In this article, we report the fabrication and analysis of 1.3 mum InAsP multiquantum well laser diodes (MQW LDs) with the n-type modulation-doped (MD) InAsP/InP/InGaP active region grown by metalorganic chemical vapor deposition. We theoretically analyze the threshold current density, differential quantum efficiency, internal quantum efficiency, and internal optical loss as a function of thickness and doping concentration of n-type Si-doped InGaP barrier and InP intermediate layer for the 1.3 mum MD-MQW LDs. The optimum thickness is 2 nm for the n-type doped barrier and 6.2 nm for the doped intermediate layer while remaining 4.4-nm-thick undoped in the InP intermediate layer to prevent from lateral diffusion of Si-doped atoms into the InAsP well. Besides, the optimum doping concentration of doped InGaP barrier and doped InP intermediate layer is 1 x 10(18) cm(-3). With these optimum conditions, the LDs will reduce the threshold current density and threshold gain to 0.8 kA/cm(2) and 43.08 cm(-1) as compared to those of 1.6 kA/cm(2) and 44.1 cm(-1) for the undoped active region, respectively. (C) 2002 American Vacuum Society.