Indium Centers Research Articles

Synthetic and structural studies on Group 13 complexes containing the M(CO)3(η-C5H5) fragment (M = Cr or Mo). Part 1. Complexes [E{M(CO)3(η-C5H5)}3](E = In or TI)

The complexes [E{M(CO)3(η-C5H5)}3](E = In, M = Mo, 1; E = In, M = Cr, 8; E = TI, M = Cr, 5; E = TI, M = Mo, 6) have been prepared and their structures determined by X-ray crystallography. All contain a trigonal-planar indium or thallium centre bonded to three M(CO)3(η-C5H5) fragments (M = Cr or Mo) by unsupported element–element bonds. Synthetic and structural comparisons are made with related complexes and the solution-state properties of all complexes in a variety of solvents are described and discussed. These studies indicate a high degree of ionic character in solution. Extended-Huckel molecular orbital calculations have also been carried out on 1 which confirm the presence of polar In–Mo bonds and also reveal that In–Mo π bonding is quite weak.

Isolation of a sulphur-rich indium polysulphide complex containing two different S x2- ligands. Synthesis and structure of [InS 10Br] 2−

The reaction of InBr 3 with K 2S 5 (or K 2S 4 and K 2S 6) and Ph 4PBr afforded yellow (Ph 4P) 2[In(S 4)(S 6)Br] ( I). Complex I crystallizes in the monoclinic space group P2 1/ c with a = 14.355(7), b = 17.723(4), c = 20.974(7) Å, β = 108.5(1)°, V = 5060.6(4) Å 3 (at 23°C), Z = 4. The [In(S 4)(S 6)Br] 2− anion features a trigonal bipyramidal indium centre coordinated by four sulphur atoms and one bromine atom. The latter occupies an axial position. The In 3+ centre is chelated by two bidentate polysulphide S 4 2− and S 6 2− ligands. The S 6 2− ligand occupies two equatorial positions. The remaining one equatorial and one axial positions are occupied by the S 4 2− ligand. The average In—S distance is 2.535(35) Å. The In—Br distance is 2.615(3) Å. Complex I shows no absorptions in the UV-vis spectrum. Two strong absorptions at 490 and 457 cm −1 in the IR spectrum are attributed to S—S vibrations.

Optical properties of atomic gallium and indium centres in KCl

In radiation-damaged In- and Ga-doped KCl crystals many In- and Ga-related defects are formed. Their optical absorption bands strongly overlap, making it impossible to determine the optical transitions of a particular defect directly. With measurements of the magnetic circular dichroism tagged by electron spin resonance absorption bands of Ga0(1) and In0(1) centres, the analogues of the laser-active Tl0(1) centres, could be identified. Ga0(1) centres have absorption bands peaking at 930, 890 and 620 nm and In0(1) centres at 965, 860 and 610 nm. Up to 2.7 mu m no emission was found for Ga0(1) centres, whereas upon excitation at 965 nm In0(1) centres probably have a very weak emission around 2.2. mu m. In a model calculation the occurrence of radiative and non-radiative transitions upon excitation of the lowest excited state in Ga0(1), In0(1) and Tl0(1) centres is discussed.

Polarized At Emission of In+ Centres in KI:In

AbstractSpectral, polarization, and kinetic characteristics are investigated at 4.2 to 300 K for the blue luminescence of KI:In crystals with various In+ concentrations. It is established that the At emission band of In+ centres is elementary and its decay consists of only one component. The At emission is polarized only at excitation in the B and A absorption bands, the polarization degree is positive and grows as the energy of exciting photons decreases. The doublet structure of the At emission band as well as the second slower decay component which shows in KI:In with large In+ concentration a large negative polarization on excitation in the C band at 80 K, are caused by the presence, besides of In+, of some anisotropic indium centres in the crystal. Their emission is shifted by about 0.04 eV to lower energies with respect to the At emission of In+ centres.

Application of the MOSFET device structure in characterizing imperfection centers in indium-doped silicon

C.T. Sah has published a review article demonstrating the application of high-frequency small signal capacitance and current transients of a space charge layer. Application of such transients is a powerful technique in characterizing deep level imperfection center concentrations, energy levels, thermal and optical emission rates and thermal capture cross sections. The MOSFET device structure is particularly convenient for low temperature measurements of shallow levels where deionization occurs and the substrate becomes highly resistive, seriously limiting capacitance transient techniques. Examples are given by results on indium-doped silicon, such as employed in extrinsic IR detectors. The emission time constant of holes from the neutral indium center has been found to depend on the indium doping. Measurements on lightly doped samples yield a value for the emission rate, 1 e p , of 6.0 msec at 77°K and a thermal activation energy of 0.15 eV. Measurements on heavily doped samples yield values of 1 e p of 20 μsec at 77°K and an activation energy of 0.117 eV. These results are consistent with the Poole-Frenkel effect describing field enhanced thermal emission of holes from the indium center. Measurements of the hole capture coefficient at 77°K yield values for c p of 3.7 × 10 −7 cm 3/sec. These measurements have been made on heavily doped samples. The capture coefficient measured is the zero field or quasi-equilibrium value. The temperature dependence of the hole capture coefficient has been found to be T −4. Small transients in the thermal emission rate measurements have been observed. These transients have thermal activation energies of around 0.08 eV and are associated with the 0.11 eV level as reported by Hughes Research Labs after accounting for barrier lowering by the Poole-Frenkel effect.

Characteristics of the indium-doped infrared sensing MOSFET(IRFET)

The operation and characteristics of the indium-doped infrared sensing MOSFET(IRFET) in the 2.0- to 7.0-µm wavelength range are described. Responsivities of 4.8 mA/µJ are easily achieved using relatively large devices with small W/L ratios. Determination of the thermal emission rate of the indium center in silicon indicates that operating temperatures of lower than 50 K are required. Application considerations in large-scale integrated infrared imaging arrays are discussed. The measurement of the thermal emission rate and photoionization cross section of indium also demonstrates the capability of the MOSFET device structure in characterizing shallower level impurity centers in silicon.

Electrical fluctuations in silicon double injection devices

Studies of the electrical noise behavior of indium-doped silicon P + πN + double injection devices are reported. The work refers to the double injection portion of the device characteristic at a temperature of 77°K. The noise studied is attributed to fluctuations in the rate of recombination of carriers via the indium centers. From fitting theoretical and experimental results, the carrier lifetime is found to be 2.5 × 10 −7 sec and the capture cross-section of neutral indium centers for electrons is determined to be 1.8 × 10 −16 cm 2.

Photoconductivity Associated with Indium Acceptors in Silicon

Experiments are described in which excess free holes are generated in $p$-type silicon by the photo-ionization of neutral indium acceptors (${E}_{a}=0.155$eV), and of the subsequent hole capture by ionized indium centers. Using chopped monochromatic radiation of small intensity for illumination, a comparison has been made of dc dark conductivity and of chopped photoconductive responsivity in order to determine the excess hole lifetime and the ionized-acceptor capture cross section as a function of temperature. For samples with an indium concentration in the range 5\ifmmode\times\else\texttimes\fi{}${10}^{15}$ to 5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, the hole-capture cross section decreases by a factor of 100 in the temperature range 70-180\ifmmode^\circ\else\textdegree\fi{}K. This cross section is \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ ${\mathrm{cm}}^{2}$ between 70 and 120\ifmmode^\circ\else\textdegree\fi{}K, a range in which the sticking probability is appreciable for capture into the first excited states of the acceptor. A cross section of \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$ at 180\ifmmode^\circ\else\textdegree\fi{}K is found in agreement with predictions that capture at this temperature can occur only into the ground state of the acceptor. The spectral dependence of photoconductive response in "optically thin" samples is compared with the quantum efficiency expected from optical-absorption measurements and from theoretical models of indium acceptors; it is found that the photoconductive efficiency is anomalously small within the range $0.155<h\ensuremath{\nu}<0.24$ eV at the lower temperatures.

PHOTOCONDUCTIVITY IN INDIUM-DOPED SILICON

Impurity photoconductivity has been studied in silicon doped with indium, at various temperatures in the range 63–90°K. The long wave limit of spectral response and analysis of the bulk electrical properties both confirm an ionization energy of 0.16 ev. for the indium centers. An apparent variation of quantum efficiency in the range 5–8 μ is noted and discussed. The magnitude of the photoconductive response suggests an effective recombination coefficient of about 10−6 cm.3/sec. at 90°K., rising steeply on further cooling. This demands a much more active recombination mechanism than present theories provide.