Staircase Avalanche Photodiodes
Abstract
The internal gain of avalanche photodiodes (APDs) can provide higher sensitivity for communications and sensing applications than p-i-n photodiodes. However, the origin of the APD gain is impact ionization, a stochastic process that results in excess noise and limits the gain-bandwidth. For the past four decades, reducing the excess noise factor, F(M), has been a focus of APD research and development. One approach has been to identify materials with advantageous impact ionization characteristics such as HgCdTe and Si. Another approach to achieving low noise is through incorporating new materials and impact ionization engineering with appropriately designed heterostructures. One structure that was proposed to achieve very low noise is the staircase APD. Avalanche events occur proximate to sharp bandgap discontinuities, which function similarly to dynodes in a photomultiplier tube. In a previous ARO program we have demonstrated, for the first time, staircase gain in a single step staircase structure based on the AlxIn1-xAsySb1-y material system, which was grown by molecular beam epitaxy. Record low noise was achieved. Since that staircase APD utilized a single staircase step in the multiplication layer, the maximum gain was two. The scientific objective of this program is to extend that groundbreaking work to staircase APDs with multiple steps in order to achieve high gain, while maintaining ultra-low noise, by determining the key semiconductor physical properties necessary to realize this functionality, including understanding the details of the amplification mechanism. It was also found in the previous program that proper design could produce a new type of photodetector that exhibited high photoconductive gain at ~ 2V bias. In this program, we will (1) extend our previous work on the staircase APD with multiple steps in order to achieve high gain while maintaining ultra-low noise and decreasing the dark current through precise semiconductor band engineering and (2) optimize the design of the staircase structure to achieve high photoconductive gain at low bias. These photodetectors have the potential to enable new classes of photodetectors that offer fundamentally improved performance for high-gain/high-bandwidth detection and low-power imaging applications, respectively. This Research Instrumentation Request is for a higher capacity source furnace for depositing gallium in our molecular beam epitaxy system to support these research goals. Molecular beam epitaxy systems are limited in the number of structures (and/or layer thicknesses) that can be grown between ÔmaintenanceÕ cycles where the vacuum is broken to reload source material. The requested instrumentation will not only increase sample/device throughput, but will also enable us to more fully explore the growth parameter space, particularly regimes that are challenging to investigate with our limited capacity source.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2019
- Source ID
- W911NF1910381
Entities
People
- Seth R. Bank
Organizations
- Army Contracting Command
- United States Army
- University of Texas at Austin