Photoluminescence Spectroscopy of many-body Effects in Heavily Doped Al$_x$Ga$_{1-x}$As

We exploit the influence of the Coulomb interaction between electrons and holes on the electron spin relaxation in a (110)-GaAs quantum well to unveil excitonic signatures within the many particle electron-hole system. The temperature dependent time- and polarization-resolved photoluminescence measurements span five decades of carrier density, comprise the transition from localized excitons over quasi free excitons to an electron-hole plasma, and reveal strong excitonic signa...

The strong effect of weak interband illumination on tunneling transport in doped GaAs/AlAs superlattices was found under conditions of electric domain formation. The photoresponse at voltages below the threshold one (before the domain formation) did not observe. The phenomenon is referred to strong carrier depletion inside the triangular high-field domain. The domain modes transformations under the illumination were also found.

We measure tunnelling currents through electrostatically defined quantum dots in a GaAs/AlGaAs heterostructure connected to two leads. For certain tunnelling barrier configurations and high sample bias we find a pronounced resonance associated with a Fermi edge singularity. This many-body scattering effect appears when the electrochemical potential of the quantum dot is aligned with the Fermi level of the lead less coupled to the dot. By changing the relative tunnelling barri...

Doping is a fundamental property of semiconductors and constitutes the basis of modern microelectronic and optoelectronic devices. Their miniaturization requires contactless characterization of doping with nanometer scale resolution. Here, we use low- and room-temperature cathodoluminescence (CL) measurements to analyze p-type and n-type GaAs thin films over a wide range of carrier densities ($2\times 10^{17}$ to $1\times 10^{19}$ cm$^{-3}$). The spectral shift and broadening...

A theoretical study of Al(1-x)Ga(x)N, based on full-potential linearized augmented plane wave method, is used to investigate the variations in the bandgap, optical properties and non-linear behavior of the compound with the variation of Ga concentration. It is found that the bandgap decreases with the increase of Ga in Al(1-x)Ga(x)N. A maximum value of 5.5 eV is determined for the bandgap of pure AlN which reaches to minimum value of 3.0 eV when Al is completely replaced by G...

Although everybody should know that measurements are never performed directly on materials but on devices, this is not generally true. Devices are physical systems able to exchange energy and thus subject to the laws of physics, which determine the information they provide. Hence, we should not overlook device effects in measurements as we do by assuming naively that photoluminescence (PL) is bulk emission free from surface effects. By replacing this unjustified assumption wi...

We studied the persistent photoconductivity (PPC) effect in AlGaN/AlN/GaN heterostructures with two different Al-compositions (x=0.15 and x=0.25). The two-dimensional electron gas formed at the AlN/GaN heterointerface was characterized by Shubnikov-de Haas and Hall measurements. Using optical illumination, we were able to increase the carrier density of the Al0.15Ga0.85N/AlN/GaN sample from 1.6x10^{12} cm^{-2} to 5.9x1012 cm^{-2}, while the electron mobility was enhanced from...

We report a persistent increase or decrease in the two-dimensional electron density of AlAs or GaAs quantum wells flanked by AlGaAs barriers, brought about by illuminating the samples at T ~ 4 K while simultaneously applying a voltage bias between a back gate and the two-dimensional electron gas. Control of the final carrier density is achieved by tuning the back gate bias during illumination. Furthermore, the strength of the persistent photoconductivity depends on the Al mol...

Fermi level pinning at the oxidized (110) surfaces of III-As nanowires (GaAs, InAs, InGaAs, AlGaAs) is studied. Using scanning gradient Kelvin probe microscopy, we show that the Fermi level at oxidized cleavage surfaces of ternary Al$_{x}$Ga$_{1-x}$As (0$\le$x$\le$0.45) and Ga$_{x}$In$_{1-x}$As (0$\le$x$\le$1) alloys is pinned at the same position of 4.8$\pm$0.1 eV with regard to the vacuum level. The finding implies a unified mechanism of the Fermi level pinning for such sur...

The quest for extremely high mobilities of 2d electron gases in MBE-grown heterostructures is hampered by the available purity of the starting materials, particularly of the gallium. Here we compare the role of different Ga lots having nominally the highest possible quality on the mobility and the photoluminescence (PL) of modulation doped single interface structures and find significant differences. A weak exciton PL reveals that the purity of the Ga is insufficient. No high...