Band discontinuity reduction of i-GaInAsP/p-InP for improving 1.55 μm GaInAsP/InP surface emitting laser performances

The long wavelength GaInAsP/InP surface emitting (SE) laser is becoming important for use in optical fiber networks. We reported a low threshold GaInAsP/InP SE laser grown by chemical beam epitaxy (CBE) with some device characteristics. However, its temperature dependence on threshold and efficiency are inferior to those of short wavelength SE lasers. The auger process and intervalence band absorption were discussed as the primary causes of the worse temperature characteristic. In addition to these, the potential spike at the active layer and p-cladding hetero-interface may require an additional voltage bias to inject holes. Takemoto et al. proposed a band discontinuity reduction (BDR) layer to reduce the spike height. Kazarinov et al. Pointed out that this spike reduces a potential barrier for electron confinement in the active layer and increases an electron overflow to the p-cladding layer. A preliminary calculation shows the carrier overflow may degrade the performance of long wavelength SE lasers. In this study, we investigate the current-voltage characteristic of the hetero-interface and introduce a BDR layer which has an intermediate composition between the active layer and the p-cladding layer in order to improve the temperature characteristic of long wavelength SE lasers