G. N. Dash

A generalized simulation method for MITATT-mode operation and studies on the influence of tunnel current on IMPATT properties

A generalized method of DC and high-frequency analysis for microwave transit time diodes in mixed tunnelling and avalanche mode, which can be applied to any type of diode structure is reported. Taking a purely field-dependent tunnel generation rate for electrons, the same is computed for holes from a simulated energy band diagram within the depletion layer of the diode. The method has been applied to a variety of Si, GaAs and InP diode structures. The results show a substantial degradation of IMPATT properties due to phase distortion caused by the tunnelling current.

An extremely low noise heterojunction IMPATT

The avalanche noise characteristics of InP/GaInAs (Ga/sub 0.47/In/sub 0.53/As) and InP/GaInAsP (Ga/sub 0.33/In/sub 0.67/As/sub 0.7/P/sub 0.3/) double drift region (DDR) heterostructure IMPact Avalanche Transit Time (IMPATTs) have been studied. The heterostructure IMPATTs in general are found to be less noisy compared to their homostructure counterparts and in particular the InP/GaInAs DDR is found to generate extremely low noise when the ternary layer width is properly selected. A noise measure of 7.7 dB has been observed at 190 GHz for a GaInAs layer width of 140 nm. Further, a study on the noise contribution from the individual space steps of the depletion layer due to individual noise sources in the generation region has revealed some interesting differences between those of homostructure and heterostructure diodes. Finally, a criterion for low-noise design is also suggested.

Prospects of 6H-SiC for operation as an IMPATT diode at 140 GHz

The potentials of 6H-SiC are explored for application as a high power IMPATT diode through computer simulation experiment. It is observed that the new material would far surpass its present rivals Si and GaAs in terms of power output at 140 GHz. However, excessive noise would put a severe restriction on the applicability of 6H-SiC for high-efficiency IMPATT structures.

Noise in mixed tunneling avalanche transit time (MITATT) diodes

Abstract A generalized method of analysis for avalanche noise in mixed tunneling and avalanche transit time (MITATT) diode is reported. This method can be applied to MITATT diodes with arbitrary doping distribution and arbitrary material combinations. The method is capable of estimating the mean-square value of the noise voltage as well as the noise distribution due to individual space steps caused by the individual noise sources. The method has been applied to a variety of Si double-drift diode structures with different levels of tunneling currents. The results indicate some new and interesting features of noise for mixed-mode operation.

Computer-aided studies on the wide-band microwave characteristics of a silicon double avalanche region (DAR) diode

The results of accurate and realistic high-frequency numerical analysis of a silicon DAR (double avalanche region) diode indicate some unique and useful microwave characteristics. The DAR diode under any structural condition exhibits multiband microwave negative resistance characteristics between 8 and 350 GHz which would make it possible to realize wide-band microwave oscillations (8 to 350 GHz) from any single DAR diode with a multituning facility. The negative resistance space distribution profiles of the diode at high frequencies of operation shows near sinusoidal variation, which suggests that a DAR diode can have several optimum diode widths for generation of a particular frequency. The results have been explained on the basis of computation of the total avalanche delay produced in both avalanche regions and transmit time delay produced in the drift region.

RF and microwave characteristics of a 10 nm thick InGaN-channel gate recessed HEMT

A new depletion-mode gate recessed AlGaN/InGaN/GaN-high electron mobility transistor (HEMT) with 10 nm thickness of InGaN-channel is proposed. A growth of AlGaN over GaN leads to the formation of two-dimensional electron gas (2DEG) at the heterointerface. High 2DEG density (ns) is achieved at the heterointerface due to a strain induced piezoelectric effect between AlGaN and GaN layers. The electrons are confined in the InGaN-channel without spilling over into the buffer layer, which also reduces the buffer leakage current. From the input transfer characteristics the threshold voltage is obtained as −4.5 V and the device conducts a current of 2 A/mm at a drain voltage of 10 V. The device also shows a maximum output current density of 1.8 A/mm at Vds of 3 V. The microwave characteristics like transconductance, cut-off frequency, max frequency of oscillation and Masons Unilateral Gain of the device are studied by AC small-signal analysis using a two-port network. The stability and power performance of the device are analyzed by the Smith chart and polar plots respectively. To our knowledge this proposed InGaN-channel HEMT structure is the first of its kind.

A New mm-Wave GaAs~Ga0.52In0.48P Heterojunction IMPATT Diode

Abstract The potentials of a new lattice-matched material combination, GaAs~Ga0.52In0.48P, is explored using a computer simulation method for application as an IMPact ionization Avalanche Transit Time diode at mm-wave frequencies. It is observed that by suitably adjusting the ternary layer width in the drift region of the diode not only is the power output enhanced from 0.38W to 0.50W but also the noise measure reduces from 26 dB to 21 dB.

Simulation studies on the noise behaviour of double avalanche region diodes

Computer simulation studies on the noise behaviour of several Si-based double avalanche region (DAR) diodes, each having two avalanche regions separated by a common drift region, are presented. Our results indicate that with a suitable choice of operating frequency, close to the design frequency, a DAR diode produces less noise as compared to a double drift region or single avalanche region diode. Further, it is interesting to note from our results that out of the several structures considered, the DAR structure having only a π-type of drift region shows the lowest noise-to-power ratio at a frequency of 115 GHz.

Small-signal computer simulation of IMPATT diodes including carrier diffusion

A generalized computer simulation method for small-signal analyses of IMPATT diodes incorporating the carrier diffusion current is presented. The method is capable of predicting the effect of carrier diffusion on the integrated devices microwave characteristics as well as on individual space-step contributions to diode negative resistance which in turn can identify the diode zone where carrier diffusion would have a pronounced effect. The results of authors investigation on the effect of carrier diffusion on performance of silicon flat-profile p+nn+, n+pp+ and n+npp+ diode structures indicate that diffusion has a pronounced effect on the p-side of the diodes whereas its effect on the n-side is only marginal. The changes in the values of diode negative conductance and diode negative resistance of the silicon flat-profile double-drift region diodes are observed to remain within ten per cent if the frequency of operation is kept within 100 GHz.

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.