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n型GaAs欧姆接触的比接触电阻ρ_c与有源层浓度N_D有反比关系,这已为很多实验事实所证明。文献中对这一现象有各种解释。本文对文献中的各种解释模型进行了分析,指出不足之处。提出ρ_c应由两部分ρ_(c_1)和ρ_(c_2)组成。ρ_(c_1)是合金与其下在合金化后形成的高掺杂层间的比接触电阻。此外,在这高掺杂层与原来有源层间有载流子浓度差,因而形成一个势垒φ_2,它带入ρ_(c_2)。当合金化良好,高掺杂层浓度N_(Dc)很高,因而ρ_(c_1)很小。这时ρ_(c_2)是ρ_c的主要组成部分。只是在这种情况下,即当N_D小于有效态密度N_c时,ρ_c与N_D才有反比关系。如N_D>N_c,由于φ_2的消失而ρ_(c_2)可忽略,ρ_c由ρ_(c_1)决定。这时ρ_c将决定于N_(Dc),而与N_D无关。所得ρ_(c_1)与ρ_(c_2)的计算式不但能很好解释n型GaAs欧姆接触的实验结果,而且也解释了文献中p-Si的欧姆接触实验结果。认为所述模型也对p型GaAs,p型InP和其他Ⅲ-V族化合物等适用,并结合文献中的实验数据进行了讨论。
The specific resistance of the n-type GaAs ohmic contact, ρ_c, is inversely proportional to the active layer concentration, N_D, which has been proved by many experimental facts. There are various explanations of this phenomenon in the literature. In this paper, various explanations of the model in the literature were analyzed, pointing out the shortcomings. It is proposed that ρ_c should consist of two parts ρ_ (c_1) and ρ_ (c_2). ρ_ (c_1) is the specific contact resistance between the alloy and the highly doped layer beneath it after alloying. In addition, there is a difference in carrier concentration between the highly doped layer and the original active layer, thereby forming a potential barrier φ_2 which is brought into ρ_ (c_2). When the alloying is good, the concentration of highly doped layer N_ (Dc) is very high, so ρ_ (c_1) is small. Now ρ_ (c_2) is the main component of ρ_c. Only in this case, that is, when N_D is less than the effective density N_c, there is an inverse relationship between ρ_c and N_D. If N_D> N_c, ρ_ (c_2) is negligible due to the disappearance of φ_2 and ρ_c is determined by ρ_ (c_1). Then ρ_c will be determined by N_ (Dc), but not with N_D. The formulas of ρ_ (c_1) and ρ_ (c_2) are not only good for explaining the experimental results of n-type GaAs ohmic contacts, but also explain the ohmic contact results of p-Si in the literature. It is considered that the model is also applicable to p-type GaAs, p-type InP and other III-V compounds, and the like, and the experimental data in the literature are discussed.