(Color online) Electron microscope images of the sample under investigation. (a) SEM micrograph of the as-grown GaN nanocolumns. (b) Plan view SEM micrograph showing the columns and compact regions. (c) SEM micrograph showing the cross section of a single hexagonal GaN nanocolumn. (d) Histogram detailing the size distribution of the nanocolumns.
(Color online) (a) A TEM image of the tip of a single GaN nanocolumn. (b) A simulation of the distribution of hydrostatic strain in a cross section through the column. (c) The strain distribution () in the region of the QDisk.
(Color online) CL emission spectrum from an ensemble of QDisk-containing nanocolumns recorded at 90 K with an accelerating voltage of 10 kV. μPL spectra from the same sample recorded at 4.2 K and 90 K are shown for comparison.
(Color online) The emission from the GaN (left), defect (middle), and QDisk (right) superimposed on a SEM micrograph of the felled nanocolumns. In contrast to the GaN and defect emission, the QDisk emission is highly spatially localized and originates near the tips of the columns.
(Color online) (a) Time-integrated spectra from the as-grown nanocolumns at temperatures from 4–70 K. (b) Time-resolved studies showing a sudden decrease in lifetime for temperatures T > 20 K.
(Color online) (a) InGaN QDisk emission as a function of excitation power. The inset shows the QDisk emission peak position with increasing excitation. The fit to the curve is quadratic and has been used to estimate the indium mole fraction. (b) A log-log plot of QDisk and GaN emission intensities.
(Color online) (a) Low excitation power (3.82 kWcm−2), and (b) high excitation power (12.73 kWcm−2) emission spectra from the nanocolumn as a function of time. Under high excitation power the QDisk emission peak is observed to dynamically return to that which is observed in the low excitation power regime.
(Color online) The luminescence intensity as a function of emission energy and time at an excitation power of 12.73 kWcm−2. The emission energy is observed to shift during the process of the decay.
(Color online) The decay spectrum at different times (recreated from the data in Fig. 8). The emission peak broadens as it shifts to lower energy due to the QCSE from the internal field.
(Color online) (a) A selection of spectra showing QDisk emissions labeled with their low power excitation lifetimes. (b) A selection of decay traces showing the monoexponential decay nature of the emission. (c) Emission lifetime against the linear gradient of the shift.
(Color online) (a) The emission in the region of 3.4 – 3.43 eV measured at 4.2 K and with an excitation power of 4.1 kWcm−2. A structure in the emission is clearly visible. (b) Log plot of the emission intensity with excitation power from another part of the same sample where the structure is less apparent. A blueshift of the emission with increasing excitation is observed.
(Color online) Normalized time-resolved decays from the GaN emission at 3.475 eV and the defect emission at 3.417 eV measured with an excitation power of 12.73 kWcm−2.
(Color online) The luminescence intensity as a function of emission energy and time at an excitation power of 12.73 kWcm−2. In contrast to the InGaN QDisk emission, the defect emission does not dynamically shift with time.
Article metrics loading...
Full text loading...