In situ reflectance difference spectroscopy of p-type ZnTe : N grown by MBE

In situ Reflectance Difference Spectroscopy (RDS) was performed during p-ty pe of nitrogen-doped ZnTe thin films grown by Molecular Beam Epitaxy (MBE). The MBE system is equipped with an electron cyclotron resonance (ECR) cell for N-plasma generation. The RDS system is attached via a strain-free fuse d silica viewport mounted for normal incidence. This allows us to take RD s pectra during the doping process in the range from 1.5 to 5.5 eV. The dopin g level of the ZnTe:N films was determined in situ by evaluating the RD spe ctra in the vicinity of the E-1 and E-1 + Delta (1) transitions. This spect ral range was used to get the optimum conditions in the online doping perfo rmance of the plasma cell. We varied cell parameters like N-pressure and in put r.f. power. Furthermore, we investigated doping-induced surface process es, like surface saturation with activated N-species. Finally, ex situ meas ured spectra are compared with in situ acquired data, in order to study the surface Fermi level pinning at ambient pressures. (C) 2000 Elsevier Scienc e S.A. All rights reserved.