silvaco-mobility models-conmob analytic arora(1)
目录
1.前一阶段的问题
大概接触了一段时间的silvaco，根据《InP基PIN开关二极管结构设计与制备》这篇文章提供的结构和一些简单的参数进行仿真。因为已经工作，没有老师在自己摸索，学习期间看到很多人写的心得或理解，或多或少都对我有所帮助。但是boss希望我能够把重点放在效应（我猜他指的是model和material的参数）对仿真结果的影响。这一部分的资料很少看到，所以我也来写下我的学习过程。也希望能够有遇上同样问题的人一起讨论。
先简单记录一下我在用这篇文章的结构仿真遇到的问题：
1、 最开始是用devedit画PIN管的结构，但是最后仿真的I-V曲线似乎与atlas通过语句（mesh、region、electron、doping）直接定义的结构仿真的I-V曲线不同。这点有待验证，可能是自己粗心少了参数。
2、 这一个重掺杂的InP基，InGaAs同质结的PIN二极管，如果不去修改x.composition（同理y.composition）、NC300、NV300（或者其他我还没发现的参数），这个结构的能带一开始就会是简并半导体的能带。但是silvaco自带的example里很少有修改NC300和NV300，如果有修改的话通常会把这两个值设置成一样；而参考altas_user_manual里6.4节计算出的NC300和NV300也同样与example里写的参数不同（计算的参数更大）。
3、 仿真出来的曲线，什么样的参数会对曲线的某个点、某段范围产生什么样的影响，要保证仿真的曲线符合物理。
2.mobility models
依然还是从最简单的diode（example里的diodeex03.in的结构）开始理解model中的Mobility models。具体model的介绍在manual的3.6.1节。Manual提到迁移率模型可以大致分成四种：低电场行为（low filed behavior），高电场行为（high filed behavior），体半导体区（bulk semiconductor regions），反型层（inversion layers）。
The low electric field behavior has carriers almost in equilibrium with the lattice and the mobility has a characteristic low-field value that is commonly denoted by the symbol μn0,μp0. The value of this mobility is dependent upon phonon and impurity scattering. Both of which act to decrease the low-field mobility.
The high electric field behavior shows that the carrier mobility declines with electric field because the carriers that gain energy can take part in a wider range of scattering processes. The mean drift velocity no longer increases linearly with increasing electric field, but rises more slowly. Eventually, the velocity doesn’t increase any more with increasing field but saturates at a constant velocity. This constant velocity is commonly denoted by the symbol Vsat. Impurity scattering is relatively insignificant for energetic carriers, and so Vsat is primarily a function of the lattice temperature.
Modeling mobility in bulk material involves: (i) characterizing μn0 and μp0 as a function of doping and lattice temperature, (ii) characterizing Vsat as a function of lattice temperature, and (iii) describing the transition between the low-field mobility and saturated velocity regions.
Modeling carrier mobilities in inversion layers introduces additional complications. Carriers in inversion layers are subject to surface scattering, extreme carrier-carrier scattering, and quantum mechanical size quantization effects. These effects must be accounted for in order to perform accurate simulation of MOS devices. The transverse electric field is often used as a parameter that indicates the strength of inversion layer phenomena.
（摘自atlas_users1）
低电场行为使载流子几乎与晶格平衡(这里没懂?)，迁移率具有特征性的低电场值，通常用符号μn0、μp0来表示。这种迁移率的大小取决于声子和杂质散射。两者都会降低低电场迁移率。
高电场行为表明，载流子迁移率随电场的增加而下降，因为获得能量的载流子可以参与更广泛的散射过程。平均漂移速度不再随电场的增大而线性增加，而是缓慢上升。最终，速度不再随电场的增加而增加，而是以恒定的速度饱和。这种恒定速度通常用符号Vsat表示。杂质散射对于含能载流子来说是相对不重要的，因此Vsat主要是晶格温度的函数。
体半导体区中的迁移率包括：（i）将μn0和μp0描述为掺杂和晶格温度的函数，（ii）将Vsat描述为晶格温度的函数，以及（iii）描述低场迁移率和饱和速度区域之间的转换。
在反转层中模拟载流子迁移率会带来额外的复杂性。反转层中的载流子受到表面散射、极端载流子散射和量子力学尺寸量子化效应的影响。为了对MOS器件进行精确的模拟，必须考虑这些影响。横向电场常被用作指示反转层现象强度的参数。
上面是理解后的翻译，但是看英文真的很难....感觉在语意理解总是有偏差，所以用直接看程序print出来的结果理解manual。这次先尝试经常看到的conmob、analytic、arora、ccsmob、fldmob、watt、kla、cvt。先研究一下前三个，根据下表manual的summary看，conmob是基本的迁移率模型，analytic比他多了温度因素，arora是在Si中替代analytic的模型？
2.1.conmob
调用不同的model，print的信息不同:
REGIONAL MOBILITY MODEL SUMMARY:
Region #1:
Model for Electrons:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using built-in model (refer to manual).
Model for Holes:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using built-in model (refer to manual).2.2.analytic
REGIONAL MOBILITY MODEL SUMMARY:
Region #1:
Model for Electrons:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Caughey-Thomas model.
mu1 = 55.24
mu2 = 1429.23
alpha = 0
beta = -2.3
gamma = -3.8
delta = 0.73
ncrit = 1.072e+17
Model for Holes:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Caughey-Thomas model.
mu1 = 49.7
mu2 = 479.37
alpha = 0
beta = -2.2
gamma = -3.7
delta = 0.7
ncrit = 1.606e+172.3.conmob+analytic
REGIONAL MOBILITY MODEL SUMMARY:
Region #1:
Model for Electrons:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Caughey-Thomas model.
mu1 = 55.24
mu2 = 1429.23
alpha = 0
beta = -2.3
gamma = -3.8
delta = 0.73
ncrit = 1.072e+17
Model for Holes:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Caughey-Thomas model.
mu1 = 49.7
mu2 = 479.37
alpha = 0
beta = -2.2
gamma = -3.7
delta = 0.7
ncrit = 1.606e+17可以从analytic和conmob+analytic的print结果以及manual的描述推测定义conmob和analytic参数都会**此模型。
2.4.arora
REGIONAL MOBILITY MODEL SUMMARY:
Region #1:
Model for Electrons:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Arora model.
mu1 = 88
mu2 = 1252
alpha = -0.57
beta = -2.33
gamma = 2.546
ncrit = 1.432e+17
Model for Holes:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Arora model.
mu1 = 54.3
mu2 = 407
alpha = -0.57
beta = -2.33
gamma = 2.546
ncrit = 2.67e+172.5.analytic+conmob+arora
REGIONAL MOBILITY MODEL SUMMARY:
Region #1:
Model for Electrons:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Arora model.
mu1 = 88
mu2 = 1252
alpha = -0.57
beta = -2.33
gamma = 2.546
ncrit = 1.432e+17
Model for Holes:
Concentration Dependent Mobility
@ Temperature = 300 Kelvin
Using Arora model.
mu1 = 54.3
mu2 = 407
alpha = -0.57
beta = -2.33
gamma = 2.546
ncrit = 2.67e+17到目前为止，先将这三个模型的组合输出正向曲线。
看起来三个模型都没有对阈值电压产生影响，电流的趋势是一样的。似乎进入了瓶颈，我原本以为三个模型会有很大差别。
3.休息
再次看看manual理解试试。
等等，打卡下班。
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