GaN-based Schottky diodes for EUV/VUV/UV photodetection

Transcription

1 1 GaN-based Schottky diodes for EUV/VUV/UV photodetection F. Shadi Shahedipour-Sandvik College of Nanoscale Science and Engineering University at Albany - SUNY, Albany NY cnse.albany.edu sshahedipour@uamail.albany.edu

2 2 Outline Background and Motivation Why GaN based photodetectors? Why Schottky MSM diode? Preliminary Data Detector response at bandgap Detector response at VUV and EUV Future plan: AlGaN-based detector for bandpass detection integration of bandgap engineered diodes and filter+diodes on the same chip

3 3 Properties of III-Nitrides Material is robust physically hard chemically inert radiation hard Devices have excellent optical and electrical properties direct wide bandgap high breakdown voltage low leakage current S.Nakamura and G. Fasol, The Blue Laser Diode,1997

4 Properties and Applications of III-Nitrides Pressure sensors Solid state lighting Information storage High voltage electronics Satellites and spacecraft High temperature electronics UV detection Wireless base stations 6/4/2009 S.Nakamura and G. Fasol, The Blue Laser Diode,1997 May 29-30, 2009 cnse.albany.edu 4

5 A better alternative for Si photodetector for EUV Si photodetectors are currently used in EUV tools to measure position, intensity, and other beam characteristics every time the light interacts with a lens or mirror There are over 18 such stages in the ASML EUV litho tool Si is a small bandgap material, it is not radiation hard. Device characteristics such as carrier collection efficiency, leakage current degrades after a short period It is important to employ detectors with long time stability and reliability in EUV lithography systems where power density and position monitoring of the beam is greatly important. GaN has the largest density amongst radiation hard material such as diamond and SiC (6.15 gcm -3 vs. 3.52, and 3.12) heavier atomic masses and largest Z per elementary cell (creating large pulses per minimal ionizing particles in thin film) low dark current due to its wide bandgap (as low as few pa at large biases) radiation hardness of GaN was measured (CCE, dark current, and responsivity) o CCE dropped to 77% from 92% after neutron irradiation with fluences up to cm-2 o significant degradation after irradiation with proton and neutron fluences of cm -2 o CCE not greatly affected by X-ray dose as high as 600 Mrad oelectrical characteristics were highly dependant on the dose and type of irradiation ounder these conditions small bandgap material such as Si and GaAs would perform poorly J. Vaitkus, et al. CP772 Physics of Semiconductors: 27 th May 29-30, 2009 cnse.albany.edu International Conference on the Physics of Semiconductors 5

6 6 GaN offers a better alternative to Si for EUV/VUV detection Vitkas et al. 27 international conference on the Physics of Semiconductor Devices, 2005 Monroy et al. APL, 2002

7 7 GaN Schottky Metal-Semiconductor-Metal Photodetectors Contact metal fingers 1 micron UGaN 3 micron GaN:Si Sapphire/Si Substrate

8 Responsivity under a broad band Xe lamp Time response in SUNYA MiMICS EUV tool Response (A/W) Bandgap response +UV/Visible rejection No Light-With glass and Zr filter: background signal wavelength (nm) Bandgap and Visible/UV rejection to verify device functionality MiMICS EUV system: high power Xe plasma: assuming direct beam, intensities before filter is ~2 mw/cm 2 for EUV (11-17nm), 10mW/cm 2 for VUV (18-120nm), and unknown for DUV and visible. Zr filter absorbs all light but EUV and would lose intensity by ~50% With glass filter only: absorbs all light except for visible May 29-30, 2009 cnse.albany.edu 8

9 9 Time response in SUNYA MiMICS, continue.. All light, neither glass nor Zr filter As shown in previous slide, the detector does not respond to visible light under all light+glass filter condition-as expected Device responds to wavelengths below its bandgap Device responds to EUV only under all light+zr filter All light, with Zr filter Successful demonstration of out-of-band, and in-band detection using the fabricated GaN MSM Schottky diode

10 10 Future Plan Optimize device performance: material quality and processing Measure important device performance parameters: responsivity, quantum efficiency, time response, noise, and detectivitiy Calibrate detector response in VUV/EUV against NIST calibrated Si photodetector Develop and demonstrate integrated filter + diode device Develop and demonstrate array of bandpass detector on a single chip