Photoreflectance studies of (Al, Ga)As/GaAs heterostructures and devices

Abstract

Dedicated to Professor Dr. K. U ' . BOER on the occasion of his 70th birthday Experimental and theoretical PR spectra are reported for (AlGa)As/GaAs single heterostructures, (AlGa)As/GaAs quantum well structures as well as MESFET and HEMT structures. The theoretical spectra are calculated by means of a novel technique which combines the two methods previously used for spatially inhomogeneous systems : the transfer matrix method for light propagation between different layers, and perturbation theory for light propagation within each weakly inhoinogeneous layer. The electric field distribution is calculated from an integral equation which holds under quite general conditions including incomplete dopant ionizations and carrier degeneracies. In most of the spectra, pronounced interference effects show up. Due to them, P R spectra from qiiantum wells are sensitive to the well distance from the surface. Besides interference effects, field inhomogeneities like broadening of Franz-Keldysh oscillations manifest themselves in the reported spectra. A controversy in the literature concerning PR spectra from (AlGa)As/GaAs single heterostructures is solved by means of the novel calculation technique.

Photoreflectance spectra from GaAs HEMT structures reinvestigated: solution of an old controversy

“…Below, we employ this approximation. The first task, the calculation of the field profile without light, is solved here as in our previous work [32][33][34]. We assume a Cartesian coordinate systems with the z axis perpendicular to the sample surface.…”

“…Since our conclusions on the origin of the SPOs depend on the overall behaviour of the potential and field profiles, rather than on the details of the well region, the quasi-classical approximation is justified here. The reflectance spectra are calculated by means of the method proposed in [32][33][34]. This method applies to heterostructures with weak optical inhomogeneities in each layer.…”

Effects of symmetry breaking in low dimensional materials

“…The presence of surface and interface states give rise to electrical potential profiles at the surface, which are located within the gap region, between the CB and VB. The surface states may arise due to either surface contamination, or imperfections at the surface, or due to dangling bonds associated with incomplete covalent bonding [35,36,37]. The surface breaks the translational symmetry of the perfect crystal, thus leading to the appearance of the known Tamm levels [38,39].…”

“…and c 0 =6.69• A for the AB system, and a 0 =2.and c 0 =6.for the AA system. The intralayer distance (C-C bond lengths) are on the order of 1.in both stacking environments, and the interlayer distance was calculated to be 3 35. …”