Mixed Tunneling Avalanche Transit Time Research Articles

Simulation on different orientation hexagonal SiC-based hetero-polytype IMPATT terahertz diodes

SiC hetero-polytypes that could be fabricated by chemical vapor deposition etc. methods can be employed to design the power devices. Herein, the 〈0 0 0 1〉(〈1 1 2¯ 0〉)4H(6H)-SiC-based hetero-polytypes are adopted to construct the n+/n/i/p/p+-type impact ionization avalanche transit time diodes (IMPATTDs) and mixed tunneling avalanche transit time diodes (MITATTDs). The DC, large-signal and noise performance of the proposed diodes operating at 0.85 THz are numerically simulated based on the fundamental equations for semiconductor devices. The results indicate that, the diodes with 〈0 0 0 1〉4H(6H)-SiC in each of the i-type, n-type and p-type regions can render higher break-down voltage and conversion efficiency while lower quality factor comparing to those with 〈1 1 2¯ 0〉4H(6H)-SiC in the three regions, the latter devices involve lower noise. The diodes contained 3C-SiC show lower break-down voltage and quality factor while higher noise than those without 3C-SiC. Little difference of DC, large-signal and noise properties between IMPATTDs and MITATTDs is implied due to very weak tunneling through thick intrinsic-region. The present diodes show higher conversion efficiency comparing to the n+/n/p/p+-type devices. In addition, the fabricating feasibility of the proposed devices is discussed. This paper can guide to design the reasonable structures by using suitable anisotropic semiconductors to achieve high-performance devices.

Optimal Design of Large Signal Performance of AlN/GaN Hetero-Structural IMPATT and MITATT Diodes

Hetero-structure of AlxGa1-xN/GaN exhibits important applications in high frequency and large power devices. In this paper, AlN/GaN is adopted to optimal design the large power impact avalanche transit time (IMPATT) and mixed tunneling avalanche transit time (MITATT) diodes operating at the atmospheric low loss window frequency of 0.85 THz. The static state and large signal characteristics of the devices are numerically simulated. The values of peak electric field strength, break-down voltage, avalanche voltage, the maximum generation rates of avalanche and tunneling, admittance-frequency relation, output power, conversion efficiency, quality factor of the proposed hetero-structural IMPATT and MITATT diodes are calculated, respectively. Via comparing the obtained results of (n)AlN/(p)GaN and (n)GaN/(p)AlN IMPATT diodes to those of the MITATT counterparts, there exists little performance difference between IMPATT and MITATT devices while implies significant difference between the (n)AlN/(p)GaN and (n)GaN/(p)AlN diodes.

Effect of Tunneling on Small Signal Characteristics of IMPATT Diodes with SiC Heteropolytype Structures

SiC heteropolytype structures indicate important applications in high frequency, large power solid devices etc. In this paper, the impact avalanche transit time (IMPATT) and mixed tunneling avalanche transit time (MITATT) diodes with heteropolytype consisting of two semiconductors among the 3C-SiC, 4H-SiC and 6H-SiC are numerically simulated to investigate the static state and small signal characteristics at the atmospheric window frequency of 1.56 THz. The breakdown voltage, avalanche voltage, peak value of static electric field, the maximum generation rates of avalanche and tunneling, power conversion efficiency, admittance-frequency relation of the proposed SiC heteropolytype diodes are calculated, respectively. Comparing the obtained parameters of IMPATT diodes with those of MITATT devices, the results imply that tunneling shows little influence on the small signal performance of the heteropolytype IMPATT diodes included 3C-SiC material, which is different from those of the homopolytype counterparts.

Prospects of gallium nitride double drift region mixed tunneling avalanche transit time diodes for operation in F, Y and THz bands

The potential of GaN as a wide band gap semiconductor is explored for application as double drift region mixed tunneling avalanche transit time (MITATT) diodes for operation at 120 GHz, 220 GHz and 0.35 THz using some computer simulation methods developed by our group. The salient features of our results have uncovered some peculiarities of the GaN based MITATT devices. An efficiency of more than 20% right up to a frequency of 0.35 THz (from the GaN MITATT diode) seems highly encouraging but a power output of only 0.76 W is indicative of its dismal fate. The existence of a noise measure minimum at the operating frequency of 0.35 THz is again exhilarating but the value of the minimum is miserably high i.e. more than 33 dB. Thus, although GaN is a wide band gap semiconductor, the disparate carrier velocities prevent its full potential from being exploited for application as MTATT diodes.

Comparative Assessment of GaN as a Microwave Source with Si and SiC for Mixed Mode Operation at Submillimetre Wave Band of Frequency

The potentials of GaN, SiC, and Si for application as microwave sources in mixed tunnelling avalanche transit time mode operation at submillimetre wave (sub-mm wave) frequency around 0.35 terahertz (THz) are investigated using some computer simulation methods. Design criteria to choose width, doping concentration, and area are highlighted. From the results of our simulation we observed that the Si diode produces the least power output of 41 mW followed by the GaN diode with 760 mW and the SiC diode with 2.89 W. In addition, the GaN diode has more noise than the SiC diode (by 5 dB) as well as the Si diode (by 10 dB). The drastically different performance between the GaN and the SiC diode is attributed to the incorporation of disparate carrier velocity in GaN which were not being used by other authors. In spite of the low power and high noise of the GaN compared to the SiC diode, the presence of several peaks in the mean square noise voltage curves and the existence of several minima in the noise measure curves would open a new direction in the design of GaN low-noise ATT diodes capable of multifrequency tuning like a DAR diode.

High Efficiency SiC Terahertz Source in Mixed Tunnelling Avalanche Transit Time Mode

High frequency properties of 4H-SiC double drift region (DDR) Mixed Tunnelling Avalanche Transit Time (MITATT) diodes are studied through computer simulation method. It is interesting to observe that the efficiency of SiC (flat) DDR MITATT diode (16%) is more than 4 times that of Si (flat) DDR MITATT diode (3.59%). In addition, a power output of more than 15 times from the SiC MITATT diode compared to the Si MITATT diode is commendable. A reduced noise measure of 17.71 dB from a low-high-low (lo-hi-lo) structure compared to that of 21.5 dB from a flat structure of SiC is indicative of the favourable effect of tunnelling current on the MITATT diode performance.

Dependence of Noise Properties on Photon Flux Incident on Silicon MITATT Device at Millimeter-Wave Window Frequencies

The effect of photon flux density on the noise properties of optically illuminated Double Drift Region (DDR) Mixed Tunneling Avalanche Transit Time (MITATT) device is investigated in this paper. An analytical model is proposed to obtain a relationship between the normalized difference of electron and hole current density of DDR device and the incident photon flux on it. Simulation is carried out to study the small signal noise spectral density and noise measure of the device under optical illumination. Two illumination configurations i.e., Flip Chip (FC) and Top Mounted (TM) structures are considered in the simulation. The device is designed to operate at mm-wave window frequency at W-band. The results show that avalanche noise measures of FC and TM structures of photo irradiated device are 37.1 dB and 40.2dB respectively for an incident photon flux density of 1024 m-2 sec-1 at 1000nm wavelength near band gap absorption of Silicon. The noise measure of the un-illuminated device is found to be 35dB. The results indicate that the increase of avalanche noise due to the incident photon flux can be reduced if FC structure is taken instead of TM structure.

Tunnelling Assisted Noise Control in InAs/InAs0.88 Sb0.12 Read Avalanche Diode

Analytical expressions for the mean-square noise voltage and noise measure of a Read-type avalanche diode in mixed mode operation are derived which reveal some new features of noise generation in MITATT (mixed tunnelling avalanche transit time) devices. These expressions have been used to explore the potential of InAs/InAs0.88 Sb0.12 for a low-noise MITATT diode. Our results indicate the lowest noise measure of 10.9dB from In As/In As0.88 Sb0.12 Read type MITATT with 32% tunnelling current as against the value of 19.26 dB from a similar Si diode structure.

Design optimization of a single-sided Si/SiGe heterostructure mixed tunnelling avalanche transit time double drift region

The potential of an Si/SiGe heterostructure mixed tunnelling avalanche transit time double drift region (DDR) with an SiGe layer on the p side alone is investigated. Our results indicate that this newly proposed structure has better mm wave properties and lower noise than the Si homostructure diode and Si/SiGe heterostructure diode with an SiGe layer on both n and p sides. Further, our results show that the diode properties are optimized for a particular width of the SiGe layer in the single-sided Si/SiGe heterostructure DDR.

Studies on the prospects of GaInAs and GaInAsP for double-drift region heterostructure IMPATTs

Double heterojunctions having the material combinations InP/GaInAs/InP, GaAs/GaInAs/GaAs and InP/GaInAsP/InP have been studied to assess their potential for double-drift region (DDR) IMPATT diodes. An accurate and realistic computer simulation program has been framed and used for the dc and high-frequency analysis of the DDRs. The analysis is carried out both in IMPATT (IMPact Avalanche Transit Time) and MITATT (MIxed Tunnelling Avalanche Transit Time) modes. Our results indicate that the GaAs/GaInAs/GaAs DDR would provide the best mm-wave performance up to sufficiently high frequencies. Further, the performance of the DDR diodes is observed to deteriorate at high frequency of operation due to phase distortion introduced by tunnel injected current, which is found to be the least in the case of GaAs/GaInAs/GaAs DDR leading to the best performance of this DDR amongst the three.

Structure, properties and applications of GexSi1-x strained layers and superlattices

The first successful pseudomorphic GexSi1-x strained layers on Si were grown in Germany in 1975. The extensive work that has been done on the production, properties and application of GexSi1-x strained layers and superlattices over the last fifteen years is described in this review. Values of critical layer thickness of the strained layers predicted by equilibrium theories are discussed and compared with experimental results. For x<0.6 the observed values are much larger than the theoretical values. The possible causes of this discrepancy are investigated and it is concluded that the layers must be metastable due to an energy barrier for the production of dislocations. Critical layer thicknesses of superlattices are also discussed and symmetrically strained superlattices are described. Results of band structure calculations of the strained layers and superlattices are given. Strain causes a large reduction in the fundamental indirect band gap of the Si/Ge alloy. Calculated band line-ups at the strained layer-substrate interface are compared with experiment. Modifications in the band structure due to strain have considerable effect on the optical and transport properties of the strained layers. Observed luminescence, photoconductivity and mobility are compared with predictions, taking strain into account. In the case of superlattices, band structure is further modified by zone folding. Superlattice structures which can produce a direct band gap are discussed. Raman scattering has proved a valuable tool for characterizing strained layers and superlattices. In the case of GexSi1-x strained layers, the Raman spectrum shows phonon lines shifted by strain. In the case of superlattices, additional lines due to zone folded LA phonons are observed. Raman measurements may be used to determine strain, thickness of a period and quality of interfaces. This review places emphasis on the use of Si/Ge strained in layers in Si-technology-based integrated circuits. The devices which have been fabricated to exploit properties of these layers include double heterostructure bipolar transistors, optical detectors, modulation doped field-effect transistors and mixed tunnelling avalanche transit time diodes. Progress made in the last 18 months has been rapid; a transistor with a cut-off frequency of 75 GHz was recently fabricated and this device has considerable promise.

Silicon-based millimeter-wave integrated circuits

Abstract Microwaves at frequencies above 30 GHz (millimeter waves), which offer several advantages, are mainly used at present for military applications. A broad civil market will be opened if a cost-effective planar integration can be achieved. The suitability of high resistivity silicon for planar millimeter-wave integration is described. To produce silicon monolithic millimeter-wave integrated circuits (SIMMWICs) the device structures are grown by molecular beam epitaxy on high-resistivity silicon substrate. Discrete impact avalanche transit time (IMPATT) and Schottky diodes fabricated from this material show excellent performances at 100 GHz: they have more than 1 W oscillator output power and a detector tangential signal sensitivity of − 52 dB m at around 90 GHz. For specific applications the device characteristics can be influenced by the introduction of SiGe heterojunctions. The MITATT (mixed tunneling avalanche transit time) oscillator and the resonant tunneling detector are given as examples. Hybrid integrated transmitters, voltage-controlled oscillators, and mixers can be fabricated on high resistivity silicon. The transmitter oscillator with a double-drift IMPATT diode as the active element emits a maximum continuous wave output power of 200 mW at 73 GHz. The advantages of the coplanar waveguide are pointed out and monolithic integrated oscillators and detectors are demonstrated. The chip with a coplanar Schottky diode as the detector element and a microstrip antenna with 36 radiating elements shows a sensitivity of 65 microV microW −1 cm −2 . The first applications of the described circuits for traffic surveillance are described and discussed.

Superlattice GaAs mixed tunneling avalanche transit time device structure

A superlattice GaAs-Ga0.7Al0.3As mixed tunneling avalanche transit time device has been fabricated and tested at 94 GHz. Two superlattice regions are utilized in order to control the avalanche and the drift currents. The superlattice in the avalanche region enhances the electron ionization rate by a factor of 8, while the superlattice in the drift region maximizes the tunneling current. At 94 GHz, pulsed output power of 0.2–0.4 W was obtained.