The modulation bandwidth of three-channel buried-crescent (TCBC) lasers was improved by reducing the ohmic contact resistance by adding a quaternary contact layer for the P-contact of the device. The ohmic resistance was reduced to 6–9 Ω, with a capacitance of 1.5–3 pF and an inductance of 1.5–2 nH. The small-signal 3 dB modulation frequency is 7.2 GHz at 2.5Ith, and is limited by the parasitic impedances of the device. Large-signal digital modulation of the laser was successfully achieved at 8 Gbit/s, which is the highest frequency for direct digital modulation yet reported.
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Koren et al. (1985) studied this question.