An InGaAsP-InP transistor laser (TL) at 1.55 microm has been designed and modeled. The proposed TL has a deep-ridge waveguide structure with the multiple quantum wells (MQWs) buried in the base-emitter junction, which provides good optical and electrical confinement and can effectively reduce the optical absorption and lateral leakage current. Good laser performance has been predicted by numerical modeling based on which the epitaxial growth was carried out by metalorganic chemical vapor deposition (MOCVD). The effect of p-dopant (Zn) diffusion on the QW performance was investigated by a re-growth procedure. By introducing a graded p-doping profile, the Zn diffusion into the MQWs was effectively controlled. With an average doping density of 1 x 10(18) cm(-3) in the base contact layer, the InGaAsP MQWs demonstrated high PL intensity at 1.51 microm and clear satellite diffraction peaks in the XRD spectrum.