The authors report on a type-II InAs∕GaSb strained layer superlattice (SLS) photodetector using an nBn design that can be used to eliminate both Shockley-Read-Hall generation currents and surface recombination currents, leading to a higher operating temperature. We present such a SLS based structure with a cutoff wavelength of 5.2μm at room temperature. Processed devices exhibited a quantum efficiency around 18%, and a shot-noise-limited specific detectivity ∼109Jones at 4.5μm and 300K, which are comparable to the state of the art values reported for p-i-n photodiodes based on strained layer superlattices.
The authors demonstrate and characterize type-II GaSb quantum dot ͑QD͒ formation on GaAs by either Stranski-Krastanov ͑SK͒ or interfacial misfit ͑IMF͒ growth mode. The growth mode selection is controlled by the gallium to antimony ͑III/V͒ ratio where a high III/V ratio produces IMF and a low ratio establishes the SK growth mode. The IMF growth mode produces strain-relaxed QDs, where the SK QDs remain highly strained. Both ensembles demonstrate strong room temperature photoluminescence ͑PL͒ with the SK QDs emitting at 1180 nm and the IMF QDs emitting at 1375 nm. Quantized energy levels along with a spectral blueshift are observed in 77 K PL. Transmission electron microscope images identify the IMF array and crystallographic shape for both types of QD formation. Atomic force microscope images characterize QD geometry and density.
We report here a heterojunction band gap engineered type-II InAs/GaSb strained layer superlattice photodiode for longwave infrared detection. The reported PbIbN architecture shows improved performance over conventional PIN design due to unipolar current blocking layers. At 77 K and Vb=−0.25 V, responsivity of 1.8 A/W, dark current density of 1.2 mA/cm2, single pass quantum efficiency of 23%, and shot noise limited detectivity (D∗) of 8.7×1010 cm Hz1/2 W−1 (λc=10.8 μm) were measured. The device demonstrated background limited performance at 100 K under 300 K for 2π field of view.
We describe optical and structure characteristics of InAs quantum dashes grown on a GaAs substrate using an AlGaAsSb metamorphic buffer. The metamorphic buffer increases the lattice constant of the growth matrix from 5.653 to 5.869 Å. The increased lattice constant of the growth matrix yields a lattice mismatch with the InAs active region of only 3.2% and accommodates a large In content to access emission wavelengths >2.0 μm. From our comparison with quantum dot structures, we conclude that the elongated quantum dash formation is due to asymmetric surface bonds in the zinc blende crystal structure that control surface migration in low strain conditions.
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