RESUMEN

III-V colloidal quantum dots (CQDs) are promising materials for optoelectronic applications, for they avoid heavy metals while achieving absorption spanning the visible to the infrared (IR). However, the covalent nature of III-V CQDs requires the development of new passivation strategies to fabricate conductive CQD solids for optoelectronics: this work shows herein that ligand exchanges, previously developed in II-VI and IV-VI quantum dots and employing a single ligand, do not fully passivate CQDs, and that this curtails device efficiency. Guided by density functional theory (DFT) simulations, this work develops a co-passivation strategy to fabricate indium arsenide CQD photodetectors, an approach that employs the combination of X-type methyl ammonium acetate (MaAc) and Z-type ligands InBr3 . This approach maintains charge carrier mobility and improves passivation, seen in a 25% decrease in Stokes shift, a fourfold reduction in the rate of first-exciton absorption linewidth broadening over time-under-stress, and leads to a doubling in photoluminescence (PL) lifetime. The resulting devices show 37% external quantum efficiency (EQE) at 950 nm, the highest value reported for InAs CQD photodetectors.

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RESUMEN

We report a new nBn photodetector (nBn-PD) design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for mid-wavelength infrared (MWIR) applications. In this structure, delta-doped compositionally graded barrier (δ-DCGB) layers are suggested, the advantage of which is creation of a near zero valence band offset in nBn photodetectors. The design of the δ-DCGB nBn-PD device includes a 3 µm absorber layer (n-InAs0.81Sb0.19), a unipolar barrier layer (AlSb), and 0.2 µm contact layer (n-InAs0.81Sb0.19) as well as a 0.116 µm linear grading region (InAlSb) from the contact to the barrier layer and also from the barrier to the absorber layer. The analysis includes various dark current contributions, such as the Shockley-Read-Hall (SRH), trap-assisted tunneling (TAT), Auger, and Radiative recombination mechanisms, to acquire more precise results. Consequently, we show that the method used in the nBn device design leads to diffusion-limited dark current so that the dark current density is 2.596 × 10-8 A/cm2 at 150 K and a bias voltage of - 0.2 V. The proposed nBn detector exhibits a 50% cutoff wavelength of more than 5 µm, the peak current responsivity is 1.6 A/W at a wavelength of 4.5 µm and a - 0.2 V bias with 0.05 W/cm2 backside illumination without anti-reflective coating. The maximum quantum efficiency at 4.5 µm is about 48.6%, and peak specific detectivity (D*) is of 3.37 × 1010 cm⋅Hz1/2/W. Next, to solve the reflection concern in this nBn devices, we use a BaF2 anti-reflection coating layer due to its high transmittance in the MWIR window. It leads to an increase of almost 100% in the optical response metrics, such as the current responsivity, quantum efficiency, and detectivity, compared to the optical response without an anti-reflection coating layer.

RESUMEN

Polarity introduced by inversion symmetry broken along <111> direction has strong impacts on the physical properties and morphological characteristics of III-V component nanostructure. Take III-V component semiconductor InSb as an example, we systematically investigate the growth sequence and morphology evolution of InSb (111) on Bi (001) substrate from adatoms to bilayers. We discovered and verified that the presence of amorphous-like morphology of monolayer InSb was attributed to the strong interaction between mix-polarity InSb and Bi substrate. Further, our comprehensive energy investigations of bilayer InSb reveal that an amorphous first layer will be crystallized and polarized driven by the low surface energy of the reconstructed second layers. Phase diagrams were developed to describe the ongoing polarization process of bilayer InSb under various chemical environments as a function of deposition time. The growth mechanism and polarity phase diagram of bilayer InSb on Bi substrate may advance the progress of polarity controllable growth of low-dimensional InSb nanostructure as well as other polar III-V compound semiconductors.

RESUMEN

An example of InAsSbP quaternary quantum dots (QDs), pits and dots-pits cooperative structures' growth on InAs(100) substrates by liquid phase epitaxy (LPE) is reported. The interaction and surface morphology of the dots-pits combinations are investigated by the high-resolution scanning electron microscope. Bimodal growth mechanism for the both QDs and pits nucleation is observed. Cooperative structures consist of the QDs banded by pits, as well as the "large" pits banded by the quantum wires are detected. The composition of the islands and the pits edges is found to be quaternary, enriched by antimony and phosphorus, respectively. This repartition is caused by dissociation of the wetting layer, followed by migration (surface diffusion) of the Sb and P atoms in opposite directions. The "small" QDs average density ranges from 0.8 to 2 × 109 cm-2, with heights and widths dimensions from 2 to 20 nm and 5 to 45 nm, respectively. The average density of the "small" pits is equal to (6-10) × 109 cm-2 with dimensions of 5-40 nm in width and depth. Lifshits-Slezov-like distribution for the amount and surface density of both "small" QDs and pits versus their average diameter is experimentally detected. A displacement of the absorption edge toward the long wavelength region and enlargement toward the short wavelength region is detected by the Fourier transform infrared spectrometry.