Quantum dot microdisk lasers

Quantum dots (QDs) in semiconductor microcavities are an invaluable tool for investigating cavity quantum electrodynamics, and also may lead to novel optical and opto-electronic devices. It has been successfully demonstrated that these QD microcavities have a great potential of playing a key role in realizing quantum cryptography and quantum computing. In this thesis, another potential application of QD for ultra-low threshold lasers has been investigated by fabricating QDs in microdisk cavity structures—both optically and electrically.; Record high quality-factor (Q ∼ 18,000) whispering gallery mode (WGM) QD microdisk cavities are fabricated using wet chemical etching. Defect-free self-assembled InGaAs quantum dots are formed spontaneously by molecular beam epitaxy on a GaAs surface via Stranski-Krastanov growth transition. Two layers of InGaAs QDs are chosen as gain material embedded within the microdisk. Optically pumped continuous-wave lasing from QDs in 1.5∼8 μm microdisk laser structures are reported. The microdisk emission spectra show lasing in 1∼5 well separated modes in the wavelength range between 900 and 990 nm. The estimated threshold pump densities are between 20 and 200 W/cm2.; QD microdisk injection lasers are further realized by introducing a double-disk structure that separates the active disk layer from the metal contact, and by implementing a new metal air-bridge contact to the top-contact disk. Single mode continuous-wave lasing around 920∼936 nm from QDs in ∼4 μm diameter microdisks is presented. The threshold current of this device was as low as 40∼69 μA. The estimated spontaneous emission factor is >0.05. At high injection level, the low threshold mode saturated and another shorter wavelength mode started lasing. We observed the blue-shift of QDs electroluminescence due to QD bandfilling effect and red-shift of the lasing modes due to thermal heating.