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Devic
e D
epth
(µm
)
40 µm heat sink
Cathode
Anode
8.015 µmGunn Diode
10µmheat sink
Device Width (µm)
Figure 4
Figure 3
CathodeHeat Sink
Gunn DiodeAnode Heat Sink
0 1 2 3 40.0
0.2
0.4
0.6
0.8
1.0
1.2 Reverse IV Curves
Current (A)
Voltage (V)
Measured 1928A 300K
Model 1928A 300K
Forward
IV Curves
Figure 5
Development of High Power THz sources for Imaging Applications
Microelectronics and Nanostructures (M&N) Group,
School of Electrical and Electronic Engineering
Faisal Amir and Mohamed Missous
Introduction
An advanced step-graded Gunn diode is presented, which has been developed through joint modelling-experimental work. The novel higher frequency devices have been realized to test GaAs based Gunn oscillators at sub-millimetre wave for use as a high power (multi mW) Terahertz source in conjunction with a mm-wave multiplier, with novel Schottky diodes.
Conclusion
A novel 2D physical model for an advanced step-graded AlGaAs hot electron injector Gunn diode was successfully extended to higher frequency ( > 100GHz). Future work includes the development of a full functional multiplier as a high power terahertz source.
The doping spike carrier concentration optimized value was used during higher frequency model development and instead the transit region length was reduced. The measured and simulated forward and reverse-bias IV characteristics of the ~100 GHz fundamental model are shown in Figure 8 and match extremely well with measured data. The manufactured device yielded a maximum fundamental power of ~22 mW at 94 GHz, the highest ever reported for a GaAs Gunn device.
Physical Model Development
The Epitaxial growth of the advanced step-graded GaAs-AlGaAs Gunn diode with hot electron injector wafers is performed at the university using a RIBER V100+ MBE reactor.
To complement experimentally obtained data and perform a sensitivity analysis on the effects of variation in epitaxial composition, especially carrier concentration in the doping spike and transit region, predictive physical models, using SILVACO, have been developed .
Harmonic generation
The THz frequencies considered (up to
600 GHz) are to be generated in a
two-stage module. The initial
frequency source is to be provided by
Contact: [email protected]
Supervisor: Professor Mo Missous
the novel high frequency Gunn diodes. The output from these diodes is then to be coupled into a multiplier module shown in figure 7.
DC IV Characteristics
The simulated forward and reverse bias IV characteristics of the 77 GHz model are shown in figure 5 and match extremely well with measured data thus validating the choice of the physical models and material parameters used. The doping spike analysis provided 1×1018 cm-3 as optimized value. The model was then used to predict and develop higher frequency devices.
A. Results from a SILVACO simulation showing the effects of the doping spike (1×1018 cm-3) on electron concentration in the transit region (——; spike present, -----; spike absent).
B. Effects of variation in doping spike carrier concentration on simulated IV characteristics (numbers next to forward bias curves represent calculated asymmetry values).
Figure 6
0 1 2 3 40.0
0.2
0.4
0.6
0.8
1.0
1.2
Forward
IV Curves
1.27
1.48
1.17
1.17
Current (A)
Voltage (V)
Spike 1×1018 cm
-3
Spike 2×1018 cm
-3
Spike 5×1017 cm
-3
Spike 2.5×1017 cm
-3
Reverse IV Curves
1.5 2.0 2.5 3.0 3.51e13
1e14
1e15
1e16
1e17
1e18
1e19
Contact
layer
Transit Region
AlGaAs Launcher
Electron Concentration (cm
-3)
Device Distance (µm)
Contact
layer
(A) (B)
SILVACO simulation results showing the measured and simulated IV characteristics at 300K
A 2D modelled structure with Gold plated heat sinks.
3D cylindrical model developed in SILVACO
SEM of a fabricated Gunn diode
Epitaxial structure and conduction band diagram
Higher Frequency Gunn
(A). Measured and modelled forward / reverse IV curves for a 100GHz fundamental device at 300K (B). Measured and modelled forward IV curves at increasing temperatures.
Figure 8
0 1 2 3 4
0.0
0.2
0.4
0.6
0.8
358K
300K323K
Current (A)
Voltage (V)
Modelled 300K
Modelled 323K
Modelled 358K
Measured 300K
Measured 323K
Measured 358K
Forward IV Curves
0 1 2 3 4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Current (A)
Voltage (V)
Measured 300K
Modelled 300K
Forward
IV Curves
Reverse IV Curves
(A) (B)
Figure 1
00.38
Conduction
Band
Typical Advanced Step-graded Injector Gunn Diode Structure
barrier
Transit
Figure 2
Figure 7
Harmonic Generation
Multiplier (x n) BlockGunn Block
Resonant
Disk
Gunn Diode
Output
(wn)Resonant
Cavity (wo)Varactor
Micropstrip
Back short
Bias Post
Choke
WG28 - Waveguide
Schottky
