Raman scattering and infrared absorption in bulk amorphous red phosphorous

Raman scattering and infrared absorption measurements in bulk amorphous red P indicate considerable spectral detail for an elemental amorphous solid, including a distinct separation of acoustic and lower lying optic-like bands. The results suggest appreciable structural correlations and weak interlayer-like bonding. Increased covalency of amorphous red P relative to amorphous As is indicated.     

Electromodulation spectroscopy of confined systems

The convolution formalism of Aspnes and Rowe for the dielectric function in the presence of an electric field is applied to electromodulation spectroscopy of confined systems. It is shown that for isolated confined systems where excitonic effects are not important, electromodulation spectroscopy leads to first derivative like optical features of two dimensional critical points. For superlattices in weak fields (neglecting excitonic interactions), the familiar third derivative forms of Aspnes and Rowe are applicable. In contrast, when moderate and high electric fields are applied to superlattices, electromodulation spectroscopy will exhibit optical features characteristic of first derivative line shapes. This phenomenon arises because the electric field causes the envelope functions of the electron and hole states to become spatially localized. The importance of excitons and their inhomogeneous broadening to the experimentally observed line shapes are considered.     

Structure of III-Sb(001) growth surfaces: the role of heterodimers

We have determined the structure of AlSb and GaSb (001) surfaces prepared by molecular beam epitaxy under typical Sb-rich device growth conditions. Within the range of flux and temperature where the diffraction pattern is nominally (1x3), we find that there are actually three distinct, stable (4x3) surface reconstructions. The three structures differ from any previously proposed for these growth conditions, with two of the reconstructions incorporating mixed III-V dimers within the Sb surface layer. These heterodimers appear to play an important role in island nucleation and growth.     

Far infrared absorption in bulk amorphous red phosphorous

Far infrared absorption measurements have been performed above 30 cm^?1 in bulk amorphous red P at 300 K. A number of low frequency spectral features are observed that are not present in the corresponding bulk amorphous As spectrum. Deep minima observed at 163 and 320 cm^?1 in α(ω) and in the Raman spectra suggest that the phonon density of states is essentially divided into 3 bands. A calculation of the mean effective charge of the bands indicates weak coupling to the lowest frequency band. A comparison with the results in a-As suggests a less rapid frequency variation in the infrared coupling parameter at low frequencies in a-$\text{P}$.     

Hydrogenic donors in doping superlattices: A model calculation

The binding energy and wavefunction of a hydrogenic donor in an effective potential ν(z) = ∣e∣?∣z∣ in a semicondusctor is calculated variationally as a function of the effective electric field ?. Such a potential represents the limit of a doping superlattice in which the donor doping layer is very thin, and it allows the properties of shallow donor states for which the effective potential varies substantially across the wavefunction to be discussed. It is found that substantial variations of the binding energy and wavefunction result for fields which are readily realizable experimentally.     

Hole intersubband transitions in GaAs/AlGaAs multiple quantum wells… A new method for determining the Luttinger parameters

Resonant electronic Raman scattering from photoexcited holes has been observed for multiple quantum wells (MQW's) grown in the [111]b and [100] directions. The measurements indicate that the heavy hole mass in the [111] direction is 0.75mo. This value is 2.2 times larger than the value characteristics of the [100] direction. The measurements also quantify the degree of anisotropy for the light holes. We propose a new set of Luttinger parameters that describe the anisotropy of the valence band in GaAs and are consistent with the interband and intersubband transitions observed in [100] and [111]b MQW's.