Due to the world wide demand for IR emitting devices like IR-LED, printhead for laser printers, readout of optical storage devices, serial and parallel fibber/guided wave optical links and free space optical interconnects for remote controllers there is a great interest in multi wafer technology. In this paper we present growth results with respect to IR applications with the Planetary Reactor® system using AlGaAs/GaAs and longer wavelength material. For the mass production of LEDs the Planetary Reactor® system fulfills not only to grow high quality films with excellent uniformities, which results on high yield on wafer, but also to grow with high precursor utilization efficiency and wafer tliroughput. This is proven for thick layers by an excellent growth stability and a thickness uniformity better than ±2%. These high uniformities are achieved at conditions of growth efficiency in the range of 30–50% for group III materials and a comparatively low V-III ratio. To increase the intensity of LEDs GaAs/AlAs Bragg reflectors were grown. Reflectivity characteristics measurement and high resolution X-ray diffractometer measurements confirmed the thickness uniformity in the order of ±1% on 4″ wafers. The excellent thickness uniformity is also achieved on a 9×6″ configuration. For the first time in this study also the 7 × 2″ performance of InP based materials is reported.

We propose a semiconductor heterostructure consisting of six coupled quantum wells of GaAs plus a larger one, all inside Al(x)Ga(l−x)As, x=0.35. Our simulation prevents that the localized electronic eigen-state at the large well, the Tamm state, will oscillate when the voltage applied across these “finite superlattice” varies fast. We include exchange and correlation effects in the local density approximation and made the self-consistent calculations to the electrons at 77K varying the voltage in a gate contact of the device. We obtain the effective potential, the sub-bands (mini-bands) and respective electronic densities which enable us to simulate the temporal evolution of an electronic wave-packet when the gate-voltage is switched fast. Such a switching turns the Tamm eigen-state in a wave-packet. By the simulation we conclude that this wave-packet oscillates a Tera-Hertz frequency that can emit electromagnetic radiation as a charge oscillator. We estimate the finite superlattice capacitance and it confirms the possibility of changing the Hamiltonian faster than the period of the oscillation.

To improve the performance of p-type SiGe-channel FEPs is important for Si-based high-speed/high-frequency applications. This work discusses the design of germamium profiles in the strained Si1−xGex channel region of p-type SiGe modulation doped FET's and studies its effect on device performance. Two-dimensional device simulator is used to simulate the large-signal device performance for various Ge distributions including triangular, trapezoidal, and flat profiles. In particular, the thickness of the strained SiGe channel layer is 15 nm and a 5 ran thick Si cap layer is on top of the channel. It is found that with the same integrated Ge content in the strained channel, graded Ge profiles lead to higher transconductances and larger threshold voltage windows than those of flat profiles, due to deeper potential wells and better carrier confinement ability. For triangularly graded profiles, the peak position must be located in the upper half portion of the channel layer to result in superior performance. By adding more Ge to extend the peak region, triangular profiles become trapezoidal ones. However, more Ge content does not necessarily produce better performance. If the well depth of trapezoidal profile is the same as that of triangular profile and if the trapezoid plateau begins at the same position as that of triangle peak, the device performance is almost the same for both profiles.

The absorption properties of high quality bulk Si1−xGex single crystals (0 ≤ × ≤ 0.16) are studied. Transmission measurements were performed at the indirect absorption edge. The shape of the absorption edge is characterized by structures attributed to the onset of no-phonon and phonon-assisted indirect optical transitions. Threshold energies have been determined using a differential method. A corrected calibration function for the dependence of the excitonic energy gap on composition is presented for the compositions, where x ranges from 0 to 0.16. The presented calibration function can be used for the composition analysis by an optical method. The analysis is independent of absolute transmission values.

A simulation of the absorption spectra by calculations based on second order perturbation theory was used to fit the experimental data This procedure allows to estimate the oscillator strength of the no-phonon transition in dependence on x.

The initial stages of MBE growth of PbSe on CaF2/Si(111) were studied by in situ XPS. The surface reaction between CaF2 and elemental Se is also studied as a comparison. Ca 2p, F 1s, Pb 4f and Se 3d peaks all shift to lower binding energies (1.2 – 1.6 eV) with increasing PbSe coverage. This indicates a strong interaction between the PbSe overlayer and the underlying CaF2 and the formation of Pb-F and Ca-Se interfacial bonds. No chemically graded reaction products are detected at the PbSe/CaF2 interface. A transition layer of about 6 ML is observed which can be partially accounted for by the open 3D structure of CaF2 where three layers of atoms are available for bonding with the deposited material. This structure allows interpenetration of the PbSe and CaF2 layers which necessarily leads to a thin transition layer. Based on our XPS results, we propose a model for the bonding arrangements at the PbSe/CaF2(111) interface.

The efficiency of group II-VI solid solutions doped with chlorine and copper as X-ray downconverting phosphors for photodetectors is investigated. It is found that the phosphors based on the group II-VI compounds and prepared in oxygen-free medium can increase the photodetectors sensitivity to X-ray radiation more than one order of magnitude and enhance the photodetectors photovoltage versus X-ray radiant flux characteristic linearity.

Theoretical dramatic improvement of the thermoelectric properties of materials by using quantum confinement in novel semiconductor nanostructures has lead to considerable interest in the thermoelectric community. Therefore, we are exploring the critical materials issues for fabrication of quantum confined structures by magnetron sputtering in the lead telluride and bismuth telluride families of materials. We have synthesized modulated structures from thermoelectric materials with bilayer periods of as little as 3.2 nm and shown that they are stable at deposition temperatures high enough to grow quality films. Issues critical to high quality film growth have been investigated such as nucleation and growth conditions and their effect on crystal orientation and growth morphology. These investigations show that nucleating the film at a temperature below the growth temperature of optimum electronic properties produces high quality films. Our work with sputter deposition, which is inherently a high rate deposition process, builds the technological base necessary to develop economical production of these advanced materials. High deposition rate is critical since, even if efficiencies comparable with CFC based refrigeration systems can be achieved, large quantities of quantum confined materials will be necessary for cost-competitive uses.

We have used a two-dimensional charge transport model to study edge effects in photorefractive thin films. Our result shows that in addition to the bulk space charges, the large surface charges near the edges make a significant contribution to the space charge field. Quadratic electro-optic material were used as an example to study the surface-charge-layer-field quantitatively. The conditions for the device performance be dominated by either surface charge or bulk trap charges are clearly demonstrated.