INVESTIGATION OF DEEP METASTABLE TRAPS IN SI DELTA-DOPED GAAS AL0.33GA0.67AS QUANTUM-WELL SAMPLES USING NOISE SPECTROSCOPY/

We show that the temperature-dependent resonances measured in the volt age noise of a series of Si delta-doped GaAs/Al0.33Ga0.67As quantum-we ll samples originate from fluctuations in the free-carrier concentrati on of electrons as they are trapped and emitted at deep metastable def ects. We identify the main defect observed as the known DX center in I II-V semiconductor alloys and present evidence for the existence of pr eviously unreported DX-like traps observed in one of the samples measu red in the dark and in the others when continually illuminated with in frared radiation. Further investigation of one of these defects using the Hall effect to measure temperature-dependent changes in free-carri er concentration shows a remarkable peak in the concentration of elect rons as a function of temperature when the sample is continuously illu minated. This peak can be understood by using rate equations to descri be the dynamics of the possible donor states. In particular, our model indicates a finite ionization energy for the Chadi and Chang DX(0)-li ke state for these defects. We propose that the observed phenomena are closely related to the spatial distribution of impurities established during growth. In particular, one might expect a significant probabil ity for the formation of clusters of two or three Si atoms on adjacent group-III sites, which could behave as DX-like states with considerab ly modified energies.