The stability of the Zn profile in modulation-doped multiple quantum well structures, which had been grown by means of low-pressure metalorganic vapor-phase epitaxy, was investigated by applying secondary ion mass spectrometric and transmission electron microscopic techniques to wedge-shaped samples. Although an excellent stability of the Zn profile was observed in as-grown samples with modulation doping (3nm, 1018Zn/cm3), the modulation-doped structure faded after the second epitaxial re-growth of a p-type InP layer (1018Zn/cm3) using either liquid-phase epitaxial or metalorganic vapor-phase epitaxial techniques. However, the modulation-doping profile was successfully preserved even after re-growth of the p-type InP layer for 1.5h (in a sample that comprised an undoped InP-clad layer, instead of a p-type InP clad layer, superposed on the modulation-doped multiple quantum well structure layers). The Zn diffusion coefficient in the modulation-doped region was less than 7 x 10-18cm2/s. The maximum Zn concentration, for obtaining a stable modulation-doping structure in the modulation-doped region of barrier layers, was found to be 2 x 1018/cm3. It was proposed that the suppression of interstitial Zn atoms, and of subsequently produced interstitial group-III atoms (which were generated in the p-type InP clad layer via a kick-out mechanism and diffused into the multiple quantum well region), was important in preserving the modulation-doped structure. Stability of Zn Doping Profile in Modulation-Doped Multiple Quantum Well Structure. N.Otsuka, M.Ishino, Y.Matsui: Journal of Applied Physics, 1996, 80[3], 1405-13