High-performance 8—14- µm Pb1-xSnxTe photodiodes

Photovoltaic detectors of Pb1-xSnxTe, sensitive in the 8- 14-µm spectral region, with near-theoretical performance characteristics, have been fabricated by a surface inversion technique. These detectors have exhibited quantum efficiencies of up to 45 percent limited by surface reflection), zero-bias resistance-area products of 21 Ωċcm²and background-limited detectivities of 1.5 × 10¹¹cm ċ Hz^1/2/W. A theoretical model consistent with experimental results is presented. Such high-performance devices are useful in guidance, reconnaissance, surveillance, ranging, and communication systems.     

Attenuation and Radiation Characteristics of the HE /Sub 11/ - Mode

The asymptotic properties of the fundamental mode HE /sub 11/ inside a large waveguide of finite surface impedances are discussed. The analysis applies to corrugated waveguides, certain optical fibers and wave-guides with metal walls coated by a dielectric layer. It is shown that for k-->/spl infin/ the HE /sub 11/ mode has the following two properties: it is polarized in one direction and the field vanishes at the boundary. Because of these properties, it is useful in the design of microwave feeds, since it minimizes cross-polarization and edge illumination at the aperture. It is also useful for long distance communication because of its low attenuation constant. Both the far field of a feed and the attenuation constant are discussed. It is shown that rectangular apertures have negligible cross-polarization over wider bandwidth than circular apertures. Furthermore, if the medium inside a waveguide is Iossless, so that power is lost only at the boundary, then the attenuation constant is very small, it is asymptotic to (ka)/sup -2/ for large ka, where k= 2 pi/lambda and a is a characteristic dimension of the waveguide. A rectangular waveguide consisting of four metal plates coated with thin dielectric layers is shown to be attractive for long distance communication, because of its simplicity of fabrication and its low attenuation.     

On the /spl eta/-/spl kappa/ distribution

For original paper by Yacoub et al., see IEEE Trans. Broadcasting., vol.51, p.504-11 (2005 December).     

RF noise in 0.18-/spl mu/m and 0.13-/spl mu/m MOSFETs

Studied the gate finger number and gate length dependence on minimum noise figure (NF/sub min/) in deep submicrometer MOSFETs. A lowest NF/sub min/ of 0.93 dB is measured in 0.18-/spl mu/m MOSFET at 5.8 GHz as increasing finger number to 50 fingers, but increases abnormally when above 50. The scaling gate length to 0.13 /spl mu/m shows larger NFmin than the 0.18-/spl mu/m case at the same finger number. From the analysis of a well-calibrated device model, the abnormal finger number dependence is due to the combined effect of reducing gate resistance and increasing substrate loss as increasing finger number. The scaling to 0.13-/spl mu/m MOSFET gives higher NF/sub min/ due to the higher gate resistance and a modified T-gate structure proposed to optimize the NF/sub min/ for further scaling down of the MOSFET.     

Frequency measurements of 9- and 10-μm N2O lasertransitions

We have measured frequencies of N₂O transitions by heterodyning sub-Doppler fluorescence-stabilized N₂O laser radiation with that from a reference CO₂ laser. A high-resolution cavity incorporates a ribbed tube and a highly reflective grating, permitting the CW oscillation of both the 10⁰ 0-02⁰0 9-μm and the 10⁰0-00⁰1 10-μm regular bands. This is the first sub-Doppler frequency measurement of the 9-μm band. The accuracy in the determination of the rotational constants for both bands has been improved by an order of magnitude, and calculated transition frequencies are presented     

Reliability of high radiance InGaAsP/InP LED́s operating in the 1.2-1.3 µm wavelength

The reliability of high radiance InGaAsP/InP DH LED's operating in the1.2-1.3 mum wavelength and the defect structures observed in this quaternary alloy have been presented. Threading dislocations and misfit dislocations do not act as strong nonradiative recombination centers, in contrast with the case in GaAs or GaAlAs optical devices. Dark-spot defects (DSD's) were sometimes generated in the emitting area during aging at elevated temperatures. These defects were analyzed microscopically using a transmission electron microscope and were identified as precipitates. To investigate the homogeneous degradation, accelerated aging at the ambient temperatures of 20, 60, 120, 170, 200, and 230°C has been carried out for over 15 000 h at the current density of 8 kA/cm²using LED's without dark structures. The degradation rates were statistically calculated by assuming the normal distribution. The mean values of degradation rates and the values of standard deviation were determined at the temperatures above 170°C. The activation energy of homogeneous degradation was determined to be 1.0 eV and the extrapolated half-life in excess of 10⁹h was estimated at the ambient temperature of 60°C.     

The effect of 1300-1380°C anneal temperatures and materialcontamination on the characteristics of CMOS/SIMOX devices

The characteristics of CMOS transistors fabrication on silicon implanted with oxygen (SIMOX) materials were measured as a function of the silicon superficial layer contamination levels. In addition, postimplant anneal temperatures of 1300°C, 1350°C, and 1380°C were examined. It is found that the transistor leakage currents as well as the integrity of the gate oxide and implanted SIMOX oxide are functions of the carbon content in the starting material. Leakage currents below 1.0×10^-12 A/μm of channel width have been measured when the carbon concentration is reduced to 2×10¹⁸/cm². In addition, the integrity of the transistor gate dielectric, SIMOX implanted oxide, and oxygen precipitate density are seen to be a function of the postimplant anneal temperature. A gate dielectric breakdown field of 10 MV/cm has been achieved when the postimplant temperature is increased to 1380°C     

Small-signal modulation characteristics of p-doped 1.1- and 1.3-/spl mu/m quantum-dot lasers

We have investigated the small-signal modulation characteristics of 1.1and 1.3-/spl mu/m p-doped quantum-dot lasers in order to evaluate the potential of acceptor doping. The maximum measured 3-dB bandwidth of the 1.1- and 1.3-/spl mu/m lasers are 11 and 8 GHz, respectively, which are only marginally higher than those in the corresponding undoped devices.     

Are transverse phonons important for Γ - X-intervalley scattering?

We employ the rigid pseudo-ion method to calculate the q-dependence of intervalley deformation potentials for GaP from the Γ-point to the X-valley. We find that the fast transverse acoustic phonon (which cannot couple to the symmetry point X) becomes as important along the XW-direction as the longitudinal acoustic phonon (which is allowed at X). We have measured the temperature dependence of the lifetime broadenings of the E₀-gap of GaP with spectroellipsometry in order to obtain an effective intervalley phonon energy from which the relative contributions of the different phonon branches can be determined, but difficulties arise as intervalley and intravalley (Fröhlich) exciton-phonon interaction both contribute to the broadenings.     

Type-II interband cascade lasers in the 4.3-4.7-/spl mu/m wavelength region

Operation of type-II interband cascade lasers in the 4.3-4.7-/spl mu/m wavelength region has been demonstrated at temperatures up to 240 K in pulsed mode. These lasers fabricated with 150-/spl mu/m-wide mesa stripes operated in continuous-wave (CW) mode up to a maximum temperature of 110 K, with an output power exceeding 30 mW/f and a threshold current density of about 41 A/cm/sup 2/ at 90 K. The maximum CW operation temperature of 110 K is largely limited by the high specific thermal resistance of the 150-/spl mu/m-wide broad area lasers. A 20-/spl mu/m-wide mesa stripe laser was able to operate in CW mode at higher temperatures up to 125 K as a result of the reduced specific thermal resistance of a smaller device.     

On the observation of the Λ-doubling in the O - O UV N2laser band

The spectral composition of the (O-O) N2UV stimulated band, as the linewidths of the individual stimulated transitions remain unchanged when the nitrogen pressure and the excitation voltage range from 40 to 100 torr and, from the threshold, to 10 kV, respectively, is observed with a laboratory superradiant emitter.     

Corrections to “Multiplierless, Folded 9/7–5/3 Wavelet VLSI Architecture” [Sep 07 770-774]

In the above titled paper (ibid., vol. 54, no. 9, pp. 770-774, Sep. 07), equation (1) was incorrect. The correct equation is presented here.     

TM/sub 0n0/ - and TM/sub m10/ - Mode Oversized Cylindrical Cavity Power Combiners

TM/sub m10/ -mode power combining is treated in addition to conventional TM/sub 0n0/-mode combining in a multiple-device oversized cylindrical cavity having a window output structure. Mode analysis gives the condition for stable power-combining operation in the desired mode. By experiments both on TM/sub 0n0/ -mode combining (n = 2, 3, and 4) and on TM/sub m10/ -mode combining (m = 2 and 8), it is shown that almost perfect power combining in the TM/sub 210/ mode can be achieved as in the TM/sub 020/ mode and that the power combining efficiency decreases gradually with increasing n or m. A possible advantage of TM/sub m10/ -mode combining in an oversized cavity is suggested based on the experimental result that power combining in the TM/sub 810/ mode gives higher efficiency than in the TM/sub 040/ mode.     

Characteristics of 0.8- and 0.2-μm gate length InxGa1-xAs/In0.52Al0.48As/InP(0.53⩽x⩽0.70) modulation-doped field-effect transistorsat cryogenic temperatures

The performance characteristics of InP-based pseudomorphic MODFETs with varying the In composition (0.53⩽x⩽0.70), which changes the strain in the channel, were studied. The temperature was varied in the range of 40-300 K, and the devices had gate lengths L _g of 0.8 and 0.2 μm. The analysis predicts an increase in the intrinsic cutoff frequency with increasing In composition and decreasing temperature and gate length. Also, the analysis predicts that the increase in cutoff frequency with decreasing temperature is less significant with increasing In composition and decreasing gate length. Preliminary experimental results show that as In composition increases from 0.53 to 0.70, f_T increases by 30-40%, and as the temperature decreases from 300 to 40 K, f_T improves by 15-30%, both for 0.8- and 0.2-μm devices     

Performance and reliability of high radiance InGaAsP/InP DH LED́s operating in the 1.15-1.5 µm wavelength region

The performance and reliability of InGaAsP/InP double heterostructure (DH) light emitting diodes (LED's) have been investigated over a wide range of emission wavelengths1.15-1.5 mum. High radiance performance has been achieved by growing optimized DH structures and adopting a method of coupling a monolithic-lensed LED to a spherical-ended fiber. Interface instability previously encountered in the liquid phase epitaxy (LPE) to grow a DH for 1.5 μm wavelength has been eliminated by a new growth method using a reduced temperature. LED's exhibiting typical output powers of 50, 44, and 21 μW at 100 mA, measured at the end of a 50 μm core 0.20 NA graded-index fiber with a length of 1 m, have been realized, respectively, at wavelengths of 1.15, 1.27, and 1.5 μm. The spectral width, coupled power and its temperature dependence, and the cutoff frequency have been analyzed in terms of the emission wavelength. Operating lives of LED's at three different wavelengths have been estimated from the result of accelerated aging carried out at the ambient temperature of 200°C and at a constant current of 100 mA. It has been found that the degradation rate exhibits no dependence on the wavelength confirming the same value of half-lives in excess of 10⁹h for the 60°C operation.     

Impact ionization resonance and auger recombination in Hg1 - xCdxTe (0.6 ≤ x ≤ 0.7)

The purpose of this paper is the study of the impact ionization and the Auger recombination in Hg1-xCdxTe avalanche photodiodes, with0.6 leq x leq 0.7. Forx sim 0.7it is shown that the spin orbit splitting Δ is lower than the bandgap energy Egso that impact ionization is initiated by holes from the Split-off valence band. Forx sim 0.6, Delta sim E_{g}, the rate of the Auger recombination is maximum, corresponding to a resonant impact ionization and to a maximum ratiok = beta / alphawhere α and β are, respectively, the impact ionization coefficient for electrons and holes.     

Analysis of the /spl Sigma/-/spl Delta/ pulsed digital oscillator for MEMS

The aim of this paper is the analysis, simulation, and experimental verification of the /spl Sigma/-/spl Delta/ pulsed digital oscillator (PDO) topology. As it has been shown in previous works, the oscillation frequency and output spectrum in the PDO depend on the sampling frequency, the natural frequency of the microelectromechanical systems (MEMS) resonator and its damping factor. Here, extensive discrete-time simulations have been carried out which show that the normalized oscillation frequency as a function of the normalized natural frequency of the resonator is very similar to a distorted Devil's Staircase fractal. This nonlinear behavior is a direct consequence of the damping losses of the MEMS resonator. Analytical conditions for a perfect oscillation at the natural frequency of the resonator are also calculated. For this set of what we call "perfect" frequencies, it is also shown that the energy transfer from the electrical to the mechanical domain is maximum. Then a more generalized structure of the oscillator is considered and the drawn conclusions are tested against experimental results obtained from an oscillator prototype which uses a MEMS resonator with thermoelectric actuation and piezoresistive position sensing.     

TLP systems with combined 50- and 500-/spl Omega/ impedance probes and Kelvin probes

Transmission line pulse (TLP) systems are mainly classified by their impedance, such as a 50- or 500-/spl Omega/ current source. A new TLP configuration allows switching between 50 and 500 /spl Omega/ by computer control to characterize a given part using both impedances. In addition, a four-needle Kelvin technique is introduced to TLP, which overcomes the measurement error from variations in contact resistance where the probe needles contact the wafer surface.