OHMIC CONTACTS TO n-GaAs USING GRADED BAND GAP LAYERS OF Ga_{1 - x}In_xAs GROWN BY MOLECULAR BEAM EPITAXY.

Ohmic contacts were studied on structures which utilize the fact that for InAs surface Fermi level pinning occurs at or in the conduction band. It is found that an epitaxial layer of n-Ga//1// minus //xIn//xAs grown by molecular beam epitaxy on n-GaAs which is graded in composition from x equals 0 at the GaAs interface to 0. 8 less than equivalent to x less than equivalent to 1. 0 at the surface will produce a structure with a nearly zero Schottky barrier height for the metal-Ga//1// minus //xIn//xAs interface and hence a low resistance ohmic contact. A transmission line measurement of non-alloyed contact resistance of 5 multiplied by 10** minus **7 less than R//c less than 5 multiplied by 10** minus **6 ohm cm**2 is obtained for a Ag/n-Ga//1// minus //xIn//xAs/n-GaAs MESFET structure.