T-branch Junctions Research Articles

Positive centre voltage in T-branch junctions on n-type GaAs/AlGaAs based on hydrodynamics

Nanoscale three-terminal T-branch junctions operated in push–pull fashion commonly exhibit a nonzero voltage at the centre electrode. In principle, their sign corresponds to the conduction type of the semiconductor material. For example is for n-type conduction, independent of the origin of the effect which could be ballistic or diffusive mode control, hot-electron thermopower or, in Y-shaped junctions, ballistic charging. We report on orthogonal four-terminal junctions on high-mobility n-type GaAs/AlGaAs, with current-carrying branches of varying length at constant widths of 410 nm and 320 nm, respectively. When operated at low temperatures as three-terminal devices, we show that under sufficiently large gate voltage the result is This is particularly pronounced at short branches where the mode effect is weak. Up to a current we observe independent of the branch length, where Around the centre voltage exhibits a parabolic behaviour, where the curvature κ is independent of electron density in the range As temperature rises κ monotonically decreases, staying positive up to 77 K. The observation of the Gurzhi effect as a signature of the hydrodynamic transport regime suggests an explanation of the mechanism in terms of the electronic analogue of the Venturi effect.

Three-dimensional Monte Carlo study of three-terminal junctions based on InGaAs/InAlAs heterostructures

We apply a three-dimensional (3D) semiclassical ensemble Monte Carlo simulation method to study T-branch junctions based on InGaAs/InAlAs heterostructures and obtain an accurate insight into the physics behind the operation of such structures. Electron transport in these devices is investigated and their rectifying behavior is demonstrated at 77 and 300 K and for different branch sizes. Detailed device analysis is performed to establish the relationship between the extent of ballistic transport and the rectifying behavior of the junctions and show the influence of surface charge effects, which are carefully included in the model. Results from the simulation of a T-branch junction with a Schottky gate terminal are presented, demonstrating the necessity of using 3D simulation models to study the physics of semiconductor junctions.

Nonlinear characteristics of T-branch junctions: Transition from ballistic to diffusive regime

Nonlinear electrical characteristics of nanostructured T-branch junctions (TBJs) made of two-dimensional electron gas in an InGaAs∕InAlAs heterostructure were studied by a systematic variation of both the device size and the operating temperature. We have found that two distinct mechanisms are responsible for the electronic transport in TBJs and their resulting nonlinear characteristics, namely, the nonlinear ballistic effect at low applied voltages and the intervalley transfer at high voltages. Detailed experimental analysis for each mechanism and their contributions with respect to the TBJ’s nanochannel length and operating temperature are discussed.

Influence of the surface charge on the operation of ballistic T-branch junctions: a self-consistent model for Monte Carlo simulations

We analyse the influence of the surface charge on the operation of ballistic T-branch junctions by means of a semi-classical 2D Monte Carlo simulator. We propose a new self-consistent model in which the local value of the surface charge is dynamically adjusted depending on the surrounding carrier density. The well-known parabolic behaviour of the central branch potential VC when biasing right and left branches in a push–pull fashion is found to be much influenced by the value of the surface charge in both the horizontal and vertical branches. With the help of experimental measurements performed in real devices, the influence of the width of the central branch on the values of VC and its relation to surface charge effects are also studied.

Nonlinear Effects in T-Branch Junctions

The negative potential appearing at the central branch of T-branch junctions (TBJs) when biasing left and right contacts in push-pull fashion has been found to appear under high biasing not only for short (ballistic) TBJs but also for long (diffusive) ones. By means of a microscopic Monte Carlo simulation we are able to explain this nonlinear effect as a consequence of intervalley scattering mechanisms leading to the emergence of an accumulation domain that modifies the electronic potential profile within the devices.

Ballistic nanodevices for terahertz data processing: Monte Carlo simulations

By using a semi-classical two-dimensional Monte Carlo simulation, simple devices(T-branch junctions (TBJs) and rectifying diodes) based on AlInAs/InGaAsballistic channels are analysed. Initially, the model is validated by means ofHall-effect measurements of mobility and electron concentration in long (diffusive)channels. Then, quasi-ballistic transport at room temperature is confirmed in a100 nm channel. Our simulations qualitatively reproduce the experimental resultsof electric potential measured in a TBJ appearing as a result of electron ballistictransport, and in close relation with the presence of space charge inside thestructure. As examples of devices exploiting the ballistic transport of electrons,preliminary simulations of a multiplexor/demultiplexor and a rectifying diodeare presented, demonstrating their capability for terahertz operation.