To obtain a small droop, which is the ratio of transient reduction of output power after the laser diode (LD) is turned on, the influence of quantum efficiency and transient thermal flow of laser diodes is investigated both theoretically and experimentally. The analysis shows that as the thermal resistance between active region and heatsink is decreased and the reflectivity of front facet is increased, the droop decreases. The results are applied to self-aligned structures with bent active layer laser diodes (SBA LD's). By employing a junction-down configuration for assembly of the SBA laser chips and silicon carbide (SiC) as a submount material, and by coating the front facet so as to have reflectivity of 50% with taking into reduction of catastrophic optical damage (COD) level, the droop is decreased to 7.0%. In contrast, in the conventional SBA LD's which have a junction-up configuration with silicon (Si) as the submount material and have only a passivation coating on the front facet, value of the droop is 17.5%. Our results serve as a guide to the design of the light source of laser beam printers (LBP's).