Determination of cut-off wavelength and composition distribution in Hg1-xCdxTe

The determination of cut-off wavelength, λ _co, and composition distribution for Hg_1-xCd_xTe has been discussed in this paper. A shift of the cut-off wavelength was found from the photo-response calculation for the HgCdTe devices with the same energy gap E_g but different thickness d. An expression of λ _co(x,T,d) has been derived from the half-maximum photo-response curve calculation. The composition uniformity has been determined from the room-temperature transmission fitting procedure. The composition real space distribution is suggested to be determined by the combination of absorption edge phenomenon and thermal imaging technique.     

An internal calibration technique for pseudobinary systems by auger electron spectroscopy

An internal calibration technique has been developed for the quantitative analysis of pseudobinary systems by means of Auger electron spectroscopy without the need for stan-dards of known composition. This technique has been used for analyzing PbO-In₂O₃ two-phase films and A1N-A1₂ O₃ , AlAs-GaAs, and GaP-InP solid solutions. The technique is applicable to systems of the type (AC_m) (BC_n)_1-x if the Auger intensities measured for elemens A, B, and C are given by the linear relationships I = xI_A ^**, I_B = (l-x)I_B ^*, and I_C = xI_C ^** + (l-x)I_{C C} ^* where I_A ^** and I_C ^** are the inten-sities for pure AC_m and I_B ^* and I* are the intensities for pure BC_n . To determine whether this criterion is satisfied, a series of Auger measurements is made on regions of dif-ferent composition within a single specimen (e.g., on speci-mens in which a concentration variation exists across the surface or surfaces exposed by repeated sputter-etching of a sample with an in-depth composition gradient), and plots of I_A vs I_B and I_C/I_B vs I_A/I_B are made. If these plots are linear over tne range of compositions investigated, it is assumed that the above linear relationships are valid over the whole range of the pseudobinary system. It is then possible to construct linear calibration plots of I_A, I_B , and I_C vs x for the whole composition range.     

Fluid flows induced in tall narrow containers by A.C.R.T.

An investigation into the flows produced by the Accelerated Crucible Rotation Technique (A.C.R.T.) in tall narrow containers has been carried out. Spiral shearing, Ekman and transient Couette flows have been demonstrated and interactions between them observed. Various crucible base configurations have been employed to simulate actual crystal growth. Ekman flow is the most important stirring mechanism in the region close to the growing crystal while unstable Couette flow is an efficient mixing process at the crucible walls. Experimentally—determined rotation rates for the onset of transient Couette flow are compared to those predicted from Rayleigh’s criterion. Present address: Philips Research Laboratories, Redhill, Surrey, RH1 5HA, U.K.     

Electrical and optical properties of N-type Alx Ga1-x as grown by MO-VPE

Growth conditions and properties of Al_xGa_1-xAs (0.1 ≤ × ≤O.3) using metalorganic vapour phase epitaxy (MO-VPE) are investigated. N-type is achieved either by silicon or by selenium doping. Properties of the layers are evaluated by Hall effect, cathodoluminescence and photoluminescence. It is shown that selenium doping leads to luminescent material : when x = O.1, the efficiency is only a factor of 2 smaller than for GaAs. Deposition temperature is a critical parameter : increasing the growth temperature yields more luminescent Al_x Ga_1-x As. This work has been partly supported by the Délégation à la Recherche Scientifique et Technique (D.G.R.S.T.)     

High‐Temperature BiScO3‐PbTiO3 Piezoelectric Vibration Energy Harvester

Conventionally, effective mechanical vibration energy harvesting is based on (Pb,Zr)TiO₃ (PZT) ceramics, poly(vinylidene fluoride) (PVDF) polymers or PVDF/PZT or other piezoelectric composite materials, and their working temperature is normally limited to room temperature (R‐T) or below 150 °C. Here, bismuth scandium lead titanate (BiScO₃‐PbTiO₃, abbreviated as BSPT) ceramic is reported which has a high Curie temperature point around 450 °C and its application for high‐temperature (H‐T) vibration energy harvesting. Experimental results show that it exhibits an excellent H‐T piezoelectricity, converting mechanical vibration energy into electric power effectively in a wide temperature range from R‐T till 250 °C. This research shows the BSPT piezoelectric energy harvester having the potential application for self‐power source of wireless sensor network system in high temperature circumstance.     

Optical properties of Pb1−xSnxSe thin layers grown by HWE

This paper concerns the optical study of Pb_1?xSn_xSe /Si layers elaborated by the Hot Wall Epitaxy (HWE) technique. Optical reflection and transmission were measured for all the composition range in the PbSe — SnSe system by using a Fourier Transform Infrared Spectrometer (FTIR). From a theoretical model and the experimental reflections coefficients R, RP for respectively layer-substrate and substrate-layer and the transmission coefficient T, we have determined simultaneously the refractive index n, the extinction coefficient k and the thickness d. Then the composition and temperature energy gap dependence have been established.     

AP-MOVPE of InGaAs on GaAs (0 0 1): Analysis of in situ reflectivity response

We have investigated in situ monitoring of growth rate and refractive index by laser reflectometry during InGaAs on GaAs (0 0 1) substrate growth in atmospheric pressure metalorganic vapour-phase epitaxy (AP-MOVPE). The indium solid composition (x_In^s) was varied by changing the substrate temperature or the indium vapour composition (x_In^v). The refractive index of InGaAs alloys as a function of temperature and composition was quantified and compared which that of GaAs for 632.8 nm wavelength by simulation of experimental reflectivity responses. Composition analyses were carried out by high-resolution X-ray diffraction (HRXRD) and optical absorption (OA). The layers thicknesses were estimated by scanning electron microscopy (SEM) observations. The temperature dependence of InGaAs growth rate has been investigated in the temperature range 420-680 °C using trimethylgallium (TMGa), trimethylindium (TMIn) and arsine (AsH₃) sources. It shows Arrhenius-type behaviour with an apparent activation energy E_a of 0.62 eV (14.26 kcal/mol). This value is close to that determinate in the AP-MOVPE of GaAs.     

In situ sensors for monitoring and control in molecular beam epitaxial growth of Hg1−xCdxTe

The current status of the implementation and refinement of two wafer state sensors forin situ monitoring and control during molecular beam epitaxial (MBE) growth of Hg_1−xCd_xTe will be reported. First a rapid scan spectral ellipsometer has been developed and employed for precisely measuring compositions of Hg_1−xCd_xTe alloys during growth. MBE films in the composition range x = 0.20 to 0.30 have been grown andin situ spectra taken at the growth temperature (180°C) and at room temperature. The MBE films were treated as single layers without the need to invoke any surface film (due to surface roughness, oxide, or of any different composition) as required for exsitu data. The least squares fit over the whole spectral range was used as a measure of the precision. The film composition was also determinedex situ by wavelength dispersive analysis of x-rays and by Fourier transform infrared (FTIR) spectrometry after verifying that there was no lateral variation. A precision of better than ±0.0015 has so far been demonstrated usingin situ spectral ellipsometry for Cd composition or CdTe mole fraction, x, measurements. This compares with ±0.003 for single wavelength ellipsometry. The composition of Hg_1−xCd_xTe films were also monitored during growth. A spectral pyrometer based on a FTIR spectrometer has also been developed for substrate temperature measurements during growth. The spectral pyrometer measures both the emission and reflectance to give the emissivity of a growing sample over a range of wavelengths spanning the peak of the grey body emission. From the reflectivity measurements, the thickness (in excess of 1 μm) of the growing film is also determined from the interference fringes. The spectral ellipsometer is only capable of measuring thicknesses up to C.a 5000°A (i.e. optically thin). Excellent agreement is obtained between thein situ (at growth temperature) andex situ (at room temperature) thickness measurements. The small discrepancy can be explained by the refractive index of Hg_1−xCd_xTe being 5% higher at the growth temperature than at room temperature. The combination ofin situ sensors now provides a means of continuously monitoring the composition and thickness of the growing Hg_1−xCd_xTe film.     

Influence of rain gauge integration time on the rain rate statistics used in microwave communications

An investigation into the effect of the integration time T on the rain rate distribution P(R) is presented using a rainfall rate data bank of 49 years recorded at Barcelona (CCIR - Zone L), using a rapid response Jardi rain rate gauge. T extends from 1 to 60 min and P(R) extends to less than 10^-3 %. The relation between the various T-distributions P(R_T) is presented as well as the values of R_T and R₁ which give the same probability. The ratio R_T/R₁ and the potential expression R₁ = aR^b _T are studied. Comparison with recent results from Canada confirms both the numerical value presented and the climatic dependence of the equi-probable ratio R_T/R₁.     

Use of tertiarybutylphosphine for the growth of InP and GaAs1-xPx

A newly-developed phosphorus source, tertiarybutylphosphine (TBP), which is much less toxic than PH₃, has been used to grow InP and GaAs_1-xP_x by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Excellent morphologies are obtained for the growth of InP between 560 and 630° C for TBP partial pressures larger than 0.5 x 10^-3. For the first time, V/III ratios as low as 3 have been used to grow InP epilayers with featureless morphologies at 600° C. To obtain good morphologies at both lower and higher temperatures, higher TBP partial pressures are necessary. The electron mobility increases and the electron density decreases as the temperature is increased. The highest room temperature mobilities and lowest electron densities, obtained at 630° C, are 3800 cm²/V-sec and 3 x 10¹⁵ cm^-3, respectively. The 10 K photoluminescence spectra of the InP epilayers at higher growth temperatures show no carbon contamination. Bound excition half widths as low as 3.0 meV have been measured. The use of TBP to replace PH₃ in the growth of GaAs_1-xP_x results in a nearly linear relationship between vapor and solid composition at 610° C,i.e., the P distribution coefficient is nearly unity. This contrasts sharply with the very low P distribution coefficient obtained using PH₃ at such low growth temperatures.     

Photoluminescence and composition of amorphous As<Subscript>2</Subscript>Se<Subscript>3</Subscript> films modified with Er(<Emphasis Type="Italic">thd</Emphasis>)<Subscript>3</Subscript> complex compound

The photoluminescence and composition of amorphous As₂Se₃ films modified with an Er(thd)₃ complex compound have been studied. A band centered at 1.54 μm, characteristic of photoluminescence from Er embedded in amorphous matrices, has been revealed at room temperature. The composition of thin amorphous As₂Se₃ films modified with an Er(thd)₃ complex compound has been examined by methods of nuclear microanalysis: Rutherford backscattering and nuclear resonant reactions. Dependences of the concentrations of Er ions, oxygen, and carbon on the growth conditions of the films are obtained. It is shown that the Er concentration in a thin film varies nonlinearly as the relative concentration of the starting complex compound increases. In addition, the increase in the Er content of a film is accompanied by a simultaneous rise in the content of such light elements as oxygen and carbon. Comparative analysis of the nuclear microanalysis data and IR spectra demonstrates that, in modification of As₂Se₃ with the Er(thd)₃ complex compound by the given method, the nearest environment of Er in the complex compound is partly preserved.     

Group-V composition control for InGaAsP grown by gas source molecular beam epitaxy

Based on our kinetics models for gas source molecular beam epitaxy of mixed group-V ternary materials, the group-V composition control in In_yGa_1−yAs_1−xP_x epilayers has been studied. The P or As composition in In_yGa_1−yAs_1−xP_x (lattice matched to InP or GaAs) can be obtained from a simple equation for substrate temperatures below 500°C. This has been verified by a series of experimental results.     

Phase Equilibria of the Sn-V System and Interfacial Reactions in Sn/V Couples

Sn-V alloys were prepared for a phase equilibrium study at 600°C and 250°C. All alloys were annealed for longer than 6 months to ensure that they reached equilibrium. There are two intermetallic compounds, namely VSn₂ (V₂Sn₃) and V₃Sn phases. The composition of the VSn₂ phase is Sn-34.0at.%V. The VSn₂ phase has the CuMg₂ structure. It was previously designated as the V₂Sn₃ phase and was renamed in this study to be consistent with its structure and composition. The composition of the V₃Sn phase is Sn-78.0at.%V, and it has the A15 structure at 600°C and 250°C. With the new experimental results, the Sn-V system has been thermodynamically assessed with the CALPHAD approach. The calculated Sn-V phase diagram is in good agreement with the experimental determinations. Sn/V interfacial reactions at 950°C and 600°C are also examined in this study. The V₃Sn phase is formed at 950°C, while the VSn₂(V₂Sn₃) phase is formed at 600°C.     

Light-induced E.S.R. in amorphous silicon

A model for defects in hydrogenated amorphous silicon (T_S > 150‡C) observed by light-induced E.S.R. is presented. It is based on a comparison with E.S.R. signals observed from irradiation defects in crystalline silicon. The magnitude of the E.S.R. signal as a function of hydrogen concentration is also discussed.     

The effect of gas phase growth parameters on the composition of InGaAs in the hydride VPE process

A 1.4-μm thick InGaAs layer exhibiting an x-ray diffraction linewidth of 18 arcs has been grown on an InP substrate. This is the best crystalline perfection ever reported for InGaAs, as far as the author is aware. The effect of gas composition on lattice mismatch has been investigated for InGaAs layers grown under a variety of conditions. An empirical equation has been developed which relates lattice mismatch(Δa/a) to metals ratio, mole fraction of AsH₃ and mole fraction of HC1. Values of(Δa/a) calculated using this equation are in good agreement with experiment. The metals ratio for lattice match is shown to vary linearly with the growth rate. This observation is shown to be consistent with mass transfer limitation in the gas phase. As a further consequence, relationships between layer thickness uniformity and lattice mismatch uniformity and between growth rate and gas composition are derived.     

Phase separation, effects of biaxial strain, and ordered phase formations in cubic nitride alloys

The thermodynamics as well as the energetics and the structural properties of cubic group-III nitrides alloys have been investigated by combining first-principles total energy calculations and cluster expansion methods. In particular results are shown for the ternary In_xGa_1−xN and the quaternary Al_xGa_yIn_1−x−yN alloys. Phase separation is predicted to occur at growth temperatures, for both fully relaxed alloys. A remarkable influence of an external biaxial strain on the phase separation, with the formation of ordered phase structures has been found for the InGaN alloy. These findings are used to clarify the origin of the light emission process in InGaN-based optoelectronic devices. Results are shown for the composition dependence of the lattice constant and of the energy gap in quaternary Al_xGa_yIn_1−x−yN alloys.     

Determination of the parameters of multilayer nanostructures using two-wave X-ray reflectometry

A method for determining the parameters of multilayer nanostructures by measuring the angular dependence of the X-ray reflectance at two wavelengths has been considered. A calculation scheme taking into account the specificity of the method was suggested, which allows operation with samples of any size and shape. The scheme was applied to C/Ni/C, Si_1?xGe_x, and Al_xGa_1?xAs multilayer structures. It was shown that two-wave reflectometry allows elimination of the influence of instrumental errors; hence, the thickness, density, and composition of both polycrystalline and monocrystalline nanostructure layers reliably determined.     

Compiler compatible 5.66 Mb/mm2 8T 1R1W register file in 14 nm FinFET technology

1-read/1-write (1R1W) register file (RF) is a popular memory configuration in modern feature rich SoCs requiring significant amount of embedded memory. A memory compiler is constructed using the 8T RF bitcell spanning a range of instances from 32 b to 72 Kb. An 8T low-leakage bitcell of 0.106 μm² is used in a 14 nm FinFET technology with a 70 nm contacted gate pitch for high-density (HD) two-port (TP) RF memory compiler which achieves 5.66 Mb/mm² array density for a 72 Kb array which is the highest reported density in 14 nm FinFET technology. The density improvement is achieved by using techniques such as leaf-cell optimization (eliminating transistors), better architectural planning, top level connectivity through leaf-cell abutment and minimizing the number of unique leaf-cells. These techniques are fully compatible with memory compiler usage over the required span. Leakage power is minimized by using power-switches without degrading the density mentioned above. Self-induced supply voltage collapse technique is applied for write and a four stack static keeper is used for read Vmin improvement. Fabricated test chips using 14 nm process have demonstrated 2.33 GHz performance at 1.1 V/25 °C operation. Overall V_min of 550 mV is achieved with this design at 25 °C. The inbuilt power-switch improves leakage power by 12x in simulation. Approximately 8% die area of a leading 14 nm SoC in commercialization is occupied by these compiled RF instances.     

Detection and mapping of oxygen in silicon wafers by scanning infrared absorption

Scanning Infrared Absorption (S.I.R.A.) setup was carried out for investigating and mapping of microdefects distribution in Czochralski silicon wafers. Using CO₂ laser, this non destructive, non contact test method allows transmitted beam local attenuation from oxygen precipitates to be determined. Transmitted intensity I_t maps from peak height of the 1080 cm^?1 absorption band were obtained. An inhomogeneous initial oxygen distribution is found in as-grown samples. The samples were then submitted to preannealing at 750°C for 16 hours, followed by annealing at 900°C for 24 hours. The obtained I_t fluctuations mapping depicts a ring-shaped distribution of oxygen precipitates.     

Properties of high-efficiency zinc-diffused Ga1-xAlxAs light-emitting diodes

The external quantum efficiency of zinc-diffused hemispherically-shaped Ga_1-xAl_xAs light-emitting diodes has been investigated as a function of temperature, peak emission energy, and current. External quantum efficiencies as high as 13.5% and 52% have been achieved at 296°K and 77°K, respectively. An analysis of the temperature dependence of the spectral characteristics (emission spectral shape, peak emission energy, and spectral half-width) shows that the improved efficiencies at room temperature result from reduced internal bulk absorption due to a composition gradient in the emitter. Values as small as 3.4 have been observed for the ratio of the 77°K efficiency to the 296°K efficiency. The decrease of the external quantum efficiency at high peak emission energies (short wavelengths) agreed with the decrease theoretically predicted from the composition dependence of the direct and indirect energy gaps of Ga_1-xAl_xAs. A decrease of external quantum efficiency at low currents was shown to be due to a nonradiative parallel component of current.