Room-temperature Operation of Low-voltage, Non-volatile, Compound-semiconductor Memory Cells.

Whilst the different forms of conventional (charge-based) memories are well suited to their individual roles in computers and other electronic devices, flaws in their properties mean that intensive research into alternative, or emerging, memories continues. In particular, the goal of simultaneously achieving the contradictory requirements of non-volatility and fast, low-voltage (low-energy) switching has proved challenging. Here, we report an oxide-free, floating-gate memory cell based on III-V semiconductor heterostructures with a junctionless channel and non-destructive read of the stored data. Non-volatile data retention of at least 104 s in combination with switching at ≤2.6 V is achieved by use of the extraordinary 2.1 eV conduction band offsets of InAs/AlSb and a triple-barrier resonant tunnelling structure. The combination of low-voltage operation and small capacitance implies intrinsic switching energy per unit area that is 100 and 1000 times smaller than dynamic random access memory and Flash respectively. The device may thus be considered as a new emerging memory with considerable potential.

An investigation of exciton behavior in type-II self-assembled GaSb/GaAs quantum dots.

We report the investigation of exciton dynamics in type-II self-assembled GaSb/GaAs quantum dots. The GaSb/GaAs quantum dots (QDs) were grown using a modified liquid phase epitaxy technique. Statistical size distributions of the uncapped QDs were investigated experimentally by field-emission scanning electron microscopy (SEM) and atomic force microscopy (AFM), and theoretically by an eight-band k  ·  p calculation, which demonstrated a dissolution effect. Furthermore, the low-temperature luminescence spectra of type-II GaSb/GaAs QDs with a thick capping layer exhibit well-resolved emission bands and LO-phonon-assisted transitions in the GaSb wetting layer. However, the luminescence lines quench at temperatures above 250 K, which is attributed to the weak quantum confinement of electrons participating in indirect exciton recombination. It was demonstrated that the room temperature stability of the excitons in type-II GaSb/GaAs QDs could be achieved by growing thin a capping layer, which provides strong quantum confinement in the conduction band and enhances the electron-hole Coulomb interaction, stabilizing the excitons.

High-accuracy analysis of nanoscale semiconductor layers using beam-exit ar-ion polishing and scanning probe microscopy.

A novel method of sample cross sectioning, beam-exit Ar-ion cross-sectional polishing, has been combined with scanning probe microscopy to study thin AlxGa1-xAs/GaAs layers. Additional contrast enhancement via a citric acid/hydrogen peroxide etch allows us to report the observation of layers as thin as 1 nm. Layer thickness measurements agree with transmission electron microscopy (TEM) data to 0.1 ± 0.2 nm, making this a very promising low-cost method for nanoscale analysis of semiconductor heterostructures.

High-field magneto-photoluminescence of semiconductor nanostructures.

We review the photoluminescence of semiconductor nanostructures in high magnetic fields, concentrating on the effects of the applied magnetic field on orbital motion (wave function extent), which is probed in experiments on large ensembles. We present an overview of the physics of excitons in high magnetic fields in 3- and 2-D before introducing the zero-dimensional case. We then discuss the physics of quantum-dot excitons in high magnetic fields with particular attention to the approximate analytical models used to interpret experimental results. This is followed by a brief description of a typical high-field magneto-photoluminescence setup. We then present four examples of magneto-photoluminescence experiments on different materials systems chosen from our own research to illustrate how high magnetic fields can be used to reveal new insights into the physics of semiconductor nanostructures.