Light emission in polar group-III nitride quantum wells (QWs) optically pumped at densities significantly below the lasing threshold is usually interpreted in terms of excitons. Whereas thin GaN QWs with fast radiative lifetimes are employed in light-emitting devices, the excitons in thick QWs (typ. 7nm) are characterized by a non-zero dipole moment and long radiative lifetimes, due to the built-in electric field. These features result in many interesting properties of dipolar excitons: they can propagate over large distances and thus cool down to the lattice temperature before recombination, offering the possibility for studies of cold and dense gas of interacting bosons. In this context, two important issues must be addressed: the strength of the exciton-exciton interaction, and the excitonic Mott transition, that sets the maximum density of excitons. Combining spatially and time-resolved photoluminescence in different excitation geometries, we provide a set of experimental data showing that the emission linewidth is proportional to the emission energy in a wide range of carrier densities and temperatures. The proportionality coefficient is almost temperature independent. These results are compared to the existing data in various material systems and discussed in terms of the Mott transition and its criteria, exciton-exciton interaction and its possible contribution to the linewidth, as well as the role of disorder in the density-dependent emission spectra.

In this paper, an overview of main results concerning THz detection by nanometer field effect transistors (FETs) and heterojunction based transistors (HBTs) is presented. Different GaInAs/InP and GaN/AlGaN nanometer field effect transistors based detectors are presented. We present also first Silicon C-MOS transistors based integrated circuits for wireless communication in sub-THz range. Special attention is given to transistors based focal plane arrays. We show, how these arrays, together with in purpose developed diffractive 3D printed optics lead to construction of the demonstrators of safety and industrial quality control scanners.

Cyclotron resonance spectra in high magnetic fields up to 34 T in InAs/GaSb/InAs “three-layer” quantum wells with gapless Dirac fermions have been studied. In quantizing magnetic fields, an absorption line associated with transitions from the lower Landau levels of electrons in a subband with a “conical” dispersion relation has been detected. Experimental energies of the transitions have been compared to theoretical calculations with the eight-band Kane Hamiltonian. The results confirm the gapless band structure of the studied samples.

—We present the low frequency noise and the photoresponse in InP double heterojunction bipolar transistor (DHBT) THz detectors. A current responsivity of 0.23 A/W and a noise equivalent power of 4·10-10 W/Hz 1/2 have been measured at 1 kHz modulation frequency. The collector bias can substantially reduce the noise equivalent power.

A graphene ballistic rectifier is used in conjunction with an antenna to demonstrate a rectenna as a terahertz (THz) detector. A small-area (<1 μm2) local gate is used to adjust the Fermi level in the device to optimize the output while minimizing the impact on the cutoff frequency. The device operates in both n- and p-type transport regimes and shows a peak extrinsic responsivity of 764 V/W and a corresponding noise equivalent power of 34 pW Hz–1/2 at room temperature with no indications of a cutoff frequency up to 0.45 THz. The device also demonstrates a linear response for more than 3 orders of magnitude of input power due to its zero threshold voltage, quadratic current–voltage characteristics and high saturation current. Finally, the device is used to take an image of an optically opaque object at 0.685 THz, demonstrating potential in both medical and security imaging applications.

Different methods for cross-section doping topography of SiC Trenched-singly-implanted vertical junction field effect transistors (TSI-VJFETs) are presented with the purpose to determine the doping distribution in the epitaxial structure and the implanted areas.