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@@ -1,6 +1,8 @@
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#import "@preview/physica:0.9.5": pdv, super-T-as-transpose
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#show: super-T-as-transpose
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= Appendix
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#include "predmode.typ"
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The center principle is to assign the Raman tensor (i.e., change of polarizability caused by atomic displacement)
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@@ -1,8 +1,11 @@
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= Introduction
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4H-SiC 性能很好、器件应用广泛,因此需要开发原位的、非破坏性的表征技术。
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4H-SiC 是一种具有优良性质的半导体材料,包括宽禁带、高临界电场强度、高热导率和沿 c 轴的高电子迁移率,因此受到了广泛的研究。
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受益于外延技术的发展和新能源产业的需求增长,4H-SiC 在功率电子器件中得到了广泛应用。
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然而,4H-SiC 器件的性能仍然受到缺陷的限制,如何在生长和工作条件下避免缺陷的产生仍然是一个挑战。
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此外,用于表征 SiC 掺杂的方案(如二次离子质谱(SIMS)和霍尔效应测量)通常是破坏性的且耗时,因此迫切需要开发原位和非破坏性的表征技术。
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// 随着尺寸缩小,4H-SiC 中的缺陷对器件性能的影响更加显著。(纳米材料?
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The 4H-silicon carbide (SiC) has long attracted a lot of research
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@@ -25,6 +28,8 @@ Furthermore,
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are destructive and time-consuming.
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Therefore, there is a pressing need to develop an in-situ and non-destructive characterization techniques.
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拉曼主要体现声子的信息,并且早已经有应用,主要用来区分 SiC 的多型。
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声子(量子化的原子振动)在理解晶体的原子结构以及热电性质方面起着重要作用。
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声子可以通过多种实验技术来探测,包括 EELS、IR 吸收谱等。
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拉曼光谱是最常用的方法,它提供了一种无损、非接触、快速和局部的声子测量方法。
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@@ -44,6 +49,8 @@ Studies in Raman scattering of 4H-SiC have been conducted since as early as 1968
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and nowadays have been widely employed to identification of different SiC polytypes
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@guo_characterization_2012 @yan_study_2016 @hundhausen_characterization_2008 @nakashima_raman_2013.
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拉曼谱中有更多信息。有一些新的研究,但他们还有不足。
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近年来,更多信息被从拉曼光谱中挖掘出来。
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LO 声子峰或 LOPC 峰已经被证明与自由载流子的类型和浓度有关,它们已经被用于估计离子注入层的厚度和 n 型 SiC 的掺杂浓度。
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部分层错的拉曼光谱也已经被研究,可以被用于检测特定结构层错的存在和位置。
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@@ -57,7 +64,6 @@ Longitudinal optical phonon–plasmon coupling (LOPC) peek
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// depth profiling xxx
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and the doping concentration in n-type SiC.
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// Raman scattering from anisotropic LO-phonon-plasmo
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Peeks associated with some stacking faults have also been investigated
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and used to detect the presence and location of specific structural faults.
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// TODO: 缺陷峰,并补充对应的文献
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@@ -71,6 +77,8 @@ In addition, relation between defects and Raman peek is still not very clear,
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potential raman peeks caused by defects and doping still need to be explored.
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// TODO: 调整语言,细化描述
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本文通过三种方式,研究 4H-SiC 中带缺陷和不带缺陷的声子。我们第一次做到了什么什么。
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In this paper, we explored the phonon in 4H-SiC by three ways:
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symmetry analysis, first-principles calculations, and Raman experiment.
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We first investigated the phonon modes in perfect 4H-SiC,
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@@ -45,50 +45,10 @@
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// 标题序号
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#set heading(numbering: "1.")
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= Introduction
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#include "section/introduction.typ"
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= Method
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#include "section/method.typ"
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= Results and Discussion
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// - 无缺陷:
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// 我们将声子分为两类,一类是极性比较弱的(18个),一类是比较强的(3个)。
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// - 弱极性的声子:
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// - TODO: 确认一下最后一次实验中,峰偏移等是否与掺杂有明显关系,以及这个关系与之前是否相同。
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// - 强极性的声子:
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// - 强极性声子在 Gamma 附近散射谱不连续,它的声子模式由入射光的方向决定。在入射光不沿 z 轴的情况下,使用 C6v 群不再适用。
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// - TODO: 写文字
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// - 在接近 y 轴入射时,可以看到分裂。这个模式可能对表面敏感。
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// - TODO: 佐证它对表面敏感
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// - 对于 LO,可能形成 LOPC
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// - 有缺陷的情况:
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// - TODO: 描述缺陷原子的振动
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// - TODO: 计算拉曼张量,描述光谱的可能变化
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== Phonons in Perfect 4H-SiC
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#include "section/perfect/default.typ"
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=== Phonons with Negligible Polarities
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#include "section/perfect/non-polar/default.typ"
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=== Strong-polar Phonons
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#include "section/perfect/polar/default.typ"
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= Appendix
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#include "section/appendix/default.typ"
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#include "掺杂晶格变化.typ"
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#include "晶格变化导致的频率变化.typ"
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// TODO: 这句话放哪里?
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// whose dispersion curves exhibit discontinuity near the #sym.Gamma point (also shown in @phonon),
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#include "introduction.typ"
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#include "method.typ"
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#include "result/default.typ"
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#include "appendix/default.typ"
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#include "others/default.typ"
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#bibliography("./ref.bib", title: "Reference", style: "american-physics-society")
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21
test-typst/method.typ
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21
test-typst/method.typ
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= Method
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== Experiment details
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外延片的厚度、掺杂浓度、生长 C/Si 比。
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拉曼设备的型号。激光的波长,背散射。共焦针孔。对焦时向上或向下调整的距离。
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画个图,表示正入射、掠入射和肩入射的角度关系。
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Only back-scattering configurations were considered in this study.
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== Simulation details
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无缺陷的模型大小。带缺陷的情况下,模型大小,每个模型的代号和缺陷结构。
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第一性原理计算使用 VASP,使用 PBE PAW,平面波截断能,K 点网格,涂抹,自洽和弛豫的 threshold。
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声子计算使用 phonopy phono3py ufo,BEC 修正的算法。
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// 在略入射的过程中,角度的关系不大(即使是 60 度入射,和 90 度入射差别也不大)。因此我们按照折射角 20 度的结果计算。
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// 考虑到斜切,则大约是 24 度。
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4
test-typst/others/default.typ
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4
test-typst/others/default.typ
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= others
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#include "掺杂晶格变化.typ"
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#include "晶格变化导致的频率变化.typ"
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21
test-typst/result/default.typ
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21
test-typst/result/default.typ
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= Results and Discussion
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我们先讨论无缺陷的情况,再讨论有缺陷的情况。
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无缺陷的情况可以解释绝大多数拉曼峰,其它情况从拉曼中的小峰和峰的改变中看出。
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// - 无缺陷:
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// 我们将声子分为两类,一类是极性比较弱的(18个),一类是比较强的(3个)。
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// - 弱极性的声子:
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// - TODO: 确认一下最后一次实验中,峰偏移等是否与掺杂有明显关系,以及这个关系与之前是否相同。
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// - 强极性的声子:
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// - 强极性声子在 Gamma 附近散射谱不连续,它的声子模式由入射光的方向决定。在入射光不沿 z 轴的情况下,使用 C6v 群不再适用。
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// - TODO: 写文字
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// - 在接近 y 轴入射时,可以看到分裂。这个模式可能对表面敏感。
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// - TODO: 佐证它对表面敏感
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// - 对于 LO,可能形成 LOPC
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// - 有缺陷的情况:
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// - TODO: 描述缺陷原子的振动
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// - TODO: 计算拉曼张量,描述光谱的可能变化
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#include "perfect/default.typ"
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#include "defect/default.typ"
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4
test-typst/result/defect/default.typ
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4
test-typst/result/defect/default.typ
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== Phonons with impurities and charge carriers
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@@ -1,3 +1,7 @@
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== Phonons in Perfect 4H-SiC
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总共有 21 个声子模式。我们把它分成 18 个极性很小的和 3 个极性很强的两类。
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// There are 21 phonons in total.
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// We classified them into two categories: 18 negligible-polar phonons and 3 strong-polar phonons.
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The phonons involved in Raman scattering are located in reciprocal space around the #sym.Gamma point,
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@@ -9,6 +13,8 @@ The 18 of 21 phonons are classified into negligible-polar phonons (i.e., phonons
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and the other three phonons are strong-polar phonons,
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where the polarity gives rise to observable effects in the Raman spectra.
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这个分类是有意义的。从微观上讲,它也和原子的振动方向有关。
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// This classification make sense.
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This classification is based on the fact that
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the four Si atoms in the primitive cell of 4H-SiC carry similar positive Born effective charges (BECs),
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@@ -22,3 +28,6 @@ In contrast, in the three strong-polar phonons,
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resulting in a strong dipole moment.
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#include "table-bec.typ"
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#include "non-polar/default.typ"
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#include "polar/default.typ"
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@@ -1,3 +1,7 @@
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=== Phonons with Negligible Polarities
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我们用 gamma 点的声子来近似弱极性的声子。
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// We investigate phonons at Gamma instead of the exact location near Gamma.
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Phonons at the #sym.Gamma point were used
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to approximate negligible-polar phonons that participating in Raman processes
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@@ -14,6 +18,8 @@ Therefore, negligible-polar phonons involved in Raman processes
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#include "figure-discont.typ"
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gamma 点处 18 个声子的表示。它们的拉曼张量的形状可以确定,但大小无法确定。
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// Representation of these 18 phonons, and the shape of their Raman tensors could be determined in advance.)
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Phonons at the #sym.Gamma point satisfy the C#sub[6v] point group symmetry,
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and the 18 negligible-polar phonons correspond to 12 irreducible representations of the C#sub[6v] point group:
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@@ -35,7 +41,7 @@ However, whether a mode is sufficiently strong to be experimentally visible
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// without first-principle calculations.
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// Here we only write out results, details are in appendix.
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// TODO: maybe it is better to assign Raman tensor to each bond, instead of atom
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我们提出了一个新的办法来估计拉曼张量大小。
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We propose a method to estimate the magnitudes of the Raman tensors of these phonons based on symmetry analysis.
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This approach is founded on the assumption that the change in polarizability induced by atomic displacements in 4H-SiC
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@@ -48,6 +54,8 @@ The parameters $a_i$ exhibit significantly larger absolute values compared to $e
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indicating the E#sub[2] mode at 756.25 cm#super[-1] in simulation (mode 8)
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possess a much higher Raman intensity than the others.
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我们使用第一性原理计算得到了拉曼张量的大小,并与我们的结果进行了比较。
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The Raman tensors and frequencies of the negligible-polar phonons were calculated using first-principles methods,
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and the results are compared with both experimental data and theoretical predictions (@table-nopol).
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The calculated phonon frequencies show good agreement with experimental data with a slight underestimation of 2-5%,
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@@ -73,6 +81,8 @@ However, it should become detectable if the incident light has a polarization co
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(as in our experiment),
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or when the excitation wavelength approaches resonance conditions (cite).
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其它峰在其它章节中解释。
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Besides, there are other peeks in the experiment.
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The peek at 796 and 980 are caused by strong-polar phonons which will be discussed later.
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Besides, there are small peeks at xxx,
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@@ -1,3 +1,6 @@
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=== Strong-polar Phonons
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沿着不同方向入射的话,强声子的模式是不同的。
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// 在半导体的极性声子模式中,原子间存在长距离的库伦相互作用,导致散射谱在 Gamma 附近不再连续(引用),如图中的彩色线所示。
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// 这导致不同方向的入射/散射光的声子模式不同。
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@@ -25,6 +28,8 @@ For example, when the light is incident along the y direction (phonon modes on t
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When the light is incident along a direction between z and y,
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three phonon modes will exist, but vibration in the mixed direction.
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实验发现的确是这样的。
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Many Raman experiments on 4H-SiC with incident light along the z direction have observed two peaks.
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However, no experiments have reported three peaks with incident light along other directions.
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In our experiment, we found the third, and it satisfied properties we expected.
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@@ -1,4 +0,0 @@
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Only back-scattering configurations were considered in this study.
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// 在略入射的过程中,角度的关系不大(即使是 60 度入射,和 90 度入射差别也不大)。因此我们按照折射角 20 度的结果计算。
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// 考虑到斜切,则大约是 24 度。
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