C. L. Littler

Temperature dependence of the energy gap of InSb using nonlinear optical techniques

We report the first use of the resonant two‐photon photo‐Hall effect as a nonlinear optical technique to measure the temperature dependence of the energy gap of InSb. Values of Eg for the temperature range 2–210 K are determined and compared with theoretical predictions and past experimental work. The technique is shown to provide an accurate, straightforward means of measuring Eg as a function of temperature in semiconductor materials.

Temperature and Composition Dependence of the Energy Gap of Hg1-xCdxTe by Two-Photon Magnetoabsorption Techniques

Accurate determinations of the energy gap Eg at liquid helium temperatures in alloys of 0.24≤x≤0.30 have been made by two‐photon magnetoabsorption techniques. They are shown to help verify the use of the Hansen–Schmit–Casselman (HSC) relation over the range 0<x<0.30 at these temperatures. In contrast, the observed temperature dependence of Eg below 77 K is nonlinear and thus cannot be described accurately by the HSC relation. Analysis of Eg (T) data for three samples with 0.24≤x≤0.26 has allowed the deduction of a new relationship for Eg (x,T) that more properly accounts for the nonlinear temperature dependence below 77 K and the linear behavior above 77 K, while still accurately describing the x dependence Eg(x,T) =−0.302 +1.93x +5.35(1−2x)(10−4) [(−1822+T 3)/(255.2+T 2)] −0.810x2 +0.832x3, for Eg in eV and T in K. This relation should apply to alloys with 0.2<x<0.3. The maximum change from the HSC relation in this range is 0.004 eV for x=0.2 at ∼10 K.

Intrinsic carrier concentration of narrow‐gap mercury cadmium telluride based on the nonlinear temperature dependence of the band gap

The intrinsic carrier concentrations of narrow‐gap Hg1−xCdxTe alloys have been calculated as a function of temperature between 0 and 300 K for x values between 0.17 and 0.30. The new and more accurate relation for the temperature dependence of the energy gap, which is based on two‐photon magnetoabsorption data, is used. This relation is further supported here by additional one‐photon magnetoabsorption measurements for x=0.20 and 0.23, which were made with a CO2 laser. In this range of composition and temperature, the energy gap of mercury cadmium telluride is small, and very accurate values for the gap are needed to obtain reliable values for the intrinsic carrier density. Kane’s k⋅p theory is used to account for the conduction‐band nonparabolicity. Large percentage differences occur between our new calculations and previously calculated values for ni at low temperatures. A nonlinear least‐squares fit was made to the results of our calculations for ease of use. The implications of these results for Hg1−xC...

Nonlinear oscillations and chaos in n-InSb

Abstract We present evidence for chaotic behavior in n-InSb. The Hall voltage exhibits a period-doubling route to chaos as the (non-ohmic) dc current is increased. The nonlinear oscillation and bifurcation processes are strongly influenced by irradiation with CO2 laser radiation.

Bending of N‐isopropylacrylamide gel under the influence of infrared light

A CO2 infrared laser has been used to irradiate a straight cylindrical N‐isopropylacrylamide gel. It is found that the infrared laser not only induces the volume phase transition in the gel, but also causes the gel to bend toward the laser beam. When the laser is blocked, the gel becomes straight again. The transition between the straight and the bending gel is fully reversible. The maximum bending strain of the gel is comparable to that obtained for poly(vinyl alcohol)–poly(sodium acrylate) copolymer gel under the influence of an electric field. The bending effect has been systematically studied as a function of CO2 laser power, time, and the sample cell temperature. The relaxation behavior for the gel restoring its original shape after blocking the infrared irradiation follows an exponential form. It is suggested that the bending effect is caused by a temperature gradient which produces an osmotic pressure difference between the front surface area of the gel and the remainder of the gel.

Temperature dependence of the band gap of GaAsSb epilayers

We have optically characterized a series of GaAs1−xSbx epilayers (0.19<x<0.71) grown by molecular bean epitaxy on semi-insulating GaAs substrates, with surface orientations of (001), (001) 8° toward (111)B, (001) 8° toward (111)A, and (115)B. For each of these samples, we have investigated the absorption as a function of temperature (4 K<T<300 K) using Fourier transform infrared spectroscopy techniques. The band gap at each temperature was determined from the photon energy dependence of the absorption coefficient and compared with theoretical predictions. From our results we have obtained the Varshni coefficients, α=(4.2±0.1)×10−4 eV/K and β=(189±9) K, which describe well not only the temperature dependence of the band gap for the entire alloy range of our samples, but also for the past experimental work of others. These values differ significantly from what we believe are the only other reported values by K. G. Merkel et al. [K. G. Merkel et al., Appl. Phys. Lett. 65, 2442 (1994)].

New method of characterizing majority and minority carriers in semiconductors

A novel characterization method using magnetoconductivity tensor components to determine the carrier concentration and mobility of majority and minority carriers is presented. Results are given for bulk n‐HgCdTe (one carrier), liquid phase epitaxial n‐HgCdTe (two carriers), and p‐InSb (two or three carriers). Advantages of this method over the standard Hall coefficient analysis are discussed.

Stoichiometry dependent electron transport and gas sensing properties of indium oxide nanowires

The effect of stoichiometry of single crystalline In2O3 nanowires on electrical transport and gas sensing was investigated. The nanowires were synthesized by vapor phase transport and had diameters ranging from 80 to 100 nm and lengths between 10 and 20 μm, with a growth direction of [001]. Transport measurements revealed n-type conduction, attributed to the presence of oxygen vacancies in the crystal lattice. As-grown In2O3 nanowires were shown to have a carrier concentration of ≈5 × 10(17) cm(-3), while nanowires that were annealed in wet O2 showed a reduced carrier concentration of less than 10(16) cm(-3). Temperature dependent conductivity measurements on the as-grown nanowires and analysis of the thermally activated Arrhenius conduction for the temperature range of 77-350 K yielded an activation energy of 0.12 eV. This is explained on the basis of carrier exchange that occurs between the surface states and the bulk of the nanowire, resulting in a depleted surface layer of thickness of the order of the Debye length (LD), estimated to be about 3-4 nm for the as-grown nanowires and about 10 times higher for the more stoichiometric nanowires. Significant changes in the electrical conductance of individual In2O3 nanowires were also observed within several seconds of exposure to NH3 and O2 gas molecules at room temperature, thus demonstrating the potential use of In2O3 nanowires as efficient miniaturized chemical sensors. The sensing mechanism is dominated by the nanowire channel conductance, and a simple energy band diagram is used to explain the change in conductivity when gas molecules adsorbed on the nanowire surface influence its electrical properties. Less stoichiometric nanowires were found to be more sensitive to oxidizing gases while more stoichiometric nanowires showed significantly enhanced response to reducing gases.

Laser‐induced resonant carrier lifetimes in n‐InSb

Transient carrier lifetimes of high‐purity n‐InSb are found to exhibit a two‐stage decay in the photoconductive response. Resonant increases in the first stage decay occur at the same magnetic field strengths as resonant interband two‐photon magnetoabsorption between Landau levels. The presence of shallow Te donors is shown to control both the observed resonant and transient behavior.

Atomic ordering-induced band gap reductions in GaAsSb epilayers grown by molecular beam epitaxy

A series of GaAs1−xSbx epilayers (0.51<x<0.71) grown by molecular-beam epitaxy on GaAs substrates with surface orientations of (001), (001) −8° toward (111)A, (001) −8° toward (111)B, (115)A, (115)B, (113)A, and (113)B were investigated using temperature-dependent Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy. Atomic ordering in these epilayers was observed from a decrease in the energy gap measured by FTIR absorption and corroborated by superlattice reflections in electron diffraction. Contrary to previous investigations of ordering in III-V alloys, a marked energy-gap reduction, corresponding to CuPt-B-type ordering, is observed in the GaAs1−xSbx grown on (111)A-type substrate offcuts.