Interface property of silicon nitride films grown by inductively coupled plasma chemical vapor deposition and plasma enhanced chemical vapor deposition on In0.82Al0.18As

Au/silicon nitride/In_0.82Al_0.18As metal insulating semiconductor (MIS) capacitors were fabricated and then investigated by capacitance voltage (C–V) test at variable frequencies and temperatures. Two different technologies silicon nitride (SiN_x) films deposited by inductively coupled plasma chemical vapor deposition (“ICPCVD”) and plasma enhanced chemical vapor deposition (“PECVD”) were applied to the MIS capacitors. Fixed charges (N_f), fast (D_it) and slow (N_si) interface states were calculated and analyzed for the different films deposition MIS capacitors. The D_it was calculated to be 4.16 × 10¹³ cm⁻² eV⁻¹ for “ICPCVD” SiN_x MIS capacitors, which was almost the same to that of “PECVD” SiN_x MIS capacitors. The D_it value is obviously higher for the extended wavelength In_xGa_1−xAs (x > 0.53) epitaxial material as a result of lattice mismatch with substrate. Compared to the results of “PECVD” SiN_x MIS capacitors, the N_si was significantly lower and the N_f was slightly lower for “ICPCVD” SiN_x MIS capacitors. X-ray photoelectron spectroscopy (XPS) analysis shows good quality of the “ICPCVD” grown SiN_x. The low temperature deposited SiN_x films grown by “ICPCVD” show better effect on decreasing the dark current of In_xGa_1−xAs photodiodes.     

Passivation of InP-based HBTs

The surface effects, the (NH₄)₂S and low-temperature-deposited SiN_x passivations of InP-based heterostructure bipolar transistors (HBTs) have been investigated. The surface recombination current of InP-based HBTs is related to the base structures. The (NH₄)₂S treatment for InGaAs and InP removes the natural oxide layer and results in sulfur-bonded surfaces. This can create surface-recombination-free InP-based HBTs. Degradation is found when the HBTs were exposed to air for 10 days. The low-temperature-deposited SiN_x passivation of InGaAs/InP HBTs causes a drastic decrease in the base current and a significant increase in the current gain. The improvement in the HBT performance is attributed to the low deposition temperature and the effect of N₂ plasma treatment in the initial deposition process. The SiN_x passivation is found to be stable. S/SiN_x passivation of InGaAs/InP HBTs results in a decrease in the base current and an increase in the current gain. The annealing process can cause the base current to decrease further and the current gain increase.     

Microstructural properties of plasma-enhanced chemical vapor deposited WNx films using WF6–H2–N2 precursor system

A WF₆–H₂–N₂ precursor system was used for plasma-enhanced chemical vapor deposition (PECVD) of WN_x films. We examined the microstructural changes of the WN_x films depending on N₂/H₂ flow-rate ratio and post-annealing (600–800 °C for 1 h). As the N₂/H₂ flow rate was increased from 0 to 1.5, as-deposited WN_x films exhibited various different crystalline states, such as nanocrystalline and/or amorphous structure comprising W, WN, and W₂N phases, a fine W₂N granular structure embedded in an amorphous matrix, and a crystalline structure of β-W₂N phase. After post-annealing above 600 °C, crystalline recovery with phase separation to β-W₂N and α-W was observed from the WN_x films deposited at an optimized deposition condition (flow-rate ratio = 0.25). From this PECVD method, an excellent step coverage of ∼90% was obtained from the WN_x films at a contact diameter of 0.4 μm and an aspect ratio of 3.5.     

New approach to the growth of SiOx nanowire bunch using Au catalyst and SiNx film on Si substrate

SiO_x nanowire bunches were fabricated on a SiN_x film with Au catalytic metal in the presence of an Ar flow of 50 sccm at 1150 °C. The resulting samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. A SiN_x film serves as a barrier to the diffusion of Si atoms from the Si substrate to the catalytic Au metal, where a substrate is a Si source material for SiO_x nanowire (NW) growth. Using this process, we could temporally control the initial growth step of SiO_x NWs and easily grow the NW bunch.     

Determination of the critical indium composition corresponding to the metal–insulator transition in InxGa1−xN (0.06 ⩽ x ⩽ 0.135) layers

The low-temperature conductivity of In_xGa_1−xN alloys (0.06 ⩽ x ⩽ 0.135) is analyzed as a function of indium composition (x). Although our In_xGa_1−xN alloys were on the metallic side of the metal–insulator transition, neither the Kubo-Greenwood nor Born approach were able to describe the transport properties of the In_xGa_1−xN alloys. In addition, all of the In_xGa_1−xN alloys took place below the Ioeffe–Regel regime with their low conductivities. The observed behavior is discussed in the framework of the scaling theory. With decreasing indium composition, a decrease in thermal activation energy is observed. For the metal–insulator transition, the critical indium composition is obtained as x_c = 0.0543 for In_xGa_1−xN alloys.     

The improvement of pyroelectric properties of PZT thick films on Si substrate by TiOx barrier layer

The effects of TiO_x diffusion barrier layer thickness on the microstructure and pyroelectric characteristics of PZT thick films were studied in this paper. The TiO_x layer was prepared by thermal oxidation of Ti thin film in air and the PZT thick films were fabricated by electrophoresis deposition method (EPD). To demonstrate the barrier effect of TiO_x layer, the electrode/substrate interface and Si content in PZT thick films were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS), respectively. The TiO_x barrier thickness shows significant influence on the bottom electrode and the pyroelectric performance of the PZT thick films. The average pyroelectric coefficient of PZT films deposited on 400 nm TiO_x layer was about 8.94 × 10⁻⁹ C/(cm² K), which was improved by 70% than those without diffusion barrier layer. The results showed in this study indicate that TiO_x barrier layer has great potential in fabrication of PZT pyroelectric device.     

A magnetic study of HoMn6Sn6−xGax single crystals (0.14⩽x⩽1.89)

Single crystals of hexagonal HfFe₆Ge₆-type HoMn₆Sn_6−xGa_x compounds (0.14⩽x⩽1.89) have been obtained by a flux method and studied by magnetisation measurements. All the compounds order ferrimagnetically (308⩽T_c⩽386 K) with moments lying in the (0 0 1) plane and undergo a moment reorientation transition at lower temperatures (156⩽T_SR⩽195 K). At 5 K, the moments are aligned along an intermediate direction (44⩽φ_c⩽50°). These results are discussed and compared with the neutron diffraction results related to the isotypic TmMn₆Sn_6−xGa_x and TbMn₆Sn_6−xGa_x series where a change of the easy direction is observed with increasing gallium contents.     

Optical properties of GaAs/Ga 1-xAlxAs ridge quantum wire: Third-harmonic generation

In this paper, the third-harmonic generation (THG) in GaAs/Ga_1 ? xAl_xAs ridge quantum wires is studied in detail. An analytic expression for the THG is obtained using a compact density matrix approach and an iterative procedure. Numerical calculations are performed for the typical GaAs/Ga_1 ? xAl_xAs ridge quantum wire. The results show that the maximum THG over 10^? 9_? m²_?/V²_? can be obtained. Another important point is that the structural parameters have great influence on the THG in this system.     

The effect of compositional disorder on electronic band structure in GaxIn1 − xAsySb1 − yalloys lattice matched to GaSb

A pseudopotential formalism coupled with the virtual crystal approximation are applied to study the effect of compositional disorder upon electronic band structure of cubic Ga_xIn_1 − xAs_ySb_1 − yquarternary alloys lattice matched to GaSb. The effects of compositional variations are properly included in the calculations. Our theoretical results show that the compositional disorder plays an important role in the determination of the energy band structure of Ga_xIn_1 − xAs_ySb_1 − y/GaSb and that the bowing parameter is dominated by the group V-anion-based sublattice. Moreover, the absorption at the fundamental optical gaps is found to be direct within a whole range of the x composition.     

Distinction investigation of InGaAs photodetectors cutoff at 2.9 μm

Using double heterojunction structure with linearly graded In_xAl_1–xAs as buffer layer and In_0.9Al_0.1As as cap layer, wavelength extended In_0.9Ga_0.1As detectors with cutoff wavelength of 2.88 μm at room temperature have been grown by using gas source molecular beam epitaxy, their characteristics have been investigated in detail and compared with the detectors cutoff at 2.4 μm with similar structure as well as commercial InAs detectors. Typical resistance area product R₀A of the detectors reaches 3.2 Ω cm² at 290 K. Measured peak detectivity reaches 6.6E9 cm Hz^1/2/W at room temperature.     

Ternary effects on the optical interface phonons in onion-like GaN/AlxGa1 − xN quantum dots

The interface optical phonons and its ternary effects in onion-like quantum dots are studied by using dielectric continuum model and the modified random-element isodisplacement model. The dispersion relations, the electron–phonon interactions and ternary effects on the interface optical phonons are calculated in the GaN/Al_xGa_1 − xN onion-like quantum dots. The results show that aluminium concentration has important influence on the interface optical phonons and electron–phonon interactions in GaN/Al_xGa_1 − xN onion-like quantum dots. The frequencies of interface optical phonons and electron–phonon coupling strengths change linearly with increase of aluminium concentration in high frequency range, and do not change linearly with increasing aluminium concentration in low frequency range.     

Spectral sensitivity dependencies of backside illuminated planar MCT photodiodes

Spectral sensitivity dependencies of Hg_1−xCd_xTe (0.20 ⩽ x ⩽ 0.25) backside illuminated planar photodiodes were investigated at T = 80 K to study their longwavelength edge features. It was shown that the longwavelength part of these spectral dependencies is mainly formed by the exponential wavelength dependence of the optical transitions. Empirical dependencies of cut-off wavelengths at different values (λ_max, λ_0.5, λ_0.9) were obtained. The influence of the epitaxial layer thickness on the maximum sensitivity position was also studied.     

Electrical and mechanical properties of diluted magnetic semiconductor Zn1−xMnxS nanocrystalline films

Nanostructured Zn_1−xMn_xS films (0 ⩽ x ⩽ 0.25) were deposited on glass substrates by simple resistive thermal evaporation technique. All the films were deposited at 300 K in a vacuum of 2 × 10⁻⁶ m bar. All the films temperature dependence of resistivity revealed semiconducting behaviour of the samples. Hot probe test revealed that all the samples exhibited n-type conductivity. The nanohardness of the films ranges from 4.7 to 9.9 GPa, Young’s modulus value ranging 69.7–94.2 GPa.     

Surface topographic study of chalcogenide thin films of GexSb(As)40−xS50Te10 glasses

The surface topography and fractal properties of Ge_xSb(As)_40−xS₅₀Te₁₀ (x = 10, 20, 27 at.%) films, evaporated onto glass substrates, have been studied by atomic force microscopic imaging at different scales. The surface of the chalcogenide films is smooth (<5 nm roughness), isotropic and having some particular differences in texture. All films are self-similar with Mean Fractal Dimension in the range of 2.25–2.63. The films with Ge_xSb_40−xS₅₀Te₁₀ composition are more uniform in terms of surface morphology (grains structure) than those with Ge_xAs_40−xS₅₀Te₁₀ composition for which the film surface exhibits a superimposed structure of large particles at x = 10 and 20 at.%.     

Excitonic magnetic polaron dynamics of MBE grown CdTe/Cd1 − xMnxTe,Cd1 − xMnxTe/Cd1 − vMgyTe single quantum wells in magneti fields

Excitonic lifetimes in Cd_1 − xMn_Ue2Te, Cd_1 − xMg_xTe epilayers and CdTe/Cd_1 − xMn_xTe, Cd_1 − xMn_xTe/Cd_1 − vMg_yTe single quantum wells with different well widths and Mn, Mg compositions are investigated. The excitonic lifetimes are found to reduce drastically by applying external magnetic fields to samples with giant Zeeman splittings. The observed phenomenon is interpreted in terms of the PL decay time contribution from the long-life dark excitons which can convert to excitons for recombinations by a spin-flip process. We attribute the lifetime reduction to the depletion of dark excitons due to their crossing over the exciton energies for dipole allowed transitions in magnetic fields.     

Observation of negative photoconductivity in (ZnO)x(CdO)1−x films

In this study, (ZnO)_x(CdO)_1?x films were prepared by ultrasonic spray pyrolysis (USP) technique at a substrate temperature of 400 °C. X-ray diffraction patterns of the films indicate that the (ZnO)_x(CdO)_1?x films have hexagonal wurtzite and cubic structure for the constituent materials. A decrease in the average transmission with increasing quantity of the cadmium acetate dehydrate in the sprayed solution was observed. The photoconductivity transients were performed using UV light, which has 360 nm wavelength. After light cut off, conductivity changed slowly, and the decay time was thousands of seconds. The films with x=0.2 and 0 exhibited negative photoconductivity. Temperature-dependent photoconductivity and dark conductivity measurements were performed and negative photoconductivity was also observed for the same films (x=0.2 and 0). Photoluminescence measurements were performed and band-to-band excitation energies of (ZnO)_x(CdO)_1?x films were determined. Band gap of the pure CdO film was found as 3.11 eV, interestingly.     

Influence of the antireflection,window, and active layers on optical properties of exponential-doping transmission-mode GaAs photocathode modules

In order to well study the influence of the thickness and doping concentration on optical properties of transmission-mode GaAs photocathode, three exponential-doping and one uniform-doping photocathode modules were prepared by molecular beam epitaxy with a structure of glass/Si₃N₄/Ga_1 ? xAl_xAs/GaAs. By use of the spectrophotometer, the optical properties were separately measured including the reflectivity and transmissivity curves. Based on thin film optical principles, the optical properties and their integral values are calculated by matrix formula for the four-layer photocathode module. The result shows that the antireflection and window layers affect the peak and valley of the optical property curves and the active layer influences the absorptivity values of the transmission-mode cathode modules. The photocathode module has high absorptivity within the response waveband when the optimal module has the Si₃N₄ antireflection layer of 0.1 μm, the Ga_1 ? xAl_xAs window layer of more than 0.4 μm, and the GaAs active layer of 1.5 μm–2 μm and low average doping concentration.     

Photodiode properties of molecular beam epitaxial InSb on a heavily doped substrate

Photodiodes of InSb were fabricated on an epitaxial layer grown using molecular beam epitaxy (MBE). Thermal cleaning of the InSb (0 0 1) substrate surface, 2° towards the (1 1 1) B plane, was performed to remove the oxide. Photodiode properties of МВЕ-formed epitaxial InSb were demonstrated. Zero-bias resistance area product (R₀A) measurements were taken at 80 K under room temperature background for a pixel size of 100 μm × 100 μm. Values were as high as 4.36 × 10⁴ Ω/cm², and the average value of R₀A was 1.66 × 10⁴ Ω/cm². The peak response was 2.44 (A/W). The epitaxial InSb photodiodes were fabricated using the same process as bulk crystal InSb diodes with the exception of the junction formation method. These values are comparable to the properties of bulk crystal InSb photodiodes.     

Nb doping effect on TiO2−x films for bolometer applications

Nb-doped TiO_2−x thin films were deposited using a 1 at% niobium doped titanium target by RF reactive magnetron sputtering at various oxygen partial pressures (pO₂). The films appeared amorphous in the pO₂ range of 4.4–4.7% with resistivity ranging from 0.39 Ω cm to 2.48 Ω cm. Compared to pure TiO_2−x films, the resistivity of the Nb-doped TiO_2−x films did not change sensitively with the oxygen partial pressure, indicating that the resistivity of the films can be accurately controlled. 1/f noise parameter of Nb-doped TiO_2−x films were found to decrease largely while the measured temperature coefficient of resistance (TCR) of the films was still high. The obtained results indicate that Nb-doped TiO_2−x films have great potential as an alternative bolometric material.     

Chirped Bloch oscillations in strain-balanced InGaAs/InGaAs superlattices

Bloch oscillations excited in a strain-balanced In_xGa_1 − xAs/In_yGa_1 − yAs superlattice by fs optical pulses at 1.55 μ m are investigated in time-resolved transmission spectroscopy. The transition from the coherent oscillatory motion to an incoherent drift transport of the electrons is observed via a transient frequency shift of the Bloch oscillations due to the associated screening of the applied electric field. These electric field changes are analyzed quantitatively as a function of the initial field strengths and excitation densities. The incoherent transport can be described by a drift-diffusion model. As a result, the carrier mobility in the superlattice is obtained on a picosecond timescale.