利用物理学基本原理对经典肖克莱半导体二极管理论的修正

Semiconductor p-n theory founded by Shockley has always been considered as the classical theory of the semiconductor devices physics. However, our accurate experimental and theoretic results confirmed that Shockley's theory basing on the classical Depletion layer assumption, therofore, can not explain some physical phonomena at high forward bias voltage. This project intends to study the Shockley theory model using the basic principles of physics from the following: 1) Using self-built method based on alternative current (AC) small signal and I-V plots we will accurately characterize the junction parameters of p-n junction samples and semiconductor devices, such as junction voltage, junction conductance, junction capacitance and ideality factor. The relation between the junction parameters and carriers' concentration and lifetime as well as the separation of the Quasi-Fermi level will also be clarified. 2) The above abnormal electrical properties and the recombination luminescent properties will be calculated by the model based on the basic principles of physics and Hess's equivalent circuit rather than the classical depletion layer assumption. 3) From analyzing the experimental and theoretical results, the mechanism of the difference results calculated by the model based on the basic principles of physics and the classical depletion layer assumption will be elaborated. The ultimate goal of this project is to point out the applicable conditions of the Shockley's classical assumptions, and confirm the correctness of the main inference of Shockley's theory, and then make a clear conclusion that whether it is suitable to be applied in the double-heterostructure and multiple-quantum well device, finally promote a revision theory of semiconductor p-n theory.

肖克莱创建的作为半导体器件物理重要基础内容的p-n结理论一直被奉为经典理论。最近我们的精确实验和理论研究表明，建立在耗尽层假设的这个理论在正向大电压下与实验严重不符。本项目拟利用物理学基本原理对肖克莱理论模型展开研究，进行修正，主要工作为：1）利用自建的正向交流小信号结合直流I-V特性的方法精确表征半导体器件的结电容、结电导、结电压、理想化因子等结参量，分析载流子浓度、寿命以及费米能级与这些结参量之间的关系；2）借鉴Hess的等效电路模型，舍弃耗尽层及其边界条件等基本假设，从基本物理原理出发，计算上述电学特性和复合发光特性；3）分析实验和理论计算结果，深入探讨利用经典肖克莱模型与基本物理原理计算结果存在差异的物理机制。本项目的最终目标是对肖克莱模型经典假设的适用条件，主要推论的正确性及其在异质结构和量子阱结构中的推广做出明确的结论，提出修正理论。

利用光致发光谱（PL）和电致发光谱（EL）以及我们自建的acIV方法对半导体发光二极管和激光二极管的光、电特性作了深入研究。在两种器件中都观察到了与经典‘肖克莱’理论相违背的负电容现象，同时在激光器阈值区还观察到了一系列的反常特性；利用Hess提出的模型、以及LASTIP软件分别对负电容，以及窄带隙和宽带隙的多量子阱激光器的反常电学特性进行了深入的模拟计算，所有这些结果都将成为经典，有可能写入未来教科书。具体结果为：1）在发光二极管方面，发现多量子阱半导体发光二极管的器件基底、波长及材料、以及尺寸等因素与器件的效率和负电容等特密切相关；无论半导体发光二极管还是激光二极管在大电压和低频率下都会出现明显的负电容，总结得出了负电容的半经验公式：Cp=-Co•ƒ(-β)•e(mV)，其中β取值在1到2之间；利用Hess的模型计算出p-n结在大电压下会出现负电容，并得到了负电容与载流子的复合寿命之间的关系。2）在激光器的研究方面发现，在阈值区，激光器的电特性曲线都会出现上跳、下跳，曲线斜率变化与制备材料密切相关；阈值后，宽带隙器件的准费米能级差并未钉扎；阈值前，宽带隙激光器在低电流下就出现了偏振度极高的激射现象，所有这些实验现象都难以用当前激光器理论解释；利用LASTIP软件分别对窄带隙和宽带隙半导体激光器特性模拟计算，得到了与实验一致的结果。3）为从理论上对上述负电容及其他电学特性解释，开展了第一性原理计算。首先，从实验上对掺杂半导体材料的电学、磁学特性做了研究；其次，试探性地计算了一些材料所形成的超晶格特性；计划在软件使用熟练后开展p-n结、异质结特性的理论研究。4）此外，我们在太阳能电池中也观察到了负电容现象。