There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Statistics for Spatial Data.

We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

Band parameters for nitrogen-containing semiconductors

High-order harmonic generation is a nonlinear optical process that enables the creation of light pulses at frequencies much higher than that from a seed laser. The host medium for this interaction is typically a gas. Now, the process has been observed in a bulk crystalline solid with important implications for attosecond science.

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Observation of high-order harmonic generation in a bulk crystal

Direct and phonon-assisted Auger recombination mechanisms are investigated in the framework of perturbation theory by using accurate electron and phonon dispersion relations. It is found that Auger recombination in narrow gap semiconductors is appreciably enhanced by phonon-assisted processes.

Auger lifetime in narrow gap semiconductors

This work presents the activities of the Center for Semiconductor Modelling in the area of infrared imaging devices. We outline a methodology that enables the study of large scale infrared detector arrays to quantify their optical and electrical performance. Furthermore, we present an approach to investigate the quantum mechanical transport properties of superlattice based detectors that are an emerging technology with potential applications both in commercial and defense system.

Understanding Fundamental Material Limitations to Enable Advanced Detector Design

Indium gallium arsenide (In 1−x Ga x As) is an ideal material choice for short wave infrared (SWIR) imaging due to its low dark current and excellent collection efficiency. By increasing the indium composition from 53% to 83%, it is possible to decrease the energy gap from 0.74 eV to 0.47 eV and consequently increase the cutoff wavelength from 1.7 μm to 2.63 μm for extended short wavelength (ESWIR) sensing. In this work, we apply our well-established numerical modeling methodology to the ESWIR InGaAs system to determine the intrinsic performance of pixel detectors. Furthermore, we investigate the effects of different buffer/cap materials. To accomplish this, we have developed composition-dependent models for In 1−x Ga x As, In 1−x Al x As, and InAs 1−y P y . Using a Green’s function formalism, we calculate the intrinsic recombination coefficients (Auger, radiative) to model the diffusion-limited behavior of the absorbing layer under ideal conditions. Our simulations indicate that, for a given total thickness of the buffer and absorbing layer, structures utilizing a linearly graded small-gap InGaAs buffer will produce two orders of magnitude more dark current than those with a wide gap, such as InAlAs or InAsP. Furthermore, when compared with experimental results for ESWIR photodiodes and arrays, we estimate that there is still a 1.5x magnitude of reduction in dark current before reaching diffusion-limited behavior.

Numerical modeling of extended short wave infrared InGaAs focal plane arrays

In this paper, we investigate a failure mode that arises in dense infrared focal plane detector arrays as a consequence of the interactions of neighboring pixels through the minority carrier profiles in the common absorber layer. We consider the situation in which one pixel in a hexagonal array becomes de-biased relative to its neighbors and show that the dark current in the six neighboring pixels increases exponentially as a function of the difference between the nominal and anomalous biases. Moreover, we show that the current increase in the six nearest-neighbor pixels is in total larger than that by which the current in the affected pixel decreases, causing a net increase in the dark current. The physical origins of this effect are explained as being due to increased lateral diffusion currents that arise as a consequence of breaking the symmetry of the minority carrier profiles. We then perform a parametric study to quantify the magnitude of this effect for a number of detector geometric parameters, operating temperatures, and spectral bands. Particularly, numerical simulations are carried out for short-, mid-, and long-wavelength HgCdTe infrared detectors operating between 77 K and 210 K. We show that this effect is most prevalent in architectures for which the lateral diffusion current is the largest component of the total dark current—high operating temperature devices with narrow epitaxial absorber thicknesses and pitches small compared to the diffusion length of minority carriers. These results could prove significant particularly for short- and mid-wave infrared detectors, which are typically designed to fit these conditions.

A Failure Mode in Dense Infrared Detector Arrays Resulting in Increased Dark Current

This paper presents one-dimensional numerical simulations and analytical modeling of InAs nBn detectors having n-type barrier layers with donor concentrations ranging from 1.8×10 15 to 2.5×10 16 cm -3 . We consider only “ideal” defect-free nBn detectors, in which dark current is due only to the fundamental mechanisms of Auger-1 and radiative recombination. We employ a simplified nBn geometry, with the absorber layer (AL) and contact layer (CL) having the same donor concentration and comparable thicknesses, to reveal more clearly the underlying device physics and operation of this novel infrared detector. Our simulations lead to a new model for the ideal nBn with an n-type barrier layer (BL) that consists of two ideal backto- back photodiodes connected by a voltage-dependent series resistance representing hole conduction within the BL. Increasing the BL donor concentration lowers exponentially the hole concentration in the BL, thereby exponentially increasing the BL series resistance. Reductions in dark current and photocurrent due to the valence band barrier in the n-type BL only become appreciable when the BL series resistance becomes comparable to or exceeds the sum of the diffusion current resistances of the AL and CL. This new model elucidates the overwhelming importance of the electrical type and doping concentration of the BL to the operation of the nBn detector.

Enrico Bellotti

Papers

Auger lifetime in narrow gap semiconductors

Understanding Fundamental Material Limitations to Enable Advanced Detector Design

Numerical modeling of extended short wave infrared InGaAs focal plane arrays

A Failure Mode in Dense Infrared Detector Arrays Resulting in Increased Dark Current

New model for the ideal nBn infrared detector