ELECTRON-BEAM MODIFICATION OF GAAS SURFACE-POTENTIAL - MEASUREMENT OFRICHARDSON CONSTANT

The surface potential of GaAs is strongly modified in the presence of a high-energy beam due to the creation of electron-hole pairs in the d epletion region and the subsequent drift of the holes to the surface w here they neutralize surface states. This effect is modeled in terms o f a parameter K = AT2/I(b)(dE/dz)eta, where I(b) is the beam current density, A is the effective Richardson constant, dE/dz is the beam en ergy loss per unit length, and eta-1 is the average energy required to create an electron-hole pair. For the sample studied here, an 0.25-mu m layer with n congruent-to 3 x 10(17) cm-3, we obtain a value K congr uent-to (7.5 +/- 0.8) x 10(4) cm at T = 296 K and I(b) = 0.33 muA/cm2, which gives A congruent-to 0.44 A/cm2 K2. Although this value of A* is much lower than the theoretical estimate of 8 A/cm2 K2, it is in go od agreement with other recent results.