I. Iniguez-de-la-Torre

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.

Searching for THz Gunn oscillations in GaN planar nanodiodes

A detailed study of GaN-based planar asymmetric nanodiodes, promising devices for the fabrication of room temperature THz Gunn oscillators, is reported. By using Monte Carlo simulations, an analysis of the static I-V curves and the time-domain evolution of the current obtained when varying some simulation parameters in the diodes has been made. Oscillation frequencies of hundreds of GHz are predicted by the simulations in diodes with micrometric channel lengths. Following simulation guidelines, a first batch of diodes was fabricated. It was found that surface charge depletion effects are stronger than expected and inhibit the onset of the oscillations. Indeed, a simple standard constant surface charge model is not able to reproduce experimental measurements and a self-consistent model must be included in the simulations. Using a self-consistent model, it was found that to achieve oscillations, wider channels and improved geometries are necessary.

Experimental demonstration of direct terahertz detection at room-temperature in AlGaN/GaN asymmetric nanochannels

The potentialities of AlGaN/GaN nanodevices as THz detectors are analyzed. Nanochannels with broken symmetry (so called self switching diodes) have been fabricated for the first time in this material system using both recess-etching and ion implantation technologies. The responsivities of both types of devices have been measured and explained using Monte Carlo simulations and non linear analysis. Sensitivities up to 100 V/W are obtained at 0.3 THz with a 280 pW/Hz1/2 noise equivalent power.

A Study of Geometry Effects on the Performance of Ballistic Deflection Transistor

We present the results of an experimental study of dimensional ratios dependencies on the performance of a ballistic deflection transistor (BDT) operating in a quasi-ballistic regime. Experimental transconductance change based on geometry variations is studied for smaller and larger devices with channel width of 300 and 500 nm, respectively. Transconductance variation for a series of drain biases is also observed for a specific geometry and dimension. By means of Monte Carlo modeling we report the effect of different geometry parameters on the transfer characteristics of BDTs. The strength of the gate control in the InGaAs channel is analyzed.

Phonon black-body radiation limit for heat dissipation in electronics

Thermal dissipation at the active region of electronic devices is a fundamental process of considerable importance. Inadequate heat dissipation can lead to prohibitively large temperature rises that degrade performance, and intensive efforts are under way to mitigate this self-heating. At room temperature, thermal resistance is due to scattering, often by defects and interfaces in the active region, that impedes the transport of phonons. Here, we demonstrate that heat dissipation in widely used cryogenic electronic devices instead occurs by phonon black-body radiation with the complete absence of scattering, leading to large self-heating at cryogenic temperatures and setting a key limit on the noise floor. Our result has important implications for the many fields that require ultralow-noise electronic devices.

Optimized V-shape design of GaN nanodiodes for the generation of Gunn oscillations

In this work, recent advances in the design of GaN planar Gunn diodes with asymmetric shape, so-called self-switching diodes, are presented. A particular geometry for the nanodiode is proposed, referred as V-shape, where the width of the channel is intentionally increased as approaching the anode. This design, which reduces the effect of the surface-charges at the anode side, is the most favourable one for the onset of Gunn oscillations, which emerge at lower current levels and with lower threshold voltages as compared to the standard square geometry, thus enhancing the power efficiency of the self-switching diode as sub-millimeter wave emitters.

Correlation between low-frequency current-noise enhancement and high-frequency oscillations in GaN-based planar nanodiodes: A Monte Carlo study

We present a spectral analysis of time sequences of current, calculated by means of Monte Carlo simulations, in GaN-based asymmetric nanodiodes, devices that are potential candidates to exhibit Gunn oscillations. It is found that the low-frequency noise increases significantly for biases close to the threshold voltage of Gunn oscillations, taking place at much higher frequencies of hundreds of gigahertz. Due to the inherent difficulty in detecting so fast fluctuations, the measurement of the low-frequency noise can be a quite useful tool for predicting current oscillations at sub-terahertz frequencies in these devices.

Terahertz tunable detection in self-switching diodes based on high mobility semiconductors: InGaAs, InAs and InSb

In this work we report on the use of high mobility materials in the channel of self-switching diodes as potential candidates for terahertz operation. By means of Monte Carlo simulations we envisage the feasibility of tuneable-by-geometry detection in the terahertz range. The low effective mass of InAs and InSb in relation to InGaAs enhances ballistic transport inside the diode, thus improving the amplitude and quality factor of the resonance found in the detection spectra of self-switching diodes. The frequency of the resonant peak is also increased with the use of these narrow band gap semiconductors. The analysis of the noise spectra provides useful information about the origin of the resonance. By decreasing temperature below 300 K, a clear improvement in detection sensitivity is also achieved.

Numerical study of sub-millimeter Gunn oscillations in InP and GaN vertical diodes: Dependence on bias, doping, and length

In this work, we report on Monte Carlo simulations of InP and GaN vertical Gunn diodes to optimize their oscillation frequency and DC to AC conversion efficiency. We show that equivalent operating conditions are achieved by the direct application of a sinusoidal AC voltage superimposed to the DC bias and by the simulation of the intrinsic device coupled with the consistent solution of a parallel RLC resonant circuit connected in series. InP diodes with active region about 1 μm offer a conversion efficiency up to 5.5% for frequencies around 225 GHz. By virtue of the larger saturation velocity, for a given diode length, oscillation frequencies in GaN diodes are higher than for InP structures. Current oscillations at frequencies as high as 675 GHz, with 0.1% efficiency, are predicted at the sixth generation band in a 0.9 μm-long GaN diode, corroborating the suitability of GaN to operate near the THz band. At the first generation band, structures with notch, in general, provide lower oscillation frequencies a...

Exploring Digital Logic Design Using Ballistic Deflection Transistors Through Monte Carlo Simulations

We present exploratory studies of digital circuit design using the recently proposed ballistic deflection transistor (BDT) devices. We demonstrate a variety of possible logic functions through simple reconfiguration of two drain-connected BDTs. We further propose the creation of a three-BDT logic cell to yield differential versions of each logic function, improving overall flexibility of BDT circuit design. Each of the proposed gate configurations has been verified through extensive numerical calculations using an in-house Monte Carlo simulator. Simulation results show that the proposed gate arrangements are capable of achieving 400-GHz operating frequencies at room temperature. A compact fit-based analytical model to aid circuit design using BDTs is also introduced.