The authors report on fabricating and characterizing a 1.3-mu m Ga0.11In0.89As0.24P0.76/ Ga0.27In0.73As0.67P0.33 compressive-strain multiple, quantum well with n-type modulation-doped GaInP intermediate-barrier laser diodes (LDs). The barrier region contains a 20 angstrom Si-doped modulation-doped GaInP intermediate layer and two 40 angstrom undoped Ga0.11In0.89As0.24P0.76 surrounding layers. The modulation-doped GaInP intermediate barrier can increase the optical gain by the modulated-electron Fermi-Dirac distribution function, and stop the electron overflow by the inherent barrier height. The surrounding layer serves as a buffer layer to prevent the overflow of Si dopant into the well; but it also alleviates the tensile strain of the modulation-doped GaInP,intermediate barrier to maintain a compressive-strain quantum well. We measured the threshold current density, differential quantum efficiency, internal quantum efficiency, and internal optical loss as a function of cavity length and doping concentration of the modulation-doped GaInP intermediate barrier. The theoretical and experimental results show that the optimal doping concentration of the modulation-doped GaInP intermediate barrier is 3 x 10(18) cm(-3). With this optimal condition, the 4 Am ridge-stripe and 600 Am cavity LDs without facet coating will exhibit the best performance, including a lower threshold current of 29 mA, a higher slope efficiency of 0.215 W/A, a higher characteristic temperature of 87.6 K, and a wavelength swing of 0.28 nm/K for the LDs operated in a temperature range of 10- 80 degrees C under continuous-wave operation. (c) 2007 American Vacuum Society.