Quantum Dot Infrared Photo-detector

1. Quantum Dot Infrared Photo-detector 16.508 Quantum Electronics for Engineer Present by: Chintana Keo Date: May 3, 2006

2. Agenda • What is a Photo-detector? • What is the different between Quantum Dot Infrared Photo-detector (QDIP) and Quantum Well Infrared Photo-detector (QWIP)? • Sample sketch or diagram of QDIP • How does the device work? • Advantage of QDIP • Dark current calculation & Why? • Detection energy calculation • Some possible applications • Conclusion

3. What is a photo-detector? • A photo-detector is a semi-conductor photodiode device that generate electrical current or electrons excitation when light source is shine onto its’ surface or when light source is entering a diode semiconductor device made from such material as GaAs & InGaAs. • A photo-detector is an opto-electronics device that allow us to produce an image of an object as a result of the electrical current produced by shining a light source within a given wavelength range depending on what materials is used.

4. What is a photo-detector? (Continues) • A photo-detector is basically a photodiode in principle. When struck by light source, the electrons within become stimulated and create current across a diode resulting in an exact duplicated image as the source.

5. The different between quantum well & quantum dot • There similarities and different characteristics of photo detectors: • Quantum Well Infrared Photo-Detector (QWIP) • Quantum Dot Photo-Detector (QDIP). • Figure shows the different between quantum dot and quantum well: • Left is quantum well infrared photo-detector • Well between barriers • Right is quantum dot infrared photo-detector • Dots between barriers

6. Schematic Sample of Quantum Dot • Boron doped Ge quantum dots growth sample • Producing using molecular-beam epitaxy (MBE) method in a thin layer of semi-conductor materials.

7. Basic Device • Both device has an emitter and a collector • The detection mechanism in both devices is by intraband photo excitation of electrons between energy levels

8. The Advantage of QDIP • QDIP allow direct incident normal to wafer surfaces. • Avoid fabricating grate coupler as in QWIP. • In producing QWIP, a grating coupler required which yield in extra fabrication steps. • It has lower dark current & high detection sensitivity than QWIP. • Better Radiant sensitivity and Efficiency resulting in better detection. • Dominant in normal direction response to growth direction.

9. Dark Current Calculation • Dark current is the current produce internal to the photodetector resulting as noise • Simplest way to calculate dark current density is to count mobile carrier barrier and carrier velocity • Jdark is a dark current • υ is a drift velocity • n3d is current density • Can be calculate using the second formula at left. • mb is a barrier effective mass • Ea is thermal activation energy

10. Radiant Sensitivity and Quantum Efficiency • Current produce when light hitting a semi-conductor radiating electrons excitation. • This can be calculate using the following formula • QE = ((S x 1240) / λ ) x 100% • Where S is the radiant sensitivity • Long exited electron lifetime lead to high responsivity, higher temp and higher dark current which will limited detectivity

11. Responsivity • Responsivity can be calculated using the formula at left, where: • υ - a phonon frequency • η- the absorption efficiency • g - photoconductive gain • Higher absorption efficiency have better detection.

12. Possible Applications • High speed infrared detection • Infrared image application—possible use in security systems to produce image of various objects. • Possible use in IR Spectrophotometer • Possible use in Cell Sorter • Could be use in Infrared Camera

13. Conclusion • There are still many challenges to overcome such fabrication or manufacturing process that will produce quantum dot to meet design requirement • Current manufacturing process limit to size and dot density that it is impractical for commercial used • Due to complex fabrication process and limited size it is expensive to manufacture • Still in its infancy—needs better doping control

14. Question? Thank You

15. Credit & Reference • Prof: Joel Therrien—UMass Lowell. • American Science & Engineering—Billerica, Ma • Prof: Sam Milshtein—UMass Lowell • Photodiodes—Hamamatsu Photonics K.K. Solid State Division • The Photonics Dictionary, 42nd Ed 1996—The Tropel Spectrum • Growth Study of Surfactant-Mediate SiGe graded layers—Thin Solid Film 380 (2000) 54-56 • Photoluminescence of multi-layer of SiGe dot growth on Si—J. Wa, H Lou—Device research laboratory, Electrical Engineering Department---University of California at Los Angeles • Reshifting and broadening of quantum well infrared photo-detector—IEEE Journal of selected topic in quantum electronics, vol 4 No 4 July/August 1998 • Intersuband absorption in boron dope multiple Ge Quantum Dot—Applied Physic Letter Vol. 74, Number 2, January 11, 1998 • Normal Incidence Mid-Range Ge Quantum dot photo-detector—Fei Lou, Song Tong, Jianlin Liu & Kang L. Wang--Journal of Electronics materials, vol. 33, Number 8, 2004 • Zhen Yang, Yi Shi, Jianlin Liu, Bo Yan, Rang Zhang, Youdou Zhen & Kanglong Wang—Optical Properties of Ge/Si quantum dot superlatices—Department of Physic and National Laboratory of Solid State Microstructure, Nanjing University & University of California. Science Direct—Material Letters 58 (2004) 3765-3768