Investigation of InAs single quantum wells buried in GaAs(001) using grazing incidence X-ray diffraction

InAs single quantum wells were grown by means of a low-pressure metal-organic chemical vapour deposition technique on GaAs(001). Their nominal thickness was varied among 0.7, 2, 3 and 4 monolayers and they were buried under a thick GaAs top layer. The samples were investigated by means of the grazing incidence X-ray diffraction using the weak (200) in-plane reflection. Depth resolution was obtained setting the angle of incidence and exit alpha i and alpha f, respectively, smaller or larger than the critical angle of total external reflection alpha c. Owing to the high sensitivity near the surface the collected rod scans show pronounced thickness oscillations for alpha i> alpha c. The thickness and the In-content, which control the scattering power of the single quantum wells were evaluated via simulation using the kinematic approach to X-ray diffraction. Partial relaxation occurs whenever the single quantum wells' thickness exceeds one monolayer. It is explained by the appearance of strain-reduced and non-tetragonally deformed islands built after the two- to three-dimensional transition of the growing mode

Extreme asymmetric X-ray Bragg reflection of semiconductor heterostructures near the edge of total external reflection

Synchrotron radiation has been used to measure the rocking curves from a (GaIn)(AsP) single layer grown on an InP (100)-oriented substrate. For angles of incidence $\Phi_B$ = ($\Theta_B$ - $\varphi$) $\leq$ 0.7° measured at the Bragg angle $\Theta_B$ ($\varphi$ is the angle between the diffracting lattice plane and the surface), the rocking curve (RC) is very strongly influenced by total external reflection (TER). This causes a decrease in the full width at half-maximum (FWHM) and an asymmetrical shape for the RC for small $Phi_B$. Both of these effects are due to the Bragg-angle shift from the actual incident angle $\Phi$ which is not considered in the conventional dynamical theory. In this paper the essential influence of TER on any thin-layer rocking curve is investigated using a numerical solution of the extended dynamical theory. The pattern can be interpreted up to $\Phi_B$ $\geq$ $\Theta_C$ ($\Theta_C$ is the angle of TER) by semiempirical incorporation of the results of the extended theory with the coupling formalism of Barrels, Hornstra & Lobeek [Acta Cryst. (1986). A42, 539-545]

Optical properties of ultrathin GaAs layers embedded in AlxGa1-xAs

We present a comparison between the predictions of two theoretical models and experimental results on ultrathin GaAs layers with a thickness in the range from 1 to 8 ML embedded in bulk (AlxGa1-x)As, 0.30 less than or equal to x less than or equal to 0.34. The theoretical predictions, obtained from an empirical tight-binding Green's-function approach and from the usual effective-mass approximation, are compared to photoluminescence and photoluminescence excitation data of a set of multiple quantum-well samples grown by metal-organic vapor-phase epitaxy on substrates with different misorientations. We find that the optical transitions are narrower in samples with slightly misoriented substrates, although their spectral position remains unchanged. This suggests that the substrate misorientation favors a good quality of the ternary alloy. The observed optical transitions of our thin layers compare well with the predictions of both models. However, the lack of a reliable exciton theory for such ultrathin layers becomes apparent