Narrow-gap Superlattices Research Articles

First-principles investigation of carrier Auger lifetime and impact ionization rate in narrow-gap superlattices

We investigate theoretically the technologically essential Auger recombination lifetime in narrow-gap semiconductor superlattices by means of a completely first-principles formalism, based on accurate energy bands and wave functions provided by the full-potential linearized augmented plane wave scheme. The minority carrier Auger lifetimes are determined by two correlated approaches: (1) direct evaluation in Fermi's golden rule, and (2) indirect evaluation, based on a detailed balance formulation relating Auger recombination and its inverse process, impact ionization, in a unified framework. Lifetimes determined by the direct and indirect methods for n -doped HgTe/CdTe and InAs/InxGa1－xSb superlattices exhibit excellent consistency with experimentally measured values. This justifies the computational formalism as a new sensitive tool in performance optimization of the synthetic narrow-gap semiconductor superlattice systems.

Auger recombination in narrow-gap semiconductor superlattices incorporating antimony

A comparison is performed between measured and calculated Auger recombination rates for four different narrow-gap superlattices based on the InAs/GaSb/AlSb material system. The structures are designed for optical or electrical injection for mid-infrared laser applications, with wavelengths ranging from 3.4 to 4.1 μm. The electronic band structures are computed employing an accurate 14-band restricted basis set (superlattice K⋅p) methodology that utilizes experimental information about the low-energy electronic structure of the bulk constituents. The superlattice band structures and their associated matrix elements are directly employed to compute Auger recombination rates. Varying amounts of Auger recombination suppression are displayed by the various superlattices as compared to bulk mid-infrared systems. The greatest disagreement between theory and experiment is shown for the structure predicted to have the most Auger suppression, suggesting the suppression is sensitive either to theoretical or growth uncertainties.

Auger recombination in narrow-gap semiconductor superlattices

An extended $\mathit{k}\ensuremath{\cdot}\mathit{p}$ formalism has been developed to describe wave functions in narrow-band-gap semiconductors and narrow-band-gap superlattices. The model shows very satisfactory agreement with various experimental results such as optical absorption spectra in both bulk narrow-gap semiconductors and in narrow-gap superlattices. Based on the model we calculate the Auger recombination rates in InAsSb alloys and in InAsSb-based superlattices. We demonstrate that the Auger recombination coefficient of the superlattices may be larger or smaller than that of bulk alloys of similar gaps depending on the superlattice structure. From the study of several structures we propose a design strategy for minimizing the Auger recombination.

Interface roughness limited electron mobility in HgTe-CdTe superlattices

We demonstrate that interface roughness is the dominant low-temperature scattering mechanism for electrons in HgTe-CdTe superlattices with thin wells. Not only do the experimental mobilities follow the expected d6W dependence, but the observed temperature dependence is accurately reproduced by theory when the treatment of interface roughness scattering is generalized for narrow-gap superlattices. The fits to data yield roughness correlation lengths in the range 60–200 Å.

Magneto-optical transitions between subbands with different quantum numbers in narrow gap HgTe–CdTe superlattices

Magneto-optical transitions induced by the coupling between the conduction and the valence bands through the momentum matrix element, and by the coupling terms between light and heavy holes resulting from an applied magnetic field are studied theoretically in narrow gap HgTe–CdTe superlattices. Selection rules and transition probabilities for the above transitions are presented and compared with allowed transitions. The numerical results for the transition probabilities show that some of the interband transitions with ΔN=±1 are significant and have to be considered in the studies of interband magneto-optical spectra of narrow gap superlattices.

Mercury-based narrow-gap superlattices

From far infrared magneto-optical absorption experiments done in n-type Hg 1−xZn xTeCdTe superlattices, the conduction band dispersion relations are obtained. Comparison with theoretical investigations evidences the semimetallic behavior of the studied superlattices at low temperatures and show that the valence band offset at each interface is certainly large (≈ 360 meV).

Pseudopotential approach to long period semiconductor superlattices

The pseudopotential method studying long-period semiconductor superlattices is introduced. The subband structures of narrow-gap superlattices InGa-GaSb and HgTeCdTe calculated with this method are described. The F-X mixing of electronic states in GaAsAlAs is discussed and the mixing parameter in the surface matrix is determined to be 0.5 by comparing with the effective-mass theory.

Pseudopotential approach to long-period narrow-gap superlattices.

The pseudopotential method is used to calculate the electronic structures of long-period narrow-gap InAs-GaSb and HgTe-CdTe superlattices. The variations of the energy gaps with the layer thicknesses and the band offsets, the subband dispersion along the ${k}_{x}$ direction, the charge distributions along the lines connecting atoms in the [011] direction, and the optical-transition matrix elements are obtained. It is found that the crossing of the lowest electronic level and the highest hole level for the superlattice (InAs${)}_{\mathrm{n}}$(GaSb${)}_{\mathrm{n}}$ occurs at the period of 160 A\r{}. The band offset has an essential effect on the energy gaps of the superlattice (HgTe${)}_{\mathrm{n}}$(CdTe${)}_{\mathrm{n}}$ with longer periods. The behavior of the interface states in the HgTe-CdTe superlattice is also discussed.