Reduction of skin effect losses in double-level-T-gate structure

in Applied Physics Letters (2014), 105

We developed a T-gate technology based on selective wet etching yielding 200 nm wide T-gate structures used for fabrication of High Electron Mobility Transistors (HEMT). Major advantages of our process ... [more ▼]

We developed a T-gate technology based on selective wet etching yielding 200 nm wide T-gate structures used for fabrication of High Electron Mobility Transistors (HEMT). Major advantages of our process are the use of only standard photolithographic process and the ability to generate T-gate stacks. A HEMT fabricated on AlGaN/GaN/sapphire with gate length Lg=200 nm and double-stacked T-gates exhibits 60 GHz cutoff frequency showing ten-fold improvement compared to 6 GHz for the same device with 2 um gate length. HEMTs with a double-level-T-gate (DLTG) structure exhibit up to 35% improvement of fmax value compared to a single T-gate device. This indicates a significant reduction of skin effect losses in DLTG structure compared to its standard T-gate counterpart. These results agree with the theoretical predictions. [less ▲]

Excitons in a mirror: Formation of “optical bilayers” using MoS2 monolayers on gold substrates

in Applied Physics Letters (2014), 104

We report coupling of excitons in monolayers of molybdenum disulphide to their mirror image in an underlying gold substrate. Excitons at the direct band gap are little affected by the substrate whereas ... [more ▼]

We report coupling of excitons in monolayers of molybdenum disulphide to their mirror image in an underlying gold substrate. Excitons at the direct band gap are little affected by the substrate whereas strongly bound C-excitons associated with a van-Hove singularity change drastically. On quartz substrates only one C-exciton is visible (in the blue) but on gold substrates a strong red-shifted extra resonance in the green is seen. Exciton coupling to its image leads to formation of a “mirror biexciton” with enhanced binding energy. Estimates of this energy shift in an emitter-gold system match experiments well. The absorption spectrum of MoS2 on gold thus resembles a bilayer of MoS2 which has been created by optical coupling. Additional top-mirrors produce an “optical bulk.” [less ▲]

Metastable defect in CuInSe2 probed by modulated photo current experiments above 390K

in APPLIED PHYSICS LETTERS (2014), 104

Magnetization reversal in Nd-Fe-B based nanocomposites as seen by magnetic small-angle neutron scattering

in Applied Physics Letters (2013), 102(2), 0224151-0224155

We have studied the magnetization-reversal process of a Nd2Fe14B/Fe3B nanocomposite using small-angle neutron scattering. Based on the computation of the autocorrelation function of the spin misalignment ... [more ▼]

We have studied the magnetization-reversal process of a Nd2Fe14B/Fe3B nanocomposite using small-angle neutron scattering. Based on the computation of the autocorrelation function of the spin misalignment, we have estimated the characteristic size lC of spin inhomogeneities around the Nd2Fe14B nanoparticles. The quantity lC approaches a constant value of about 12.5 nm ( ∼ average Nd2Fe14B particle radius) at 14 T and takes on a maximum value of about 18.5 nm at the coercive field of −0.55 T. The field dependence of lC can be described by a model that takes into account the convolution relationship between the nuclear and the magnetic microstructure. [less ▲]

On the specific absorption rate of hyperthermia fluids

in Applied Physics Letters (2013), 103

The specific absorption rate (SAR) concept of hyperthermia ferrofluids is discussed. It is first suggested that SAR can be characterized at the steady state condition, taking into account the heating flow ... [more ▼]

The specific absorption rate (SAR) concept of hyperthermia ferrofluids is discussed. It is first suggested that SAR can be characterized at the steady state condition, taking into account the heating flow mechanism from the ferrofluid to the external environment. The temperature dependence of SAR is then addressed, indicating that the influence arises from both magnetic susceptibility and relaxation time of the system. At last, a single equation able to express the temperature versus time profile of a ferrofluid, when SAR is virtually temperature independent, is proposed up to the equilibrium condition. [less ▲]

Atom probe study of Cu2ZnSnSe4 thin-films prepared by co-evaporation and post-deposition annealing

in Applied Physics Letters (2013), 102

Raman analysis of monoclinic Cu2SnS3 thin films

in Applied Physics Letters (2012), 100

Lone conduction band in Cu2ZnSnSe4

in Applied Physics Letters (2012), 100

Detection of a ZnSe secondary phase in coevaporated Cu2ZnSnSe4 thin films

in Applied Physics Letters (2011), 98(101907), 1019071-1019073

Influence of secondary phase CuxSe on the optoelectronic quality of chalcopyrite thin films

in Applied Physics Letters (2011), 98(201910), 2019101-2019103