Modulation properties and the phonon bottleneck in self-organized single and multilayer In_0.4Ga_0.6As/GaAs quantum dot room temperature lasers

The modulation bandwidth of various quantum well lasers has been reported to be limited by device heating, gain compression, multimode behaviour or the power handling capacity of the facet. While the effect of transport and carrier capture effects can be demonstrated in quantum well lasers, usually the maximum bandwidth due to carrier capture time is much higher than limits due to other factors and can be neglected. However, the capture times are predicted to be much longer in quantum dot lasers. Analysis of high frequency electrical impedance data shows that the capture times are about 30 ps in quantum dot lasers, compared to the 1-5 ps typical of quantum well lasers. This confirms theoretical predictions that the phonon bottleneck may be particularly severe in quantum dot lasers. Measurements on both single and multiple layer self organized In_0.4Ga_0.6As/GaAs quantum dot lasers show modulation bandwidths of 4-6 GHz, even though measured differential gains are extremely high (approximately 10^-14 cm²), and the gain compression limited bandwidths is 9 GHz. The typical capture time limited modulation bandwidth limit of 5 GHz is comparable to the maximum measured modulation bandwidth, which suggests that carrier capture may be significantly limiting the bandwidth in these devices.