= Method

== Experiment details

外延片的厚度、掺杂浓度、生长 C/Si 比，斜切角度。

5 个 6 寸的 p 型外延片被使用，我们将它们称为 W#sub[i]。
使用的衬底都是 n 型，前四个外延片的厚度为 1 微米，第五个外延片的厚度为 2 微米。
外延层的 Al 掺杂浓度分别为 0.1 3.8 5.1 6.4 10 E18 cm#super[-3]，使用 SIMS 测试。
生长时 Si/C 比分别为 0.7 1.2 1.6 2.4 2.0。、
所有外延片都有 4 度斜切。

Five 6-inch p-type epitaxial wafers on n-type substrates were used, denoted as W#sub[1]-W#sub[5].
All epitaxial layers were grown using step-flow method with a 4° offcut angle.
The Al doping concentrations in the epitaxial layers
  were 0.1, 3.8, 5.1, 6.4, and 10 #sym.times 10 cm#super[-3] (measured using SIMS)
  with W#sub[1]-W#sub[4] having a thickness of 1 μm and W#sub[5] having a thickness of 2 μm, respectively.
The Si/C ratios of the five wafers during growth were 0.7, 1.2, 1.6, 2.4, and 2.0, respectively.

拉曼设备的型号。激光的波长，背散射。共焦针孔。

拉曼设备的型号是 LabRAM HR Evolution，使用背散射。
大部分实验中，我们使用 532 nm 的激光，少部分实验中使用 325 nm 的激光以观测紫外拉曼。
有三个不同的入射配置，包括正入射、掠入射、边入射。
考虑到 4 度斜切和 4H-SiC 几乎各向同性的折射率（2.73） @shaffer_refractive_1971 ，掠入射的入射角大约为 25 度。
在正散射过程中，我们使用 100 微米的共焦针孔，以尽可能提高 z 方向的分辨率 @song_depth_2020。

All our Raman experiments were performed using a LabRAM HR Evolution system with back-scattering configuration,
  where collected scattered light has a reversed wavevector direction compared to the incident light.
A 532 nm laser was used in most experiments,
  while a 325 nm laser was used to observe Raman signals under ultraviolet excitation.
Three different incidece configurations were used, as shown in @figure-incidence,
  including normal incidence, where the laser beam is perpendicular to the epitaxial surface;
  grazing incidence, where the laser beam is nearly parallel to the epitaxial surface;
  and edge incidence, where the laser beam is incident at the edge of the wafer, instead of the epitaxial surface.
Taking the 4° offcut angle
    and the nearly isotropic refractive index 2.73 of 4H-SiC @shaffer_refractive_1971 into account,
  the wavevector in 4H-SiC during grazing incidence is about 25° to the c axis.
During normal incidence, a 100 μm confocal pinhole was used to improve the z-direction resolution @song_depth_2020;
  while during other configurations, 200 μm confocal pinhole was used to improve the signal-to-noise ratio.

#include "figure-incidence.typ"

== Simulation details

无缺陷的声子在多大的模型中计算。
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 ufo，BEC 修正的算法。