Recombination Dynamics at InP/Liquid Interfaces

The relaxation dynamics of photoexcited charge carriers at the interface between InP and several metal ion solutions has been studied using picosecond time-resolved photoluminescence and electrochemical techniques. The results show that for p-InP, the controlling recombination process follows the nonradiative Shockley-Read-Hall (SRH) mechanism, while on the other hand, radiative bulk recombination is the controlling process in n-type crystals. The surface recombination velocities (SRV) of both conductivity types were found to be strongly dependent (varying over the range of 500 to 2 × 10⁵ cm/s) on the ionic solution composition and concentration. The SRV of the etched n-InP surface is retained and remains low when it is in contact with nonoxidizing ions like Zn²⁺ or Cr³⁺. On the other hand, for n-InP, the SRV increases sharply when the crystal is dipped into stronger oxidizing species like Ag⁺ (SRV = 1.4 × 10⁵ cm/s) or Cu²⁺ (SRV = 3.4 × 10⁴ cm/s). The electrochemical measurements provided firm evidence for chemisorbed-induced surface states in the case of the more strongly oxidizing solutions. The distribution of the surface states was extracted from a frequency dispersion analysis of the electrodes' impedance and was found to correlate with the SRVs. We discuss the SRV dependence on the redox potentials of the various solutions and the similarity of the results to those obtained in the past for CdS and CdSe.