Investigation of the Field in a Tunnel Diode with a Heterojunction
A system of equations is derived for calculating the field in a degenerate heterojunction, taking into account the presence of mobile carriers, special features of the energy bands, and the interfacial charge. Two cases are considered in these calculations: 1) heterojunctions between crystals with similar lattice constants; 2) heterojunctions in which the interfacial charge has to be taken into account because the lattice constants are different. A solution of the system for the first case gives graphs showing the devia - tion of the asymmetry coefficient β = w 2 ’ /w 1 ’ , calculated using the formulas in the present paper, from the usual definition β = 1/r. Calculations are carried out for different values of the parameters of the system and it is clear from the graphs that, in some cases, β may differ considerably from the value calculated in the usual way. Consequently, such deviations of the asymmetry coefficient must be allowed for in calculations of the characteristics of a tunnel heterodiode. When mobile charges are taken into account, the system of equations becomes more complicated. Its solution is obtained in two cases: A) when the dependence of the magnitude of the interfacial charge on the bias cannot be ignored; B) when this dependence is negligible. A method for solving the initial system of equations is given for both cases. Next, the asymmetry coefficient β is calculated taking into account the additional asymmetry solely due to the interfacial charge. This calculation is carried out for different parameters of the system. It is concluded that the asymmetry of the interfacial charge must be allowed for if correct results are to be obtained. Moreover, the position of a band of additional levels in the junction is important in computations of the interfacial charge.
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