Light Hole Related Transitions Research Articles

Growth of wurtzite CdTe nanowires on fluorine-doped tin oxide glass substrates and room-temperature bandgap parameter determination

The growth of CdTe nanowires, catalyzed by Sn, was achieved on fluorine-doped tin oxide glass by physical vapor transport. CdTe nanowires grew along the 〈0001〉 direction, with a very rare and phase-pure wurtzite structure, at 290 °C. CdTe nanowires grew under Te-limited conditions by forming SnTe nanostructures in the catalysts and the wurtzite structure was energetically favored. By polarization-dependent and power-dependent micro-photoluminescence measurements of individual nanowires, heavy and light hole-related transitions could be differentiated, and the fundamental bandgap of wurtzite CdTe at room temperature was determined to be 1.562 eV, which was 52 meV higher than that of zinc-blende CdTe. From the analysis of doublet photoluminescence spectra, the valence band splitting energy between heavy hole and light hole bands was estimated to be 43 meV.

Strong quantum-confined Stark effect from light hole related direct-gap transitions in Ge quantum wells

A strong quantum-confined Stark effect (QCSE) from light hole related transitions at the Γ point (LH1-cΓ1) in Ge/Si0.15Ge0.85 multiple quantum wells is demonstrated from both photocurrent and optical transmission measurements. Our experimental results show a large and sharp optical absorption peak due to LH1-cΓ1 transitions, and its associated strong absorption change based on the QCSE. By exploiting LH1-cΓ1 transitions, optical modulators with improved compactness and competitive extinction ratio and optical loss can be envisioned for low energy chip-scale optical interconnect applications.

Optical characteristics of lowly strained GaInAs quantum dots

AbstractWe have investigated the optical properties of lowly strained GaInAs quantum dots (QDs). The structures were grown for a constant nominal GaInAs layer thickness but varying content (strain) from below to far above the critical thickness conditions. In order to investigate the properties of such an uncommon QD system, photoreflectance (PR) and photoluminescence, combined with scanning electron microscopy, have been used. Optical transitions connected with the ternary layer have been observed and followed from the lowest content quantum well case through the transformation into 3D islands on the wetting layer (WL) and a coexistence of the QD‐related and WL‐related transitions. Due to the observation of both heavy hole and light hole related transitions in PR spectra, the thickness of the wetting layer versus changed indium content could be determined by comparing the experimental data with the results of the effective mass envelope function calculations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical properties of low-strained InxGa1−xAs∕GaAs quantum dot structures at the two-dimensional–three-dimensional growth transition

In x Ga 1 − x As ∕ Ga As quantum dots (QDs) were grown by solid source molecular beam epitaxy for indium contents of around 30%, which assures the QD growth in the very low strain limit. The structures were fabricated for a constant nominal InxGa1−xAs layer thickness but varying content (strain) from below to far above the critical thickness conditions, which has allowed to detect the onset of three-dimensional island formation and their evolution with the increasing material amount (for higher In contents the critical thickness for island formation is smaller and hence a larger fraction of the InxGa1−xAs layer is spent on dot formation). In order to investigate the properties of such an uncommon QD system, photoreflectance and photoluminescence, combined with scanning electron microscopy, have been used. Optical transitions connected with the ternary layer have been observed and followed from the lowest content quantum well case through the transformation into three-dimensional islands on the wetting layer (WL) and a coexistence of the QD-related and WL-related transitions. Due to the observation of both heavy hole and light hole related transitions in photoreflectance spectra, the thickness of the wetting layer versus changed indium content could be determined, comparing the experimental data with the results of the effective mass envelope function calculations.

Optical properties of ZnMnSe heteroepitaxial layers

Zn1−xMnxSe heteroepitaxial layers were grown on GaAs (001) substrates by MBE for Mn compositon x = 0–0.2. Elastic lattice strain in the grown layer was measured by X-ray diffraction. The heteroepitaxial layers were partially relaxed. Excitonic photoluminescence (PL) peak energy was corrected for the energy gap shift due to the lattice strain, and the peak energy in the strain free condition was obtained as a function of Mn composition. Magnetic field depencences of PL and reflection spectra were measured for B = 0–2 T. Heavy hole related and light hole related transitions were observed in the reflection spectra, and the heavy and light hole splitting was in agreement with that expected from the lattice strain. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of GaP / InGaP and GaP / GaAsP strained-layer quantum wells grown by metalorganic chemical vapor deposition

GaP/InGaP and GaP/GaAsP strained-layer quantum well (QW) structures with 3.0–5.0 nm thick well layers in the direct gap region were grown on GaP substrates by metalorganic chemical vapor deposition (MOCVD) using triethylgallium (TEGa) and ethyldimethylindium (EDMIn) for the column III sources and 100% AsH 3 and PH 3 for the column V sources. The strained QW structures were characterized using TEM and 4.2 K photoluminescence (PL). Transmission electron microscope (TEM) images indicate that the structures are uniform with sharp, defect-free interfaces. The QW layers are clearly resolved and appear to be free of misfit dislocations or other defects. The InGaP QW structures exhibit improved 4.2 K PL linewidths and a shift of the peak energies to shorter wavelengths compared to InGaP bulk layers of the same compositions. The GaAsP QW structures also exhibit sharp PL emission linewidths. The band alignments for the GaP/InGaP and GaP/GaAsP strained heterojunctions were calculated using local-density-functional pseudopotential formalism and the model-solid approach. Optical transition energies between the conduction band and valence subbands at the Γ point were calculated for the InGaP and GaAsP strained QWs, taking into account both the strain-modified band structures and quantum confinement effects. By employing the results derived from the theoretical predictions, we show that the 4.2 K PL spectra of the InGaP strained wells exhibit both the n = 1 heavy-hole and light-hole related transitions. We also show that the degree of removal of valence band degeneracy can be determined from the PL spectra.