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Asymmetric quantum wells (AQWs) utilizing interband transitions enhance second-order susceptibility over a wide wavelength range compared to natural crystals. The nonlinear susceptibility is further enhanced in AQWs with type-II band alignment as compared to type-I band alignment, a result of the larger interband charge shift. This enhancement is demonstrated in this work by analyzing three type-I and type-II AQW designs based on the lattice-matched InP/AlGaInAs materials systems using the envelope wavefunction approximation. The calculated interband second-order susceptibility tensor elements in type-II structures range between 20 and 1.60 × 103 pm/V for nearly resonant optical rectification and difference frequency generation applications at near-infrared and terahertz wavelengths, an improvement of nearly 1 order of magnitude over the type-I structures and 1–2 orders of magnitude over natural crystals such as LiNbO3, KTiOPO4 (KTP), or GaAs. A factor of 2–3 further enhancement of the tensor elements is achieved by optimizing the well widths and band offsets of the type-II asymmetric quantum wells. The type-II structure can be implemented in other material systems spanning the longwave infrared to visible wavelengths, enhancing nonlinear susceptibility for various applications, including photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Monocrystalline 1.7 eV Mg0.13Cd0.87Te/MgxCd1−xTe (x > 0.13) double heterostructure (DH) solar cells with varying Mg compositions in the barrier layers are grown by molecular beam epitaxy. A Mg0.13Cd0.87Te/Mg0.37Cd0.63Te DH solar cell featuring abrupt interfaces between barriers and absorber and the addition of a SiO2 anti-reflective coating demonstrate open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF), and device active-area efficiencies up to 1.129 V, 17.3 mA/cm2, 77.7%, and 15.2%, respectively. The VOC and FF vary oppositely with the MgxCd1−xTe barrier height, indicating an optimal design of the MgCdTe DHs as a trade-off between carrier confinement and carrier transport. Temperature-dependent VOC measurements reveal that the majority of carrier recombination in the devices occurs outside the DHs, in the a-Si:H hole-contact layer, and at the interface between the a-Si:H layer and the MgxCd1−xTe top barrier at room temperature. Simulation results for the device with the highest efficiency show that the p-type a-Si:H layer and the Mg0.37Cd0.63Te top barrier contribute 1.3 and 2.4 mA/cm2JSC loss, respectively. [ABSTRACT FROM AUTHOR]

Gallium is incorporated into the strain-balanced In(Ga)As/InAsSb superlattice system to achieve the same mid-wave infrared cutoff tunability as conventional Ga-free InAs/InAsSb type-II superlattices, but with an additional degree of design freedom to enable optimization of absorption and transport properties. Time-resolved photoluminescence measurements of InGaAs/InAsSb superlattice characterization- and doped device structures are reported from 77 to 300 K and compared to InAs/InAsSb. The low-injection photoluminescence decay yields the minority carrier lifetime, which is analyzed with a recombination rate model, enabling the determination of the temperature-dependent Shockley–Read–Hall, radiative, and Auger recombination lifetimes and extraction of defect energy levels and capture cross section defect concentration products. The Shockley–Read–Hall-limited lifetime of undoped InGaAs/InAsSb is marginally reduced from 2.3 to 1.4 μs due to the inclusion of Ga; however, given that Ga improves the vertical hole mobility by a factor of >10×, a diffusion-limited InGaAs/InAsSb superlattice nBn could expect a lower bound of 2.5× improvement in diffusion length with significant impact on photodetector quantum efficiency and radiation hardness. At temperatures below 120 K, the doped device structures are Shockley–Read–Hall limited at 0.5 μs, which shows promise for detector applications. [ABSTRACT FROM AUTHOR]

The growth of Bi-containing III-V alloys requires careful control over temperature and group-V fluxes due to the low equilibrium solubility of Bi and its tendency to surface segregate into Bi-rich droplet features. A model for molecular beam epitaxy growth based on the kinetics of atomic desorption, incorporation, surface accumulation, and droplet formation is applied to the bismide alloy InAsSbBi grown on GaSb substrates. A steady-state solution is derived for the Bi, Sb, and As mole fractions and surface layer coverages based on the Bi, Sb, and As fluxes. A nonlinear least-squares algorithm is used to fit the growth model parameters to experimentally measured Bi mole fractions in bulk and quantum well InAsSbBi samples grown at 400 °C and 420 °C. The Bi mole fraction ranges from 0.12% to 1.86% among 17 samples examined. The results indicate that as the growth temperature increases, the rate of Bi incorporation decreases and the rate of Bi self-desorption increases. A strong interaction is observed between Bi and As that plays a role in the desorption of excess Bi from the growth surface, thus reducing the likelihood of Bi-rich droplet formation when an excess As flux is present. Significantly, the model predicts that the incorporation of Bi is limited to mole fractions of 1.43% at 400 °C and 0.30% at 420 °C in lattice-matched bulk InAsSbBi grown on GaSb substrates. [ABSTRACT FROM AUTHOR]