On the imaging of electron transport in semiconductor quantum structures by scanning-gate microscopy: successes and limitations

This paper presents a brief review of scanning-gate microscopy applied to the imaging of electron transport in buried semiconductor quantum structures. After an introduction to the technique and to some of its practical issues, we summarise a selection of its successful achievements found in the literature, including our own research. The latter focuses on the imaging of GaInAs-based quantum rings both in the low magnetic field Aharonov-Bohm regime and in the high-field quantum Hall regime. Based on our own experience, we then discuss in detail some of the limitations of scanning-gate microscopy. These include possible tip induced artefacts, effects of a large bias applied to the scanning tip, as well as consequences of unwanted charge traps on the conductance maps. We emphasize how special care must be paid in interpreting these scanning-gate images.Comment: Special issue on (nano)characterization of semiconductor materials and structure

Caractérisation électro-optique de composants térahertz par échantillonnage Franz-Keldysh subpicoseconde

L'augmentation du débit des télécommunications nécessite la réalisation de circuits intégrés utilisant des transistors dont les fréquences de coupure sont de plus en plus élevées. L'évaluation des perfonnances intrinsèques de ces composants fonctionnant aujourd'hui jusqu'à plusieurs centaines de GHz pose un gros problème d'instrumentation. Les capacités des analyseurs de réseaux généralement utilisés pour ces caractérisations sont en effet dépassées. Les méthodes d'échantillonnage électro-optique basées sur l'utilisation d'un laser impulsionnel femtoseconde constituent une méthode alternative de caractérisation hyperfréquences. Ces mesures dont la résolution temporelle peut être inférieure à la picoseconde permettent d'étudier la répcmse en fréquence de composants intégrés jusqu'à plus de 1 THz. La méthode d'échantillonnage ultra-rapide que nous proposons est basée sur un effet d'électroabsorption présent dans de nombreux semiconducteurs massifs: l'effet Franz-Keldysh. Cet effet nous permet de sonder optiquement des impulsions électriques ultra-brèves se propageant sur une ligne de transmission déposée sur Arséniure de Gallium (GaAs). Ces impulsions sont également générées par voie optique grâce à un matériau photoconducteur ultra-rapide: le GaAs épitaxié à basse température. La démonstration expérimentale de cette méthode de caractérisation est tout d'abord effectuée en utilisant les propriétés intrinsèques du substrat semiconducteur. Dans un deuxième temps, des améliorations technologiques sont apportées au dispositif expérimental pour pennettre une généralisation de la technique de mesure à tout type de substrat semi-isolant. Pour cela, nous avons en particulier mis au point une technique de "lift-off" épitaxial permettant le report des matériaux nécessaires à la mesure sur un circuit ayant déjà subi les étapes technologiques. Enfin, ces différentes méthodes de mesure sont appliquées à la caractérisation de lignes de transmission ou de composants passifs THz. EJJes ont permis entre autre la mise en évidence du phénomène de couplage par onde de choc électromagnétique entre deux lignes de transmission coplanaires, ou l'évaluation des paramètres S d'un filtre réjecteur de Bragg intégré sur substrat de quartz jusqu'à 1,2 THz. Enfin, la possibi1ité d'étudier un transistor bipolaireà hétérojonction à doigt d'émetteur submicronique par cette technique de mesure est envisagée.LILLE1-BU (590092102) / SudocSudocFranceF

Terahertz Detection in Zero-Bias InAs Self-Switching Diodes at Room Temperature

RF characterization of InAs self-switching diodes (SSDs) is reported. On-wafer measurements revealed no roll-off in responsivity in the range 2-315 GHz. At 50 GHz, a responsivity of 17 V/W and a noise-equivalent power (NEP) of 150 pW/sqrt(Hz) was observed for the SSD when driven by a 50 Ω source. With a conjugately matched source, a responsivity of 34 V/W and an NEP of 65 pW/sqrt(Hz) were estimated. An antenna-coupled SSD demonstrated a responsivity of 0.7 V/W at 600 GHz. The results demonstrate the feasibility of zero-bias terahertz detection with high-electron mobility InAs SSDs up to and beyond 100 GHzROOTHz (FP7-243845

Growth mode dependence of misfit dislocation configuration at lattice mismatched III-V semiconductor interfaces

In GaSb/GaAs hetero-epitaxy, it is shown that a two-dimensional growth of GaSb promotes the generation of Lomer dislocations and confines the lattice mismatched strain at the hetero-interface. In contrast, 60° dislocations and closely spaced 60° pairs are predominantly generated in the three-dimensional growth mode. Consequently, a 60° dislocation glide model in combination with surface effects is able to account for the formation of Lomer, 60°, and 60° dislocation pair at high or low mismatch at hetero-interface between zinc-blende materials

Gate length dependent transport properties of in-plane core-shell nanowires with raised contacts

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DC and RF cryogenic behaviour of InAs/AlSb HEMTs

DC and RF properties are reported for InAs/AlSb HEMTs operating under cryogenic conditions (6 K) for a drain source bias up to 0.3 V. Compared to room temperature (300 K), a large improvement in device properties was observed: lower R on , lower g ds , a more distinct knee in the I ds (V ds ) characteristics, increased f T and a reduction of the gate leakage current of more than two orders of magnitude. This makes InAs/AlSb HEMT technology of large interest in cryogenic low-noise amplifier designs with high constraints on power dissipation

DC and RF cryogenic behaviour of InAs/AlSb HEMTs

DC and RF properties are reported for InAs/AlSb HEMTs operating under cryogenic conditions (6 K) for a drain source bias up to 0.3 V. Compared to room temperature (300 K), a large improvement in device properties was observed: lower R on , lower g ds , a more distinct knee in the I ds (V ds ) characteristics, increased f T and a reduction of the gate leakage current of more than two orders of magnitude. This makes InAs/AlSb HEMT technology of large interest in cryogenic low-noise amplifier designs with high constraints on power dissipation

Gate-recess Technology for InAs/AlSb HEMTs

The gate-recess technology for Si δ-doped InAs/AlSbhigh-electron-mobility transistors (HEMTs) has been investigated by combining atomic force microscopy (AFM) inspection of the gate-recess versus time with electrical device characterization. Deposition of the gate metal on the In0.5Al0.5As protection layer or on the underlying AlSb Schottky layer resulted in devices suffering from high gate-leakage current. Superior dc and high frequency device performance were obtained for HEMTs with an insulating layer between the gate and the Schottky layer resulting in a reduction of the gate leakage current IG by more than two orders of magnitude at a drain-to-source voltage VDS of 0.1 V. The existence of this intermediate insulating layer was evident from the electrical measurements. AFM measurements suggested that the insulating layer was due to a native oxidation of theAlSb Schottky layer. The insulated-gate HEMT with a gate length of 225 nm exhibited a maximum drain current ID higher than 500 mA/mm with good pinchoff characteristics, a dc transconductance gm of 1300 mS/mm, and extrinsic values for cutoff frequency fT and maximum frequency of oscillation fmax of 160 and 120 GHz, respectively

Electrical Characterization and Small-Signal Modeling of InAs/AlSb HEMTs for Low-Noise and High-Frequency Applications

Electrical characterization and modeling of 2 times 50 um gatewidth InAs/AlSb HEMTs with 225 nm gate-length have been performed. The fabricated devices exhibited a transconductance gm of 650 mS/mm, an extrinsic cutoff frequency fT and an extrinsic maximum frequency of oscillation fmax of 120 and 90 GHz, respectively, already at a low VDS of 0.2 V. A minimum noise figure less than 1 dB between 2-18 GHz was achieved at a dc power consumption of only 10 mW/mm. This demonstrates the potential of InAs/AlSb HEMTs for low-power, low-noise applications. To account for the elevated gate-leakage current lG in the narrow-bandgap InAs/AlSb HEMT, the conventional field-effect transistor small-signal model has been extended. The relatively high IG was modeled by shunting both Cgs and Cgd with Rgs and Rgd, respectively. As a result, the small-signal S-parameters were more accurately modeled, especially for frequencies below 10 GHz. Utilizing this modeling approach, excellent agreement was obtained between measured and modeled S-parameters, unilateral power gain U (Mason\u27s gain) and stability factor K