Interface phonons in InAs and AlAs quantum dot structures

We present an experimental study of $\mathrm{In}\mathrm{As}∕\mathrm{Al}\mathrm{As}\left(\mathrm{Ga}\mathrm{As}\right)$ periodical structures with InAs and AlAs quantum dots by means of Raman spectroscopy. Experiments on the asymmetric $\mathrm{Ga}\mathrm{As}∕\mathrm{In}\mathrm{As}∕\mathrm{Al}\mathrm{As}$ quantum dot structures allowed us to investigate the interface phonons localized in the vicinity of corrugated dot/matrix interface and planar interface between the matrix and wetting layer. The interface phonon frequencies in the quantum dot structures determined from the experiment are compared to those calculated in the framework of the dielectric continuum model. A good agreement is obtained, especially if the preferential shape of the quantum dots determined from transmission electron microscopy is taken into account.

Figure 1

Cross-sectional TEM images of samples with (a) AlAs (sample A) and (b) InAs QDs (sample ${\mathrm{B}}^{\prime }$). HRTEM images are shown in the insets.

Figure 2

Raman spectra of sample A at $T=80\mathrm{K}$ measured in the $y^{\prime }(x^{\prime },x^{\prime })\overline{y^{\prime }}$ and $y^{\prime }(z,x^{\prime })\overline{y^{\prime }}$ scattering geometries excited by the $514.5\mathrm{nm}$ laser line. Closed and open triangles show the frequency positions of the IF phonons calculated for ellipsoidal and spherical QDs, respectively.

Figure 3

Raman spectra of samples B, C, and D at $T=20\mathrm{K}$ measured with the $647.1\mathrm{nm}$ laser line in the $z(x,x)\overline{z}$ and $z(y,x)\overline{z}$ (dashed lines) scattering geometries in the spectral regions of GaAs, InAs (a) and AlAs (b). Raman spectra of samples ${\mathrm{C}}^{\prime }$ and ${\mathrm{D}}^{\prime }$ measured in the $z(x,x)\overline{x}$ scattering geometries are shown for comparison. For samples B and D, the experimental spectra are shown by open circles, and thin solid lines represent the results of fitting by Lorentzian curves. Closed triangles show the calculated frequency positions of the IF phonons for QDs with the shape of oblate capsules. Horizontal bars show the calculated positions of interface phonon bands for planar interfaces in $\mathrm{Al}\mathrm{As}∕\mathrm{In}\mathrm{As}$ superlattices. Dashed-dotted lines are guides to the eye.