An extremely low-threshold current of 6 mA in cw mode at 22 °C was achieved in 1.55-μm InGaAsP/InP buried heterostructure distributed feedback lasers with a first-order grating and a normal cavity length of 300 μm. These lasers exhibited an average differential efficiency of 30% total at 4 mW without any coating on the facets, and a T0 (25–70 °C) value of 55 K. A spectral linewidth as low as 8 MHz at cw mode was obtained. The lasers showed high-speed pulse modulation response to 2.4 Gb/s (NRZ).
Negative-electron-affinity (NEA) GaAs/GaP photocathodes have been grown by MBE for the first time. The surfaces of GaAs emitters are atomically smooth. The compositionally graded interface layer GaAsP produced by infer-diffusion at the GaAs/GaP interface has played an important role for a high photoemissive quantum yield and for the spectral response curves of photoemission from the thin GaAs layers.
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