The structural and optical properties of InGaSb/GaP(001) type‐II quantum dots (QDs) grown by metalorganic vapor phase epitaxy (MOVPE) are studied. Growth strategies as growth interruption (GRI) after deposition of InGaSb and Sb‐flush prior to QD growth are used to tune the structural and optical properties of InGaSb QDs. The Sb‐flush affects the surface diffusion leading to more homogeneous QDs and to a reduction of defects. A ripening process during GRI occurs, where QD size is increased and QD‐luminescence remarkably improved. InGaSb QDs are embedded in GaP n + p‐diodes, employing an additional AlP barrier, and characterized electrically. A localization energy of 1.15 eV for holes in QDs is measured by using deep‐level transient spectroscopy (DLTS). The use of Sb in QD growth is found to decrease the associated QD capture cross‐section by one order of magnitude with respect to the one of In0.5Ga0.5As/GaP QDs. This leads to a hole storage time of almost 1 h at room temperature, which represents to date the record value for MOVPE‐grown QDs, making MOVPE of InGaSb/GaP related QDs a promising technology for QD‐based nano‐memories.

Self‐organized GaSb quantum dots are embedded in GaP by molecular beam epitaxy and n+p‐diodes are fabricated. The structure of the sample is investigated using transmission electron microscopy with atomic resolution. The presence of quantum dots on top of a wetting layer and interdiffusion processes between Sb and P are observed. The localization energy, capture cross‐section, and storage time of holes in the ground state of the quantum dots are determined via deep‐level transient spectroscopy. Their localization energy of 1.18false(±0.01false)eV is found to agree with the theoretical prediction of 1.4 eV once the observed interdiffusion is taken into account. A storage time of holes of 3.9false(±0.3false) days at room temperature is calculated, marking an improvement of 3 orders of magnitude from previous record figures. GaSb/GaP quantum dots are, thus, promising candidates for future non‐volatile DRAMs or fast Flash. Schematic representation of the quantum dots (left) and of the valence band in their vicinity (right). The localization energy is marked on the scheme. The localization of the quantum dots prevents thermal emission of holes, generating a storage time at room temperature of 3.9 days.

Moore's law, being essentially based on the downscaling of device sizes, is bound to expire soon because of the importance of quantum effects at the nanometre scale. A novel memory architecture, fast and non‐volatile at the same time, is needed to merge the functionalities of DRAM and Flash, thereby radically revolutionizing complex computer architectures and driving energy consumption down. The QD‐Flash is a prototype of such a novel type of memory. It employs III–V semiconductors combined into heterostructures with extreme band gap discontinuities, self‐organised quantum dots and a two‐dimensional hole gas to create the “ultimate memory”. QD‐Flash memories recently demonstrated write times in the range of DRAM, storage times of a few seconds at room temperature and erase times much shorter than conventional Flash. In this issue, Bonato et al. (http://doi.wiley.com/10.1002/pssb.201600274) study the storage time of holes in GaSb quantum dots embedded in GaP. They find a storage time as long as 3.9 days at room temperature, marking an improvement of three orders of magnitude from the previous record figure and bringing QDFlash closer to the goal of non‐volatility.

Quantum dot (QD) based memories offer new functionalities as compared to present main stream ones by combining the advantages of DRAM (fast access and write/erase time, good endurance) and Flash memories (long storage time). The present storage times in such memories are demonstrated to be several days at room temperature for GaP-based devices, while write times as short as picoseconds are possible. There exists however a trade-off between storage time and erase time. To eliminate this trade-off, resonant tunneling effects in single or double quantum well structures are studied here as a promising approach. The quantum well structures based on GaAs/ Al 0.9 Ga 0.1 As and GaP/AlP quantum wells inserted in QD-based memories are designed and simulated using a Schrödinger-Poisson solver and nonequilibrium Green's functions (NEGF) to calculate the transparency at a given voltage. By choosing the width of the quantum wells, precise positioning of their energy levels allows for transparency engineering. Our simulations show an increase in transparency by at least 7 orders of magnitude at resonance, leading indeed to sufficiently fast erase times, thus solving the trade-off problem.

No abstract