PERSISTENT-PHOTOCONDUCTIVITY EFFECT IN DELTA-DOPED AL0.48IN0.52AS GA0.47IN0.53AS HETEROSTRUCTURES/

We have studied the electronic properties of delta-doped Al0.48In0.52A s/Ga0.47In0.53As heterostructure samples by Shubnikov-de Haas and quan tum-Hall-effect measurements. The well-defined two-subband occupied tw o-dimensional electron gas was detected. From the Fermi level at these two subbands, we calculate the energy difference between the lowest t wo subbands' minima to be 54 meV. After illuminating the sample at low temperature, we did observe a persistent photoconductivity. The elect ron densities of the first and second subbands for the sample with pre annealed substrate were increased by the illumination from 17.3 to 18. 2X10(11) cm(-2) and 3.6 to 4.1X10(11) cm(-2), respectively. The onset of the second subband occurs at n(0)=10.3X10(11) cm(-2). We also found that the concentration of deep donor traps is about 1.4X10(11) cm(-2) and the deep donor traps are not affected by the preannealed substrat e. We believe that the model to describe the persistent-photoconductiv ity effect in semiconductor heterostructure samples needs to be extend ed to those deep donor levels below Fermi energy and it does not have to be the DX center.