Single Drift Region Research Articles

Edge-Terminated AlGaN/GaN/AlGaN Multi-Quantum Well Impact Avalanche Transit Time Sources for Terahertz Wave Generation

Edge-Terminated AlGaN/GaN/AlGaN Multi-Quantum Well Impact Avalanche Transit Time Sources for Terahertz Wave Generation

Direct observation of radio-frequency negative differential resistance in GaN-based single drift region IMPATT diodes

We report the direct observation of radio-frequency negative differential resistance, via on-wafer S-parameter measurements, in GaN-based impact ionization avalanche transit time (IMPATT) diodes. Clear signatures of reflection gain are observed from 18.7 to 30.6 GHz. These observations have been made possible by suppressing the reverse leakage current (and thereby parasitic shunt conductance) by optimization of the fabrication process, in conjunction with the use of pulsed measurements to suppress device self-heating. Consistent with avalanche-dominated behavior, the measured DC reverse bias current–voltage measurements show a positive temperature coefficient of breakdown. For the high-frequency on-wafer characterization, pulsed-bias S-parameter measurements with low (0.0067%) duty cycle were used to mitigate thermal effects. The measured avalanche frequency aligns closely with theoretical predictions based on Gilden and Hines' small signal model [Gilden and Hines, IEEE Trans. Electron Devices ED-13(1), 169–175 (1966)], measured impact ionization coefficients [Cao et al., Appl. Phys. Lett. 112(26), 262103 (2018)], and experimental saturation velocity measurements [Bajaj et al., Appl. Phys. Lett. 107(15), 153504 (2015)]; this excellent agreement confirms IMPATT operation and provides insights needed to further optimize device performance.

Junction Diameter Dependence of Oscillation Frequency of GaN IMPATT Diode Up to 21 GHz

An experimental study on the effects of junction capacitance and current density on the oscillation characteristics of GaN single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes were carried out using GaN p+-n abrupt junction diodes of various diameters, 200, 150, and 100 μm, with a depletion layer width of 2 μm. The fabricated diodes showed a clear avalanche breakdown at 315 V and a pulsed microwave oscillation with a peak output power exceeding 30 dBm. The oscillation frequency depended on junction diameter and current density. It was widely modulated from 8.56 to 21.1 GHz with decreasing junction diameter and increasing current density. The highest oscillation frequency was obtained with a current density of 13.8 kA/cm2 and a junction diameter of 100 μm. A numerical calculation based on Read-type small-signal theory was carried out and found to well explain the experimental results.

Study on Schottky Al x Ga1-x N/GaN IMPATT Diodes for Millimeter-Wave Application

This article proposes a Schottky aluminum gallium nitride (AlGaN)/GaN single-drift-region (SDR) IMPATT diode that uses AlGaN as the avalanche active layer. Compared with GaN, AlGaN has a wider bandgap and better breakdown characteristics. These features can significantly improve the device performance. We simulated the direct current (DC) and radio frequency (RF) performances of the new structure for the 0.2–0.6 Al composition under the millimeter-wave band and compared the results with the conventional GaN avalanche layer IMPATT. The results indicate that the AlGaN avalanche layer IMPATT significantly improves the breakdown voltage, RF voltage, and RF current performances. Furthermore, the application of AlGaN avalanche layer increases the RF efficiency from 18.16% to 21.98% and increases the RF power from 1.56 to 2.67 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . As this structure has greater potential for the millimeter wave, even terahertz application, this article brings a new reference for the design of GaN-based IMPATT diodes.

Study on Electric Field Modulation and Avalanche Enhancement of SiC/GaN IMPATT Diode

This paper proposes a 6H-materials silicon carbide (SiC)/gallium nitride (GaN) heterogeneous p-n structure to replace the GaN homogenous p-n junction to manufacture an impact-ionization-avalanche-transit-time (IMPATT) diode, and the performance of this 6H-SiC/GaN heterojunction single-drift-region (SDR) IMPATT diode is simulated at frequencies above 100 GHz. The performance parameters of the studied device were simulated and compared with the conventional GaN p-n IMPATT diode. The results show that the p-SiC/n-GaN IMPATT performance is significantly improved, and this is reflected in the enhanced characteristics in terms of operating frequency, rf power, and dc-rf conversion efficiency by the two mechanisms. One such characteristic that the new structure has an excessive avalanche injection of electrons in the p-type SiC region owing to the ionization characteristics of the SiC material, while another is a lower electric field distribution in the drift region, which can induce a higher electron velocity and larger current in the structure. The work provides a reference to obtain a deeper understanding of the mechanism and design of IMPATT devices based on wide-bandgap semiconductor materials.

Study of p-SiC/n-GaN Hetero-Structural Double-Drift Region IMPATT Diode.

Nowadays, the immature p-GaN processes cannot meet the manufacturing requirements of GaN impact ionization avalanche transit time (IMPATT) diodes. Against this backdrop, the performance of wide-bandgap p-SiC/n-GaN heterojunction double-drift region (DDR) IMPATT diode is investigated in this paper for the first time. The direct-current (DC) steady-state, small-signal and large-signal characteristics are numerically simulated. The results show that compared with the conventional GaN single-drift region (SDR) IMPATT diode, the performance of the p-SiC/n-GaN DDR IMPATT proposed in this design, such as breakdown voltage, negative conductance, voltage modulation factor, radio frequency (RF) power and DC-RF conversion efficiency have been significantly improved. At the same time, the structure proposed in this design has a larger frequency bandwidth. Due to its greater potential in the RF power density, which is 1.97 MW/cm2 in this study, indicates that the p-SiC/n-GaN heterojunction provides new possibilities for the design and manufacture of IMPATT diode.

A JL-SDR-IMPATT Device with Improved Efficiency

An attempt has been made to present a new device which will function as a highly efficient SDR (Single Drift Region) P+-N-N+ IMPATT diode utilizing the advantages of a junctionless field effect transistor. The basic idea is to convert a uniform N+ region into a (P+–N–N+) structure without any requirement of physical doping. As the present device works on the principle of a junctionless channel, variability and short channel effects are significantly reduced as compared to the conventional TFET though the requirement of an extra gate increases a few fabrication steps. Further, efficiency more than conventional SDR IMPATT diode is achievable without any physical doping.

Influence of the anisotropy on the performance of D-band SiC IMPATT diodes

Numerical simulation has been made to predict the RF performance of direction and < $$ 11\bar{2}0 $$ > direction p+/n/n−/n+ (single drift region) 4H silicon carbide (4H-SiC) impact-ionization-avalanche-transit-time (IMPATT) diodes for operation at D-band frequencies. We observed that the output performance of 4H-SiC IMPATT diode is sensitive to the crystal direction of the one-dimensional current flow. The simulation results show that direction 4H-SiC IMPATT diode provides larger breakdown voltage for its lower electron and hole ionization rates and higher dc-to-rf conversion efficiency (η) for its higher ratio of drift zone voltage drop (VD) to breakdown voltage (VB) compared with those for < $$ 11\bar{2}0 $$ > direction 4H-SiC IMPATT diode, which lead to higher-millimeter-wave power output for direction 4H-SiC IMPATT compared to < $$ 11\bar{2}0 $$ > direction. However, the quality factor Q for the < $$ 11\bar{2}0 $$ > direction 4H-SiC IMPATT diode is lower than that of direction, which implies that the < $$ 11\bar{2}0 $$ > direction 4H-SiC IMPATT diode exhibits better stability and higher growth rate of microwave oscillation compared with direction 4H-SiC IMPATT diode.

Influence of skin effect on the series resistance of millimeter-wave IMPATT devices

An attempt is made in this paper to study the influence of skin depth on the parasitic series resistance of millimeter-wave IMPATT devices based on Silicon. The method is based on the concept of depletion width modulation of the device under large-signal condition. A large-signal simulation model based on non-sinusoidal voltage excitation is used for this study. The electric field snap-shots of 35 GHz Single-Drift Region (SDR) and 94 GHz Double-Drift Region (DDR) IMPATT devices are first obtained from which the series resistances are estimated by incorporating the effect of skin depth in the modeling and simulation. The series resistances of these devices are also obtained by neglecting the effect of skin depth. The values of series resistances obtained from the simulation are compared with the corresponding experimentally reported values. It is observed that the series resistance estimated by including the skin effect is in closer agreement with the experimental values as compared to that without including the same. Thus the skin effect plays an important role for determining the series resistance of IMPATT devices at millimeter-wave frequency bands.

A proposed simulation technique to study the series resistance and related millimeter-wave properties of Ka-band Si IMPATTs from the electric field snapshots

A large-signal model and a simulation technique based on non-sinusoidal voltage excitation are used to obtain the electric field snapshots from which the series resistance and related high-frequency properties of a 35 GHz Silicon Single-Drift Region (SDR) Impact Avalanche Transit Time (IMPATT) device have been estimated for different bias current densities. A novel method is proposed in this paper to determine the parasitic series resistance of a millimeter-wave IMPATT device from large-signal electric field snapshots at different phase angles of a full cycle of steady-state oscillation. The method is based on the depletion width modulation of the device under a large-signal condition. The series resistance of the device is also obtained from the large-signal admittance characteristics at threshold frequency. The values of series resistance of a 35 GHz SDR IMPATT diode obtained from the proposed method and the large-signal admittance method are compared with experimentally reported values. The results show that the proposed method provides better and closer agreement with the experimental value.

Photosensitivity Analysis of Gallium Nitride and Silicon Carbide Terahertz IMPATT Oscillators: Comparison of Theoretical Reliability and Study on Experimental Feasibility

Reliability of terahertz-frequency (~1.0 THz) characteristics of wide-bandgap (WBG) wurtzite (Wz)-GaN- and 4H-SiC-based p++nn++-type single-drift-region (SDR) impact avalanche transit time (IMPATT) devices (normal and photoilluminated) is compared through a simulation scheme. The simulation experiment reveals that an RF power density of 3.37 times 1011 W middotm-2 (efficiency of 18.2%) at around 1.126 THz may be realized from the optimized unilluminated GaN IMPATT device, whereas the unilluminated 4H-SiC IMPATT device is expected to generate an RF power density of 1.35 times 1011 W middotm-2 (efficiency of 9%) at 1.05 THz. However, the parasitic series resistance reduces the maximum exploitable power density from the terahertz devices. Under optical illumination, additional photogenerated carriers are created in the devices, and these carriers change the admittance and negative resistance properties of the terahertz IMPATT diodes. The performance modulation of the terahertz devices is simulated, and the results are compared in this paper. Under external radiation, the operating frequencies of the GaN- and SiC-based diodes are found to shift upward by 6.0 and 40.0 GHz, respectively, with degradation of maximum output-power density level and device negative resistance. The extensive simulation experiments establish that, although the photosensitivity of the 4H-SiC-based IMPATT device is better than its GaN counterpart, the overall terahertz performance of the unilluminated GaN IMPATT device is far better than the 4H-SiC-based device, particularly in terms of output power and efficiency. The simulation results and the proposed experimental methodology presented here can be used for realizing optically tuned WBG IMPATT oscillators for terahertz communication.

GaN IMPATT diode: a photo-sensitive high power terahertz source

The prospects of wurtzite phase single-drift-region (SDR), flat and single-low-high-low (SLHL) type GaN IMPATT devices as terahertz sources are studied through a simulation experiment. The study indicates that GaN IMPATT diodes are capable of generating high RF power (at least 2.5 W) at around 1.45 THz with high efficiency (17–20%). The superior electronic properties of GaN make this a promising candidate for IMPATT operation in the THz regime, unapproachable by conventional Si, GaAs and InP based IMPATT diodes. The effect of parasitic series resistance on the THz performance of the device is further simulated. It is interesting to note that the presence of a charge bump in a flatly doped SDR structure reduces the value of parasitic series resistance by 22%. The effects of photo- illumination on the devices are also investigated using a modified double iterative simulation technique. Under photo-illumination (i) the negative conductance and (ii) the negative resistance of the devices (both flat and SLHL) decrease, while the frequency of operation and the device quality factor shift upwards. However, the upward shift in operating frequency is found to be more (∼16 GHz) in the case of the SLHL SDR IMPATT device. The study indicates that GaN IMPATT is a promising opto-sensitive high power THz source.

Epitaxial layer induced series resistance and microwave properties of N+NP+ Si X band impatt diodes

Following Gummel-Blue approach [1] [H.K. Gummel, J. L. Blue, IEEE Trans. Electron. Devices 14(1967) pp. 569–572.], the effect of undepleted epitaxial layers on the series resistance (Rs) as well as on its microwave properties of single drift region (n+np+) Si IMPATT diodes [2] [M. Mitra, M. Das, S. Kar, S.K. Roy, IEEE Trans. Electron. Devices 40(1993) pp. 1890–1893.] with flat doping profile with capacity 0.2PF at X band under experimental bias current of 25mA and temperature 373K have been studied. The computation for series resistance fits well with the device data for flat doping profile [2] [M. Mitra, M. Das, S. Kar, S.K. Roy, IEEE Trans. Electron. Devices 40(1993) pp. 1890–1893.]. The same study has also been simulated on its low–high–low (lhl) doping profile counterpart. The value of Rs increases approximately linearly with the increase of undepleted epi-layer thickness determined by the doping density for both flat and lhl structure. The value of Rs decreases remarkably as the doping profile changes from flat to lhl type.

Effect of punch through on the microwave series resistance of n+np+ Si IMPATT diodes around the X band

The effect of punch through on the series resistance of n+np+ single drift region Si HP [5082-0432] IMPATT diodes of capacity 0.02 pf around the X band has been studied. The computed result for series resistance fits well with the device data. The analysis shows that for a constant bias current density, when the space charge effect is not prominent, the value of series resistance decreases with the decrease of punch through, determined by the doping density and thickness of the active layer. The decrease of punch through produces an upward shift in the operating frequency of the device. It is also observed that an increase of punch through factor leads to a decrease in negative resistance, conversion efficiency and the susceptance of the device.

Avalanche Noise Generation Profile along Active Zone of Impatt Diodes

A generalised computer method to study the avalanche noise generation profile along the depletion layer of IMPATT diodes has been described. The method has been applied to different silicon flat profile SDR (single drift region) and DDR (double drift region) structures. The results of the analysis provide the intensity of noise generation at every space point in the active layer of the diode due to individual noise sources located at various space points. The results indicate that the noise generation profile, for any location of the noise sources, is characterised by one peak close to the field maximum and the magnitude of the peak and the profile are observed to be very sensitive to the diode structures and operating parameters, thus can provide means for minimisation of avalanche noise.

Space charge dependence of negative resistance, avalanche layer width, and avalanche resonance frequency of SDR p+ nn+ Si IMPATT diodes with optimised doping profile

Computer studies are carried out on the mobile space charge dependence of breakdown voltage, avalanchezone width, avalanche resonance frequency, and negative resistance of a single drift region (SDR) p+nn+ Si IMPATT diode designed for operation in the X, Ku, and K frequency bands, i.e., 8 to 26 GHz. The doping profile of the diode is optimised by varying the diffusion length, i.e., time and temperature of diffusion, so that the device may provide maximum output power and efficiency. The results show that the dc and high frequency properties of SDR Si IMPATT diodes are modified by the mobile space charge at high current density, but the space charge dependence of the above properties becomes considerable at lower dc current density for SDR diodes compared to their double drift region (DDR) counterparts.

Effect of Enhanced Leakage Current on the Microwave Negative Resistance of High Efficiency GaAs Double Drift Region IMPATT Diode

The effect of enhanced electron and hole leakage currents on (i) the negative resistance profiles, (ii) the admittance characteristics, and (iii) the device quality factor (Q) of K-band GaAs low-high-low double drift region IMPATT has been studied through computer simulation. The results show that the diode negative resistance increases first and then starts decreasing with the increase of electron leakage current. This oscillatory character of negative resistance due to enhanced leakage current bears a striking similarity to the previous result from a GaAs single drift region IMPATT diode [7]. It is also observed that the frequency or operation of the high efficiency diode shifts upwards and the device Q increases with increasing leakage current.

Studies on the high-frequency properties of ?111?, ?110? and ?100? oriented GaAs IMPATT diodes

High-frequency analysis has been carried out to predict the rf performance of 〈111〉, 〈110〉 and 〈100〉 oriented p+nn+, n+pp+ (single drift region) and n+npp+ (double drift region) GaAs IMPATT diodes for opertion at 35 and 60 GHz. The microwave performance is observed to be highly sensitive to crystal orientation in case of p+nn+ and n+npp+ diodes whereas orientation of the substrate has negligible effect on n+pp+ avalanche diodes. The calculation shows that 〈111〉 oriented GaAs IMPATT diode would provide the largest magnitude of negative resistance and negative conductance for both SDR p+nn+ and DDR n+npp+ diodes which indicates that high microwave power with high conversion efficiency can be realised from these 〈111〉 oriented GaAs devices. This result can be explained from the experimental data of electron and hole ionization rates for different orientations in GaAs.

Simulation of the Diffusion Profile for Enhancement of Negative Resistance and Efficiency of Silicon Single Drift Region IMPATT Diodes

The diffusion profile of a single drift region (SDR) p+nn+ silicon IMPATT diode is simulated using simple, generalized, and accurate computer methods for dc and small signal analysis of the diode for realizing high negative resistance and conversion efficiency at X-band (8 to 12 GHz). The results show that the optimized diffusion profile provides a junction depth of 0.83 to 0.86 μm with a surface concentration of 7.5 × 1025 to 1026 m−3. The optimized diode has a narrow avalanche zone with breakdown voltage of 89.3 V and conversion efficiency of 11%. The negative resistance and the negative conductance of the diode are also considerably enhanced due to optimization of the diffusion profile. Das Diffusionsprofil einer SDR (single-drift region)-p+ nn+ -Silizium-IMPATT-Diode wird mit einfachen, verallgemeinerten und genauen Computermethoden für eine Gleichspannungs- und Klein-signalanalyse der Diode zur Realisierung eines hohen negativen Widerstands und Konversionswirkungs-grades im X-Band (8 bis 12 GHz) simuliert. Die Ergebnisse zeigen, daß das optimierte Diffusionsprofil eine Übergangstiefe von 0,83 bis 0,86 μm mit einer Oberflächenkonzentration von 7,5 × 1025 bis 1026 m−3 aufweist. Die optimierte Diode hat eine schmale Lawinenzone mit einer Durchbruchs-spannung von 89,3 V und einem Konversionswirkungsgrad von 11%. Der negative Widerstand und der negative Leitwert der Diode sind infolge der Optimierung des Diffusionsprofils ebenfalls beträchtlich erhöht.

Computer studies on the space charge dependence of avalanche zone width and conversion efficiency, of single driftp +nn+ andn +pp+ indium phosphide impatts

The effect of mobile space charge on avalanche zone width and conversion efficiency of single drift region (SDR) indium phosphide impatts at 12 and 60 GHz has been investigated. The results show thatp +nn+ InP diodes have a narrower avalanche zone and a higher conversion efficiency compared ton +pp+ diodes for both the frequencies at normal operating current densities. The expansion of avalanche zone and efficiency degradation at high current levels are more pronounced inp +nn+ at 12 GHz and inn +pp+ at 60 GHz.