Electroreflectance of surface-intrinsic- n+-type doped GaAs

The electroreflectance spectra of surface-intrinsic- $n^{+}$ -type-doped GaAs were measured at various bias voltages ${\mathrm{(V}}_{\mathrm{bias}}\mathrm{).}$ Results revealed many Franz–Keldysh oscillations (FKOs) above the band-gap energy, which have been attributed to a uniform electric field $\mathrm{(F)}$ in the undoped layer below the surface. However, there has been no other evidence for the uniformity of $F$ in the undoped layer. Since it is known that $F$ can be deduced from the periods of the FKOs, the relations between $F$ and $V_{\mathrm{bias}}$ can, thereby, be obtained. The nearly linear relation, thus found, confirms the existence of a nearly uniform field in the undoped layer. From the plot of $F$ against $V_{\mathrm{bias}},$ the values of the thickness of the undoped layer and the barrier height can also be evaluated.