975-nm laser diodes (LDs) are of great demand as pumping sources for Yb-doped fiber lasers. They should provide high output power with high efficiency and good beam quality. In order to satisfy these requirements, the LD structure should be carefully designed. In this paper, we report the results of our investigation in which the influence of the LD emitter width on the maximum output power, power-conversion efficiency (PCE) and beam parameter product (BPP) are analyzed with self-consistent electro-thermal-optical simulation of LDs. In order to establish the accuracy of our simulation, we carefully determine the numerical values of key LD parameters by fitting the simulation results to the measured results for a fabricated 975-nm LD. The device has 15-nm-thick tensile-strained InGaAsP single quantum well with asymmetric AlGaAs separate confinement heterostructure layers, 90-μm wide ridge, and 4-mm long cavity. With the parameter values obtained, LDs having various emitter widths are simulated and their maximum output powers, PCEs, and BPPs are determined as well as the temperature profiles inside the device. The results show that the device with the smaller emitter width has both of thermal roll-over, thermal blooming at the lower output power, mostly due to higher series resistance. However, it provides better BPP. These results are useful for optimizing LD array structures so that the optimal structure for each array element can be determined that can provide the highest possible output power with the best BPP.