Electronic and optical properties of Ti-doped GaAs and InP; semi-insulating InP

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Abstract
A systematic study of the effects of Ti doping on the electrical and optical properties of GaAs and InP has been carried out employing both melt and solution-grown crystals. Utilizing deep level transient spectroscopy, Hall effect measurements, photoconductivity, and optical absorption measurements, it was found that Ti introduces two deep levels in GaAs at Ec −0.23 eV and Ec −1.00 eV which were identified as the Ti3+/Ti2+ acceptor level and the Ti4+/Ti3+ donor level, respectively. In InP the Ti4+/Ti3+ donor level was found near midgap at Ec −0.63 eV, while the Ti3+/Ti2+ acceptor level was found to lie within the conduction band. As a consequence of the midgap position of this donor level, we developed a formulation for producing semi-insulating InP based on doping with Ti to compensate shallow acceptors. Resistivities in excess of 107 Ω cm can easily be obtained using this technique. This is the first semi-insulating III-V compound having a compensation mechanism based on a deep donor impurity. In view of the fact that Ti is expected to have a very low diffusivity in InP, Ti-doped semi-insulating InP should exhibit far greater thermal stability than Fe-doped InP and thus it should prove technologically significant.