ALBERT

Notes: Multiple twinning in GaAs epitaxial layers grown on Si by metalorganic vapor phase epitaxy has been studied by transmission electron microscopy. The primary and multiple twin reflections in the diffraction patterns were indexed in terms of matrix indices for the electron beam parallel to the 〈001〉, 〈110〉, and 〈111〉 directions in GaAs.

Notes: In this study transmission electron microscopy (TEM), photoluminescence spectroscopy (PL), and electrochemical capacitance-voltage measurements were used to characterize undoped GaAs films, grown by organometallic vapor phase epitaxy on (001) Si substrates. TEM studies indicated that the high defect density (threading dislocations and microtwins), present close to the interfacial region, drops rapidly with distance away from the interface. PL studies also indicated an increase in PL intensity and significant narrowing of the full-width at half-maximum of the excitonic transition with an increase in layer thickness, indicating an improvement in the optical quality of the epilayers. Electrochemical capacitance-voltage measurements indicated a uniform carrier concentration (low to mid 1015 cm−3 range), which is among the lowest yet to be reported for GaAs/Si grown by organometallic vapor phase epitaxy.

Notes: Optical properties of Cu-rich CuInSe2 thin films prepared by the selenization of Cu/In/Cu alloys in a H2Se atmosphere have been studied by photoluminescence (PL) spectroscopy. PL spectra of as-grown samples were dominated by transitions due to intrinsic defect levels, which are ascribed to VIn (24 meV), CuIn (75 meV), and Cui (53 meV). After chemical etching (10% KCN), emission lines attributed to free and bound excitonic emissions and their LO phonon replica became visible. Accurate analysis of the peak positions revealed values of 4.3 meV, 1.0441 eV, and 28.7 meV for the binding energy of the free exciton, the band gap, and the value for the LO phonon, respectively. © 1997 American Institute of Physics.

Notes: In this study the material properties of metallic alloys were evaluated at different stages of reaction to H2Se/Ar. Precursors of identical composition (Cu/In atomic ratio=0.96) were considered and the temperature was rapidly (in 2 min) increased to the specific selenization temperature (i.e., 200, 300, 400, and 600 °C). The composition of the films remained virtually unchanged when selenized at low temperatures below 400 °C. The material properties of these films were dominated by the presence of binary phases and photoluminescence (PL) studies revealed the presence of only one broad transition around 0.83 eV. Structural analysis revealed a significant increase in the Cu/In atomic ratio with associated Cu-selenide secondary phases and inhomogeneous film morphologies in the case of samples selenized at temperatures around 400 °C. In this case, PL studies revealed relatively sharp and well-defined transitions which are typical for Cu-rich films. The most significant result that followed from this study is the vast improvement in the material quality of films rapidly heated and selenized at elevated temperatures above 400 °C. Scanning electron microscopy and x-ray diffraction studies revealed homogeneous and dense films with no evidence of secondary phases. Even more important, energy dispersive x-ray spectroscopy measurements indicated no change in the initial composition of samples selenized under these conditions (at temperatures above 400 °C while ramping the temperature in 2 min to the specific reaction temperature). The high material quality of these films was also confirmed by PL studies, revealing only one broad transition at 0.932 eV which is generally reported for device quality material. It is suggested that the rapid heating of samples and subsequent quick passage through the critical temperature range around 400 °C is responsible for the improved material properties of these selenized films. © 1998 American Institute of Physics.

Notes: Admittance spectroscopy was measured on Cu(In,Ga)(S,Se)2 thin film and single crystal heterojunctions. The emission rates of defects for various near-stoichiometric compositions follow a Meyer–Neldel rule, showing increasing attempt-to-escape frequencies with increasing defect depth. Defects in highly (In,Ga)-rich material showed lower attempt-to-escape frequencies and follow a separate Meyer–Neldel relation. Repetitive air annealing of a CuInSe2 heterojunction revealed a shift of the depth and capture cross section of an observed defect. © 1996 American Institute of Physics.

Notes: Abstract A fundamental understanding of the mechanism of growth of CuInSe2 is essential for the production of device quality material. In this contribution, the growth kinetics of thin film CuInSe2 are investigated in the special case of H2Se/Ar treated copper-indium metallic alloys. A systematic study was conducted in which the evolution of surface morphologies by scanning electron microscopy (SEM), formation of crystalline X-ray diffraction (XRD) and variation in film composition, energy dispersive spectrometry (EDS) were evaluated during various stages of selenization. SEM and XRD studies revealed a dramatic improvement in crystalline quality with increasing selenization temperature. SEM studies indicated a substantial increase in grain size (0.2μm → 1μm) when the reaction temperature was increased from 150 °C to 450 °C. XRD studies revealed the presence of mostly binary phases (i.e. Cu11In9, InSe, In6Se7 and CuSe) at selenization temperatures up to 250 °C. CuInSe2 was found to be the dominant phase at 350 °C and the film was almost completely converted to single phase material at 450 °C. The composition of the selenized films remained virtually unchanged in the temperature range between 150 °C and 350 °C. However, reaction of the metallic alloys to H2Se/Ar at temperatures around 450 °C resulted in a significant loss of indium from the films and subsequently to an increase in the Cu/In atomic ratio. The variation in crystalline quality of the films during various stages of selenization was also clearly reflected by low temperature photoluminescence (PL) studies. Virtually no PL response was detected from samples selenized at low temperatures below 350 °C, compared to rather strong emissions from samples selenized at higher temperatures around 450 °C. Furthermore, a significant difference in PL response was detected from samples selenized at 350 °C and 450 °C, respectively. Comparative studies indicated the presence of a free-to-bound transition (at 0.992 eV) only in the case of samples selenized at 450 °C, which indicated that these specific point defects (Vln) are created at high selenization temperatures. This observation is consistent with EDS results, indicating a substantial loss of In from samples selenized in this high temperature range. PL spectra from samples selenized at 350 °C were also characterized by a broad peak close to the band gap value, which was attributed to the presence of point defects associated with In-rich secondary phases. The improvement in crystalline quality with increased selenization temperatures and reaction periods was also clearly reflected by the reduction in the FWHM values of the PL peaks. The information gained from this study played an important role in the production of high quality films in our laboratories.

Notes: Abstract The nucleation and growth of Ge on Si(111) substrates were investigated by transmission electron microscopy (TEM). It was found that growth is initiated by the formation of three-dimensional islands. At a very early stage of growth a polycrystalline layer was obtained. The orientation of this Ge film, however, improved as growth proceeded, resulting in an epitaxial film when the islands were fully coalesced. It was found that the major defects present in the Ge epilayer were microtwins (primary and secondary twins) occurring on the inclined {111} planes of Ge.

Notes: Abstract The nucleation and growth of AIGaAs on (0 0 1) Si substrates were investigated by transmission electron microscopy (TEM). It was found that the growth temperature, growth time and V/III ratio are important parameters determining the quality of the AIGaAs nucleation layers. Decreases in the growth temperature resulted in decreases in the island size and separation, while the density increased. TEM studies also revealed that the AIGaAs islands formed under low As4 overpressures were flatter and had higher initial densities than those grown under high As4 overpressures. The major defects present in the AIGaAs nucleation layers were microtwins (primary and multiple twins) occurring on the inclined 1 1 1 planes of AIGaAs.