By μ-Raman spectroscopy the formation of hydrogen related defects (vacancy-hydrogencomplexes, hydrogen saturated silicon dangling bonds, H2 molecules in multi-vacancies andvoids/platelets) has been investigated in H-implanted and subsequently H-plasma exposed andannealed Czochralski (Cz) silicon wafers. Annealing was done either in air or in an ambientcontaining hydrogen (forming gas). The investigations were applied under conditions, which arerelevant for ion-cut processes and layer exfoliation in Cz Si for SOI-wafer fabrication at reducedimplantation doses (as compared to standard procedures like the smart-cut® process).

In this paper, various types of defects (both threading dislocation and misfit dislocations) in strained Si (sSi) have been analyzed by transmission electron microscopy (TEM). Germanium upper-diffusion has been studied by scanning transmission electron microscopy (STEM) for strained Si on SiGe/SOI. SGOI-devices processed using an optimized thermal budget show minimal Ge diffusion and minimal process related defects. Correlation between the device performance (such as leakage current and reliability) and structural information found in TEM has been established.

We performed a quantum chemical molecular dynamics analysis for SiO2-x structure under strain to make clear the effect of the strain and intrinsic defects on both electronic and structural characteristics of SiO2-x. The SiO2-x showed a large change of the structure during the simulation. This is mainly because that the Si-O bonds near an oxygen vacancy were broken and a free silicon monoxide molecule was generated in the SiO2-x structure. The magnitude of the band gap of the SiO2-x decreased drastically due to the formation of the free monoxide. In addition, the band gap decreased further under large tensile strain of about 10%. We can conclude therefore, that both the existence of oxygen vacancies and tensile strain in SiO2-x films deteriorate the electronic reliability of the oxide film seriously.

The dilute-nitride GaInNAs shows great promise in becoming the next choice for 1 eV photodetector and multi-junction photovoltaic applications due to the ability for it to be grown lattice-matched on GaAs substrates. This paper will present results from high-power photodetector devices fabricated from high-quality thick GaInNAs and metamorphic InGaAs materials grown by MBE. The internal quantum efficiency of rear-illuminated PIN photodiodes with thick GaInNAs films as the intrinsic region (roughly 62% at 1064 nm) is somewhat lower than comparable metamorphic InGaAs devices (roughly 75% at 1064 nm). However, the dark current density of the GaInNAs devices is also somewhat lower (roughly 3 μA/cm2 at 2×104 V/cm bias) than the InGaAs devices (roughly 20 μA/cm2 at 2×104 V/cm bias), while the breakdown voltages (beyond -20 V) are comparable. Materials characterization of each structure, including x-ray diffraction and room-temperature as well as temperature-dependent photoluminescence studies will be presented in order to explain the characteristics observed in the devices composed of the two different material systems.

Based on first principles density functional theory calculations, we identify the structure and diffusion pathway for a fluorine-silicon interstitial complex (F-Sii). We find the F-Sii complex to be most stable in the singly positive charge state at all Fermi leVels. At mid-gap, the complex is found to have a binding energy of 1.08 eV relative to bond-centered F+ and (110)-split Sii. We find the F-Sii complex has an overall migration barrier of 0.76 eV, which suggests that this complex may play an important role in fluorine diffusion. Our results should lead to more accurate models that describe the behavior of fluorine co-implants crystalline silicon.

When platinum is diffused at temperatures higher than 900°C in Cz or FZ low doped n-type silicon samples, which are then cooled slowly in the range [1-10]°C/min, a p-type doping leading to the formation of a pn junction can be observed by spreading resistance measurement. The lower the cooling rate, the deeper the junction is. This junction disappears after a second thermal treatment finishing with a quenching step. A platinum related complex formation is considered to explain this reversible doping behaviour. Different possible interactions between platinum and other impurities such as dopant atoms, intrinsic point defects, and common residual impurities (C, Oi, transition metallic atoms) are studied here. Experimental results from Pt diffusion processes in different qualities of silicon wafers, and simulation results, lead to the conclusion that the platinum related p-type doping effect is due to the formation of a Pts-Oi complex.

We are currently investigating the infrared (IR) optical properties of Cr doped ternary cadmium chalcogenides for potential applications in solid-state lasers and passive optical Qswitches. In this paper, we present compositional changes in the IR optical properties of Cr doped Cd1-xZnxTe single crystals with x=0.05, 0.1, and 0.2. Undoped CdZnTe crystals were grown by vertical Bridgman technique. Cr doping of CdZnTe was achieved through either in-situ doping or through a thermal diffusion process. For comparison, Cr: CdTe and Cr: ZnTe crystals were also prepared. The optical properties of Cr2+ ions were strongly dependent on the host composition and spectral blue shifts were observed with increasing Zn content in Cr: CdZnTe. The IR absorption peak of Cr2+ ions shifted from ∼1910 nm for Cr: CdTe to ∼1815 nm for Cr: Cd0.8Zn0.2Te. Less pronounced blue shifts were observed for the IR emission from Cr: CdZnTe crystals. The spectral shifts can be explained by the decrease in bond-length when going from CdTe to CdZnTe leading to an increased crystal-field effect experienced by Cr2+ ions. A slight broadening of the absorption and emission was also observed in ternary Cr: CdZnTe compounds compared to Cr: CdTe, which suggests that Cr2+ ions were incorporated in multiple lattice sites in CdZnTe. Moreover, the Cr2+ emission dynamics revealed a slightly non-exponential decay behavior for Cr: CdZnTe crystals, whereas the decay time of Cr: CdTe was single-exponential.

We have carried out hydrogen-plasma (H-plasma) treatments on a quantum dot infrared photodetector (QDIP) structure, with a 5-stacked InAs dots in an InGaAs well structure and a Al0.3Ga0.7As/GaAs superlattice barrier. The sample structures were grown by molecular beam epitaxy. The H-plasma treatment has been carried out at 150 °C for 3 min – 40 min with 40 sccm of H2 gas flow rate and 10 W of RF power. After H-plasma treatment, photoluminescence (PL) intensities of the samples were slightly reduced compared to that of as-grown sample, without any changes in their PL peak position. The dark currents of H-plasma treated samples were much smaller by many orders of magnitudes than that for as-grown sample. The sample exposed to Hplasma for 10 min showed the lowest dark current, enabling the observation of photocurrent with a wide spectrum between 3 – 12 μim at 11 K.

Multicrystalline Si wafers used in commercial solar cell fabrication exhibit a tendency to form large “clusters” of defects, which remain laterally separated from each other. Defect clusters are also sites of impurity precipitation. Because precipitated impurities cannot be gettered by the conventional processes used in Si solar cell fabrication, defect clusters constitute low-performing regions in the cell. They shunt the device and constitute the primary efficiency limiting mechanism in current solar cells. We show that the efficiency loss caused by defect clusters can exceed 3–4 absolute points.

A nanometer-scale dislocation network is artificially formed in thin top Si layer of silicon-on-insulator (SOI) structure, and effect of the dislocation network on the transport property is examined from the viewpoint of nanodevice applications. The artificial network of screw dislocations was formed in the Si layer using a wafer bonding of a pair of (001) SOI wafers with a slight misalignment of the in-plane crystalline directions to cause a lattice mismatch. The transmission electron microscopy clearly revealed the formation of dislocation network at the bonding interface with the period less than ∼20 nm. The dislocation network was found to enhance the conductivity in the Si bicrystal layer more than one order of magnitude in comparison with that in the monocrystal layer free from the dislocations. The enhanced conductivity is probably derived from an increased concentration of electrons around the dislocations due to the formation of donor-like gap states.

Nanoindentations were created in the GaAs(100) surface to act as strain centers for the controlled nucleation and patterning of InAs quantum dots. A systematic approach is taken to understand the indent deformation processes that may lead to precision patterning capabilities for a broad range of nanostructures. Indents were generated using loads below 450 μN with a sharp cube corner indenter. Site-specific cross-sectional thinning of nanoindents (down to 100 nm in size) has been achieved using the in-situ ‘lift-out’ technique. This allowed for observation of subsurface deformation by transmission electron microscopy (TEM). The crystal was observed to deform solely by dislocation activity with no evidence of amorphization, twinning, fracture, or phase transformation. It is shown that the single phase deformation of GaAs can be well characterized and controlled, which should allow for exploitation of the dislocation strain field to bias nucleation of self-assembled quantum dots.

Metal-Semiconductor-Metal photodetectors (MSM-PD's) and simple Schottky diodes were fabricated using a low temperature (LT) technique to greatly reduce the device dark current. LT processing for metal deposition increased Schottky barrier height by improving the interface between metal and semiconductor to reduce the leakage current of the device. The structure consists of a 20 Å oxide over the active area to passivate surface states, a thicker oxide under contact pads to reduce dark current and the interdigitated Schottky contacts. A comparison was made for Schottky metal deposited with the substrate at 25 °C or -50 °C (LT). The devices fabricated using the LT process had better I-V characteristics compared to detectors fabricated using the standard room temperature (RT) metal deposition technique. The dark current for the LT film was found to be one to three orders lower in magnitude compared to the film deposited at RT. In one case, for example, the dark current was significantly reduced from 1.69 nA to 4.58 pA at 1.0 V. The active area for the device was determined to be 36 × 50 μm2 with 4 μm electrode width and 4 μm electrode spacing. Additionally, LT-MSM-PD's exhibited an excellent linear relationship between the photo-current and the incident light power. The Schottky barrier height for LT processing was found to be 0.79 eV; however, this value was 0.1 eV more than that of the same contact obtained by RT processing.

MOVPE of GaSb grown on (100), (111)A and (111)B GaSb substrates were investigated to study the effect of substrate orientation on the growth rate and surface morphology. Besides growth temperature and V/III ratio, the GaSb growth rate strongly depends on the crystallographic orientation. As the V/III ratio rises, the growth rate on the (111)B oriented substrate decreases, whereas that on the (111)A oriented substrate increases. The surface morphology on different substrates was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). On (111)A substrates, triangular hillocks are the dominant defects, while on (111)B planes, three distinct types of hexagonal hillocks are observed, namely, non-flat top hexagonal structure with spiral growth features (Type I), flat top structure with lateral growth features (Type II), and non-flat top hexagonal structure with multiple islands (Type III). For all types, the basal edges of each hillock are preferentially aligned along <110> directions. A closer look reveals that the top surface of Type II feature consists of many levels of small hexagonal shaped terraces, with each step height in the monolayer range, indicating a step flow growth involved.

The paper reports results of theoretical calculations of the redistribution of electrons and electrostatic potential in the implanted crystalline matrix (100)-GaAs+Si(Ar) due to electrondeformation effects. The model requires a self-consistent solution of the set of following equations: 1)the time-independent Schroedinger equation; 2) the equation of mechanical equilibrium: 3) the Poisson equation for determining electrostatic potential distribution; 4) the equation for calculation of the electron concentration, and 5) the equation for the chemical potential calculation in the implanted system. The most important result is: it is shown that in the elastic region of the implanted matrix n-n+-junction is formed. Current-voltage characteristics of the junction are numerically simulated.

We have carried out a systematic study of the effects of irradiation on the electronic and optical properties of InGaN alloys over the entire composition range. High energy electrons, protons, and 4He+ were used to produce displacement damage doses (Dd) spanning over five orders of magnitude. The free electron concentrations in InN and In-rich InGaN increase with Dd and finally saturate after a sufficiently high Dd. The saturation of carrier density is attributed to the formation of native donors and the Fermi level pinning at the Fermi Stabilization Energy (EFS), as predicted by the amphoteric native defect model. Electrochemical capacitance-voltage (ECV) measurements reveal a surface electron accumulation whose concentration is determined by pinning at EFS.

Recent progress in experimental technique made it possible to improve the sensitivity of microwave detected photoconductivity by several orders of magnitude. This opens completely new possibilities for a contact less non-destructive electrical defect characterization of silicon wafers and even of epitaxial layers on substrates with extremely low resistivity. Electrical properties such as lifetime, mobility and diffusion length can be measured without contacts also at very low injection levels with a resolution only limited by the diffusion length of the charge carriers. The doping level of the material plays no major role.

Owing to the high sensitivity, thermal excitation of charge carriers out of defect levels filled during the photo pulse can also be observed. This leads to defect specific photoconductivity transients which deliver pieces of information like DLTS, however, again without contacts, non critical doping, and with high spatial resolution.

In this paper, using chemical etching, atomic force microscope (AFM) and High- resolution X-ray diffraction (HRXRD), we report a study of the effect of various small miscuts of (0001) sapphire substrate (<1°) and the way to further improve the material quality. A set of AlN epilayers and AlN/AlxGa1-xN Superlattices (SLs) were grown by Migration-enhanced Metalorganic Chemical Vapor Deposition (MEMOCVD) on vicinal (0001) sapphire substrates. The threading dislocation density was found to be very sensitive to the miscut angles. The etch pit density reduced to 7×106 cm-2 for normal-oriented (0°-off) from the starting value of 7×107 cm-2 for 0.5°-off. We found the surface morphologies can be easily controlled by the different substrate miscut angles. The 1-2 Monolayers (MLs) step flow morphology for normal- oriented substrate changed to step bunches of 10 MLs height for 0.5°-off substrate. Correspondingly, AFM Root Mean Square (RMS) increased from 1.52 to 9.15 Å with a 5um×5um scan. This finding may help enhance the quality of full structure UVLED material and eventually improve the lifetime of UVLEDs.

A new method to synthesize highly luminescent GaN:Mg powders has been developed. This method has a high control over the concentration of magnesium in the final product. The method consists of reacting a high purity (99.999 %) galliummagnesium alloy with ultra-high purity ammonia in a horizontal quartz tube reactor at high temperatures for several hours. Electron microscopy showed that the light-gray powders produced by this method consist of at least two different shaped crystallites; large columnar crystals sized around 10 μm and small platelets crystals between 1 and 2 μm. X-ray diffraction showed that those crystallites have a well defined wurtzite structure. Room temperature photoluminescence (PL) and cathodoluminescence (CL) showed a high intensity blue emission around 2.94 eV (422 nm). At helium temperature the well known Mg-related donor-acceptor pair band was observed at 3.25 eV (380 nm) by PL and CL.

Carrier lifetime degradation in crystalline silicon solar cells under illumination with white light is a frequently observed phenomenon. Two main causes of such degradation effects have been identified in the past, both of them being electronically driven and both related to the most common acceptor element, boron, in silicon: (i) the dissociation of iron-boron pairs and (ii) the formation of recombination-active boron-oxygen complexes. While the first mechanism is particularly relevant in metal-contaminated solar-grade multicrystalline silicon materials, the latter process is important in monocrystalline Czochralski-grown silicon, rich in oxygen. This paper starts with a short review of the characteristic features of the two processes. We then briefly address the effect of iron-boron dissociation on solar cell parameters. Regarding the boron-oxygen-related degradation, the current status of the physical understanding of the defect formation process and the defect structure are presented. Finally, we discuss different strategies for effectively avoiding the degradation.

We report on the preparation and optical spectroscopy of diffusion doped Cr: ZnSe and Cr: CdTe windows for applications in mid-infrared (MIR) solid-state lasers. Cr doping was achieved in both materials through a thermal diffusion process controlled by temperature (750°-850 °C) and time (∼0.25-6 days). Commercial CrSe powder (99.5% purity) was used as the dopant source. All samples exhibited the characteristic spectroscopic features of tetrahedrally coordinated Cr2+ ions with absorption bands centered between 1700-1900 nm and MIR emission bands extending from 2000-3200 nm. Various samples of Cr: ZnSe and Cr: CdTe were prepared with Cr2+ peak absorption coefficients from ∼0.1 cm-1 to ∼29 cm-1. The calculated Cr2+ concentration ranged from ∼1×1017cm-3 to 3×1019cm-3 using absorption-cross sections of 1.1×10-18 cm2 for Cr: ZnSe and 2.2×10-18 cm2 for Cr: CdTe. The room temperature decay times for Cr: ZnSe and Cr: CdTe were measured to be between 5-6 μs and 3-4 μs, respectively. Quenching of the Cr emission was observed for Cr concentrations above ∼1×1019 cm-3 for Cr: ZnSe and ∼0.5×1019 cm-3 for Cr: CdTe. The absorption and MIR emission properties of diffusion doped Cr: ZnSe and Cr: CdTe windows as a function of Cr concentration will be discussed.