半导体掺杂nand 从能级的角度来看半导体的掺杂

发布时间 : 2025-04-02

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从能级的角度来看半导体的掺杂

半导体掺杂技术

半导体的常用掺杂技术主要有两种，即高温（热）扩散和离子注入。

掺入的杂质主要有两类：

第一类是提供载流子的受主杂质或施主杂质（如Si中的B、P、As）；

第二类是产生复合中心的重金属杂质（如Si中的Au）。

(1)热扩散技术

对于施主或受主杂质的掺入，就需要进行较高温度的热扩散。因为施主或受主杂质原子的半径一般都比较大，它们要直接进入半导体晶格的间隙中去是很困难的；只有当晶体中出现有晶格空位后，杂质原子才有可能进去占据这些空位，并从而进入到晶体。

为了让晶体中产生出大量的晶格空位，所以，就必须对晶体加热，让晶体原子的热运动加剧，以使得某些原子获得足够高的能量而离开晶格位置、留下空位（与此同时也产生出等量的间隙原子，空位和间隙原子统称为热缺陷），也因此原子的扩散系数随着温度的升高而指数式增大。对于Si晶体，要在其中形成大量的空位，所需要的温度大致为1000℃左右，这也就是热扩散的温度。

(2)离子注入技术

为了使施主或受主杂质原子能够进入到晶体中去，需要首先把杂质原子电离成离子，并用强电场加速、让这些离子获得很高的动能，然后再直接轰击晶体、并“挤”进到里面去；这就是“注入”。当然，采用离子注入技术掺杂时，必然会产生出许多晶格缺陷，同时也会有一些原子处在间隙中。所以，半导体在经过离子注入以后，还必须要进行所谓退火处理，以消除这些缺陷和使杂质“激活"。

(3)与掺杂有关的问题

①Si的热氧化技术： 因为当Si表面原子与氧原子结合成一层SiO2后，若要进一步增厚氧化层的话，那么就必须要让外面的氧原子扩散穿过已形成的氧化层、并与下面的Si原子结合，而SiO2膜是非晶体，氧原子在其中的扩散速度很小，因此，往往要通过加热来提高氧原子的热运动能量，使得能够比较容易地进入到氧化层中去，这就是热氧化。所以，Si的热氧化温度一般也比较高（～1000℃左右）。

②杂质的激活： 因为施主或受主杂质原子要能够提供载流子，就必须处于替代Si原子的位置上。这样才有多余的或者缺少的价电子、以产生载流子。所以在半导体中，即使掺入了施主或受主杂质，但是如果这些杂质原子没有进入到替代位置，那么它们也将起不到提供载流子的作用。为此，就还需要进行一定的热处理步骤——激活退火。

③Au、Pt等重金属杂质原子的扩散： 重金属杂质与施主或受主杂质不同，因为重金属杂质的原子半径很小，即使在较低温度下也能够很容易地通过晶格间隙而进入到半导体中去，所以扩散的温度一般较低。例如扩散Au，在700℃下，只要数分钟，Au原子即可分布到整个Si片。

从能级的角度来看半导体的掺杂

半导体一般由锗和硅两种材料构成，而由于我们生活的环境的温度不是绝对零度，所有会有本征激发(电子脱离质子的吸引力而转变成为自由电子如下图)，这就是温度可以改变半导体的特性。那么我就要引入能级了。

本征激发就是将电子从价带激发到导带去，而禁带就是最外层轨道杂化使得本来处于同一轨道的电子分开成两个轨道，轨道之间就是禁带。而内层轨道形成价带，无能量进入时充满电子，外层轨道形成导带，无能量进入时无电子。我以前不能理解能级，但是现在懂了，希望可以帮到你。

而为什么掺杂可以帮助半导体提高他的导电性。

以N型半导体来举例子。

半导体掺杂了五价的元素，比如磷形成N型半导体，那么便会多出一个电子，多出来的电子就成为了施主能级，他们极易成为自由电子，上面说了自由电子形成导带，所以施主能级中的电子极易转移到导带中。由于导带中自由电子增多，所以导电性增加了。

然后就是P型半导体

半导体掺杂了三价元素，比如硼就会形成P型半导体，那么由于硼的电子只有三个，便会多出一个空位，这些空位(空穴)形成了受主能级，上面由本征激发的电子也就是价带中的电子不会那么容易成为自由电子，而是被这些空位所吸附，也就是价带中的电子转移到了受主能级，电子从受主能级中也能激发到导带，形成自由电子。

由于空穴的数量增多导致自由电子的转移变得“通畅”(也可以理解为停车，车位更多的地方，来往的车辆也就越多)，这就导致了掺杂后的半导体导电性增加。

总结：

自由电子形成导带;

未激发或者在电子对中的电子和空穴形成价带;

掺入五价元素而形成的多余但是没有激发的电子形成施主能级;

掺入三价元素而形成的多余的空穴形成受主能级。

“材料界”（微信号: Material-World）最具影响力和最受欢迎的各类新材料微信公众号之一！

夏建白院士：超宽禁带半导体高效p型掺杂

超宽禁带半导体高效P型掺杂

超宽带半导体（UWBG）具有直接带隙可调、击穿电压高、化学稳定性好和热稳定性好等优点。然而大多数UWBG半导体都存在严重的掺杂不对称问题，即它们可以很容易地掺杂p型或n型，但不能同时实现两种掺杂。影响掺杂极限的主要因素有三个：（1）高生成焓导致掺杂剂的溶解度有限；(2）掺杂能级深导致的高激活能；以及（3）缺陷或复合物的存在产生严重的自补偿。随着材料生长技术的迅速发展，低溶解度和自补偿问题得到了很大的改善。然而，高激活能问题是由宿主材料和掺杂剂的自身物理性质决定的，如何降低激活能仍然是重大挑战。

中国科学院半导体所夏建白院士在最新出版的《半导体学报》2021年第6期上发表题为《Efficient p-type doping in ultra-wide band-gap nitrides using non-equilibrium doping method》的评论短文。中国科学院长春光学精密机械与物理研究所黎大兵研究员课题组和中国科学院半导体所邓惠雄研究员课题组合作，提出了一种基于量子工程的非平衡掺杂方法，并成功应用于高Al组分AlxGa1-xN的p型掺杂。首先，通过第一性原理分析，揭示了该方法的物理过机制，然后对这一掺杂方案进行了系统实验研究和器件验证。他们通过非平衡掺杂技术将GaN量子点（QDs）嵌入Mg掺杂的AlxGa1-xN合金中，引入了局域高能级VBM。由于GaN量子点与AlxGa1-xN之间存在VBM带阶，激发电子从GaN的VBM跃迁到受主能级，激活能明显降低。本研究不仅可以提高超宽带氮化物光电器件的量子效率，而且为实现超宽带材料的高效掺杂提供了新的解决方案。

专刊

#Full Text

Al-rich nitride, as one of the most important ultra-wide band-gap (UWBG) semiconductors, currently plays the key role of deep ultraviolet (DUV) optoelectronics and potentially possesses the advantages of the huge global investment in the manufacturing infrastructure associated with InGaN material that has become the second most important semiconductor material after Si in the late 2010s[1, 2]. However, the p-doping of Al-rich nitrides has long been blocking the improvement of quantum efficiency of DUV optoelectronics. The activation energy (Ea) of the most-frequently used acceptor dopant Mg increases from 200 meV in GaN to as high as 630 meV in AlN[3-5]. Once the p-doping problem of Al-rich nitrides is solved, the DUV or even the high-frequency and high-power industries probably usher in an era of rapid development based on the existing manufacturing infrastructure.

Actually, most wide band-gap (WBG) semiconductors usually experience an asymmetry doping problem, i.e., they can only be easily doped n-type or p-type, while not both, which is because that they either have a low valance band maximum (VBM) or a high conduction band minimum (CBM), resulting extremely high acceptor or donor Ea[6, 7]. And for UWBG semiconductors, the problem gets even worse. For example, the Ea of N-doped or P-doped n-type diamond is generally higher than 0.5 eV and that of Mg-doped or N-doped p-type β-Ga2O3 is even higher than 1 eV[8-10]. These doping asymmetry problems have seriously hindered the potential applications of many WBG materials.

In the past decades, great efforts have been devoted to theoretically overcome the high Ea problem in WBG semiconductors. In these investigations, researchers tried their best to develop novel approaches to tune the dopant level. For n-type doping, to lift the impurity level up close to the CBM of the host, while for p-type doping, to lower the impurity level down close to the VBM of host. The generally used dopant delta-doping and co-doping in WBG semiconductors are all based on the principle[11, 12]. Later, Yanfa Yan et al. proposed an approach to solve the asymmetry doping problem by introducing impurity band below the CBM or above the VBM via passive donor–acceptor complexes or isovalent impurities and effectively doping the passivated impurity band, which essentially changed the band edge[13]. Clas Persson et al. found the S dopants in ZnO would form local ZnS like bonds in the ZnO host and could result in a strong VB offset bowing, making the p-doping of ZnO enhanced[14]. From this point of view, it is possible to reduce the Ea by tuning the band edge. However, it is difficult and uncontrollable to form such impurity band or local bonds as the authors declared.

Recently, Prof. Dabing Li’s group in Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CAS), cooperating with Prof. Hui-Xiong Deng in Institute of Semiconductors, CAS, reported an interesting work in p-doping of Al-rich nitrides[15]. They proposed a non-equilibrium doping model to achieve low acceptor Ea in Al-rich nitrides, in which GaN quantum dots (QDs) are buried in AlN host to lift the VBM up, the Mg dopants are doped at the AlN host, and the Mg dopants are concentrated near the interface between GaN QDs and AlN host, as shown in Figs. 1(a)–1(c). In their model, Mg acceptor Ea below 0.1 eV is achieved according to the first principles calculations. Based on the model, p-type Al-rich AlGaN materials with Al contents of 50%–70% are experimentally realized. The hole concentrations reach the magnitude of 1018 cm–3 at room temperature and the measured acceptor Ea is several tens of meV as expected. The turn-on voltage of the DUV light-emission diode (LED) based on the non-equilibrium doping method is reduced compared to that based on the uniform doping method, as shown in Fig. 1(d). It is an exciting result for Al-rich nitrides.

Figure 1. (Color online) Non-equilibrium doping method to lower the acceptor Ea in UWBG nitride semiconductors and its application in DUV-LED. Acceptors are randomly doped in (a) AlN and (c) GaN. Both have high Ea in this condition. (b) GaN-QDs are embedded in AlN host and acceptors are doped in AlN host and concentrate near the interface. (d) Current–voltage curves of the devices. Device A uses the non-equilibrium doping method and Device B uses the uniform doping method. The insets are the device structure diagram and the cross-sectional scanning transmission electronic microscopy for the active region of the devices. Cited from Ref. [15].

This work is an important progress in WBG semiconductor doping. It has strongly developed the non-equilibrium doping process that to lower the dopant Ea by tuning the band edge of the host. Besides, it has found a good method to bury narrow band-gap QDs in their wide band-gap congener host, which will not significantly affect the optical properties of the host and is feasible in many element and compound semiconductors. It seems more controllable and designable compared to the formation of impurity band or local bonds. Moreover, it also demonstrates that not only the dopants formed based on non-equilibrium techniques like the dopant delta-doping, but also controlled growth of host materials based on non-equilibrium technology can power up the doping efficiency of WBG semiconductors. Therefore, this work has developed the doping conception that to lower the Ea of WBG semiconductors by tuning the band edge using non-equilibrium doping method. The follow-up studies should be carried out soon, breaking new frontiers in the doping of WBG and UWBG semiconductors.

References:

[1] Tsao J Y, Han J, Haitz R H, et al. The blue LED Nobel Prize: Historical context, current scientific understanding, human benefit. Ann Phys, 2015, 527, A53

[2] Tsao J Y, Chowdhury S, Hollis M A, et al. Ultrawide-bandgap semiconductors: Research opportunities and challenges. Adv Electron Mater, 2018, 4, 1600501

[3] Taniyasu Y, Kasu M, Makimoto T. An aluminium nitride light-emitting diode with a wavelength of 210 nanometres. Nature, 2006, 441, 325

[4] Simon J, Protasenko V, Lian C, et al. Polarization-induced hole doping in wide-band-gap uniaxial semiconductor heterostructures. Science, 2010, 327, 60

[5] Li D B, Jiang K, Sun X J, et al. AlGaN photonics: Recent advances in materials and ultraviolet devices. Adv Opt Photonics, 2018, 10, 43

[6] Zhang S B, Wei S H, Zunger A. Overcoming doping bottlenecks in semiconductors and wide-gap materials. Physica B, 1999, 273/274, 976

[7] Wei S H. Overcoming the doping bottleneck in semiconductors. Comput Mater Sci, 2004, 30, 337

[8] Lyons J L. A survey of acceptor dopants for β-Ga2O3. Semicond Sci Technol, 2018, 33, 05LT02

[9] Kyrtsos A, Matsubara M, Bellotti E. On the feasibility of p-type Ga2O3. Appl Phys Lett, 2018, 112, 032108

[10] Wong M H, Lin C H, Kuramata A, et al. Acceptor doping of β-Ga2O3 by Mg and N ion implantations. Appl Phys Lett, 2018, 113, 102103

[11] Nakarmi M L, Kim K H, Li J, et al. Enhanced p-type conduction in GaN and AlGaN by Mg-δ-doping. Appl Phys Lett, 2003, 82, 3041

[12] Nishimatsu T, Katayama-Yoshida H, Orita N. Ab initio study of donor–hydrogen complexes for low-resistivity n-type diamond semiconductor. Jpn J Appl Phys, 2002, 41, 1952

[13] Yan Y, Li J, Wei S H, et al. Possible approach to overcome the doping asymmetry in wideband gap semiconductors. Phys Rev Lett, 2007, 98, 135506

[14] Persson C, Platzer-Björkman C, Malmström J, et al. Strong valence-band offset bowing of ZnO1–xSx enhances p-type nitrogen doping of ZnO-like alloys. Phys Rev Lett, 2006, 97, 146403

[15] Jiang K, Sun X J, Shi Z M, et al. Quantum engineering of non-equilibrium efficient p-doping in ultra-wide band-gap nitrides. Light: Sci Appl, 2021, 10, 1

夏建白院士文章：

Efficient p-type doping in ultra-wide band-gap nitrides using non-equilibrium doping method

Jianbai Xia

J. Semicond. 2021, 42(6): 060402

doi: 10.1088/1674-4926/42/6/060402

从能级的角度来看半导体的掺杂

半导体掺杂技术

从能级的角度来看半导体的掺杂

而为什么掺杂可以帮助半导体提高他的导电性。

总结：

夏建白院士：超宽禁带半导体高效p型掺杂

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