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20 changed files with 92 additions and 52 deletions

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#import "@preview/physica:0.9.5": pdv, super-T-as-transpose
#show: super-T-as-transpose
= Appendix
#include "predmode.typ"
The center principle is to assign the Raman tensor (i.e., change of polarizability caused by atomic displacement)

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= Introduction
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。
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。
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。
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。
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。
// 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?
The 4H-silicon carbide (SiC) has long attracted a lot of research
@@ -25,6 +28,8 @@ Furthermore,
are destructive and time-consuming.
Therefore, there is a pressing need to develop an in-situ and non-destructive characterization techniques.
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。
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。
声子可以通过多种实验技术来探测,包括 EELS、IR 吸收谱等。
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。
@@ -44,6 +49,8 @@ Studies in Raman scattering of 4H-SiC have been conducted since as early as 1968
and nowadays have been widely employed to identification of different SiC polytypes
@guo_characterization_2012 @yan_study_2016 @hundhausen_characterization_2008 @nakashima_raman_2013.
拉曼谱中有更多信息。有一些新的研究,但他们还有不足。
近年来,更多信息被从拉曼光谱中挖掘出来。
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 SiC 的掺杂浓度。
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。
@@ -57,7 +64,6 @@ Longitudinal optical phononplasmon coupling (LOPC) peek
// depth profiling xxx
and the doping concentration in n-type SiC.
// Raman scattering from anisotropic LO-phonon-plasmo
Peeks associated with some stacking faults have also been investigated
and used to detect the presence and location of specific structural faults.
// TODO: 缺陷峰,并补充对应的文献
@@ -71,6 +77,8 @@ In addition, relation between defects and Raman peek is still not very clear,
potential raman peeks caused by defects and doping still need to be explored.
// TODO: 调整语言,细化描述
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。
In this paper, we explored the phonon in 4H-SiC by three ways:
symmetry analysis, first-principles calculations, and Raman experiment.
We first investigated the phonon modes in perfect 4H-SiC,

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// 标题序号
#set heading(numbering: "1.")
= Introduction
#include "section/introduction.typ"
= Method
#include "section/method.typ"
= Results and Discussion
// - 无缺陷:
// 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
// - 弱极性的声子:
// - 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。
// - 强极性的声子:
// - 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。
// - TODO: 写文字
// - 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。
// - TODO: 佐证它对表面敏感
// - 对于 LO可能形成 LOPC
// - 有缺陷的情况:
// - TODO: 描述缺陷原子的振动
// - TODO: 计算拉曼张量,描述光谱的可能变化
== Phonons in Perfect 4H-SiC
#include "section/perfect/default.typ"
=== Phonons with Negligible Polarities
#include "section/perfect/non-polar/default.typ"
=== Strong-polar Phonons
#include "section/perfect/polar/default.typ"
= Appendix
#include "section/appendix/default.typ"
#include "掺杂晶格变化.typ"
#include "晶格变化导致的频率变化.typ"
// TODO: 这句话放哪里?
// whose dispersion curves exhibit discontinuity near the #sym.Gamma point (also shown in @phonon),
#include "introduction.typ"
#include "method.typ"
#include "result/default.typ"
#include "appendix/default.typ"
#include "others/default.typ"
#bibliography("./ref.bib", title: "Reference", style: "american-physics-society")

21
test-typst/method.typ Normal file
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= Method
== Experiment details
外延片的厚度、掺杂浓度、生长 C/Si 比。
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。
画个图,表示正入射、掠入射和肩入射的角度关系。
Only back-scattering configurations were considered in this study.
== Simulation details
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。
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。
声子计算使用 phonopy phono3py ufoBEC 修正的算法。
// 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。
// 考虑到斜切,则大约是 24 度。

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= others
#include "掺杂晶格变化.typ"
#include "晶格变化导致的频率变化.typ"

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= Results and Discussion
我们先讨论无缺陷的情况,再讨论有缺陷的情况。
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。
// - 无缺陷:
// 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
// - 弱极性的声子:
// - 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。
// - 强极性的声子:
// - 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。
// - TODO: 写文字
// - 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。
// - TODO: 佐证它对表面敏感
// - 对于 LO可能形成 LOPC
// - 有缺陷的情况:
// - TODO: 描述缺陷原子的振动
// - TODO: 计算拉曼张量,描述光谱的可能变化
#include "perfect/default.typ"
#include "defect/default.typ"

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== Phonons with impurities and charge carriers

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== Phonons in Perfect 4H-SiC
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。
// There are 21 phonons in total.
// We classified them into two categories: 18 negligible-polar phonons and 3 strong-polar phonons.
The phonons involved in Raman scattering are located in reciprocal space around the #sym.Gamma point,
@@ -9,6 +13,8 @@ The 18 of 21 phonons are classified into negligible-polar phonons (i.e., phonons
and the other three phonons are strong-polar phonons,
where the polarity gives rise to observable effects in the Raman spectra.
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。
// This classification make sense.
This classification is based on the fact that
the four Si atoms in the primitive cell of 4H-SiC carry similar positive Born effective charges (BECs),
@@ -22,3 +28,6 @@ In contrast, in the three strong-polar phonons,
resulting in a strong dipole moment.
#include "table-bec.typ"
#include "non-polar/default.typ"
#include "polar/default.typ"

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=== Phonons with Negligible Polarities
我们用 gamma 点的声子来近似弱极性的声子。
// We investigate phonons at Gamma instead of the exact location near Gamma.
Phonons at the #sym.Gamma point were used
to approximate negligible-polar phonons that participating in Raman processes
@@ -14,6 +18,8 @@ Therefore, negligible-polar phonons involved in Raman processes
#include "figure-discont.typ"
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。
// Representation of these 18 phonons, and the shape of their Raman tensors could be determined in advance.)
Phonons at the #sym.Gamma point satisfy the C#sub[6v] point group symmetry,
and the 18 negligible-polar phonons correspond to 12 irreducible representations of the C#sub[6v] point group:
@@ -35,7 +41,7 @@ However, whether a mode is sufficiently strong to be experimentally visible
// without first-principle calculations.
// Here we only write out results, details are in appendix.
// TODO: maybe it is better to assign Raman tensor to each bond, instead of atom
我们提出了一个新的办法来估计拉曼张量大小。
We propose a method to estimate the magnitudes of the Raman tensors of these phonons based on symmetry analysis.
This approach is founded on the assumption that the change in polarizability induced by atomic displacements in 4H-SiC
@@ -48,6 +54,8 @@ The parameters $a_i$ exhibit significantly larger absolute values compared to $e
indicating the E#sub[2] mode at 756.25 cm#super[-1] in simulation (mode 8)
possess a much higher Raman intensity than the others.
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。
The Raman tensors and frequencies of the negligible-polar phonons were calculated using first-principles methods,
and the results are compared with both experimental data and theoretical predictions (@table-nopol).
The calculated phonon frequencies show good agreement with experimental data with a slight underestimation of 2-5%,
@@ -73,6 +81,8 @@ However, it should become detectable if the incident light has a polarization co
(as in our experiment),
or when the excitation wavelength approaches resonance conditions (cite).
其它峰在其它章节中解释。
Besides, there are other peeks in the experiment.
The peek at 796 and 980 are caused by strong-polar phonons which will be discussed later.
Besides, there are small peeks at xxx,

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=== Strong-polar Phonons
沿着不同方向入射的话,强声子的模式是不同的。
// 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。
// 这导致不同方向的入射/散射光的声子模式不同。
@@ -25,6 +28,8 @@ For example, when the light is incident along the y direction (phonon modes on t
When the light is incident along a direction between z and y,
three phonon modes will exist, but vibration in the mixed direction.
实验发现的确是这样的。
Many Raman experiments on 4H-SiC with incident light along the z direction have observed two peaks.
However, no experiments have reported three peaks with incident light along other directions.
In our experiment, we found the third, and it satisfied properties we expected.

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Only back-scattering configurations were considered in this study.
// 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。
// 考虑到斜切,则大约是 24 度。