Persistent photoconductivity and deep levels in aluminum gallium indium phosphide

Abstract

The quaternary material aluminum gallium indium prosphide (($\rm Al\sb{x}Ga\sb{1-x})\sb{y}In\sb{1-y}P$) is used in the fabrication of visible lasers and light emitting diodes. There are problems in this material related to the observation of persistent photoconductivity at certain compositions. In this thesis the persistent photoconductivity and related deep levels in ($\rm Al\sb{x}Ga\sb{1-x})\sb{0.5}In\sb{0.5}P$ were studied by capacitance versus temperature measurements and by constant capacitance deep level transient spectroscopy. The samples studied were grown lattice matched to gallium arsenide (GaAs) by metalorganic chemical vapor deposition. Several samples with different aluminum compositions were studied; one set of samples was doped n-type with selenium (Se) and the other set was doped n-type with tellurium (Te).

It was found that the persistent photoconductivity in both the Se and Te doped samples is caused by a deep electron trap with an energy of 0.30 eV and a capture barrier energy of 0.18 eV. Both the persistent photoconductivity and the deep trap concentration are maximum at an Al composition of 0.5. The energies measured for the deep trap in this material are very similar to those reported for the DX center in Se doped and Te doped aluminum gallium arsenide (AlGaAs). This similarity and the observation of persistent photoconductivity indicate that this deep level is also a DX center.