Modulation-Doped Multi-Quantum Well (MD-MQW) Lasers. II. Experiment

Detailed experimental results on p-type modulation-doped multi-quantum well (MD-MQW) lasers are discussed. The GaAs/GaAlAs MD-MQW laser was grown by low temperature (600°C) molecular beam epitaxy using Be as the p-type dopant. The realization of the p-type MD-MQW structure was fully confirmed by high resolution secondary ion mass spectroscopy, transmission electron microscopy, and photoluminescence measurement. An ultrahigh relaxation oscillation frequency of up to 30 GHz was realized, which is 2.5 times that of undoped MQW lasers and also 5 times that of double heterostructure lasers. In addition, the spectral chirping width of p-type MD-MQW lasers was experimentally confirmed to be 1/5 that of undoped MQW lasers. These improvements result from the enhancement of the differential gain due to the modulation doping effect in addition to the quantum size effect. These results are in good agreement with the theoretical analyis.