““Steps to the exploitation of Steps to the exploitation of millimeter and submillimeter and sub--millimeter millimeter

wave generation and wave generation and detection for communication, detection for communication,

sensing, and imagingsensing, and imaging””

Collaboration:Collaboration:Germany:Germany:•• TU Darmstadt, TU Darmstadt, InstitutInstitut ffüürr HochfrequenztechnikHochfrequenztechnik, ,

Department of High Frequency Electronics Department of High Frequency Electronics (Prime Contractor), Prof. D.(Prime Contractor), Prof. D. PavlidisPavlidis, Prof. H. L. , Prof. H. L. HartnagelHartnagel

•• ForschungszentrumForschungszentrum JuelichJuelich, Prof. H. , Prof. H. LuethLueth, Dr. S. , Dr. S. ViltusevichViltusevich

Ukraine:Ukraine:•• Institute of Semiconductor Physics (Prime Institute of Semiconductor Physics (Prime

Contractor), NASU, Contractor), NASU, •• Prof. A. Prof. A. BelyaevBelyaev, Prof. V. , Prof. V. KochelapKochelap, Prof. , Prof.

V.V.LitovchenkoLitovchenko..•• Institute of Physics, NASU, Prof. B. Institute of Physics, NASU, Prof. B. DanilchenkoDanilchenko•• SRI SRI ““OrionOrion””, Dr. N. , Dr. N. BoltovetsBoltovets

Goals of the ProjectGoals of the Project

•• to explore efficient carrier response to explore efficient carrier response mechanisms in ultramechanisms in ultra--high frequencieshigh frequencies

•• to demonstrate their feasibility in the to demonstrate their feasibility in the generation/detection of subgeneration/detection of sub--millimeter millimeter electromagnetic waves in electromagnetic waves in nanoscalenanoscalenitridenitride--based structures.based structures.

How to approach the goals?How to approach the goals?

We will utilize the unique advantages of We will utilize the unique advantages of various electron transport regimes of the various electron transport regimes of the nitridesnitrides in a simple twoin a simple two--terminal device terminal device configurationconfiguration

Why nitrides?Why nitrides?

Energy Gap Energy Gap vsvs Lattice ConstantLattice Constant

Semiconductor material Semiconductor material properties at 300Kproperties at 300K

PropertyProperty SiSi GaAsGaAs 4H4H--SiCSiC GaNGaN

BandgapBandgap EEgg ((eVeV)) 1.121.12 1.421.42 3.253.25 3.403.40

BreakdownBreakdown fieldfield EEBB (M(MV/cmV/cm)) 0.250.25 0.40.4 3.03.0 4.04.0

Electron mobility Electron mobility µ µ (cm(cm22/V s)/V s)

13501350 60006000 800800 13001300

Maximum velocity Maximum velocity vvss

(10(1077 cm/s)cm/s)1.01.0 2.02.0 2.02.0 3.03.0

Thermal conductivity Thermal conductivity χχ ((WW/cm K)/cm K) 1.51.5 0.50.5 4.94.9 1.31.3

Dielectric constant Dielectric constant εε 11.811.8 12.812.8 9.79.7 9.09.0

Semiconductor materials for Semiconductor materials for rfrfapplicationsapplications

Gunn effectGunn effect

•• The NDC predicted for the nitrides and observed inThe NDC predicted for the nitrides and observed in GaNGaNwas used to propose a Gunn generator working in the was used to propose a Gunn generator working in the regime of domain formation regime of domain formation

•• However, one can utilize an alternative regime with However, one can utilize an alternative regime with suppressed Gunn domain formation [i.e., the sosuppressed Gunn domain formation [i.e., the so--called called limited spacelimited space--charge accumulation charge accumulation (LSA)(LSA) modemode] ] determined by 1/(3determined by 1/(3ττMM) ) << νν << 1/1/ττmm ((ττmm is the dielectric is the dielectric relaxation time calculated at prerelaxation time calculated at pre--threshold fields). threshold fields).

•• LSA Advantages: High Power/Efficiency & High LSA Advantages: High Power/Efficiency & High FrequencyFrequency

•• Hence, Hence, generation of THz microwave may be generation of THz microwave may be achievable under the LSA mode in a properly achievable under the LSA mode in a properly designed nitride devicedesigned nitride device. .

SteadySteady--state characteristics of state characteristics of bulkbulk GaNGaN

Max Vdr ≈ 3.1 107 cm/s at F ≈ 153 kV/cm.Other features: a portion of I-V with ‘a turn-up’ (the rudiment of the

runaway effect), a sharp increase in the temperature (Te > 3150:::4200 K).), negative resistance.

HighHigh--frequency smallfrequency small--signal conductivity of signal conductivity of hot electrons in nitride semiconductorshot electrons in nitride semiconductors

(sub(sub--threshold fields)threshold fields)

•• (a) Real part and (b) imaginary part of the small(a) Real part and (b) imaginary part of the small--signal conductivity as functionsignal conductivity as functionssof normalized frequencyof normalized frequency ff//ff00 forfor GaNGaN at at didifffferenterent values of values of subsub--threshold fieldthreshold field

(solid squares in(solid squares in the insets): 1 the insets): 1 -- εε = 0.13 (33 kV/cm), 2 = 0.13 (33 kV/cm), 2 -- εε = 0.24 (63 kV/cm),= 0.24 (63 kV/cm), 3 3 –– εε= 0.56 (144 kV/cm), 4 = 0.56 (144 kV/cm), 4 -- εε = 0.59 (151 kV/cm). The= 0.59 (151 kV/cm). The insets show the steadyinsets show the steady--state state

velocity (a) and electronvelocity (a) and electron temperaturetemperature (b) characteristics(b) characteristics, , ff00 = 8.9 THz.= 8.9 THz.

HighHigh--frequency smallfrequency small--signal conductivity signal conductivity of hot electrons in nitridesof hot electrons in nitrides

•• smallsmall--signal conductivity signal conductivity of the hot electrons shows of the hot electrons shows a large and very fast a large and very fast response response for the for the nitridesnitrides

•• cutcut--off frequency of off frequency of the the electrical electrical (Gunn) (Gunn) instability iinstability is in s in the THz the THz frequency rangefrequency range(5.5 THz for(5.5 THz for GaNGaN)).

ε / ε0.

DriftDrift velocity ofvelocity of 22DD electrons inelectrons in AlGaNAlGaN//GaNGaNheterostructureheterostructure

10 -3 10 -2 10 -1 10 0 10 1 10 210 3

10 4

10 5

10 6

10 7

3 0 0 K 4 .2K T h e o ry

E lectric F ield (kV /cm )

Drif

t Vel

ocity

(cm

/s)

SelfSelf--heating effect on conductivity of 2D channelheating effect on conductivity of 2D channel

0 10 20 300

50

100

150

I, m

A

E , kV/cm

Sapphire 30ns 1µs dc

SiC dc

Streaming transportStreaming transport

•• The nitrides provide another interesting possibility for electriThe nitrides provide another interesting possibility for electrically cally pumped subpumped sub--millimeter wave generators. The approach is based on millimeter wave generators. The approach is based on strong electronstrong electron--optical phonon coupling and large optical phonon optical phonon coupling and large optical phonon energy characteristic for the nitrides. When the coupling is strenergy characteristic for the nitrides. When the coupling is strong, ong, the electron motion may become nearly periodicthe electron motion may become nearly periodic if optical if optical phonon emission is the dominant scattering mechanism. Indeed, inphonon emission is the dominant scattering mechanism. Indeed, inan appropriate range of the an appropriate range of the dcdc electric field, an electron accelerates electric field, an electron accelerates quasiquasi--ballisticallyballistically until it reaches the optical phonon energyuntil it reaches the optical phonon energy ħωħωopop. . Then, the electron loses its energy by emitting an optical phonoThen, the electron loses its energy by emitting an optical phonon n and starts the next period of acceleration. This periodic motioand starts the next period of acceleration. This periodic motion n [often called the optical[often called the optical--phonon transitphonon transit--time (OPTT) resonance] time (OPTT) resonance] provides the operating principles for electrically pumped subprovides the operating principles for electrically pumped sub--millimeter wave sources and has been observed experimentally in millimeter wave sources and has been observed experimentally in InPInP only at low temperatures only at low temperatures

Transport at low electron concentrationsTransport at low electron concentrations(idealized picture)(idealized picture)

ε

εЋω

PassiveRegionE< Ћω

•• If If electronelectrons have individual moment and s have individual moment and energy balance, theirenergy balance, their motion becomesmotion becomesnearly periodic nearly periodic at low at low crystal crystal temperaturestemperatures, when , when optopt. p. phh. . emission is a emission is a dominant scattering mechanism.dominant scattering mechanism.IIn an appropriate range of the dc electric n an appropriate range of the dc electric field, anfield, an electron accelerates quasielectron accelerates quasi--ballisticallyballistically until it reaches the until it reaches the opt. ph. opt. ph. energy. The electron then loses its energy energy. The electron then loses its energy by emitting anby emitting an opt. ph. And opt. ph. And starts the next starts the next period of acceleration.period of acceleration.This results inThis results in an anisotropic, streamingan anisotropic, streaming--like steadylike steady--state distribution.state distribution.

ActiveRegionE> Ћω

V

t

THzTHz--frequency resonancefrequency resonancess and negative and negative dynamic conductivitydynamic conductivity ofof twotwo--dimensional hot dimensional hot

electrons in groupelectrons in group--III nitridesIII nitrides (I)(I)Optical phonon transient time resonance Optical phonon transient time resonance

inin50 A50 A GaNGaN QW at 77 K and F= 1.87 kV/cmQW at 77 K and F= 1.87 kV/cm

Real and imaginary parts of microwaveReal and imaginary parts of microwavemobility as functions of the frequency.mobility as functions of the frequency.

The fundamental resonance at 0.44 THzThe fundamental resonance at 0.44 THzThe second resonance at 0.88 THzThe second resonance at 0.88 THz

Near first two resonances there are Near first two resonances there are ““frequency windowsfrequency windows”” with negative with negative

microwave mobility:microwave mobility:The first band The first band 00:4:41::1::::00:52 :52 THzTHz..The second band The second band 00:8:84::4::::00:96 :96 THTHz.z.In the inset: microwave mobility as a function of In the inset: microwave mobility as a function of

the field at the field at νν = 1.09 THz= 1.09 THz

THzTHz--frequency resonancefrequency resonancess and negative and negative dynamic conductivitydynamic conductivity (2)(2)

The fundamental OPTTR The fundamental OPTTR resonance at F = 4.5 kV/cmresonance at F = 4.5 kV/cm

νν = = 1.09 THz1.09 THz‘‘WindowWindow’’ of negative of negative microwave mobility: microwave mobility:

11……1.26 THz1.26 THz

Conclusions Conclusions --11

•• Band structure and electronBand structure and electron--phonon interaction in phonon interaction in nitride semiconductors bring a number of unique nitride semiconductors bring a number of unique properties of highproperties of high--field electron transport. These field electron transport. These include:include:

•• Very large peak drift velocities of steady state regime.Very large peak drift velocities of steady state regime.•• Very large electron heating.Very large electron heating.•• A large overshoot effect (high transient velocity).A large overshoot effect (high transient velocity).•• Very fast response to a microwave field Very fast response to a microwave field

(a few THz cut(a few THz cut--off frequency).off frequency).•• Negative differential conductivity. Negative differential conductivity.

Conclusions Conclusions --22

•• In short diodes (<1000 In short diodes (<1000 ǺǺ) transient time below 0.1 ) transient time below 0.1 pspsand and cuttcutt--off frequency up to 1 THz is expected.off frequency up to 1 THz is expected.

•• At low electron concentrations the streaming At low electron concentrations the streaming transport regime and OPTT resonance may occur in transport regime and OPTT resonance may occur in both 3D and 2D structures.both 3D and 2D structures.

•• For nitride based For nitride based QWsQWs OPTT resonance is realized in OPTT resonance is realized in modest electric fields (1modest electric fields (1……5 kV/cm) for frequency 5 kV/cm) for frequency range 0.3range 0.3……2.5 THz.2.5 THz.

•• Considerable negative microwave mobility can be Considerable negative microwave mobility can be reached in THz reached in THz ‘‘windowswindows’’ near OPTT resonances at near OPTT resonances at 77K and higher temperatures.77K and higher temperatures.

•• We We suggest that an electrically pumped THzsuggest that an electrically pumped THz laser laser operating above the nitrogen temperature can beoperating above the nitrogen temperature can beachieved by using the streaming effect in 2D achieved by using the streaming effect in 2D electron gas inelectron gas in nitride nitride heterostructuresheterostructures. .

PROPOSED RESEARCHPROPOSED RESEARCH

•• Task 1: SubTask 1: Sub--millimeter emission based on the high millimeter emission based on the high field transport (Gunn effect, etc)field transport (Gunn effect, etc)

We will concentrate primarily on the LSA mode with We will concentrate primarily on the LSA mode with suppressed Gunn domainssuppressed Gunn domains

PROPOSED RESEARCHPROPOSED RESEARCH

•• Task 2: SubTask 2: Sub--millimeter emission based on the millimeter emission based on the streaming regimestreaming regime

WWe wille will designdesign anan optimaloptimal structurestructure forfor thethe OPTTOPTT--basedbased THzTHz generationgeneration

PROPOSED RESEARCHPROPOSED RESEARCH

•• Task 3: Resonant environment and subTask 3: Resonant environment and sub--millimeter millimeter microwave resonatorsmicrowave resonators

WWe wille will analyzeanalyze differentdifferent methodsmethods toto imposeimpose resonantresonantconditionsconditions forfor frequencyfrequency selectionselection andand tuning. Thesetuning. Thesewillwill include: traditionalinclude: traditional microwavemicrowave resonatorsresonators ononwaveguides, microstripwaveguides, microstrip resonanceresonance transmissiontransmissionlines, quasilines, quasi--opticaloptical cavities, andcavities, and surfacesurface--plasmonplasmonresonators.resonators.

THE PROJECT CONSORTIUMTHE PROJECT CONSORTIUM

•• TechnischeTechnische UniversitUniversitäätt DarmstadtDarmstadt

-- overall cooverall co--ordination;ordination;-- provision of MOCVD and MBEprovision of MOCVD and MBE--grown grown AlGaNAlGaN//GaNGaN

heterostructuresheterostructures, including non, including non--polar structures, polar structures, and resonant tunnelling structures;and resonant tunnelling structures;

-- processing of devices using dry and wet etch processing of devices using dry and wet etch methods and contacting;methods and contacting;

-- electrical transport, C(V), optical Xelectrical transport, C(V), optical X--ray and TEM ray and TEM characterisation of structures and devices.characterisation of structures and devices.

-- Initial high frequency characterization of lateral and Initial high frequency characterization of lateral and vertical transport devices;vertical transport devices;

High Frequency Electronics at TUDHigh Frequency Electronics at TUD•• ProfessorProfessor Dimitris PavlidisDimitris Pavlidis

•• GaNGaN Devices and Nanostructures for HighDevices and Nanostructures for High--Power, Power, HighHigh--Frequency Applications and SensorsFrequency Applications and Sensors

–– MOCVD MOCVD GrwothGrwoth ofof GaNGaN MaterialsMaterials–– High Electron Mobility Transistors (High Electron Mobility Transistors (GaNGaN) and Diodes) and Diodes

•• HeterostructureHeterostructure Components for High Frequency Components for High Frequency CommunicationsCommunications

–– InPInP--, , GaAsGaAs-- and and GaAsSbGaAsSb--based based HBTsHBTs–– MMICsMMICs with with HBTsHBTs and and HEMTsHEMTs–– Tunable Optical Receivers, lasers and filtersTunable Optical Receivers, lasers and filters

•• Microwave Monolithic integrated Circuits (Microwave Monolithic integrated Circuits (MMICsMMICs))–– InPInP-- andand GaNGaN--based HEMT based HEMT MMICsMMICs–– Power Electronics with IIIPower Electronics with III--Nitride devicesNitride devices–– Tunable Tunable MMICsMMICs with Ferrowith Ferro--, Semiconductor, Semiconductor--componentscomponents

•• Terahertz Technology for Sensing and Terahertz Technology for Sensing and CommunicationCommunication

–– THz signal Generation with Traditional andTHz signal Generation with Traditional and WidebandgapWidebandgapSemiconductorsSemiconductors

•• Advanced Electronic Materials and ComponentsAdvanced Electronic Materials and Components–– SpintronicsSpintronics–– IIIIII--V/IIIV/III--Nitride Sensors and Integrated SolutionsNitride Sensors and Integrated Solutions

Typical HBT structure

Integrated T-Ray - MEMS Components

• Biomedical Applications• T-ray III-V Components and Systems• Optoelectronic MEMS Probes

Micromachined Cavity

GaN device

Material Growth (MOCVD, MBE)

Lithography and Microscopy

Thermal processes (RTP, RTA)

Evaporation (e-beam, thermal) and sputtering

Measurements and Characterisation (DC, microwave, etc.)

Post-processing (dicing, etc.)

HFE/TUD Facilities

Cleaning and wet / dry etching processes

Material characterisation (Hall, PL, XRD etc.)

ProfessorProfessor Dimitris PavlidisDimitris Pavlidis

THE PROJECT CONSORTIUMTHE PROJECT CONSORTIUM•• ForschungszentrumForschungszentrum--JuelichJuelich

-- high frequency characterization of lateral and high frequency characterization of lateral and vertical transport devices including fabrication, vertical transport devices including fabrication, testing and analysis oftesting and analysis of GaN nanowiresGaN nanowires;;

-- optimisation of characteristics of devices and circuit optimisation of characteristics of devices and circuit components aimed towards a reduction of the noise components aimed towards a reduction of the noise level; level;

-- lowlow--temperature (down to 30 temperature (down to 30 mKmK) and high magnetic ) and high magnetic field characterisation (up to 14 T) of transport field characterisation (up to 14 T) of transport properties and capacitanceproperties and capacitance--voltage (Cvoltage (C--V) V) measurement;measurement;

-- the evaluation of excess noise sources by the evaluation of excess noise sources by measuring spectral density of noise, comparing with measuring spectral density of noise, comparing with quantum 1/f theory and with its prediction for the quantum 1/f theory and with its prediction for the resulting phase noise in various systems.resulting phase noise in various systems.

THE PROJECT CONSORTIUMTHE PROJECT CONSORTIUM

•• ISPISP--KievKiev

-- complex electrocomplex electro--physical investigation and testing of physical investigation and testing of lateral and vertical transport in nitride lateral and vertical transport in nitride heterostructuresheterostructures and devices; investigation of and devices; investigation of radiation effects;radiation effects;

-- investigation of the physics of electron fluctuations investigation of the physics of electron fluctuations in semiconductor nanostructures related to a nonin semiconductor nanostructures related to a non--equilibrium steady state; equilibrium steady state;

-- simulation of equilibrium electric characteristics of simulation of equilibrium electric characteristics of conductive channels in nitride conductive channels in nitride heterostructuresheterostructurestaking into account the specific features of their taking into account the specific features of their formation. formation.

THE PROJECT CONSORTIUMTHE PROJECT CONSORTIUM

•• IInstitutenstitute of of PPhysicshysics--KievKiev

-- measurements of the fundamental physical measurements of the fundamental physical properties of structures and devices using properties of structures and devices using magnetotunnellingmagnetotunnelling spectroscopy, CW, nsspectroscopy, CW, ns--time time resolved and resolved and ultrafastultrafast spectroscopy and phonon spectroscopy and phonon transport;transport;

-- studiesstudies ofof nonnon--linearlinear electronelectron transporttransport andand nonnon--equilibriumequilibrium fluctuationfluctuation phenomenaphenomena

THE PROJECT CONSORTIUMTHE PROJECT CONSORTIUM

•• ““OrionOrion””--KievKiev

The highThe high--frequency laboratory at SRIfrequency laboratory at SRI””OrionOrion”” will be will be involved in the highinvolved in the high--frequency studies in the course frequency studies in the course of the project. Specifically, optimisation of the of the project. Specifically, optimisation of the contact systems and resonant environment for contact systems and resonant environment for microwave study will be carried out.microwave study will be carried out.

Conclusions-Nanosize structures based on III-Nitrides are promising for millimeter and sub-millimeter wave generation and detection for communication, sensing, and imaging.

-The Ukraine-German consortium involved in this Project has the necessary expertise and capabilities to perform the proposed work.

TRANSFORMATION of the ELECTRON BAND STRUCTURETRANSFORMATION of the ELECTRON BAND STRUCTUREUNDER TRANSITION from BULK UNDER TRANSITION from BULK (SOLID LINE)(SOLID LINE) to to QUANTUMQUANTUM--SIZE (QS) SIZE (QS) –– STRUCTURESTRUCTURE (DOTTED LINES)(DOTTED LINES) –– for for SiSi(on the left) AND (on the left) AND GaAsGaAs (on the right(on the right))

GaAs

Possibility to control the separation between central and satellite valleys and thus NDCthrough nanoostructuring.