SPECTROSCOPIC CHARACTERIZATION AND ROUGHNESS-SPECTRUM OF INTERFACES IN III-V MULTIPLE-QUANTUM-WELL STRUCTURES

Resonance Raman spectroscopy and resonant excitation of luminescence have been applied to a p-doped GaAs-(Al,Ga)As multiple-quantum-well structure to determine the effects of well thickness variations and of interface roughness from observed shifts of hole-intersubband transitions with the exciting laser frequency. Energy and intensity variations of luminescence transitions have also been studied, again depending on laser energy. A fitting procedure is described that provides, e.g., data on the distribution of the well widths, i.e., on the interface quality. From these data along with other data available in the literature, a few semiquantitative but representative values of the power spectrum S(k) of the interface roughness at different spatial frequencies k have been determined. These values are averages over the frequency intervals of specific sensitivity of the different methods, which overlap only partially but cover almost the whole range of spatial frequencies k (D-1 less-than-or-equal-to k less-than-or-equal-to a0(-1)), where D is the sample size and a0 the thickness of a monolayer. It appears that the power spectra derived are "red" (dS/dk < 0) or, for some structures, possibly "white" (dS/dk = 0).