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一、引言 众所周知,高纯外延材料是器件制作的基础。但是,在实际工艺过程中,尽管采用高纯源,总不免有不同种类、不同含量的杂质进入外延层。这就是非有意掺杂。MOCVD生长纯度GaAs中非有意掺杂元素主要来源于TMG。在AsH_3-TMG体系MOCVD生长GaAs中,非有意掺杂载流子浓度随As/Ga比变化,并存在由p至n型导电类型的变化。由于AsH_3分压成为导电类型变化的界限,那末,在外延层中起支配作用的电活性杂质就是起着两性杂质作用的Ⅳ族元素。本文根据对不同纯度TMG的比较,结合对外延层的理化分析,认为起支配作用的是C和Si。文中建立了简单的热力学模型,用实验数据确定平衡常数,获得了载流子浓度和类型随输入As/Ga比变化的解析公式,并与实验结果符合良好。生长的GaAs电参数为:N=9×10~(14)cm~(-3),μ=5100cm~2/V·S。
I. Introduction As we all know, high-purity epitaxial material is the basis for device fabrication. However, in the actual process, despite the use of high-purity source, there are always different types, different levels of impurities into the epitaxial layer. This is non-intentional doping. MOCVD growth purity Unintentional doping elements in GaAs mainly come from TMG. In MAsVD grown GaAs in AsH_3-TMG system, unintentional doping carrier concentration changes with As / Ga ratio and there is a change from p to n conductivity. Since the partial pressure of AsH_3 becomes the limit of variation of the conductivity type, then the electroactive impurity that plays a dominant role in the epitaxial layer is a Group IV element that acts as an amphipathic impurity. Based on the comparison of TMG with different purity, combined with physical and chemical analysis of the epitaxial layer, it is considered that C and Si dominate. In this paper, a simple thermodynamic model was established, and the equilibrium constants were determined by experimental data. The analytic formulas of carrier concentration and type with As / Ga ratio were obtained and the results were in good agreement with the experimental results. The GaAs parameters for growth are N = 9 × 10 ~ (14) cm ~ (-3) and μ = 5100cm ~ 2 / V · S.