Heterointerface flatness and abruptness of GaAs/AlGaAs quantum wells are controlled during metalorganic vapor phase epitaxy (MOVPE). Various growth modes such as two-dimensional (2D) nucleation, step flow, and step bunching are achieved by changing the growth temperature and substrate surface misorientation angle. The degree of monolayer step smoothness and ordering are also changed. The effects of these nanometer-scale morphologies and interface abruptness on the full width at half maximum (FWHM) of 4.2-K photoluminescence spectra from quantum wells (QWs) are individually determined. The FWHM is increased in order by degraded interface abruptness, step roughness, multisteps, and 2D islands. Effective thickness variations introduced by these features are roughly >2.0, 1.0, 0.6, and 0.2 monolayers (ML), respectively, for 7-ML-thick QWs. Some of these effects on current-voltage characteristics of double barrier resonant tunneling diodes (DBRTDs) are also investigated. The factor most strongly affecting the characteristics of DBRTDs is step disordering, that is, a difference in step edge location between the top and the bottom surfaces of barriers. By making this difference smaller than the electron’s de Broglie wavelength using vicinal substrates, we obtain the best negative resistance characteristics ever reported for MOVPE growth.