Charge carrier transport in graphene field-effect transistor scaled down to submicron gate lengths

We present a preliminary study of charge carrier transport in graphene field-effect transistor with gate lengths ranging from 2 μm down to 0.2 μm applying a model of the quasi-ballistic charge carrier transport. The analysis indicates that, in particular, at the gate length of 0.2 μm the fraction of the ballistic carriers can be up to 60 %. Our finding can be used as a guidance for further development of the graphene field-effect transistors with submicron gate length for variety of the advanced and emerging applications

Low-field mobility and high-field velocity of charge carriers in InGaAs/InP high-electron-mobility transistors

Development of transistors for advanced low noise amplifiers requires better understanding of mechanisms governing the charge carrier transport in correlation with the noise performance. In this paper, we report on study of the carrier velocity in InGaAs/InP high-electron-mobility transistors (HEMTs) found via geometrical magnetoresistance in the wide range of the drain fields, up to 2 kV/cm, at cryogenic temperature of 2 K. We observed, for the first time experimentally, the velocity peaks with peak velocity and corresponding field decreasing significantly with the transverse field. The low-field mobility and peak velocity are found to be up to 65000 cm2/Vs and 1.2x106\ua0cm/s, respectively. Extrapolations to the lower transverse fields show that the peak velocity can be as high as 2.7x107\ua0cm/s. The corresponding intrinsic transit frequency can be up to 172 GHz at the gate length of 250 nm. We demonstrated, for the first time, that the low-field mobility and peak velocity reveal opposite dependencies on the transverse field, indicating the difference in carrier transport mechanisms dominating at low- and high-fields. Therefore, the peak velocity is an appropriate parameter for characterization and development of the low noise HEMTs, complementary to the low-field mobility. The results of the research clarify the ways of the further development of the HEMTs for advanced applications

Charge carrier transport in graphene field-effect transistor scaled down to submicron gate lengths

We present a preliminary study of charge carrier transport in graphene field-effect transistor with gate lengths ranging from 2 μm down to 0.2 μm applying a model of the quasi-ballistic charge carrier transport. The analysis indicates that, in particular, at the gate length of 0.2 μm the fraction of the ballistic carriers can be up to 60 %. Our finding can be used as a guidance for further development of the graphene field-effect transistors with submicron gate length for variety of the advanced and emerging applications

Cryogenic InP High Electron Mobility Transistors in a Magnetic Field

The InGaAs-InAlAs-InP high electron mobility transistor (InP HEMT) is the preferred active device used in a cryogenic low noise amplifier (LNA) for sensitive detection of microwave signals. In this thesis it is demonstrated that the InP HEMT, when placed in a magnetic field, has a strong angular dependence in its output current. This has important implications for the alignment of cryogenic InP HEMT LNAs in microwave detection experiments involving magnetic fields.InP HEMTs with various gate lengths and gate widths have been fabricated and characterized. The output current for the InP HEMTs was measured in static magnetic fields up to 14 T at different angles in an ambient temperature of 2 K. The results showed that for all InP HEMT devices placed in a perpendicular arrangement, the output current is drastically suppressed. It is shown that the reduction in output current is negligible once placed parallel to the applied field. Furthermore, it was found that the output current strongly depends on the angle between the current direction and the magnetic field. In the investigated device geometry, the output current in the InP HEMT is limited by geometrical magnetoresistance. This was expressed in an output current equation which showed excellent agreement with measured data as a function of angle and magnetic field. Device parameters such as transconductance and on-resistance were found to be significantly affected even at small angles and magnetic fields.A 0.3-14 GHz cryogenic LNA module based on the same transistor technology used in device experiments was measured in a perpendicular magnetic field at 2 K. The LNA was heavily degraded in gain and average noise temperature already up to 1.5 T. In comparison with previous work reported for GaAs single-heterojunction HEMT LNAs, it is shown here that the effect is much stronger for InP HEMT cryogenic LNAs

Mobility and quasi-ballistic charge carrier transport in graphene field-effect transistors

The optimization of graphene field-effect transistors (GFETs) for high-frequency applications requires further understanding of the physicalmechanisms concerning charge carrier transport at short channel lengths. Here, we study the charge carrier transport in GFETs with gatelengths ranging from 2 μm down to 0.2 μm by applying a quasi-ballistic transport model. It is found that the carrier mobility, evaluated viathe drain–source resistance model, including the geometrical magnetoresistance effect, is more than halved with decreasing the gate lengthin the studied range. This decrease in mobility is explained by the impact of ballistic charge carrier transport. The analysis allows for evaluationof the characteristic length, a parameter of the order of the mean-free path, which is found to be in the range of 359–374 nm. Themobility term associated with scattering mechanisms is found to be up to 4456 cm2/Vs. Transmission formalism treating the electrons aspurely classical particles allows for the estimation of the probability of charge carrier transport without scattering events. It is shown that atthe gate length of 2 μm, approximately 20% of the charge carriers are moving without scattering, while at the gate length of 0.2 μm, thisnumber increases to above 60%

On the Angular Dependence of InP High Electron Mobility Transistors for Cryogenic Low Noise Amplifiers in a Magnetic Field

The InGaAs-InAlAs-InP high electron mobility transistor (InP HEMT) is the preferred active device used in a cryogenic low noise amplifier (LNA) for sensitive detection of microwave signals. We observed that an InP HEMT 0.3-14GHz LNA at 2K, where the in-going transistors were oriented perpendicular to a magnetic field, heavily degraded in gain and average noise temperature already up to 1.5T. Dc measurements for InP HEMTs at 2K revealed a strong reduction in the transistor output current as a function of static magnetic field up to 14T. In contrast, the current reduction was insignificant when the InP HEMT was oriented parallel to the magnetic field. Given the transistor layout with large gate width/gate length ratio, the results suggest a strong geometrical magnetoresistance effect occurring in the InP HEMT. This was confirmed in the angular dependence of the transistor output current with respect to the magnetic field. Key device parameters such as transconductance and on-resistance were significantly affected at small angles and magnetic fields. The strong angular dependence of the InP HEMT output current in a magnetic field has important implications for the alignment of cryogenic LNAs in microwave detection experiments involving magnetic fields

Angular Dependence of InP High Electron Mobility Transistors for Cryogenic Low Noise Amplifiers under a magnetic field

This work addresses the angular dependence of DC properties in 100nm InP HEMT devices under the influence of applied static magnetic field at 2 K. When kept at an angle 90o towards a magnetic field of 14 T, the maximum output drain current Ids was reduced more than 99 %. A rotation sweep of the transistor revealed a strong angular and B-field dependence on Ids. This was correlated with a reduction in dc transconductance and increase in on-resistance of the transistor. The RF properties of the transistor were tested by measuring an 0.3-14 GHz InP HEMT MMIC low-noise amplifier (LNA) at 2 K kept at an angle 90o towards a magnetic field up to 10 T. The gain and noise temperature were strongly decreased and increased, respectively, already below 1 T. The results show that precise alignment of the cryogenic InP HEMT LNA is crucial in a magnetic field. Even a slight mis-orientation of a few degrees leads to a strong degradation of the gain and noise temperature

Geometrical magnetoresistance effect and mobility in graphene field-effect transistors

Further development of the graphene field-effect transistors (GFETs) for high-frequency electronics requires accurate evaluation and study of the mobility of charge carriers in a specific device. Here, we demonstrate that the mobility in the GFETs can be directly characterized and studied using the geometrical magnetoresistance (gMR) effect. The method is free from the limitations of other approaches since it does not require an assumption of the constant mobility and the knowledge of the gate capacitance. Studies of a few sets of GFETs in the wide range of transverse magnetic fields indicate that the gMR effect dominates up to approximately 0.55 T. In higher fields, the physical magnetoresistance effect starts to contribute. The advantages of the gMR approach allowed us to interpret the measured dependencies of mobility on the gate voltage, i.e., carrier concentration, and identify the corresponding scattering mechanisms. In particular, the range of the fairly constant mobility is associated with the dominating Coulomb scattering. The decrease in mobility at higher carrier concentrations is associated with the contribution of the phonon scattering. Analysis shows that the gMR mobility is typically 2-3 times higher than that found via the commonly used drain resistance model. The latter underestimates the mobility since it does not take the interfacial capacitance into account.Comment: The following article has been submitted to Applied Physics Letters. After it is published, the DOI will be found her