Hole localization energy of 1.18 eV in GaSb quantum dots embedded in GaP (Phys. Status Solidi B 10/2016)

Abstract

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.

Novel InGaSb/AlP Quantum Dots for Non-Volatile Memories

“…The novel GaSb/AlP heterosystem is most similar to the more investigated GaSb/GaP system. As was mentioned in [ 28 , 29 , 41 ], the GaSb deposition on GaP results in the GaSbP/GaP SAQD formation, with the Sb fraction lying in the range of 0.3–0.7, depending on the growth conditions. This information is optimistic for the successful growth of the GaSbP/AlP SAQDs with the required Sb content.…”

“…According to [ 12 , 13 ], the hole storage time can be estimated by relation: where T is the temperature, σ inf is the capture cross-section at a high temperature and γ is the coefficient independent of temperature. Localization energies of 1.35–1.50 eV are high enough for the hole storage times of ~10 years, depending on the capture cross-section σ inf which varied in the range of 10 −12 –10 −9 cm 2 in GaSb/GaP [ 29 ], InGaAs/GaP [ 27 ] and InGaSb/GaP [ 31 ] SAQDs, according to the available experimental results. Since the hole capture cross-section in SAQD is determined not only by the SAQD sizes but also by the hole–phonon interaction efficiency, Auger scattering and other factors [ 29 ], the prediction of the σ inf value for the SAQD with specified alloy composition and size is a complicated task.…”

“…Localization energies of 1.35–1.50 eV are high enough for the hole storage times of ~10 years, depending on the capture cross-section σ inf which varied in the range of 10 −12 –10 −9 cm 2 in GaSb/GaP [ 29 ], InGaAs/GaP [ 27 ] and InGaSb/GaP [ 31 ] SAQDs, according to the available experimental results. Since the hole capture cross-section in SAQD is determined not only by the SAQD sizes but also by the hole–phonon interaction efficiency, Auger scattering and other factors [ 29 ], the prediction of the σ inf value for the SAQD with specified alloy composition and size is a complicated task. Therefore, to simplify the task, the SAQDs were considered with an E loc value lying in the range of 1.35–1.50 eV and with the critical dot size.…”

“…Further investigations were focused on the SAQD formation in III–V heterosystems with a higher E loc value. This trend has involved such well-known SAQDs system as GaSb/GaAs [ 19 , 20 , 21 ] and relatively novel heterosystems, for instance, GaSb/AlGaAs [ 22 , 23 ], GaSb/AlAs [ 24 ], InSb/AlAs [ 25 ], InGaAs/GaP [ 26 , 27 ], GaSb/GaP [ 28 , 29 ], InGaSb/GaP [ 30 , 31 ] and others, as discussed in [ 32 ]. The highest E loc value was obtained for GaSbP/GaP SAQDs (about 1.18 eV [ 29 ]), and it results in a storage time of about four days.…”

“…However, despite such optimistic forecasts, the InGaSb/AlP heterosystem remains unexplored either theoretically or experimentally. Earlier, the Sb-based SAQDs in the AlP matrix were just briefly mentioned in [ 29 , 32 , 34 ], and no detailed SAQD energy spectrum calculations and, especially, attempts of epitaxial growth can be found in the literature. Embedding AlGaP barriers in the heterostructures with InGaSb/GaP SAQDs [ 31 ] and AlP barriers growing close to InGaAs/GaP SAQDs [ 27 ] were only discussed.…”