Impact Ionization Engineered MWIR Type-II Strain Layer Superlattice Avalanche Photodiodes for Dual Mode Imaging Applications
Feb 29, 2012
from 01:00 PM to 02:00 PM
|Where||ENGR. IV Bldg. Elliott 53-135E|
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University of Illinois –Chicago
Our work on HgCdTe/Si and Type II SLS bandstructure engineered avalanche photodiodes will be discussed. Preliminary results from a novel heterostructured extremely high gain MWIR InAs/InGaSb Type II Strain Layer Superlattice (T2SLS) impact ionization engineered (I2E) APD for dual mode imaging applications will also be discussed. In the process of our work on infrared APDs, we did a substantial amount of study on surface passivation of mid-wave and long-wave detector structures. Some key results from the passivation study will also be presented.
Spatially separated T2SLS electron and hole multiplication regions were designed using 14 bank k.p bandstructure modeling. Bandstructure engineered energy resonance in the conduction (for electron multiplication region) and valence bands (for hole multiplication region) results in extremely low and high values of k , ratio of electron to hole impact ionization coefficients, respectively. This helps us achieve extremely low excess noise multiplication regions. We have demonstrated electron only and hole only multiplication in T2SLS devices with 4.75mm cut-off. This was confirmed with excess noise measurements.
In the novel dual mode device, the I2E T2SLS electron and hole multiplication regions are placed right next to each other. This allows for a carrier feedback between the electron and hole multiplication regions. The holes generated, by impact ionization, in the electron multiplication region move to the hole multiplication region and create secondary electrons and holes. The secondary electrons move to the electron multiplication region and continue the impact ionization process. This feedback between the electron and hole multiplication regions allows for extremely high gain values for the overall device. However, the individual gain of the electron (Me) and hole multiplication (Mh) regions can be kept extremely low ( for Me = 17 and Mh = 1.3 – both multiplication regions are below breakdown , the overall gain M = 25000 , this can be achieved at a reverse bias of 5.4V in a T2SLS dual carrier multiplication MWIR APD (lc = 4.75mm)). The effective k is designed to be approximately .03. Such low bias (Vreverse = 5.4V) operation of the MWIR APD (M = 25000) allows for single photon counting (active operation) and passive mode operation on the same pixel using standard ROIC and this opens up possibility of large format dual mode imaging arrays. More details regarding device design, MBE growth, device fabrication and characterization will be presented at the seminar.
Prof. Sid Ghosh is Associate Professor of Electrical and Computer Engineering at University of Illinois at Chicago. He received his Ph.D in Electrical Engineering from University of Michigan in 2003. Over the past 9 years, he has been heavily involved with design, fabrication and characterization of HgCdTe and InAs/GaSb type II superlattice based infrared photovoltaic detectors and avalanche photodiodes. He has set up state of the art gain, excess noise, bandwidth and photon counting measurement systems for characterizing avalanche photodiodes. Other areas of his research include MBE growth of multiferroic complex oxide thin films and nanostructures for developing field tunable RF devices on GaN substrates.
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