Static and dynamic spectroscopy of $(\mathrm{Al},\mathrm{Ga})\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ microdisk lasers with interface fluctuation quantum dots

We have studied the steady state and dynamic optical properties of semiconductor microdisk lasers whose active region contains interface fluctuation quantum dots in $\mathrm{Ga}\mathrm{As}∕(\mathrm{Ga},\mathrm{Al})\mathrm{As}$ quantum wells. Steady-state measurements of the stimulated emission via whispering gallery modes yield a quality factor $Q\sim 5600$ and a coupling constant $\beta \sim 0.09$. The broad gain spectrum produces mode hopping between spectrally adjacent whispering gallery modes as a function of temperature and excitation power. Time- and energy-resolved photoluminescence measurements show that the emission rise and decay rates increase significantly with excitation power. Marked differences are observed between the radiative decay rates in processed and unprocessed samples.

Figure 1

(a) Microphotoluminescence measurements carried out on unpatterned samples through a $1\mu \mathrm{m}$ diameter gold aperture. Resolution-limited spectral features characteristic of QD states $(\mathrm{FWHM}⩽200\mu \mathrm{eV})$ are only seen in the sample with growth interruptions. (b) SEM image of microdisk laser structure. (c) Excitation power dependence of the emission spectrum of a single microdisk at $T=5.8\mathrm{K}$. The inset shows the polarization-resolved far field emission from the side of a single microdisk. The top and the bottom spectra are polarization parallel and perpendicular to the disk plane. (d) Intensity of the stimulated emission (mode ${\mathrm{TE}}_{35,1}$) and spontaneous emission vs pump power, respectively.

Figure 2

(a) Power dependence of lasing intensity plotted on a log-log scale. The arrow indicates the laser threshold. Solid curves are based on Eq. (1) with coupling constant $\beta =1,0.1,0.01$. (b) Power dependence of the energy (open circles) and width (solid circles) of the lasing mode. (c) Temperature dependence of microdisk emission spectrum, showing mode hopping between the ${\mathrm{TE}}_{35,1}$ (circle), ${\mathrm{TE}}_{30,2}$ (triangle), and ${\mathrm{TE}}_{26,3}$ (star) WGMs. (d) Pump power dependence of microdisk emission spectra at a sample mount temperature of $T=5\mathrm{K}$.

Figure 3

(a) Temporal evolution of microdisk emission at $1.615\mathrm{eV}$. Data at different pump intensities (indicated next to each spectrum) have been normalized and vertically shifted for clarity. The zero of time is fixed at the arrival of the excitation laser pulse (tuned to $1.676\mathrm{eV}$). (b) Power dependence of decay and delay times. Decay time, defined as the $(1∕e)\text{th}$ time constant of the decay tail, is determined from exponential fits to the data. Delay time is defined as the interval between the peaks of the excitation and microdisk emission pulses [arrow in (a)]. Both show a marked decrease with increasing pump power. (c) The unprocessed part of the sample does not show any noticeable changes in either the pulse width or the delay time as input power is increased. All data in (a)–(c) are taken at $5\mathrm{K}$.