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Strained HgTe/CdZnTe or InAs/GaInSb, and essentially unstrained HgTe/CdTe superlattices (SLs), are possible materials systems for implementation in future-generation infrared imaging systems. In addition to cutoff wavelengths spanning the infrared spectrum, they offer degrees of freedom in their design (e.g., layer thicknesses, alloy compositions, and number of layers in one superlattice period) that permit the optimization of an infrared detector’s figures of merit such as detectivity through the tuning of material properties such as recombination lifetimes and optical absorption. This paper provides a brief overview of the anticipated advantages of the SLs over HgCdTe alloy-based infrared photon detector technology and the relative merits of the II–VI and III–V semiconductor-based SLs. [ABSTRACT FROM AUTHOR]

Minority carrier recombination lifetime calculations for narrow-gap semiconductors are of direct practical interest in establishing whether a material's recombination is extrinsically or intrinsically limited, and therefore in guiding research and development programs regarding material quality improvements. We describe efforts to obtain accurate electronic band structures of HgCdTe alloy-based materials with infrared energy gaps and employ them to evaluate Auger recombination lifetimes. We use a 14-band k · p formalism to compute and optimize electronic band structures, and use the obtained electronic energies and matrix elements directly in the numerical evaluation of Auger and radiative lifetimes. [ABSTRACT FROM AUTHOR]

Controlling and monitoring individual spins is desirable for building spin-based devices, as well as implementing quantum information processing schemes. As with trapped ions in cold gases, magnetic ions trapped on a semiconductor lattice have uniform properties and relatively long spin lifetimes. Furthermore, diluted magnetic moments in semiconductors can be strongly coupled to the surrounding host, permitting optical or electrical spin manipulation. Here we describe the zero-field optical manipulation of a few hundred manganese ions in a single gallium arsenide quantum well. Optically created mobile electron spins dynamically generate an energy splitting of the ion spins and enable magnetic moment orientation solely by changing either photon helicity or energy. These polarized manganese spins precess in a transverse field, enabling measurements of the spin lifetimes. As the magnetic ion concentration is reduced and the manganese spin lifetime increases, coherent optical control and readout of single manganese spins in gallium arsenide should be possible. [ABSTRACT FROM AUTHOR]

An analytical model describing the absorption behavior of Hg1-xCdxTe is developed. It simultaneously considers the contributions from non-parabolic conduction/light hole bands and parabolic heavy hole bands obtained from 14-band k.p electronic structure calculations and the Urbach tail. This model smoothly fits experimental absorption coefficients over energies ranging from the Urbach tail region to the intrinsic absorption region up to at least 300 meV above the band gap. [ABSTRACT FROM AUTHOR]

Transition-metal dopants such as Mn determine the ferromagnetism in dilute magnetic semiconductors such as Ga1−xMnxAs. Recently, the acceptor states of Mn dopants in GaAs were found to be highly anisotropic owing to the symmetry of the host crystal. Here, we show how the shape of such a state can be modified by local strain. The Mn acceptors near InAs quantum dots are mapped at room temperature by scanning tunnelling microscopy. Dramatic distortions and a reduction in the symmetry of the wavefunction of the hole bound to the Mn acceptor are observed originating from strain induced by quantum dots. Calculations of the acceptor-state wavefunction in the presence of strain, within a tight-binding model and within an effective-mass model, agree with the experimentally observed shape. The magnetic easy axes of strained lightly doped Ga1−xMnxAs can be explained on the basis of the observed local density of states for the single Mn spin. [ABSTRACT FROM AUTHOR]

The type III band alignment of HgTe/CdTe superlattices leads to the interesting possibility of achieving very long wavelength infrared (VLWIR) (15 µm and longer) cutoff wavelengths with either normal (HgTe layer thickness less than about 70 Å for CdTe layer thickness of 50 Å) or inverted (HgTe thickness greater than about 70 Å) band structures. The inverted band structure superlattices promise even greater cutoff wavelength control than the normal band structure ones. However, the electronic band gaps of inverted band structure superlattices are substantially less than their optical band gaps, leading to large thermal carrier concentrations even at temperature as low as 40 K. These high carrier concentrations in turn give rise to more rapid Auger recombination than normal band structure superlattices with the same cutoff wavelengths. We conclude that the highest performance is expected from VLWIR HgTe/CdTe superlattice-based detectors with normal band structure absorber layers. [ABSTRACT FROM AUTHOR]