Project: IEEE P Working Group for Wireless Personal Area Networks N

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1 Slide 1 Project: IEEE P Working Group for Wireless Personal Area Networks N (WPANs( WPANs) Title: Room temperature THz sources and detectors with semiconductor nanodevices, the ROOTHz project Date Submitted: 11 March 2011 Source: Javier Mateos, Universidad de Salamanca Address: Facultad de Ciencias, Pza. Merced s/n, Salamanca, Spain Voice: , FAX: , javierm@usal.es Abstract: ROOTHz is a 3 year project funded within the European 7th Framework Program that addresses the fabrication of room temperature, continuous wave, compact, tunable and powerful T-ray sources (at low cost, if possible). For this sake we propose to exploit THz Gunn oscillations in novel (narrow and wide bandgap) semiconductor nanodevices, which have been predicted by simulations but not experimentally confirmed yet. The fabrication of THz detectors with the same technology will complement this objective and make possible the demonstration of a simple THz detection/emission subsystem. Purpose: Dissemination of the ROOTHz project objectives and achievements Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P

2 Room temperature THz sources and detectors with semiconductor nanodevices, the ROOTHz project Javier Mateos University of Salamanca, Spain Slide 2

3 Outline Outline Introduction: Importance of THz ROOTHz Project Self Switching Diodes (SSDs) Slot Diodes Conclusions Slide 3

4 Importance of THz: T-raysT THz radiation can penetrate poor weather, dust and smoke far better than infrared or visible systems. Satellite Telemetry Aeronautics: guidance and landing Image of sea surface temperature (European Space Agency) Slide 4

5 Importance of THz: T-raysT THz radiation can penetrate organic materials without ionizing. Readily absorbed by water: distinguish between materials with varying water content Medical imaging Skin Cancer Detection Courtesy of Teraview Courtesy of Teraview Slide 5

6 Importance of THz: T-raysT THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls Slide 6

7 Importance of THz: T-raysT THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls Weapon or Explosive Detection (metallic or non metallic) Courtesy of Qinetiq Courtesy of Qinetiq Courtesy of Thruvision Slide 7

8 Importance of THz: T-raysT THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls Weapon or Explosive Detection (metallic or non metallic) Slide 8

9 Importance of THz: T-raysT THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls Non-destructive testing: lntegrated Circuit Package lnspection Courtesy of Teraview Slide 9

10 Importance of THz: T-raysT THz radiation can be used to identify spectral fingerprints of explosives, narcotics, or active pharmaceutical ingredients Slide 10

11 The THz Gap PHOTONICS THz Gap ELECTRONICS All-optical sources Mixing lasers with close frequencies Excitation of semiconductors or superconductors with femtosecond laser pulses Quantum cascade lasers Bulky and expensive equipment Slide 11 Semiconductor Nanodevices for Room Temperature THz Emission and Detection (ROOTHz Project)

12 The THz Gap 500 GHz 2 THz Quantum cascade lasers (QCL) QCL at cyogenic T Frequency multipliers _ Other electronic devices: amplifiers, RTDs, IMPATT and Gunn diodes Semiconductor Nanodevices for Room Temperature THz Emission and Detection (ROOTHz Project) Slide 12

13 Outline Outline Introduction: Importance of THz ROOTHz Project Self Switching Diodes (SSDs) Slot Diodes Conclusions Slide 13

14 Semiconductor Nanodevices for Room Temperature THz Emission and Detection (ROOTHz Project) Funded under: 7th FWP (Seventh Framework Programme) Area: FET Open (ICT ) Project Reference: Total cost: 2.1 M EU contribution: 1.57 M Execution: from 1st January 2010 to 31st December 2012 Duration: 36 months Web: Slide 14

15 Semiconductor Nanodevices Self Switching Diodes (SSDs) Ohmic Contact Cap Layer Barrier Channel Narrow Bandgap Semiconductors (NBG): InGaAs/AlInAs AlInAs InAs/AlSb AlSb InSb/AlInSb Semiconductors Buffer (NBG): Ohmic Contact Contact Current Insulating Trenches Slot Diodes (Ungated GaN/AlGaN HEMTs) Top View Wide Bandgap Semiconductors (WBG): Contact Slide 15

16 Partners Chalmers University of Technology Gothenburg, Sweden The University of Manchester Manchester, UK Coordinator: University of Salamanca Salamanca, Spain Institut d Electronique Microélectronique et de Nanotechnologie Lille, France Slide 16

17 Outline Outline Introduction: Importance of THz ROOTHz Project Self Switching Diodes (SSDs) Slot Diodes Conclusions Slide 17

18 Self Switching Diodes (SSDs( SSDs) 1 µm Current ( A) W approx. 60 nm W approx. 70 nm V (V) nanochannel InP InP InGaAs doping + V<0, channel closed V>0, channel open InP - substrate InGaAs channel Slide 18

19 Self Switching Diodes (SSDs( SSDs) Simple technological process: etching of insulating trenches on a semiconductor surface Tuneable threshold voltage from almost zero to more than ten volts by adjusting the channel width Easy downscaling and parallelization: THz operation can be obtained Optimum geometry for the onset of Gunn oscillations Slide 19

20 Self Switching Diodes (SSDs( SSDs) THz Detection: non-linear I-V characteristics Use of NBG materials (Room Temperature ballistic transport) for increased sensitivity and broadband THz Emission: Gunn Effect in InGaAs, and GaN! Use of WBG materials for increased power Planar geometry (and antennas) allow for a better coupling Parallelization for enhanced performances (and correct thermal management) Slide 20

21 Outline Outline Introduction: Importance of THz ROOTHz Project Self Switching Diodes (SSDs) Slot Diodes Conclusions SSDs as THz detectors SSDs as THz emitters Slide 21

22 SSDs as THz detectors: Experiments 100 V out (mv) 10 I bias = 6 A I bias = 0 A 18 diodes in parallel 300 K, 75 GHz Freq. (GHz) C. Balocco, A. M. Song, M. Aberg, A. Forchel, T. González, J. Mateos et al., Nano Lett. 5, 1423 (2005) 10 K, operative in the THz range (drop in the response above 70 K) 2.5 THz 1.3 THz C. Balocco, M. Marshall, N. Q. Vinh and A. M. Song, J. Phys.: Condens. Matter 20, (2008) 6 diodes in parallel Slide 22

23 SSDs as THz detectors: Monte Carlo Simulations THz Detection: non-linear I-V characteristics Use of NBG materials (Room Temperature ballistic transport) for increased sensitivity and broadband 2.0 AC to DC rectification 1.4 THz W V =20 nm W H =5 nm In 0.53 Ga 0.47 As T=300 K W C =50 nm Rectified DC current (A/m) V o =0.25 V I V=V o sen(2pf) 175 nm L C =250 nm 175 nm Frequency (THz) Enhanced rectification in the THz range (tunable by geometry) Slide 23

24 First Experimental Results Interdigital InGaAs mesa with 2000 etched SSDs 600nm 10 A 10 B RF power detector up to 110 GHz DC output (mv) DC output (mv) GHz 50GHz 10GHz 1GHz Freq. (GHz) Power (dbm) Slide 24

25 Outline Outline Introduction: Importance of THz ROOTHz Project Self Switching Diodes (SSDs) Slot Diodes Conclusions SSDs as THz detectors SSDs as THz emitters Slide 25

26 SSDs as THz emitters: Gunn Oscillations Suitable Focused electric field geometry Electron concentration increased by the side field effect InGaAs channels (narrow band gap) Electron velocity (10 5 m/s) In 0.7 Ga 0.3 As (n.i.d.) In 0.53 Ga 0.47 As (n.i.d.) In 0.53 Ga 0.47 As (N D =6x10 18 cm -3 ) - Pronounced NDM - Low saturation velocity (low frequency) - Low threshold field low power Electric Field (kv/cm) Drift velocity (10 7 cm/s) GaN Electric field (kv/cm) GaN channels (wide band gap) - Less pronounced NDM - High saturation velocity + high frequency Low energy relaxation time - High threshold field high power Slide 26

27 SSDs as THz emitters: Gunn Oscillations Monte Carlo Simulations V (a) W V =100 nm W H =50 nm W C =75 nm GaN T=300 K I (ma) V 40 V Gunn Oscillations in GaN SSDs 150 nm L C =900 nm 500 nm 30 V Time (ps) I (ma) V (V) Frequency (GHz) 450 (b) V (V) Oscillation frequencies above 400 GHz (voltage controlled and tunable by geometry) Slide 27

28 First Experimental Results 16 parallel GaN SSDs Slide 28

29 First Experimental Results DC curves: Fabrication of 32 SSDs in parallel validated Current (ma) SSD 4 SSD's 16 SSD's 32 SSD's Voltage (V) Sensitivity (V/W) Frequency (GHz) Slide 29 RF detection demonstrated even if with small sensitivity (maximum of 50 V/W) Gunn oscillations not observed yet

30 Outline Outline Introduction: Importance of THz ROOTHz Project Self Switching Diodes (SSDs) Slot Diodes Conclusions Slide 30

31 Slot Diodes: Ultra fast Gunn effect for THz generation Source L S The recess focuses the High Electric field region L D Drain 10 nm L R InGaAs N D =6x10 18 cm nm InAlAs InAlAs InAlAs n.i.d. =6x10 12 cm -2 n.i.d. 15 nm 200 nm Ballistic electrons Fast InGaAs drift of a high field n.i.d. domain along the drain region Oscillations InAlAs in the THz range n.i.d. InP Planar geometry and Parallelization Slide 31

32 Slot Diodes: Ultra fast Gunn effect for THz generation Monte Carlo Simulations V V DS DS V V th th 0.6 V 0.6 V Low-amplitude plasma oscillations High-amplitude Gunn-like oscillations Current density (x10 3 A/m) Current (x 10 3 A/m) V DS =0.6 V V DS =0.4 V V DS =0.1 V V DS =0.8 V V DS =1.0 V V DS =1.2 V Time (ps) Time (ps) Applied voltage (V) Main Peak Amplitude (10-7 A 2 m -1 s) Plasma Oscillations Gunn Oscillations V DS (V) Main Peak Frequency (THz) Ultra fast Gunn-like oscillations in the THz range (voltage controlled and tunable by geometry) Slide 32

33 Slot Diodes: Ultra fast Gunn effect for THz generation Domain moves at the very fast velocity of -electrons that refill the depleted region Intervalley energy level (0.6 ev) Electric Potential (V) Electron Concentration (10 19 cm -3 ) Longitudinal Electic Field (kv/cm) High electric field domain created, increase of the potential drop within the drain region (and injection of -electrons) Concentration decrease due to the small velocity of electrons injected into the drain region (and fast -electrons run away) Injection into the upper valleys when there is enough potential drop in the recess region (and current decreases) Slide 33

34 Slot Diodes: Ultra fast Gunn effect for THz generation Source (L S ) InGaAs - 10nm InAlAs 17nm InGaAs - 15nm InAlAs - 200nm InP - 200nm Recess (L R ) X position Drain (L D ) N D =6x10 18 cm -3 n.i.d. =6x10 12 cm -2 n.i.d. n.i.d. n.i.d. Longer recess lengths decrease the oscillation frequency due to the attenuation of the electron-launching effect Frequency (THz) Transit time and frequency 1.4 scale for long L D Frequency (THz) /L D ( m -1 ) 1/L D Y Data Influence of L D Frequency not scaling for short L D due to the increase of L-valley population Influence of L R L R ( m -1 ) Slide 34

35 First Experimental Results 200 R1A, = cm R2A, = cm Strong kink in the I-V curve of all the slot diodes fabricated Drain current [ma/mm] W=50 L r =0.3 L d =0.55 (μm) [ *mm] W=50 L r =0.5 L d =0.55 (μm) [ *mm] 20 W=50 L r =0.9 L d =0.55 (μm) [ *mm] Drain voltage [V] Drain current [ma/mm] W=50 L r =0.3 L d =0.55 (μm) [ *mm] W=50 L r =0.5 L d =0.55 (μm) [ *mm] 20 W=50 L r =0.9 L d =0.55 (μm) [ *mm] Drain voltage [V] Slide 35

36 Outline Outline Introduction: Importance of THz ROOTHz Project Self Switching Diodes (SSDs) Slot Diodes Conclusions Slide 36

37 Conclusions: ROOTHz objectives Exploiting the special geometry and versatility of SSDs and Slot Diodes based on NBG and WBG semiconductors we aim to confirm the results of MC simulations for fabricating and demonstrating: THz Detectors: sensitivity above 500 mv/mw in the THz band THz Emitters: power exceeding 1mW Narrowband emitters at discrete frequencies of: 1.0, 1.5 and 2.0 THz Broadband emitter in the THz Integrated THz detector/emitter prototype: broadband emitter-detector in the range of THz able to obtain the transmission or reflection spectrum of certain benchmark substances Room Temperature operation Demonstration of Gunn oscillations in GaN SSDs Slide 37

38 Acknowledgements ROOTHz Semiconductor Nanodevices for Room Temperature THz Emission and Detection T. González D. Pardo S. Pérez B. G. Vasallo H. Rodilla I. Íñiguez-de la-torre A. Íñiguez-de la-torre C. Gaquiere G. Ducournau P. Sangaré A. M. Song A. Rezazadeh M. Hallsall C. Balocco L. Zhang Y. Alimi J. Grahn P. A. Nilsson A. Westlund H. Zhao Slide 38