10.1088/1674-4926/40/9/091001Xin Cong, Miaoling Lin, Ping-Heng Tan. Lattice vibration and Raman scattering of two-dimensional van der Waals heterostructure[J]. 合乐彩票, 2019, 40(9): 091001. doi: 10.1088/1674-4926/40/9/091001.
X Cong, M L Lin, P H Tan, Lattice vibration and Raman scattering of two-dimensional van der Waals heterostructure[J]. J. Semicond., 2019, 40(9): 091001. doi: 10.1088/1674-4926/40/9/091001.Export: BibTex EndNote
J. Semicond. 2019, 40 (9): 091002
doi: 10.1088/1674-4926/40/9/091002Weisheng Li, Hongkai Ning, Zhihao Yu, Yi Shi, Xinran Wang. Reducing the power consumption of two-dimensional logic transistors[J]. 合乐彩票, 2019, 40(9): 091002. doi: 10.1088/1674-4926/40/9/091002.
W S Li, H K Ning, Z H Yu, Y Shi, X R Wang, Reducing the power consumption of two-dimensional logic transistors[J]. J. Semicond., 2019, 40(9): 091002. doi: 10.1088/1674-4926/40/9/091002.Export: BibTex EndNote
The growing demand for high-performance logic transistors has driven the exponential rise in chip integration, while the transistors have been rapidly scaling down to sub-10 nm. The increasing leakage current and subthreshold slope (SS) induced by short channel effect (SCE) result in extra heat dissipation during device operation. The performance of electronic devices based on two-dimensional (2D) semiconductors such as the transition metal dichalcogenides (TMDC) can significantly reduce power consumption, benefiting from atomically thin thickness. Here, we discuss the progress of dielectric integration of 2D metal–oxide–semiconductor field effect transistors (MOSFETs) and 2D negative capacitance field effect transistors (NCFETs), outlining their potential in low-power applications as a technological option beyond scaled logic switches. Above all, we show our perspective at 2D low-power logic transistors, including the ultra-thin equivalent oxide thickness (EOT), reducing density of interface trap, reliability, operation speed etc. of 2D MOSFETs and NCFETs.
Some recent advances in ab initio calculations of nonradiative decay rates of point defects in semiconductors
J. Semicond. 2019, 40 (9): 091101
doi: 10.1088/1674-4926/40/9/091101Linwang Wang. Some recent advances in ab initio calculations of nonradiative decay rates of point defects in semiconductors[J]. 合乐彩票, 2019, 40(9): 091101. doi: 10.1088/1674-4926/40/9/091101.
L W Wang, Some recent advances in ab initio calculations of nonradiative decay rates of point defects in semiconductors[J]. J. Semicond., 2019, 40(9): 091101. doi: 10.1088/1674-4926/40/9/091101.Export: BibTex EndNote
In this short review, we discuss a few recent advances in calculating the nonradiative decay rates for point defects in semiconductors. We briefly review the debates and connections of using different formalisms to calculate the multi-phonon processes. We connect Dr. Huang’s formula with Marcus theory formula in the high temperature limit, and point out that Huang’s formula provide an analytical expression for the phonon induced electron coupling constant in the Marcus theory formula. We also discussed the validity of 1D formula in dealing with the electron transition processes, and practical ways to correct the anharmonic effects.
J. Semicond. 2019, 40 (9): 091102
doi: 10.1088/1674-4926/40/9/091102Yong Zhang. Applications of Huang–Rhys theory in semiconductor optical spectroscopy[J]. 合乐彩票, 2019, 40(9): 091102. doi: 10.1088/1674-4926/40/9/091102.
Y Zhang, Applications of Huang–Rhys theory in semiconductor optical spectroscopy[J]. J. Semicond., 2019, 40(9): 091102. doi: 10.1088/1674-4926/40/9/091102.Export: BibTex EndNote
A brief review of Huang–Rhys theory and Albrechtos theory is provided, and their connection and applications are discussed. The former is a first order perturbative theory on optical transitions intended for applications such as absorption and emission involving localized defect or impurity centers, emphasizing lattice relaxation or mixing of vibrational states due to electron–phonon coupling. The coupling strength is described by the Huang–Rhys factor. The latter theory is a second order perturbative theory on optical transitions intended for Raman scattering, and can in-principle include electron–phonon coupling in both electronic states and vibrational states. These two theories can potentially be connected through the common effect of lattice relaxation – non-orthonormal vibrational states associated with different electronic states. Because of this perceived connection, the latter theory is often used to explain resonant Raman scattering of LO phonons in bulk semiconductors and further used to describe the size dependence of electron–phonon coupling or Huang–Rhys factor in semiconductor nanostructures. Specifically, the A term in Albrechtos theory is often invoked to describe the multi-LO-phonon resonant Raman peaks in both bulk and nanostructured semiconductors in the literature, due to the misconception that a free-exciton could have a strong lattice relaxation. Without lattice relaxation, the A term will give rise to Rayleigh or elastic scattering. Lattice relaxation is only significant for highly localized defect or impurity states, and should be practically zero for either single particle states or free exciton states in a bulk semiconductor or for confined states in a semiconductor nanostructure that is not extremely small.
J. Semicond. 2019, 40 (8): 081501
doi: 10.1088/1674-4926/40/8/081501Qiang Cao, Shishen Yan. The predicaments and expectations in development of magnetic semiconductors[J]. 合乐彩票, 2019, 40(8): 081501. doi: 10.1088/1674-4926/40/8/081501.
Q Cao, S S Yan, The predicaments and expectations in development of magnetic semiconductors[J]. J. Semicond., 2019, 40(8): 081501. doi: 10.1088/1674-4926/40/8/081501.Export: BibTex EndNote
Over the past half a century, considerable research activities have been directing towards the development of magnetic semiconductors that can work at room temperature. These efforts were aimed at seeking room temperature magnetic semiconductors with strong and controllable s, p-d exchange interaction. With this s, p-d exchange interaction, one can utilize the spin degree of freedom to design applicable spintronics devices with very attractive functions that are not available in conventional semiconductors. Here, we first review the progress in understanding of this particular material and the dilemma to prepare a room temperature magnetic semiconductor. Then we discuss recent experimental progresses to pursue strong s, p-d interaction to realize room temperature magnetic semiconductors, which are achieved by introducing a very high concentration of magnetic atoms by means of low-temperature nonequilibrium growth.
J. Semicond. 2019, 40 (8): 081502
doi: 10.1088/1674-4926/40/8/081502Lin Chen, Jianhua Zhao, Dieter Weiss, Christian H. Back, Fumihiro Matsukura, Hideo Ohno. Magnetization dynamics and related phenomena in semiconductors with ferromagnetism[J]. 合乐彩票, 2019, 40(8): 081502. doi: 10.1088/1674-4926/40/8/081502.
L Chen, J H Zhao, D Weiss, C H Back, F Matsukura, H Ohno, Magnetization dynamics and related phenomena in semiconductors with ferromagnetism[J]. J. Semicond., 2019, 40(8): 081502. doi: 10.1088/1674-4926/40/8/081502.Export: BibTex EndNote
We review ferromagnetic resonance (FMR) and related phenomena in the ferromagnetic semiconductor (Ga,Mn)As and single crystalline Fe/GaAs (001) hybrid structures. In both systems, spin-orbit interaction is the key ingredient for various intriguing phenomena.
J. Semicond. 2019, 40 (8): 081503
doi: 10.1088/1674-4926/40/8/081503Sanghoon Lee, Sunjae Chung, Hakjoon Lee, Xinyu Liu, M. Dobrowolska, J. K. Furdyna. Interlayer exchange coupling in (Ga,Mn)As ferromagnetic semiconductor multilayer systems[J]. 合乐彩票, 2019, 40(8): 081503. doi: 10.1088/1674-4926/40/8/081503.
S Lee, S Chung, H Lee, X Y Liu, M Dobrowolska, J K Furdyna, Interlayer exchange coupling in (Ga,Mn)As ferromagnetic semiconductor multilayer systems[J]. J. Semicond., 2019, 40(8): 081503. doi: 10.1088/1674-4926/40/8/081503.Export: BibTex EndNote
This paper describes interlayer exchange coupling (IEC) phenomena in ferromagnetic multilayer structures, focusing on the unique IEC features observed in ferromagnetic semiconductor (Ga,Mn)As-based systems. The dependence of IEC on the structural parameters, such as non-magnetic spacer thickness, number of magnetic layers, and carrier density in the systems has been investigated by using magnetotransport measurements. The samples in the series show both a typical anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR)-like effects indicating realization of both ferromagnetic (FM) and antiferromagnetic (AFM) IEC in (Ga,Mn)As-based multilayer structures. The results revealed that the presence of carriers in the non-magnetic spacer is an important factor to realize AFM IEC in this system. The studies further reveal that the IEC occurs over a much longer distance than predicted by current theories, strongly suggesting that the IEC in (Ga,Mn)As-based multilayers is a long-range interaction. Due to the long-range nature of IEC in the (Ga,Mn)As-based systems, the next nearest neighbor (NNN) IEC cannot be ignored and results in multi-step transitions during magnetization reversal that correspond to diverse spin configurations in the system. The strength of NNN IEC was experimentally determined by measuring minor loops that correspond to magnetization flips in specific (Ga,Mn)As layer in the multilayer system.
J. Semicond. 2019, 40 (8): 081504
doi: 10.1088/1674-4926/40/8/081504Bo Gu. High temperature magnetic semiconductors: narrow band gaps and two-dimensional systems[J]. 合乐彩票, 2019, 40(8): 081504. doi: 10.1088/1674-4926/40/8/081504.
B Gu, High temperature magnetic semiconductors: narrow band gaps and two-dimensional systems[J]. J. Semicond., 2019, 40(8): 081504. doi: 10.1088/1674-4926/40/8/081504.Export: BibTex EndNote
Magnetic semiconductors have been demonstrated to work at low temperatures, but not yet at room temperature for spin electronic applications. In contrast to the p-type diluted magnetic semiconductors, n-type diluted magnetic semiconductors are few. Using a combined method of the density function theory and quantum Monte Carlo simulation, we briefly discuss the recent progress to obtain diluted magnetic semiconductors with both p- and n-type carriers by choosing host semiconductors with a narrow band gap. In addition, the recent progress on two-dimensional intrinsic magnetic semiconductors with possible room temperature ferromangetism and quantum anomalous Hall effect are also discussed.
J. Semicond. 2019, 40 (8): 081505
doi: 10.1088/1674-4926/40/8/081505Guoqiang Zhao, Zheng Deng, Changqing Jin. Advances in new generation diluted magnetic semiconductors with independent spin and charge doping[J]. 合乐彩票, 2019, 40(8): 081505. doi: 10.1088/1674-4926/40/8/081505.
G Q Zhao, Z Deng, C Q Jin, Advances in new generation diluted magnetic semiconductors with independent spin and charge doping[J]. J. Semicond., 2019, 40(8): 081505. doi: 10.1088/1674-4926/40/8/081505.Export: BibTex EndNote
As one branch of spintronics, diluted magnetic semiconductors (DMSs) are extensively investigated due to their fundamental significance and potential application in modern information society. The classical materials (Ga,Mn)As of III–V group based DMSs has been well studied for its high compatibility with the high-mobility semiconductor GaAs. But the Curie temperature in (Ga,Mn)As film is still far below room temperature because the spin & charge doping is bundled to the same element that makes the fabrication very difficult. Alternatively, the discovery of a new generation DMSs with independent spin and charge doping, such as (Ba,K)(Zn,Mn)2As2 (briefly named BZA), attracted considerable attention due to their unique advantages in physical properties and heterojunction fabrication. In this review we focus on this series of new DMSs including (I) materials in terms of three types of new DMSs, i.e. the " 111”, " 122” and " 1111” system; (II) the physical properties of BZA; (III) single crystals & prototype device based on BZA. The prospective of new type of DMSs with independent spin and charge doping is briefly discussed.
J. Semicond. 2019, 40 (8): 081506
doi: 10.1088/1674-4926/40/8/081506Yilun Gu, Shengli Guo, Fanlong Ning. Progress on microscopic properties of diluted magnetic semiconductors by NMR and μSR[J]. 合乐彩票, 2019, 40(8): 081506. doi: 10.1088/1674-4926/40/8/081506.
Y L Gu, S L Guo, F L Ning, Progress on microscopic properties of diluted magnetic semiconductors by NMR and μSR[J]. J. Semicond., 2019, 40(8): 081506. doi: 10.1088/1674-4926/40/8/081506.Export: BibTex EndNote
Diluted magnetic semiconductors (DMSs) that possess both properties of semiconductors and ferromagnetism, have attracted a lot of attentions due to its potential applications for spin-sensitive electronic devices. Recently, a series of bulk form DMSs isostructural to iron-based superconductors have been reported, which can be readily investigated by microscopic experimental techniques such as nuclear magnetic resonance (NMR) and muon spin rotation (μSR). The measurements have demonstrated that homogeneous ferromagnetism is achieved in these DMSs. In this review article, we summarize experimental evidences from both NMR and μSR measurements. NMR results have shown that carriers facilitate the interactions between distant Mn atoms, while μSR results indicate that these bulk form DMSs and (Ga,Mn)As share a common mechanism for the ferromagnetic exchange interactions.
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