Inhomogeneous electron distribution in InN nanowires: Influence on the optical properties

in Physica Status Solidi C. Current Topics in Solid State Physics (2012), 9(3-4), 1001--1004

In this work, we study theoretically and experimentally the influence of the surface electron accumulation on the optical properties of InN nanowires. For this purpose, the photoluminescence and ... [more ▼]

In this work, we study theoretically and experimentally the influence of the surface electron accumulation on the optical properties of InN nanowires. For this purpose, the photoluminescence and photoluminescence excitation spectra have been measured for a set of self-assembled InN NWs grown under different conditions. The photoluminescence excitation experimental lineshapes have been reproduced by a self-consistent calculation of the absorption in a cylindrical InN nanowires. With the self-consistent model we can explore how the optical absorption depends on nanowires radius and doping concentration. Our model solves the Schrödinger equation for a cylindrical nanowire of infinite length, assuming a parabolic conduction band. The columnar geometry introduces effects in both the electron density and in the self-consistent conduction band profile, with no equivalence in planar layer. On the other hand, the differences in the photoluminescence excitation spectra are related to the inhomogeneous electron distribution inside the nanowires, caused by a bulk donor concentration and a two-dimensional density of ionized surface states. For nanowire radii larger than 30 nm, such concentrations modify the absorption edge and the lineshape, respectively, and can be determined from the comparison with the experimental data (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [less ▲]

Quantum transport in narrow-gap semiconductor nanocolumns

in Physica Status Solidi C. Current Topics in Solid State Physics (2010), 7(2), 386-389

An AlGaN/GaN two-color photodetector based on AlGaN/GaN/SiC HEMT layer structure

in Physica Status Solidi C. Current Topics in Solid State Physics (2006), 3(6), 2261-2264

The optoelectronic properties of MSM diodes that are based on an AlGaN/GaN HEMT layer system are investigated as function of the applied bias. For low voltages, the two-dimensional electron gas acts as a ... [more ▼]

The optoelectronic properties of MSM diodes that are based on an AlGaN/GaN HEMT layer system are investigated as function of the applied bias. For low voltages, the two-dimensional electron gas acts as a barrier for the depletion layer. Therefore, only the upper AlGaN barrier layer contributes to the photocurrent. In the high voltage regime the depletion region penetrates the GaN buffer that adds the spectral responsivity of GaN to the pure AlGaN behaviour in the low voltage regime. The ratio of the responsivities at 350 nm and 300 nm wavelength can be switched from 0.01 at 2.5 V to 0.8 at 4 V bias. This property makes the MSM-2DEG a candidate for use as two-color photodetector. Device fabrication uses standard HEMT processing steps, allowing integration in HEMT circuits without the need of sophisticated growth or etching techniques. [less ▲]

Low Current Dispersion and Low Bias-stress Degradation of Unpassivated GaN/AlGaN/GaN/SiC HEMTs

in Physica Status Solidi C. Current Topics in Solid State Physics (2005), 2(7), 2676-2679

The performance of unpassivated GaN/AlGaN/GaN/SiC HEMTs with intentionally undoped and doped barrier structures are extensively studied. No drain current dispersion between DC and 50 ns pulses on doped ... [more ▼]

The performance of unpassivated GaN/AlGaN/GaN/SiC HEMTs with intentionally undoped and doped barrier structures are extensively studied. No drain current dispersion between DC and 50 ns pulses on doped devices and less than 10% dispersion on undoped ones is observed. The full (100%) current recovery on undoped sample was measured in 1μs. The drain current extrapolated from 2 GHz large signal measurements corresponds to the measured static drain current confirming negligible current dispersion of our devices. Insignificant (<5 %) degradation in overall device performance parameters (IDs, gm, fT, fmax, Pout) on both undoped and doped structures after 12-hour-long bias stress was obtained. These results documents that suitable device performances can be obtained also on unpassivated GaN-based HEMTs. [less ▲]

Investigation of traps in AlGaN/GaN HEMTs on silicon substrate

in Physica Status Solidi C. Current Topics in Solid State Physics (2003), (7), 2360-2363

Deep levels in AlGaN/GaN heterostructures are known to be responsible for trapping processes like current collapse or dispersion. In order to investigate these processes we performed different ... [more ▼]

Deep levels in AlGaN/GaN heterostructures are known to be responsible for trapping processes like current collapse or dispersion. In order to investigate these processes we performed different measurements on HEMTs fabricated with heterostructures grown on silicon substrate. First by photoionization spectroscopy we found three different traps with activation energies of about 2.1 eV, 2.9 eV and 3.2 eV. Secondly, the temperature dependent relaxation of the drain current was investigated by the backgating current deep level transient spectroscopy (DLTS) method. Hereby we detected majority and minority carrier traps in the GaN buffer at the energies EV + 0.41 eV and EC – 0.55 eV, respectively. The latter energy can be attributed to the well known “E2” level in GaN. [less ▲]

Investigation of AlGaN/GaN HEMTs on Si substrate using backgating

in Physica Status Solidi C. Current Topics in Solid State Physics (2002), (1), 65-68

The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN HEMT on silicon (111) substrate is investigated. This effect, known as backgating, is used to study traps that are located ... [more ▼]

The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN HEMT on silicon (111) substrate is investigated. This effect, known as backgating, is used to study traps that are located between substrate and 2DEG channel. The transient of the drain current after applying a negative substrate voltage is evaluated for measurements with and without illumination. Several trap contributions are resolved by measurements at different photon energies. A photocurrent is observed up to 600 nm wavelength. Up to this wavelength the backgating effect can be compensated and the drain current restored by a short light pulse. The experiments are performed on completed HEMTs, allowing investigation of the influence of device fabrication technology. [less ▲]