Electron beam modification of GaAs surface potential : measurement of Richardson constant

The surface potential of GaAs is strongly modified in the presence of a high-energy electron beam due to the creation of electron-hole pairs in the depletion region and the subsequent drift of the holes to the surface where they neutralize surface states. This effect is modeled in terms of a parameter K=A*T2/Ib(dE/dz)η, where Ib is the beam current density, A* is the effective Richardson constant, dE/dz is the beam energy loss per unit length, and η−1 is the average energy required to create an electron-hole pair. For the sample studied here, an 0.25-μm layer with n≂3×1017 cm−3, we obtain a value K≂(7.5±0.8)×104 cm at T=296 K and Ib=0.33 μA/cm2, which gives A*≂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 good agreement with other recent results.