IWORID 2004 Ga N UV detectors for synchrotronbased

IWORID 2004 Ga. N UV detectors for synchrotron-based protein structure studies Andrew Bluea M. Rahmana, W. Cunninghama, J. Granta, F. Quaratia & S. Manolopoulosb, I. Watsonc a University of Glasgow, b RAL, c Compound Semiconductor Technologies 26 th July 2004 Andrew Blue

Outline Biological Applications for UV detectors ● Proteomics ● Circular Dichroism (CD) ● Diode requirements for Synchrotron based CD experiment Gallium Nitride ● Properties of Ga. N ● Design & Fabrication of Ga. N UV Diodes ● Material Characterisation & Optimisation ● Diode designs for Synchrotron Conclusions 26 th July 2004 Andrew Blue

Proteomics – the study of the full expression of proteins by cells in their lifetime ● Proteins are chains of amino acids For amino acids to form a protein the extended chain of amino acids must "fold" into a compact globular object with exactly the right shape • We would like to know more about the “dynamic” and folded structures ● ● Offers insight to diseases such as Alzheimer's disease and Cystic fibrosis, caused by “mis-folding” of proteins 26 th July 2004 Andrew Blue

Circular Dichroism CD is the measurement of the difference in absorption between left and right circularly polarised light as it passes through a medium SR CD Conventional + SR CD Wallace, B. A. and Janes, R. W. (2001) SRCD Spectroscopy of Proteins: Secondary Structure, Fold Recognition and Structural Genomics. Curr. Opin. in Chemical Biology 26 th July 2004 Andrew Blue

Synchrotron based CD experiment Current Method ● Measure CD at a ● Repeat for each Slow (can take 2 days/run) ● Uses large amounts of protein New Method ● Use Array to measure all simultaneously ● Require design for diode with 46 channels 26 th July 2004 Andrew Blue

Properties of Ga. N (Gallium Nitride) • Compound Semiconductor • Direct Wide Bandgap (~3. 4 e. V) • Solar Blind Material ( cut~360 nm) => Higher SNR for UV than for eg Si. => Ideal Material for UV detectors 1 -2 m n-type Ga. N Sapphire (440 m) 26 th July 2004 Andrew Blue

Design & Fabrication of Ga. N Diodes MSM (Metal-Semiconductor-Metal) Diodes • Schottky (Rectifying) Contacts • Interleaving Finger Design • minimised response time • Increased active area 2000 m Pitch =100 m, Width=100 m Pitch =25 m, Width=25 m 1000 m Pitch =25 m, Width=25 m 26 th July 2004 Andrew Blue

I-V Characteristics 26 th July 2004 Andrew Blue

UV Response 26 th July 2004 Andrew Blue

UV Response • Material response to UV @ 0 V • Spectral response to Deuterium Source 26 th July 2004 Andrew Blue

Responsivity 26 th July 2004 Andrew Blue

Finger Separation • Fabricated samples have too large a finger separation • Larger finger separation (100 m) tc ~2 s Monroy et al, Vol 77 (22) Applied Physics Letters (2002) • Need to decrease finger separation <10 m 26 th July 2004 Andrew Blue

Schottky Contacts I-V’s similar But - Pd more successful than Au at lift-off - Pd more transparent than Au for UV (Pd~70%, Au~55%) => Semi-transparent Contacts 26 th July 2004 Andrew Blue

Semi-Insulating Material Grown by 1 m Mg Doped Ga. N 3. 2/6. 2 x 1019 cm-3 1 m Undoped Ga. N Compound Semiconductor Technologies Sapphire 100 m 600 m 300 m 26 th July 2004 Andrew Blue

Semi-Insulating Material 26 th July 2004 Andrew Blue

Surface Preperation 26 th July 2004 Andrew Blue

Design for Synchrotron Diodes 65 mm 15. 5 mm Green - Ga. N fingers (10 m width, 10 m pitch) 10 nm Pd contacts Purple - PCB design for integration to DIP socket Entire Ga. N diode = 6 x 20 mm 2 ● Solar Blind – No need for setup to be “light tight” ● Diode can be operated unbiased – 0 V ● 26 th July 2004 Andrew Blue

Conclusions ● UV detectors successfully fabricated on Ga. N ● Progress made in optimising of ● ● ● Device Geometry Schottky Metals De-oxidation Unactivated Mg Doped Ga. N looks promising Finished Design for Ga. N Diodes for CD measurements at Synchrotron Thanks for your attention! 26 th July 2004 Andrew Blue

26 th July 2004 Andrew Blue