Prospects of wide band gap material ZB-GaN over low band gap GaAs-based IMPATT Devices
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Wide-bandgap semiconductor
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The electric field and width of the avalanche region are vital while determining the performance of an IMPATT diode. In an attempt to optimize the same a new doping pattern in the form of doping steps is introduced in the avalanche zone and its effects on the terahertz characteristics of a 4H-SiC IMPATT Diode are explored. It is exciting to observe a conversion efficiency of 17.24 % from the IMPAT T diode with the proposed doping steps.
IMPATT diode
Realization (probability)
Avalanche diode
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IMPact-ionization-Avalanche-Transit-Time (IMPATT) diodes are widely used as microwave sources in transmitters in pulsed radar systems. Under pulsed conditions, the peak output power of an IMPATT diode at a given frequency is limited by its underlying material properties. Due to the high breakdown field and high electron saturation velocity of silicon carbide (SiC), a SiC IMPATT diode is expected to produce microwave power at least 100 times higher than Si or GaAs IMPATT diodes. We reported the first demonstration of a SiC IMPATT diode last year. In this work, the microwave characteristics of the diode are presented.
IMPATT diode
Avalanche diode
Step recovery diode
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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.
IMPATT diode
Wide-bandgap semiconductor
Impact ionization
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An analysis of current situation in silicon carbide R&D shows that it is most real to fabricate SiC IMPATT diode on an epitaxial pn structure grown on the (0001)Si face of 6H-SiC crystal. The operating frequency of this diode will be in the range 90-250 GHz. We calculated numericallydynamic characteristics of the SiC IMPATT diode for pulse mode of operation at the frequency 140 GHz. Results show that the diode conductivity is negative in a wide range of reverse current density (25 - 220 kA/cm2). The maximum microwave power generation efficiency of 6% has been calculated for current density of 90 kA/cm2 and specific input power of 10 MM/cm2. Experiments have been done on 6H-SiC pn structures grown by liquid phase epitaxy (LPE). Fabricated diodes revealed avalanche voltages V b from 30 to 200 V. A pulse avalanche current was passed through the diodes. The avalanche current density, J o , of 60 kA/cm2 and the specific dissipated power, P in , of 9 MW/cm2 were reached at 60 ns current pulse length. A temperature coefficient of V b (s=V-1dV/dT) was measured at high avalanche current density. For the first time, SiC varactor operated at 150 GHz has been fabricated.
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Microwave power at Q band is reported from GaAs Schottky-barrier avalanche diodes. A nickel-contacted epitaxial GaAs structure in a flipped mesa configuration was used. In a Q band waveguide cavity, 0.5 W was obtained at 26.7 GHz using a pulsed voltage source.
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In this paper, vertical p-n diodes fabricated on pseudobulk gallium nitride (GaN) substrates are discussed. The measured devices demonstrate breakdown voltages of 2600 V with a differential specific on-resistance of 2 mΩ cm 2 . This performance places these structures beyond the SiC theoretical limit on the power device figure of merit chart. Contrary to common belief, GaN devices do possess avalanche capability. The temperature coefficient of the breakdown voltage is positive, showing that the breakdown is indeed because of impact ionization and avalanche. This is an important property of the device for operation in inductive switching environments. Critical electric field and mobility parameters for epitaxial GaN layers grown on bulk GaN are extracted from electrical measurements. The reverse recovery time of the vertical GaN p-n diode is not discernible because it is limited by capacitance rather than minority carrier storage, and because of this its switching performance exceeds the highest speed silicon diode.
Avalanche diode
Avalanche breakdown
Impact ionization
Figure of Merit
Wide-bandgap semiconductor
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IMPATT diode
Equivalent series resistance
Saturation current
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Schottky-barrier hi-lo GaAs Impatt diodes with Ti-Pt-Au contacts have been fabricated for the 10.7–11.7 GHz band. At 180°C junction temperature rise the diodes have produced over 5 W of output power and up to 24% efficiency from an 11 GHz oscillator. Initial life tests show potential for high reliability.
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A detailed simulation investigation is carried out on the hetero-structure complimentary (p + -p - -p-n + ) IMPATT oscillator for Terahertz power generation. It is observed that this newly proposed GaN/AlGaN IMPATT may generate a pulsed power density of ~8×10 10 Wm -2 with an efficiency of 11%, whereas it's flatly doped counterpart is capable of delivering a pulsed power density of only 3×10 10 Wm -2 with 7% efficiency. The total parasitic series resistance, R S , including that due to the un-depleted region in device and also the effects of ohmic contact resistances, has been found to be a major problem that reduces the negative resistance significantly and thus it has a detrimental effect on THz oscillation of the device. The study reveals that the value of R S decreases by 40% as the structure, semiconductor material pair as well as doping profile of the diode changes suitably from conventional to the proposed hetero-structure p + -p - -p-n + type, by incorporating a 300A 0 Al 0.4 Ga 0.6 N layer in the p-drift region. This first study will be a useful guide in the THz-sector to meet the ever-increasing demand of semiconductor THz-sources for application in Imaging or in improvised explosive device (IED) detection.
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