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We have investigated the effects of oxygen codoping and thermal annealing on the deep level spectrum and carrier lifetime of Er implanted crystalline Si. It is found that oxygen codoping produces a dramatic modification in the concentration and energetic position of Er-related deep levels in the Si band gap. In particular the formation of Er-O complexes is shown to produce a promotion from deep to shallow levels. This effect is the major responsible of the enhancement of Er donor behaviour in presence of oxygen and also produces a large increase in the minority carrier lifetime

Capacitance DLTS measurements have been performed in VPE GaAs MESFETs prepared on Bridgman Cr-doped and LEC undoped semi-insulating substrates. A band of electron traps not intrinsically related to the VPE growth process and accumulating near the metal (gate) — semiconductor interface was detected in all the samples. Deeper regions into the channel were free from any detectable trap. Near pinch-off conditions, a positive capacitance signal was found to dominate the DLTS spectra only in the case of samples prepared on Cr-doped substrates. The hypothesis of this positive transient being related to changes in the occupation of surface states in the ungated surface access regions has been checked by comparing experimental and calculated dependencies of the signal amplitude on reverse gate voltage. Unexplained discrepancies, together with the absence of positive signal in MESFETs prepared on LEC undoped substrates, suggest the possibility of hole emission from hole traps within the bulk of the device.

Admittance measurements have been performed to reveal trap levels within the space charge region of CdZnS/p-GaAs heterojunctions prepared by chemical vapour deposition in the close-spaced geometry. The presence, between GaAs and the CdZnS layer, of a transition region containing a high concentration of acceptor-like traps is hypothesized. Taking into account electric field effects, a ionization energy greater than 0.28 eV is estimated for the trap state.

Cd1−xZnxS/p-GaAs heterojunctions for solar cell applications have been prepared by growing single crystal Cd1−xZnxS epitaxial layers on (111)GaAs substrates through a vapour phase chemical transport method using the close-spaced geometry and H2 as a transport agent. Electrical and photovoltaic properties of the heterojunctions have been investigated and discussed in connection with the main features of the growth technique. AM1 power conversion efficiencies up to 6.2% have been measured and possible improvements have been examined.

The small-signal a.c. admittance of a p +/n junction with gap states having a continuous distribution in energy is considered. Approximate analytical solutions for both diode conductance and capacitance are derived, through a space charge analysis, in the case of a low density of gap states. Numerical results on the zero-bias admittance are given and discussed for two particular energy distributions: i) Gaussian shapes and ii) exponential tails at the conduction band edge. It is shown that in both cases incomplete admittance spectroscopy experiments may lead to mistake the occurrence of a continuous distribution of gap states for an apparent discrete deep level. Unambiguous criteria to avoid misleading procedures are given and discussed.