Large signal and noise properties of heterojunction Al_xGa_(1-x)As/GaAs DDR IMPATTs

Simulation studies are carried out on the large signal and noise properties of heterojunction（HT）Al_xGa_（1-x）As/GaAs double drift region（DDR） IMPATT devices at V-band（60 GHz）.The dependence of Al mole fraction on the aforementioned properties of the device has been investigated.A full simulation software package has been indigenously developed for this purpose.The large signal simulation is based on a non-sinusoidal voltage excitation model.Three mole fractions of Al and two complementary HT DDR structures for each mole fraction i.e.,six DDR structures are considered in this study.The purpose is to discover the most suitable structure and corresponding mole fraction at which high power,high efficiency and low noise are obtained from the device.The noise spectral density and noise measure of all six HT DDR structures are obtained from a noise model and simulation method.Similar studies are carried out on homojunction（HM） DDR GaAs IMPATTs at 60 GHz to compare their RF properties with those of HT DDR devices.The results show that the HT DDR device based on N-Al_xGa_（1-x）As/p-GaAs with 30%mole fraction of Al is the best one so far as large signal power output,DC to RF conversion efficiency and noise level are concerned.

Effect of junction temperature on the large-signal properties of a 94 GHz silicon based double-drift region impact avalanche transit time device

The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a non-sinusoidal voltage excitation and studied the effect of junction temperature between 300 and 550 K on the large-signal characteristics of the device for both continuous wave （CW） and pulsed modes of operation. Results show that the large-signal RF power output of the device in both CW and pulsed modes increases with the increase of voltage modulation factor up to 60%, but decreases sharply with further increase of voltage modulation factor for a particular junction temperature; while the same parameter increases with the increase of junction temperature for a particular voltage modulation factor. Heat sinks made of copper and type-IIA diamond are designed to carry out the steady-state and transient thermal analysis of the device operating in CW and pulsed modes respectively. Authors have adopted Olson＇s method to carry out the transient analysis of the device, which clearly establishes the superiority of type-IIA diamond over copper as the heat sink material of the device from the standpoint of the undesirable effect of frequency chirping due to thermal transients in the pulsed mode.

Heterojunction DDR THz IMPATT diodes based on Al_xGa_(1-x)N/Ga N material system

Simulation studies are made on the large-signal RF performance and avalanche noise properties ofhet- erojunction double-drift region （DDR） impact avalanche transit time （IMPATT） diodes based on AlxGal-xN/GaN material system designed to operate at 1.0 THz frequency. Two different heterojunction DDR structures such as n-Al0.4Ga0.6N/p-GaN and n-GaN/p-Al0.4Ga0.6N are proposed in this study. The large-signal output power, con- version efficiency and noise properties of the heterojunction DDR IMPATTs are compared with homojunction DDR IMPATT devices based on GaN and Al0.4Ga0.6N. The results show that the n-Al0.4Ga0.6N/p-GaN heterojunction DDR device not only surpasses the n-GaN/p-Al0.4Ga0.6N DDR device but also homojunction DDR IMPATTs based on GaN and Al0.4Ga0.6N as regards large-signal conversion efficiency, power output and avalanche noise performance at 1.0 THz.

Large-signal characterization of DDR silicon IMPATTs operating in millimeter-wave and terahertz regime

The authors have carried out the large-signal characterization ofsilicon-based double-drift region （DDR） impact avalanche transit time （IMPATT） devices designed to operate up to 0.5 THz using a large-signal simulation method developed by the authors based on non-sinusoidal voltage excitation. The effect of band-to-band tunneling as well as parasitic series resistance on the large-signal properties of DDR Si IMPATTs have also been studied at different mm-wave and THz frequencies. Large-signal simulation results show that DDR Si IMPATT is capable of delivering peak RF power of 633.69 mW with 7.95% conversion efficiency at 94 GHz for 50% voltage modulation, whereas peak RF power output and efficiency fall to 81.08 mW and 2.01% respectively at 0.5 THz for same voltage modulation. The simulation results are compared with the experimental results and are found to be in close agreement.

Potentiality of semiconducting diamond as the base material of millimeter-wave and terahertz IMPATT devices

An attempt is made in this paper to explore the potentiality of semiconducting type-IIb diamond as the base material of double-drift region（DDR） impact avalanche transit time（IMPATT） devices operating at both millimetre-wave（mm-wave） and terahertz（THz） frequencies. A rigorous large-signal（L-S） simulation based on the non-sinusoidal voltage excitation（NSVE） model developed earlier by the authors is used in this study. At first,a simulation study based on avalanche response time reveals that the upper cut-off frequency for DDR diamond IMPATTs is 1.5 THz, while the same for conventional DDR Si IMPATTs is much smaller, i.e. 0.5 THz. The L-S simulationresultsshowthattheDDRdiamondIMPATTdevicedeliversapeakRFpowerof7.79Wwithan18.17%conversion efficiency at 94 GHz; while at 1.5 THz, the peak power output and conversion efficiency decrease to6.19mWand8.17%respectively,taking50%voltagemodulation.AcomparativestudyofDDRIMPATTsbasedon diamond and Si shows that the former excels over the later as regards high frequency and high power performance at both mm-wave and THz frequency bands. The effect of band to band tunneling on the L-S properties of DDR diamond and Si IMPATTs has also been studied at different mm-wave and THz frequencies.