Figures

Figure 1

Schematic picture of the multiple quantum well sample structure used for this work.

Figure 2a

Photoluminescence topograph at 300 K of the total emission from an InGaN/GaN MQW sample with the InGaN growth temperature 700 °C. Note that the laser spot has a Gaussian intensity profil. Intensity fluctuations on a length scale of a few µm are observed.

Figure 2b

The same type of data at 300 K for an InGaN/GaN MQW sample with the InGaN growth temperature at 780 °C. The length scale of intensity fluctuations is now smaller, but still resolved

Figure 2c

Monochromatic cathodoluminescence topograph at 6 K from an InGaN/GaN MQW sample with the InGaN growth temperature at 700 °C. Again intensity fluctuations over a length scale of about 1 µm are observed.

Figure 3

Stationary PL spectra at 2 K of two coherently strained thick In0.15Ga0.85N epilayers grown on sapphire at the temperatures indicated: (a) left panel, 700 °C, (0.06 µm thick layer) (b) right panel, 780 °C (0.10 µm thick layer). Note that the presence of a spectral contribution at lower photon energies in (b) indicates some segregation.

Figure 3c

In (c) are shown two PLE spectra for the same sample as in (b), detected at two different photon energies. The PL spectrum obtained with low intensity lamp excitation is also shown.

Figure 4

PL transient response at 2 K of the PL peak for the sample in Figure 3 (a). Note the welldefined radiative lifetime of 0.85 ns.

Figure 5

Stationary PL spectra as well as PLE spectra at 2 K of two coherently strained and nominally undoped In0.15Ga0.85N/GaN MQWs grown on sapphire with the InGaN layer growth temperatures indicated: (a) left panel, 700 °C, (b) right panel, 780 °C. The spectra are obtained with low intensity excitation employing a Xe lamp. The PL signal at lower photon energies is very weak in both cases. The PLE spectra are obtained with detection at the peak of the PL signal.

Figure 5c

In Fig 5 (c) is shown the dependence of the peak position on the excitation intensity for the same sample as in 5 (b).

Figure 6

Stationary PL spectra at 2 K of three coherently strained In0.15Ga0.85N/GaN MQWs grown on sapphire at 700 °C. Sample 1 is nominally undoped, but has a background Si donor doping of about 1 x 1017 cm-3 in the well. The other two samples are Si-doped in the wells, to a density of about 4 x 1017 cm-3for sample 2 and about 2 x 1018 cm-3 for sample 3. The GaN barriers are not Si-doped.

Figure 7

Streak camera panel at 2 K for the same MQW sample as in Figure 5 (a), obtained with fs pulse excitation at about 3.2 eV. Each transient is marked with the corresponding PL emission wavelength (in Å units). Note the short rise time across the whole broad PL spectrum.

Figure 8

Timeresolved PL spectra for two MQW samples obtained at 2 K with excitation at 3.6 eV. The time interval between each spectrum is 0.8 ns. In (a) left panel, are shown spectra for the undoped sample D1 in Figure 6, and in (b) right panel, are shown corresponding data for the doped sample D3 in Figure 6. Note the strong spectral shift between the two samples.

Figure 9

Decay curves at different photon energies within the broad PL peak, obtained at 2 K with excitation at 3.2 eV for the same MQW samples at in Figure 5 (b). In (a) left panel, is shown the intermediate time regime, on the right panel (b) is shown the long time behavior.

Figure 10

Timeresolved PL spectra for an MQW sample with the InGaN layer grown at 700 °C, obtained at 2 K, left panel (a) and at 300 K, right panel (b), respectively, and with excitation at 3.2 eV. The 300 K spectra are broadened towards higher energy, and also have shorter decay time.

Figure 11

Effective decay times for the same two MQW samples as in Figure 5 (a), left panel, and (b), right panel, respectively. The data are shown for 3 different measurement temperatures, 2K, 100 K, and 300 K, and for a number of different wavelengths across the broad PL emission. The excitation wavelength is about 3.2 eV.

Figure 12

(a). The screening effect on a gaussian potential of width 100 Å in one of the quantum wells. The dotted curve is the bare potential. The dash-dotted, dashed, full and dash-triple-dotted curves are for the carrier concentrations 2x1017 cm-3, 4x1017 cm-3, 2x1018 cm-3 and 1x1019 cm-3, respectively. All curves have been scaled to the value at the center of the unscreened potential. We have plotted the potentials with reverted sign to get the impression of a potential well. The screened potentials have Friedel oscillations at large separations. (b). The well depths of screened gaussian potentials for different carrier concentrations, indicated in the figure, as functions of potential width.

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