OPTIMIZATION OF COMPOSITIONAL GRADING IN ZN(SE,TE) GRADED OHMIC CONTACTS TO P-TYPE ZNSE

The energy barrier at heterojunctions can be minimized by introducing a parabolic grading potential. For ternary materials with a strong bowing effect in band gap energy, such as Zn(Se,Te), the composition must vary nonparabolically in order to have the required parabolic grading potential. In this letter, a new compositional grading style for Zn(Se,Te) graded band gap ohmic contacts to p-type ZnSe has been obtained through a simplified analytical model where both the bowing factor in ternary band gap energy and the change in electron affinity (chi) with alloy composition are included. To show the effectiveness of the proposed grading style, it is compared with both parabolic and linear grading in numerical calculations. The specific contact resistance of the proposed optimized compositional grading is about two orders of magnitude lower than that of a linear grading over a grading distance of 170 to 310 Angstrom, and about one order of magnitude lower than that of a parabolic grading at a grading distance less than 220 Angstrom. (C) 1995 American Institute of Physics.