We have studied the dopant redistribution between a chemical beam epitaxy (CBE) grown InGaAsP laser structure and a metalorganic vapor phase epitaxy overgrown InP layer. Secondary ion mass spectroscopy analysis reveals that Zn and Be atoms deeply interdiffuse in the adjacent InP layers for a Zn doping of1018 cm−3and that a fraction of Zn atoms go through the CBE InP and penetrate the laser structure guide layer. We have found that the Zn outdiffusion is significantly suppressed by reducing the Be doping concentration from1018to5×1017 cm−3.As a result, for tensile-strained InGaAsP multiquantum well (MQW) buried-heterostructure (BH) lasers, the threshold current and internal loss decrease from 13 to 9 mA and 15 to10 cm−1by lowering the Be doping, respectively. InAsP MQW BH lasers have an internal loss of5.5 cm−1.©1997 American Institute of Physics.